Abstract 1289: Role of deregulation of Pol III-dependent transcription in phenotypic alteration.

Abstract The products of RNA polymerase III (Pol III)-dependent genes, such as tRNAs and 5S rRNA, are elevated in both transformed and tumor cells suggesting that they play a crucial role in tumorigenesis. An increase in Brf1 (TFIIIB-related factor 1), a subunit of TFIIIB in Pol III transcription machinery, augments Pol III gene transcription and is sufficient for cell transformation and tumor formation (1). We have demonstrated, for the first time, that enhancement of Brf1 expression and Pol III gene transcription are correlated to liver tumor formation in mice (2). This implies that Brf1 may be a key molecule during liver tumor development. Our early study demonstrated that MSK1 (mitogen- and stress-activated protein kinase 1) mediates H3S28ph (3), Our recent study have indicated that reduction of H3S28ph (histone H3 phosphorylation at serine 28) results in repression of Brf1 and Pol III gene transcription (4). Blocking MSK1 inhibits cell transformation (5) and tumor formation (6). To further determine the role of Brf1 and the signaling and epigenetic regulating events in phenotypic alteration induced by DEN (diethylnitrosamine) which is a chemical carcinogen and is used to induce liver tumor (7), we utilized DEN (200μg/ml) to treat AML-12 cells, an immortalized mouse hepatocyte line to extract cell lysates and total RNA. Our results indicate that DEN treatment increased Brf1 expression and Pol III gene, tRNALeu and 5S rRNA, transcription. DEN strongly induced phosphorylation of MSK1 at serine 376 and Threonine 581. DEN also induces H3phs at both H3S10ph and H3S28ph in AML-12 cells. Interestingly, DEN-induced H3ph in tumor stem cells of mouse liver is significantly stronger than in non-tumor AML-12 cells. MSK1 chemical inhibitor, H89 decreased the induction of Pol III genes. DEN increased the rate of AML-12 cell proliferation. Furthermore, DEN induced colony formation of AML-12 cells in soft agar. Repression of Brf1 by its siRNA reduced Pol III gene transcription and inhibited the cell transformation by DEN. Taken together, these results demonstrate that DEN activates MSK1 and induces H3ph, which in turn mediate Brf1 expression to upregulate RNA Pol III transcription, resulting in increasing in cell proliferation and cell transformation. These studies will allow us to further uncover a novel molecular mechanism of hepatocellular carcinoma by using MSK KO mice and conditional Brf1 KO mice. [This project was supported by NIH grant AA017288 and AA021114 to Shuping Zhong.] Citation Format: Shuping Zhong, Qingsong Zhang, Ganggang Shi. Role of deregulation of Pol III-dependent transcription in phenotypic alteration. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1289. doi:10.1158/1538-7445.AM2013-1289