LAUSR

Background: DNA methylation is involved in numerous biologic events and associates with transcriptional gene silencing, playing an important role in the pathogenesis of endometrial cancer. ESR1/PGR frequently undergoes de novo methylation and loss expression in a wide variety of tumors, including breast, colon, lung, and brain tumors. However, the mechanisms underlying estrogen and progesterone receptors (ER/PR) loss in endometrial cancer have not been studied extensively. The aims of this study were to determine the expression of DNA (cytosine-5)-methyltransferase 3A/3B (DNMT3A/3B) in endometrial cancer to investigate whether the methylation catalyzed by DNMT3A/3B contributes to low ER/PR expression. Methods: The clinicopathologic information and RNA-Seq expression data of DNMT3A/3B of 544 endometrial cancers were derived from The Cancer Genome Atlas (TCGA) uterine cancer cohort in May 2018. RNA-Seq level of DNMT3A/3B was compared between these clinicopathologic factors with t-test or one-way analysis of variance. Results: DNMT3A/3B was overexpressed in endometrioid carcinoma (EEC) and was even higher in non-endometrioid carcinoma (NEEC) (DNMT3A, EEC vs. NEEC: 37.6% vs. 69.9%, t = −7.440, P < 0.001; DNMT3B, EEC vs. NEEC: 42.4% vs. 72.8%, t = −6.897, P < 0.001). In EEC, DNMT3A overexpression was significantly correlated with the hypermethylation and low expression of the ESR1 and PGR (P < 0.05). The same trend was observed in the DNMT3B overexpression subgroup. In the ESR1/PGR low-expression subgroups, as much as 83.1% of ESR1 and 59.5% of PGR were hypermethylated, which was significantly greater than the ESR1/PGR high-expression subgroups (31.3% and 11.9%, respectively). However, the above phenomena were absent in NEEC, while DNMT3A/3B overexpression, ESR1/PGR hypermethylation, and low ER/PR expression occurred much more often. In univariate analysis, DNMT3A/3B overexpressions were significantly correlated with worse prognosis. In multivariate analysis, only DNMT3A was an independent predictor of disease-free survival (P < 0.05). Conclusions: DNMT3A/3B expression increases progressively from EEC to NEEC and is correlated with poor survival. The mechanisms underlying low ER/PR expression might be distinct in EEC vs. NEEC. In EEC, methylation related to DNMT3A/3B overexpression might play a major role in ER/PR downregulation.