CpG hypermethylation in gene promoters is a frequent mechanism of tumor suppressor gene silencing in various types of
cancers. It usually occurs at early steps of
cancer progression and can be detected easily, giving rise to development of promising
biomarkers for both detection and progression of
cancer, including
breast cancer.
5-aza-2'-deoxycytidine (AZA) is
a DNA demethylating and anti-
cancer agent resulting in induction of genes suppressed via
DNA hypermethylation.
RESULTS: Using microarray expression profiling of AZA- or
DMSO-treated
breast cancer and non-tumorigenic breast (NTB) cells, we identified for the first time TAGLN gene as a target of
DNA hypermethylation in
breast cancer. TAGLN expression was significantly and frequently downregulated via promoter
DNA hypermethylation in
breast cancer cells compared to NTB cells, and also in 13/21 (61.9 %) of
breast tumors compared to matched normal tissues. Analyses of public microarray methylation data showed that TAGLN was also hypermethylated in 63.02 % of
tumors compared to normal tissues; relapse-free survival of patients was worse with higher TAGLN methylation; and methylation levels could discriminate between
tumors and healthy tissues with 83.14 % sensitivity and 100 % specificity. Additionally, qRT-PCR and immunohistochemistry experiments showed that TAGLN expression was significantly downregulated in two more independent sets of
breast tumors compared to normal tissues and was lower in
tumors with poor prognosis. Colony formation was increased in TAGLN silenced NTB cells, while decreased in overexpressing BC cells.
CONCLUSIONS: TAGLN gene is frequently downregulated by
DNA hypermethylation, and TAGLN promoter methylation profiles could serve as a future diagnostic
biomarker, with possible clinical impact regarding the prognosis in
breast cancer.