Abstract 4864: EGF-induced RNA pol III transcription mediated by epigenetic modification of histone H3

Cancer cells have a consistent cytological feature of nucleolar hypertrophy, where RNA Pol I and Pol III genes are transcripted. This implies that transformation in situ is closely linked to the deregulation of rRNA transcription, because the size of the nucleolus reflects the levels of rRNA synthesis. RNA Pol III genes encode a variety of untranslated RNAs, including tRNAs and 5S rRNAs. Deregulation of RNA Pol III transcription enhances cellular tRNAs and 5S rRNA production, leading to an increase in translational capacity to promote cell proliferation, transformation, and tumor formation. tRNA gene promoters require the transcription factor complexes, TFIIIB (TBP, Brf1 and Bdp1) and TFIIIC in addition to RNA pol III, to specify accurate and efficient transcription. The TFIIIB subunits, Brf1 and Bdp1, are specifically used in the RNA pol III transcription. Recent study demonstrated that the induction of Brf1 caused an increase in cell proliferation and oncogenic transformation, whereas depletion of Brf1 impeded transformation. These results demonstrate that increases in RNA Pol III transcription are necessary for cellular transformation. Our previous study showed that EGF induces TBP expression through MAP kinases, mediating RNA Pol III transcription. We had identified that MAK kinases mediated phosphorylation of histone H3 at serine 10 and 28. However, it is not clear which upstream of MAP kinases involves in EGF-induced RNA Pol III transcription and whether epigenetic modifications of H3 mediate the induction genes. Our recent studies showed that EGF strongly induces phosphorylation of H3 serine 28 (H3S28). Furhermore, we found that EGFR inhibitor AG1517 reduced EGF-induced both RNA Pol III transcription and phosphorylation of H3S28, but PI3K inhibitor LY 294002 did not decrease the inductions. EGFR deficient blocked the induction of RNA Pol III genes and phosphorylation of H3S28. In contrast, dominant negative mutant PI3K, Δp85 did not repress the inductions by EGF. To further explore the mechanism underlying EGF-induced RNA Pol III transcription, we found that EGF increases TFIIIB subunit, Brf1 expression. To investigate whether the epigenetic modification phosphor-H3S28 mediates RNA Pol III transcription, we determined phosphorylated H3S28 occupancy on Brf1 promoter by using CHIP assay. The result indicates that phospho-H3S28 specifically occupant on Elk-1 binding site of mouse Brf1 promoter at −507/−346, but not at −71/+98, regulating RNA Pol III transcription. Taken together, these results indicate that EGF activates EGFR and induces phosphorylation of H3S28, which mediate Brf1 expression to upregulate RNA Pol III transcription. This project was supported by NIH grant AA017288 to S.Z. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4864.