Human Vav1 expression in hematopoietic and cancer cell lines is regulated by c-Myb and by CpG methylation

Inducible overexpression of a FAM3C/ILEI transgene has pleiotropic effects with shortened life span, liver fibrosis and anemia in mice

FAM3C/ILEI is an important factor in epithelial-to-mesenchymal transition (EMT) induction, tumor progression and metastasis. Overexpressed in many cancers, elevated ILEI levels and secretion correlate with poor patient survival. Although ILEI's causative role in invasive tumor growth and metastasis has been demonstrated in several cellular tumor models, there are no available transgenic mice to study these effects in the context of a complex organism. Here, we describe the generation and initial characterization of a Tet-ON inducible Fam3c/ILEI transgenic mouse strain. We find that ubiquitous induction of ILEI overexpression (R26-ILEIind) at weaning age leads to a shortened lifespan, reduced body weight and microcytic hypochromic anemia. The anemia was reversible at a young age within a week upon withdrawal of ILEI induction. Vav1-driven overexpression of the ILEIind transgene in all hematopoietic cells (Vav-ILEIind) did not render mice anemic or lower overall fitness, demonstrating that no intrinsic mechanisms of erythroid development were dysregulated by ILEI and that hematopoietic ILEI hyperfunction did not contribute to death. Reduced serum iron levels of R26-ILEIind mice were indicative for a malfunction in iron uptake or homeostasis. Accordingly, the liver, the main organ of iron metabolism, was severely affected in moribund ILEI overexpressing mice: increased alanine transaminase and aspartate aminotransferase levels indicated liver dysfunction, the liver was reduced in size, showed increased apoptosis, reduced cellular iron content, and had a fibrotic phenotype. These data indicate that high ILEI expression in the liver might reduce hepatoprotection and induce liver fibrosis, which leads to liver dysfunction, disturbed iron metabolism and eventually to death. Overall, we show here that the novel Tet-ON inducible Fam3c/ILEI transgenic mouse strain allows tissue specific timely controlled overexpression of ILEI and thus, will serve as a versatile tool to model the effect of elevated ILEI expression in diverse tissue entities and disease conditions, including cancer.

Unraveling the Oncogenic Potential of VAV1 in Human Cancer: Lessons from Mouse Models

VAV1 is a hematopoietic signal transducer that possesses a GDP/GTP nucleotide exchange factor (GEF) that is tightly regulated by tyrosine phosphorylation, along with adapter protein domains, such as SH2 and SH3. Research on VAV1 has advanced over the years since its discovery as an in vitro activated oncogene in an NIH3T3 screen for oncogenes. Although the oncogenic form of VAV1 first identified in the screen has not been detected in human clinical tumors, its wild-type and mutant forms have been implicated in mammalian malignancies of various tissue origins, as well as those of the hematopoietic system. This review article addresses the activity of human VAV1 as an overexpressed or mutated gene and also describes the differences in the distribution of VAV1 mutations in the hematopoietic system and in other tissues. The knowledge accumulated thus far from GEMMs expressing VAV1 is described, with the conclusion that GEMMs of both wild-type VAV1 and mutant VAV1 do not form tumors, yet these will be generated when additional molecular insults, such as loss of p53 or KRAS mutation, occur.

Vav1 Promotes B-Cell Lymphoma Development

Vav1 is normally and exclusively expressed in the hematopoietic system where it functions as a specific GDP/GTP nucleotide exchange factor (GEF), firmly regulated by tyrosine phosphorylation. Mutations and overexpression of Vav1 in hematopoietic malignancies, and in human cancers of various histologic origins, are well documented. To reveal whether overexpression of Vav1 in different tissues suffices for promoting the development of malignant lesions, we expressed Vav1 in transgenic mice by using the ubiquitous ROSA26 promoter (Rosa Vav1). We detected Vav1 expression in epithelial tissues of various organs including pancreas, liver, and lung. While carcinomas did not develop in these organs, surprisingly, we noticed the development of B-cell lymphomas. Rac1-GTP levels did not change in tissues from Rosa Vav1 mice expressing the transgenic Vav1, while ERK phosphorylation increased in the lymphomas, suggesting that signaling pathways are evoked. One of the growth factors analyzed by us as a suspect candidate to mediate paracrine stimulation in the lymphocytes was CSF-1, which was highly expressed in the epithelial compartment of Rosa Vav1 mice. The expression of its specific receptor, CSF-1R, was found to be highly expressed in the B-cell lymphomas. Taken together, our results suggest a potential cross-talk between epithelial cells expressing Vav1, that secrete CSF-1, and the lymphocytes that express CSF-1R, thus leading to the generation of B-cell lymphomas. Our findings provide a novel mechanism by which Vav1 contributes to tumor propagation.

Cancer-associated mutations in VAV1 trigger variegated signaling outputs and T-cell lymphomagenesis

Mutations in VAV1, a gene that encodes a multifunctional protein important for lymphocytes, are found at different frequencies in peripheral T‐cell lymphoma (PTCL), non‐small cell lung cancer, and other tumors. However, their pathobiological significance remains unsettled. After cataloguing 51 cancer‐associated VAV1 mutations, we show here that they can be classified in five subtypes according to functional impact on the three main VAV1 signaling branches, GEF‐dependent activation of RAC1, GEF‐independent adaptor‐like, and tumor suppressor functions. These mutations target new and previously established regulatory layers of the protein, leading to quantitative and qualitative changes in VAV1 signaling output. We also demonstrate that the most frequent VAV1 mutant subtype drives PTCL formation in mice. This process requires the concurrent engagement of two downstream signaling branches that promote the chronic activation and transformation of follicular helper T cells. Collectively, these data reveal the genetic constraints associated with the lymphomagenic potential of VAV1 mutant subsets, similarities with other PTCL driver genes, and potential therapeutic vulnerabilities.

A long intergenic non-coding RNA regulates nuclear localization of DNA methyl transferase-1

DNA methyl transferase-1 or DNMT1 maintains DNA methylation in the genome and is important for regulating gene expression in cells. Aberrant changes in DNMT1 activity and DNA methylation are commonly observed in cancers and many other diseases. Recently, a number of long intergenic non-protein-coding RNAs or lincRNAs have been shown to play a role in regulating DNMT1 activity. CCDC26 is a nuclear lincRNA that is frequently mutated in cancers and is a hotbed for disease-associated single nucleotide changes. However, the functional mechanism of CCDC26 is not understood. Here, we show that this lincRNA is concentrated on the nuclear periphery. Strikingly, in the absence of CCDC26 lincRNA, DNMT1 is mis-located in the cytoplasm, and the genomic DNA is significantly hypomethylated. This is accompanied by double-stranded DNA breaks and increased cell death. These results point to a previously unrecognized mechanism of lincRNA-mediated subcellular localization of DNMT1 and regulation of DNA methylation.

Identification of Targetable Pathways in Oral Cancer Patients via Random Forest and Chemical Informatics

Treatment of head and neck cancer has been slow to change with epidermal growth factor receptor (EGFR) inhibitors, PD1 inhibitors, and taxane-/plant-alkaloid-derived chemotherapies being the only therapies approved by the U.S. Food and Drug Administration (FDA) in the last 10 years for the treatment of head and neck cancers. Head and neck cancer is a relatively rare cancer compared to breast or lung cancers. However, it is possible that existing therapies for more common solid tumors or for the treatment of other diseases could also prove effective against oral cancers. Many therapies have molecular targets that could be appropriate in oral cancer as well as the cancer in which the drug gained initial FDA approval. Also, there may be targets in oral cancer for which existing FDA-approved drugs could be applied. This study describes informatics methods that use machine learning to identify influential gene targets in patients receiving platinum-based chemotherapy, non-platinum-based chemotherapy, and genes influential in both groups of patients. This analysis yielded 6 small molecules that had a high Tanimoto similarity (>50%) to ligands binding genes shown to be highly influential in determining treatment response in oral cancer patients. In addition to influencing treatment response, these genes were also found to act as gene hubs connected to more than 100 other genes in pathways enriched with genes determined to be influential in treatment response by a random forest classifier with 20 000 trees trying 320 variables at each tree node. This analysis validates the use of multiple informatics methods to identify small molecules that have a greater likelihood of efficacy in a given cancer of interest.

The Vav GEF Family: An Evolutionary and Functional Perspective

Vav proteins play roles as guanosine nucleotide exchange factors for Rho GTPases and signaling adaptors downstream of protein tyrosine kinases. The recent sequencing of the genomes of many species has revealed that this protein family originated in choanozoans, a group of unicellular organisms from which animal metazoans are believed to have originated from. Since then, the Vav family underwent expansions and reductions in its members during the evolutionary transitions that originated the agnates, chondrichthyes, some teleost fish, and some neoaves. Exotic members of the family harboring atypical structural domains can be also found in some invertebrate species. In this review, we will provide a phylogenetic perspective of the evolution of the Vav family. We will also pay attention to the structure, signaling properties, regulatory layers, and functions of Vav proteins in both invertebrate and vertebrate species.

Integrative analysis of DNA methylation and mRNA expression during differentiation of umbilical cord blood derived mononuclear cells to endothelial cells

Differentiation of umbilical cord blood derived mononuclear cells to endothelial cells is accompanied by massive changes in gene expression. Although methylation and demethylation of DNA likely play crucial roles in regulating gene expression, their interplay during differentiation remains elusive. To address this question, we performed deep sequencing of DNA methylation and mRNA expression to profile global changes in promoter methylation and gene expression during differentiation from mononuclear cells to outgrowing cells. We identified 61 downregulated genes with hypermethylation, including CD74, VAV1, TLR8, and NCF4, as well as 21 upregulated genes with hypomethylation, including ECSCR, MCAM, PGF, and ARHGEF15. Interestingly, gene ontology analysis showed that downregulated genes with hypermethylation were enriched in immune-related functions, and upregulated genes with hypomethylation were enriched in the developmental process and angiogenesis, indicating the important roles of DNA methylation in regulating differentiation. We performed polymerase chain reaction analyses and bisulfite sequencing of representative genes (CD74, VAV1, ECSCR, and MCAM) to verify the negative correlation between DNA methylation and gene expression. Further, inhibition of DNA methyltransferase and demethylase activities using 5'-aza-dc and shRNAs, specific for TET1 and TET2 mRNAs, respectively, revealed that DNA methylation was the main regulator of the reversible expression of functionally important genes. Collectively, our findings implicate DNA methylation as a critical regulator of gene expression during umbilical cord blood derived mononuclear cells to endothelial cell differentiation.

Pancreatic Cancer, A Mis-interpreter of the Epigenetic Language

Pancreatic cancer is the third leading cause of cancer mortality in the U.S. with close to 40,000 deaths per year. Pancreatic ductal adenocarcinoma (PDAC) represents approximately 90 percent of all pancreatic cancer cases and is the most lethal form of the disease. Current therapies for PDAC are ineffective and most patients cannot be treated by surgical resection. Most research efforts have primarily focused on how genetic alterations cause, alter progression, contribute to diagnosis, and influence PDAC management. Over the past two decades, a model has been advanced of PDAC initiation and progression as a multi-step process driven by the acquisition of mutations leading to loss of tumor suppressors and activation of oncogenes. The recognition of the essential roles of these genetic alterations in the development of PDAC has revolutionized our knowledge of this disease. However, none of these findings have turned into effective treatment for this dismal malignancy. In recent years, studies in the areas of chromatin modifications, and non-coding RNAs have uncovered mechanisms for regulating gene expression which occur independently of genetic alterations. Chromatin-based mechanisms are interwoven with microRNA-driven regulation of protein translation to create an integrated epigenetic language, which is grossly dysregulated in PDAC. Thus in PDAC, key tumor suppressors that are well established to play a role in PDAC may be repressed, and oncogenes can be upregulated secondary to epigenetic alterations. Unlike mutations, epigenetic changes are potentially reversible. Given this feature of epigenetic mechanisms, it is conceivable that targeting epigenetic-based events promoting and maintaining PDAC could serve as foundation for the development of new therapeutic and diagnostic approaches for this disease.

Vav1: A Dr. Jekyll and Mr. Hyde protein--good for the hematopoietic system, bad for cancer

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.

Vav family exchange factors: an integrated regulatory and functional view

The Vav family is a group of tyrosine phosphorylation-regulated signal transduction molecules hierarchically located downstream of protein tyrosine kinases. The main function of these proteins is to work as guanosine nucleotide exchange factors (GEFs) for members of the Rho GTPase family. In addition, they can exhibit a variety of catalysis-independent roles in specific signaling contexts. Vav proteins play essential signaling roles for both the development and/or effector functions of a large variety of cell lineages, including those belonging to the immune, nervous, and cardiovascular systems. They also contribute to pathological states such as cancer, immune-related dysfunctions, and atherosclerosis. Here, I will provide an integrated view about the evolution, regulation, and effector properties of these signaling molecules. In addition, I will discuss the pros and cons for their potential consideration as therapeutic targets.

Estrogen induces Vav1 expression in human breast cancer cells

Vav1, a guanine nucleotide exchange factor (GEF) for Rho family GTPases, is a hematopoietic protein involved in a variety of cellular events. In recent years, aberrant expression of Vav1 has been reported in non-hematopoietic cancers including human breast cancer. It remains to be answered how Vav1 is expressed and what Vav1 does in its non-resident tissues. In this study, we aimed to explore the mechanism for Vav1 expression in breast cancer cells in correlation with estrogen-ER pathway. We not only verified the ectopic expression of Vav1 in human breast cancer cell lines, but also observed that Vav1 expression was induced by 17β-estradiol (E₂), a typical estrogen receptor (ER) ligand, in ER-positive cell lines. On the other hand, Tamoxifen, a selective estrogen receptor modulator (SERM), and ICI 182,780, an ER antagonist, suppressed the expression of Vav1. The estrogen receptor modulating Vav1 expression was identified to be α form, not β. Furthermore, treatment of E₂ increased the transcription of vav1 gene by enhancing the promoter activity, though there was no recognizable estrogen response element (ERE). Nevertheless, two regions at the vav1 gene promoter were defined to be responsible for E₂-induced activation of vav1 promoter. Chromatin immunoprecipitation (ChIP) and co-immunoprecipitation (Co-IP) analyses suggested that ERα might access to the vav1 promoter via interacting with transcription factors, c-Myb and ELF-1. Consequently, the enhanced expression of Vav1 led to the elevation of Cyclin D1 and the progression of cell cycle. The present study implies that estrogen-ER modulates the transcription and expression of Vav1, which may contribute to the proliferation of cancerous cells.

VAV1 represses E-cadherin expression through the transactivation of Snail and Slug: a potential mechanism for aberrant epithelial to mesenchymal transition in human epithelial ovarian cancer

Ovarian cancer is the most lethal gynecological malignancy in the western world. Although patients with early-stage ovarian cancer generally have a good prognosis, approximately 20%-30% of patients will die of the disease, and 5-year recurrence rates are 25%-45%, highlighting the need for improved detection and treatment. We investigated the role of VAV1, a protein with guanine nucleotide exchange factor activity, which is associated with survival in patients with early-stage ovarian cancer (International of Obstetrics and Gynecology [FIGO] stages I and II). We analyzed 88 samples from patients with primary epithelial ovarian cancer, which were divided into FIGO stages I and II (n = 46), and III and IV (n = 42). Prognostic analysis revealed that upregulated VAV1 expression correlated significantly with poor prognosis in patients with early-stage epithelial ovarian cancer (P ≤ 0.05), but not with other clinicopathologic features. Stable overexpression of VAV1 in human high-grade serous ovarian cancer SKOV3 cells induced morphologic changes indicative of loss of intercellular adhesions and organized actin stress fibers. Western blotting and real-time reverse transcriptase-polymerase chain reaction demonstrated that these cells had downregulated E-cadherin protein and messenger RNA levels, respectively. This downregulation is associated with epithelial-mesenchymal transition (EMT) and invasive cancer. Furthermore, VAV1 overexpression in both SKOV3 and human ovarian surface epithelial cells demonstrated that its upregulation of an E-cadherin transcriptional repressor, Snail and Slug, was not confined to ovarian cancer cells. Conversely, knockdown of VAV1 by RNA interference reduced Snail and Slug. Our findings suggest that VAV1 may play a role in the EMT of ovarian cancer, and may serve as a potential therapeutic target.

Development of EHop-016: a small molecule inhibitor of Rac

The Rac inhibitor EHop-016 was developed as a compound with the potential to inhibit cancer metastasis. Inhibition of the first step of metastasis, migration, is an important strategy for metastasis prevention. The small GTPase Rac acts as a pivotal binary switch that is turned "on" by guanine nucleotide exchange factors (GEFs) via a myriad of cell surface receptors, to regulate cancer cell migration, survival, and proliferation. Unlike the related GTPase Ras, Racs are not usually mutated, but overexpressed or overactivated in cancer. Therefore, a rational Rac inhibitor should block the activation of Rac by its upstream effectors, GEFs, and the Rac inhibitor NSC23766 was developed using this rationale. However, this compound is ineffective at inhibiting the elevated Rac activity of metastatic breast cancer cells. Therefore, a panel of small molecule compounds were derived from NSC23766 and screened for Rac activity inhibition in metastatic cancer cells. EHop-016 was identified as a compound that blocks the interaction of Rac with the GEF Vav in metastatic human breast cancer cells with an IC50 of ~1μM. At higher concentrations (10μM), EHop-016 inhibits the related Rho GTPase Cdc42, but not Rho, and also reduces cell viability. Moreover, EHop-016 inhibits the activation of the Rac downstream effector p21-activated kinase, extension of motile actin-based structures, and cell migration. Future goals are to develop EHop-016 as a therapeutic to inhibit cancer metastasis, either individually or in combination with current anticancer compounds. The next generation of EHop-016-based Rac inhibitors is also being developed.

Splice variants and promoter methylation status of the Bovine Vasa Homology (Bvh) gene may be involved in bull spermatogenesis

Background

Vasa is a member of the DEAD-box protein family that plays an indispensable role in mammalian spermatogenesis, particularly during meiosis. Bovine vasa homology (Bvh) of Bos taurus has been reported, however, its function in bovine testicular tissue remains obscure. This study aimed to reveal the functions of Bvh and to determine whether Bvh is a candidate gene in the regulation of spermatogenesis in bovine, and to illustrate whether its transcription is regulated by alternative splicing and DNA methylation.

Results

Here we report the molecular characterization, alternative splicing pattern, expression and promoter methylation status of Bvh. The full-length coding region of Bvh was 2190 bp, which encodes a 729 amino acid (aa) protein containing nine consensus regions of the DEAD box protein family. Bvh is expressed only in the ovary and testis of adult cattle. Two splice variants were identified and termed Bvh-V4 (2112 bp and 703 aa) and Bvh-V45 (2040 bp and 679 aa). In male cattle, full-length Bvh (Bvh-FL), Bvh-V4 and Bvh-V45 are exclusively expressed in the testes in the ratio of 2.2:1.6:1, respectively. Real-time PCR revealed significantly reduced mRNA expression of Bvh-FL, Bvh-V4 and Bvh-V45 in testes of cattle-yak hybrids, with meiotic arrest compared with cattle and yaks with normal spermatogenesis (P < 0.01). The promoter methylation level of Bvh in the testes of cattle-yak hybrids was significantly greater than in cattle and yaks (P < 0.01).

Conclusion

In the present study, Bvh was isolated and characterized. These data suggest that Bvh functions in bovine spermatogenesis, and that transcription of the gene in testes were regulated by alternative splice and promoter methylation.

Vav1 fine tunes p53 control of apoptosis versus proliferation in breast cancer

Vav1 functions as a signal transducer protein in the hematopoietic system, where it is exclusively expressed. Vav1 was recently implicated in several human cancers, including lung, pancreatic and neuroblasoma. In this study, we analyzed the expression and function of Vav1 in human breast tumors and breast cancer cell lines. Immunohistochemical analysis of primary human breast carcinomas indicated that Vav1 is expressed in 62% of 65 tumors tested and is correlated positively with estrogen receptor expression. Based on published gene profiling of 50 breast cancer cell lines, several Vav1-expressing cell lines were identified. RT-PCR confirmed Vav1 mRNA expression in several of these cell lines, yet no detectable levels of Vav1 protein were observed due to cbl-c proteasomal degradation. We used two of these lines, MCF-7 (Vav1 mRNA negative) and AU565 (Vav1 mRNA positive), to explore the effect of Vav1 expression on breast cell phenotype and function. Vav1 expression had opposite effects on function in these two lines: it reduced proliferation and enhanced cell death in MCF-7 cells but enhanced proliferation in AU565 cells. Consistent with these findings, transcriptome analysis revealed an increase in expression of proliferation-related genes in Vav1-expressing AU565 cells compared to controls, and an increase in apoptosis-related genes in Vav1-expressing MCF-7 cells compared with controls. TUNEL and γ-H2AX foci assays confirmed that expression of Vav1 increased apoptosis in MCF-7 cells but not AU565 cells and shRNA experiments revealed that p53 is required for this pro-apoptotic effect of Vav1 in these cells. These results highlight for the first time the potential role of Vav1 as an oncogenic stress activator in cancer and the p53 dependence of its pro-apoptotic effect in breast cells.

Small noncoding differentially methylated copy-number variants, including lncRNA genes, cause a lethal lung developmental disorder

An unanticipated and tremendous amount of the noncoding sequence of the human genome is transcribed. Long noncoding RNAs (lncRNAs) constitute a significant fraction of non-protein-coding transcripts; however, their functions remain enigmatic. We demonstrate that deletions of a small noncoding differentially methylated region at 16q24.1, including lncRNA genes, cause a lethal lung developmental disorder, alveolar capillary dysplasia with misalignment of pulmonary veins (ACD/MPV), with parent-of-origin effects. We identify overlapping deletions 250 kb upstream of FOXF1 in nine patients with ACD/MPV that arose de novo specifically on the maternally inherited chromosome and delete lung-specific lncRNA genes. These deletions define a distant cis-regulatory region that harbors, besides lncRNA genes, also a differentially methylated CpG island, binds GLI2 depending on the methylation status of this CpG island, and physically interacts with and up-regulates the FOXF1 promoter. We suggest that lung-transcribed 16q24.1 lncRNAs may contribute to long-range regulation of FOXF1 by GLI2 and other transcription factors. Perturbation of lncRNA-mediated chromatin interactions may, in general, be responsible for position effect phenomena and potentially cause many disorders of human development.

Rho GEFs and cancer: linking gene expression and metastatic dissemination

Guanine nucleotide exchange factors (GEFs) that promote GTP loading onto the guanosine triphosphatases (GTPases) Rho and Rac are prominent players in cancer progression. Recent studies have highlighted the relevance of several GEFs, including the phosphatidylinositol 3,4,5-trisphosphate Rac exchangers P-Rex1 and P-Rex2a, in breast tumorigenesis. New evidence suggests that the exchange factors Vav2 and Vav3 play synergistic roles in breast cancer by sustaining tumor growth, neoangiogenesis, and metastasis. The identification of a Vav-regulated transcriptome and Vav-related genes that control specific steps of metastatic dissemination of breast cancer cells to the lungs highlights the complexities of the signaling networks regulated by Rho/Rac GTPases and may lead to novel therapeutic targets.