Abstract 467: Angiotensin II induces Expression of the Orphan Nuclear Receptor Nor-1 in Vascular Smooth Muscle Cells through cAMP response Element binding Protein Activation
Members of the nuclear hormone receptor superfamily function as key transcriptional regulators of gene expression programs controlling inflammation in vascular diseases. Although much attention has focused on the role of the peroxisome proliferators activated receptor (PPAR) and liver X receptor (LXR) subfamilies, this family comprises a large number of orphan nuclear receptors, whose target genes and physiological functions are unknown. The neuron-derived orphan receptor-1 (Nor-1) belongs to the NR4A subfamily of the nuclear receptor superfamily and has recently been implicated to play a critical role for cell survival, proliferation, and inflammation. Angiotensin II (AngII) has a well-established role to promote vascular smooth muscle cell (SMC) proliferation and inflammation and in the present study we demonstrate AngII-induced Nor-1 expression in SMC. In response to stimulation with AngII quiescent SMC rapidly express Nor-1 mRNA and protein. AngII-induced Nor-1 expression was mediated through an AT1-receptor-dependent mechanism as it was abolished in SMC isolated from AT1A-receptor deficient mice. Transient transfection experiments and 5′-deletion analysis of the Nor-1 promoter demonstrated that AngII-induced Nor-1 expression in SMC is mediated through a transcriptional mechanism dependent on transcription factor binding sites located between -162 to -42 relative to the transcription initiation site. This promoter region contains three putative binding sites for cAMP response element-binding protein (CREB). Site-directed mutagenesis of these CRE sites and overexpression of a dominant-negative CREB mutant in transactivation assays completely abolished AngII-induced Nor-1 promoter activity. Finally, AngII induced Ser133 phosphorylation of CREB and subsequent binding to the CRE sites of the endogenous Nor-1 promoter in chromatin immunoprecipitation assays. These experiments indicate that AngII-induced Nor-1 transcription in SMC is mediated through CREB-dependent transactivation of the Nor-1 promoter and point to a previously unrecognized mechanism by which AngII exerts its proliferative and proinflammatory vascular effects.