Gene Summary

Gene:MCF2; MCF.2 cell line derived transforming sequence
Aliases: DBL, ARHGEF21
Summary:The oncogenic protein encoded by this gene is a guanine nucleotide exchange factor (GEF) that exerts control over some members of the Rho family of small GTPases. Several transcript variants encoding different isoforms have been found for this gene. These isoforms exhibit different expression patterns and varying levels of GEF activity.[provided by RefSeq, Jan 2010]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:proto-oncogene DBL
Source:NCBIAccessed: 13 March, 2017


What does this gene/protein do?
Show (14)

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 13 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.

  • Ewing's Sarcoma
  • rho GTP-Binding Proteins
  • src Homology Domains
  • Gene Expression
  • Molecular Sequence Data
  • Cell Movement
  • Messenger RNA
  • Neoplastic Cell Transformation
  • Proto-Oncogenes
  • Neuroblastoma
  • Gene Expression Regulation
  • Proto-Oncogene Proteins
  • Northern Blotting
  • Oncogenes
  • Viral Structural Proteins
  • rac GTP-Binding Proteins
  • Cell Line
  • Signal Transduction
  • Testicular Cancer
  • Sequence Homology
  • Single Nucleotide Polymorphism
  • Testis
  • Vesicular Transport Proteins
  • Oncogenic Retroviridae Proteins
  • Guanine Nucleotide Exchange Factors
  • Western Blotting
  • X Chromosome
  • Peripheral Primitive Neuroectodermal Tumors
  • MCF2
  • 3T3 Cells
  • Transfection
  • Base Sequence
  • Amino Acid Sequence
  • Cell Differentiation
  • RHOA
  • Genetic Predisposition
  • Translocation
  • Tissue Distribution
  • Transformation, Genetic
  • Genetic Markers
Tag cloud generated 13 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (4)

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

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

Latest Publications: MCF2 (cancer-related)

Wang B, Fang J, Qu L, et al.
Upregulated TRIO expression correlates with a malignant phenotype in human hepatocellular carcinoma.
Tumour Biol. 2015; 36(9):6901-8 [PubMed] Related Publications
Triple functional domain protein (TRIO) is an evolutionarily conserved Dbl family guanine nucleotide exchange factors (GEFs) involved in cell proliferation and progression of some types of cancer. However, the expression and prognostic role of TRIO in hepatocellular carcinoma (HCC) have not yet been determined. Therefore, we attempted to determine the impact of TRIO on the clinical outcome of HCC patients to further identify its role in HCC. TRIO expression was examined using quantitative real-time PCR (qRT-PCR) and Western blotting in nonmalignant liver cells, HCC cells, and 93 paired of HCC tissues and adjacent noncancerous tissues. Statistical analyses were used to assess associations between TRIO expression and clinicopathological and prognostic factors. Small interfering RNA (siRNA)-mediated TRIO inhibition was performed in Hep3B and Huh7 cells to elucidate its roles in HCC. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was employed to measure cell proliferation, and apoptosis assay was analyzed by flow cytometry, respectively. Adhesion and transwell invasion assay were performed to determine the invasion ability of HCC cells in vitro. TRIO was significantly upregulated in the HCC cell lines and tissues compared with the nonmalignant liver cells and adjacent noncancerous liver tissues. In addition, high TRIO expression level associated with lymph node metastasis (P = 0.0183), clinical tumor node metastasis (TNM) stage (P = 0.0.0106), and decrease in overall survival (OS) (P = 0.017). Knockdown of TRIO on Hep3B and Huh7 cell lines suppressed cell proliferation and migration and induced apoptosis. Furthermore, silencing TRIO expression led to decrease of ras-related C3 botulinum toxin substrate 1 (Rac1), p-P38, B cell lymphoma 2 (BCL-2), and matrix metallopeptidase 9 (MMP-9). Our results demonstrated that TRIO protein expression is elevated and associated with a worse over survival rates in patients with HCC. Aberrant expression of TRIO might play an important role in HCC through promoting cell proliferation and invasion, and TRIO may be a novel therapeutic target for the treatment of HCC.

Vanni C, Ognibene M, Finetti F, et al.
Dbl oncogene expression in MCF-10 A epithelial cells disrupts mammary acinar architecture, induces EMT and angiogenic factor secretion.
Cell Cycle. 2015; 14(9):1426-37 [PubMed] Free Access to Full Article Related Publications
The proteins of the Dbl family are guanine nucleotide exchange factors (GEFs) of Rho GTPases and are known to be involved in cell growth regulation. Alterations of the normal function of these proteins lead to pathological processes such as developmental disorders, neoplastic transformation, and tumor metastasis. We have previously demonstrated that expression of Dbl oncogene in lens epithelial cells modulates genes encoding proteins involved in epithelial-mesenchymal-transition (EMT) and induces angiogenesis in the lens. Our present study was undertaken to investigate the role of Dbl oncogene in epithelial cells transformation, providing new insights into carcinoma progression.To assess how Dbl oncogene can modulate EMT, cell migration, morphogenesis, and expression of pro-apoptotic and angiogenic factors we utilized bi- and 3-dimensional cultures of MCF-10 A cells. We show that upon Dbl expression MCF-10 A cells undergo EMT. In addition, we found that Dbl overexpression sustains Cdc42 and Rac activation inducing morphological alterations, characterized by the presence of lamellipodia and conferring a high migratory capacity to the cells. Moreover, Dbl expressing MCF-10 A cells form altered 3D structures and can induce angiogenesis by producing proangiogenic factors such as CCL2. These results support a role for Dbl oncogene in epithelial cell differentiation and transformation and suggest the relevance of GEF deregulation in tumor onset and progression.

Alam M, Ahmad R, Rajabi H, Kufe D
MUC1-C Induces the LIN28B→LET-7→HMGA2 Axis to Regulate Self-Renewal in NSCLC.
Mol Cancer Res. 2015; 13(3):449-60 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: The LIN28B→let-7 pathway contributes to regulation of the epithelial-mesenchymal transition (EMT) and stem cell self-renewal. The oncogenic MUC1-C transmembrane protein is aberrantly overexpressed in lung and other carcinomas; however, there is no known association between MUC1-C and the LIN28B→let-7 pathway. Here in non-small cell lung cancer (NSCLC), silencing MUC1-C downregulates the RNA-binding protein LIN28B and coordinately increases the miRNA let-7. Targeting MUC1-C function with a dominant-negative mutant or a peptide inhibitor provided confirming evidence that MUC1-C induces LIN28B→let-7 signaling. Mechanistically, MUC1-C promotes NF-κB p65 chromatin occupancy of the LIN28B first intron and activates LIN28B transcription, which is associated with suppression of let-7. Consistent with let-7-mediated inhibition of HMGA2 transcripts, targeting of MUC1-C also decreases HMGA2 expression. HMGA2 has been linked to stemness, and functions as a competing endogenous RNA (ceRNA) of let-7-mediated regulation of the TGFβ coreceptor TGFBR3. Accordingly, targeting MUC1-C suppresses HMGA2 mRNA and protein, which is associated with decreases in TGFBR3, reversal of the EMT phenotype, and inhibition of self-renewal capacity. These findings support a model in which MUC1-C activates the ⇑LIN28B→⇓let-7→⇑HMGA2 axis in NSCLC and thereby promotes EMT traits and stemness.
IMPLICATIONS: A novel pathway is defined in which MUC1-C drives LIN28B→let-7→HMGA2 signaling, EMT, and self-renewal in NSCLC.

Cook DR, Rossman KL, Der CJ
Rho guanine nucleotide exchange factors: regulators of Rho GTPase activity in development and disease.
Oncogene. 2014; 33(31):4021-35 [PubMed] Free Access to Full Article Related Publications
The aberrant activity of Ras homologous (Rho) family small GTPases (20 human members) has been implicated in cancer and other human diseases. However, in contrast to the direct mutational activation of Ras found in cancer and developmental disorders, Rho GTPases are activated most commonly in disease by indirect mechanisms. One prevalent mechanism involves aberrant Rho activation via the deregulated expression and/or activity of Rho family guanine nucleotide exchange factors (RhoGEFs). RhoGEFs promote formation of the active GTP-bound state of Rho GTPases. The largest family of RhoGEFs is comprised of the Dbl family RhoGEFs with 70 human members. The multitude of RhoGEFs that activate a single Rho GTPase reflects the very specific role of each RhoGEF in controlling distinct signaling mechanisms involved in Rho activation. In this review, we summarize the role of Dbl RhoGEFs in development and disease, with a focus on Ect2 (epithelial cell transforming squence 2), Tiam1 (T-cell lymphoma invasion and metastasis 1), Vav and P-Rex1/2 (PtdIns(3,4,5)P3 (phosphatidylinositol (3,4,5)-triphosphate)-dependent Rac exchanger).

Gunjima K, Tomiyama R, Takakura K, et al.
3,4-dihydroxybenzalacetone protects against Parkinson's disease-related neurotoxin 6-OHDA through Akt/Nrf2/glutathione pathway.
J Cell Biochem. 2014; 115(1):151-60 [PubMed] Related Publications
UNLABELLED: Oxidative stress is implicated in the pathogenesis of various neurodegenerative diseases including Parkinson's disease (PD). 3,4-Dihydroxybenzalacetone (DBL) is a small catechol-containing compound isolated from Chaga (Inonotus obliquus [persoon] Pilat), and has been reported to have beneficial bioactivities, including antioxidative, anti-inflammatory, and anti-tumorigenic activities, with a relatively low toxicity to normal cells. We, therefore, investigated the neuroprotective activity of DBL against the PD-related neurotoxin 6-hydroxydopamine (6-OHDA). Pretreatment of human neuroblastoma SH-SY5Y cells with DBL, but not with another Chaga-derived catechol-containing compound, caffeic acid, dose-dependently improved the survival of 6-OHDA-treated cells. Although DBL did not reduce 6-OHDA-induced reactive oxygen species in the cell-free system, it promoted the translocation of Nrf2 to the nucleus, activated the transcription of Nrf2-dependent antioxidative genes, and increased glutathione synthesis in the cells. Buthionine sulfoximine, an inhibitor of glutathione synthesis, but not Sn-mesoporphyrin IX, a heme oxygenase-1 inhibitor, or dicoumarol, an
NAD(P)H: quinone oxidoreductase 1 inhibitor, abolished the protective effect of DBL against 6-OHDA. Furthermore, DBL activated stress-associated kinases such as Akt, ERK, and p38 MAPK, and PI3K or Akt inhibitors, but not ERK, p38, or JNK inhibitors, diminished DBL-induced glutathione synthesis and protection against 6-OHDA. These results suggest that DBL activates the Nrf2/glutathione pathway through PI3K/Akt, and improves survival of SH-SY5Y cells against 6-OHDA toxicity.

Zhu JM, Yu PW
Downregulation of T‑cell lymphoma invasion and metastasis‑inducing factor 1 induces cytoskeletal rearrangement and inhibits the invasive capacity of gastric cancer cells.
Mol Med Rep. 2013; 8(2):425-33 [PubMed] Related Publications
T-cell lymphoma invasion and metastasis-inducing factor 1 (Tiam-1) is an important member of the diffuse B-cell lymphoma (Dbl) oncogene family. In a previous study, the overexpression of Tiam-1 protein was identified by immunohistochemistry in human gastric cancer tissues, indicating that Tiam-1 may represent a candidate biomarker of the invasive and metastatic capacity of gastric cancer and for patient prognosis. In the present study, in vitro adhesion selection was used to separate two subpopulations with high (MH) or low (ML) invasive and metastatic potential from the MKN-45 human gastric cancer cell line (M0). A positive correlation was observed between Tiam-l mRNA and protein expression levels and the invasive capacity of the cells using RT-PCR and quantitative cellular-ELISA, respectively. To determine the mechanism by which Tiam-1 affects the invasive capacities of gastric cancer cells, Tiam-1 expression was downregulated in the MH subclone by liposomal transfection of antisense oligodeoxynucleotides (ASODNs). Following 48 h of treatment with ASODNs (0.43 µM), Tiam-1 mRNA transcription and protein expression levels in MH cells was decreased by 80 and 24%, respectively, compared with untreated controls. In addition, the in vitro invasive potential of MH cells was suppressed by 60%. Morphological and ultrastructural observations also demonstrated that ASODN-treated MH cells exhibited a smooth surface with markedly reduced filopodia and microspikes, which resembled M0 and ML cells. In addition, cytoskeletal distribution was markedly altered from disordered to regular with reduced long filament-like structures, projections, pseudopodia on the cell surface and decreased actin bodies in the cytoplasm. Results of the current study indicate that the overexpression of Tiam-1 contributes to the invasive phenotypes of gastric cancer cells. These observations are likely to provide an improved insight into the biological mechanisms of Tiam-1 and promote the development of novel treatment strategies in gastric cancer.

Rohon P, Divoka M, Calabkova L, et al.
Identification of e6a2 BCR-ABL fusion in a Philadelphia-positive CML with marked basophilia: implications for treatment strategy.
Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub. 2011; 155(2):187-90 [PubMed] Related Publications
AIM: This is a case report of a 51 year old male with marked splenomegaly, basophilia, severe thrombocytopenia, anemia and high SFKL phosphorylation downstream of Bcr-Abl, investigated for association of the e6a2 BCR-ABL fusion gene and marked basophilia. The treatment strategy implications in patients with Philadelphia positive CML are described.
METHODS: RT-PCR and sequencing were carried out on the peripheral blood leukocytes to detect the type of BCR-ABL transcript. The BCR-ABL mutational status was assessed using sequencing of the RT-PCR products. The in vitro test of sensitivity to TKIs was based on detecting inhibited phosphorylation of the Crkl and Phospho-Src family kinases (SFK, Tyr416) using immunodetection.
RESULTS: The cytogenetics revealed 90% of Ph+ (Philadelphia) cells in the bone marrow aspirate with no additional clonal chromosomal abnormalities at diagnosis. This correlated with an accelerated phase of the CML. Sequencing analysis of reverse transcribed and PCR amplified BCR-ABL transcript revealed a rare e6a2 fusion, with no evidence for Bcr-Abl kinase domain mutation. Western blot analysis showed high phosphorylation (activation) of Crkl and the Src family of kinases (P-SFK). In vitro test of sensitivity of the patients' leukemic cells to imatinib demonstrated sensitivity of Bcr-Abl tyrosine kinase to imatinib, as assessed by a decrease in phosphorylated Crkl and the disappearance of P-SFK, suggesting that P-Src reflects only the Bcr-Abl-dependent Src activity. The initial treatment strategy was reduced imatinib and search for an unrelated hematopoietic stem cell donor (according to the ELN recommendations). The patient was allografted with peripheral stem cells from an HLA- identical male donor but on day +70 graft failure occurred. He was allografted again with the peripheral stem cells from an HLA-identical female donor, engrafted on day +15 and showed 100% donor chimerism with no evidence of the e6a2 BCR-ABL fusion transcript on day +30.
CONCLUSION: The clinical disease course in patients with the rare e6a2 BCR-ABL transcript variant is aggressive. This may be the result of increased kinase activity due to partial loss of the guanine exchange factor/dbl-like domain which mediates the interaction with several Ras-like G-proteins involved in cell proliferation, signal transduction, and cytoskeletal organization. For the above reasons, these patients should receive stem cell transplant immediately after a short course of treatment with imatinib/ dual Src/Abl kinase inhibitor or they should be registered in clinical trials with experimental agents.

Ognibene M, Barbieri O, Vanni C, et al.
High frequency of development of B cell lymphoproliferation and diffuse large B cell lymphoma in Dbl knock-in mice.
J Mol Med (Berl). 2011; 89(5):493-504 [PubMed] Related Publications
Dbl is the prototype of a large family of GDP-GTP exchange factors for small GTPases of the Rho family. In vitro, Dbl is known to activate Rho, Rac, and Cdc42 and to induce a transformed phenotype in murine fibroblasts. We previously reported that Dbl-null mice are viable and fertile but display defective dendrite elongation of distinct subpopulations of cortical neurons, suggesting a role of Dbl in controlling dendritic growth. To gain deeper insights into the role of Dbl in development and disease, we attempted a knock-in approach to create an endogenous allele that encodes a missense-mutation-mediated loss of function in the DH domain. We generated, by gene targeting technology, a mutant mouse strain by inserting a mutagenized human proto-Dbl cDNA clone expressing only the Dbl N terminus regulatory sequence at the starting codon of murine exon 1. Animals were monitored over a 21-month period, and necropsy specimens were collected for histological examination and immunohistochemistry analysis. Dbl knock-in mice are viable and did not manifest either decreased reproductive performances or gross developmental phenotype but revealed a reduced lifespan compared to wild-type (w.t.) mice and showed, with aging, a B cell lymphoproliferation that often has features of a frank diffuse large B cell lymphoma. Moreover, Dbl knock-in male mice displayed an increased incidence of lung adenoma compared to w.t. mice. These data indicate that Dbl is a tumor susceptibility gene in mice and that loss of function of Dbl DH domain by genetic missense mutations is responsible for induction of diffuse large B cell lymphoma.

Xu X, Omelchenko T, Hall A
LKB1 tumor suppressor protein regulates actin filament assembly through Rho and its exchange factor Dbl independently of kinase activity.
BMC Cell Biol. 2010; 11:77 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Germline mutations in LKB1 result in Peutz-Jeghers Syndrome characterized by intestinal hamartomas and increased incidence of epithelial cancers. LKB1 encodes a serine/threonine kinase that plays an important role in regulating energy metabolism through the AMPK/mTOR signaling pathway. In addition, LKB1 is homologous to PAR-4, a polarity protein first described in C. elegans, while activation of LKB1 in mammalian epithelial cells induces the polarized assembly of actin filaments.
RESULTS: To explore the mechanism by which LKB1 interacts with the actin cytoskeleton, we introduced LKB1 into HeLa cells that lack endogenous LKB1. This results in activation of the small GTPase Rho and the assembly of linear actin filaments associated with focal adhesions. These effects on the actin cytoskeleton are attenuated by siRNA-mediated depletion of the guanine nucleotide exchange factor Dbl. Co-expression of the LKB1 with the adaptor protein STRAD induces actin filament puncta associated with phospho-ezrin.
CONCLUSIONS: This study reveals that LKB1 regulates the actin cytoskeleton through a Dbl/Rho pathway.

Zheng Q, Shi Y, Yang Z, et al.
Family-based association study of the MCF2L2 gene and polycystic ovary syndrome.
Gynecol Obstet Invest. 2009; 68(3):171-3 [PubMed] Related Publications
OBJECTIVE: The aim of the study was to determine the association between three single nucleotide polymorphism (SNP) variants (rs35368790, rs35069869 and rs684846) of the MCF2 cell line-derived transforming sequence-like 2 (MCF2L2) gene and polycystic ovary syndrome (PCOS) in PCOS family trios.
METHODS: Genotyping was done by TaqMan assay that incorporates minor groove-binding probe technology for allelic discrimination. One hundred and fifty-two unrelated PCOS probands and their biological parents were recruited. All subjects were of Han Chinese origin and from Shandong Province.
RESULTS: The transmission disequilibrium test (TDT) for allelic association demonstrated that a weak association was detected in SNP rs35368790 with p = 0.008. However, we found no significant transmission distortion of the other two SNPs (rs35069869, chi(2) = 3.645, p = 0.056; rs684846, chi(2) = 1.429, p = 0.232, respectively).
CONCLUSIONS: These results suggest that the genetic polymorphisms within MCF2L2 are likely to confer an increased susceptibility to PCOS in the Chinese population. Our present data may provide a basis for further studies of the role of the MCF2L2 gene in the etiology of PCOS.

Xu WH, Zhang C, Zhao WM, et al.
Mutational analysis of proto-oncogene Dbl on Xq27 in testicular germ cell tumors reveals a rare SNP in a patient with bilateral undescended testis.
World J Urol. 2009; 27(6):811-5 [PubMed] Related Publications
OBJECTIVES: An abundance of X chromosomes in testicular germ cell tumors (TGCTs), and a candidate TGCTs susceptibility gene (TGCT1) on Xq27 highlight the potential involvement of X chromosomes in TGCT pathogenesis. However, the TGCT1 on Xq27 has so far not been identified. We hypothesized that a somatic mutation of dbl oncogene on Xq27 may play a role for the development of TGCTs.
METHODS: We have screened 41 TGCT tissues for dbl mutations using single-strand conformation polymorphism (SSCP) analysis. These tissues are composed of 25 seminomatous TGCTs tissues and 16 non-seminomatous TGCTs tissues, including two cases with a rhabdomyosarcoma component.
RESULTS: Somatic mutations were not detected in the 25 exons of dbl in these TGCTs. However, we found a rare single nucleotide polymorphism (SNP) (T to C nucleotide change) within intron 22 in one out of the 41 TGCTs cases (2%). Furthermore, the sample with the rare SNP was identified as the sole TGCTs case associated with bilateral undescended testis in our series.
CONCLUSIONS: Our results indicate that proto-oncogene dbl is not a major target for sporadic TGCTs. However, the rare SNP in dbl may affect the susceptibility to undescended testis. Determining the frequency of this SNP in patients with various types of undescended testis in different ethnic groups is a warranted study.

Murakami M, Meneses PI, Knight JS, et al.
Nm23-H1 modulates the activity of the guanine exchange factor Dbl-1.
Int J Cancer. 2008; 123(3):500-10 [PubMed] Related Publications
Cytoskeleton rearrangement is necessary for tumor invasion and metastasis. Cellular molecules whose role is to regulate components of the cytoskeletal structure can dictate changes in cellular morphology. One of these molecules is the suppressor of tumor metastasis Nm23-H1. The level of Nm23-H1 expression has been linked to the invasiveness and metastatic potential of human cancers including melanoma and breast cancer. In this report, we demonstrate an interaction between the suppressor of tumor metastasis Nm23-H1, and Dbl-1, an oncoprotein which is associated with guanine exchange and belongs to a family of Guanine Exchange Factors (GEF). Nm23-H1 also was shown to bind pDbl which is the proto-oncoprotein of Dbl. Interestingly, the interaction between Nm23-H1 and Dbl-1 rescues the suppression of the cell motility activity Nm23-H1. Moreover, this interaction results in loss of the ability of the Dbl-1 oncoprotein to function as a GEF for the critical Rho-GTPase family member Cdc42. The loss of GTP loading onto Cdc42 resulted in a dramatic reduction in adhesion stimulated ruffles and suggests that Nm23-H1 can negatively regulate cell migration and tumor metastasis by modulating the activity of Cdc42 through direct interaction with Dbl-1.

Sung B, Pandey MK, Nakajima Y, et al.
Identification of a novel blocker of IkappaBalpha kinase activation that enhances apoptosis and inhibits proliferation and invasion by suppressing nuclear factor-kappaB.
Mol Cancer Ther. 2008; 7(1):191-201 [PubMed] Related Publications
3,4-dihydroxybenzalacetone (DBL) is a polyphenol derived from the medicinal plant Chaga [Inonotus obliquus (persoon) Pilat]. Although Chaga is used in Russia folk medicine to treat tumors, very little is known about its mechanism of action. Because most genes involved in inflammation, antiapoptosis, and cell proliferation are regulated by the transcription factor nuclear factor-kappaB (NF-kappaB), we postulated that DBL activity is mediated via modulation of the NF-kappaB activation pathway. We investigated the effects of DBL on NF-kappaB activation by electrophoretic mobility shift assay and on NF-kappaB-regulated gene expression by Western blot analysis. We found that DBL suppressed NF-kappaB activation by a wide variety of inflammatory agents, including tumor necrosis factor (TNF), interleukin-1beta, epidermal growth factor, okadaic acid, phorbol 12-myristate 13-acetate, and lipopolysaccharide. The suppression was not cell type specific and inhibited both inducible and constitutive NF-kappaB activation. DBL did not interfere with the binding of NF-kappaB to DNA but rather inhibited IkappaBalpha kinase activity, IkappaBalpha phosphorylation and degradation, p65 phosphorylation, and translocation. DBL also suppressed the expression of TNF-induced and NF-kappaB-regulated proliferative, antiapoptotic, and metastatic gene products. These effects correlated with enhancement of TNF-induced apoptosis and suppression of TNF-induced invasion. Together, our results indicate that DBL inhibits NF-kappaB activation and NF-kappaB-regulated gene expression, which may explain the ability of DBL to enhance apoptosis and inhibit invasion.

Kostenko EV, Olabisi OO, Sahay S, et al.
Ccpg1, a novel scaffold protein that regulates the activity of the Rho guanine nucleotide exchange factor Dbs.
Mol Cell Biol. 2006; 26(23):8964-75 [PubMed] Free Access to Full Article Related Publications
Dbs is a Rho-specific guanine nucleotide exchange factor (RhoGEF) with in vitro exchange activity specific for RhoA and Cdc42. Like many RhoGEF family members, the in vivo exchange activity of Dbs is restricted in a cell-specific manner. Here we report the characterization of a novel scaffold protein (designated cell cycle progression protein 1 [Ccpg1]) that interacts with Dbs and modulates its in vivo exchange specificity. When coexpressed in mammalian cells, Ccpg1 binds to the Dbl homology/pleckstrin homology domain tandem motif of Dbs and inhibits its exchange activity toward RhoA, but not Cdc42. Expression of Ccpg1 correlates with the ability of Dbs to activate endogenous RhoA in cultured cells, and suppression of endogenous Ccpg1 expression potentiates Dbs exchange activity toward RhoA. The isolated Dbs binding domain of Ccpg1 is not sufficient to suppress Dbs exchange activity on RhoA, thus suggesting a regulatory interaction. Ccpg1 mediates recruitment of endogenous Src kinase into Dbs-containing complexes and interacts with the Rho family member Cdc42. Collectively, our studies suggest that Ccpg1 represents a new class of regulatory scaffold protein that can function as both an assembly platform for Rho protein signaling complexes and a regulatory protein which can restrict the substrate utilization of a promiscuous RhoGEF family member.

Morley S, Wagner J, Kauppinen K, et al.
Requirement for Akt-mediated survival in cell transformation by the dbl oncogene.
Cell Signal. 2007; 19(1):211-8 [PubMed] Related Publications
The dbl oncogene product is the founding member of a large family of oncogenic proteins that function by activating the small GTP-binding proteins Cdc42, Rac and Rho. Through its substrate GTPases, Dbl transduces proliferative signals from cell-surface receptors to diverse cellular effectors and signaling pathways. The mechanisms by which these multiple signals are integrated, as well as their relative contribution to Dbl-induced cell transformation, are presently poorly understood. We investigated the role of the survival regulators PI3-kinase and Akt in Dbl-induced cell transformation. We found that Dbl induced the phosphorylation of Akt on threonine 308, through the GTPases Rac and Cdc42 and in a PI3-kinase dependent manner. Pharmacological or biochemical interference with this pathway lead to a marked, dose-dependent inhibition of the focus formation activity exhibited by Dbl-expressing cells. Dbl expression stimulated the phosphorylation of the anti-apoptotic Akt substrate Bad, and caused a marked decrease in basal levels of apoptosis. Finally, we found that activated Cdc42 existed in cells in complex with phosphoionositide-dependent kinase-1 (PDK1), the downstream mediator of PI3-kinase action. The data indicate that Dbl signaling stimulate the formation of a novel survival complex, through which anti-apoptotic signals are generated and propagated.

Segal NH, Blachere NE, Guevara-Patiño JA, et al.
Identification of cancer-testis genes expressed by melanoma and soft tissue sarcoma using bioinformatics.
Cancer Immun. 2005; 5:2 [PubMed] Related Publications
Cancer-testis or germ cell antigens (GCAs) are a category of tumor antigens expressed by male germ cells and by cancers of diverse histological origin, but not usually by normal adult somatic tissue. These antigens include products encoded by the MAGE, BAGE, GAGE, SSX, and LAGE/NY-ESO-1 families that encode antigenic peptides recognized by T lymphocytes. In this study, we exploit oligonucleotide technology to identify genes in melanoma and soft tissue sarcoma (STS) that display a cancer-testis/GCA expression profile. We identified 59 such genes, including GCAs we knew to be recognized by T lymphocytes. Among our findings are the expression of PRAME in monophasic synovial sarcoma, PRAME and NY-ESO-1 in myxoid/round cell liposarcoma, and SSX2 and members of the GAGE family in malignant fibrous histiocytoma. Furthermore, the proto-oncogene DBL/MCF2 was identified as encoding a novel candidate GCA expressed by clear cell sarcoma/melanoma of soft parts (MSP). DBL/MCF2 peptides that are bound to HLA-A*0201 were identified and recognized by T lymphocytes. These results show the utility of high-throughput expression analysis in the efficient screening and identification of GCA candidates in cancer, and its application to the discovery of candidate targets for T cell immunity against GCAs expressed by cancer.

Telegeev GD, Dubrovska AN, Dybkov MV, Maliuta SS
Influence of BCR/ABL fusion proteins on the course of Ph leukemias.
Acta Biochim Pol. 2004; 51(3):845-9 [PubMed] Related Publications
The hallmark of chronic myeloid leukemia (CML) and a subset of acute lymphoblastic leukemia (ALL) is the presence of the Philadelphia chromosome as a result of the t(9;22) translocation. This gene rearrangement results in the production of a novel oncoprotein, BCR/ABL, a constitutively active tyrosine kinase. There is compelling evidence that the malignant transformation by BCR/ABL is critically dependent on its Abl tyrosine kinase activity. Also the bcr part of the hybrid gene takes part in realization of the malignant phenotype. We supposed that additional mutations accumulate in this region of the BCR/ABL oncogene during the development of the malignant blast crisis in CML patients. In ALL patients having p210 fusion protein the mutations were supposed to be preexisting. Sequencing of PCR product of the BCR/ABL gene (Dbl, PH region) showed that along with single-nucleotide substitutions other mutations, mostly deletions, had occurred. In an ALL patient a deletion of the 5th exon was detected. The size of the deletions varied from 36 to 220 amino acids. For one case of blast crisis of CML changes in the character of actin organization were observed. Taking into account the functional role of these domains in the cell an etiological role of such mutations on the disease phenotype and leukemia progression is plausible.

Pegram MD, Konecny GE, O'Callaghan C, et al.
Rational combinations of trastuzumab with chemotherapeutic drugs used in the treatment of breast cancer.
J Natl Cancer Inst. 2004; 96(10):739-49 [PubMed] Related Publications
BACKGROUND: Trastuzumab, a humanized anti-HER2 antibody, increases the clinical benefit of first-line chemotherapy in patients with metastatic breast cancers that overexpress HER2. We characterized interactions between trastuzumab and chemotherapeutic agents commonly used in the treatment of breast cancer.
METHODS: Multiple drug effect/combination index isobologram analysis was used to study the efficacy of chemotherapeutic drug plus trastuzumab combinations tested against four HER2-overexpressing breast cancer cell lines (SK-BR-3, BT-474, MDA-MB-361, and MDA-MB-453). Combination index values were derived from parameters of the median effect plots, and statistical tests were used to determine whether the mean combination index values at multiple effect levels were statistically significantly different from a combination index value of 1.0. Values less than 1.0 indicate synergistic interactions, values greater than 1.0 indicate antagonistic interactions, and values equal to 1.0 indicate additive interactions.
RESULTS: At a wide range of clinically achievable drug concentrations, synergistic interactions were observed in all four breast cancer cell lines for trastuzumab plus carboplatin (mean combination index values ranged from 0.32 [P<.001] to 0.53 [P<.001]), 4-hydroxycyclophosphamide (mean combination index values ranged from 0.38 [P<.001] to 0.73 [P =.010]), docetaxel (mean combination index values ranged from 0.30 [P<.001] to 0.62 [P<.001]), and vinorelbine (mean combination index values ranged from 0.24 [P<.001] to 0.78 [P<.034]). Additive interactions were observed in all four cell lines with trastuzumab plus doxorubicin, epirubicin, and paclitaxel. Interactions between trastuzumab and gemcitabine were synergistic at low concentrations of gemcitabine and antagonistic at high concentrations. A synergistic interaction was observed with a three-drug combination of docetaxel plus carboplatin plus trastuzumab in SK-BR-3 cells (mean combination index value = 0.09; P<.001).
CONCLUSION: Consistent synergistic interactions of trastuzumab plus carboplatin, 4-hydroxycyclophosphamide, docetaxel, or vinorelbine across a wide range of clinically relevant concentrations in HER2-overexpressing breast cancer cells indicate that these are rational combinations to test in human clinical trials.

Lutz S, Freichel-Blomquist A, Rümenapp U, et al.
p63RhoGEF and GEFT are Rho-specific guanine nucleotide exchange factors encoded by the same gene.
Naunyn Schmiedebergs Arch Pharmacol. 2004; 369(5):540-6 [PubMed] Related Publications
Activation of Rho GTPases, which play pivotal roles in diverse cellular functions, is catalysed by specific guanine nucleotide exchange factors (GEFs). We and others (Souchet et al. (2002)) independently cloned a human cDNA encoding a 580 aa protein (p63RhoGEF), which contains a tandem of Dbl homology and pleckstrin homology domains typical for RhoGEFs. In accordance with Souchet et al., recombinant p63RhoGEF interacted with and catalysed GDP/GTP exchange at RhoA, but not Rac1 or Cdc42. Recently, an N-terminally truncated form of p63RhoGEF, termed GEFT, was described as a Rac/Cdc42-specific GEF (Guo et al. 2003). As judged by RT-PCR with specific primers, we were able to detect mRNA variants encoding p63RhoGEF and GEFT within several tissues and cell lines. Apparently, they co-exist within one cell and are derived from the same gene. When expressed in human embryonic kidney cells, both p63RhoGEF and GEFT caused activation of RhoA, but not Rac1 or Cdc42, and induced serum response factor-mediated gene transcription, which was fully blunted by the Rho-inactivating C3 transferase. In line with these data, expression of either p63RhoGEF or GEFT in J82 human bladder carcinoma cells induced the formation of actin stress fibres. We therefore conclude that p63RhoGEF and GEFT are apparently isoforms derived from the same gene and that GEFT, similar to p63RhoGEF, activates RhoA in several cell types.

Qi H, Fournier A, Grenier J, et al.
Isolation of the novel human guanine nucleotide exchange factor Src homology 3 domain-containing guanine nucleotide exchange factor (SGEF) and of C-terminal SGEF, an N-terminally truncated form of SGEF, the expression of which is regulated by androgen in prostate cancer cells.
Endocrinology. 2003; 144(5):1742-52 [PubMed] Related Publications
In searching for androgen-responsive genes in human prostate cancer cells, we have isolated two cDNAs that encode alternate forms of a novel Src homology 3 domain-containing guanine nucleotide exchange factor (SGEF). The SGEF mRNA is widely expressed in human tissues, and the predicted 871-amino acid SGEF protein contains Dbl homology and pleckstrin homology domains as well as an N-terminal proline-rich domain, a C-terminal Src homology 3 domain, and two nuclear localization signals. The second cDNA encodes a 139-amino acid N-terminally truncated form of SGEF designated C-terminal SGEF (CSGEF). In contrast to SGEF, CSGEF mRNA expression is restricted to prostate and liver. Moreover, CSGEF expression is up-regulated by androgens in LNCaP cells, whereas that of SGEF is not. Up-regulation of CSGEF was sensitive to actinomycin D but did not require new protein synthesis. The SGEF gene is located on chromosome 3q25.2 and consists of at least 15 exons. Based on the structure of the SGEF and CSGEF cDNAs, we deduced that CSGEF expression is controlled by an alternate androgen-responsive promoter of the SGEF gene. We hypothesize that SGEF is a ubiquitous regulator of Rho guanosine triphosphatases, whereas CSGEF may function as an androgen-induced regulator of Rho guanosine triphosphatase activity in epithelial cells of the human prostate.

Arthur WT, Ellerbroek SM, Der CJ, et al.
XPLN, a guanine nucleotide exchange factor for RhoA and RhoB, but not RhoC.
J Biol Chem. 2002; 277(45):42964-72 [PubMed] Related Publications
Rho proteins cycle between an inactive, GDP-bound state and an active, GTP-bound state. Activation of these GTPases is mediated by guanine nucleotide exchange factors (GEFs), which promote GDP to GTP exchange. In this study we have characterized XPLN, a Rho family GEF. Like other Rho GEFs, XPLN contains a tandem Dbl homology and pleckstrin homology domain topography, but lacks homology with other known functional domains or motifs. XPLN protein is expressed in the brain, skeletal muscle, heart, kidney, platelets, and macrophage and neuronal cell lines. In vitro, XPLN stimulates guanine nucleotide exchange on RhoA and RhoB, but not RhoC, RhoG, Rac1, or Cdc42. Consistent with these data, XPLN preferentially associates with RhoA and RhoB. The specificity of XPLN for RhoA and RhoB, but not RhoC, is surprising given that they share over 85% sequence identity. We determined that the inability of XPLN to exchange RhoC is mediated by isoleucine 43 in RhoC, a position occupied by valine in RhoA and RhoB. When expressed in cells, XPLN activates RhoA and RhoB, but not RhoC, and stimulates the assembly of stress fibers and focal adhesions in a Rho kinase-dependent manner. We also found that XPLN possesses transforming activity, as determined by focus formation assays. In conclusion, here we describe a Rho family GEF that can discriminate between the closely related RhoA, RhoB, and RhoC, possibly giving insight to the divergent functions of these three proteins.

Martinelli G, Amabile M, Giannini B, et al.
Novel types of bcr-abl transcript with breakpoints in BCR exon 8 found in Philadelphia positive patients with typical chronic myeloid leukemia retain the sequence encoding for the DBL- and CDC24 homology domains but not the pleckstrin homology one.
Haematologica. 2002; 87(7):688-94; discussion 694 [PubMed] Related Publications
BACKGROUND AND OBJECTIVES: We previously described a novel type of the chimeric bcr-abl mRNA transcript in a patient with a Philadelphia chromosome positive chronic myeloid leukemia. A similar bcr-abl transcript has also been described by others.
DESIGN AND METHODS: Sequence analysis of the fusion region showed a join between part of exon e8 of the bcr gene and an intronic sequence of abl intron 1b spliced on exon a2 of the abl gene, giving rise to an in-frame e8-int-a2 bcr-abl transcript, translated into a 197.5 kDa BCR-ABL protein of 1804 amino acid residues, which we named p200 BCR-ABL.
RESULTS: In this work, employing protein comparison analysis (pFAM) we show that these novel bcr-abl transcripts retain the DBL homology (DH) domain and the recently recognized CDC24 homology domain, but not the pleckstrin homology (PH) domain of the bcr gene.
INTERPRETATION AND CONCLUSIONS: This observation, along with the myeloid immunophenotype of the tumor and, at least in one case, the patient's correspondingly good response to alpha-interferon therapy, suggests that p200 BCR-ABL is more similar to p210 BCR-ABL, in which the DH, CDC24 and PH domains are all maintained, than to p185, in which these domains are all lost.

Himmel KL, Bi F, Shen H, et al.
Activation of clg, a novel dbl family guanine nucleotide exchange factor gene, by proviral insertion at evi24, a common integration site in B cell and myeloid leukemias.
J Biol Chem. 2002; 277(16):13463-72 [PubMed] Related Publications
Retroviruses induce leukemia in inbred strains of mice by activating cellular proto-oncogenes and/or inactivating tumor suppressors. The proviral integration sites in these leukemias provide powerful genetic tags for disease gene identification. Here we show that Evi24, a common site of retroviral integration in AKXD B cell and BXH-2 myeloid leukemias, contains a novel Dbl family guanine nucleotide exchange factor gene. We have designated this gene Clg (common-site lymphoma/leukemia guanine nucleotide exchange factor). Proviral integrations on chromosome 7 at Evi24 are located 7.6-10.3 kb upstream of Clg and increased Clg expression 2-5-fold compared with leukemias lacking proviral integrations at Evi24. Clg contains Dbl/pleckstrin homology domains with substantial sequence homology to many Rho family activators, including the transforming Dbl and Dbs/Ost oncogenes. Nucleotide exchange assays indicated that Clg specifically activated nucleotide exchange on Cdc42, but not RhoA or Rac1, in vitro. NIH 3T3 transfection studies showed that overexpression of full-length and carboxyl-terminally truncated forms of Clg morphologically transformed NIH 3T3 cells. This study and studies showing that the human homolog of EVI24 is located in a region of 19q13 frequently amplified in B cell lymphomas and pancreatic and breast cancers implicate Clg and Cdc42 activation in mouse and human cancers.

De Toledo M, Coulon V, Schmidt S, et al.
The gene for a new brain specific RhoA exchange factor maps to the highly unstable chromosomal region 1p36.2-1p36.3.
Oncogene. 2001; 20(50):7307-17 [PubMed] Related Publications
Guanine nucleotide exchange factors from the Dbl family are proto-oncogenic proteins that activate small GTPases of the Rho family. Here we report the characterization of GEF720, a novel Dbl-like protein related to p115Rho-GEF. GEF720 activated RhoA both in our recently developed Yeast Exchange Assay and in biochemical in vitro exchange assays. GEF720 induced RhoA dependent assembly of actin stress fibers in REF52 fibroblastic cells. In NIH3T3 cells this Dbl-like protein elicited formation of transformation foci with a morphology similar to RhoA-V14 induced foci. In the PC12 neuron-like cell line, expression of GEF720, whose mRNA is brain specific, inhibited NGF-induced neurite outgrowth. Finally, GEF720 gene is located on human chromosome 1 on band 1p36, between Tumor Protein 73 and Tumor Necrosis Factor Receptor 12, two genes rearranged in many neuroblastoma cell lines. Together, these results show that this new Dbl related protein, GEF720, is an exchange factor that can directly activate RhoA in vivo and is potentially involved in the control of neuronal cell differentiation. GEF720 is also a new candidate gene involved in the progression of neuroblastoma and developmental abnormalities associated with rearrangements in the 1p36 chromosomal region.

Matsumoto Y, Takano H, Kunishio K, et al.
Hypophosphorylation of topoisomerase IIalpha in etoposide (VP-16)-resistant human carcinoma cell lines associated with carboxy-terminal truncation.
Jpn J Cancer Res. 2001; 92(7):799-805 [PubMed] Related Publications
Topoisomerase IIalpha is a target for many chemotherapeutic agents in clinical use. To define mechanisms of resistance and regions crucial for the function of topoisomerase IIalpha, drug-resistant cell lines have been isolated following exposure to topoisomerase II poisons. Two resistant sublines, T47D-VP and MCF-7-VP, were isolated from human carcinoma cell lines following exposure to 300 or 500 ng / ml etoposide (VP-16). Cytotoxicity studies confirmed resistance to etoposide and other topoisomerase II poisons. KCl-sodium dodecyl sulfate (K-SDS) precipitation assays using intact cells showed reduced DNA-topoisomerase II complex formation following VP-16 or amsacrine (m-AMSA). RNAse protection analysis identified a deletion of 200 base pairs in the topoisomerase IIalpha cDNA of T47D-VP and rising dbl quote, left (low)AA insertion" in the topoisomerase IIalpha cDNA of MCF-7-VP. Reduced topoisomerase IIalpha mRNA and protein levels were observed in both cell lines. It was somewhat surprising to find that nuclear extracts from T47D-VP and MCF-7-VP cells had comparable topoisomerase II activity to that of parental cells. Analysis of the extent of phosphorylation demonstrated that topoisomerase IIalpha from the resistant cells was relatively hypophosphorylated compared to that of parental cells. In these cell lines, hypophosphorylation secondary to loss of a portion of the C-terminal domain of topoisomerase IIalpha mediated the restored activity, despite a fall in topoisomerase IIalpha mRNA and protein, and this resulted in cross resistance to topoisomerase II poisons.

Mine N, Kurose K, Konishi H, et al.
Fusion of a sequence from HEI10 (14q11) to the HMGIC gene at 12q15 in a uterine leiomyoma.
Jpn J Cancer Res. 2001; 92(2):135-9 [PubMed] Related Publications
Uterine leiomyoma, a benign smooth-muscle tumor of the myometrium, is the most commonly encountered neoplasm in women of reproductive age. Band q15 of chromosome 12 is often rearranged in benign mesenchymal tumors such as uterine leiomyomas, and the HMGIC gene, encoding a protein of the high-mobility-group (HMG), is present in that region. Using 3' rapid amplification of cDNA ends (3'RACE) experiments, we isolated an ectopic sequence that was fused to HMGIC in a uterine leiomyoma. Cloning of the fusion cDNA identified a gene termed rising dbl quote, left (low)homo sapiens enhancer of invasion 10" (HEI10) as the fusion partner. Radiation hybrid mapping revealed that the normal location of HEI10 is at 14q11. In the fusion transcript the first two exons of the HMGIC gene, which encode DNA-binding domains, were fused to the 3' portion of the HEI10 gene. This rearrangement implicates HMGIC in the tumorigenesis of uterine leiomyoma, and suggests that its fusion HMGIC product may play a role in mesenchymal differentiation.

Rodrigues NR, Theodosiou AM, Nesbit MA, et al.
Characterization of Ngef, a novel member of the Dbl family of genes expressed predominantly in the caudate nucleus.
Genomics. 2000; 65(1):53-61 [PubMed] Related Publications
We have identified Ngef as a novel member of the family of Dbl genes. Many members of this family have been shown to function as guanine nucleotide exchange factors for the Rho-type GTPases. Ngef is predominantly expressed in brain, with the strongest signal in the caudate nucleus, a region associated with the control of movement. Ngef contains a translated trinucleotide repeat, a polyglutamic acid stretch interrupted by a glycine. We have localized the Ngef gene to mouse chromosome 1 and the human homologue of Ngef to human chromosome 2q37. We have shown in preliminary experiments that Ngef has transforming potential in cell culture and is able to induce tumors in nude mice.

Miller BT, Rubino DM, Driggers PH, et al.
Expression of brx proto-oncogene in normal ovary and in epithelial ovarian neoplasms.
Am J Obstet Gynecol. 2000; 182(2):286-95 [PubMed] Related Publications
OBJECTIVE: We previously identified a protein, Brx, that interacted with estrogen receptor alpha. Sequence analysis determined that Brx is a novel member of the Dbl family of oncoproteins involved in signaling pathways that regulate cell growth. Because the Brx protein was found to be highly expressed in hormoneresponsive breast epithelium, the objective of this study was to determine whether Brx was expressed in both normal and neoplastic ovarian tissues.
STUDY DESIGN: A polyclonal antiserum directed against the Brx protein was used to perform immunolocalization on sections from 5 normal ovaries and 20 ovarian neoplasms. Chromosomal localization of the brx gene was accomplished by means of fluorescence in situ hybridization. Northern and Western blot analyses were performed on extracts prepared from human ovaries.
RESULTS: Brx protein was localized to the cytoplasm of granulosa cells from mature graafian follicles, the corpus luteum, and islands of hilar cells in normal ovaries. In tumors with low malignant potential and ovarian carcinomas the neoplastic epithelium stained strongly for Brx protein. Northern and Western blot analyses, respectively, confirmed expression of Brx messenger ribonucleic acid and protein in normal ovary. Finally, the brx gene was localized to 15q25.
CONCLUSION: The proto-oncogene brx is expressed in specific normal human ovarian tissues and is also present in ovarian epithelial neoplasms.

Kourlas PJ, Strout MP, Becknell B, et al.
Identification of a gene at 11q23 encoding a guanine nucleotide exchange factor: evidence for its fusion with MLL in acute myeloid leukemia.
Proc Natl Acad Sci U S A. 2000; 97(5):2145-50 [PubMed] Free Access to Full Article Related Publications
We have identified a gene at 11q23, telomeric to MLL, that encodes a guanine nucleotide exchange factor (GEF). This gene is transcribed into a 9.5-kb mRNA containing a 4.6-kb ORF. By Northern analysis, it was found to be expressed in all human tissues examined including peripheral blood leukocytes, spleen, prostate, testis, ovary, small intestine, colon, and minimally in thymus. Analysis of the predicted protein sequence indicates that it has strong homology to several members of the family of Rho GEFs that includes such oncogenes as Dbl, Vav, Tiam, and Bcr. A patient with primary acute myeloid leukemia (AML) and a karyotype of 51,XY,+8,+19,+3mar was found to have the 5' end of MLL at exon 6 fused in-frame with the 3' end of almost the entire ORF of this gene, which we named LARG for leukemia-associated Rho GEF. Transcriptional orientation of both genes at 11q23 is from centromere to telomere, consistent with other data that suggest the MLL-LARG fusion resulted from an interstitial deletion rather than a balanced translocation. LARG does not appear to have any homology with other MLL partner genes reported thus far. Thus, LARG represents an additional member of the GEF family and a novel MLL fusion partner in acute myeloid leukemia.

Movilla N, Bustelo XR
Biological and regulatory properties of Vav-3, a new member of the Vav family of oncoproteins.
Mol Cell Biol. 1999; 19(11):7870-85 [PubMed] Free Access to Full Article Related Publications
We report here the identification and characterization of a novel Vav family member, Vav-3. Signaling experiments demonstrate that Vav-3 participates in pathways activated by protein tyrosine kinases. Vav-3 promotes the exchange of nucleotides on RhoA, on RhoG and, to a lesser extent, on Rac-1. During this reaction, Vav-3 binds physically to the nucleotide-free states of those GTPases. These functions are stimulated by tyrosine phosphorylation in wild-type Vav-3 and become constitutively activated upon deletion of the entire calponin-homology region. Expression of truncated versions of Vav-3 leads to drastic actin relocalization and to the induction of stress fibers, lamellipodia, and membrane ruffles. Moreover, expression of Vav-3 alters cytokinesis, resulting in the formation of binucleated cells. All of these responses need only the expression of the central region of Vav-3 encompassing the Dbl homology (DH), pleckstrin homology (PH), and zinc finger (ZF) domains but do not require the presence of the C-terminal SH3-SH2-SH3 regions. Studies conducted with Vav-3 proteins containing loss-of-function mutations in the DH, PH, and ZF regions indicate that only the DH and ZF regions are essential for Vav-3 biological activity. Finally, we show that one of the functions of the Vav-3 ZF region is to work coordinately with the catalytic DH region to promote both the binding to GTP-hydrolases and their GDP-GTP nucleotide exchange. These results highlight the role of Vav-3 in signaling and cytoskeletal pathways and identify a novel functional cross-talk between the DH and ZF domains of Vav proteins that is imperative for the binding to, and activation of, Rho GTP-binding proteins.

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