title: Platelet-derived growth factor-induced stabilization of cyclooxygenase 2 mRNA in rat smooth muscle cells requires the c-Src family of protein-tyrosine kinases.
abstract: Cyclooxygenases (COXs) are crucial rate-limiting enzymes required for the biosynthesis of prostaglandins. COX-2 is an inducible isoform of this enzyme, which is believed to play important roles in the development of atherosclerotic vascular disease. We found that COX-2 expression rapidly increases in response to various signaling events, including activation of the platelet-derived growth factor (PDGF) pathway. Activation of PDGF receptor (PDGFR) in rat aortic vascular smooth muscle cells leads to c-Src-dependent stabilization of COX-2 mRNA requiring an AU-rich region within the 3'-untranslated region of this transcript. This regulation correlates with tyrosine phosphorylation of the RNA-associated protein, CUG-binding protein 2 (CUGBP2), which appears to enhance its interaction with COX-2 mRNA. Site-directed mutagenesis of putative tyrosine phosphorylation sites in CUGBP2 identified tyrosine 39 as a c-Src target, and a CUGBP2 with a mutated tyrosine 39 displayed an attenuated ability to bind COX-2 mRNA. We further show that silencing of CUGBP2 with specific small interference RNAs significantly reduces PDGF-dependent induction of COX-2 at both mRNA and protein levels. Furthermore, forced expression of CUGBP2 or constitutively active c-Src leads to stabilization of co-expressed COX-2 mRNA. Finally, in vitro RNA decay assay demonstrates that CUGBP2 is functionally required for the stabilization of COX-2 mRNA. Therefore, our data suggest that tyrosine phosphorylation of CUGBP2 is an important underlying mechanism for the ability of PDGFR/c-Src signaling to control the stability of COX-2 mRNA.
authors.affiliation: Department of Pharmacology, Emory University, 1510 Clifton Road, Atlanta, GA 30322, USA. kxu@emory.edu
authors.forename: Kaiming
authors.initials: K
authors.lastname: Xu
authors.forename: Chad M
authors.initials: CM
authors.lastname: Kitchen
authors.forename: Hui-Kuo G
authors.initials: HK
authors.lastname: Shu
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Murphy
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000235:genetics* / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D016297:Mutagenesis, Site-Directed; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000201:enzymology*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000235:genetics / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D020871:RNA Stability / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D016601:RNA-Binding Proteins / Q000378:metabolism; D051381:Rats; D020218:Response Elements
chemical_list: D009419:Nerve Tissue Proteins; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D019000:Phosphotyrosine; D051546:Cyclooxygenase 2; C489691:Ptgs2 protein, rat; D016392:Proto-Oncogene Proteins pp60(c-src)