SUV39H1-Mediated DNMT1 is Involved in the Epigenetic Regulation of Smad3 in Cervical Cancer

Background: SMAD3 is a pivotal intracellular mediator for participating in the activation of multiple immune signal pathways. Objective: The epigenetic regulation mechanism of the positive immune factor SMAD3 in cervical cancer remains unknown. Therefore, the epigenetic regulation on SMAD3 is investigated in this study. Methods: The methylation status of SMAD3 was detected by Methylation-Specific PCR (MS-PCR) and Quantitative Methylation-Specific PCR (MS-qPCR) in cervical cancer tissues and cell lines. The underlying molecular mechanisms of SUV39H1-DNMT1-SMAD3 regulation were elucidated using cervical cancer cell lines containing siRNA or/and over-expression systems. The regulation of DNMT1 by SUV39H1 was confirmed using Chromatin Immunoprecipitation-qPCR (ChIP-qPCR). The statistical methods used for comparing samples between groups were paired t-tests and one-way ANOVAs. Results: H3K9me3 protein regulated by SUV39H1 directly interacts with the DNMT1 promoter region to regulate its expression in cervical cancer cells, resulting in the reduced expression of the downstream target gene DNMT1. In addition, DNMT1 mediates the epigenetic modulation of the SMAD3 gene by directly binding to its promoter region. The depletion of DNMT1 effectively restores the expression of SMAD3 in vitro. Moreover, in an in vivo assay, the expression profile of SUV39H1-DNMT1 was found to correlate with SMAD3 expression in accordance with the expression at the cellular level. Notably, the promoter region of SMAD3 was hypermethylated in cervical cancer tissues, and this hypermethylation inhibited the subsequent gene expression. Conclusion: These results indicate that SUV39H1-DNMT1 is a crucial SMAD3 regulatory axis in cervical cancer. SUV39H1-DNMT1 axis may provide a potential therapeutic target for the treatment of cervical cancer.