title: Transcriptional regulation of S phase kinase-associated protein 2 by NR4A orphan nuclear receptor NOR1 in vascular smooth muscle cells.
abstract: Members of the NR4A subgroup of the nuclear hormone receptor superfamily have emerged as key transcriptional regulators of proliferation and inflammation. NOR1 constitutes a ligand-independent transcription factor of this subgroup and induces cell proliferation; however, the transcriptional mechanisms underlying this mitogenic role remain to be defined. Here, we demonstrate that the F-box protein SKP2 (S phase kinase-associated protein 2), the substrate-specific receptor of the ubiquitin ligase responsible for the degradation of p27(KIP1) through the proteasome pathway, constitutes a direct transcriptional target for NOR1. Mitogen-induced Skp2 expression is silenced in vascular smooth muscle cells (VSMC) isolated from Nor1-deficient mice or transfected with Nor1 siRNA. Conversely, adenovirus-mediated overexpression of NOR1 induces Skp2 expression in VSMC and decreases protein abundance of its target p27. Transient transfection experiments establish that NOR1 transactivates the Skp2 promoter through a nerve growth factor-induced clone B response element (NBRE). Electrophoretic mobility shift and chromatin immunoprecipitation assays further revealed that NOR1 is recruited to this NBRE site in the Skp2 promoter in response to mitogenic stimulation. In vivo Skp2 expression is increased during the proliferative response underlying neointima formation, and this transcriptional induction depends on the expression of NOR1. Finally, we demonstrate that overexpression of Skp2 rescues the proliferative arrest of Nor1-deficient VSMC. Collectively, these results characterize Skp2 as a novel NOR1-regulated target gene and detail a previously unrecognized transcriptional cascade regulating mitogen-induced VSMC proliferation.
authors.affiliation: Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington, Kentucky 40536.
authors.forename: Florence
authors.initials: F
authors.lastname: Gizard
authors.affiliation: Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington, Kentucky 40536; Graduate Center for Nutritional Sciences, University of Kentucky College of Medicine, Lexington, Kentucky 40536.
authors.forename: Yue
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington, Kentucky 40536.
authors.forename: Hannes M
authors.initials: HM
authors.lastname: Findeisen
authors.affiliation: Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington, Kentucky 40536.
authors.forename: Hua
authors.initials: H
authors.lastname: Qing
authors.affiliation: Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington, Kentucky 40536.
authors.forename: Dianne
authors.initials: D
authors.lastname: Cohn
authors.affiliation: Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington, Kentucky 40536.
authors.forename: Elizabeth B
authors.initials: EB
authors.lastname: Heywood
authors.affiliation: Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington, Kentucky 40536.
authors.forename: Karrie L
authors.initials: KL
authors.lastname: Jones
authors.affiliation: Department of Endocrinology and Diabetes Mellitus, School of Medicine, Fukuoka University, Fukuoka City, Fukuoka 814-0180, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nomiyama
authors.affiliation: Saha Cardiovascular Research Center, University of Kentucky College of Medicine, Lexington, Kentucky 40536; Graduate Center for Nutritional Sciences, University of Kentucky College of Medicine, Lexington, Kentucky 40536. Electronic address: Dennis.Bruemmer@uky.edu.
authors.forename: Dennis
authors.initials: D
authors.lastname: Bruemmer
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D002478:Cells, Cultured; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D051379:Mice; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D058426:Neointima / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D011987:Receptors, Steroid / Q000235:genetics / Q000378:metabolism*; D011988:Receptors, Thyroid Hormone / Q000235:genetics / Q000378:metabolism*; D020218:Response Elements; D044786:S-Phase Kinase-Associated Proteins / Q000096:biosynthesis* / Q000235:genetics; D015533:Transcriptional Activation / Q000235:genetics
chemical_list: C493961:Cdkn1b protein, mouse; D004268:DNA-Binding Proteins; D009419:Nerve Tissue Proteins; C490411:Nr4a3 protein, mouse; D011987:Receptors, Steroid; D011988:Receptors, Thyroid Hormone; D044786:S-Phase Kinase-Associated Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27