title: β2-adrenergic receptors inhibit the expression of collagen type II in growth plate chondrocytes by stimulating the AP-1 factor Jun-B.
abstract: The sympathetic nervous system can regulate both osteoblast and chondrocyte growth and activity through β(2)-adrenergic receptors (β(2)-AR). We have shown previously that β(2)-AR activate both adenylyl cyclase and mitogen-activated protein kinases ERK1/2 in growth plate chondrocytes prepared from ribs of embryonic E18.5 mice. Here we examined β(2)-AR inhibition of collagen type II (Col II) expression in growth plate chondrocytes and the molecular pathways involved. Stimulation of β(2)-AR by isoproterenol inhibited Col II mRNA and protein levels by ∼50% beginning at 2 h, with both remaining suppressed over 24 h. This inhibition was blocked by propranolol and inhibitors of either MEK1 or PKA. Isoproterenol stimulated an AP-1-luciferase reporter and increased the expression of AP-1 factors c-Fos, Fra-1, Fra-2, c-Jun, and Jun-B but had no effect on Jun-D. Stimulation of AP-1 activity was blocked by inhibitors of MEK1 or PKA. siRNA inhibition of AP-1 factors showed that depletion of only Jun-B attenuated isoproterenol-mediated inhibition of Col II. Transfection with jun-B or c-fos showed selective inhibition of Col II mRNA and a Col II luciferase reporter construct by jun-B. Isoproterenol as well as jun-B overexpression in the chondrocytes also inhibited the expression of Sox-6 mRNA and protein, and depletion of Jun-B abrogated β(2)-AR inhibition of Sox-6. Collectively, these findings demonstrate regulation of chondrocyte differentiation through β(2)-AR mediated by ERK1/2 and PKA stimulation of the AP-1 factor Jun-B that inhibits the expression of Sox-6 and Col II.
authors.affiliation: Dept. of Pharmacology and Toxicology, University of Toronto, Ontario, Canada. jane.mitchell@utoronto.ca
authors.forename: Jane
authors.initials: J
authors.lastname: Mitchell
authors.forename: Lick Pui
authors.initials: LP
authors.lastname: Lai
authors.forename: Faye
authors.initials: F
authors.lastname: Peralta
authors.forename: Yenan
authors.initials: Y
authors.lastname: Xu
authors.forename: Kim
authors.initials: K
authors.lastname: Sugamori
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism*; D024043:Collagen Type II / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004622:Embryo, Mammalian; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D006132:Growth Plate / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D011247:Pregnancy; D016755:Proto-Oncogene Proteins c-jun / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism / Q000502:physiology*; D055755:SOXD Transcription Factors / Q000235:genetics / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000318:Adrenergic beta-Agonists; D024043:Collagen Type II; D016755:Proto-Oncogene Proteins c-jun; D034741:RNA, Small Interfering; D018343:Receptors, Adrenergic, beta-2; D055755:SOXD Transcription Factors; C095939:Sox6 protein, mouse; D018808:Transcription Factor AP-1; D007545:Isoproterenol