Overexpression of OCT4 induced by modulation of histone marks plays crucial role in breast cancer progression

Abstract

OCT4 is known as the gatekeeper of pluripotent embryonic state as it is responsible for maintenance of pluripotency via self-renewal of embryonic stem cells and acquisition of induced pluripotency via somatic cell reprogramming. OCT4 is responsible for oncogenic transformation by disrupting pre-scheduled differentiation programs and in general, favoring evolution of cancer cells into a more aggressive cancer stem cell phenotype. In this study, we have investigated in details, the epigenetic regulatory mechanisms responsible for over-expression and subsequent aberrant function of OCT4 in breast cancer. Expression of OCT4 in breast cancer tissues and cell lines was determined by qRT-PCR, Western blot, immunohistochemistry and immunocytochemistry followed by investigation of pro-tumorigenic properties such as cell proliferation, migration and apoptosis by gene knockdown and treatment with epigenetic modulators. Ectopic treatment of epigenetic modulators was done followed by MS-PCR and chromatin immunoprecipitation. OCT4 is over-expressed in both of the breast cancer cell lines; MCF7 and MDA-MB-231 and its inhibition resulted in drastic decrease in rate of cell proliferation, metastatic ability and induced apoptosis. After treatment with epigenetic modulators, general increase in expression of OCT4 was observed at both gene and protein levels; however, changes of promoter DNA methylation was not found to be significant during OCT4 over-expression. Active histone marks especially H3K4me3 and H3K9acS10p were enriched in the promoter region with very low levels of repressive marks H3K9me3 and H3K27me3 indicating that active histone modifications are the deciding factor in inducing over-expression of OCT4 during breast carcinogenesis. These findings could provide the basis on which epigenetic therapy, targeting reversible epigenetic modifications and their perpetuating enzymes, can be designed for effective treatment of aggressive breast cancer.