<p>microRNAs (miRNAs) downregulate the expression of numerous mRNAs and are involved in almost every biological process where they have been examined. Inherent sequence or cis-elements located in mRNA termini and 5' and 3' UTRs likewise influence post-transcriptional gene regulation. We delineate the relative importance of the 5' m7G-cap, the 3' poly(A) tail, and Internal Ribosome Entry Sites (IRESs) in miRNA-mediated repression. mRNA targets must contain a m7G-cap to be repressed, are repressed to a greater extent when containing a poly(A) tail, and are not precluded from repression when translating via an IRES. </p><p> miRNAs can inhibit translation and / or induce mRNA decay. While the core effector proteins are established, mechanistic details of how miRNAs interfere with mRNA translation and stability remain elusive. Contrary to the repressive effects of miRNAs, the poly(A)-binding protein (PABP) (through binding to the poly(A) tail and eIF4G) can increase both translation and mRNA stability independently. We elucidate a functional role for the PABP in miRNA repression; manipulation of `active' PABP levels affects repression conversely in part by inhibiting miRNA-induced deadenylation. Furthermore, we find that expression changes in the PABP binding partner PABP interacting protein 2 (Paip2) modulates both miRNA repression and PABP protein complex formation. Additionally, we establish Paip2 as a bona fide miR-128 target, and demonstrate miR-128 de-repression of non-miR-128 target mRNAs through this targeting event.</p> / Dissertation

BACKGROUND:Colony stimulating factor-1 (CSF-1) plays an important role in ovarian cancer biology and as a prognostic factor in ovarian cancer. Elevated levels of CSF-1 promote progression of ovarian cancer, by binding to CSF-1R (the tyrosine kinase receptor encoded by c-fms proto-oncogene).Post-transcriptional regulation of CSF-1 mRNA by its 3' untranslated region (3'UTR) has been studied previously. Several cis-acting elements in 3'UTR are involved in post-transcriptional regulation of CSF-1 mRNA. These include conserved protein-binding motifs as well as miRNA targets. miRNAs are 21-23nt single strand RNA which bind the complementary sequences in mRNAs, suppressing translation and enhancing mRNA degradation.RESULTS:In this report, we investigate the effect of miRNAs on post-transcriptional regulation of CSF-1 mRNA in human ovarian cancer. Bioinformatics analysis predicts at least 14 miRNAs targeting CSF-1 mRNA 3'UTR. By mutations in putative miRNA targets in CSF-1 mRNA 3'UTR, we identified a common target for both miR-128 and miR-152. We have also found that both miR-128 and miR-152 down-regulate CSF-1 mRNA and protein expression in ovarian cancer cells leading to decreased cell motility and adhesion in vitro, two major aspects of the metastatic potential of cancer cells.CONCLUSION:The major CSF-1 mRNA 3'UTR contains a common miRNA target which is involved in post-transcriptional regulation of CSF-1. Our results provide the evidence for a mechanism by which miR-128 and miR-152 down-regulate CSF-1, an important regulator of ovarian cancer.

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