BRCA1 Can Modulate RNA Polymerase II Carboxy-Terminal Domain Phosphorylation Levels

Abstract

A high incidence of breast and ovarian cancers has been linked to mutations in the BRCA1 gene. BRCA1 has been shown to be involved in both positive and negative regulation of gene activity as well as in numerous other processes such as DNA repair and cell cycle regulation. Since modulation of the RNA polymerase II carboxy-terminal domain (CTD) phosphorylation levels could constitute an interface to all these functions, we wanted to directly test the possibility that BRCA1 might regulate the phosphorylation state of the CTD. We have shown that the BRCA1 C-terminal region can negatively modulate phosphorylation levels of the RNA polymerase II CTD by the Cdk-activating kinase (CAK) in vitro. Interestingly, the BRCA1 C-terminal region can directly interact with CAK and inhibit CAK activity by competing with ATP. Finally, we demonstrated that full-length BRCA1 can inhibit CTD phosphorylation when introduced in the BRCA1^−/− HCC1937 cell line. Our results suggest that BRCA1 could play its ascribed roles, at least in part, by modulating CTD kinase components.

We thank A. Barberis, R. Blouin, B. Coulombe, M. Erdos, R. P. Fisher, and M. Glover for expression plasmids and baculoviruses and J.-M. Egly for TFIIH. We are grateful to Nadia Boufaied for the original idea of an implication of BRCA1 in the modulation of phosphorylation and to Joëlle Brodeur, Marco Di Fruscio, Benoît Leblanc, Karine Lemieux, and Sébastien Rodrigue for critical comments on the manuscript.

This work was supported by the Cancer Research Society Inc. of Canada to L.G. L.G. holds a Canada Research Chair on mechanisms of gene transcription. A.M. and B.G. are recipients of a fellowship from the Natural Sciences and Engineering Research Council of Canada.