The role of miR-203 and miR-34a in EGFR activation prostate cancer metastasis

Several mechanisms have been suggested to affect prostate cancer progression, including mutation of Ras, either genetically or epigenetically during prostate cancer metastasis. MicroRNAs (miRs) regulate embryonic development and play key roles in the development of tumor and progression, including prostate cancer. MiR-203 and miR-34a expression has been found to be downregulated in prostate cancer clinical cases relative to normal prostate tissue. It is not clear how miR-203 and miR-34a expression related to EGFR signaling in prostate cancer metastasis. In this proposed study, we hypothesize that upon activation of EGFR signaling genes, reduced expression of miR-203 and miR-34a is required for prostate cancer metastasis. The preliminary results showed that enhanced miR-203 and miR-34a expression in a human metastatic prostate cancer cell line, DU145 with RasV12G37 mutant, displayed reduction of bone metastasis and survival rate in vivo, and decreased expression of EGFR signaling related genes expression in vitro. Following bioinformatic analysis of clinical gene expression databases, our preliminary results suggest that the expression of decreased miR-203 and miR-34a and increased EGFR ligands, AREG, EREG and TGFA, correlated to prostate cancer progression. The next study will use human AREG, EREG, and TGFA 3’UTR reporters containing wild type or mutated miR-203 and/or miR-34a homology sites to identify the regulatory role of miR-203 and miR-34a by reporter assays. Our preliminary results also found that in the presence of EGF the decreased miR-203 and miR-34a are associated with and induced Snail and polycomb repressive complexes (PRCs) by qRT-PCR. To investigate the role of Snail/PRCs in regulating miR-203 and miR-34a expression, we have found several E-boxes locate in the primary mir-203 and mir-34a stem-loop promoter/enhancer region by TFsearch analysis. Next study will measure the binding and functional capacity of Snail/PRCs to the primary mir-203 and mir-34a stem-loop promoter and analyze how Snail/PRCs participate in methylation of CpG islands at the primary mir-203 and mir-34a stem-loop promoter. The presence of Ras mutations has significantly been shown associated with tyrosine kinase inhibitors (TKIs) resistance in non-small-cell lung cancer (NSCLC). However, the intrinsic molecular mechanisms of resistance to these drugs in prostate cancer remain largely unknown. To study the effect of miR-203 and miR-34a contributing to apoptosis in TKIs-resistant prostate cancer cells, our preliminary studies showed that in the presence of TKIs the RasV12G37 mutation DU145 cells with miR-203 and miR-34a overexpression significantly displayed more cell death compared to parental line. We hypothesize that miR-203 and miR-34a overexpression will induce sensitivity to TKIs resistance in RasV12G37 mutation cells. It may be through miR-203 and miR-34a that downregulate EGFR pathway by target AREG, EREG, and TGFA genes. In addition, we hypothesize the TKIs-resistant effects in RasV12G37 mutated prostate cancer cells may require Snail/PRCs to shut down these miRNAs and cells survival. In this four-year research project, we plan to incorporate the preliminary results to test a linked role between miR-203 and miR-34a loss and increased Snail/PRCs and provide evidence to show how miR-203 and miR-34a regulates EGFR signaling genes in prostate cancer metastasis and TKIs resistance.