Krüppel-like factor 4 mediates histone deacetylase inhibitor-induced prevention of cardiac hypertrophy

Recently, we reported that histone deacetylase (HDAC) inhibitors block cardiac hypertrophy and that activation of HDAC2, one of the class I HDACs, is required for hypertrophy. In the present study, we tried to find the downstream target of HDAC inhibitor by utilizing cardiomyocytes and H9c2 cells. Both trichostatin A (TSA, class I and II HDAC inhibitor) and SK7041 (SK, class I HDAC blocker) attenuated the expression level and promoter activity of Nppa (natriuretic polypeptide precursor type A) and Myh7 (myosin heavy polypeptide 7), which are fetal genes associated with hypertrophy. Promoter-mapping revealed that the Nppa promoter region from −130 to approximately −105, which contains binding sites for Krüppel-like factor 4 (KLF4), is responsible for the HDAC inhibitor-mediated inhibition. SK-induced repression of Nppa promoter activity was attenuated when the KLF4-binding element was deleted or disrupted. Klf4 was upregulated by HDAC inhibitors, whereas it was down-regulated by phenylephrine in cardiomyocytes or by partial aortic constriction in mice. Klf4 successfully recruited the proximal Nppa promoter region flanking the KLF4-binding element in cardiomyocytes, and the recruitment was reduced by treatment with phenylephrine, which was recovered by SK. Overexpression of Klf4 blocked the agonist-induced increase in cardiomyocyte size, [3H]-leucine incorporation, and Nppa promoter activation. However, promoter activity was not prominently inhibited when the KLF4-binding element was disrupted or when a small inhibitory RNA to KLF4 was transfected into cells. Hypertrophic phenotypes were enhanced in Klf4-knockdown cells. These results suggest that KLF4, a novel anti-hypertrophic transcriptional regulator, mediates the HDAC inhibitor-induced prevention of cardiac hypertrophy.