Abstract 259: Sam68 Regulates Endothelin-Converting Enzyme-1b Expression and Blood Pressure Homeostasis
We have previously reported that E2F2, a transcription factor known for its role in cell cycle, regulates the expression of endothelin-converting enzyme-1b (ECE-1b) in endothelial cells and contributes to the maintenance of vascular contractility and blood pressure (BP). However, the molecular mechanisms underlying this novel, cell-cycle independent function of E2F2 remain largely elusive. In this study, we profiled E2F2 interactome in the nucleus of human umbilical vein endothelial cells by utilizing a proteomic approach. We identified that Sam68, a classic RNA-binding protein and Src kinase substrate, acts as an E2F2-interacting protein; co-immunoprecipitation analyses confirmed that both endogenous and ectopically-expressed Sam68 interact with E2F2. Overexpression of Sam68 repressed whereas knockdown of Sam68 increased E2F2-induced ECE-1b promoter activity and mRNA expression. Chromatin immunoprecipitation assays further confirmed that E2F2 and Sam68 co-localize on ECE-1b promoter, indicating that ECE-1b is a direct transcriptional target of E2F2 and Sam68. In vivo, Sam68 knockout (KO) mice displayed a significantly lowered BP as compared to WT littermates (tail-cuff measurements of mean BP, KO vs. WT: 104 ± 6 vs. 123 ± 7 mmHg, n=25 males of age 4-6 months, P<0.05). Together, our studies have revealed a previously unknown function of Sam68 as a transcriptional co-repressor of E2F2 and a critical regulator of BP homeostasis.
- © 2012 by American Heart Association, Inc.