Methyltransferase 3A-mediated promoter methylation represses retinoic acid receptor responder 3 expression in basal-like breast cancer

Retinoic acid receptor responder 3 (RARRES3) has been characterized as a tumor suppressor in multiple types of cancer. This study aimed to examine the expression profile of RARRES3 across the PAM50 subtypes of breast cancer. The DNA methylation status of RARRES3 was checked in the basal-like subtype, and the underlying mechanisms of its dysregulation were explored. RNA-sequencing (seq) and methylation data from The Cancer Genome Atlas were used for in-silico analysis. Basal-like representative SUM149 and MDA-MB-468 cell lines were used for in vitro and in vivo studies. Compared to tumor-adjacent normal tissues, only the basal-like tumor tissues had significantly downregulated RARRES3 expression. The methylation level of four CpG sites in the promoter region showed a strong negative correlation with RARRES3 expression. The gene coding for DNA methyltransferase 3A (DNMT3A) had consistent positive correlations with the methylation of the CpG sites. Chromatin Immunoprecipitation-quantitative polymerase chain-reaction and bisulfite sequencing PCR showed that DNMT3A could bind to the promoter region of RARRES3 and promote methylation of the CpG sites within the region. DNMT3A knockdown significantly restored RARRES3 expression at the mRNA and protein level in the two cell lines. CCK-8, colony formation, and flow cytometric analysis showed that RARRES3 overexpression attenuated the growth-promoting effects of DNMT3A overexpression and also weakened the DNMT3A overexpression-induced activation of ERK1/2 and PI3K/AKT signaling. In summary, this study revealed that DNMT3A enhances promoter methylation of the RARRES3 gene and suppresses its transcription in basal-like breast cancer. The DNMT3A-RARRES3 signaling pathway might be a potential target for the treatment of this tumor subtype.