The BRCA1 COOH-terminal region acts as an RNA polymerase II carboxyl-terminal domain kinase inhibitor that modulates p21WAF1/CIP1 expression.
BRCA1 is involved both in positive and negative regulation of gene activity as well as in numerous other processes, such as DNA damage response and repair. We recently reported that BRCA1 inhibits RNA polymerase II carboxyl-terminal domain (CTD) phosphorylation by TFIIH and decreases serine 5 phosphorylation levels when introduced into a BRCA1(-/-) cell line. Regulation of CTD phosphorylation is crucial for proper gene expression and response to cellular stresses, such as DNA damage and transcription arrest. A key player in this process, P-TEFb, phosphorylates the CTD on serine 2 of transcriptionally engaged RNA polymerase II, and its kinase activity was shown to be up-regulated when cells are exposed to transcriptional stress such as UV irradiation. Here, we investigate the effect of BRCA1 on serine 2 phosphorylation and UV-activated P-TEFb kinase activity. We now show that BRCA1 inhibits immunoprecipitated P-TEFb kinase activity from UV-irradiated cells and preferentially decreases UV-induced serine 2 phosphorylation of soluble, rather than chromatin-bound, RNAPII. We further show that BRCA1 rescues the UV-mediated inhibition of transcriptional activity from nuclear extracts and stimulates endogenous p21 gene expression upon UV irradiation, a function that is dependent of the inhibition of CTD kinase activity. Our results suggest that BRCA1 could act as a CTD kinase inhibitor and, as such, contribute to the regulation of p21 gene expression.
Moisan
Annie
A
Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada.
Gaudreau
Luc
L
Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada. Electronic address: Luc.Gaudreau@USherbrooke.ca.
D019313:BRCA1 Protein / Q000737:chemistry*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000737:chemistry / Q000502:physiology*; D004249:DNA Damage; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D010766:Phosphorylation; D042925:Positive Transcriptional Elongation Factor B / Q000737:chemistry; D017434:Protein Structure, Tertiary; D012319:RNA Polymerase II / Q000737:chemistry*; D014158:Transcription, Genetic
D019313:BRCA1 Protein; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004791:Enzyme Inhibitors; D042925:Positive Transcriptional Elongation Factor B; D012319:RNA Polymerase II