MiR-17-92 is an oncogenic miRNA cluster implicated in the development of several human cancers; however, it remains unknown whether miR-17-92 cluster is able to regulate hepatobiliary carcinogenesis. This study was designed to investigate the biological functions and molecular mechanisms of miR-17-92 cluster in primary liver cancer.<br>In-situ hybridization and qRT-PCR analysis showed that miR-17-92 cluster is highly expressed in human cholangiocarcinoma cells compared to the non-neoplastic biliary epithelial cells. Forced overexpression of the miR-17-92 cluster or its members, miR-92a and miR-19a, in cultured human cholangiocarcinoma cells enhanced tumor cell proliferation, colony formation and invasiveness, in vitro. Overexpression of miR-17-92 cluster or miR-92a also enhanced cholangiocarcinoma growth in vivo in SCID hairless outbred mice. The tumor suppressor PTEN was identified as a bona fide target of both miR-92a and miR-19a in cholangiocarcinoma cells. Accordingly, overexpression of PTEN open reading frame protein (devoid of 3’UTR) prevented miR-92a- or miR-19a-induced cholangiocarcinoma cell growth. Microarray analysis revealed additional targets of miR-17-92 cluster in human cholangiocarcinoma cells, including APAF-1 and PRDM2. Moreover, we observed that the expression of miR-17-92 cluster is regulated by IL-6/Stat3, a key oncogenic signaling pathway pivotal in cholangiocarcinogenesis. Taken together, our findings in this study disclose a novel IL-6/Stat3 miR-17-92 cluster PTEN signaling axis that is crucial for cholangiocarcinogenesis and tumor progression.<br>We also found the miR-17-92 is highly expressed in tumor tissue compared to non-tumor adjacent tissue in hepatocellular carcinoma patient tissue. Forced overexpression of the miR-17-92 cluster in cultured human hepatocellular carcinoma cells enhanced tumor growth in vitro; on contrast, inhibition of miR-17-92 cluster inhibited cell growth. MiR-17-92 cluster promote diethylnitrosamine-induced hepatocarcinogenesis in liver-specific miR-17-92 cluster transgenic mice. Binding sequence and mice whole genome microarray analysis revealed about 300 possible targets. RNA-sequencing data analysis showed both individual miRNAs and the host gene of miR-17-92 cluster was highly expressed in hepatocellular carcinoma patients and had negative correlation with several genes (CREBL2, PRRG1, and NTN4), among which, CREBL2 may play an important role in the hepatocarcinogenesis. / acase@tulane.edu

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miR-17-92 cluster (Oncomir1) encodes seven microRNAs (miRNA, miR) regulating many biological processes including proliferation, differentiation or apoptosis. Overexpression of microRNAs encoded by miR-17-92 cluster is found in a number of tumors including acute and chronic myeloid leukemias (Dixon-McIver et al., 2008; Li et al., 2008; Venturini et al., 2007). Myeloid progenitors express miR-17-92 cluster at a high level, while macrophage differentiation associates with its downregulation. Our laboratory found, that miR-17-92 cluster is repressed by transcription factor Early growth response 2 (Egr2) upon differentiation of primary myeloid PUER progenitors, induced with transcription factor PU.1. Aim of this thesis is to further test the abovementioned data by preparing a reporter vectors set, carrying various fragments of miR-17-92 putative promoter, which enables us to study regulation of transcription of miR-17-92 cluster. This task complicated by presence of increased GC content of the miR-17-92 promoter was successfully accomplished resulting in amplification of eight fragments containing the various parts of miR-17-92 promoter including region -3.3 to 0 kb relative to the start of miR-17-5p sequence, that were inserted into pGL3 reporter vector. Transfection of pGL3 reporter vector carrying...

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