Abstract 4445: Post-transcriptional inhibition of PTPN23 by SND1: Potential mechanism for hepatocellular carcinoma

Oncoprotein SND1 regulates gene expression at a post-transcriptional level in multiple cancers including hepatocellular carcinoma (HCC). Staphylococcal nuclease domains of SND1 function as an RNAse and tudor domain facilitates protein-oligonucleotide interaction. In the present study, we aimed to identify RNA interactome of SND1 to obtain better insights into gene regulation by SND1. RNA interactome was identified by immunoprecipitation of RNA using anti-SND1 antibody from human HCC cells followed by RNA-sequencing (RIP-Seq). With an adjusted p value of <0.01 and >2-fold enrichment over control, 282 mRNAs were identified to significantly associate with SND1 protein. We focused on the tumor suppressor PTPN23 because its regulation by SND1 and its role in HCC are not known. PTPN23 levels were downregulated in human HCC cells versus normal hepatocytes and in human HCC tissues versus normal adjacent liver as revealed by immunohistochemistry. In human HCC cells, knocking down SND1 increased and overexpression of SND1 decreased PTPN23 protein. RNA binding and degradation assays revealed that SND1 specifically binds to and degrades 3'-UTR of PTPN23 mRNA. Tetracycline-inducible PTPN23 overexpression in human HCC cells resulted in significant inhibition in proliferation, migration and invasion and in vivo tumorigenesis. PTPN23 induction caused inhibition in activation of c-Met, EGFR, Src and FAK, suggesting that as a phosphatase PTPN23 inhibits activation of these oncogenic kinases. The present study unravels a novel function of SND1 in targeting PTPN23 and identifies PTPN23 as a unique tumor suppressor for HCC. PTPN23 might function as a homeostatic regulator of multiple kinases restraining their activation.

Citation Format: Nidhi H. Jariwala, Rachel G. Mendoza, Garcia Dawn, Lai Zhao, Mark A. Subler, Jolene J. Windle, Paul B. Fisher, Chen Yidong, Devanand Sarkar. Post-transcriptional inhibition of PTPN23 by SND1: Potential mechanism for hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4445.