Regulation of MDA-MB-231 cell proliferation by GSK-3β involves epigenetic modifications under high glucose conditions

Hyperglycemia is a critical risk factor for development and progression of breast cancer. We have recently reported that high glucose induces phosphorylation of histone H3 at Ser 10 as well as dephosphorylation of GSK-3 beta at Ser 9 in MDA-MB-231 cells. Here, we elucidate the mechanism underlying hyperglycemia-induced proliferation in MDA-MB-231 breast cancer cells. We provide evidence that hyperglycemia led to increased DNA methylation and DNMT1 expression in MDA-MB-231 cells. High glucose condition led to significant increase in the expression of PCNA, cyclin D1 and decrease in the expression of PTPN 12, p21 and PTEN. It also induced hypermethylation of DNA at the promoter region of PTPN 12, whereas hypomethylation at Vimentin and Snail. Silencing of GSK-3 beta by siRNA prevented histone H3 phosphorylation and reduced DNMT1 expression. We show that chromatin obtained after immunoprecipitation with phospho-histone H3 was hypermethylated under high glucose condition, which indicates a cross-talk between DNA methylation and histone H3 phosphorylation. ChIP-qPCR analysis revealed up-regulation of DNMTI and metastatic genes viz Vimentin, Snail and MMP-7 by phospho-histone H3, which were down-regulated upon GSK-3 beta silencing. To the best of our knowledge, this is the first report which shows that interplay between GSK-3 beta activation, histone H3 phosphorylation and DNA methylation directs proliferation of breast cancer cells. (C) 2014 Elsevier Inc. All rights reserved.