BRCA1 is a component of the RNA polymerase II holoenzyme

Abstract

The familial breast-ovarian tumor suppressor gene product BRCA1 was found to be a component of the RNA polymerase II holoenzyme by several criteria. BRCA1 was found to copurify with the holoenzyme over multiple chromatographic steps. Other tested transcription activators that could potentially contact the holoenzyme were not stably associated with the holoenzyme as determined by copurification. Antibody specific for the holoenzyme component hSRB7 specifically purifies BRCA1. Immunopurification of BRCA1 complexes also specifically purifies transcriptionally active RNA polymerase II and transcription factors TFIIF, TFIIE, and TFIIH. Moreover, a BRCA1 domain, which is deleted in about 90% of clinically relevant mutations, participates in binding to the holoenzyme complex in cells. These data are consistent with recent data identifying transcription activation domains in the BRCA1 protein and link the BRCA1 tumor suppressor protein with the transcription process as a holoenzyme-bound protein.BRCA1 is a tumor suppressor gene that is mutated in a significant fraction of cases of inherited breast and ovarian cancer. Approximately 3% of breast cancer is attributable to inherited mutations in BRCA1. Indeed, in ϳ50% of families with an abnormally high incidence of breast cancer through multiple generations, the offending mutation is in the BRCA1 gene (1-3). The BRCA1 product is likely to have tumor suppression function, since tumors arising in members of BRCA1-linked families show loss of heterozygosity at the BRCA1 locus, with retention of the mutant͞disease-predisposing allele (4, 5).The BRCA1 gene encodes a 1,863-amino acid protein without extensive homology to other proteins (1, 2). The primary sequence is noteworthy for a RING-finger motif and an acidic carboxyl terminus (1), both of which are characteristics of certain transcription factors. The BRCA1 7.8-kb mRNA is observed in many tissues, with expression highest in testis and thymus (1). About 90% of the mutations observed in the BRCA1 gene result in truncations, and the remainder of clinically relevant mutations are individual missense abnormalities that are scattered along the entire coding unit (3).A defined carboxyl-terminal segment of BRCA1 can activate transcription when fused to the DNA binding domain of GAL4 (6, 7). These fusion proteins activated transcription from promoters containing a GAL4 binding site. Importantly, fusion proteins bearing clinically relevant point mutations were inactive in this assay, implying, at a minimum, that the transcription assay is a faithful monitor of the native structure of a segment of the protein. Although there are other interpretations, these data have licensed the speculation that BRCA1 is, at least in part, a transcription factor. Whatever the significance of the transactivation potential of its carboxylterminal region, there is now evidence pointing to a role for BRCA1 in the control of DNA repair and genome stability (8). Hence, if it proves to have genuine transcription regulation function, it will be int...

BRCA1 physically associates with p53 and stimulates its transcriptional activity

“…The role of p53 as a transcription factor is well-established (Vogelstein and Kinzler, 1992) and appears to be important for its ability to arrest cell cycle progression as well as to induce apoptosis (Levine, 1997). BRCA1 has been postulated to function as a coactivator of transcription, based on its localization as a component of RNA polymerase II holoenzyme and transactivation function (Chapman and Verma, 1996;Monteiro et al, 1996;Somasundaram et al, 1997;Scully et al, 1997a). The observation that BRCA1 is a transcriptional coactivator of p53, including strong upregulation of expression of the bax gene, provides a novel mechanism for apoptosis induction and tumor suppression by BRCA1.…”

“…Evidence implicates a role for BRCA1 in the control gene expression. BRCA1 contains a nuclear localization signal (Thakur et al, 1997), a C-terminal domain that transactivates gene expression when fused to a heterologous DNA binding domain (Chapman and Verma, 1996;Monteiro et al, 1996) and BRCA1 has been found as a component of RNA polymerase II (Scully et al, 1997a).…”

Genetic sequence variations of BRCA1-interacting genes AURKA, BAP1, BARD1 and DHX9 in French Canadian Families with high risk of breast cancer

“…Deleterious mutations in BRCA1/BRCA2 were identified in 24% of our 256 high-risk French Canadian breast/ovarian cancer families, 4 supporting that a significant proportion of high-risk breast cancer families still remain unexplained by either germline mutations in high penetrance BRCA1/2 alleles or other lower penetrance genes. [5][6][7][8][9][10] Several structural motifs allow the BRCA1 protein to interact with cellular proteins to regulate diverse biological functions such as control of transcription 11 and DNA damage repair. 12 Therefore, BRCA1-interacting proteins implicated in these cellular pathways represent attractive candidates with regard to breast cancer susceptibility.…”

“…28 BAP1 was suggested to regulate the BRCA1/BRCA2-RAD51 DNA repair complex. 29 Given the known implication of BRCA1 in DNA repair 12 and its interaction with RNA pol II, 11 which is linked to transcription-coupled repair (TCR) processes, a role for BAP1 in TCR has been suggested. 30 It has been reported that mutation of an amino acid of BAP1 in its BRCA1-binding domain (L691P) abolishes the BAP1-BRCA1 interaction.…”

Down-regulation of BRCA1 in human sporadic breast cancer; analysis of DNA methylation patterns of the putative promoter region

“…In addition, recent ®ndings demonstrating an association between BRCA1 and Rad 51 proteins suggest a role for this protein in DNA repair (Scully et al, 1997a). However, the presence of a transactivation domain in BRCA1 and its stable association with RNA Polymerase II holenzyme (Scully et al, 1997b) indicate that BRCA1 might also be involved in the regulation of transcription. These two hypotheses, which are not mutually exclusive, stress that BRCA1 may have an important role in cellular di erentiation and proliferation.…”