Abstract A42: Elucidating the role of c-Met overexpression and its regulation in prostate cancer progression

Prostate cancer (PCa) is the 2nd leading cause of cancer deaths in men in the United States, with fatality generally resulting from bone metastases. Genetic and epigenetic alterations that lead to PCa metastasis are still poorly understood. Many receptor and nonreceptor protein tyrosine kinases are involved in PCa growth, development, progression and metastasis. c-Met (Met) is a receptor protein tyrosine kinase implicated in PCa growth and metastasis. Met expression is increased in progressive stages of PCa and correlates with poor prognosis. However, the mechanisms by which c-Met is increased during PCa progression and whether this overexpression is critical for metastasis has yet to be elucidated. In cell culture, ligand binding of hepatocyte growth factor/scatter factor (HGF/SF) or Met receptor overexpression activates downstream signaling pathways involved in cell motility, migration, invasion, proliferation and survival. Our goal is to determine the mechanism of Met overexpression and how overexpression affects the above Met-mediated processes. Although Met can be regulated through protein-protein interaction, receptor degradation, transcriptionally and posttranscriptionally, we have recently focused on regulation of expression by microRNAs. MicroRNAs (miRNAs or miR) are small 18–22 nucleotide long non-coding RNA units that regulate many molecules involved in tumor development and progression at the post-transcriptional level. MicroRNAs have been shown to target and regulations Met in different cancers; for example, miR-34 family has been shown to target Met in lung and liver cancer cell lines, miR-199a-3p targets and inhibits Met function in a lung cancer cell line, miR-23b targets Met in hepatocellular carcinoma and miR-133b downregulates it in colon cancer. We thus, determined the expression level of miR-199a-3p, miR-34a and miR-34c in PCa cell lines and found differential expression of miR-34a in low metastatic vs. high metastatic cell lines. Met levels are higher in more metastatic cell lines compared to their isogenic low metastatic variant and miR-34a levels were lower in high metastatic and higher in low metastatic cell lines. This is the first demonstration of differential miRNA expression regulating c-Met in isogenic variants of PCa cells with different metastatic potential. We next overexpressed miR-34a which was downregulated in high metastatic cells that led to decreased Met at the protein level. Also, we downregulated miR-34a expressed at high levels in low metastatic cells, and found an increase in Met protein levels. We are examining Met functional assays to determine the effects of miR-34a overexpression and downregulation on Met mediated biology. Preliminary data indicates that knockdown of miR-34a in Lncap cells that have low metastatic and low migratory potential, increases their migration in Boyden chamber assays. We will be testing the effects of Met knockdown through miR-34a and through shRNA on the metastatic potential of these cells in an in vivo mouse model to elucidate the role of c-Met in PCa progression and metastasis. Also, we will ascertain Met expression and miRNA correlation in patient samples from primary tumor and bone metastasis. We hypothesize that there would be lower expression of miRNA-34a and higher expression of its target Met in bone metastasis and primary PCa compared to normal and that one of the mechanisms of Met overexpression in PCa is through the downregulation of miR-34a. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A42.