REGULATION OF MIEN1 IN PROSTATE CANCER

Migration and Invasion ENhancer 1 (MIEN1) is a novel gene located in the 17q12 region of the human chromosome. While there is minimal expression of MIEN1 in multiple normal tissues and cells, it is abundantly elevated in many human cancers including the breast, prostate, gastrointestinal and oral. MIEN1 is a membrane bound signaling molecule that triggers downstream signaling through the AKT/NF-κB pathway (common oncogenic pathways) by up-regulating key proteases (thus aiding cancer progression). MIEN1 has also been shown to have a role in migration and invasion (key processes in cancer spread) of cancer cells by enabling filopodia formation (extensions that enable a cell to move). Thus, by various known and unknown mechanisms, MIEN1 promotes prostate cancer progression. While the cellular functions of MIEN1 have been deciphered, the reasons for its aberrant increased expression in cancer cells are still unclear. Understanding the mechanism(s) involved in the regulation of MIEN1 will aid in developing diagnostic marker(s) or in designing effective therapeutic approach(es) to treat prostate cancer patients. Purpose (a): The overall objective of this study is to identify the deregulated mechanisms leading to the differential regulation of MIEN1 between normal and cancer cells. Commonly deregulated mechanisms encompass alterations at DNA (chromosome) to destabilization at protein (translational) levels. Our study focuses on regulation by microRNA (miR) and methylation. Our hypothesis is that MIEN1 is post-transcriptionally regulated by a specific miR and its proximal putative promoter region is hypermethylated in normal cells. Deregulation of these mechanisms together explain the aberrant increased expression of MIEN1 in cancer. Methods (b): To validate the role of miR in MIEN1 regulation, we have performed various in vitro studies. To determine the global role of the miR, we ectopically expressed it in cancer cells. Additionally, we have used human tissue and serum samples to predict the use of miR-MIEN1 as biomarkers. To demonstrate the importance of methylation in the regulation of MIEN1, we performed global methylation inhibition and specific methyltransferase knockdown. Results (c): Our data indicate that MIEN1 is post-transcriptionally regulated by a specific miR which is highly expressed in normal cells compared to various cancer cells, inversely correlating with MIEN1. Ectopic expression of the miR led to decrease in MIEN1 expression, migratory and invasive potential and anchorage dependent growth of cells and impeded mesenchymal transition. Additionally, the miR expression was higher in the normal glands of prostate tissue compared to the tumor; while the secreted/circulating miR was higher in serum from cancer patients, much like PSA expression patterns; but with more significance than PSA. Inhibition of methylation by pharmacological inhibitors or by individually knocking down the methyltransferases increased MIEN1 in normal cells, indicating the role of methylation in the regulation of this gene. Conclusions (d): After proving our results in a larger cohort of patient specimen, this miR could be a useful non-invasive diagnostic biomarker. Additionally, understanding the regulation of MIEN1 by methylation will provide reasons to revisit the current strategies of methylation inhibition for cancer treatment. Overall, since the importance of MIEN1 as a key signaling molecule in cancer is well established, understanding the mechanisms involved in the regulation will aid in designing more effective therapeutic strategies to treat cancer patients.