Oestrogen‐mediated phosphorylation and stabilization of BRCA2 protein in breast

Abstract

Disease-associated BRCA2 mutations typically result in protein truncations that delete the phosphorylation-regulated S3291 BRCA2 domain that interacts with Rad51. BRCA2 hereditary breast cancers are usually ER+, differing from BRCA1 hereditary cancers, which are usually ER negative. We studied BRCA2 protein expression and S3291 phosphorylation in normal breast tissues and in sporadic breast cancers and observed that BRCA2 is expressed and phosphorylated in normal breast and 10 ER+ breast cancers but not in 10 ER negative breast cancers. In order to study this correlation between ER and BRCA2 expression we studied ER+ breast cancer cell lines. We found that a rapid increase in BRCA2 S3291 phosphorylation occurs following 17-beta-oestradiol (E2) treatment. This increase seen in BRCA2 total and phospho-S3291 protein levels was found to be unaffected with cycloheximide pre-treatment, but decreased following tamoxifen, ICI 182,780, or roscovitine treatment. This suggests a requirement for ER and cdk (cyclin-dependent kinase) in mediating the increased protein levels. MCF7 cell cycle distribution analysis following E2 both in the presence and absence of roscovitine (a cdk inhibitor) did not demonstrate any changes during an 8 hour period, which further supports our hypothesis that mitogenic effects of E2 are not predominant at early time points. Studies with MG132 proteasome inhibitor and siRNA to skp2 support a model in which skp2-mediated proteasomal degradation of BRCA2 rapidly degrades BRCA2 protein in the absence of hormone treatment which likely inhibits this pathway. E2 was shown to improve survival of MCF7 cells upon radiation treatment and roscovitine partially reversed this effect. We have demonstrated that BRCA2 protein is specifically expressed in ER+ breast cancers and are investigating a pathway that may show a link between E2 action and BRCA2 protein function in breast cancer.

Hepatitis B virus X protein mutant upregulates CENP-A expression in hepatoma cells

“…In this study, we further confirm and extend our previous findings (14,15) that CENP-A expression is significantly elevated in HCC tissues. RNAi-mediated CENP-A depletion suppresses HCC cell growth both in vitro and in vivo, blocks cell-cycle progression at the G1 phase, and promotes apoptosis.…”

“…RNAi-mediated CENP-A depletion suppressed HCC cell growth both in vitro and in vivo, blocked cell cycle progression at the G1 phase, and promoted apoptosis in HCC cells. The anticancer effects of CENP-A depletion are likely mediated by a large number of genes involved in cell cycle control and apoptosis, including CHK2, P21waf1, P27 Kip1, SKP2, MDM2, Bcl-2, and Bax (14,15). Furthermore, CENP-A over expression was correlated with serum HBsAg states, tumor histological grade and P53 immunopositivity (16).…”

Oral contraceptives and postmenopausal hormones and risk of contralateral breast cancer among BRCA1 and BRCA2 mutation carriers and noncarriers: the WECARE Study

“…Mutations in BRCA1 may remove this inhibitory effect, thereby increasing epithelial proliferation in the breast. Estrogen also activates BRCA2 function to increase DNA repair responses in ER-positive breast cancer cells [30]. In addition, BRCA1 regulates progesterone receptor signaling [31] and a progesterone antagonist has been shown to prevent BRCA1 -mediated tumorigenesis in mouse models [31].…”

Prospective multicenter cohort study of estrogen and insulin-like growth factor system in BRCA mutation carriers

“…Wild-type BRCA 1 gene was found to negatively regulate aromatase expression in a human granulosa cell line, likely resulting in decreased estrogen levels [9], and estrogen action was reported to be linked to BRCA 2 protein function in breast cancer [10,11]. IGF-1, a peptide that stimulates mitosis and inhibits apoptosis, is related to the development and progression of malignant disease directly [12,13], as well as indirectly through regulation of insulin resistance, which is also known to be associated with breast cancer risk and outcome [14][15][16].…”