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 down-regulated, 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.

The DUX4 protein is a co‐repressor of the progesterone and glucocorticoid nuclear receptors

“…The PR in T47D cells is considered to have normal gene expression and protein structure, and we next explored if the observed repressor activity of DUX4 on PR was exclusive to T47D cells or also observed in other cells types that do not normally express PR. To do this, we transiently transfected plasmid‐encoded PR (hPR) in HepG2 and HEK293 cells, which do not show endogenous PR activity [34]. In these studies, HepG2 and HEK293 cells were transfected with: (a) plasmid hPR, expressing the gene encoding human PR, (b) either MMTV‐Luc or 2XPRE‐Luc, plus the pRL‐ Renilla reporter, and (c) either an empty vector or plasmid pcDNA3.1‐DUX4.…”

Progesterone receptors in normal breast development and breast cancer

“…PR post-translational modifications include phosphorylation, SUMOylation, acetylation, depicted in Figure 1B, as well as methylation, and ubiquitination (reviewed in [26,27]). These modifications alter PR hormone sensitivity, transcriptional activities, protein down-regulation, nuclear localization, and protein-protein interactions [28]. [10]), predicted variants according to alternative splicing (modified from Hirata et al [32], Samalecos et al [30], Cork et al [31] and Patel et al [190]), and post-translational modifications (phosphorylations, acetylations and sumoylation; modified from Diep et al [133]).…”