Progesterone promotes differentiation coupled to proliferation and prosurvival in the breast, but inhibits estrogen-driven growth in the reproductive tract and ovaries. Herein, it is demonstrated, using progesterone receptor (PR) isoform-specific ovarian cancer model systems, that PR-A and PR-B promote distinct gene expression profiles that differ from PR-driven genes in breast cancer cells. In ovarian cancer models, PR-A primarily regulates genes independently of progestin, while PR-B is the dominant ligand-dependent isoform. Notably, FOXO1 and the PR/FOXO1 target gene p21 (CDKN1A) are repressed by PR-A, but induced by PR-B. In the presence of progestin, PR-B, but not PR-A, robustly induced cellular senescence via FOXO1-dependent induction of p21 and p15 (CDKN2B). Chromatin immunoprecipitation (ChIP) assays performed on PR isoform-specific cells demonstrated that while each isoform is recruited to the same PRE-containing region of the p21 promoter in response to progestin, only PR-B elicits active chromatin marks. Overexpression of constitutively active FOXO1 in PR-A-expressing cells conferred robust ligand-dependent upregulation of the PR-B target genes GZMA, IGFBP1, and p21, and induced cellular senescence. In the presence of endogenous active FOXO1, PRA was phosphorylated on Ser294 and transactivated PR-B at PR-B target genes; these events were blocked by the FOXO1 inhibitor (AS1842856). PR isoform-specific regulation of the FOXO1/p21 axis recapitulated in human primary ovarian tumor explants treated with progestin; loss of progestin sensitivity correlated with high AKT activity. Implications: This study indicates FOXO1as a critical component for progesterone signaling to promote cellular senescence and reveals a novel mechanism for transcription factor control of hormone sensitivity.
Bibliographical noteFunding Information:
The authors thank members of the University of Minnesota Masonic Cancer Center''s Flow Cytometry Core Facility, the University Imaging Centers, the Minnesota Supercomputing Institute, and the University of Minnesota Genomics Center for their assistance in data acquisition, processing, and analysis. CDB-4124 (Proellex) was a kind gift from Ronald Wiehle (Repros Therapeutics). This study was supported by NIH grant R01 CA159712 and R01 CA159712-S1 (to C.A. Lange), Cancer Biology Training Grant NIH T32 CA009138 (to C.H. Diep), National Center for Advancing Translational Sciences of the NIH Award UL1TR000114 (to C.H. Diep), and a University of Minnesota Doctoral Dissertation Fellowship (to C.H. Diep). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
© 2016 American Association for Cancer Research.