Gene Summary

Gene:ABCB5; ATP binding cassette subfamily B member 5
Aliases: ABCB5beta, EST422562, ABCB5alpha
Summary:ABCB5 belongs to the ATP-binding cassette (ABC) transporter superfamily of integral membrane proteins. These proteins participate in ATP-dependent transmembrane transport of structurally diverse molecules ranging from small ions, sugars, and peptides to more complex organic molecules (Chen et al., 2005 [PubMed 15760339]).[supplied by OMIM, Mar 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:ATP-binding cassette sub-family B member 5
Source:NCBIAccessed: 15 March, 2017


What does this gene/protein do?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 15 March 2017 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 15 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (4)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: ABCB5 (cancer-related)

Seo EJ, Saeed M, Law BY, et al.
Pharmacogenomics of Scopoletin in Tumor Cells.
Molecules. 2016; 21(4):496 [PubMed] Related Publications
Drug resistance and the severe side effects of chemotherapy necessitate the development of novel anticancer drugs. Natural products are a valuable source for drug development. Scopoletin is a coumarin compound, which can be found in several Artemisia species and other plant genera. Microarray-based RNA expression profiling of the NCI cell line panel showed that cellular response of scopoletin did not correlate to the expression of ATP-binding cassette (ABC) transporters as classical drug resistance mechanisms (ABCB1, ABCB5, ABCC1, ABCG2). This was also true for the expression of the oncogene EGFR and the mutational status of the tumor suppressor gene, TP53. However, mutations in the RAS oncogenes and the slow proliferative activity in terms of cell doubling times significantly correlated with scopoletin resistance. COMPARE and hierarchical cluster analyses of transcriptome-wide mRNA expression resulted in a set of 40 genes, which all harbored binding motifs in their promoter sequences for the transcription factor, NF-κB, which is known to be associated with drug resistance. RAS mutations, slow proliferative activity, and NF-κB may hamper its effectiveness. By in silico molecular docking studies, we found that scopoletin bound to NF-κB and its regulator IκB. Scopoletin activated NF-κB in a SEAP-driven NF-κB reporter cell line, indicating that NF-κB might be a resistance factor for scopoletin. In conclusion, scopoletin might serve as lead compound for drug development because of its favorable activity against tumor cells with ABC-transporter expression, although NF-κB activation may be considered as resistance factor for this compound. Further investigations are warranted to explore the full therapeutic potential of this natural product.

Saeed ME, Meyer M, Hussein A, Efferth T
Cytotoxicity of South-African medicinal plants towards sensitive and multidrug-resistant cancer cells.
J Ethnopharmacol. 2016; 186:209-23 [PubMed] Related Publications
ETHNOPHARMACOLOGICAL RELEVANCE: Traditional medicine plays a major role for primary health care worldwide. Cancer belongs to the leading disease burden in industrialized and developing countries. Successful cancer therapy is hampered by the development of resistance towards established anticancer drugs.
AIM: In the present study, we investigated the cytotoxicity of 29 extracts from 26 medicinal plants of South-Africa against leukemia cell lines, most of which are used traditionally to treat cancer and related symptoms.
MATERIAL AND METHODS: We have investigated the plant extracts for their cytotoxic activity towards drug-sensitive parental CCRF-CEM leukemia cells and their multidrug-resistant P-glycoprotein-overexpressing subline, CEM/ADR5000 by means of the resazurin assay. A panel of 60 NCI tumor cell lines have been investigated for correlations between selected phytochemicals from medicinal plants and the expression of resistance-conferring genes (ABC-transporters, oncogenes, tumor suppressor genes).
RESULTS: Seven extracts inhibited both cell lines (Acokanthera oppositifolia, Hypoestes aristata, Laurus nobilis, Leonotis leonurus, Plectranthus barbatus, Plectranthus ciliates, Salvia apiana). CEM/ADR5000 cells exhibited a low degree of cross-resistance (3.35-fold) towards the L. leonurus extract, while no cross-resistance was observed to other plant extracts, although CEM/ADR5000 cells were highly resistant to clinically established drugs. The log10IC50 values for two out of 14 selected phytochemicals from these plants (acovenoside A and ouabain) of 60 tumor cell lines were correlated to the expression of ABC-transporters (ABCB1, ABCB5, ABCC1, ABCG2), oncogenes (EGFR, RAS) and tumor suppressors (TP53). Sensitivity or resistance of the cell lines were not statistically associated with the expression of these genes, indicating that multidrug-resistant, refractory tumors expressing these genes may still respond to acovenoside A and ouabain.
CONCLUSION: The bioactivity of South African medicinal plants may represent a basis for the development of strategies to treat multidrug-resistant tumors either by phytotherapeutic approaches with whole plant preparations or by classical drug development with isolated compounds such as acovenoside A or ouabain.

Jongkhajornpong P, Nakamura T, Sotozono C, et al.
Elevated expression of ABCB5 in ocular surface squamous neoplasia.
Sci Rep. 2016; 6:20541 [PubMed] Free Access to Full Article Related Publications
ATP-binding cassette subfamily B member 5 (ABCB5) is a new member of the ATP-binding cassette superfamily and has been reported as a novel marker for limbal stem cell (LSC), which is essential for corneal homeostasis. ABCB5 expression has also been discovered in the subpopulation of several cancer cells containing the cancer stem cell (CSC). However, the pathogenetic relationship between LSC and CSC and ABCB5 in the ocular surface squamous neoplasm (OSSN) is still entirely unknown. To improve understanding of the role of ABCB5 in OSSN, we performed immunohistochemistry for ABCB5 in nine OSSN case series. While expression of ABCB5 is restricted to the basal epithelial cell layer in the normal limbus, elevated expressions of ABCB5 were clearly observed in all OSSN, and there was some breadth in the range of intensity of ABCB5 expression. Interestingly, the elevated expression patterns of ABCB5 in OSSN could be classified in three categories: perivascular, marginal and diffuse patterns. Our findings demonstrated for the first time that the expression of ABCB5 was upregulated in OSSN and that elevated expression of ABCB5 may be involved in the pathogenesis of OSSN.

Wozniak M, Sztiller-Sikorska M, Czyz M
Diminution of miR-340-5p levels is responsible for increased expression of ABCB5 in melanoma cells under oxygen-deprived conditions.
Exp Mol Pathol. 2015; 99(3):707-16 [PubMed] Related Publications
Melanoma is usually highly refractory to chemotherapy. This resistance to treatment is mainly due to high heterogeneity and plasticity of melanoma cells strictly connected to changes in tumor microenvironment. Hypoxia can drastically alter cancer biology. Solid tumor cells under hypoxia gain stem-like features, they are more invasive and drug-resistant than their normoxic counterparts. These effects could be mediated by changes in miRNA expression under hypoxia. MiRNAs are small non-coding RNA molecules that can negatively control gene expression. In the present study using microarray technology we evaluated the expression of miRNAs in melanoma cells derived from nodular melanoma and grown under normoxic and hypoxic conditions. Using R environment for statistical analysis we found that 70 miRNAs were differentially-expressed, and 16 of them were significantly down-regulated in melanoma cells grown in hypoxic conditions compared to cells grown in normoxia. We intended to find transcripts whose expression is increased due to down-regulation of selected miRNAs. Bioinformatics analysis revealed that increased levels of HIF-2α, ABCB5, OCT4, SOX2 and ZEB1 in different melanoma populations under hypoxia could be a result of significant down-regulation of miR-340-5p. Inhibition of miR-340-5p confirmed that this miRNA negatively influences the expression of ABCB5. This is the first study showing the relationship between miR-340-5p and expression of ABCB5, a transmembrane transporter involved in drug resistance considered as a marker of melanoma stem-like cells.

Yang G, Jiang O, Ling D, et al.
MicroRNA-522 reverses drug resistance of doxorubicin-induced HT29 colon cancer cell by targeting ABCB5.
Mol Med Rep. 2015; 12(3):3930-6 [PubMed] Related Publications
MicroRNAs (miRNAs) are small non-coding RNAs, which are important in the development of multidrug resistance in cancer by regulating gene expression at the post‑transcriptional level. The present study investigated the functional effects of miR‑522 in chemoresistant colon cancer cells. The results demonstrated that miR‑522 was significantly downregulated in doxorubicin (DOX) resistant colon cell line, HT29/DOX, compared with the parental HT29 colon cancer cell line. Overexpression of miR‑522 in the HT29/DOX cells partially restored DOX sensitivity. miRNA target prediction algorithms suggested that ABCB5 was a target gene for miR‑522. A fluorescent reporter assay confirmed that miR‑522 was able to specifically bind to the predicted site of the ABCB5 mRNA 3'‑untranslated region. When miR‑522 was overexpressed in the HT29/DOX cells, the protein expression levels of ABCB5 were downregulated. Furthermore, knockdown of ABCB5 significantly increased the growth inhibition rate of the HT29/DOX cells, compared with the control group. These results suggested that miR‑522 may affect the sensitivity of colon cancer cell lines to DOX treatment by targeting ABCB5.

Sztiller-Sikorska M, Hartman ML, Talar B, et al.
Phenotypic diversity of patient-derived melanoma populations in stem cell medium.
Lab Invest. 2015; 95(6):672-83 [PubMed] Related Publications
Melanomas are highly heterogeneous tumors and there is no treatment effective at achieving long-term remission for metastatic melanoma patients. Thus, an appropriate model system for studying melanoma biology and response to drugs is necessary. It has been shown that composition of the medium is a critical factor in preserving the complexity of the tumor in in vitro settings, and melanospheres maintained in stem cell medium are a good model in this respect. In the present study, we observed that not all nodular melanoma patient-derived cell populations grown in stem cell medium were capable of forming melanospheres, and cell aggregates and anchorage-independent single-cell cultures emerged instead. Self-renewing capacity and unlimited growth potential indicated the presence of cells with stem-like properties in all patient-derived populations but immunophenotype and MITF expression exhibited variability. Enhanced MITF expression and activity was observed in melanospheres in comparison with cell aggregates and single-cell culture, and hypoxic-like conditions that increased the ability of single-cell population to form melanospheres enhanced MITF expression and cell pigmentation as well. Thus, MITF seems to be a critical transcription factor for formation of both patient-derived and hypoxia-induced melanospheres. After 2 years of continuous culturing, melanospheres progressively underwent transition into cell aggregates that was accompanied by changes in expression of several MITF-dependent genes associated with melanogenesis and survival and alterations in the composition of subpopulations but not in the frequency of ABCB5-positive cells. Several biological properties of parent tumor are well preserved in patient-derived melanospheres, but during prolonged culturing the heterogeneity is substantially lost when the melanospheres are substituted by cell aggregates. This should be considered when cell aggregates instead of melanospheres are used in the study of melanoma biology and cell response to drugs.

Vendittelli F, Paolillo C, Autilio C, et al.
Absolute quantitative PCR for detection of molecular biomarkers in melanoma patients: a preliminary report.
Clin Chim Acta. 2015; 444:242-9 [PubMed] Related Publications
BACKGROUND: Malignant melanoma is the most malignant tumours of skin and mucous membranes mainly due to its aggressive biological behaviour and tendency to generate early metastases. Unfortunately, the mechanisms underlying the development, progression and the expression of an aggressive melanoma phenotype still remain largely unknown.
OBJECTIVES: The purpose of this study was to determine whether a multi-panel of molecular transcripts can be predictive for risk of recurrent disease in malignant melanoma patients.
RESULTS: Peripheral blood was collected from 31 malignant melanoma patients in follow-up for melanoma and from 30 healthy volunteers randomly selected. Each specimen was examined by qRT-PCR analysis for the expression of six markers: PAX3d, TYR, MITFm, MCAM, TGFβ2 and ABCB5. Malignant melanoma patients expressed an important number of markers, with a median value of four markers. Only PAX3d displayed a trend in terms of differences when the levels of gene expression were made in function of Breslow index. Furthermore, PAX3d showed the best diagnostic capacity among the remaining residual markers or in combination with TGFβ2 and MTIF.
CONCLUSIONS: We demonstrated the usefulness of multimarker qRT-PCR to detect circulating melanoma cells in blood and to potentially assessing patient disease status or progression, especially when PAX3d was used in combination with MTIFm and TGFβ2.

Kugimiya N, Nishimoto A, Hosoyama T, et al.
The c-MYC-ABCB5 axis plays a pivotal role in 5-fluorouracil resistance in human colon cancer cells.
J Cell Mol Med. 2015; 19(7):1569-81 [PubMed] Free Access to Full Article Related Publications
c-MYC overexpression is frequently observed in various cancers including colon cancer and regulates many biological activities such as aberrant cell proliferation, apoptosis, genomic instability, immortalization and drug resistance. However, the mechanism by which c-MYC confers drug resistance remains to be fully elucidated. In this study, we found that the c-MYC expression level in primary colorectal cancer tissues correlated with the recurrence rate following 5-fluorouracil (5-FU)-based adjuvant chemotherapy. Supporting this finding, overexpression of exogenous c-MYC increased the survival rate following 5-FU treatment in human colon cancer cells, and knockdown of endogenous c-MYC decreased it. Furthermore, c-MYC knockdown decreased the expression level of ABCB5, which is involved in 5-FU resistance. Using a chromatin immunoprecipitation assay, we found that c-MYC bound to the ABCB5 promoter region. c-MYC inhibitor (10058-F4) treatment inhibited c-MYC binding to the ABCB5 promoter, leading to a decrease in ABCB5 expression level. ABCB5 knockdown decreased the survival rate following 5-FU treatment as expected, and the ABCB5 expression level was increased in 5-FU-resistant human colon cancer cells. Finally, using a human colon cancer xenograft murine model, we found that the combined 5-FU and 10058-F4 treatment significantly decreased tumorigenicity in nude mice compared with 5-FU or 10058-F4 treatment alone. 10058-F4 treatment decreased the ABCB5 expression level in the presence or absence of 5-FU. In contrast, 5-FU treatment alone increased the ABCB5 expression level. Taken together, these results suggest that c-MYC confers resistance to 5-FU through regulating ABCB5 expression in human colon cancer cells.

Kaushik G, Venugopal A, Ramamoorthy P, et al.
Honokiol inhibits melanoma stem cells by targeting notch signaling.
Mol Carcinog. 2015; 54(12):1710-21 [PubMed] Free Access to Full Article Related Publications
Melanoma is an aggressive disease with limited therapeutic options. Here, we determined the effects of honokiol (HNK), a biphenolic natural compound on melanoma cells and stemness. HNK significantly inhibited melanoma cell proliferation, viability, clonogenicity and induced autophagy. In addition, HNK significantly inhibited melanosphere formation in a dose dependent manner. Western blot analyses also demonstrated reduction in stem cell markers CD271, CD166, Jarid1b, and ABCB5. We next examined the effect of HNK on Notch signaling, a pathway involved in stem cell self-renewal. Four different Notch receptors exist in cells, which when cleaved by a series of enzymatic reactions catalyzed by Tumor Necrosis Factor-α-Converting Enzyme (TACE) and γ-secretase protein complex, results in the release of the Notch intracellular domain (NICD), which then translocates to the nucleus and induces target gene expression. Western blot analyses demonstrated that in HNK treated cells there is a significant reduction in the expression of cleaved Notch-2. In addition, there was a reduction in the expression of downstream target proteins, Hes-1 and cyclin D1. Moreover, HNK treatment suppressed the expression of TACE and γ-secretase complex proteins in melanoma cells. To confirm that suppression of Notch-2 activation is critical for HNK activity, we overexpressed NICD1, NICD2, and performed HNK treatment. NICD2, but not NICD1, partially restored the expression of Hes-1 and cyclin D1, and increased melanosphere formation. Taken together, these data suggest that HNK is a potent inhibitor of melanoma cells, in part, through the targeting of melanoma stem cells by suppressing Notch-2 signaling.

El-Khattouti A, Sheehan NT, Monico J, et al.
CD133⁺ melanoma subpopulation acquired resistance to caffeic acid phenethyl ester-induced apoptosis is attributed to the elevated expression of ABCB5: significance for melanoma treatment.
Cancer Lett. 2015; 357(1):83-104 [PubMed] Related Publications
According to the cancer stem-like cell (CSC) hypothesis, neoplastic clones are maintained by a small fraction of cells with stem cell properties. Also, melanoma resistance to chemo- and radiotherapy is thought to be attributed to melanoma stem-like cells (MSCs). Caffeic acid phenethyl ester (CAPE) is a bioactive molecule, whose antitumor activity is approved in different tumor types. CAPE induced both apoptosis and E2F1 expression in CD133(-), but not in CD133(+) melanoma subpopulations. The resistance of CD133(+) melanoma subpopulation is attributed to the enhanced drug efflux mediated by ATP-binding cassette sub-family B member 5 (ABCB5), since the knockdown of ABCB5 was found to sensitize CD133(+) cells to CAPE. CAPE-induced apoptosis is mediated by E2F1 as evidenced by the abrogation of apoptosis induced in response to the knockdown of E2F1. The functional analysis of E2F1 in CD133(+) melanoma subpopulation demonstrated the ability of E2F1 gene transfer to trigger apoptosis of CD133(+) cells and to enhance the activation of apoptosis signal-regulating kinase (ASK1), c-Jun N-terminal kinase and p38, and the DNA-binding activities of the transcription factors AP-1 and p53. Also, the induction of E2F1 expression was found to enhance the expression of the pro-apoptotic proteins Bax, Noxa and Puma, and to suppress the anti-apoptotic protein Mcl-1. Using specific pharmacological inhibitors we could demonstrate that E2F1 overcomes the chemo-resistance of MSCs/CD133(+) cells by a mechanism mediated by both mitochondrial dysregulation and ER-stress-dependent pathways. In conclusion, our data addresses the mechanisms of CAPE/E2F1-induced apoptosis of chemo-resistant CD133(+) melanoma subpopulation.

Yao CJ, Han TY, Shih PH, et al.
Elimination of cancer stem-like side population in human glioblastoma cells accompanied with stemness gene suppression by Korean herbal recipe MSC500.
Integr Cancer Ther. 2014; 13(6):541-54 [PubMed] Related Publications
BACKGROUND: High-grade gliomas are the most common and invasive malignant brain tumors in adults, and they are almost universally fatal because of drug resistance and recurrence. In spite of the progress in adjuvant therapy (like temozolomide) and irradiation after surgery, no effective salvage therapy is currently available for relapsed patients. A Korean herbal recipe MSC500 has been reported to have beneficial therapeutic effects in patients with high-grade gliomas who are relapsed or refractory to conventional treatments. But the underlying molecular mechanisms remain unclear.
METHODS: As Cancer stem cell (CSC) plays a pivotal role in the resistance to conventional cancer therapy, we explored the effects of MSC500 on the CSC-like side population (SP) in GBM8401 human glioblastoma multiforme cells.
RESULTS: Compared with the parental cells, the SP cells were more resistant to temozolomide but sensitive to MSC500. The mRNA levels of stemness genes such as Nanog, CD133, and ABCG2 were much higher in the SP cells, and so was E-cadherin, which was reported to correlate with the aggressiveness of glioblastoma multiforme. Treatment with MSC500 decreased the proportion of SP cells and high ALDH activity cells from 1.6% to 0.3% and from 0.9% to 0.1%, respectively, accompanied with suppression of the aforementioned stemness genes and E-cadherin, as well as other CSC markers such as ABCB5, Oct-4, Sox-2, β-catenin, Gli-1, and Notch-1.
CONCLUSION: Our results suggest the potential role of MSC500 as an integrative and complementary therapeutic for advanced or refractory high-grade glioma patients.

Cheli Y, Bonnazi VF, Jacquel A, et al.
CD271 is an imperfect marker for melanoma initiating cells.
Oncotarget. 2014; 5(14):5272-83 [PubMed] Free Access to Full Article Related Publications
Understanding the molecular and cellular processes underlying melanoma plasticity and heterogeneity is of paramount importance to improve the efficiency of current treatment and to overcome resistance to chemotherapy drugs. The notion of plasticity and heterogeneity implies the existence of melanoma cell populations with different phenotypic and tumorigenic properties. Using melanoma cell lines and melanoma cells freshly isolated from patient biopsies, we investigated the relationship between ABCB5+, CD271+ and low-MITF, expressing populations that were reported to display melanoma initiating cell properties. Here, we showed that ABCB5+ and CD271+ populations poorly overlap. However, we found that the CD271+ population is enriched in low-MITF cells and expresses a higher level of stemness genes, such as OCT4, NANOG and NES. These features could explain the increased tumorigenicity of the CD271+ cells. The rapid conversion of CD271+ to CD271- cells in vitro demonstrates the plasticity ability of melanoma cells. Finally, we observed that the transient slow-growing population contains only CD271+ cells that are highly tumorigenic. However, the fast growing/CD271+ population exhibits a poor tumorigenic ability. Taking together, our data show that CD271 is an imperfect marker for melanoma initiating cells, but may be useful to identify melanoma cells with an increased stemness and tumorigenic potential.

Wilson BJ, Saab KR, Ma J, et al.
ABCB5 maintains melanoma-initiating cells through a proinflammatory cytokine signaling circuit.
Cancer Res. 2014; 74(15):4196-207 [PubMed] Free Access to Full Article Related Publications
The drug efflux transporter ABCB5 identifies cancer stem-like cells (CSC) in diverse human malignancies, where its expression is associated with clinical disease progression and tumor recurrence. ABCB5 confers therapeutic resistance, but other functions in tumorigenesis independent of drug efflux have not been described that might help explain why it is so broadly overexpressed in human cancer. Here we show that in melanoma-initiating cells, ABCB5 controls IL1β secretion, which serves to maintain slow cycling, chemoresistant cells through an IL1β/IL8/CXCR1 cytokine signaling circuit. This CSC maintenance circuit involved reciprocal paracrine interactions with ABCB5-negative cancer cell populations. ABCB5 blockade induced cellular differentiation, reversed resistance to multiple chemotherapeutic agents, and impaired tumor growth in vivo. Together, our results defined a novel function for ABCB5 in CSC maintenance and tumor growth.

Farawela HM, Khorshied MM, Kassem NM, et al.
The clinical relevance and prognostic significance of adenosine triphosphate ATP-binding cassette (ABCB5) and multidrug resistance (MDR1) genes expression in acute leukemia: an Egyptian study.
J Cancer Res Clin Oncol. 2014; 140(8):1323-30 [PubMed] Related Publications
AIM: Multidrug resistance (MDR1) represents a major obstacle in the chemotherapeutic treatment of acute leukemia (AL). Adenosine triphosphate ATP-binding cassette (ABCB5) and MDR1 genes are integral membrane proteins belonging to ATP-binding cassette transporters superfamily.
PURPOSE: The present work aimed to investigate the impact of ABCB5 and MDR1 genes expression on the response to chemotherapy in a cohort of Egyptian AL patients. The study included 90 patients: 53 AML cases and 37 ALL cases in addition to 20 healthy volunteers as controls.
METHODS: Quantitative assessment of MDR1 and ABCB5 genes expression was performed by quantitative real-time polymerase chain reaction. Additional prognostic molecular markers were determined as internal tandem duplications of the FLT3 gene (FLT3-ITD) and nucleophosmin gene mutation (NPM1) for AML cases, and mbcr-abl fusion transcript for B-ALL cases.
RESULTS: In AML patients, ABCB5 and MDR1 expression levels did not differ significantly between de novo and relapsed cases and did not correlate with the overall survival or disease-free survival. AML patients were stratified according to the studied genetic markers, and complete remission rate was found to be more prominent in patients having low expression of MDR1 and ABCB5 genes together with mutated NPM1 gene. In ALL patients, ABCB5 gene expression level was significantly higher in relapsed cases and MDR1 gene expression was significantly higher in patients with resistant disease.
CONCLUSION: In conclusion, the results obtained by the current study provide additional evidence of the role played by these genes as predictive factors for resistance of leukemic cells to chemotherapy and hence treatment outcome.

Sztiller-Sikorska M, Koprowska K, Majchrzak K, et al.
Natural compounds' activity against cancer stem-like or fast-cycling melanoma cells.
PLoS One. 2014; 9(3):e90783 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Accumulating evidence supports the concept that melanoma is highly heterogeneous and sustained by a small subpopulation of melanoma stem-like cells. Those cells are considered as responsible for tumor resistance to therapies. Moreover, melanoma cells are characterized by their high phenotypic plasticity. Consequently, both melanoma stem-like cells and their more differentiated progeny must be eradicated to achieve durable cure. By reevaluating compounds in heterogeneous melanoma populations, it might be possible to select compounds with activity not only against fast-cycling cells but also against cancer stem-like cells. Natural compounds were the focus of the present study.
METHODS: We analyzed 120 compounds from The Natural Products Set II to identify compounds active against melanoma populations grown in an anchorage-independent manner and enriched with cells exerting self-renewing capacity. Cell viability, cell cycle arrest, apoptosis, gene expression, clonogenic survival and label-retention were analyzed.
FINDINGS: Several compounds efficiently eradicated cells with clonogenic capacity and nanaomycin A, streptonigrin and toyocamycin were effective at 0.1 µM. Other anti-clonogenic but not highly cytotoxic compounds such as bryostatin 1, siomycin A, illudin M, michellamine B and pentoxifylline markedly reduced the frequency of ABCB5 (ATP-binding cassette, sub-family B, member 5)-positive cells. On the contrary, treatment with maytansine and colchicine selected for cells expressing this transporter. Maytansine, streptonigrin, toyocamycin and colchicine, even if highly cytotoxic, left a small subpopulation of slow-dividing cells unaffected. Compounds selected in the present study differentially altered the expression of melanocyte/melanoma specific microphthalmia-associated transcription factor (MITF) and proto-oncogene c-MYC.
CONCLUSION: Selected anti-clonogenic compounds might be further investigated as potential adjuvants targeting melanoma stem-like cells in the combined anti-melanoma therapy, whereas selected cytotoxic but not anti-clonogenic compounds, which increased the frequency of ABCB5-positive cells and remained slow-cycling cells unaffected, might be considered as a tool to enrich cultures with cells exhibiting melanoma stem cell characteristics.

Saeed M, Khalid H, Sugimoto Y, Efferth T
The lignan, (-)-sesamin reveals cytotoxicity toward cancer cells: pharmacogenomic determination of genes associated with sensitivity or resistance.
Phytomedicine. 2014; 21(5):689-96 [PubMed] Related Publications
(-)-Sesamin is a lignan present in sesam oil and a number of medicinal plants. It exerts various pharmacological effects, such as prevention of hyperlipidemia, hypertension, and carcinogenesis. Moreover, (-)-sesamin has chemopreventive and anticancer activity in vitro and in vivo. Multidrug resistance (MDR) of tumors leads to fatal treatment outcome in many patients and novel drugs able to kill multidrug-resistant cells are urgently needed. P-glycoprotein (MDR1/ABCB1) is the best known ATP-binding cassette (ABC) drug transporter mediating MDR. ABCB5 is a close relative to ABCB1, which also mediates MDR. We found that the mRNA expressions of ABCB1 and ABCB5 were not related to the 50% inhibition concentrations (IC50) for (-)-sesamin in a panel of 55 cell lines of the National Cancer Institute, USA. Furthermore, (-)-sesamin inhibited ABCB1- or ABCB5-overexpressing cells with similar efficacy than their drug-sensitive parental counterparts. In addition to ABC transporter-mediated MDR, we attempted to identify other molecular determinants of (-)-sesamin resistance. For this reason, we performed COMPARE and hierarchical cluster analyses of the transcriptome-wide microarray-based mRNA expression of the NCI cell panel. Twenty-three genes were identified, whose mRNA expression correlated with the IC50 values for (-)-sesamin. These genes code for proteins of different biological functions, i.e. ribosomal proteins, components of the mitochondrial respiratory chain, proteins involved in RNA metabolism, protein biosynthesis, or glucose and fatty acid metabolism. Subjecting this set of genes to cluster analysis showed that the cell lines were assembled in the resulting dendrogram according to their responsiveness to (-)-sesamin. In conclusion, (-)-sesamin is not involved in MDR mediated by ABCB1 or ABCB5 and may be valuable to bypass chemoresistance of refractory tumors. The microarray expression profile, which predicted sensitivity or resistance of tumor cells to (-)-sesamin consisted of genes, which do not belong to the classical resistance mechanisms to established anticancer drugs.

Mathieu MG, Miles AK, Ahmad M, et al.
The helicase HAGE prevents interferon-α-induced PML expression in ABCB5+ malignant melanoma-initiating cells by promoting the expression of SOCS1.
Cell Death Dis. 2014; 5:e1061 [PubMed] Free Access to Full Article Related Publications
The tumour suppressor PML (promyelocytic leukaemia protein) regulates several cellular pathways involving cell growth, apoptosis, differentiation and senescence. PML also has an important role in the regulation of stem cell proliferation and differentiation. Here, we show the involvement of the helicase HAGE in the transcriptional repression of PML expression in ABCB5+ malignant melanoma-initiating cells (ABCB5+ MMICs), a population of cancer stem cells which are responsible for melanoma growth, progression and resistance to drug-based therapy. HAGE prevents PML gene expression by inhibiting the activation of the JAK-STAT (janus kinase-signal transducers and activators of transcription) pathway in a mechanism which implicates the suppressor of cytokine signalling 1 (SOCS1). Knockdown of HAGE led to a significant decrease in SOCS1 protein expression, activation of the JAK-STAT signalling cascade and a consequent increase of PML expression. To confirm that the reduction in SOCS1 expression was dependent on the HAGE helicase activity, we showed that SOCS1, effectively silenced by small interfering RNA, could be rescued by re-introduction of HAGE into cells lacking HAGE. Furthermore, we provide a mechanism by which HAGE promotes SOCS1 mRNA unwinding and protein expression in vitro. Finally, using a stem cell proliferation assay and tumour xenotransplantation assay in non-obese diabetic/severe combined immunodeficiency mice, we show that HAGE promotes MMICs-dependent tumour initiation and tumour growth by preventing the anti-proliferative effects of interferon-α (IFNα). Our results suggest that the helicase HAGE has a key role in the resistance of ABCB5+ MMICs to IFNα treatment and that cancer therapies targeting HAGE may have broad implications for the treatment of malignant melanoma.

Wozniak M, Szulawska-Mroczek A, Hartman ML, et al.
Parthenolide complements the cell death-inducing activity of doxorubicin in melanoma cells.
Anticancer Res. 2013; 33(8):3205-12 [PubMed] Related Publications
BACKGROUND: Melanoma is characterized by high resistance to chemotherapy. The aim of this study was to investigate combined effects of doxorubicin and parthenolide on melanoma cells.
MATERIALS AND METHODS: Thiazolyl blue tetrazolium bromide (MTT) assay and flow cytometry were used to evaluate viability. The p53 levels and Poly-ADP ribose polymerase (PARP) cleavage were assessed by western blot. Electrophoretic mobility shift assay (EMSA) and quantitative real-time polymerase chain reaction (qRT-PCR) were used to evaluate changes in nuclear factor-κB (NF-κB) activity and gene expression, respectively.
RESULTS: Both drugs reduced the viability of melanoma cells and induced apoptosis. Expression of the ATP-binding cassette sub-family B member-5 (ABCB5) transporter was enhanced by doxorubicin. Doxorubicin induced activity of p53 and NF-κB. Parthenolide markedly reduced the constitutive and doxorubicin-induced NF-κB activity measured as the nuclear NF-κB, and expression of matrix metalloproteinase-9 (MMP9) and it had no effect on p53.
DISCUSSION: Doxorubicin and parthenolide affected distinct pathways in melanoma, and parthenolide was capable of combating some pro-survival effects of doxorubicin in the combined treatment. This provides a rationale for in vivo investigation of this drug combination.

Lin JY, Zhang M, Schatton T, et al.
Genetically determined ABCB5 functionality correlates with pigmentation phenotype and melanoma risk.
Biochem Biophys Res Commun. 2013; 436(3):536-42 [PubMed] Free Access to Full Article Related Publications
ABCB5 is a multidrug resistance (MDR) member of the ATP-binding cassette (ABC) superfamily of active transporters and represents a marker for chemoresistant malignant melanoma-initiating cells. ABCB5 expression is closely linked to tumorigenicity and progression of diverse human malignancies, including melanoma, and is functionally required for tumor growth. Here, we genotyped 585 melanoma cases and 605 age-matched controls for 44 ABCB5 tagging single nucleotide polymorphisms (SNPs) to span a region covering 108.2kb of the gene on the 7p21.1 locus. We identified three SNPs that were associated with decreased melanoma risk in additive models: rs10231520 (OR: 0.83, 95% CI: 0.70-0.98), rs17817117 (OR: 0.82, 95% CI: 0.68-0.98), and rs2301641 (OR: 0.83, 95% CI: 0.69-0.98). Additionally, the rs2301641 SNP was associated with non-red compared to red hair color (OR: 0.38, 95% CI: 0.14-1.03) in controls. Twelve human melanoma cell lines were genotyped for the rs2301641 SNP, which encodes a non-synonymous ABCB5 amino acid change (K115E). Functional studies revealed that the E form associated with lower melanoma risk correlated significantly with decreased ABCB5 transport capacity (P<0.01) and increased melanin production (P<0.05). Our results identify novel associations of the ABCB5 K115E polymorphism with human pigmentation phenotype and melanoma risk and point to potential functional roles of ABCB5 in melanomagenesis. Moreover, they provide a first example that functional variation in a prospective cancer stem cell marker can be associated with disease risk for the corresponding malignancy.

Govindan R, Ding L, Griffith M, et al.
Genomic landscape of non-small cell lung cancer in smokers and never-smokers.
Cell. 2012; 150(6):1121-34 [PubMed] Free Access to Full Article Related Publications
We report the results of whole-genome and transcriptome sequencing of tumor and adjacent normal tissue samples from 17 patients with non-small cell lung carcinoma (NSCLC). We identified 3,726 point mutations and more than 90 indels in the coding sequence, with an average mutation frequency more than 10-fold higher in smokers than in never-smokers. Novel alterations in genes involved in chromatin modification and DNA repair pathways were identified, along with DACH1, CFTR, RELN, ABCB5, and HGF. Deep digital sequencing revealed diverse clonality patterns in both never-smokers and smokers. All validated EFGR and KRAS mutations were present in the founder clones, suggesting possible roles in cancer initiation. Analysis revealed 14 fusions, including ROS1 and ALK, as well as novel metabolic enzymes. Cell-cycle and JAK-STAT pathways are significantly altered in lung cancer, along with perturbations in 54 genes that are potentially targetable with currently available drugs.

Lai CY, Schwartz BE, Hsu MY
CD133+ melanoma subpopulations contribute to perivascular niche morphogenesis and tumorigenicity through vasculogenic mimicry.
Cancer Res. 2012; 72(19):5111-8 [PubMed] Free Access to Full Article Related Publications
Tumor cell subpopulations that express cancer stem cell markers such as CD133 (prominin1) or ABCB5 are thought to be crucial for tumor initiation and heterogeneity, but their biological significance in melanoma has been controversial. Here, we report that CD133(+) and ABCB5(+) subpopulations are colocalized in melanomas in perivascular niches that contain CD144 (VE-cadherin)(+) melanoma cells forming vessel-like channels, a phenomenon termed vasculogenic mimicry (VM). RNAi-mediated attenuation of CD133 established its critical function in morphogenesis of these perivascular niches as well as in melanoma tumorigenicity. Niche-associated genes CD144 and ABCB5 were downregulated in tumors derived from CD133 knockdown (KD) melanoma cells compared with controls. CD133KD cells also lacked the ability to form CD144(+) VM-like channels in a manner that was associated with a depletion of the ABCB5(+) cell subpopulation. Finally, CD133 KD cells exhibited poorer tumor growth in vivo. Taken together, our findings corroborate models in which CD133(+)/ABCB5(+) melanoma cells reside in a complex anastomosing microvascular niche that encompasses CD144(+) VM channels as well as authentic endothelial cell-lined blood vessels. Further, they indicate that CD133(+) cells act as stem-like cells, which drive tumor growth by promoting VM and the morphogenesis of a specialized perivascular niche in melanoma.

Grimm M, Krimmel M, Polligkeit J, et al.
ABCB5 expression and cancer stem cell hypothesis in oral squamous cell carcinoma.
Eur J Cancer. 2012; 48(17):3186-97 [PubMed] Related Publications
INTRODUCTION: The vast majority of oral cancers are squamous cell carcinomas (OSCC). The effectiveness of adjuvant cytostatic chemotherapy for OSCC is frequently restricted due to an inducible cellular mechanism called multidrug resistance (MDR) and a putative cancer stem cell (CSC) compartment in human carcinogenesis expressing multidrug efflux pumps. The novel human ATP-binding cassette (ABC) transporter ABCB5 [subfamily B (MDR/TAP) member 5] acts as an energy-dependent drug efflux transporter and marks tumour cells of a putative CSC compartment. However, to date, there is no link between ABCB5 expression and OSCC.
MATERIALS AND METHODS: Expression of ABCB5 was analysed in OSCC specimen (n=191) and cancer cell lines (BICR3, BICR56) by immunohistochemistry, real-time polymerase chain reaction (RT-PCR) analysis and western blotting. Scanned images were digitally analysed using ImageJ and the immunomembrane plug-in. ABCB5 expression on protein level was correlated with clinical characteristics and impact on survival. ABCB5 was co-labelled with CD44 in immunohistochemical and immunofluorescence double labelling experiments. Expression subgroups were identified by receiver operating characteristics (ROC) analysis.
RESULTS: High ABCB5 expression was significantly associated with tumour progression and recurrence of the tumour. Multivariate analysis demonstrated high ABCB5 expression as an independent prognostic factor (p=0.0004). Immunohistochemical and immunofluorescence double labelling experiments revealed ABCB5 expression by CD44+ cancer cells. ABCB5 specificity was confirmed by western blot and RT-PCR analysis.
CONCLUSIONS: For the first time, this study provides evidence that ABCB5 expression in OSCC might be associated with tumour formation, metastasis and a putative CSC compartment. One of the principal mechanisms for protecting putative cancer stem cells is through the expression of multifunctional efflux transporters from the ABC gene family, like ABCB5. This provides one mechanism in which putative cancer stem cells could survive and may lead to tumour relapse. Knowledge of expression profiles of ABC transporters and other genes involved in MDR will likely help therapeutic optimisation for cancer patients in clinic. However, this hypothesis requires further in vitro and in vivo studies.

Chartrain M, Riond J, Stennevin A, et al.
Melanoma chemotherapy leads to the selection of ABCB5-expressing cells.
PLoS One. 2012; 7(5):e36762 [PubMed] Free Access to Full Article Related Publications
Metastatic melanoma is the most aggressive skin cancer. Recently, phenotypically distinct subpopulations of tumor cells were identified. Among them, ABCB5-expressing cells were proposed to display an enhanced tumorigenicity with stem cell-like properties. In addition, ABCB5(+) cells are thought to participate to chemoresistance through a potential efflux function of ABCB5. Nevertheless, the fate of these cells upon drugs that are used in melanoma chemotherapy remains to be clarified. Here we explored the effect of anti-melanoma treatments on the ABCB5-expressing cells. Using a melanoma xenograft model (WM266-4), we observed in vivo that ABCB5-expressing cells are enriched after a temozolomide treatment that induces a significant tumor regression. These results were further confirmed in a preliminary study conducted on clinical samples from patients that received dacarbazine. In vitro, we showed that ABCB5-expressing cells selectively survive when exposed to dacarbazine, the reference treatment of metastatic melanoma, but also to vemurafenib, a new inhibitor of the mutated kinase V600E BRAF and other various chemotherapeutic drugs. Our results show that anti-melanoma chemotherapy might participate to the chemoresistance acquisition by selecting tumor cell subpopulations expressing ABCB5. This is of particular importance in understanding the relapses observed after anti-melanoma treatments and reinforces the interest of ABCB5 and ABCB5-expressing cells as potential therapeutic targets in melanoma.

Luo Y, Ellis LZ, Dallaglio K, et al.
Side population cells from human melanoma tumors reveal diverse mechanisms for chemoresistance.
J Invest Dermatol. 2012; 132(10):2440-50 [PubMed] Free Access to Full Article Related Publications
Side population (SP) cells are identified as cells capable of excluding the fluorescent Hoechst dye and anticancer drugs, and it represents hematopoietic stem cells and chemoresistant cells from several solid tumors. In this study, we confirmed the presence of SP cells in tumors from melanoma patients. Melanoma SP cells overexpressed ATP-binding-cassette (ABC) transporters, ABCB1 and ABCB5. We generated a direct in vivo xenograft model, and demonstrated that SP cells were resistant to paclitaxel, a substrate of ABCB1, both in vitro and in vivo. However, melanoma SP cells were also resistant to temozolomide, which is not a substrate for ABC transporters, through IL-8 upregulation. In addition, gene profiling studies identified three signaling pathways (NF-κB, α6-β4-integrin, and IL-1) as differentially upregulated in melanoma SP cells, and there was a significant increase of PCDHB11 and decrease of FUK and TBX2 in these cells. Therefore, we provide evidence that SP is an enriched source of chemoresistant cells in human melanomas, and suggest that the selected genes and signaling pathways of SP cells may be a potential target for effective melanoma therapies. To our knowledge, this is a previously unreported study to isolate SP cells from melanoma patients and to investigate the gene expression profiling of these cells.

Setia N, Abbas O, Sousa Y, et al.
Profiling of ABC transporters ABCB5, ABCF2 and nestin-positive stem cells in nevi, in situ and invasive melanoma.
Mod Pathol. 2012; 25(8):1169-75 [PubMed] Related Publications
Distinct ABCB5 forms and ABCF2, members of the ATP-binding cassette (ABC) superfamily of transporters, are normally expressed in various tissues and cells, and enhanced expression of both has been demonstrated in select cancers. In melanoma cell lines, gene expression profiling of ABC transporters has revealed enhanced expression of melanocyte-specific ABCB5 and ABCF2 proteins. Given this, our primary aim was to ascertain immunohistochemical expression of the ABC transporters ABCB5 and ABCF2 and, the stem cell marker, nestin in a spectrum of benign and malignant nevomelanocytic proliferations, including nevi (n=30), in situ (n=31) and invasive (n=24) primary cutaneous melanomas to assess their role in the stepwise development of malignancy. In addition, their expression was compared with established melanoma prognosticators to ascertain their utility as independent prognosticators. A semiquantitative scoring system was utilized by deriving a cumulative score (based on percentage positivity cells and intensity of expression) and statistical analyses was carried out using analysis of variance with linear contrasts. Mean cumulative score in nevi, in situ and invasive melanoma were as follows: 3.8, 4.4 and 5.3 for ABCB5, respectively (P<0.005 for all), and 4.6, 4.6 and 5.3 for nestin, respectively (P=not significant for all). No appreciable expression of ABCF2 was noted in any of the groups. While ulcerated lesions of melanoma demonstrated lower levels of expression of ABCB5 and nestin than non-ulcerated lesions, and nestin expression was lower in lesions with mitoses >1, after controlling for the presence of ulceration and mitotic activity, the expression of both proteins did not significantly correlate with known melanoma prognosticators. The gradual increase in the expression of ABCB5 from benign nevus to in situ to invasive melanoma suggests that it plays a role in melanomagenesis. On the basis of our findings, a prospective study with follow-up data is required to ascertain the utility of ABCB5 as a therapeutic target.

Linley AJ, Mathieu MG, Miles AK, et al.
The helicase HAGE expressed by malignant melanoma-initiating cells is required for tumor cell proliferation in vivo.
J Biol Chem. 2012; 287(17):13633-43 [PubMed] Free Access to Full Article Related Publications
Malignant melanoma-initiating cells (MMIC) are a subpopulation of cells responsible for melanoma tumor growth and progression. They are defined by the expression of the ATP-binding cassette (ABC) subfamily B member 5 (ABCB5). Here, we identified a critical role for the DEAD-box helicase antigen (HAGE) in ABCB5+ MMIC-dependent tumorigenesis and show that HAGE-specific inactivation inhibits melanoma tumor growth mediated by this tumor-initiating population. Knockdown of HAGE led to a significant decrease in RAS protein expression with a concomitant decrease in activation of the AKT and ERK signaling pathways implicated to play an important role in melanoma progression. To confirm that the reduction in NRAS (Neuroblastoma RAS) expression was dependent on the HAGE helicase activity, we showed that NRAS, effectively silenced by siRNA, could be rescued by reintroduction of HAGE in cells lacking HAGE. Furthermore, we provide a mechanism by which HAGE promotes NRAS unwinding in vitro. We also observed using tumor transplantation in Non-obese diabetic/severe combined immunodeficiency mice that the HAGE knockdown in a ABCB5+ melanoma cell line displayed a significant decrease in tumor growth and compared with the control. Our results suggest that the helicase HAGE is required for ABCB5+ MMIC-dependent tumor growth through promoting RAS protein expression and that cancer therapies targeting HAGE helicase may have broad applications for treating malignant melanoma and potentially other cancer types.

Kumar SM, Liu S, Lu H, et al.
Acquired cancer stem cell phenotypes through Oct4-mediated dedifferentiation.
Oncogene. 2012; 31(47):4898-911 [PubMed] Free Access to Full Article Related Publications
There is enormous interest to target cancer stem cells (CSCs) for clinical treatment because these cells are highly tumorigenic and resistant to chemotherapy. Oct4 is expressed by CSC-like cells in different types of cancer. However, function of Oct4 in tumor cells is unclear. In this study, we showed that expression of Oct4 gene or transmembrane delivery of Oct4 protein promoted dedifferentiation of melanoma cells to CSC-like cells. The dedifferentiated melanoma cells showed significantly decreased expression of melanocytic markers and acquired the ability to form tumor spheroids. They showed markedly increased resistance to chemotherapeutic agents and hypoxic injury. In the subcutaneous xenograft and tail vein injection assays, these cells had significantly increased tumorigenic capacity. The dedifferentiated melanoma cells acquired features associated with CSCs such as multipotent differentiation capacity and expression of melanoma CSC markers such as ABCB5 and CD271. Mechanistically, Oct4-induced dedifferentiation was associated with increased expression of endogenous Oct4, Nanog and Klf4, and global gene expression changes that enriched for transcription factors. RNAi-mediated knockdown of Oct4 in dedifferentiated cells led to diminished CSC phenotypes. Oct4 expression in melanoma was regulated by hypoxia and its expression was detected in a sub-population of melanoma cells in clinical samples. Our data indicate that Oct4 is a positive regulator of tumor dedifferentiation. The results suggest that CSC phenotype is dynamic and may be acquired through dedifferentiation. Oct4-mediated tumor cell dedifferentiation may have an important role during tumor progression.

Yang M, Li W, Fan D, et al.
Expression of ABCB5 gene in hematological malignances and its significance.
Leuk Lymphoma. 2012; 53(6):1211-5 [PubMed] Related Publications
We examined ABCB5 gene expression using real-time polymerase chain reaction (PCR) in leukemia cells from 29 patients with acute lymphoblastic leukemia (ALL), 24 patients with chronic lymphocytic leukemia (CLL), 42 with acute myeloid leukemia (AML), 22 with chronic myeloid leukemia (CML), 17 with lymphoma and 10 with multiple myeloma (MM). It was confirmed that expression of the ABCB5 gene is highly increased in B-precursor ALL and French-American-British (FAB) M1 and M2 types of AML and lymphoma. The ABCB5 gene is expressed more highly in patients with relapsed or refractory disease than in patients with drug sensitive acute leukemia. Furthermore, there was an evident positive correlation between ABCB5 mRNA expression and MDR1 mRNA expression, but no correlation with MRP mRNA expression or BCRP mRNA expression. Quantification of the ABCB5 gene by real-time PCR offers particular promise as a prognostic marker and a marker for drug resistance in acute leukemia. Our findings raise the possibility that ABCB5 may be responsible for both the progression and chemotherapeutic refractoriness of advanced acute leukemia, and that ABCB5-targeted approaches might therefore represent novel and translationally relevant therapeutic strategies for drug resistance in leukemia.

Cigna E, Gradilone A, Sorvillo V, Scuderi N
ABCB5 in peripheral blood of a patient affected by multiple primary malignancies.
Ann Ital Chir. 2011 Jan-Feb; 82(1):49-53 [PubMed] Related Publications
BACKGROUND: Multiple primary neoplasm malignancies syndrome (MPMN), is the presence of two or more abnormal growths of tissue, occurring simultaneously. Although the number of second malignancies is increasing, due to several factors, the presence of triple or quadruple malignancies is still very rare.
PATIENT AND METHODS: We report a case of a 78-year-old man, with six primaries: a prostatic adenocarcinoma, breast cancer, two melanoma, a basal cell carcinoma, and a lymphoma in a four years period.
RESULTS: The onset of MPMN is probably caused by a mutation of DNA repair genes, probably the TP53 gene. Common features of this syndrome are early rise and low tendency to metastatize. We reviewed the markers of staminality for various tumors: RNA expression of ALDH1, CD 133, and ABCB 5, extracted from the sentinel lymph node (SLN) and from the peripheral blood of the patient, was verified.
CONCLUSION: People with multiple tumors represent a segment of the cancer-survivor population, which is continuously increasing (10%). Several genetic mutation can be involved in this kind of population. Our patient was positive for the expression of ABCB5, a marker for staminality of melanoma, in periphal blood.

Moitra K, Scally M, McGee K, et al.
Molecular evolutionary analysis of ABCB5: the ancestral gene is a full transporter with potentially deleterious single nucleotide polymorphisms.
PLoS One. 2011; 6(1):e16318 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: ABCB5 is a member of the ABC protein superfamily, which includes the transporters ABCB1, ABCC1 and ABCG2 responsible for causing drug resistance in cancer patients and also several other transporters that have been linked to human disease. The ABCB5 full transporter (ABCB5.ts) is expressed in human testis and its functional significance is presently unknown. Another variant of this transporter, ABCB5 beta possess a "half-transporter-like" structure and is expressed in melanoma stem cells, normal melanocytes, and other types of pigment cells. ABCB5 beta has important clinical implications, as it may be involved with multidrug resistance in melanoma stem cells, allowing these stem cells to survive chemotherapeutic regimes.
METHODOLOGY/PRINCIPAL FINDINGS: We constructed and examined in detail topological structures of the human ABCB5 protein and determined in-silico the cSNPs (coding single nucleotide polymorphisms) that may affect its function. Evolutionary analysis of ABCB5 indicated that ABCB5, ABCB1, ABCB4, and ABCB11 share a common ancestor, which began duplicating early in the evolutionary history of chordates. This suggests that ABCB5 has evolved as a full transporter throughout its evolutionary history.
CONCLUSIONS/SIGNIFICANCE: From our in-silco analysis of cSNPs we found that a large number of non-synonymous cSNPs map to important functional regions of the protein suggesting that these SNPs if present in human populations may play a role in diseases associated with ABCB5. From phylogenetic analyses, we have shown that ABCB5 evolved as a full transporter throughout its evolutionary history with an absence of any major shifts in selection between the various lineages suggesting that the function of ABCB5 has been maintained during mammalian evolution. This finding would suggest that ABCB5 beta may have evolved to play a specific role in human pigment cells and/or melanoma cells where it is predominantly expressed.

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