Neuron-derived orphan receptor-1 (NOR-1) modulates vascular smooth muscle cell proliferation

Martinez-Gonzalez J, Rius J, Castellܳ A, Cases-Langhoff C and Badimon L
Source: Circ Res
Publication Date: (2003)
Issue: 92: 96-103
Research Area:
The understanding of the molecular mechanisms involved in vascular smooth muscle cell (VSMC) activation and dedifferentiation requires an accurate mapping of the cascade of transcription factors induced by atherogenic stimuli. In the present study the authors identified neuron-derived orphan receptor-1 (NOR-1) as an early response gene in VSMCs. The NOR-1 promoter contains three putative CRE sites. To further elucidate the involvement of CRE motifs in the upregulation of NOR-1 by serum, NIH3T3 cells were nucleofected with luciferase expression plasmids encoding either the wild type promoter or the promoter without the three CRE sites. Serum increased NOR-1 promoter activity in cells transfected with the wild type promoter but not with the mutant version. The results indicate a key role for the CRE motifs present in NOR-1 promoter in NOR-1 upregulation produced by mitogenic stimuli.
Vascular smooth muscle cells (VSMCs) migration and proliferation play a key role in the pathophysiology of cardiovascular disease. However, the transcription factors that regulate VSMC activation are not completely characterized. By a mRNA-differential display approach, we have identified neuron-derived orphan receptor-1 (NOR-1), a transcription factor within the NGFI-B subfamily of nuclear receptors, as a immediate-early gene in VSMCs. Two NOR-1 isoforms (alpha and beta) were identified and cloned from serum-induced porcine VSMC that shared high homology with the human isoforms. Northern blot analysis revealed a strong and transient (1 to 6 hours) upregulation of NOR-1 in both porcine and human coronary SMCs by growth factors (serum, platelet-derived growth factor-BB, and epidermal growth factor) and alpha-thrombin but not by cytokines. NOR-1 upregulation is processed through G protein-coupled receptors and tyrosine kinase receptors, and involves Ca2+ mobilization, protein kinase C activation, and the mitogen-activated protein kinase pathway. This induction was closely dependent of the cAMP response elements present in NOR-1 promoter as transfection assays indicate. Human coronary atherosclerotic lesions overexpress NOR-1, and balloon angioplasty transiently induces NOR-1 in porcine coronary arteries with a pattern similar to that observed in VSMCs in culture. Antisense oligonucleotides against NOR-1 inhibited human coronary SMC proliferation (reduced de novo DNA synthesis, cell cycle progression, and VSMC wound repair) as efficiently as antisense against the protooncogene c-fos. These results show that NOR-1 modulates VSMC proliferation, and suggest that this transcription factor may play a role in both spontaneous and accelerated atherosclerosis.