Abstract
Platelet-derived growth factors are a family of potent mitogens and chemoattractants for fibroblasts and other cells of mesenchymal origin. Platelet-derived growth factor (PDGF) dimeric ligands (composed of A-, B-, C-, and D-chains) exert their biological activity through high affinity interactions with cell surface receptor subunits (alpha and beta). PDGF-receptor-alpha is widely implicated in the pathogenesis of hyperplastic fibrotic disease, yet the molecular mechanisms controlling its expression in response to injury are poorly understood. Here we show that PDGF-R alpha expression is induced in fibroblasts by mechanical injury and interleukin (IL)-1beta, which was abolished by neutralizing IL-1beta antibodies in the culture supernatant or inhibitors of NF-kappaB. Chromatin immunoprecipitation and electrophoretic mobility shift assays revealed the existence of a new NF-kappaB binding site at -531/-521 bp in the PDGF-R alpha promoter. We have recently shown that ATF-4 is also induced by injury (Malabanan, K. P., Kanellakis, P., Bobik, A., and Khachigian, L. M. (2008) Circ. Res. 103, 378-387), and we demonstrate here that ATF-4 binds a novel element -259/-254 and stimulates PDGF-R alpha transcription. ATF-4 and NF-kappaB interact, occupy the PDGF-R alpha promoter, and induce PDGF-R alpha transcription in a cooperative manner. IL-1beta facilitates the dissociation of histone deacetylase (HDAC)-1/2 from the PDGF-R alpha promoter, whereas the HDAC inhibitors suberoylanilide hydroxamic acid and trichostatin A potentiate IL-1beta induction of PDGF-R alpha transcription. These findings, taken together, demonstrate that injury stimulates IL-1beta secretion by fibroblasts, which activates NF-kappaB and ATF-4 and stimulates interaction with the PDGF-R alpha promoter, triggering PDGF-R alpha transcription. Physical and functional interactions between NF-kappaB and ATF-4 have not been reported in any gene. This is also the first report of HDAC regulation of PDGF-R alpha transcription.