Research Grants Awarded
Dominant Inhibitory Role of the Progesterone Receptor (PR) in Breast Cancer
In addition to their vital role in reproduction, estrogens have been implicated in the pathophysiology of several diseases, including cancer of the breast and endometrium. Synthesis of estrogens from C 19 -steroids is catalyzed by aromatase P450 (P450arom, product of the CYP19 gene), which is upregulated in 70% of all breast cancers. Aromatase induction in breast cancer appears to be mediated by prostaglandin E 2 stimulation of promoter switching from the relatively weak promoter I.4 to the powerful ovary- and breast cancer-specific promoters IIa and I.3 , respectively . Aromatase is expressed both in the breast tumor and surrounding adipose stromal cells. Thus, aromatase activity within and surrounding the breast tumor can result in high local levels of estrogen production that stimulate tumor growth. The efficacy of current therapies using third generation aromatase inhibitors, selective estrogen receptor (ER) modulators and ER antagonists is predicted only if the tumor contains significant amounts of ER. Presence of PR in the tumor also is an important predictor of responsiveness to endocrine therapy and a negative indicator of tumor aggressiveness. Aromatase expression in human breast tumors is highly correlated with COX-2, the rate-determining enzyme in prostanoid biosynthesis. Recently, using T47D breast cancer cells, we made the remarkable discovery that mRNA levels of COX-2, CYP19, and the oncogene HER-2/neu were greatly induced by cytokines ( e.g. IL-1 b ) and cAMP, and inhibited by progesterone. Furthermore, progesterone acting through PR blocked IL-1 b -induced NF- k B activation and binding to the COX-2 promoter and increased expression of the NF- k B inhibitor, I k B a . Notably, knockdown of PR using specific siRNAs greatly enhanced expression of COX-2, CYP19, and HER-2/neu mRNA in the absence or presence of IL-1 b . Based on these findings, we postulate that PR plays a dominant protective role in breast cancer cells by antagonizing NF- k B activation of COX-2, resulting in decreased CYP19 and HER-2/neu expression. To test this hypothesis, we propose: (1) to analyze >60 human breast cancer specimens and correlate expression of CYP19 (and promoter usage), COX-2 , ER a and ER ß , PR and I k B a with the oncogenic markers HER-2/neu, EGFR and SRC-3/AIB1 , and markers of proliferative activity; (2) to create mice with a mammary-specific knockout of PR to analyze the protective role of endogenous PR in spontaneous and carcinogen-induced breast tumorigenesis.
There is compelling evidence that the sex steroid hormone estrogen, along with associated mediators of inflammation, play important roles in growth and progression of breast cancer in women. In fact, 70% of all breast cancers contain high levels of aromatase, the enzyme responsible for estrogen production. Thus, increased aromatase activity within the breast tumor and in surrounding connective tissue cells can result in high local levels of estrogen production that stimulate tumor growth. In women with breast tumors containing significant amounts of estrogen receptor (ER), aromatase inhibitors have been found to be as effective as tamoxifen in enhancing disease-free survival. High levels of aromatase in human breast tumors are also tightly correlated with levels of cyclooxygenase-2 (COX-2), the critical enzyme in prostaglandin biosynthesis and with the oncogene, HER-2/neu, which is over-expressed in ~30% of all breast tumors. As a result, clinical trials using COX-2 inhibitors in the absence or presence of aromatase inhibitors also are in progress. The presence of the progesterone receptor (PR) in a breast tumor has long been known to serve as an important predictor of responsiveness to endocrine therapy and as a negative indicator of tumor aggressiveness. Recently, using T47D breast cancer cells, we made the remarkable discovery that mRNA levels of COX-2, aromatase, and HER-2/neu were greatly induced by cytokines ( e.g. IL-1 b ), and inhibited by progesterone. Furthermore, knockdown of PR levels using specific siRNAs greatly enhanced expression of COX-2, aromatase, and HER-2/neu. Based on these findings, we postulate that PR plays a dominant protective role in breast cancer cells by antagonizing activation of COX-2, resulting in decreased aromatase and HER-2/neu expression. To test this hypothesis, we propose: (1) to analyze >60 human breast cancer specimens and correlate expression of aromatase, COX-2, ER, PR and markers of tumorigenesis, such as HER-2/neu and the steroid hormone receptor cofactor AIB1/SRC-3 ; (2) to create mice in which PR is specifically ablated in the mammary gland to analyze its protective role in spontaneous and carcinogen-induced breast cancers. We believe that findings from these studies will enhance our understanding of the protective role of PR in breast tumor biology and will hopefully lead to new therapeutic regimens to enhance survival in breast cancer patients.