Abstract 373: Regulation of Hypoxia by Chromatin Reader Protein Kinase C Binding Protein 1 (PRKCBP1)

Abstract

PRKCBP1 (also known as RACK7 and Zmynd8) is a polyvalent chromatin reader known to cooperatively bind acetylated and methylated nucleosomes. Recently it has been shown to regulate transcription and cancer progression by coordinating histone methylation modifications affecting enhancer and promoter regions of genes. The role of PRKCBP1 in the cardiac myocardium is unexplored. Hypoxia-inducible factor 1α (HIF-1α) upregulation and stabilization is a common feature of both cancer and myocardial ischemia, promoting cellular functions such as proliferation, glucose metabolism and angiogenesis. Here we investigated the mechanism by which PRKCBP1 modulates the cardiac hypoxic response. We hypothesize that PRKCBP1 inhibits the HIF-1 response in the hypoxic heart by reducing enhancer activity of HIF-1 target genes and altering availability of HIF-1 binding sites. We have found that in transgenic mice with a mutation that increases HIF-induced expression of PRKCBP, the effect of induced oxygen-stable HIF is markedly diminished. These mice did not exhibit the typical HIF-1 over-expression phenotype of dilated vessels, increased heart size and reduced ventricular function. Semi-quantitative rtPCR analysis of mouse neonatal cardiomyocytes transfected with CMV-driven expression plasmids for PRKCBP1 and oxygen-stable HIF-1α showed striking reduction of multiple HIF-1 target genes such as PDK1 (45% reduction relative to Ehbp1) compared to the HIF-1α plasmid alone. RNAi mediated knockdown of PRKCBP1 removed this negative regulation (65% increase). Analysis of human PRKCBP1 and HIF-1α ChIP-seq data indicate that PRKCBP1 binds to the enhancer of 78% of HIF-1 regulated genes. ATAC-seq data suggest that PRKCBP1 affects genome-wide chromatin accessibility, with loci-specific modifications at numerous HIF-1 target genes, such as EGLN3. These data suggest that PRKCBP1 may be acting both by modulating enhancer activity in cis - to HIF-1 target genes and by preventing HIF-1 binding to hypoxia response elements of target genes. We have discovered a new regulator of HIF-1 action that modifies the hypoxic response, likely through chromatin remodeling. This new form of regulation may modify the pathophysiology of ischemia and provide new targets for therapy.