Neuron-Derived Orphan Receptor-1 (NOR-1) Modulates Vascular Smooth Muscle Cell Proliferation

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Abstract
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.

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