Abstract P254: Protein Kinase C Binding Protein 1 Inhibits Hypoxia-Inducible Factor 1 Action in the Heart

Abstract

The response to hypoxia in tissues is regulated by the heterodimeric transcription factor hypoxia inducible factor-1 (HIF-1). We have investigated the transcriptional effects of hypoxia-inducible factor 1 alpha (HIF-1α) in the heart by expressing an oxygen-stable form of HIF-1α in cardiac myocytes of transgenic mice. The result in most cases is regulation of an expected panoply of genes that restore homeostasis during hypoxia, with corresponding phenotypic changes including contractile dysfunction and increased capillary density. In mice that do not show this phenotype, the mRNA for protein kinase c binding protein 1 isoform 2 (PRKCBP1) was much more abundant, as was the protein, and chromatin immunoprecipitation shows a predominant binding of HIF to the promoter of this gene. Sequencing of the promoter region of the PRKCBP1 gene from the two phenotypes revealed an unexpected 480 bp insert in the HIF-resistant animals containing two canonical HIF binding sites. The protein co-immunoprecipitates with HIF and inhibits HIF transcriptional activity in cell culture. In FVB mice, that contain the promoter insert, PRKCBP is induced by ischemia and co-localizes with HIF in the infarct region. It may be responsible for the greater susceptibility of this strain to heart failure after infarction. We have confirmed with genetic, transcriptional, biochemical, and physiological data that Prkcbp1 inhibits HIF activity through direct interaction, in a mechanism mediated by transcriptional control.