Gene Summary

Gene:MERTK; MER proto-oncogene, tyrosine kinase
Aliases: MER, RP38, c-Eyk, c-mer, Tyro12
Summary:This gene is a member of the MER/AXL/TYRO3 receptor kinase family and encodes a transmembrane protein with two fibronectin type-III domains, two Ig-like C2-type (immunoglobulin-like) domains, and one tyrosine kinase domain. Mutations in this gene have been associated with disruption of the retinal pigment epithelium (RPE) phagocytosis pathway and onset of autosomal recessive retinitis pigmentosa (RP). [provided by RefSeq, Jul 2008]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:tyrosine-protein kinase Mer
Source:NCBIAccessed: 25 June, 2015


What does this gene/protein do?
Show (29)

Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 26 June 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

Tag cloud generated 25 June, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (5)

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: MERTK (cancer-related)

Krause S, Pfeiffer C, Strube S, et al.
Mer tyrosine kinase promotes the survival of t(1;19)-positive acute lymphoblastic leukemia (ALL) in the central nervous system (CNS).
Blood. 2015; 125(5):820-30 [PubMed] Related Publications
Patients with t(1;19)-positive acute lymphoblastic leukemia (ALL) are prone to central nervous system (CNS) relapses, and expression of the TAM (Tyro3, Axl, and Mer) receptor Mer is upregulated in these leukemias. We examined the functional role of Mer in the CNS in preclinical models and performed correlative studies in 64 t(1;19)-positive and 93 control pediatric ALL patients. ALL cells were analyzed in coculture with human glioma cells and normal rat astrocytes: CNS coculture caused quiescence and protection from methotrexate toxicity in Mer(high) ALL cell lines, which was antagonized by short hairpin RNA-mediated knockdown of Mer. Mer expression was upregulated, prosurvival Akt and mitogen-activated protein kinase signaling were activated, and secretion of the Mer ligand Galectin-3 was stimulated. Mer(high) t(1;19) primary cells caused CNS involvement to a larger extent in murine xenografts than in their Mer(low) counterparts. Leukemic cells from Mer(high) xenografts showed enhanced survival in coculture. Treatment of Mer(high) patient cells with the Mer-specific inhibitor UNC-569 in vivo delayed leukemia onset, reduced CNS infiltration, and prolonged survival of mice. Finally, a correlation between high Mer expression and CNS positivity upon initial diagnosis was observed in t(1;19) patients. Our data provide evidence that Mer is associated with survival in the CNS in t(1;19)-positive ALL, suggesting a role as a diagnostic marker and therapeutic target.

Stanford JC, Young C, Hicks D, et al.
Efferocytosis produces a prometastatic landscape during postpartum mammary gland involution.
J Clin Invest. 2014; 124(11):4737-52 [PubMed] Free Access to Full Article Related Publications
Breast cancers that occur in women 2-5 years postpartum are more frequently diagnosed at metastatic stages and correlate with poorer outcomes compared with breast cancers diagnosed in young, premenopausal women. The molecular mechanisms underlying the malignant severity associated with postpartum breast cancers (ppBCs) are unclear but relate to stromal wound-healing events during postpartum involution, a dynamic process characterized by widespread cell death in milk-producing mammary epithelial cells (MECs). Using both spontaneous and allografted mammary tumors in fully immune-competent mice, we discovered that postpartum involution increases mammary tumor metastasis. Cell death was widespread, not only occurring in MECs but also in tumor epithelium. Dying tumor cells were cleared through receptor tyrosine kinase MerTK-dependent efferocytosis, which robustly induced the transcription of genes encoding wound-healing cytokines, including IL-4, IL-10, IL-13, and TGF-β. Animals lacking MerTK and animals treated with a MerTK inhibitor exhibited impaired efferocytosis in postpartum tumors, a reduction of M2-like macrophages but no change in total macrophage levels, decreased TGF-β expression, and a reduction of postpartum tumor metastasis that was similar to the metastasis frequencies observed in nulliparous mice. Moreover, TGF-β blockade reduced postpartum tumor metastasis. These data suggest that widespread cell death during postpartum involution triggers efferocytosis-induced wound-healing cytokines in the tumor microenvironment that promote metastatic tumor progression.

Lv H, Pei J, Liu H, et al.
A polymorphism site in the pre‑miR‑34a coding region reduces miR‑34a expression and promotes osteosarcoma cell proliferation and migration.
Mol Med Rep. 2014; 10(6):2912-6 [PubMed] Free Access to Full Article Related Publications
Osteosarcoma (OS) is the most prevalent primary malignant bone tumor in children and young adults, its complex etiology involving a combination of environmental and genetic factors. MicroRNA (miRNA) is a short, non‑coding regulatory RNA molecule that represses gene expression by imperfectly base‑pairing to the 3' untranslated region of target mRNAs. Evidence has shown that alterations in the expression of miRNA are involved in the initiation, progression, and metastasis of human cancers. It is believed that miRNAs function both as tumor suppressors and oncogenes during cancer development. In the present study, three tumor-associated miRNAs (miR‑21, miR‑34a and miR‑146a) coding regions were screened in Chinese‑Han OS patients. A G>A variation in the pre‑miR‑34a coding region was found to be associated with higher OS morbidity. By detecting the mature miR‑34a expression in cells transfected with pre‑miR‑34a expression vectors of different genotypes using quantitative polymerase chain reaction, it was demonstrated that the G>A variation reduced miR‑34a expression in vitro. This was in accordance with the data collected from tumor tissue and patient serum samples. Subsequently, a dual‑luciferase reporter assay and western blot analysis were used to detect the site variation effect on the expression of c‑Met, a target gene of miR‑34a. The G>A variation downregulated the suppression of c‑Met in two OS cell lines. Furthermore, it was found that reduced miR‑34a expression decreased the suppression of OS cell proliferation in vitro. In conclusion, the present study established the association between miR‑34a and the risk of suffering OS in a Chinese Han population by identifying one functional single nucleotide polymorphism site in pre‑miR‑34a. These findings may give insight into the mechanism of OS development and create an opportunity to approach the diagnosis and treatment of OS.

Waizenegger JS, Ben-Batalla I, Weinhold N, et al.
Role of Growth arrest-specific gene 6-Mer axis in multiple myeloma.
Leukemia. 2015; 29(3):696-704 [PubMed] Related Publications
Multiple myeloma is a mostly incurable malignancy characterized by the expansion of a malignant plasma cell (PC) clone in the human bone marrow (BM). Myeloma cells closely interact with the BM stroma, which secretes soluble factors that foster myeloma progression and therapy resistance. Growth arrest-specific gene 6 (Gas6) is produced by BM-derived stroma cells and can promote malignancy. However, the role of Gas6 and its receptors Axl, Tyro3 and Mer (TAM receptors) in myeloma is unknown. We therefore investigated their expression in myeloma cell lines and in the BM of myeloma patients and healthy donors. Gas6 showed increased expression in sorted BMPCs of myeloma patients compared with healthy controls. The fraction of Mer(+) BMPCs was increased in myeloma patients in comparison with healthy controls whereas Axl and Tyro3 were not expressed by BMPCs in the majority of patients. Downregulation of Gas6 and Mer inhibited the proliferation of different myeloma cell lines, whereas knocking down Axl or Tyro3 had no effect. Inhibition of the Gas6 receptor Mer or therapeutic targeting of Gas6 by warfarin reduced myeloma burden and improved survival in a systemic model of myeloma. Thus, the Gas6-Mer axis represents a novel candidate for therapeutic intervention in this incurable malignancy.

Nguyen KQ, Tsou WI, Calarese DA, et al.
Overexpression of MERTK receptor tyrosine kinase in epithelial cancer cells drives efferocytosis in a gain-of-function capacity.
J Biol Chem. 2014; 289(37):25737-49 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
MERTK, a member of the TAM (TYRO3, AXL, and MERTK) receptor tyrosine kinases, has complex and diverse roles in cell biology. On the one hand, knock-out of MERTK results in age-dependent autoimmunity characterized by failure of apoptotic cell clearance, while on the other, MERTK overexpression in cancer drives classical oncogene pathways leading to cell transformation. To better understand the interplay between cell transformation and efferocytosis, we stably expressed MERTK in human MCF10A cells, a non-tumorigenic breast epithelial cell line devoid of endogenous MERTK. While stable expression of MERTK in MCF10A resulted in enhanced motility and AKT-mediated chemoprotection, MERTK-10A cells did not form stable colonies in soft agar, or enhance proliferation compared with parental MCF10A cells. Concomitant to chemoresistance, MERTK also stimulated efferocytosis in a gain-of-function capacity. However, unlike AXL, MERTK activation was highly dependent on apoptotic cells, suggesting MERTK may preferentially interface with phosphatidylserine. Consistent with this idea, knockdown of MERTK in breast cancer cells MDA-MB 231 reduced efferocytosis, while transient or stable expression of MERTK stimulated apoptotic cell clearance in all cell lines tested. Moreover, human breast cancer cells with higher endogenous MERTK showed higher levels of efferocytosis that could be blocked by soluble TAM receptors. Finally, through MERTK, apoptotic cells induced PD-L1 expression, an immune checkpoint blockade, suggesting that cancer cells may adopt MERTK-driven efferocytosis as an immune suppression mechanism for their advantage. These data collectively identify MERTK as a significant link between cancer progression and efferocytosis, and a potentially unrealized tumor-promoting event when MERTK is overexpressed in epithelial cells.

Ortona E, Pierdominici M, Berstein L
Autoantibodies to estrogen receptors and their involvement in autoimmune diseases and cancer.
J Steroid Biochem Mol Biol. 2014; 144 Pt B:260-7 [PubMed] Related Publications
The involvement of estrogens, which influence many physiologic processes, has been shown in the development or progression of several diseases including some cancers, most notably breast cancer, and autoimmune disorders. Estrogenic signal is transferred via estrogen receptors (ER) which have dual localization, predominantly intracellular but also in plasma membrane. The discovery of membrane-associated ER (mER) has greatly expanded our understanding of estrogen action; upon ligand binding, mER rapidly activate different signaling pathways inducing downstream transcription factors. Some target genes of the mER pathway may be activated independently of the intracellular ER. Additionally, intracellular ER action can be modulated by mER-initiated signaling. Most notably, the identification of autoantibodies reacting with ER (ERAB) and their possible pathogenic role in autoimmunity and cancer have opened a new path for the research in the estrogen-related receptor activity. In this review, we briefly recapitulate the localization and function of ER and mostly discuss the possible role of ERAB as novel potential prognostic and/or predictive tools in autoimmunity and cancer.

Kim KC, Choi EH, Lee C
Axl receptor tyrosine kinase is a novel target of apigenin for the inhibition of cell proliferation.
Int J Mol Med. 2014; 34(2):592-8 [PubMed] Related Publications
The Axl receptor tyrosine kinase (RTK), along with Tyro 3 and Mer, belongs to the TAM subfamily that promotes survival, stimulates proliferation and/or inhibits apoptosis. In various types of human cancer, including breast, lung and prostate cancer, Axl expression is increased and correlates with an advanced clinical stage. In this study, we examined whether apigenin has an effect on Axl expression, which in turn can affect cell proliferation. The treatment of the non‑small cell lung cancer (NSCLC) cells, A549 and H460, with apigenin decreased Axl mRNA and protein expression in a dose‑dependent manner. Axl promoter activity was also inhibited by apigenin, indicating that apigenin suppressed Axl expression at the transcriptional level. Upon treatment with apigenin, the viability of both the A549 and H460 cells was gradually decreased and the anti-proliferative effects were further confirmed by the dose‑dependent decrease in the clonogenic ability of the apigenin‑treated cells. Subsequently, we found that the viability and clonogenic ability of the cells treated with apigenin was less or more affected by transfection of the cells with a Axl-expressing plasmid or Axl targeting siRNA, compared to transfection with the empty vector or control siRNA, respectively. In addition, apigenin increased the expression of p21, a cyclin-dependent kinase inhibitor, but reduced the expression of X-linked inhibitor of apoptosis protein (XIAP). These cell cycle arrest and pro-apoptotic effects of apigenin were also attenuated or augmented by the up- or downregulation of Axl expression, respectively, which suggests that Axl is a novel target of apigenin through which it exerts its inhibitory effects on cell proliferation. Taken together, our data indicate that apigenin downregulates Axl expression, which subsequently results in the inhibition of NSCLC cell proliferation through the increase and decrease of p21 and XIAP expression, respectively.

Rothlin CV, Leighton JA, Ghosh S
Tyro3, Axl, and Mertk receptor signaling in inflammatory bowel disease and colitis-associated cancer.
Inflamm Bowel Dis. 2014; 20(8):1472-80 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Three receptor tyrosine kinases, Tyro3, Axl, and Mertk (TAM) and their ligands Gas6 and Protein S, have emerged as potent negative regulators of innate immune responses. A number of studies using genetic ablation of TAM loci in mice have elucidated the mechanism of TAM engagement and function during the immune response and removal of apoptotic cells. Following phagocytosis of apoptotic cells or the induction of T-cell dependent adaptive immune responses, ligand-induced TAM signaling dampens proinflammatory cytokine production and thus prevents exaggerated or prolonged inflammation. It is believed that the TAM pathway may play an important role in the pathogenesis of inflammatory bowel disease. Suppression of inflammation and removal of apoptotic cells followed by tissue repair are essential processes for disease remission and the successful management of inflammatory bowel disease. In light of the key role of TAMs in controlling inflammatory responses, here, we review the recent advances on TAM research vis-à-vis the resolution of intestinal inflammation. Targeted activation of TAM receptor tyrosine kinases may represent a potent therapeutic opportunity in inflammatory bowel disease.

Ding Y, Wu M, Liu J, et al.
Seed-targeting anti-miR-21 inhibiting malignant progression of retinoblastoma and analysis of their phosphorylation signaling pathways.
Exp Eye Res. 2014; 122:1-8 [PubMed] Related Publications
MiR-21 acts as a ubiquitous oncogene in major classes of human cancers and is a potential target for therapeutic intervention. However, the relative expression of miR-21 in retinoblastoma is poorly understood. Here we detected miR-21 expression in HXO-RB44 cell line human normal retinal tissues and retinoblastoma (Rb) tissue specimens, and studied its function using an 8-mer tiny seed-targeting anti-miR-21 (t-anti-miR-21). RT-PCR revealed that miR-21 was highly overexpressed in HXO-RB44 cells and Rb tissue specimens compared with normal human retinal tissues. The localization and transfection efficiency of t-anti-miR-21 and the cell cycle distribution were detected by confocal microscopy and flow cytometry. In addition, we found that t-anti-miR-21 led to a significant inhibition of retinoblastoma cell proliferation, migration and colony formation in vitro, with a similar effect to anti-miR-21. Anti-miR-21 down-regulated the miR-21 level, whereas both 8-mer t-anti-miR-21 and 15-mer m-anti-miR-21 had no impact on miR-21 expression levels. Finally, the phosphorylation signaling pathway, down-regulated by t-anti-miR-21, was integrated by KEGG assay, which elucidated the potential mechanisms of inhibition of miR-21 in retinoblastoma. Taken together, knockdown of miR-21 in the HXO-RB44 cell is capable of inhibiting cancer progression in retinoblastoma. Seed-targeting t-anti-miR-21 was a novel strategy for mir-21-based therapeutics and drug discovery.

Oji Y, Tatsumi N, Fukuda M, et al.
The translation elongation factor eEF2 is a novel tumor‑associated antigen overexpressed in various types of cancers.
Int J Oncol. 2014; 44(5):1461-9 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Recent studies have shown that cancer immunotherapy could be a promising therapeutic approach for the treatment of cancer. In the present study, to identify novel tumor-associated antigens (TAAs), the proteins expressed in a panel of cancer cells were serologically screened by immunoblot analysis and the eukaryotic elongation factor 2 (eEF2) was identified as an antigen that was recognized by IgG autoantibody in sera from a group of patients with head and neck squamous cell carcinoma (HNSCC) or colon cancer. Enzyme-linked immunosorbent assay showed that serum eEF2 IgG Ab levels were significantly higher in colorectal and gastric cancer patients compared to healthy individuals. Immunohistochemistry experiments showed that the eEF2 protein was overexpressed in the majority of lung, esophageal, pancreatic, breast and prostate cancers, HNSCC, glioblastoma multiforme and non-Hodgkin's lymphoma (NHL). Knockdown of eEF2 by short hairpin RNA (shRNA) significantly inhibited the growth in four eEF2-expressing cell lines, PC14 lung cancer, PCI6 pancreatic cancer, HT1080 fibrosarcoma and A172 glioblastoma cells, but not in eEF2-undetectable MCF7 cells. Furthermore, eEF2-derived 9-mer peptides, EF786 (eEF2 786-794 aa) and EF292 (eEF2 292-300 aa), elicited cytotoxic T lymphocyte (CTL) responses in peripheral blood mononuclear cells (PBMCs) from an HLA-A*24:02- and an HLA-A*02:01-positive healthy donor, respectively, in an HLA-A-restricted manner. These results indicated that the eEF2 gene is overexpressed in the majority of several types of cancers and plays an oncogenic role in cancer cell growth. Moreover, the eEF2 gene product is immunogenic and a promising target molecule of cancer immunotherapy for several types of cancers.

Di Martino MT, Gullà A, Gallo Cantafio ME, et al.
In vitro and in vivo activity of a novel locked nucleic acid (LNA)-inhibitor-miR-221 against multiple myeloma cells.
PLoS One. 2014; 9(2):e89659 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
BACKGROUND & AIM: The miR-221/222 cluster is upregulated in malignant plasma cells from multiple myeloma (MM) patients harboring the t(4;14) translocation. We previously reported that silencing of miR-221/222 by an antisense oligonucleotide induces anti-MM activity and upregulates canonical miR-221/222 targets. The in vivo anti-tumor activity occurred when miR-221/222 inhibitors were delivered directly into MM xenografts. The aim of the present study was to evaluate the anti-MM activity of a novel phosphorothioate modified backbone 13-mer locked nucleic acid (LNA)-Inhibitor-miR-221 (LNA-i-miR-221) specifically designed for systemic delivery.
METHODS: In vitro anti-MM activity of LNA-i-miR-221 was evaluated by cell proliferation and BrdU uptake assays. In vivo studies were performed with non-obese diabetic/severe combined immunodeficient (NOD.SCID) mice bearing t(4;14) MM xenografts, which were intraperitoneally or intravenously treated with naked LNA-i-miR-221. RNA extracts from retrieved tumors were analyzed for miR-221 levels and modulation of canonical targets expression. H&E staining and immunohistochemistry were performed on retrieved tumors and mouse vital organs.
RESULTS: In vitro, LNA-i-miR-221 exerted strong antagonistic activity against miR-221 and induced upregulation of the endogenous target p27Kip1. It had a marked anti-proliferative effect on t(4;14)-translocated MM cells but not on MM cells not carrying the translocation and not overexpressing miR-221. In vivo, systemic treatment with LNA-i-miR-221 triggered significant anti-tumor activity against t(4;14) MM xenografts; it also induced miR-221 downregulation, upregulated p27Kip1 and reduced Ki-67. No behavioral changes or organ-related toxicity were observed in mice as a consequence of treatments.
CONCLUSIONS: LNA-i-miR-221 is a highly stable, effective agent against t(4;14) MM cells, and is suitable for systemic use. These data provide the rationale for the clinical development of LNA-i-miR-221 for the treatment of MM.

Sumarheni S, Hong SS, Josserand V, et al.
Human full-length coagulation factor X and a GLA domain-derived 40-mer polypeptide bind to different regions of the adenovirus serotype 5 hexon capsomer.
Hum Gene Ther. 2014; 25(4):339-49 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
The interaction of human adenovirus (HAdV)-C5 and many other adenoviruses with blood coagulation factors (e.g., human factor X, FX) involves the binding of their GLA domain to the hexon capsomers, resulting in high levels of hepatotropism and potential hepatotoxicity. In this study, we tested the possibility of preventing these undesirable effects by using a GLA-mimicking peptide as a competitor. An FX GLA domain-derived, 40-mer polypeptide carrying 12 carboxyglutamate residues was synthesized (GLA(mim)). Surface plasmon resistance (SPR) analysis showed that GLA(mim) reacted with free and capsid-embedded hexon with a nanomolar affinity. Unexpectedly, GLA(mim) failed to compete with FX for hexon binding, and instead significantly increased the formation of FX-hexon or FX-adenovirion complexes. This observation was confirmed by in vitro cell transduction experiments using HAdV-C5-Luciferase vector (HAdV5-Luc), as preincubation of HAdV5-Luc with GLA(mim) before FX addition resulted in a higher transgene expression compared with FX alone. HAdV-C5 virions complexed with GLA(mim) were analyzed by cryoelectron microscopy. Image reconstruction demonstrated the bona fide hexon-GLA(mim) interaction, as for the full-length FX, although with considerable differences in stoichiometry and relative location on the hexon capsomer. Three extra densities were found at the periphery of each hexon, whereas one single FX molecule occupied the central cavity of the hexon trimeric capsomer. A refined analysis indicated that each extra density is found at the expected location of one highly variable loop 1 of the hexon, involved in scavenger receptor recognition. HAdV5-Luc complexed with a bifunctional GLA(mim)RGD peptide showed a lesser hepatotropism, compared with control HAdV5-Luc alone, and efficiently targeted αβ-integrin-overexpressing tumor cells in an in vivo mouse tumor model. Collectively, our findings open new perspectives in the design of adenoviral vectors for biotherapy.

Nishida S, Koido S, Takeda Y, et al.
Wilms tumor gene (WT1) peptide-based cancer vaccine combined with gemcitabine for patients with advanced pancreatic cancer.
J Immunother. 2014 Feb-Mar; 37(2):105-14 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Wilms tumor gene (WT1) protein is an attractive target for cancer immunotherapy. We aimed to investigate the feasibility of a combination therapy consisting of gemcitabine and WT1 peptide-based vaccine for patients with advanced pancreatic cancer and to make initial assessments of its clinical efficacy and immunologic response. Thirty-two HLA-A*24:02 patients with advanced pancreatic cancer were enrolled. Patients received HLA-A*24:02-restricted, modified 9-mer WT1 peptide (3 mg/body) emulsified with Montanide ISA51 adjuvant (WT1 vaccine) intradermally biweekly and gemcitabine (1000 mg/m) on days 1, 8, and 15 of a 28-day cycle. This combination therapy was well tolerated. The frequencies of grade 3-4 adverse events for this combination therapy were similar to those for gemcitabine alone. Objective response rate was 20.0% (6/30 evaluable patients). Median survival time and 1-year survival rate were 8.1 months and 29%, respectively. The association between longer survival and positive delayed-type hypersensitivity to WT1 peptide was statistically significant, and longer survivors featured a higher frequency of memory-phenotype WT1-specific cytotoxic T lymphocytes both before and after treatment. WT1 vaccine in combination with gemcitabine was well tolerated for patients with advanced pancreatic cancer. Delayed-type hypersensitivity-positivity to WT1 peptide and a higher frequency of memory-phenotype WT1-specific cytotoxic T lymphocytes could be useful prognostic markers for survival in the combination therapy with gemcitabine and WT1 vaccine. Further clinical investigation is warranted to determine the effectiveness of this combination therapy.

Azuma K, Komatsu N, Hattori S, et al.
Humoral immune responses to EGFR-derived peptides predict progression-free and overall survival of non-small cell lung cancer patients receiving gefitinib.
PLoS One. 2014; 9(1):e86667 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Somatic mutations in the epidermal growth factor receptor (EGFR) gene are associated with clinical response to EGFR tyrosine kinase inhibitors (TKIs), such as gefitinib, in patients with non-small cell lung cancer (NSCLC). However, humoral immune responses to EGFR in NSCLC patients have not been well studied. In this study, we investigated the clinical significance of immunoglobulin G (IgG) responses to EGFR-derived peptides in NSCLC patients receiving gefitinib. Plasma IgG titers to each of 60 different EGFR-derived 20-mer peptides were measured by the Luminex system in 42 NSCLC patients receiving gefitinib therapy. The relationships between the peptide-specific IgG titers and presence of EGFR mutations or patient survival were evaluated statistically. IgG titers against the egfr_481-500, egfr_721-740, and egfr_741-760 peptides were significantly higher in patients with exon 21 mutation than in those without it. On the other hand, IgG titers against the egfr_841-860 and egfr_1001-1020 peptides were significantly lower and higher, respectively, in patients with deletion in exon 19. Multivariate Cox regression analysis showed that IgG responses to egfr_41_ 60, egfr_61_80 and egfr_481_500 were significantly prognostic for progression-free survival independent of other clinicopathological characteristics, whereas those to the egfr_41_60 and egfr_481_500 peptides were significantly prognostic for overall survival. Detection of IgG responses to EGFR-derived peptides may be a promising method for prognostication of NSCLC patients receiving gefitinib. Our results may provide new insight for better understanding of humoral responses to EGFR in NSCLC patients.

Zhang X, Zhang X, Liu C, et al.
MiR‑224 promotes colorectal cancer cells proliferation via downregulation of P21WAF1/CIP1.
Mol Med Rep. 2014; 9(3):941-6 [PubMed] Related Publications
MicroRNAs (miRNAs) are between 19 and 25 mer non‑coding RNAs involved in cancer cell proliferation, apoptosis, stress responses and maintenance of stem cell potency. In the present study, miR‑224 was observed to be upregulated in colorectal cancer (CRC) tissue. Overexpression of miR‑224 facilitated proliferation of the CRC cell lines, HCT‑116 and SW‑480. Bioinformatics analysis revealed a putative miR‑224 binding site in the 3'‑untranslated region of CDKI1A (P21WAF1/CIP1). Western blot analysis and the luciferase reporter assay proved that miR‑224 represses P21WAF1/CIP1 expression and promotes cell cycle G1/S transition. These results suggest that the downregulation of miR‑224 in CRC is a novel potential therapeutic strategy.

Zwenger A, Rabassa M, Demichelis S, et al.
High expression of sLex associated with poor survival in Argentinian colorectal cancer patients.
Int J Biol Markers. 2014 Jan-Mar; 29(1):e30-9 [PubMed] Related Publications
AIM: Colorectal cancer (CRC) is one of the most prevalent malignancies in Argentina with 11,043 new cases and 6,596 deaths estimated to have occurred in 2008. The present study was developed to clarify the differential expression of MUC1, MUC2, sLex, and sLea in colorectal cancer patients and their relationship with survival and clinical and histological features.
METHODS: Ninety primary tumor samples and 43 metastatic lymph nodes from CRC patients were studied; follow-up was documented. Twenty-six adenoma and 68 histological normal mucosa specimens were analyzed. An immunohistochemical approach was applied and statistical analysis was performed.
RESULTS: In tumor samples, MUC1, sLea, and sLex were highly expressed (94%, 67%, and 91%, respectively); also, we found a significantly increased expression of the 3 antigens in primary tumors and metastatic lymph nodes compared with normal mucosa and adenomas. MUC2 was expressed in 52% of both normal mucosa and CRC samples; this reactivity significantly decreased in metastatic lymph nodes (p<0.05). A multiple comparison analysis showed that MUC1 and sLex discriminated among 3 groups: normal, adenoma, and CRC tissues. The increase of sLex expression showed an association with recurrence, and survival analysis showed that a high sLex staining was significantly associated with a poor survival. By multivariate analysis MUC1 inmunoreactivity correlated positively and significantly with tumor size, while MUC2 expression showed the opposite correlation.
CONCLUSIONS: The correlation of sLex overexpression in primary tumors and metastatic lymph nodes, the discrimination among the normal, adenoma, and CRC groups based on sLex expression, as well as its association with recurrence and survival, all suggest a prognostic role of sLex in Argentinian CRC patients.

Saheb A, Patterson S, Josowicz M
Probing for DNA methylation with a voltammetric DNA detector.
Analyst. 2014; 139(4):786-92 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
A label-free electrochemical detection of DNA hybridization is used for probing synthetic methylated ssDNA 27-mer or 33-mer targets from the GSTP1-gene. The method is based on electrostatic modulation of the anion-exchange kinetics of a polypyrrole bilayer film deposited on platinum-microelectrodes to which a synthetic single-stranded 15-mer GSTP-1 promoter probe DNA has been attached (DNA detector). The effect of the contact of this DNA-detector with non-methylated and methylated complementary DNA sequences in Tris-buffer is compared using cyclic voltammetry (CV). The DNA-hybridization taking place at the electrode surface leads to a significant decrease of the CV area recorded after exposure to complementary target DNA in comparison to the CV change recorded for non-complementary DNA target. The performance of this miniaturized DNA detector was optimized with respect to hybridization time, temperature, and concentration of the target. It was also evaluated with respect to selectivity, sensitivity, and reproducibility. These results are significant for their possible use as a screening test for hypermethylated DNA sequences.

Whitman SP, Kohlschmidt J, Maharry K, et al.
GAS6 expression identifies high-risk adult AML patients: potential implications for therapy.
Leukemia. 2014; 28(6):1252-8 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Emerging data demonstrate important roles for the TYRO3/AXL/MERTK receptor tyrosine kinase (TAM RTK) family in diverse cancers. We investigated the prognostic relevance of GAS6 expression, encoding the common TAM RTK ligand, in 270 adults (n=71 aged<60 years; n=199 aged ⩾60 years) with de novo cytogenetically normal acute myeloid leukemia (CN-AML). Patients expressing GAS6 (GAS6+), especially those aged ⩾60 years, more often failed to achieve a complete remission (CR). In all patients, GAS6+ patients had shorter disease-free (DFS) and overall (OS) survival than patients without GAS6 expression (GAS6-). After adjusting for other prognostic markers, GAS6+ predicted CR failure (P=0.02), shorter DFS (P=0.004) and OS (P=0.04). To gain further biological insights, we derived a GAS6-associated gene-expression signature (P<0.001) that in GAS6+ patients included overexpressed BAALC and MN1, known to confer adverse prognosis in CN-AML, and overexpressed CXCL12, encoding stromal cell-derived factor, and its receptor genes, chemokine (C-X-C motif) receptor 4 (CXCR4) and CXCR7. This study reports for the first time that GAS6 expression is an adverse prognostic marker in CN-AML. Although GAS6 decoy receptors are not yet available in the clinic for GAS6+ CN-AML therapy, potential alternative therapies targeting GAS6+-associated pathways, for example, CXCR4 antagonists, may be considered for GAS6+ patients to sensitize them to chemotherapy.

Zhao H, Dong T, Zhou H, et al.
miR-320a suppresses colorectal cancer progression by targeting Rac1.
Carcinogenesis. 2014; 35(4):886-95 [PubMed] Related Publications
MicroRNAs (miRNAs) have emerged as critical epigenetic regulators involved in cancer progression. miR-320a has been identified to be a novel tumour suppressive miRNA in colorectal cancer (CRC). However, the detailed molecular mechanisms are not fully understood. Here, we reported that miR-320a inversely associated with CRC aggressiveness in both cell lines and clinical specimens. Functional studies demonstrated that miR-320a significantly decreased the capability of cell migration/invasion and induced G0/G1 growth arrest in vitro and in vivo. Furthermore, Rac1 was identified as one of the direct downstream targets of miR-320a and miR-320a specifically binds to the conserved 8-mer at position 1140-1147 of Rac1 3'-untranslated region to regulate Rac1 protein expression. Over-expression of miR-320a in SW620 cells inhibited Rac1 expression, whereas reduction of miR-320a by anti-miR-320a in SW480 cells enhanced Rac1 expression. Re-expression of Rac1 in the SW620/miR-320a cells restored the cell migration/invasion inhibited by miR-320a, whereas knockdown of Rac1 in the SW480/anti-miR-320a cells repressed these cellular functions elevated by anti-miR-320a. Conclusively, our results demonstrate that miR-320a functions as a tumour-suppressive miRNA through targeting Rac1 in CRC.

Lemke G
Biology of the TAM receptors.
Cold Spring Harb Perspect Biol. 2013; 5(11):a009076 [PubMed] Related Publications
The TAM receptors--Tyro3, Axl, and Mer--comprise a unique family of receptor tyrosine kinases, in that as a group they play no essential role in embryonic development. Instead, they function as homeostatic regulators in adult tissues and organ systems that are subject to continuous challenge and renewal throughout life. Their regulatory roles are prominent in the mature immune, reproductive, hematopoietic, vascular, and nervous systems. The TAMs and their ligands--Gas6 and Protein S--are essential for the efficient phagocytosis of apoptotic cells and membranes in these tissues; and in the immune system, they act as pleiotropic inhibitors of the innate inflammatory response to pathogens. Deficiencies in TAM signaling are thought to contribute to chronic inflammatory and autoimmune disease in humans, and aberrantly elevated TAM signaling is strongly associated with cancer progression, metastasis, and resistance to targeted therapies.

Murphy BL, Obad S, Bihannic L, et al.
Silencing of the miR-17~92 cluster family inhibits medulloblastoma progression.
Cancer Res. 2013; 73(23):7068-78 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Medulloblastoma, originating in the cerebellum, is the most common malignant brain tumor in children. Medulloblastoma consists of four major groups where constitutive activation of the Sonic Hedgehog (SHH) signaling pathway is a hallmark of one group. Mouse and human SHH medulloblastomas exhibit increased expression of microRNAs encoded by the miR-17~92 and miR-106b~25 clusters compared with granule progenitors and postmitotic granule neurons. Here, we assessed the therapeutic potential of 8-mer seed-targeting locked nucleic acid (LNA)-modified anti-miR oligonucleotides, termed tiny LNAs, that inhibit microRNA seed families expressed by miR-17~92 and miR-106b~25 in two mouse models of SHH medulloblastomas. We found that tumor cells (medulloblastoma cells) passively took up 8-mer LNA-anti-miRs and specifically inhibited targeted microRNA seed-sharing family members. Inhibition of miR-17 and miR-19a seed families by anti-miR-17 and anti-miR-19, respectively, resulted in diminished tumor cell proliferation in vitro. Treatment of mice with systemic delivery of anti-miR-17 and anti-miR-19 reduced tumor growth in flank and brain allografts in vivo and prolonged the survival of mice with intracranial transplants, suggesting that inhibition of the miR-17~92 cluster family by 8-mer LNA-anti-miRs might be considered for the treatment of SHH medulloblastomas.

Christoph S, Deryckere D, Schlegel J, et al.
UNC569, a novel small-molecule mer inhibitor with efficacy against acute lymphoblastic leukemia in vitro and in vivo.
Mol Cancer Ther. 2013; 12(11):2367-77 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. Although survival rates have improved, patients with certain biologic subtypes still have suboptimal outcomes. Current chemotherapeutic regimens are associated with short- and long-term toxicities and novel, less toxic therapeutic strategies are needed. Mer receptor tyrosine kinase is ectopically expressed in ALL patient samples and cell lines. Inhibition of Mer expression reduces prosurvival signaling, increases chemosensitivity, and delays development of leukemia in vivo, suggesting that Mer tyrosine kinase inhibitors are excellent candidates for targeted therapies. Brain and spinal tumors are the second most common malignancies in childhood. Multiple chemotherapy approaches and radiotherapies have been attempted, yet overall survival remains dismal. Mer is also abnormally expressed in atypical teratoid/rhabdoid tumors (AT/RT), providing a rationale for targeting Mer as a therapeutic strategy. We have previously described UNC569, the first small-molecule Mer inhibitor. This article describes the biochemical and biologic effects of UNC569 in ALL and AT/RT. UNC569 inhibited Mer activation and downstream signaling through ERK1/2 and AKT, determined by Western blot analysis. Treatment with UNC569 reduced proliferation/survival in liquid culture, decreased colony formation in methylcellulose/soft agar, and increased sensitivity to cytotoxic chemotherapies. MYC transgenic zebrafish with T-ALL were treated with UNC569 (4 μmol/L for two weeks). Fluorescence was quantified as indicator of the distribution of lymphoblasts, which express Mer and enhanced GFP. UNC569 induced more than 50% reduction in tumor burden compared with vehicle- and mock-treated fish. These data support further development of Mer inhibitors as effective therapies in ALL and AT/RT.

Ben-Batalla I, Schultze A, Wroblewski M, et al.
Axl, a prognostic and therapeutic target in acute myeloid leukemia mediates paracrine crosstalk of leukemia cells with bone marrow stroma.
Blood. 2013; 122(14):2443-52 [PubMed] Related Publications
Acute myeloid leukemia (AML) represents a clonal disease of hematopoietic progenitors characterized by acquired heterogenous genetic changes that alter normal mechanisms of proliferation, self-renewal, and differentiation.(1) Although 40% to 45% of patients younger than 65 years of age can be cured with current therapies, only 10% of older patients reach long-term survival.(1) Because only very few novel AML drugs were approved in the past 2 decades, there is an urgent need to identify novel targets and therapeutic strategies to treat underserved AML patients. We report here that Axl, a member of the Tyro3, Axl, Mer receptor tyrosine kinase family,(2-4) represents an independent prognostic marker and therapeutic target in AML. AML cells induce expression and secretion of the Axl ligand growth arrest-specific gene 6 (Gas6) by bone marrow-derived stromal cells (BMDSCs). Gas6 in turn mediates proliferation, survival, and chemoresistance of Axl-expressing AML cells. This Gas6-Axl paracrine axis between AML cells and BMDSCs establishes a chemoprotective tumor cell niche that can be abrogated by Axl-targeting approaches. Axl inhibition is active in FLT3-mutated and FLT3 wild-type AML, improves clinically relevant end points, and its efficacy depends on presence of Gas6 and Axl. Axl inhibition alone or in combination with chemotherapy might represent a novel therapeutic avenue for AML.

Qin B, Chen Z, Jin W, Cheng K
Development of cholesteryl peptide micelles for siRNA delivery.
J Control Release. 2013; 172(1):159-68 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Despite the rapid progress in the siRNA field, developing a safe and efficient delivery system of siRNA remains to be an obstacle in the therapeutical application of siRNA. The purpose of this study is to develop an efficient peptide-based siRNA delivery system for cancer therapy. To this end, cholesterol was conjugated to a series of peptides composed of lysine and histidine residues. The resultant cholesteryl peptides were characterized, and their potential for siRNA delivery was evaluated. Our results indicate that short peptides (11-21 mer) composed of various numbers of lysine and histidine residues alone are not sufficient to mediate efficient siRNA delivery. However, the amphiphilic cholesteryl peptides can self-assemble to form a micelle-like structure in aqueous solutions, which significantly promotes the siRNA condensation capability of the peptides. The cholesteryl peptides form stable complex with siRNA and effectively protect siRNA from degradation in rat serum up to three days. Furthermore, the cholesteryl peptides efficiently transfect siRNA into different cancer cells and trigger potent gene silencing effect, whereas peptides without cholesterol modification cannot deliver siRNA into the cells. In addition, one of the cholesteryl peptides Chol-H3K2s displays comparable cellular uptake and gene silencing effect but less cytotoxicity compared with branched polyethylenimine (bPEI) and Lipofectamine-2000. Our results reveal that the cholesteryl peptides possess great potential as an efficient siRNA delivery system.

Suleiman L, Négrier C, Boukerche H
Protein S: A multifunctional anticoagulant vitamin K-dependent protein at the crossroads of coagulation, inflammation, angiogenesis, and cancer.
Crit Rev Oncol Hematol. 2013; 88(3):637-54 [PubMed] Related Publications
Since its discovery in 1970, protein S (PS) has emerged as a key vitamin K-dependent natural anticoagulant protein at the crossroads of multiple biological processes, including coagulation, apoptosis, atherosclerosis, angiogenesis/vasculogenesis, and cancer progression. Following the binding to a unique family of protein tyrosine kinase receptors referred to as Tyro-3, Axl and Mer (TAM) receptors, PS can lead to regulation of coagulation, phagocytosis of apoptotic cells, cell survival, activation of innate immunity, vessel integrity and angiogenesis, and local invasion and metastasis. Because of these dynamics and multiple functions of PS, which are largely lost following invalidation of the mouse PROS1 gene, this molecule is currently intensively studied in biomedical research. The purpose of this review is to provide a brief chronicle of the discovery and current understanding of the mechanisms of PS signaling, and how PS and their signaling partners regulate various cellular functions, with a particular focus on TAM receptors.

Shen D, Xie F, Edwards WB
Evaluation of phage display discovered peptides as ligands for prostate-specific membrane antigen (PSMA).
PLoS One. 2013; 8(7):e68339 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
The aim of this study was to identify potential ligands of PSMA suitable for further development as novel PSMA-targeted peptides using phage display technology. The human PSMA protein was immobilized as a target followed by incubation with a 15-mer phage display random peptide library. After one round of prescreening and two rounds of screening, high-stringency screening at the third round of panning was performed to identify the highest affinity binders. Phages which had a specific binding activity to PSMA in human prostate cancer cells were isolated and the DNA corresponding to the 15-mers were sequenced to provide three consensus sequences: GDHSPFT, SHFSVGS and EVPRLSLLAVFL as well as other sequences that did not display consensus. Two of the peptide sequences deduced from DNA sequencing of binding phages, SHSFSVGSGDHSPFT and GRFLTGGTGRLLRIS were labeled with 5-carboxyfluorescein and shown to bind and co-internalize with PSMA on human prostate cancer cells by fluorescence microscopy. The high stringency requirements yielded peptides with affinities KD~1 µM or greater which are suitable starting points for affinity maturation. While these values were less than anticipated, the high stringency did yield peptide sequences that apparently bound to different surfaces on PSMA. These peptide sequences could be the basis for further development of peptides for prostate cancer tumor imaging and therapy.

Linger RM, Lee-Sherick AB, DeRyckere D, et al.
Mer receptor tyrosine kinase is a therapeutic target in pre-B-cell acute lymphoblastic leukemia.
Blood. 2013; 122(9):1599-609 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Acute lymphoblastic leukemia (ALL) is currently treated with an intense regimen of chemotherapy yielding cure rates near 85%. However, alterations to treatment strategies using available drugs are unlikely to provide significant improvement in survival or decrease therapy-associated toxicities. Here, we report ectopic expression of the Mer receptor tyrosine kinase in pre-B-cell ALL (B-ALL) cell lines and pediatric patient samples. Inhibition of Mer in B-ALL cell lines decreased activation of AKT and MAPKs and led to transcriptional changes, including decreased expression of antiapoptotic PRKCB gene and increase in proapoptotic BAX and BBC3 genes. Further, Mer inhibition promoted chemosensitization, decreased colony-forming potential in clonogenic assays, and delayed disease onset in a mouse xenograft model of leukemia. Our results identify Mer as a potential therapeutic target in B-ALL and suggest that inhibitors of Mer may potentiate lymphoblast killing when used in combination with chemotherapy. This strategy could reduce minimal residual disease and/or allow for chemotherapy dose reduction, thereby leading to improved event-free survival and reduced therapy-associated toxicity for patients with B-ALL. Additionally, Mer is aberrantly expressed in numerous other malignancies suggesting that this approach may have broad applications.

Dall M, Calloe K, Haupt-Jorgensen M, et al.
Gliadin fragments and a specific gliadin 33-mer peptide close KATP channels and induce insulin secretion in INS-1E cells and rat islets of langerhans.
PLoS One. 2013; 8(6):e66474 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
In non-obese diabetic (NOD) mice, diabetes incidence is reduced by a gluten-free diet. Gluten peptides, such as the compound gliadin, can cross the intestinal barrier and may directly affect pancreatic beta cells. We investigated the effects of enzymatically-digested gliadin in NOD mice, INS-1E cells and rat islets. Six injections of gliadin digest in 6-week-old NOD mice did not affect diabetes development, but increased weight gain (20% increase by day 100). In INS-1E cells, incubation with gliadin digest induced a dose-dependent increase in insulin secretion, up to 2.5-fold after 24 hours. A similar effect was observed in isolated rat islets (1.6-fold increase). In INS-1E cells, diazoxide reduced the stimulatory effect of gliadin digest. Additionally, gliadin digest was shown to decrease current through KATP-channels. A specific gliadin 33-mer had a similar effect, both on current and insulin secretion. Finally, INS-1E incubation with gliadin digest potentiated palmitate-induced insulin secretion by 13% compared to controls. Our data suggest that gliadin fragments may contribute to the beta-cell hyperactivity observed prior to the development of type 1 diabetes.

Taichman RS, Patel LR, Bedenis R, et al.
GAS6 receptor status is associated with dormancy and bone metastatic tumor formation.
PLoS One. 2013; 8(4):e61873 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
Disseminated tumor cells (DTCs) are believed to lie dormant in the marrow before they can be activated to form metastases. How DTCs become dormant in the marrow and how dormant DTCs escape dormancy remains unclear. Recent work has shown that prostate cancer (PCa) cell lines express the growth-arrest specific 6 (GAS6) receptors Axl, Tyro3, and Mer, and become growth arrested in response to GAS6. We therefore hypothesized that GAS6 signaling regulates the proliferative activity of DTCs in the marrow. To explore this possibility, in vivo studies were performed where it was observed that when Tyro3 expression levels exceed Axl expression, the PCa cells exhibit rapid growth. When when Axl levels predominate, PCa cells remain largely quiescent. These findings suggest that a balance between the expression of Axl and Tyro3 is associated with a molecular switch between a dormant and a proliferative phenotype in PCa metastases.

Tworkoski KA, Platt JT, Bacchiocchi A, et al.
MERTK controls melanoma cell migration and survival and differentially regulates cell behavior relative to AXL.
Pigment Cell Melanoma Res. 2013; 26(4):527-41 [PubMed] Article available free on PMC after 12/09/2015 Related Publications
The receptor tyrosine kinase AXL regulates melanoma cell proliferation and migration. We now demonstrate that AXL and the related kinase MERTK are alternately expressed in melanoma and are associated with different transcriptional signatures. MERTK-positive melanoma cells are more proliferative and less migratory than AXL-positive melanoma cells and overexpression of AXL increases cell motility relative to MERTK. MERTK is expressed in up to 50% of melanoma cells and shRNA-mediated knockdown of MERTK reduces colony formation and cell migration in a CDC42-dependent fashion. Targeting MERTK also decreases cell survival and proliferation in an AKT-dependent manner. Finally, we identify a novel mutation in the kinase domain of MERTK, MERTK(P) (802S) , that increases the motility of melanoma cells relative to wild-type MERTK. Together, these data demonstrate that MERTK is a possible therapeutic target in melanoma, that AXL and MERTK are associated with differential cell behaviors, and that mutations in MERTK may contribute to melanoma pathogenesis.

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