CpG promoter hypo-methylation and up-regulation of microRNA-190b in hormone receptor-positive breast cancer

Abstract

Estrogen receptor-positive breast cancer is subdivided into subtypes LuminalA and LuminalB, based on different expression patterns. MicroRNA-190b has been reported to be up-regulated in estrogen receptor-positive breast cancers. In this study we aimed to investigate the role of CpG promoter methylation in regulating miR-190b expression and its impact on clinical presentation and prognosis. DNA methylation analysis for the promotor of microRNA-190b was performed by pyrosequencing 549 primary breast tumors, of which 62 were carriers of the BRCA2^999del5 founder mutation, 71 proximal normal breast samples and 16 breast derived cell lines. MicroRNA-190b expression was analysed in 67 primary breast tumors, 14 paired normal breast samples and 16 breast derived cell lines. Tissue microarrays (TMAs) were available for ER (n = 436), PR (n = 436), HER-2 (N = 258) and Ki67 (n = 248). MiR-190b had reduced promoter methylation in estrogen receptor-positive breast cancers (P = 1.02e–12, Median values: ER+ 24.3, ER– 38.26) and miR-190b’s expression was up-regulated in a correlative manner (P = 1.83e–06, Spearman’s rho –0.62). Through breast cancer specific survival analysis, we demonstrated that LuminalA patients exhibiting miR-190b hypo-methylation had better survival than other patients (P = 0.034, HR = 0.29, 95% CI 0.09-0.91). We, furthermore, demonstrated that miR-190b hypo-methylation occurs less frequently in ER+ tumors from BRCA2^999del5 mutation carriers than in non-mutated individuals (P = 0.038, Χ² = 4.32, n = 335). Our results suggest that upregulation of miR-190b may occur through loss of promoter DNA methylation during the development of estrogen-receptor (ER) positive breast cancers, and that miR-190b hypo-methylation leads to increased breast cancer specific survival within the LuminalA- subtype but not LuminalB.