IQGAP1 Stimulates Proliferation and Enhances Tumorigenesis of Human Breast Epithelial Cells

Abstract

The scaffold protein IQGAP1 integrates signaling pathways and participates in diverse cellular activities. IQGAP1 is overexpressed in a number of human solid neoplasms, but its functional role in tumorigenesis has not been previously evaluated. Here we report that IQGAP1 contributes to neoplastic transformation of human breast epithelial cells. The amount of IQGAP1 in breast carcinoma is greater than that in normal tissue, with highly metastatic breast epithelial cells expressing the highest levels. Overexpression of IQGAP1 enhances proliferation of MCF-7 breast epithelial cells. Reduction of endogenous IQGAP1 by RNA interference impairs both serum-dependent and anchorage-independent growth of MCF-7 cells. Consistent with these in vitro observations, immortalized MCF-7 cells overexpressing IQGAP1 form invasive tumors in immunocompromised mice, whereas tumors derived from MCF-7 cells with stable knockdown of IQGAP1 are smaller and less invasive. In vitro analysis with selected IQGAP1 mutant constructs and a chemical inhibitor suggests that actin, Cdc42/Rac1, and the mitogen-activated protein kinase pathway contribute to the mechanism by which IQGAP1 increases cell invasion. Collectively, our data reveal that IQGAP1 enhances mammary tumorigenesis, suggesting that it may be a target for therapeutic intervention.Tumor progression that culminates in clinically relevant metastatic lesions is the end point of a complex sequence of interrelated cellular events. After the initial transforming event, tumor cell proliferation, invasion, and migration, as well as vascularization of the tumor mass, occur. A thorough understanding of the molecular mechanisms that regulate tumor progression will provide the biological foundation for improving the efficacy of current therapeutic interventions (1-3).IQGAP1 is a 189-kDa scaffolding protein that contains multiple protein-interacting domains (for reviews see Refs. 4 -7). These include a calponin homology domain, a polyprolinebinding domain, four calmodulin-binding motifs, and a Ras-GAP-related domain. The motifs present in IQGAP1 are involved in the interaction of IQGAP1 with specific proteins, such as actin, calmodulin, members of the Rho GTPase family (i.e. Rac1 and Cdc42), Rap1, E-cadherin, ␤-catenin, members of the mitogen-activated protein kinase (MAPK) 4 pathway, and adenomatous polyposis coli (7,8). By interacting with these proteins, IQGAP1 regulates multiple fundamental cellular activities including cytoskeletal organization, cell-cell adhesion, cell migration, transcription, and signal transduction. For example, binding of IQGAP1 to ␤-catenin both disrupts the E-cadherin-catenin complex, inhibiting epithelial cell-cell adhesion (9), and increases ␤-catenin-mediated transcriptional activation (10). IQGAP1 increases active Cdc42 in mammalian cells, resulting in formation of actin filopodia and microspikes (11), and promotion of cell migration and invasion (12). These morphological and functional changes are not observed with a mutant IQGAP1 construct with impeded Cdc42-me...

Genetic variants at the miR-124 binding site on the cytoskeleton-organizing IQGAP1 gene confer differential predisposition to breast cancer

“…Although this does not prove that IQGAP1 plays a role in tumor suppression, the result is consistent with the knockout mouse studies that suggest that IQGAP1 is a negative regulator for cancer development. We also examined IQGAP1 expression in breast cancer tissues and their adjacent pathologically normal tissues and found that indeed, IQGAP1 was up-regulated in breast cancer tissue, similar to findings in other previously reported studies (33). moreover, IQGAP1 knockdown experiments showed that reduction of IQGAP1 resulted in increased cell growth in non-cancer breast epithelial cells but resulted in decreased cell growth in breast cancer cells, supporting that IQGAP1 plays an opposite role in normal development and cancer.…”

RACK1 stabilises the activity of PP2A to regulate the transformed phenotype in mammary epithelial cells

“…Interest in such finessed approaches to chemotherapeutic target exploitation is clearly increasing, as evinced by the growing body of work with IQ motif-containing GTPase activating protein 1 (IQGAP1) a scaffold within the MAPK pathway that is responsible for assembling the kinases within this pathway to effect signal transmission [66,67]. IQGAP1 has been linked to the progression of cancer and drives tumourigenesis in both mouse models and human tissue [66,68]. Up-regulation of the ERK1/2 MAPK cascade is seen in 30% of cancers and IQGAP1 binds to ERK1/2 through a highly conserved 32 amino acid 'WW domain' to facilitate activation of ERK in response to certain stimuli.…”

G-protein–coupled receptor GPR161 is overexpressed in breast cancer and is a promoter of cell proliferation and invasion

“…IQGAP1 has been reported to interact with βArr2, a scaffold protein that binds to activated GPCRs and regulates signaling and receptor endocytosis (20). IQGAP1 promotes proliferation and migration, and overexpression has been associated with poor prog-nosis in advanced colorectal cancer (21)(22)(23). Interestingly, IQGAP1 can coordinate cell growth and division in a phosphorylation-dependent manner (24).…”