Abstract
BackgroundCpG 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.ResultsUsing 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.ConclusionsTAGLN 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13148-015-0138-5) contains supplementary material, which is available to authorized users.
Highlights
CpG hypermethylation in gene promoters is a frequent mechanism of tumor suppressor gene silencing in various types of cancers
We found that 17 and 22 % of the probe sets induced in MCF7 or MDA-MB-231 cells, respectively, were induced in common while the remaining genes were cell-line specific
We found that the expression of TAGLN was higher in grade 1 and 2 tumors compared to grade 3, suggesting that TAGLN expression could be decreased even more when the tumor progresses into a more undifferentiated state in breast cancer
Summary
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 giving rise to development of promising biomarkers for both detection and progression of cancer, including breast cancer. Use of demethylating agents together with expression microarrays enables the analysis of genes that may be regulated by hypermethylation of their promoter regions [11]. Discovering these genes is essential for therapeutic achievements but can serve diagnostic, prognostic, and monitoring purposes [12]
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