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SUMOylation Regulates Transcription by the Progesterone Receptor A Isoform in a Target Gene Selective Manner

ABSTRACT: Luminal breast cancers express estrogen (ER) and progesterone (PR) receptors, and respond to endocrine therapies. However, some ER+PR+ tumors display intrinsic or acquired resistance, possibly related to PR. Two PR isoforms, PR-A and PR-B, regulate distinct gene subsets that may differentially influence tumor fate. A high PR-A:PR-B ratio is associated with poor prognosis and tamoxifen resistance. We speculate that excessive PR-A marks tumors that will relapse early. Here we address mechanisms by which PR-A regulate transcription, focusing on SUMOylation. We use receptor mutants and synthetic promoter/reporters to show that SUMOylation deficiency or the deSUMOylase SENP1 enhance transcription by PR-A, independent of the receptors’ dimerization interface or DNA binding domain. De-SUMOylation exposes the agonist properties of the antiprogestin RU486. Thus, on synthetic promoters, SUMOylation functions as an independent brake on transcription by PR-A. What about PR-A SUMOylation of endogenous human breast cancer genes? To study these, we used gene expression profiling. Surprisingly, PR-A SUMOylation influences progestin target genes differentially, with some upregulated, others downregulated, and others unaffected. Hormone-independent gene regulation is also PR-A SUMOylation dependent. Several SUMOylated genes were analyzed in clinical breast cancer database. In sum, we show that SUMOylation does not simply repress PR-A. Rather, it regulates PR-A activity in a target selective manner including genes associated with poor prognosis, shortened survival, and metastasis.

ORGANISM(S): Homo sapiens

PROVIDER: GSE108607 | GEO | 2018/02/02

REPOSITORIES: GEO

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Project description:Major roadblocks to developing effective progesterone receptor (PR)-targeted therapies in breast cancer include the lack of highly-specific PR modulators, a poor understanding of the pro- or anti-tumorigenic networks for PR isoforms and ligands, and an incomplete understanding of the cross talk between PR and estrogen receptor (ER) signaling. Through genomic analyses of xenografts treated with various clinically-relevant ER and PR-targeting drugs, we describe how the activation or inhibition of PR dictates distinct ER and PR chromatin binding and differentially reprograms estrogen signaling, resulting in the segregation of transcriptomes into separate PR agonist and antagonist-mediated groups. These findings address an ongoing controversy regarding the clinical utility of PR agonists and antagonists, alone or in combination with tamoxifen, for breast cancer management. Genomic analyses of the two PR isoforms, PRA and PRB, indicate that these isoforms bind distinct genomic sites and interact with different sets of co-regulators to differentially modulate gene expression as well as pro- or anti-tumorigenic phenotypes. Of the two isoforms, PRA inhibited gene expression and ER chromatin binding significantly more than PRB. Of note, the two isoforms reprogrammed estrogen activity to be either pro or anti-tumorigenic. In concordance to the in-vitro observations, differential gene expression was observed in PRA and PRB-rich patient tumors and importantly, PRA-rich gene signatures had poorer survival outcomes. In support of antiprogestin responsiveness of PRA-rich tumors, gene signatures associated with PR antagonists, but not PR agonists, predicted better survival outcomes. This differential of better patient survival associated with PR antagonists versus PR agonists treatments was further reflected in the higher anti-tumor activity of combination therapies of tamoxifen with PR antagonists and modulators. Knowledge of various determinants of PR action and their interactions with estrogen signaling to differentially modulate breast cancer biology should serve as a guide to the development of biomarkers for patient selection and translation of PR-targeted therapies to the clinic.

Project description:Major roadblocks to developing effective progesterone receptor (PR)-targeted therapies in breast cancer include the lack of highly-specific PR modulators, a poor understanding of the pro- or anti-tumorigenic networks for PR isoforms and ligands, and an incomplete understanding of the cross talk between PR and estrogen receptor (ER) signaling. Through genomic analyses of xenografts treated with various clinically-relevant ER and PR-targeting drugs, we describe how the activation or inhibition of PR differentially reprograms estrogen signaling, resulting in the segregation of transcriptomes into separate PR agonist and antagonist-mediated groups. These findings address an ongoing controversy regarding the clinical utility of PR agonists and antagonists, alone or in combination with tamoxifen, for breast cancer management. Additionally, the two PR isoforms PRA and PRB, bind distinct genomic sites and interact with different sets of co-regulators to differentially modulate estrogen signaling to be either pro- or anti-tumorigenic. Of the two isoforms, PRA inhibited gene expression and ER chromatin binding significantly more than PRB. Differential gene expression was observed in PRA and PRB-rich patient tumors and importantly, PRA-rich gene signatures had poorer survival outcomes. In support of antiprogestin responsiveness of PRA-rich tumors, gene signatures associated with PR antagonists, but not PR agonists, predicted better survival outcomes. This better patient survival associated with PR antagonists versus PR agonists treatments was further reflected in the higher anti-tumor activity of combination therapies of tamoxifen with PR antagonists and modulators. The study suggests that distinguishing common effects observed due to concomitant interaction of another receptor with its ligand (agonist or antagonist) from unique isoform and ligand-specific effects will guide the development of biomarkers for patient selection and translation of PR-targeted therapies to the clinic.

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SUMOylation Regulates Transcription by the Progesterone Receptor A Isoform in a Target Gene Selective Manner

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