Expression of DNA Methyltransferase 3B Isoforms Is Associated with DNA Satellite 2 Hypomethylation and Clinical Prognosis in Advanced High-Grade Serous Ovarian Carcinoma

Abstract

Alterations in DNA methylation are critical for the carcinogenesis of ovarian tumors, especially ovarian carcinoma (OC). DNMT3B, a de novo DNA methyltransferase (DNMT), encodes for fifteen spliced protein products or isoforms. DNMT3B isoforms lack exons for the catalytic domain, with functional consequences on catalytic activity. Abnormal expression of DNMT3B isoforms is frequently observed in several types of cancer, such as breast, lung, kidney, gastric, liver, skin, leukemia, and sarcoma. However, the expression patterns and consequences of DNMT3B isoforms in OC are unknown. In this study, we analyzed each DNMT and DNMT3B isoforms expression by qPCR in 63 OC samples and their association with disease-free survival (DFS), overall survival (OS), and tumor progression. We included OC patients with the main histological subtypes of EOC and patients in all the disease stages and found that DNMTs were overexpressed in advanced stages (p-value < 0.05) and high-grade OC (p-value < 0.05). Remarkably, we found DNMT3B1 overexpression in advanced stages (p-value = 0.0251) and high-grade serous ovarian carcinoma (HGSOC) (p-value = 0.0313), and DNMT3B3 was overexpressed in advanced stages (p-value = 0.0098) and high-grade (p-value = 0.0004) serous ovarian carcinoma (SOC). Finally, we observed that overexpression of DNMT3B isoforms was associated with poor prognosis in OC and SOC. DNMT3B3 was also associated with FDS (p-value = 0.017) and OS (p-value = 0.038) in SOC patients. In addition, the ovarian carcinoma cell lines OVCAR3 and SKOV3 also overexpress DNMT3B3. Interestingly, exogenous overexpression of DNMT3B3 in OVCAR3 causes demethylation of satellite 2 sequences in the pericentromeric region. In summary, our results suggest that DNMT3B3 expression is altered in OC.

Comprehensive Analysis of DNA Methyltransferases Expression in Primary and Relapsed Ovarian Carcinoma

“…Another study showed significantly lower expression of DNMT3A1 and DNMT2 mRNAs, the latter in agreement with our results, but higher expression of DNMT3B1/B2 mRNA isoforms in carcinomas than in low malignant potential tumors and that DNMT3B1/3B2 mRNA levels were associated with the methylation status of CDH13, MLH-M2B, SEZ6L and MINT31-M1B [37]. In accordance with this, using qPCR in 63 ovarian cancer patient samples, DNMT3B1 and DNMT3B3 overexpression was seen in advanced stages and high-grade serous carcinomas [51]. More recently, the expression of DNMT1, DNMT3A, and DNMT3B was examined by immunohistochemistry in ovarian cancers and benign tumors.…”

“…The combined expression of both markers had a better statistical correlation [35]. Analysis of DNMT3B isoforms expression using qPCR in 63 OEC showed that DNMT3B1 and DNMT3B3 overexpression was associated with poor prognosis [51]. This agrees with our results, albeit we did not specifically analyze the different isoforms of the molecule.…”

Current data and future perspectives on DNA methylation in ovarian cancer (Review)

“…Therefore, blocking DNMT3B can reduce the growth, migration and invasion of OC cells. However, in HGSOC, DNMT3B1 and DNMT3B3 are overexpressed, and the overexpression of DNMT3B3 leads to the marginal gene demethylation of OVCAR3 human OC cells, which is associated with a poor prognosis ( 177 ). DNMTis, which are chemically similar to deoxycytidine, have been shown to block methyl transfer by inhibiting DNMT activity.…”