Recent studies have identified a polymorphism in the ECE-1b promoter (−338C/A) that is strongly associated with hypertension in women, and the polymorphism is located in a consensus binding sequence for the E2F family of transcription factors. E2F proteins are crucially involved in cell-cycle regulation, but their roles in cardiovascular function are poorly understood. Here, we investigated the potential role of E2F2 in blood pressure (BP) regulation.
Methods and Results
Tail-cuff measurements of systolic and diastolic BP were significantly higher in E2F2-null (E2F2−/−) mice than in their wild-type (WT) littermates, and in ex vivo ring assays, aortas from the E2F2−/− mice exhibited significantly greater contractility in response to big endothelin-1 (BigET-1). BigET-1 is activated by endothelin converting enzyme-1 (ECE-1), and mRNA levels of ECE-1b, the repressive ECE-1 isoform, were significantly lower in E2F2−/− mice than in WT mice. In endothelial cells, chromatin-immunoprecipitation (ChIP) assays confirmed that E2F2 binds the ECE-1b promoter, and promoter-reporter assays indicated that E2F2 activates ECE-1b transcription. Furthermore, loss or downregulation of E2F2 led to a decline in ECE-1b levels, to higher levels of the membranous ECE-1 isoforms (i.e., ECE-1a, -1c, and -1d), and to deregulated ECE-1 activity. Lastly, Sam68 co-immunopreciptated with E2F2, occupied the ECE-1b promoter (ChIP), and repressed E2F2-mediated ECE-1b promoter activity (promoter-reporter assays).
Our results identify a cell cycle-independent mechanism by which E2F2 regulates endothelial function, arterial contractility, and BP.