IQ motif-containing GTPase-activating protein 2 (IQGAP2) is a multidomain scaffolding protein that plays a role in cytoskeleton regulation by juxtaposing Rho GTPase and Ca2+/calmodulin signals. While IQGAP2 suppresses tumorigenesis in liver, its role in pathophysiology of the gastrointestinal tract remains unexplored. Here we report that IQGAP2 is required for the inflammatory response in colon. Mice lacking Iqgap2 gene (Iqgap2-/- mice) were resistant to chemically-induced colitis. Unlike wild-type controls, Iqgap2-/- mice treated with 3% dextran sulfate sodium (DSS) in water for 13 days displayed no injury to colonic epithelium. Mechanistically, resistance to colitis was associated with suppression of colonic NF-κB signaling and IL-6 synthesis, along with diminished neutrophil and macrophage production and recruitment in Iqgap2-/- mice. Finally, alterations in IQGAP2 expression were found in colons of patients with inflammatory bowel disease (IBD). Our findings indicate that IQGAP2 promotes inflammatory response at two distinct levels; locally, in colonic epithelium through TLR4/NF-κB signaling pathway, and systemically, via control of maturation and recruitment of myeloid immune cells. This work identifies a novel mechanism of colonic inflammation mediated by signal transducing scaffolding protein IQGAP2. IQGAP2 domain-specific blocking agents may represent a conceptually novel strategy for therapy of IBD and other inflammation-associated disorders, including cancer.

YopM is a leucine-rich repeat (LRR)-containing effector in several Yersinia species, including Yersinia pestis and Y. pseudotuberculosis. Different Yersinia strains encode distinct YopM isoforms with variable numbers of LRRs but conserved C-terminal tails. A 15-LRR isoform in Y. pseudotuberculosis YPIII was recently shown to bind and inhibit caspase-1 via a YLTD motif in LRR 10, and attenuation of YopM(-) YPIII was reversed in mice lacking caspase-1, indicating that caspase-1 inhibition is a major virulence function of YopM(YPIII). To determine if other YopM proteins inhibit caspase-1, we utilized Y. pseudotuberculosis strains natively expressing a 21-LRR isoform lacking the YLTD motif (YopM(32777)) or ectopically expressing a Y. pestis 15-LRR version with a functional (YopM(KIM)) or inactivated (YopM(KIM) D(271)A) YLTD motif. Results of mouse and macrophage infections with these strains showed that YopM(32777), YopM(KIM), and YopMKIM D271A inhibit caspase-1 activation, indicating that the YLTD motif is dispensable for this activity. Analysis of YopMKIM deletion variants revealed that LRRs 6 to 15 and the C-terminal tail are required to inhibit caspase-1 activation. YopM(32777), YopM(KIM), and YopM(KIM) deletion variants were purified, and binding partners in macrophage lysates were identified. Caspase-1 bound to YopMKIM but not YopM(32777). Additionally, YopM(KIM) bound IQGAP1 and the use of Iqgap1(-/-) macrophages revealed that this scaffolding protein is important for caspase-1 activation upon infection with YopM(-) Y. pseudotuberculosis. Thus, while multiple YopM isoforms inhibit caspase-1 activation, their variable LRR domains bind different host proteins to perform this function and the LRRs of YopM(KIM) target IQGAP1, a novel regulator of caspase-1, in macrophages.IMPORTANCE Activation of caspase-1, mediated by macromolecular complexes termed inflammasomes, is important for innate immune defense against pathogens. Pathogens can, in turn, subvert caspase-1-dependent responses through the action of effector proteins. For example, the Yersinia effector YopM inhibits caspase-1 activation by arresting inflammasome formation. This caspase-1 inhibitory activity has been studied in a specific YopM isoform, and in this case, the protein was shown to act as a pseudosubstrate to bind and inhibit caspase-1. Different Yersinia strains encode distinct YopM isoforms, many of which lack the pseudosubstrate motif. We studied additional isoforms and found that these YopM proteins inhibit caspase-1 activation independently of a pseudosubstrate motif. We also identified IQGAP1 as a novel binding partner of the Yersinia pestis YopMKIM isoform and demonstrated that IQGAP1 is important for caspase-1 activation in macrophages infected with Yersinia. Thus, this study reveals new insights into inflammasome regulation during Yersinia infection.

Hepatocellular carcinoma (HCC) is a highly prevalent and deadly cancer. In the United States, HCC incidence rates tripled between 1975 and 2005. HCC is mostly diagnosed in late stage and treatment of advanced HCC remains an area of high unmet medical need. Discovery of novel, more molecularly targeted therapeutic modalities and also diagnostic and prognostic biomarkers for early detection of HCC is urgent. While many molecules have been implicated in hepatic carcinogenesis over the years, a comprehensive mechanistic understanding of the intricate signaling networks responsible for HCC development is still lacking. To establish the physiological role of IQ-motif containing GTPase-activating-like protein 2 (IQGAP2), we generated a conventional Iqgap2 knockout mouse model. It was discovered that 86% of Iqgap2-/- mice developed spontaneous HCC, while mice deficient in both Iqgap2 and its close homolog Iqgap1 genes (Iqgap1-/-/Iqgap2-/-) displayed relative protection against HCC and improved long-term survival (Schmidt et al, MCB 2008). We also showed that IQGAP2 protein expression was reduced and IQGAP1 expression elevated in the majority of human HCC tumors studied [(N = 82), White et al, BMC Gastroenterology 2010]. These suggested that IQGAP2 may be a novel tumor suppressor and IQGAP1, a bona fide oncogene, antagonizes activity of IQGAP2 in liver. To delineate the mechanism behind the tumor suppressive action of IQGAP2 in the pathogenesis of HCC, an array of assays was conducted, including Affymetrix RNA microarray, cell-based assays such as proliferation, migration and invasion, and also immunoprecipitation and LC-MS/MS proteomics. Further, to establish the relevance of the Iqgap2-/- model to human disease, a cross-species comparison of human and Iqgap2-/- HCC tumors was performed using Significance Analysis of Microarray (SAM) and unsupervised hierarchical clustering analysis. We found that IQGAP2 silencing results in PI3K/Akt signaling activation in liver. Insulin stimulation experiments showed that both Iqgap2−/− and Iqgap1−/−/Iqgap2−/− mice had elevated (~3-fold) hepatic levels of the phosphorylated (at Ser473) form of Akt kinase, along with increased levels of the phosphorylated (at Ser9) form of GSK3β compared to wild-type controls. Similar data were obtained in HepG2 cells stably expressing IQGAP2 shRNA and stimulated with either insulin or IGF-1. Next, IQGAP2 was identified as an Akt binding partner in mouse liver lysates. In vitro studies in both HCC cell lines and MEFs showed that lack of IQGAP2 was associated with increased cell proliferation and migration, consistent with PI3K/Akt signaling activation. RNA microarray also identified the Wnt/β-catenin signaling pathway as the top canonical pathway dysregulated in Iqgap2-/- mouse livers. This suggests that IQGAP2, being a scaffolding protein, may realize its tumor suppressing function through cross-linking several signaling pathways in liver. Finally, Iqgap2-/- mouse hepatic tumors shared genetic signatures with HCC tumors from patients with advanced disease as evidenced by a 78% mouse-to-human microarray data set concordance rate with 117 out of 151 identified ortholog genes having similar expression profiles across the two species. Collectively, our results indicate that the Iqgap2 knockout mouse model closely recapitulates human HCC at the molecular level and supports its further application for the study of this disease. Modulation of both IQGAP1 and IQGAP2 expression represents a new potential therapeutic strategy for liver cancer. Citation Format: Dmitri V. Gnatenko, Xiao Xu, Joseph LaComb, Beatrix Ueberheide, Wei Zhu, Valentina A. Schmidt. Iqgap2-/- mouse as a model for advanced human hepatocellular carcinoma. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr B33.

Elevated bile acid levels increase hepatocellular carcinoma by unknown mechanisms. Here, we show that mice with a severe defect in bile acid homeostasis due to the loss of the nuclear receptors FXR and SHP have enlarged livers, progenitor cell proliferation, and Yes-associated protein (YAP) activation and develop spontaneous liver tumorigenesis. This phenotype mirrors mice with loss of hippo kinases or overexpression of their downstream target, YAP. Bile acids act as upstream regulators of YAP via a pathway dependent on the induction of the scaffold protein IQGAP1. Patients with diverse biliary dysfunctions exhibit enhanced IQGAP1 and nuclear YAP expression. Our findings reveal an unexpected mechanism for bile acid regulation of liver growth and tumorigenesis via the Hippo pathway.

It is broadly accepted that genetically engineered animal models do not always recapitulate human pathobiology. Therefore identifying best-fit mouse models of human cancers that truly reflect the corresponding human disease is of vital importance in elucidating molecular mechanisms of tumorigenesis and developing preventive and therapeutic approaches. A new hepatocellular carcinoma (HCC) mouse model lacking a novel putative tumor suppressor IQGAP2 has been generated by our laboratory. The aim of this study was to obtain the molecular signature of Iqgap2−/− HCC tumors and establish the relevance of this model to human disease. Here we report a comprehensive transcriptome analysis of Iqgap2−/− livers and a cross-species comparison of human and Iqgap2−/− HCC tumors using Significance Analysis of Microarray (SAM) and unsupervised hierarchical clustering analysis. We identified the Wnt/β-catenin signaling pathway as the top canonical pathway dysregulated in Iqgap2−/− livers. We also demonstrated that Iqgap2−/− hepatic tumors shared genetic signatures with HCC tumors from patients with advanced disease as evidenced by a 78% mouse-to-human microarray data set concordance rate with 117 out of 151 identified ortholog genes having similar expression profiles across the two species. Collectively, these results indicate that the Iqgap2 knockout mouse model closely recapitulates human HCC at the molecular level and supports its further application for the study of this disease.

Polymorphisms of hormone receptor genes have been linked to modifications in reproductive factors and to an increased risk of breast cancer (BC). In the present study, we have determined the allelic and genotypic frequencies of the ERα-397 PvuII C/T, ERα-351 XbaI A/G and PGR PROGINS polymorphisms and investigated their relationship with mammographic density, body mass index (BMI) and other risk factors for BC. A consecutive and unselected sample of 750 Brazilian BC-unaffected women enrolled in a mammography screening program was recruited. The distribution of PGR PROGINS genotypic frequencies was 72.5, 25.5 and 2.0% for A1A1, A1A2 and A2A2, respectively, which was equivalent to that encountered in other studies with healthy women. The distribution of ERα genotypes was: ERα-397 PvuII C/T: 32.3% TT, 47.5% TC, and 20.2% CC; ERα-351 XbaI A/G: 46.3% AA, 41.7% AG and 12.0% GG. ERα haplotypes were 53.5% PX, 14.3% Px, 0.3% pX, and 32.0% px. These were significantly different from most previously published reports worldwide (P < 0.05). Overall, the PGR PROGINS genotypes A2A2 and A1A2 were associated with fatty and moderately fatty breast tissue. The same genotypes were also associated with a high BMI in postmenopausal women. In addition, the ERα-351 XbaI GG genotype was associated with menarche ≥ 12 years (P = 0.02). ERα and PGR polymorphisms have a phenotypic effect and may play an important role in BC risk determination. Finally, if confirmed in BC patients, these associations could have important implications for mammographic screening and strategies and may be helpful to identify women at higher risk for the disease.

Abstract While hepatocellular carcinoma (HCC) is the fifth most commonly diagnosed cancer worldwide, the signaling pathways involved are not fully understood and treatment of advanced disease still represents an area of high unmet medical need. We previously reported that IQ-motif-containing GTPase-activating-like proteins IQGAP1 and IQGAP2 play opposing roles in hepatic carcinogenesis. IQGAP2 was identified as a novel tumor suppressor linked to the Wnt/β-catenin signaling pathway in HCC. In this study, mouse embryonic fibroblasts (MEFs) isolated from Iqgap2−/- mice displayed higher proliferation and migration rates compared to wild-type MEFs as evident by MTT proliferation assay and wound healing assay. In contrast to HepG2, the SK-Hep1 and SNU387 HCC cell lines are characterized by low expression of IQGAP2 and relatively high levels of IQGAP1. Migration assay using blind well chambers with polycarbonate filters revealed 2-fold increased motility for both SK-Hep1 and SNU387 compared to HepG2 (p < 0.05). HepG2 cells stably expressing IQGAP2-specific shRNA showed an increase in their motility. Conversely, overexpression of IQGAP2 in HEK293 resulted in up to 50% inhibition of their migration rate. qRT-PCR of naïve SK-Hep1 and SNU387 cells and HepG2 cells overexpressing IQGAP2 shRNA confirmed upregulation of genes encoding MET, MMP1, MMP2, MTA2 and TWIST1, reinforcing a role of IQGAP2 in cell migration. Akt kinase, one of the key regulators of cell migration, co-immunoprecipitated with IQGAP2 in both mouse liver lysates and HEK293 cells transiently expressing human IQGAP2. IQGAP2, but not IQGAP1, also co-immunoprecipitated with GSK3β kinase in mouse liver lysates. Furthermore, to address whether IQGAP2 affects Akt function in liver, insulin stimulation experiments were performed with wild-type, Iqgap2−/- and Iqgap1−/−/Iqgap2−/- mice. It was shown that upon stimulation with a single intraperitoneal injection of 5 U/kg insulin, levels of the phosphorylated (at Ser9) form of GSK3β were elevated in both Iqgap2−/- and Iqgap1−/−/Iqgap2−/- livers compared to wild-type, suggesting that in IQGAP2-deficiency, GSK3β kinase activity is inhibited by, perhaps, Akt activation. Additionally, the strength of the GSK3β - β-catenin interaction was found to be dependent on the presence of both IQGAP1 and IQGAP2, with Iqgap2−/- livers showing weaker interaction and Iqgap1−/−/Iqgap2−/- livers the weakest compared to wild-type. Using IQGAP2 deletional mutants, it was determined that IQ domains may be primarily responsible for IQGAP2 interactions with both Akt and GSK3β. While it remains unclear whether IQGAP2 binds Akt and GSK3β directly or as part of a larger protein complex, these findings suggest that tumor suppressive function of IQGAP2 in the liver may be realized through inhibition of cell proliferation and migration. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3989. doi:1538-7445.AM2012-3989

IQ motif-containing GTPase-activating proteins IQGAP1 and IQGAP2 are highly homologous multidomain scaffolding proteins. Their major function consists of integration of Rho GTPase and Ca(2+)/calmodulin signals with cell adhesive and cytoskeletal reorganizational events. Recent studies showed that they play an important role in carcinogenesis. There is growing evidence that IQGAP2 is a novel tumor suppressor counteracting the effects of IQGAP1, an oncogene, in several cancers, especially in hepatocellular carcinoma (HCC). While HCC is highly prevalent and one of the deadliest cancers worldwide, the signaling pathways involved are not fully understood and treatment of advanced disease still represents an area of high unmet medical need. This paper compiles various findings from studies in mouse models, cell lines, and patient samples that support future development of IQGAPs into new therapeutic targets. It also discusses distinct features of IQGAP2 in an attempt to provide insight into the mechanism of the seemingly paradoxical opposing roles of the two very similar IQGAP proteins in carcinogenesis.

Long-chain fatty adds (LCFA) serve as structural components for membrane biogenesis and as primary energy sources during mitochondrial beta-oxidation reactions. Hepatic LCFA uptake is complex, with characteristics suggestive of a dual-kinetic model manifested by rapid (carrier-assisted/facilitated) and delayed (passive diffusional) phases. Our previous work using mice deficient of the Iqgap2 gene established a highly novel link between IQGAP2, a putative GTPase-activating protein, and hepatocarcinogenesis. Now we report that Iqgap2 deficiency also results in selective loss of the facilitated phase of hepatocyte LCFA uptake with preservation of the diffusional component. This molecular defect was seen in Iqgap2(-/-) hepatocytes of all ages studied (1-, 4-, 8-months). The loss of facilitated LCFA uptake protected against development of hepatic triglyceride accumulation in Iqgap2-deficient mice fed high-fat diet, consistent with a fundamental role in physiological fat partitioning. These phenotypic changes could not be explained by genetic loss of fatty add processing proteins known to regulate lipid uptake or metabolic processing pathways. Iqgap2-deficient livers also displayed enhanced insulin sensitivity. Conclusion: These observations identify a novel property of the putative GTPase-activating protein IQGAP2 in LCFA uptake in vitro and in vivo, and implicate IQGAP2 in an intracellular signaling pathway necessary for functional fatty add uptake, lipid processing, and, possibly, glucose homeostasis. (C) 2011 Elsevier B.V. All rights reserved.

Loss of IQGAP2 contributes to the tumorigenesis of hepatocellular carcinoma and gastric cancer. However, whether IQGAP2 also suppresses prostate tumorigenesis remains unclear. We report here that IQGAP2 is a candidate tumour suppressor of prostate cancer (PC). Elevated IQGAP2 was detected in prostatic intraepithelial neoplasia (PIN), early stages of PCs (Gleason score ≤3), and androgen-dependent LNCaP PC cells. However, IQGAP2 was expressed at substantially reduced levels not only in prostate glands and non-tumorigenic BPH-1 prostate epithelial cells but also in advanced (Gleason score 4 or 5) and androgen-independent PCs. Furthermore, xenograft tumours that were derived from stem-like DU145 cells displayed advanced features and lower levels of IQGAP2 in comparison to xenograft tumours that were produced from non stem-like DU145 cells. Collectively, these results suggest that IQGAP2 functions in the surveillance of prostate tumorigenesis. Consistent with this concept, ectopic IQGAP2 reduced the proliferation of DU145, PC3, and 293T cells as well as the invasion ability of DU145 cells. While ectopic IQGAP2 up-regulated E-cadherin in DU145 and PC3 cells, knockdown of IQGAP2 reduced E-cadherin expression. In primary PC and DU145 cells-derived xenograft tumours, the majority of tumours with high levels of IQGAP2 were strongly-positive for E-cadherin. Therefore, IQGAP2 may suppress PC tumorigenesis, at least in part, by up-regulation of E-cadherin. Mechanistically, overexpression of IQGAP2 significantly reduced AKT activation in DU145 cells and inhibition of AKT activation upregulated E-cadherin, suggesting that IQGAP2 increases E-cadherin expression by inhibiting AKT activation. Taken together, we demonstrate here that IQGAP2 is a candidate tumour suppressor of PC.

Several studies have identified the single nucleotide polymorphism STK15 F31I as a low-penetrance risk allele for breast cancer, but its prevalence and risk association in the Brazilian population have not been determined. The goal of this study was to identify the frequency of this polymorphism in the Brazilian setting. Considering the high degree of admixture of our population, it is of fundamental importance to validate the results already reported in the literature and also to verify the relationship between this variant and breast cancer risk. A total of 750 women without breast cancer were genotyped using the TaqMan PCR assay for STK15 F31I polymorphism. Clinical information was obtained from review of the medical records and mammographic density from the images obtained using the BI-RADS System. The estimated risk of developing cancer was calculated according to the Gail model. The genotypic frequencies observed in this study were 4.5, 38.7, and 56.6%, respectively, for the STK15 F31I AA, AT and TT genotypes. The AT and AA genotypes were encountered significantly more often in premenopausal women with moderately dense, dense and heterogeneously dense breast tissue (P = 0.023). In addition, the presence of the TT genotype was significantly associated with age at menarche ≥12 years (P = 0.023). High mammographic density, associated with increased breast cancer risk, was encountered more frequently in premenopausal women with the risk genotypes STK15 F31I AA and AT. The genotypic frequencies observed in our Brazilian sample were similar to those described in other predominantly European populations.

Nuclear factor of activated T cells (NFAT) proteins are Ca 2+ -regulated transcription factors that control gene expression in many cell types. NFAT proteins are heavily phosphorylated and reside in the cytoplasm of resting cells; when cells are stimulated by a rise in intracellular Ca 2+ , NFAT proteins are dephosphorylated by the Ca 2+ / calmodulin -dependent phosphatase calcineurin and translocate to the nucleus to activate target gene expression. Here we show that phosphorylated NFAT1 is present in a large cytoplasmic RNA-protein scaffold complex that contains a long intergenic noncoding RNA (lincRNA), NRON [noncoding (RNA) repressor of NFAT]; a scaffold protein, IQ motif containing GTPase activating protein (IQGAP); and three NFAT kinases, casein kinase 1, glycogen synthase kinase 3, and dual specificity tyrosine phosphorylation regulated kinase. Combined knockdown of NRON and IQGAP1 increased NFAT dephosphorylation and nuclear import exclusively after stimulation, without affecting the rate of NFAT rephosphorylation and nuclear export; and both NRON -depleted T cells and T cells from IQGAP1-deficient mice showed increased production of NFAT-dependent cytokines. Our results provide evidence that a complex of lincRNA and protein forms a scaffold for a latent transcription factor and its regulatory kinases, and support an emerging consensus that lincRNAs that bind transcriptional regulators have a similar scaffold function.

Background IQGAP1 and IQGAP2 are homologous members of the IQGAP family of scaffold proteins. Accumulating evidence implicates IQGAPs in tumorigenesis. We recently reported that IQGAP2 deficiency leads to the development of hepatocellular carcinoma (HCC) in mice. In the current study we extend these findings, and investigate IQGAP1 and IQGAP2 expression in human HCC. Methods IQGAP1 and IQGAP2 protein expression was assessed by Western blotting and immunohistochemistry. IQGAP mRNA was measured by quantitative RT-PCR. The methylation status of the Iqgap2 promoter was determined by pyrosequencing of bisulfite-treated genomic DNA. Results IQGAP1 and IQGAP2 expression was reciprocally altered in 6/6 liver cancer cell lines. Similarly, immunohistochemical staining of 82 HCC samples showed that IQGAP2 protein expression was reduced in 64/82 (78.0%), while IQGAP1 was present in 69/82 (84.1%). No IQGAP1 staining was detected in 23/28 (82.1%) normal livers, 4/4 (100.0%) hepatic adenomas and 23/23 (100.0%) cirrhosis cases, while IQGAP2 was increased in 22/28 (78.6%), 4/4 (100.0%) and 23/23 (100.0%), respectively. Although the Iqgap2 promoter was not hypermethylated in HCC at any of the 25 CpG sites studied (N = 17), IQGAP2 mRNA levels were significantly lower in HCC specimens (N = 23) than normal livers (N = 6). Conclusions We conclude that increased IQGAP1 and/or decreased IQGAP2 contribute to the pathogenesis of human HCC. Furthermore, downregulation of IQGAP2 in HCC occurs independently of hypermethylation of the Iqgap2 promoter. Immunostaining of IQGAP1 and IQGAP2 may aid in the diagnosis of HCC, and their pharmacologic modulation may represent a novel therapeutic strategy for the treatment of liver cancer.

Abstract Highly homologous putative GTPase-activating proteins IQGAP1 and IQGAP2 are multidomain scaffolding proteins that juxtapose Rho GTPases Rac1 and Cdc42, Ca2+/calmodulin signals and cytoskeletal reorganization events. Previously, we found that IQGAP2 deficiency in mice leads to the development of hepatocellular carcinoma (HCC), identifying IQGAP2 as a potential tumor suppressor gene (Schmidt VA, et al. MCB 2008; 28:1489-502). Moreover, mice deficient in both Iqgap1 and Iqgap2 genes displayed relative protection against HCC and enhanced long-term survival, indicating opposing roles for IQGAP2 and IQGAP1 in hepatic carcinogenesis. We hypothesized that diminished levels of hepatic IQGAP2 expression, along with subsequent upregulation of IQGAP1, may have a causative effect in the development of HCC in humans. To test this, we first evaluated mRNA transcript and protein expression in an array of liver samples from patients with HCC of different etiologies using qRT-PCR and immunohistochemistry (IHC). qPCR TissueScan Array™ containing 23 individual cDNAs from patients with primary HCC of different stages and non-malignant adjacent tissue controls demonstrated decreased expression of IQGAP2 transcript in HCC tumors compared to normal tissue, and the magnitude of the decrease in expression correlated with progression of disease. The lowest IQGAP2 transcript expression was observed at the most advanced stage IV HCC, a 4-fold decrease compared to the non-malignant controls. At the protein level, lack of IQGAP2 expression was confirmed in 100% (36/36) of formalin-fixed paraffin-embedded human HCC livers studied by IHC. All samples also showed a significant overexpression of IQGAP1. Normal livers (13/13), cirrhotic livers (23/23), and benign hepatic adenomas (4/4) showed the reverse, i.e. a high level of IQGAP2 expression and very low levels of IQGAP1. Next, functional studies using RNAi technology showed that knockdown of IQGAP2 expression in HepG2 cells leads to a 50% increase in their migratory capacity, while IQGAP1 siRNA has the opposite effect. Finally, the gene expression profile of Iqgap2−/− mouse liver using the Mouse Genome 430 2.0 Array chip (Affymetrix) identified 294 genes which were expressed differentially in Iqgap2−/− HCC livers compared to age-matched disease-free wild-type controls (N=3 in each group). The differentially expressed genes (at least 2-fold change, p<0.05) included those encoding proteins associated with Wnt/beta-catenin signaling pathway activation (Igf2r, Sp5, Ccnb2, Ccnd1, Wif1 and Ctnnbip1) and tumor metastasis (Cdh1, Ctsl, Hgf, Fn1, Hpse and Timp2). Collectively, these findings validate the relevance of the Iqgap2−/− mouse model to human disease and identify a novel IQGAP-dependent pathway regulating HCC development. Modulation of both IQGAP1 and IQGAP2 expression represents a new potential therapeutic strategy for liver cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4996.

4600 Background: GTPase-activating proteins (IQGAPs) are multidomain proteins that integrate Rho GTPase and Ca2+/calmodulin signals with cell adhesive and cytoskeletal reorganizational events. In m...

IQGAPs are multidomain scaffolding proteins that integrate Rho GTPase and Ca2+/calmodulin signals with cell adhesive and cytoskeletal reorganizational events. Targeted disruption of the murine Iqgap2 gene resulted in the age-dependent development of apoptosis and hepatocellular carcinoma (HCC), characterized by the overexpression of IQGAP1, the loss of membrane E-cadherin expression, the cytoplasmic translocation (and activation) of beta-catenin, and the overexpression of a nuclear target of beta-catenin, cyclin D1. In normal hepatocytes, IQGAP2 was found to exist as one component of a multifunctional scaffolding complex comprising IQGAP1, beta-catenin, and E-cadherin, with no evidence for direct IQGAP1-IQGAP2 interactions. Interbreeding of Iqgap2(-/-) mice into the Iqgap1(-/-) background resulted in the phenotypic correction of the preexisting hepatopathy, decreases in the incidence and sizes of HCC tumors, and the normalization of overall survival rates compared to those of Iqgap2(-/-) mice, suggesting that maximal penetrance of the Iqgap2(-/-) HCC phenotype requires the coordinate expression of IQGAP1. These results identify Iqgap2 as a novel tumor suppressor gene specifically linked to the development of HCC and the activation of the Wnt/beta-catenin signaling pathway, while also suggesting that IQGAP1 and IQGAP2 retain functionally divergent roles in hepatocellular carcinogenesis.