Abstract 211: Sam68 Is a Transcriptional Repressor of Endothelin-Converting Enzyme-1b Gene and Regulates Blood Pressure
We have recently reported that E2F2, a transcription factor known for its role in cell proliferation and apoptosis, regulates the expression of endothelin-converting enzyme-
1b (ECE-1b) in endothelial cells and contributes to the maintenance of vascular contractility and blood pressure. However, the molecular mechanisms that underlie this novel, cell-cycle independent function of E2F2 remain largely elusive. In this current study, we profiled E2F2 interactome in the nucleus of human umbilical vein endothelial cells by utilizing a proteomic approach. Of 20 E2F2-interacting proteins identified is the Sam68, a classic RNA-binding protein known as a Src kinase substrate. Both endogenous and ectopically expressed Sam68 interact with E2F2 as confirmed by coimmunoprecipitation. Overexpression of Sam68 repressed whereas knockdown of Sam68 increased E2F2-induced ECE-1b promoter activity and mRNA expression. Chromatin immunoprecipitation analyses further confirmed that E2F2 and Sam68 colocalize 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 blood pressure (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 in the regulation of ECE-1b expression. Sam68 may link endothelial Src kinase pathways to BP regulation
- © 2012 by American Heart Association, Inc.