IQGAP2 acts as a tumor suppressor in breast cancer and its reduced expression promotes cancer growth and metastasis by MEK/ERK signalling pathways

IQGAP2 is a member of IQGAPs scaffolding protein family. It has been reported as a tumor suppressor in various cancers, as well as, an oncogene in some cancers, suggesting organ specific role. Need to identify therapeutic targets which function in ER/PR independent way, prompted us to explore role of IQGAP2 in molecular mechanism in breast cancer, which was completely unknown. In vitro studies in estrogen receptor positive breast cancer cell line (MCF7) showed that low IQGAP2 expression results in increased cell proliferation, migration and invasion of cells whereas an opposite effect was observed with ectopic expression of IQGAP2. Triple negative breast cancer cell line (MDA-MB-468), with IQGAP2 depletion showed similar effect, supporting its role in ER/PR independent manner. Furthermore, we found that reduced IQGAP2 expression induces the expression of EMT markers; twist and N-cadherin and decreases the expression of MET marker, E-cadherin via the MEK/ERK pathway but not via AKT pathway. Validation of findings in patients showed a reduced IQGAP2 expression in breast cancer tissues compared to normal tissue. Patients with low levels of IQGAP2 showed correlation with higher tumor stage. Our results suggest that IQGAP2 acts as a tumor suppressor and its down regulation results in cell growth, cell invasion and EMT through the MEK/ERK signalling pathways and it hence may be a potential therapeutic target in breast cancer.