Recent observations suggest that noncoding microRNA-mediated translational repression may be linked to the development of colon cancer. Unfortunately, to date, the effect of chemopreventive agents on microRNAs and their messenger RNA (mRNA) targets during different stages of colon cancer has not been determined. Interestingly, with respect to the functional mapping of gene expression signatures, the steady-state mRNA expression level does not always accurately reflect the status of critical signaling proteins. In these cases, control is exerted at the epigenetic level of recruitment of mRNAs to polysomes, the factories of ribosomes that mediate efficient translation of many cellular messages. However, to date, a genome-wide perspective of the effect of microRNAs on actively translated (polysomal) mRNA populations has not been performed. Therefore, the overall goal of this proposal is to understand, at the actively translated mRNA level, how microRNAs interact to influence gene expression at different stages of colon cancer development. Consistent with the objectives and scope of PA-06-412, """"""""Diet, epigenetic events, and cancer prevention"""""""", we propose to use a well established in vivo colitis-associated colon cancer model, i.e., the azoxymethane (AOM)-dextran sodium sulfate (DSS) treated rat in combination with a chemoprotective diet extensively studied in our laboratory, i.e., n-3 polyunsaturated fatty acids (PUFA). This experimental model will be used to test our hypothesis that n-3 PUFA suppression of oncogene-direeled microRNA """"""""signatures"""""""" will favorably modulate the levels of actively translated mRNAs in colonocytes, resulting in reduced tumor formation. The proposed experiments will elucidate how diet and chronic inflammation alter: (i) microRNA, (ii) actively translated (polysomal) and (iii) total (steady-state) mRNA populations in normal, uninvolved and malignant transformed colonic mucosa. Specifically, in aim 1, microarray analysis of colonic total (steady-state) mRNA and actively translated mRNA populations will be performed.
Aim 2 will investigate the effects of disease progression on microRNAs and their mRNA targets by evaluating both microRNAs and actively translated mRNA transcripts following AOM/DSS or saline (control) treatment, and aim 3 will determine if a molecular portrait of microRNA expression signatures, actively translated mRNAs and/or steady-state total mRNAs can be used to classify colon tumor development. Findings from these experiments will quantify regulatory relationships among microRNAs and their target mRNAs in a highly relevant colon cancer model. This effort will identify new molecular targets for chemotherapeutic tools to both prevent and treat colon cancer.
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