The progesterone receptor (PR) plays roles in normal mammary development and breast cancer formation, where it may exert both stimulatory and inhibitory actions. Previously, the breast cancer susceptibility gene product BRCA1 was found to interact with and inhibit the transcriptional activity of estrogen receptor-alpha. In this study, we found that exogenous wild-type BRCA1 inhibited the activity of the PR in transient transfection assays utilizing a mouse mammary tumor virus-Luc reporter. Wild-type BRCA1 inhibited the activity of endogenous PR in human breast cancer cells (T47D and MCF-7) and inhibited the activity of exogenous PR-A, PR-B, and [PR-A plus PR-B] isoforms. On the other hand, knockdown of endogenous BRCA1 using small interfering RNA enhanced the progesterone-stimulated activity of the PR by about 4-fold. We documented an in vivo association of the endogenous BRCA1 with PR isoforms A and B and a direct in vitro interaction between BRCA1 and PR, which was partially mapped. Whereas down-regulation of the coactivator p300 contributes to the BRCA1-mediated repression of estrogen receptor-alpha, this mechanism does not contribute to inhibition of PR activity, because exogenous p300 did not rescue the BRCA1 repression of PR activity. The BRCA1-PR interaction has functional consequences. Thus, we showed that BRCA1 inhibits the expression of various endogenous progesterone-responsive genes and inhibits progesterone-stimulated proliferation of T47D cells. Finally, exogenous progesterone caused an exaggerated proliferative response in the mammary glands of mice harboring a mammary-targeted conditional deletion of the full-length isoform of Brca1. These findings suggest that BRCA1 regulates the activity of progesterone, a major hormone of pregnancy that may also participate in mammary carcinogenesis.

Previously, we reported that BRCA1 strongly represses the transcriptional activity of estrogen receptor-␣ (ER-␣) in human breast and prostate cancer cells but only weakly inhibits ER-␣ in cervical cancer cells. We now report that introduction of the human papillomavirus E7 or E6 oncogenes into human papillomavirus-negative cells rescues the BRCA1 repression of ER-␣ activity and that the E7 and E6 oncoproteins interact directly with BRCA1 in vitro and associate with BRCA1 in vivo in cultured cells. This interaction involves at least two contact points on BRCA1, one within an N-terminal site shown previously to interact with ER-␣ and the other in a C-terminal region of BRCA1 containing the first BRCA1 C-terminal domain. Point mutations within the zinc finger domains of E7 and E6 inactivated the binding to the N terminus of BRCA1 and reduced their ability to rescue BRCA1 inhibition of ER-␣. E6 and E7 also antagonized the ability of BRCA1 to inhibit c-Myc E-box-mediated transactivation and human telomerase reverse transcriptase promoter activity, in a manner dependent upon the zinc finger domains. Finally, the ability of E6 and E7 to antagonize BRCA1 did not involve proteolytic degradation of BRCA1. These findings suggest functional interactions of BRCA1 with E7 and E6. The potential significance of these findings is discussed.Mutations of the breast cancer susceptibility gene 1 (BRCA1) 2 (chromosome 17q21) are linked to a high risk for breast and ovarian cancers in hereditary early onset breast and breast-ovarian cancer families (1, 2). These mutations also confer and increased risk for these cancer types in Ashkenazi Jewish women unselected for a family history of cancer (3). A large study of cancer risk in BRCA1 cancer families in Europe and North America revealed that BRCA1 mutation carriers are also at significantly increased risk for the development of several other cancer types, including pancreatic cancer, uterine cancer, cervical cancer, and prostate cancer (in men younger than age 65) (4). For cervical cancer, the relative risk of BRCA1 mutation carriers compared with noncarriers was 3.72 (95% confidence interval ϭ 2.26 -6.10, p Ͻ 0.001, two-sided test). A subset of patients with sporadic invasive cervical cancer shows hypermethylation of the BRCA1 promoter (5), as do patients with sporadic breast and ovarian cancers (6, 7). BRCA1 promoter methylation may predict a worse prognosis in cervical cancer (8), although this point requires further study. An earlier and smaller study of cancer incidence in the relatives of BRCA1 and BRCA2 mutation carriers revealed about a 4-fold increased risk of cervical cancer in BRCA2-associated families, although the risk in BRCA1 families was not similarly elevated (9). Most interestingly, loss of heterozygosity at chromosome 17q, a site that contains the BRCA1 gene, appears to be a common event in cervical cancer (10).Previously, we found that the overexpression of BRCA1 inhibits the estrogen (E 2 )-induced transcriptional activity of the estrogen receptor-␣ (ER-␣) and inhi...

The forkhead transcription factor, Foxd3, plays a critical role during development by controlling the lineage specification of neural crest cells. Notably, Foxd3 is highly expressed during the wave of neural crest cell migration that forms peripheral neurons and glial cells but is down-regulated prior to migration of cells that give rise to the melanocytic lineage. Melanoma is the deadliest form of skin cancer and is derived from melanocytes. Recently, we showed that FOXD3 expression is elevated following the targeted inhibition of the B-RAF-MEK-ERK1/2 pathway in mutant B-RAF melanoma cells. Since melanoma cells are highly migratory and invasive in a B-RAF-dependent manner, we explored the role of FOXD3 in these processes. In this study, we show that ectopic FOXD3 expression inhibits the migration, invasion and spheroid outgrowth of mutant B-RAF melanoma cells. Up-regulation of FOXD3 expression following inhibition of B-RAF and MEK correlates with the down-regulation of Rnd3, a Rho GTPase and inhibitor of RhoA-ROCK signaling. Indeed, expression of FOXD3 alone was sufficient to down-regulate Rnd3 expression at the mRNA and protein levels. Mechanistically, FOXD3 was found to be recruited to the Rnd3 promoter. Inhibition of ROCK partially restored migration in FOXD3-expressing cells. These data show that FOXD3 expression down-regulates migration and invasion in melanoma cells and Rnd3, a target known to be involved in these properties.

Inherited mutations of the BRCA1 gene (chromosome 17q21), a tumor suppressor, lead to an increased risk of breast cancer, ovarian cancer, and several other hormone-responsive tumor types. Over the last ten years, BRCA1 has been found to play major roles in DNA damage signaling, repair, and cell cycle checkpoints. In addition, unfolding evidence suggests that BRCA1 functions as a co-regulator for steroid hormone receptors and modulates steroid hormone action. In this paper, we will briefly review this evidence and present a model to address the role of the progesterone and estrogen receptors in BRCA1 mutant mammary carcinogenesis. Finally, we will consider some of the clinical implications of this model. IntroductionMutations of the breast cancer susceptibility gene 1 (BRCA1) are linked to familial breast and ovarian cancer [Miki et al., 1994]. BRCA1 mutation carriers also experience a significantly increased risk for other hormone-responsive tumor types, including uterine, cervical, and prostate cancers [Thompson and Easton, 2002]. Accumulating evidence suggests that BRCA1 functions as a "caretaker" to maintain genomic integrity [Rosen et al., 2003]. However, this function does not explain the predilection of BRCA1 carriers to develop hormone-dependent cancers. We will discuss evidence that physiologic interactions between BRCA1 and steroid hormone receptors [progesterone receptor (PR) and estrogen receptor (ER-α)] contribute to the tissue-specific pattern of tumorigenesis in BRCA1 carriers. The PR in mammary cancerProgesterone physiologically regulates growth in the breast and uterus. The PR, a transcriptional target of ER-α, plays a key role in mammary growth and development, especially during pregnancy. Its role in breast cancer is not as well-established as for ER-α, but available data indicate that PR signaling can stimulate breast cancer development [Conneely et al., 2003;Lange et al., 1999;Schairer, 2002]. Progesterone can exert a biphasic effect on the mammary epithelium, where growth stimulation is followed by inhibition, depending upon the context [Musgrove et al., 1991]. It has been proposed that progesterone primes mammary epithelial cells to respond to other growth regulatory signals [Lange et al., 1999]. Studies in PR-/-mice have uncovered roles for PR in mammary ductal branching and lobulo-alveolar differentiation during pregnancy. A role in cancer is implied by the finding that PR-/-mice are resistant to carcinogen-induced mammary tumorigenesis [Conneely et al., 2003]. In the human menstrual cycle, breast epithelial cell proliferation peaks during the luteal phase, when circulating progesterone levels are maximal, consistent with progesterone stimulation of proliferation in the adult breast [Lange et al., 1999].Epidemiologic studies have revealed a small but significant increase in breast cancer risk associated with menopausal hormone replacement therapy (HRT) using combined estrogen-progestin treatment, relative to estrogen alone [Schairer, 2002]. In contrast, combined HRT reduces the incidence...