HDAC2- and EZH2-Mediated Histone Modifications Induce PDK1 Expression through miR-148a Downregulation in Breast Cancer Progression and Adriamycin Resistance

Background: Breast Cancer has one of highest morbidity and mortality rates for women. Abnormalities regarding Epigenetics modification and pyruvate dehydrogenase kinase 1 (PDK1)-induced unusual metabolism contribute to breast Cancer progression and chemotherapy resistance. However, the role and mechanism of epigenetic change in regulating PDK1 in breast Cancer remains to be elucidated.

Methods: Gene set enrichment analysis (GSEA) and Pearson's correlation analysis were performed to analyze the relationship between histone deacetylase 2 (HDAC2), enhancer of zeste homologue 2 (EZH2), and PDK1 in database and human breast Cancer tissues. Dual luciferase reporters were used to test the regulation between PDK1 and miR-148a. HDAC2 and EZH2 were found to regulate miR-148a expression through Western blotting assays, qRT-PCR and co-immunoprecipitation assays. The effects of PDK1 and miR-148a in breast Cancer were investigated by immunofluorescence (IF) assay, Transwell assay and flow cytometry assay. The roles of miR-148a/PDK1 in tumor growth were investigated in vivo.

Results: We found that PDK1 expression was upregulated by epigenetic alterations mediated by HDAC2 and EZH2. At the post-transcriptional level, PDK1 was a new direct target of miR-148a and was upregulated in breast Cancer cells due to miR-148a suppression. PDK1 overexpression partly reversed the biological function of miR-148a-including miR-148a's ability to increase cell sensitivity to Adriamycin (ADR) treatment-inhibiting cell glycolysis, invasion and epithelial-mesenchymal transition (EMT), and inducing Apoptosis and repressing tumor growth. Furthermore, we identified a novel mechanism: DNMT1 directly bound to EZH2 and recruited EZH2 and HDAC2 complexes to the promoter region of miR-148a, leading to miR-148a downregulation. In breast Cancer tissues, HDAC2 and EZH2 protein expression levels also were inversely correlated with levels of miR-148a expression.

Conclusion: Our study found a new regulatory mechanism in which EZH2 and HDAC2 mediate PDK1 upregulation by silencing miR-148a expression to regulate Cancer development and Adriamycin resistance. These new findings suggest that the HDAC2/EZH2/miR-148a/PDK1 axis is a novel mechanism for regulating Cancer development and is a potentially promising target for therapeutic options in the future.