Abstract 19657: Histone Variant H2a.z And Cdk9 Differentially Regulate Transcriptional Rates During Cardiac Hypertrophy

Abstract

Genome-wide modifications in basic transcriptional activity underlie cardiac development and disease. We have previously reported that transcriptional regulation by RNA polymerase II (pol II) distinguishes different functional gene categories. In particular, transcription of constitutive, housekeeping, genes is regulated by a pause/release mechanism vs. de novo recruitment of pol II to cardiac-specific and inducible genes during cardiac hypertrophy in mice. Our objective is to identify the epigenetics and nuclear proteins that distinguish these transcriptional patterns. Using chromatin immunoprecipitation-deep sequencing (ChIP-Seq) we identified relatively high levels of H2A.z at the transcriptional start site of all housekeeping and inducible genes that exhibited only minimal or no changes in the heart before or after induction of pressure overload. In contrast, however, all cardiac-specific genes were consistently devoid of H2A.z. We also identified the specific interaction between H2A.z and acidic nuclear protein 32e (ANP32e), which inhibits the dephosphorylation and deactivation of cyclin-dependent kinase 9 (Cdk9) by protein phosphatase 2A (PP2A) and enhances its recruitment to chromatin. Accordingly, cardiac-specific and inducible genes diverge with regards to their regulation by Cdk9, where pressure overload induces a strict decrease vs. increase of Cdk9, respectively, at the promoter and gene body regions of these gene categories. Paradoxically, the reduction in Cdk9 in the former genes is accompanied by an increase in pol II levels, with a net result of little or no change in transcriptional rates. On the other hand, inducible genes are characterized by high levels of de novo recruitment of both pol II and Cdk9, with a sharp increase in transcriptional rates, which was specifically and completely inhibited by knockdown of Cdk9, or its inhibitors 5, 6- dichloro-1-β-D-ribofuranosyl-1H-benzimidazole or inhibitor II. Thus, the differential recruitment of H2A.z and Cdk9 determines the elongational rate of pol II that discriminates between the transcriptional rates of pressure overload-induced v. constitutively-expressed cardiac-specific genes.