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RPB5会合性蛋白RMPはTFIIBにも作用する負の転写修飾因子である：　Dorjbal DORJSUREN, Yida YANG, Yong LIN, WenXiang WEI, 林直之, 野村孝弘, 村上清史 （金沢大・がん研・分子腫瘍）

RPB5-mediating protein, RMP, a negative transcriptional modulator that interact with general transcription factor TFIIB: Dorjbal DORJSUREN, Yida YANG, Yong LIN, WenXiang WEI, Naouyki HAYASHI, Takahiro NOMURA and Seishi MURAKAMI (Dept. Mol. Oncol., Cancer Res. Inst., Kanazawa Univ.)

Hepatitis B virus X protein (HBx) has been suspected to have positive roles in hepatocarcinogenesis. Previously we reported that RNA polymerase II subunit 5 (RPB5) is one of the targets of HBx and that the trimeric interaction among HBx, RPB5 and TFIIB is necessary for HBx transactivation. To get insight into molecular roles of HBx and RPB5 in transcriptional regulation, we searched for protein(s) which interacts with RPB5, and isolated a novel RPB5-mediating protein (RMP).
Bacterial recombinant RMP strongly bound RPB5 but neither HBx nor TBP in vitro. The specific interaction of RMP and RPB5 was immunologically detected in transiently expressed HepG2 cells. Overexpression of RMP, but not mutant RMP lacking the RPB5-binding region, inhibited HBx transactivation on reporters with HBx responsive cis-elements in transiently transfected cells. The repression by RMP was counteracted by HBx in a dose dependent manner. Furthermore, RMP acts as a co-repressor since it inhibits transcriptional activation by Gal-VP16. These results suggest that RMP negatively modulates transcription process at the interaction step between RPB5 and TFIIB which might be a target of HBx. Supporting this notion, HBx competes with RMP for RPB5 binding as detected in vitro by GST-pull down assay and immunologically detected in a transient expression mammalian system.