The second BRCT domain of BRCA1 proteins interacts with p53 and stimulates transcription from the p21WAF1/CIP1 promoter

Abstract

Inherited mutations in the breast and ovarian cancer susceptibility gene BRCA1 are associated with high risk for developing breast and ovarian cancers. Several studies link BRCA1 to transcriptional regulation, DNA repair, apoptosis and growth/tumor suppression. BRCA1 associates with p53 and stimulates transcription in both p53 dependent and p53-independent manners. BRCA1 splice variants BRCA1a (p110) and BRCA1b (p100) associates with CBP/p300 co-activators. Here we show that BRCA1a and BRCA1b proteins stimulate p53-dependent transcription from the p21 WAF1/CIP1 promoter. In addition, the C-terminal second BRCA1 (BRCT) domain is su cient for p53 mediated transactivation of the p21 promoter. Previous studies emphasized the importance of the BRCT domain, which shows homology with p53 binding protein (53BP1), in transcriptional activation, growth inhibition and tumor suppression. Our ®ndings demonstrate an additional function for this domain in protein ± protein interaction and co-activation of p53. We also found that BRCA1a and BRCA1b proteins interact with p53 in vitro and in vivo. The p53 interaction domain of BRCA1a/1b maps, in vitro, to the second BRCT domain (aa 1760 ± 1863). The BRCT domain binds to the central domain of p53 which is required for sequence speci®c DNA binding. These results demonstrate for the ®rst time the presence of a second p53 interaction domain in BRCA1 proteins and suggests that BRCA1a and BRCA1b proteins, like BRCA1, function as p53 co-activators. This BRCT domain also binds in vitro to CBP. These results suggest that one of the mechanisms by which BRCA1 proteins function is through recruitment of CBP/p300 associated HAT/FAT activity for acetylation of p53 to speci®c promoters resulting in transcriptional activation.

Regulation of BRCA1 by protein degradation

“…However, functional impairment of BRCA1 is di cult to identify, because its critical role in the cell remains nebulous. In fact, BRCA1 appears to possess multiple activities, including modulation of p53 activity (Ouchi et al, 1998;Zhang et al, 1998;Chai et al, 1999), independent transactivating activity (Chapman and Verma, 1996;Monteiro et al, 1996;Somasundaram et al, 1997), a role in DNA damage sensing/repair (Scully et al, 1997;Brugarolas and Jacks, 1997;Andres et al, 1998) and, most recently described, transcriptional repression of estrogen-dependent signaling (Fan et al, 1999).…”

BRCA1 gene in breast cancer

“…Various classes of proteins interact with BRCA1, including: (1) components of the basal transcription machinery [e.g., RNA helicase A and RNA pol II (Anderson et al, 1998;Schlegel et al, 2000a)]; (2) generalized transcriptional coactivators [p300, CBP, Brg1 (Bochar et al, 2000;Pao et al, 2000)] and corepressors [e.g., RbAp46, RbAp48, histone deacetylases-1,2, and CtIP (Yarden and Brody, 1998;Yu et al, 1998)]; (3) tumor suppressors [e.g., p53, RB1, BRCA2 (Chen et al, 1998;Ouichi et al, 1998;Yarden and Brody, 1998;Zhang et al, 1998;Aprelikova et al, 1999;Chai et al, 1999;Fan et al, 2001c)]; (4) steroid hormone receptors, estrogen receptor-a, and androgen receptor (Yeh et al, 2000;Fan et al, 2001a); (5) DNA repair proteins [e.g., Rad51, Rad50, hMSH2 (Scully et al, 1997b;Zhong et al, 1999;Wang et al, 2001a)]; (6) other sequence-specific transcription factors [e.g., c-Myc, Oct-1, and NF-YA Fan et al, 2002b)]; and (7) cell cycle regulatory proteins [e.g., BARD1, E2F1, cyclins (Wu et al, 1996;Wang et al, 1997)]. These interactions are summarized in Figure 1; and the significance of these interactions is discussed in ''Functional Activities of BRCA1''.…”

“…Recently, BRCA1 was found to bind directly to p53, via an interaction involving the DNA-binding domain of p53 and an N-terminal site localized to aa 224-500 of BRCA1 (Ouichi et al, 1998;Zhang et al, 1998). A second p53 binding site was identified within the C-terminal second BRCT domain (aa 1,760-1,863) of BRCA1 (Chai et al, 1999). The BRCA1:p53 interaction results in enhanced p53 transactivational activity.…”

Caspase-3 mediated cleavage of BRCA1 during UV-induced apoptosis

“…The C-terminus of BRCA1, when fused to the GAL4 DNA binding domain activated GAL4 promoter. In transient transfection assays, BRCA1 increased p53-dependent and independent transcription from the p21 WAF1/CIP1 and GADD45 promoters (Chai et al, 1999;Jin et al, 2000). In addition, BRCA1 caused accumulation of p53 after gamma-irradiation through transcriptional stimulation of the p53-responsive promoter, MDM2.…”