Abstract 125: MicroRNA-34a dysregulation promotes tumor growth and tumor angiogenesis in head and neck squamous cell carcinoma

Abstract

Abstract Objectives: Head and Neck squamous cell carcinoma (HNSCC) results from deregulation of multiple signaling pathways leading to tumor cells acquiring proliferative, invasive, angiogenic and metastatic properties. Interactions between neoplastic cells and the surrounding microenvironment also play a major role in tumor progression. Recent studies have demonstrated that microRNA's (miRs) play a critical role in cancer development where they can act as oncogenes or as onco-suppressors. A microRNA array analysis of a panel of ten HNSCC cell lines reveled that miR-34a is significantly downregulated in all these cell lines as compared to normal human oral keratinocyes (HOK). In addition, miR-34a expression was also downregulated in highly angiogenic endothelial cells (endothelial cells overexpressing Bcl-2; EC-Bcl-2) as compared to normal human endothelial cells. However, little is known about the role of miR-34a in HNSCC tumor growth and tumor angiogenesis. In this study, we examined if dysregulation of miR-34a in HNSCC promotes tumor growth and tumor angiogenesis. Methods and Results: miR-34a expression in tumor samples, HNSCC cell lines and endothelial cells was examined by real time PCR. Lipofectamine-2000 was used to transfect miR-34a in HNSCC cell lines and human endothelial cells. Cell-proliferation and migration was examined by Xcelligence system. miR-34a effect on tumor growth and tumor angiogenesis was examined by in vivo SCID mouse xenograft model. Our results demonstrate that miR-34a is significantly downregulated in HNSCC tumors and cell lines. Ectopic expression of miR-34a in HNSCC cell lines significantly inhibited tumor cell proliferation, colony formation and migration. Tumor cells expressing miR-34a also showed marked decrease in the levels of a key transcription factor, E2F3. Rescue experiments using microRNA resistant E2F3 isoforms suggest that miR-34a-mediated inhibition of cell proliferation and colony formation is predominantly mediated by E2F3a isoform. In addition, tumor samples from HNSCC patients showed inverse relationship between miR-34a and survivin expression. Overexpression of E2F3a completely rescued survivin expression in miR-34a expressing cells, thereby suggesting that miR-34a may be regulating survivin expression via E2F3a. Ectopic expression of miR-34a also significantly inhibited tumor growth and tumor angiogenesis in a SCID mouse xenograft model. Interestingly, miR-34a inhibited tumor angiogenesis by blocking VEGF production by tumor cells as well as directly inhibiting endothelial cell functions. Conclusions: Taken together, these findings suggest that dysregulation of miR-34a expression is common in HNSCC and modulation of miR34a activity might represent a novel therapeutic strategy for the treatment of HNSCC. 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 125. doi:1538-7445.AM2012-125