Gene Summary

Gene:ARHGEF1; Rho guanine nucleotide exchange factor 1
Aliases: LSC, GEF1, LBCL2, SUB1.5, P115-RHOGEF
Summary:Rho GTPases play a fundamental role in numerous cellular processes that are initiated by extracellular stimuli that work through G protein coupled receptors. The encoded protein may form complex with G proteins and stimulate Rho-dependent signals. Multiple alternatively spliced transcript variants have been found for this gene, but the full-length nature of some variants has not been defined. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:rho guanine nucleotide exchange factor 1
Source:NCBIAccessed: 11 March, 2017


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 11 March 2017 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 11 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (6)

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: ARHGEF1 (cancer-related)

Grassilli S, Nika E, Lambertini E, et al.
A network including PU.1, Vav1 and miR-142-3p sustains ATRA-induced differentiation of acute promyelocytic leukemia cells - a short report.
Cell Oncol (Dordr). 2016; 39(5):483-489 [PubMed] Related Publications
PURPOSE: Reduced expression of miR-142-3p has been found to be associated with the development of various subtypes of myeloid leukemia, including acute promyelocytic leukemia (APL). In APL-derived cells, miR-142-3p expression can be restored by all-trans retinoic acid (ATRA), which induces the completion of their maturation program. Here, we aimed to assess whether PU.1, essential for ATRA-induced gene transcription, regulates the expression of miR-142-3p in APL-derived cells and, based on the established cooperation between PU.1 and Vav1 in modulating gene expression, to evaluate the role of Vav1 in restoring the expression of miR-142-3p.
METHODS: ATRA-induced increases in PU.1 and Vav1 expression in APL-derived NB4 cells were counteracted with specific siRNAs, and the expression of miR-142-3p was measured by quantitative real-time PCR (qRT-PCR). The recruitment of PU.1 and/or Vav1 to the regulatory region of miR-142 was assessed by quantitative chromatin immunoprecipitation (Q-ChIP). Synthetic inhibitors or mimics for miR-142-3p were used to assess whether this miRNA plays a role in regulating the expression of PU.1 and/or Vav1.
RESULTS: We found that the expression of miR-142-3p in differentiating APL-derived NB4 cells is dependent on PU.1, and that Vav1 is essential for the recruitment of this transcription factor to its cis-binding element on the miR-142 promoter. In addition, we found that in ATRA-treated NB4 cells miR-142-3p sustains agonist-induced increases in both PU.1 and Vav1.
CONCLUSIONS: Our results suggest the existence of a Vav1/PU.1/miR-142-3p network that supports ATRA-induced differentiation in APL-derived cells. Since selective regulation of miRNAs may play a role in the future treatment of hematopoietic malignancies, our results may provide a basis for the development of new therapeutic strategies to restore the expression of miR-142-3p.

Li WH, Zhou ZJ, Huang TH, et al.
Detection of OSR2, VAV3, and PPFIA3 Methylation in the Serum of Patients with Gastric Cancer.
Dis Markers. 2016; 2016:5780538 [PubMed] Free Access to Full Article Related Publications
AIM: This study was to evaluate the diagnostic value of OSR2, VAV3, and PPFIA3 hypermethylation in gastric cancer (GC) patients.
PATIENTS AND METHODS: By using methylation-specific polymerase chain reaction (MSP), we detected the methylation status in tissue and serum samples from 48 gastric cancer (GC) patients and 25 normal individuals.
RESULTS: We found that OSR2, VAV3, and PPFIA3 were methylated in 70.8% (34/48), 54.2% (26/48), and 60.4% (29/48) of GC tissue, respectively. On the contrary, those genes were barely methylated in their paired paracancerous histological normal tissues (PCHNTs) (all P values < 0.01). We next analyzed the methylated OSR2, VAV3, and PPFIA3 in serum DNA. Compared with 25 normal individuals, those three genes were significantly hypermethylated in GC patients serum samples (all P values < 0.01). Regarding their diagnostic value in serum samples, the combined sensitivity of at least one positive among the three markers in serum was 83.3%, with a specificity of 88%.
CONCLUSION: Our test suggested that methylation of OSR2, VAV3, and PPFIA3 genes in serum sample may offer a good alternative in a simple, promising, and noninvasive detection of GC.

Feng Q, Leong WS, Liu L, Chan WI
Peruvoside, a Cardiac Glycoside, Induces Primitive Myeloid Leukemia Cell Death.
Molecules. 2016; 21(4):534 [PubMed] Related Publications
Despite the available chemotherapy and treatment, leukemia remains a difficult disease to cure due to frequent relapses after treatment. Among the heterogeneous leukemic cells, a rare population referred as the leukemic stem cell (LSC), is thought to be responsible for relapses and drug resistance. Cardiac glycosides (CGs) have been used in treating heart failure despite its toxicity. Recently, increasing evidence has demonstrated its new usage as a potential anti-cancer drug. Ouabain, one of the CGs, specifically targeted CD34⁺CD38(-) leukemic stem-like cells, but not the more mature CD34⁺CD38⁺ leukemic cells, making this type of compounds a potential treatment for leukemia. In search of other potential anti-leukemia CGs, we found that Peruvoside, a less studied CG, is more effective than Ouabain and Digitoxin at inducing cell death in primitive myeloid leukemia cells without obvious cytotoxicity on normal blood cells. Similar to Ouabain and Digitoxin, Peruvoside also caused cell cycle arrest at G₂/M stage. It up-regulates CDKN1A expression and activated the cleavage of Caspase 3, 8 and PARP, resulting in apoptosis. Thus, Peruvoside showed potent anti-leukemia effect, which may serve as a new anti-leukemia agent in the future.

Gao Y, Gao J, Li M, et al.
Rheb1 promotes tumor progression through mTORC1 in MLL-AF9-initiated murine acute myeloid leukemia.
J Hematol Oncol. 2016; 9:36 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The constitutive hyper-activation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathways has frequently been associated with acute myeloid leukemia (AML). While many inhibitors targeting these pathways have been developed, the anti-leukemic effect was not as robust as expected. As part of the molecular link between PI3K/Akt and mTOR kinase, the role of Rheb1 in AML remains unexplored. Our study aims to explore the role of Rheb1 in AML and estimate whether Rheb1 could be a potential target of AML treatment.
METHODS: The expressions of Rheb1 and other indicated genes were analyzed using real-time PCR. AML mouse model was established by retrovirus transduction. Leukemia cell properties and related signaling pathways were dissected by in vitro and in vivo studies. The transcriptional changes were analyzed via gene chip analysis. Molecular reagents including mTOR inhibitor and mTOR activator were used to evaluate the function of related signaling pathway in the mouse model.
RESULTS: We observed that Rheb1 is overexpressed in AML patients and the change of Rheb1 level in AML patients is associated with their median survival. Using a Rheb1-deficient MLL-AF9 murine AML model, we revealed that Rheb1 deletion prolonged the survival of AML mice by weakening LSC function. In addition, Rheb1 deletion arrested cell cycle progression and enhanced apoptosis of AML cells. Furthermore, while Rheb1 deletion reduced mTORC1 activity in AML cells, additional rapamycin treatment further decreased mTORC1 activity and increased the apoptosis of Rheb1 (Δ/Δ) AML cells. The mTOR activator 3BDO partially rescued mTORC1 signaling and inhibited apoptosis in Rheb1 (Δ/Δ) AML cells.
CONCLUSIONS: Our data suggest that Rheb1 promotes AML progression through mTORC1 signaling pathway and combinational drug treatments targeting Rheb1 and mTOR might have a better therapeutic effect on leukemia.

Xie T, Ren HY, Lin HQ, et al.
Sinomenine prevents metastasis of human osteosarcoma cells via S phase arrest and suppression of tumor-related neovascularization and osteolysis through the CXCR4-STAT3 pathway.
Int J Oncol. 2016; 48(5):2098-112 [PubMed] Related Publications
Osteosarcoma is the most common primary malignant tumor of the bone. The long-term survivals continue to be unsatisfactory for patients with metastatic and recurrent disease. Metastasis is still a severe challenge in osteosarcoma treatment. Sinomenine, an alkaloid from traditional Chinese medicine, has been proved to possess potent antitumor and anti-invasion effect on various cancers. However, the effect of sinomenine on human osteosarcoma and the underlying mechanisms remains unknown. We report here that sinomenine inhibited proliferation by inducing S phase arrest and suppressing the clone formation. Significant inhibitory effects were found in invasion and metastasis in osteosarcoma, but little cytotoxicity was observed in tested concentrations. Exposure to sinomenine resulted in suppression of invasion and migration in osteosarcoma cells as well as tube formation ability in the human umbilical vein endothelial cells (HUVEC) and U2OS cells. Furthermore, it demonstrated that CXCR4 played a key role contributing to invasion in osteosarcoma which is considered to be a core target site in sinomenine treatment. Sinomenine inhibited invasion by suppressing CXCR4 and STAT3 phosphorylation then downregulating the expression of MMP-2, MMP-9, RANKL, VEGF downstream. In addition, then RANKL-mediated bone destruction stimulated by osteoclastogenesis and VEGF-related neovascularization were restrained. Importantly, in vivo, sinomenine suppressed proliferation, osteoclastogenesis and bone destruction. Through these various comprehensive means, sinomenine inhibits metastasis in osteosarcoma. Taken together, our results revealed that sinomenine caused S phase arrest, inhibited invasion and metastasis via suppressing the CXCR4-STAT3 pathway and then osteoclastogenesis-mediated bone destruction and neovascularization in osteosarcoma. Sinomenine is therefore a promising adjuvant agent for metastasis control in osteosarcoma.

Zhang Y, Zhou SY, Yan HZ, et al.
miR-203 inhibits proliferation and self-renewal of leukemia stem cells by targeting survivin and Bmi-1.
Sci Rep. 2016; 6:19995 [PubMed] Free Access to Full Article Related Publications
Drug resistance is one of the leading causes of failed cancer therapy in the treatment of acute myeloid leukemia. Although the mechanisms of resistance are poorly understood, they may be related to the presence of leukemia stem cells (LSCs). Down-regulation of the miR-203 reportedly contributes to oncogenesis and chemo-resistance in multiple cancers. We found that miR-203 expression was down-regulated in CD34 + AML cells as compared with CD34- cells isolated from patients as well as in LSC-enriched (CD34 + CD38-) cell lines KG-1a or MOLM13. Additionally, re-expression of miR-203 led to decreased cell proliferation, self-renewal, and sphere formation in LSCs. Moreover, miR-203 was found to directly target the 3'un-translated regions of survivin and Bmi-1 mRNAs affecting proliferation and self-renewal in LSCs. In this study, we identified a novel miR-203/survivin/Bmi-1 axis involved in the regulation of biological properties of LSCs. This axis may represent a new therapeutic target for acute myeloid leukemia and a potential prognosis/diagnostic marker for LSCs therapy.

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.

Pabst C, Bergeron A, Lavallée VP, et al.
GPR56 identifies primary human acute myeloid leukemia cells with high repopulating potential in vivo.
Blood. 2016; 127(16):2018-27 [PubMed] Related Publications
Acute myeloid leukemia (AML) is a genetically heterogeneous hematologic malignancy, which is initiated and driven by a rare fraction of leukemia stem cells (LSCs). Despite the difficulties of identifying a common LSC phenotype, there is increasing evidence that high expression of stem cell gene signatures is associated with poor clinical outcome. Identification of functionally distinct subpopulations in this disease is therefore crucial to dissecting the molecular machinery underlying LSC self-renewal. Here, we combined next-generation sequencing technology with in vivo assessment of LSC frequencies and identified the adhesion G protein-coupled receptor 56 (GPR56) as a novel and stable marker for human LSCs for the majority of AML samples. High GPR56 expression was significantly associated with high-risk genetic subgroups and poor outcome. Analysis of GPR56 in combination with CD34 expression revealed engraftment potential of GPR56(+)cells in both the CD34(-)and CD34(+)fractions, thus defining a novel LSC compartment independent of the CD34(+)CD38(-)LSC phenotype.

Lechman ER, Gentner B, Ng SW, et al.
miR-126 Regulates Distinct Self-Renewal Outcomes in Normal and Malignant Hematopoietic Stem Cells.
Cancer Cell. 2016; 29(2):214-28 [PubMed] Free Access to Full Article Related Publications
To investigate miRNA function in human acute myeloid leukemia (AML) stem cells (LSC), we generated a prognostic LSC-associated miRNA signature derived from functionally validated subpopulations of AML samples. For one signature miRNA, miR-126, high bioactivity aggregated all in vivo patient sample LSC activity into a single sorted population, tightly coupling miR-126 expression to LSC function. Through functional studies, miR-126 was found to restrain cell cycle progression, prevent differentiation, and increase self-renewal of primary LSC in vivo. Compared with prior results showing miR-126 regulation of normal hematopoietic stem cell (HSC) cycling, these functional stem effects are opposite between LSC and HSC. Combined transcriptome and proteome analysis demonstrates that miR-126 targets the PI3K/AKT/MTOR signaling pathway, preserving LSC quiescence and promoting chemotherapy resistance.

Pharoah PD, Song H, Dicks E, et al.
PPM1D Mosaic Truncating Variants in Ovarian Cancer Cases May Be Treatment-Related Somatic Mutations.
J Natl Cancer Inst. 2016; 108(3) [PubMed] Free Access to Full Article Related Publications
Mosaic truncating mutations in the protein phosphatase, Mg(2+)/Mn(2+)-dependent, 1D (PPM1D) gene have recently been reported with a statistically significantly greater frequency in lymphocyte DNA from ovarian cancer case patients compared with unaffected control patients. Using massively parallel sequencing (MPS) we identified truncating PPM1D mutations in 12 of 3236 epithelial ovarian cancer (EOC) case patients (0.37%) but in only one of 3431 unaffected control patients (0.03%) (P = .001). All statistical tests were two-sided. A combination of Sanger sequencing, pyrosequencing, and MPS data suggested that 12 of the 13 mutations were mosaic. All mutations were identified in post-chemotherapy treatment blood samples from case patients (n = 1827) (average 1234 days post-treatment in carriers) rather than from cases collected pretreatment (less than 14 days after diagnosis, n = 1384) (P = .002). These data suggest that PPM1D variants in EOC cases are primarily somatic mosaic mutations caused by treatment and are not associated with germline predisposition to EOC.

Dokduang H, Yongvanit P, Namwat N, et al.
Xanthohumol inhibits STAT3 activation pathway leading to growth suppression and apoptosis induction in human cholangiocarcinoma cells.
Oncol Rep. 2016; 35(4):2065-72 [PubMed] Related Publications
STAT3 plays a significant role in the development of cholangiocarcinoma (CCA) associated with the liver fluke (Opisthorchis viverrini; Ov). Xanthohumol (XN), a prenylated flavonoid extracted from hops, has known anticancer activity and could potentially target STAT3. The present study determined the effect of XN on STAT3, as well as ascertained its usefulness against CCA. The CCA cell proliferation at 20 µM and 50 µM of XN was shown to inhibited, while 20 µM partially inhibited IL-6-induced STAT3 activation. At 50 µM, the inhibition was complete. The reduction in STAT3 activity at 20 and 50 µM was associated with a significant reduction of CCA cell growth and apoptosis. We also found that the administration of 50 µM XN orally in drinking water to nude mice inoculated with CCA led to a reduction in tumor growth in comparison with controls. In addition, apoptosis of cancer cells increased although there was no visible toxicity. The present study shows that XN can inhibit STAT3 activation both in vivo and in vitro due to suppression of the Akt-NFκB signaling pathway. XN should be considered as a possible therapeutic agent against CCA.

Dubois F, Keller M, Calvayrac O, et al.
RASSF1A Suppresses the Invasion and Metastatic Potential of Human Non-Small Cell Lung Cancer Cells by Inhibiting YAP Activation through the GEF-H1/RhoB Pathway.
Cancer Res. 2016; 76(6):1627-40 [PubMed] Related Publications
Inactivation of the tumor suppressor gene RASSF1A by promoter hypermethylation represents a key event underlying the initiation and progression of lung cancer. RASSF1A inactivation is also associated with poor prognosis and may promote metastatic spread. In this study, we investigated how RASSF1A inactivation conferred invasive phenotypes to human bronchial cells. RNAi-mediated silencing of RASSF1A induced epithelial-to-mesenchymal transition (EMT), fomenting a motile and invasive cellular phenotype in vitro and increased metastatic prowess in vivo. Mechanistic investigations revealed that RASSF1A blocked tumor growth by stimulating cofilin/PP2A-mediated dephosphorylation of the guanine nucleotide exchange factor GEF-H1, thereby stimulating its ability to activate the antimetastatic small GTPase RhoB. Furthermore, RASSF1A reduced nuclear accumulation of the Hippo pathway transcriptional cofactor Yes-associated protein (YAP), which was reinforced by RhoB activation. Collectively, our results indicated that RASSF1 acts to restrict EMT and invasion by indirectly controlling YAP nuclear shuttling and activation through a RhoB-regulated cytoskeletal remodeling process, with potential implications to delay the progression of RASSF1-hypermethylated lung tumors.

Schulze I, Rohde C, Scheller-Wendorff M, et al.
Increased DNA methylation of Dnmt3b targets impairs leukemogenesis.
Blood. 2016; 127(12):1575-86 [PubMed] Related Publications
The de novo DNA methyltransferases Dnmt3a and Dnmt3b are of crucial importance in hematopoietic stem cells. Dnmt3b has recently been shown to play a role in genic methylation. To investigate how Dnmt3b-mediated DNA methylation affects leukemogenesis, we analyzed leukemia development under conditions of high and physiological methylation levels in a tetracycline-inducible knock-in mouse model. High expression of Dnmt3b slowed leukemia development in serial transplantations and impaired leukemia stem cell (LSC) function. Forced Dnmt3b expression induced widespread DNA hypermethylation inMyc-Bcl2-induced leukemias, preferentially at gene bodies.MLL-AF9-induced leukemogenesis showed much less pronounced DNA hypermethylation upon Dnmt3b expression. Nonetheless, leukemogenesis was delayed in both models with a shared core set of DNA hypermethylated regions and suppression of stem cell-related genes. Acute myeloid leukemia patients with high expression of Dnmt3b target genes showed inferior survival. Together, these findings indicate a critical role for Dnmt3b-mediated DNA methylation in leukemia development and maintenance of LSC function.

Tan BB, Zhang MM, Li Y, et al.
Inhibition of Vav3 gene can promote apoptosis of human gastric cancer cell line MGC803 by regulating ERK pathway.
Tumour Biol. 2016; 37(6):7823-33 [PubMed] Related Publications
Previous studies proved that Vav3 gene was overexpressed in cancers. However, the molecular mechanism of Vav3 in apoptosis still keeps unclear; therefore, the relationship between Vav3 gene and apoptosis of gastric cancer (GC) was explored in the present study. Vav3-siRNA was transfected into MGC803 cells, and then cell activity and apoptosis rate were tested with MTT and FCM; apoptosis-related genes and proteins in MAPK signaling pathway were also tested. Results showed that Vav3 was overexpressed in GC than in adjacent normal tissues (all P < 0.05), and expression of Vav3 was related to degree of histological differentiation, cancer invasion depth, and lymphatic metastasis (Χ (2)  = 7.185, P = 0.007; Χ (2)  = 18.654, P < 0.001; Χ (2)  = 5.058, P = 0.025). Vav3 silencing inhibited activity of MGC803 cells, and apoptosis rate of cells was affected. Vav3-siRNA transfection led to changes of apoptosis-related genes such as Survivin, xIAP, Bcl-2, caspase-3, and Bax (all P < 0.01). After transfection, ratio of phosphorylation of ERK significantly reduced. We concluded that Vav3 inhibition can suppress cell activity and promote apoptosis by regulating the apoptosis-related genes through the ERK pathway.

Hu Y, Li S
Survival regulation of leukemia stem cells.
Cell Mol Life Sci. 2016; 73(5):1039-50 [PubMed] Related Publications
Leukemia stem cells (LSCs) are a subpopulation cells at the apex of hierarchies in leukemia cells and responsible for disease continuous propagation. In this article, we discuss some cellular and molecular components, which are critical for LSC survival. These components include intrinsic signaling pathways and extrinsic microenvironments. The intrinsic signaling pathways to be discussed include Wnt/β-catenin signaling, Hox genes, Hh pathway, Alox5, and some miRNAs, which have been shown to play important roles in regulating LSC survival and proliferation. The extrinsic components to be discussed include selectins, CXCL12/CXCR4, and CD44, which involve in LSC homing, survival, and proliferation by affecting bone marrow microenvironment. Potential strategies for eradicating LSCs will also discuss.

Vukovic M, Guitart AV, Sepulveda C, et al.
Hif-1α and Hif-2α synergize to suppress AML development but are dispensable for disease maintenance.
J Exp Med. 2015; 212(13):2223-34 [PubMed] Free Access to Full Article Related Publications
Leukemogenesis occurs under hypoxic conditions within the bone marrow (BM). Knockdown of key mediators of cellular responses to hypoxia with shRNA, namely hypoxia-inducible factor-1α (HIF-1α) or HIF-2α, in human acute myeloid leukemia (AML) samples results in their apoptosis and inability to engraft, implicating HIF-1α or HIF-2α as therapeutic targets. However, genetic deletion of Hif-1α has no effect on mouse AML maintenance and may accelerate disease development. Here, we report the impact of conditional genetic deletion of Hif-2α or both Hif-1α and Hif-2α at different stages of leukemogenesis in mice. Deletion of Hif-2α accelerates development of leukemic stem cells (LSCs) and shortens AML latency initiated by Mll-AF9 and its downstream effectors Meis1 and Hoxa9. Notably, the accelerated initiation of AML caused by Hif-2α deletion is further potentiated by Hif-1α codeletion. However, established LSCs lacking Hif-2α or both Hif-1α and Hif-2α propagate AML with the same latency as wild-type LSCs. Furthermore, pharmacological inhibition of the HIF pathway or HIF-2α knockout using the lentiviral CRISPR-Cas9 system in human established leukemic cells with MLL-AF9 translocation have no impact on their functions. We therefore conclude that although Hif-1α and Hif-2α synergize to suppress the development of AML, they are not required for LSC maintenance.

Pathak HB, Zhou Y, Sethi G, et al.
A Synthetic Lethality Screen Using a Focused siRNA Library to Identify Sensitizers to Dasatinib Therapy for the Treatment of Epithelial Ovarian Cancer.
PLoS One. 2015; 10(12):e0144126 [PubMed] Free Access to Full Article Related Publications
Molecular targeted therapies have been the focus of recent clinical trials for the treatment of patients with recurrent epithelial ovarian cancer (EOC). The majority have not fared well as monotherapies for improving survival of these patients. Poor bioavailability, lack of predictive biomarkers, and the presence of multiple survival pathways can all diminish the success of a targeted agent. Dasatinib is a tyrosine kinase inhibitor of the Src-family kinases (SFK) and in preclinical studies shown to have substantial activity in EOC. However, when evaluated in a phase 2 clinical trial for patients with recurrent or persistent EOC, it was found to have minimal activity. We hypothesized that synthetic lethality screens performed using a cogently designed siRNA library would identify second-site molecular targets that could synergize with SFK inhibition and improve dasatinib efficacy. Using a systematic approach, we performed primary siRNA screening using a library focused on 638 genes corresponding to a network centered on EGFR, HER2, and the SFK-scaffolding proteins BCAR1, NEDD9, and EFS to screen EOC cells in combination with dasatinib. We followed up with validation studies including deconvolution screening, quantitative PCR to confirm effective gene silencing, correlation of gene expression with dasatinib sensitivity, and assessment of the clinical relevance of hits using TCGA ovarian cancer data. A refined list of five candidates (CSNK2A1, DAG1, GRB2, PRKCE, and VAV1) was identified as showing the greatest potential for improving sensitivity to dasatinib in EOC. Of these, CSNK2A1, which codes for the catalytic alpha subunit of protein kinase CK2, was selected for additional evaluation. Synergistic activity of the clinically relevant inhibitor of CK2, CX-4945, with dasatinib in reducing cell proliferation and increasing apoptosis was observed across multiple EOC cell lines. This overall approach to improving drug efficacy can be applied to other targeted agents that have similarly shown poor clinical activity.

Lund HL, Hughesman CB, McNeil K, et al.
Initial diagnosis of chronic myelogenous leukemia based on quantification of M-BCR status using droplet digital PCR.
Anal Bioanal Chem. 2016; 408(4):1079-94 [PubMed] Related Publications
Formed from a reciprocal translocation t(9:22)(q34;q11) of genetic material between the long arms of human chromosomes 9 and 22, the constitutively active breakpoint cluster region (BCR) Abelson 1 (ABL) tyrosine kinase BCR-ABL is known to be causative of chronic myelogenous leukemia (CML). In 98% of CML patients harboring the t(9:22)(q34;q11) translocation, known as the Philadelphia chromosome, the chimeric BCR-ABL oncogene is created through cleavage of the BCR gene within its major breakpoint region (M-BCR) and breakage of the ABL gene within a 100-kbp region downstream of exon 2a. Clinical detection of the fused BCR-ABL oncogene currently relies on direct visualization by fluorescence in situ hybridization (FISH), a relatively tedious assay that typically offers a detection limit of ca. 2%. Here, we describe a novel assay that uses droplet digital PCR (ddPCR) technology to reliably measure M-BCR status and the presence of BCR-ABL. When applied to cell-line models of CML, the assay accurately quantifies BCR-ABL frequency to a detection limit of 0.25%. It therefore offers improved specificity relative to FISH, and may allow identification of variant translocation patterns, including derivative chromosome 9 deletions.

Holm F, Hellqvist E, Mason CN, et al.
Reversion to an embryonic alternative splicing program enhances leukemia stem cell self-renewal.
Proc Natl Acad Sci U S A. 2015; 112(50):15444-9 [PubMed] Free Access to Full Article Related Publications
Formative research suggests that a human embryonic stem cell-specific alternative splicing gene regulatory network, which is repressed by Muscleblind-like (MBNL) RNA binding proteins, is involved in cell reprogramming. In this study, RNA sequencing, splice isoform-specific quantitative RT-PCR, lentiviral transduction, and in vivo humanized mouse model studies demonstrated that malignant reprogramming of progenitors into self-renewing blast crisis chronic myeloid leukemia stem cells (BC LSCs) was partially driven by decreased MBNL3. Lentiviral knockdown of MBNL3 resulted in reversion to an embryonic alternative splice isoform program typified by overexpression of CD44 transcript variant 3, containing variant exons 8-10, and BC LSC proliferation. Although isoform-specific lentiviral CD44v3 overexpression enhanced chronic phase chronic myeloid leukemia (CML) progenitor replating capacity, lentiviral shRNA knockdown abrogated these effects. Combined treatment with a humanized pan-CD44 monoclonal antibody and a breakpoint cluster region - ABL proto-oncogene 1, nonreceptor tyrosine kinase (BCR-ABL1) antagonist inhibited LSC maintenance in a niche-dependent manner. In summary, MBNL3 down-regulation-related reversion to an embryonic alternative splicing program, typified by CD44v3 overexpression, represents a previously unidentified mechanism governing malignant progenitor reprogramming in malignant microenvironments and provides a pivotal opportunity for selective BC LSC detection and therapeutic elimination.

Sadovnik I, Hoelbl-Kovacic A, Herrmann H, et al.
Identification of CD25 as STAT5-Dependent Growth Regulator of Leukemic Stem Cells in Ph+ CML.
Clin Cancer Res. 2016; 22(8):2051-61 [PubMed] Free Access to Full Article Related Publications
PURPOSE: In chronic myelogenous leukemia (CML), leukemic stem cells (LSC) represent a critical target of therapy. However, little is known about markers and targets expressed by LSCs. The aim of this project was to identify novel relevant markers of CML LSCs.
EXPERIMENTAL DESIGN: CML LSCs were examined by flow cytometry, qPCR, and various bioassays. In addition, we examined the multipotent CD25(+)CML cell line KU812.
RESULTS: In contrast to normal hematopoietic stem cells, CD34(+)/CD38(-)CML LSCs expressed the IL-2 receptor alpha chain, IL-2RA (CD25). STAT5 was found to induce expression of CD25 in Lin(-)/Sca-1(+)/Kit(+)stem cells in C57Bl/6 mice. Correspondingly, shRNA-induced STAT5 depletion resulted in decreased CD25 expression in KU812 cells. Moreover, the BCR/ABL1 inhibitors nilotinib and ponatinib were found to decrease STAT5 activity and CD25 expression in KU812 cells and primary CML LSCs. A CD25-targeting shRNA was found to augment proliferation of KU812 cellsin vitroand their engraftmentin vivoin NOD/SCID-IL-2Rγ(-/-)mice. In drug-screening experiments, the PI3K/mTOR blocker BEZ235 promoted the expression of STAT5 and CD25 in CML cells. Finally, we found that BEZ235 produces synergistic antineoplastic effects on CML cells when applied in combination with nilotinib or ponatinib.
CONCLUSIONS: CD25 is a novel STAT5-dependent marker of CML LSCs and may be useful for LSC detection and LSC isolation in clinical practice and basic science. Moreover, CD25 serves as a growth regulator of CML LSCs, which may have biologic and clinical implications and may pave the way for the development of new more effective LSC-eradicating treatment strategies in CML.

Pelosi E, Castelli G, Testa U
Targeting LSCs through membrane antigens selectively or preferentially expressed on these cells.
Blood Cells Mol Dis. 2015; 55(4):336-46 [PubMed] Related Publications
Studies of xenotransplantation of bone marrow and blood cells of AML patients have supported the existence of rare leukemic stem cells, able to initiate and maintain the leukemic process and bearing the typical leukemic abnormalities. LSCs possess self-renewal capacity and are responsible for the growth of the more differentiated leukemic progeny in the bone marrow and in the blood. These cells are more resistant than bulk leukemic cells to anti-leukemic drugs, thus survive to treatment and are, at a large extent, responsible for leukemia relapse. During the last two decades, considerable progresses have been made in the understanding of the peculiar cellular and molecular properties of LSCs. In this context, particularly relevant was the discovery of several membrane markers, selectively or preferentially expressed on LSCs. These membrane markers offer now unique opportunities to identify LSCs and to distinguish them from normal HSCs, to monitor the response of the various anti-leukemic treatments at the level of the LSC compartment, to identify relevant therapeutic targets. Concerning this last point, the most promising therapeutic targets are CD33 and CD123.

Iwasaki M, Liedtke M, Gentles AJ, Cleary ML
CD93 Marks a Non-Quiescent Human Leukemia Stem Cell Population and Is Required for Development of MLL-Rearranged Acute Myeloid Leukemia.
Cell Stem Cell. 2015; 17(4):412-21 [PubMed] Free Access to Full Article Related Publications
Leukemia stem cells (LSCs) are thought to share several properties with hematopoietic stem cells (HSCs), including cell-cycle quiescence and a capacity for self-renewal. These features are hypothesized to underlie leukemic initiation, progression, and relapse, and they also complicate efforts to eradicate leukemia through therapeutic targeting of LSCs without adverse effects on HSCs. Here, we show that acute myeloid leukemias (AMLs) with genomic rearrangements of the MLL gene contain a non-quiescent LSC population. Although human CD34(+)CD38(-) LSCs are generally highly quiescent, the C-type lectin CD93 is expressed on a subset of actively cycling, non-quiescent AML cells enriched for LSC activity. CD93 expression is functionally required for engraftment of primary human AML LSCs and leukemogenesis, and it regulates LSC self-renewal predominantly by silencing CDKN2B, a major tumor suppressor in AML. Thus, CD93 expression identifies a predominantly cycling, non-quiescent leukemia-initiating cell population in MLL-rearranged AML, providing opportunities for selective targeting and eradication of LSCs.

Curi DA, Beauchamp EM, Blyth GT, et al.
Pre-clinical evidence of PIM kinase inhibitor activity in BCR-ABL1 unmutated and mutated Philadelphia chromosome-positive (Ph+) leukemias.
Oncotarget. 2015; 6(32):33206-16 [PubMed] Free Access to Full Article Related Publications
We investigated the efficacy of targeting the PIM kinase pathway in Philadelphia chromosome-positive (Ph+) leukemias. We provide evidence that inhibition of PIM, with the pan-PIM inhibitor SGI-1776, results in suppression of classic PIM effectors and also elements of the mTOR pathway, suggesting interplay between PIM and mTOR signals. Our data demonstrate that PIM inhibition enhances the effects of imatinib mesylate on Ph+ leukemia cells. We also found that PIM inhibition results in suppression of leukemic cell proliferation and induction of apoptosis of Ph+ leukemia cells, including those resistant to imatinib mesylate. Importantly, inhibition of PIM results in enhanced suppression of primary leukemic progenitors from patients with CML. Altogether these findings suggest that pharmacological PIM targeting may provide a unique therapeutic approach for the treatment of Ph+ leukemias.

Katzav S
Vav1: A Dr. Jekyll and Mr. Hyde protein--good for the hematopoietic system, bad for cancer.
Oncotarget. 2015; 6(30):28731-42 [PubMed] Free Access to Full Article Related Publications
Many deregulated signal transducer proteins are involved in various cancers at numerous stages of tumor development. One of these, Vav1, is normally expressed exclusively in the hematopoietic system, where it functions as a specific GDP/GTP nucleotide exchange factor (GEF), strictly regulated by tyrosine phosphorylation. Vav was first identified in an NIH3T3 screen for oncogenes. Although the oncogenic form of Vav1 identified in the screen has not been detected in clinical human tumors, its wild-type form has recently been implicated in mammalian malignancies, including neuroblastoma, melanoma, pancreatic, lung and breast cancers, and B-cell chronic lymphocytic leukemia. In addition, it was recently identified as a mutated gene in human cancers of various origins. However, the activity and contribution to cancer of these Vav1 mutants is still unclear. This review addresses the physiological function of wild-type Vav1 and its activity as an oncogene in human cancer. It also discusses the novel mutations identified in Vav1 in various cancers and their potential contribution to cancer development as oncogenes or tumor suppressor genes.

Prost S, Relouzat F, Spentchian M, et al.
Erosion of the chronic myeloid leukaemia stem cell pool by PPARγ agonists.
Nature. 2015; 525(7569):380-3 [PubMed] Related Publications
Whether cancer is maintained by a small number of stem cells or is composed of proliferating cells with approximate phenotypic equivalency is a central question in cancer biology. In the stem cell hypothesis, relapse after treatment may occur by failure to eradicate cancer stem cells. Chronic myeloid leukaemia (CML) is quintessential to this hypothesis. CML is a myeloproliferative disorder that results from dysregulated tyrosine kinase activity of the fusion oncoprotein BCR-ABL. During the chronic phase, this sole genetic abnormality (chromosomal translocation Ph(+): t(9;22)(q34;q11)) at the stem cell level causes increased proliferation of myeloid cells without loss of their capacity to differentiate. Without treatment, most patients progress to the blast phase when additional oncogenic mutations result in a fatal acute leukaemia made of proliferating immature cells. Imatinib mesylate and other tyrosine kinase inhibitors (TKIs) that target the kinase activity of BCR-ABL have improved patient survival markedly. However, fewer than 10% of patients reach the stage of complete molecular response (CMR), defined as the point when BCR-ABL transcripts become undetectable in blood cells. Failure to reach CMR results from the inability of TKIs to eradicate quiescent CML leukaemia stem cells (LSCs). Here we show that the residual CML LSC pool can be gradually purged by the glitazones, antidiabetic drugs that are agonists of peroxisome proliferator-activated receptor-γ (PPARγ). We found that activation of PPARγ by the glitazones decreases expression of STAT5 and its downstream targets HIF2α and CITED2, which are key guardians of the quiescence and stemness of CML LSCs. When pioglitazone was given temporarily to three CML patients in chronic residual disease in spite of continuous treatment with imatinib, all of them achieved sustained CMR, up to 4.7 years after withdrawal of pioglitazone. This suggests that clinically relevant cancer eradication may become a generally attainable goal by combination therapy that erodes the cancer stem cell pool.

Ramus SJ, Song H, Dicks E, et al.
Germline Mutations in the BRIP1, BARD1, PALB2, and NBN Genes in Women With Ovarian Cancer.
J Natl Cancer Inst. 2015; 107(11) [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Epithelial ovarian cancer (EOC) is the most lethal gynecological malignancy, responsible for 13 000 deaths per year in the United States. Risk prediction based on identifying germline mutations in ovarian cancer susceptibility genes could have a clinically significant impact on reducing disease mortality.
METHODS: Next generation sequencing was used to identify germline mutations in the coding regions of four candidate susceptibility genes-BRIP1, BARD1, PALB2 and NBN-in 3236 invasive EOC case patients and 3431 control patients of European origin, and in 2000 unaffected high-risk women from a clinical screening trial of ovarian cancer (UKFOCSS). For each gene, we estimated the prevalence and EOC risks and evaluated associations between germline variant status and clinical and epidemiological risk factor information. All statistical tests were two-sided.
RESULTS: We found an increased frequency of deleterious mutations in BRIP1 in case patients (0.9%) and in the UKFOCSS participants (0.6%) compared with control patients (0.09%) (P = 1 x 10(-4) and 8 x 10(-4), respectively), but no differences for BARD1 (P = .39), NBN1 ( P = .61), or PALB2 (P = .08). There was also a difference in the frequency of rare missense variants in BRIP1 between case patients and control patients (P = 5.5 x 10(-4)). The relative risks associated with BRIP1 mutations were 11.22 for invasive EOC (95% confidence interval [CI] = 3.22 to 34.10, P = 1 x 10(-4)) and 14.09 for high-grade serous disease (95% CI = 4.04 to 45.02, P = 2 x 10(-5)). Segregation analysis in families estimated the average relative risks in BRIP1 mutation carriers compared with the general population to be 3.41 (95% CI = 2.12 to 5.54, P = 7×10(-7)).
CONCLUSIONS: Deleterious germline mutations in BRIP1 are associated with a moderate increase in EOC risk. These data have clinical implications for risk prediction and prevention approaches for ovarian cancer and emphasize the critical need for risk estimates based on very large sample sizes before genes of moderate penetrance have clinical utility in cancer prevention.

Zhou X, Zhou S, Li B, et al.
Transmembrane TNF-α preferentially expressed by leukemia stem cells and blasts is a potent target for antibody therapy.
Blood. 2015; 126(12):1433-42 [PubMed] Related Publications
To design an effective antibody therapy to improve clinical outcomes in leukemia, the identification of novel cell surface antigens is needed. Herein, we demonstrate a role for transmembrane tumor necrosis factor-α (tmTNF-α) in leukemia. To characterize tmTNF-α expression in acute leukemia (AL), normal hematopoietic cells, and nonhematopoietic tissues, we used a monoclonal antibody, termed C1, which specifically recognizes the tmTNF-α domain. We found that tmTNF-α was preferentially expressed by AL and leukemia stem cells (LSCs). More abundant expression correlated with poor risk stratification, extramedullary infiltration, and adverse clinical parameters. Moreover, knockdown of tmTNF-α(+) expression rendered leukemia cells more sensitive to chemotherapy in vitro and delayed regeneration of leukemia in NOD-SCID mice. Targeting tmTNF-α by C1 resulted in leukemia cell killing via antibody-dependent cell-mediated and complement-dependent cytotoxicity in vitro and inhibited leukemia cell growth in vivo while simultaneously sparing normal hematopoietic cells. Notably, C1 administration impaired the regeneration of leukemia in secondary serial transplantation into NOD-SCID mice. In conclusion, tmTNF-α has a favorable AL- and LSC-associated expression profile and is important for the survival and proliferation of these cells. C1-mediated targeting shows potent anti-LSC activity, indicating that tmTNF-α represents a novel target antigen in AL.

Wong SH, Goode DL, Iwasaki M, et al.
The H3K4-Methyl Epigenome Regulates Leukemia Stem Cell Oncogenic Potential.
Cancer Cell. 2015; 28(2):198-209 [PubMed] Free Access to Full Article Related Publications
The genetic programs that maintain leukemia stem cell (LSC) self-renewal and oncogenic potential have been well defined; however, the comprehensive epigenetic landscape that sustains LSC cellular identity and functionality is less well established. We report that LSCs in MLL-associated leukemia reside in an epigenetic state of relative genome-wide high-level H3K4me3 and low-level H3K79me2. LSC differentiation is associated with reversal of these broad epigenetic profiles, with concomitant downregulation of crucial MLL target genes and the LSC maintenance transcriptional program that is driven by the loss of H3K4me3, but not H3K79me2. The H3K4-specific demethylase KDM5B negatively regulates leukemogenesis in murine and human MLL-rearranged AML cells, demonstrating a crucial role for the H3K4 global methylome in determining LSC fate.

Shao L, Miller S, Keller-Ramey J, et al.
Cytogenetic, fluorescence in situ hybridization, and genomic array characterization of chronic myeloid leukemia with cryptic BCR-ABL1 fusions.
Cancer Genet. 2015 Jul-Aug; 208(7-8):396-403 [PubMed] Related Publications
Chronic myeloid leukemia (CML) is characterized by the breakpoint cluster region (BCR)-Abelson murine leukemia (ABL1) fusion gene. In approximately 1% of CML cases, the Philadelphia chromosome associated with the BCR-ABL1 fusion gene is not present, and the BCR-ABL1 fusion gene is generated by cryptic insertion or sequential translocations. In this study, we describe the cytogenetic and molecular features of five CML patients with cryptic BCR-ABL1 fusion genes using karyotype, fluorescence in situ hybridization (FISH), and whole genome single nucleotide polymorphism array techniques. Two cases of CML in the chronic phase (CP) had a normal karyotype, and three cases of CML in the blast phase (BP) had an abnormal karyotype with neither a typical nor variant t(9;22). By BCR-ABL1 metaphase FISH analysis, we found that fusion signals were localized on chromosomes 9 (3 cases), 22 (1 case), and both 9 and 22 (1 case). In two cases of CML-BP, duplication of the BCR-ABL1 fusion gene occurred as a result of mitotic recombination between homologous chromosomes. Copy number losses involving the IKZF1 gene were observed in two patients with CML-BP. This study demonstrates for the first time the acquisition of additional BCR-ABL1 fusion genes through mitotic recombination in CML with cryptic BCR-ABL1.

Sharma N, Magistroni V, Piazza R, et al.
BCR/ABL1 and BCR are under the transcriptional control of the MYC oncogene.
Mol Cancer. 2015; 14:132 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Chronic Myeloid Leukaemia (CML) is caused by the BCR/ABL1 fusion gene. Both the presence and the levels of BCR/ABL1 expression seem to be critical for CML progression from chronic phase (CP) to blast crisis (BC). After the oncogenic translocation, the BCR/ABL1 gene is under the transcriptional control of BCR promoter but the molecular mechanisms involved in the regulation of oncogene expression are mostly unknown.
METHODS: A region of 1443bp of the functional BCR promoter was studied for transcription factor binding sites through in-silico analysis and Chromatin Immunoprecipitation experiments. BCR and BCR/ABL1 expression levels were analysed in CML cell lines after over-expression or silencing of MYC transcription factor. A luciferase reporter assay was used to confirm its activity on BCR promoter.
RESULTS: In the present study we demonstrate that MYC and its partner MAX bind to the BCR promoter, leading to up-regulation of BCR and BCR/ABL1 at both transcriptional and protein levels. Accordingly, silencing of MYC expression in various BCR/ABL1 positive cell lines causes significant downregulation of BCR and BCR/ABL1, which consequently leads to decreased proliferation and induction of cell death.
CONCLUSIONS: Here we describe a regulatory pathway modulating BCR and BCR/ABL1 expression, showing that the BCR promoter is under the transcriptional control of the MYC/MAX heterodimer. Since MYC is frequently over-expressed in BC, this phenomenon could play a critical role in BCR/ABL1 up-regulation and blast aggressiveness acquired during CML evolution.

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