Systematic dissection of the mechanisms underlying progesterone receptor downregulation in endometrial cancer

Abstract

Progesterone, acting through its receptor, PR (progesterone receptor), is the natural inhibitor of uterine endometrial carcinogenesis by inducing differentiation. PR is downregulated in more advanced cases of endometrial cancer, thereby limiting the effectiveness of hormonal therapy. Our objective was to understand and reverse the mechanisms underlying loss of PR expression in order to improve therapeutic outcomes. Using endometrial cancer cell lines and data from The Cancer Genome Atlas, our findings demonstrate that PR expression is downregulated at four distinct levels. In well-differentiated cancers, ligand-induced receptor activation and downregulation are intact. miRNAs mediate fine tuning of PR levels. As differentiation is lost, PR silencing is primarily at the epigenetic level. Initially, recruitment of the polycomb repressor complex 2 to the PR promoter suppresses transcription. Subsequently, DNA methylation prevents PR expression. Appropriate epigenetic modulators reverse these mechanisms. These data provide a rationale for combining epigenetic modulators with progestins as a therapeutic strategy for endometrial cancer.Significance: Traditional hormonal therapy for women with endometrial cancer can be molecularly enhanced by combining progestins with epigenetic modulators, thereby increasing progesterone receptor expression and significantly improving treatment efficacy.

Downregulation of FOXO1 mRNA levels predicts treatment failure in patients with endometrial pathology conservatively managed with progestin-containing intrauterine devices

“…However, ER and PRB levels in the post-IUD insertion biopsies were significantly higher in the “Progression” group as compared to the “No progression” group (Figure 3B–D). These data suggest that the expected ligand-mediated downregulation of PR [25] is lost in patients with CAH that progress to endometrioid adenocarcinoma. It was next important to determine whether the increase in PRB expression correlated with enhanced or loss of expression of the expected progestin-controlled genes associated with endometrial differentiation.…”

“…In theory, receptor transcriptional activity requires rapid recycling on and off DNA in order to promote maximal gene expression. Hence, the initial loss of PR in response to hormonal therapy is expected and is actually a potential marker for drug activity [25]. However, in the patients who progressed, the magnitude of the expected decrease in PR was blunted, and there was a trend towards enhanced non-nuclear (cytoplasmic) PRB.…”

“…Thus, we concluded that our original hypothesis was too simplistic, and we must consider the differences in short-term (natural) vs. long-term (pathological) downregulation of hormone receptors. In a separate study, we examined the different mechanisms underlying short-term vs. long-term PR downregulation using a panel of endometrial cancer cells as models [25]. Whereas the well-differentiated endometrial cancer cell line ECC1 demonstrated canonical ligand-mediated PR downregulation in response to progesterone, we found that PR is downregulated through epigenetic silencing in the moderately-differentiated Ishikawa line and the poorly-differentiated Hec50co line.…”

“…Whereas the well-differentiated endometrial cancer cell line ECC1 demonstrated canonical ligand-mediated PR downregulation in response to progesterone, we found that PR is downregulated through epigenetic silencing in the moderately-differentiated Ishikawa line and the poorly-differentiated Hec50co line. Depending on the mechanism of downregulation, a histone deacetylase inhibitor or a hypomethylating agent effectively restored functional PR expression (including expression of PR target genes) and thereby sensitivity to progestin therapy [25]. Therefore, we put forth the concept both PR expression and activity should be analyzed in patients being managed with a progestin-containing IUD.…”

“…Quantitative RT-PCR was performed on available pre- and post-IUD insertion biopsy samples (N=9) as previously described [25]. …”