GIULIANELLI Sebastian Jesus
congresos y reuniones científicas
The antiestrogen ICI 182.780 inhibits progestin induced cell proliferation by blocking the genomic interaction between ER£\ and PR at the CCND1/MYC promoters.
San Francisco, California
Congreso; Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; 2011
Institución organizadora:
The mechanisms by which progestins participate in breast cancer growth are not completely elucidated. Although most of the evidence suggests estrogens as the major etiological factor in breast cancer, there is experimental and epidemiological data that also points to the involvement of the progesterone receptors (PR) in mammary gland carcinogenesis and breast cancer growth. It has been proposed that an early interaction between estrogen receptor alpha (ER£\ƒw) and PRB is necessary for c-Src/p21Ras/Erk or PI3K/Akt activation by progestins. Conversely, other authors have shown that a polyproline domain in PR is sufficient to activate the afore mentioned cytoplasmic pathways. Both models suggest that these non-genomic effects induced by progestins activate other transcription factors at the Cyclin D1 (CCND1) promoter inducing gene transcription and cell proliferation.             Using two models of ER£\+/PR+ breast cancer, the human T47D cells and the C4-HD mouse mammary carcinomas, we have shown that medroxyprogesterone acetate (MPA) induces a nuclear physical association between ER£\ and both PR isoforms. The pure antiestrogen ICI 182.780 (ICI) blocked this interaction and the MPA-induced cell proliferation (AACR 2009). We hypothesize that this nuclear association between both hormone receptors is necessary to trigger progestin-induced cell proliferation/tumor growth. The aim of this study was a) to characterize the regression induced by ICI in C4-HD tumors growing with MPA and b) to investigate whether the nuclear complexes involving ER£\ and PR mediate MPA-induced CCND1 and MYC expression.             ICI treatment (5 mg/week) induced the complete regression of C4-HD tumors growing with MPA. After 48 h of treatment, a decrease in the mitotic index (p<0.001), Ki67 expression (p<0.001) as well as in the MPA-regulated proteins CCND1 (p<0.001) and MYC (p<0.001) were observed. In addition, an increase in apoptosis associated with a decrease in BCL/XL staining and an increase in the proapoptotic molecules BAX and AIF was also registered in ICI-treated tumors, indicating that in spite of the presence of MPA, ICI induces cytostasis and apoptosis.              To evaluate the mechanism by which ICI exerts these inhibitory effects, we first evaluated the time-dependent increase in CCND1 and MYC mRNA expression in T47D cells after MPA (10 nM) treatment. We observed that this increase is evident 15 min after MPA incubation (p<0.001 for CCND1 and p<0.05 for MYC) and remains high during 24 h, except for a decrease observed 1 h (CCND1) or 3 h (MYC) after treatment initiation. The blockage of ER£\ by siRNA or ICI (0.1 or 1 £gM), prevented the MPA-dependent transcription of both genes (p<0.001). Specific binding of PR/ER£\ was detected at the same MPA-sensitive regions at the CCND1 and MYC gene promoters after chromatin immunoprecipitation (ChIP) analysis. To our surprise, PR binding to both gene regulatory sequences was unaffected by the presence of ICI while it blocked that of ER£\.             All this data indicates that the presence of ER£\ interacting with activated PR at the CCND1 and MYC promoters is required to trigger MPA-induced gene transcription and cell proliferation.