Hydrocortisone down‐regulates the tumor suppressor gene BRCA1 in mammary cells: A possible molecular link between stress and breast cancer

Abstract

Psychological stress has been correlated with breast cancer development in numerous epidemiological studies. However, physiological and molecular models which may account for this association are not readily available. We have found that the stress hormone hydrocortisone (cortisol) down-regulates the expression of the breast cancer susceptibility gene BRCA1 in the nonmalignant mouse mammary cell line EPH4. This effect is concentration-dependent, is reliant on the continuous presence of hydrocortisone, and is not affected by the addition of lactogenic hormones, or growth conditions. Hydrocortisone was also found to negate a known positive effect of estrogen on BRCA1 expression and, therefore, may interfere with estrogen-related signaling in mammary epithelial cells. The repressive effect of hydrocortisone is diminished or lost in the mouse mammary lines HC-11 and SP1, respectively, suggesting regulation of the BRCA1 may differ between lines. We have uncovered two promoter regulatory sites, which are involved in BRCA1 regulation by hydrocortisone, namely the RIBS and UP regulatory elements. Binding of the transcription factor GABP to both sites is lost upon hydrocortisone addition, though the levels of these factors are not altered by hydrocortisone treatment. Because BRCA1 activity is important for a number of intracellular pathways involved in prevention of tumorigenesis, its observed down-regulation may represent a novel molecular mechanism for cortisol's involvement in breast cancer development.

The Unliganded Glucocorticoid Receptor Positively Regulates the Tumor Suppressor GeneBRCA1through GABP Beta

“…Furthermore, specific studies have suggested that the cancer-causing effects of stress may be fairly specific to the breast (17,18). We previously presented the first molecular evidence for a connection between stress and breast cancer with our observation that BRCA1 expression is repressed by the synthetic stress hormone hydrocortisone in nonmalignant mouse mammary cells (19). This work was the first breast-specific molecular mechanism linking stress and breast cancer development.…”

“…The human breast carcinoma cell lines MCF-10A and MCF-7 were obtained from American Type Culture Collection. All cells were cultured as previously described (15,19). Cell treatments were completed using media lacking FBS or horse serum and containing either 1 mg/mL hydrocortisone (Sigma), 1, 5, or 10 mmol/L RU-486 (Sigma), or ethanol vehicle for 24 or 48 hours.…”

“…Transfections were carried out as described previously (15,19). For standard transfection assays, control cytomegalovirus (CMV)-luc vector (Promega) was used at 25 ng per well, as were GR expression vectors and empty vector controls.…”

“…RNA and RT products were prepared as described previously (15,19). Quantitative real-time PCR (qRT-PCR) reactions for human BRCA1 were carried out as described previously (15), with the exception that hypoxanthine phosphoribosyltransferase 1 (HPRT1) was used as an internal control instead of TBP (primers listed in Supplementary Table S5).…”

“…qRT-PCR reactions for mouse BRCA1 (with TBP as an internal control) were carried out as described previously (ref. 19; primers listed in Supplementary Table S6). BRCA1 expression for each cell line was calculated relative to the results for the untreated sample with the DD C t method presented by PE Applied Biosystems (Perkin Elmer).…”