Abstract 18622: Protein Kinase C Binding Protein 1 Dampens the Response to Hypoxia-Inducible Factor 1 Alpha in the Heart
The response to hypoxia in tissues is regulated by the heterodimeric transcription factor hypoxia inducible factor-1 (HIF-1). We have investigated the effects of stable HIF-1 in the heart by expressing a cardiac-specific, oxygen-stable HIF-1α mutant. While the result in most cases is upregulation of many genes, with corresponding phenotypic changes including cardiac dilation and increased capillary density, we have identified a novel interaction between HIF-1α and protein kinase c binding protein 1 (prkcbp1), seen specifically in mice lacking the expected phenotypic changes. Expression of the mutated HIF-1α for 1 and 3 days each reveal a bimodal phenotypic response, with most mice demonstrating a 40-80% increase in heart size with left ventricular dilation (LVEDD: 3.05 ±0.4mm vs. 2.09±0.06mm; p=0.006). Approximately 25% of the mice in some matings do not show this robust phenotype. Chromatin immunoprecipitation studies on the dilated hearts revealed expected downstream gene regulation, including VEGF, while the resistant phenotype demonstrated an overwhelming association with the prkcbp1 isoform 2 gene. Co-immunoprecipitation assays have revealed a direct interaction between HIF-1 α and prkcbp1. Additionally, a co-transfection study with the mutated HIF-1α and prkcbp1, and a luciferase reporter cell line sensitive to HIF-1α activity, confirmed the ability of prkcbp1 to substantially down-regulate HIF-1 activity. Preliminary sequence analysis of the upstream promoter region of the two phenotypes shows a 400-500 bp insertion associated with the poor responding mice. The muted phenotype in the subpopulation associated with prkcbp1 suggests that prkcbp1 has a role in oxygen-independent regulatory pathways of HIF, dampening the response to HIF, likely through direct physical interaction. The role of prkcbp1 in normal physiologic response to hypoxia can now be explored; the novel interaction with HIF identified in this study suggests that it may be a target for anti-ischemic and anti-angiogenesis therapies. This work has been supported by NIH grants HL080532, HL073449 and RR16453 as well as AHA Grant-in-Aid 0150586N (to RVS).
- © 2010 by American Heart Association, Inc.