Parathyroid hormone (PTH) down-regulates PTH/PTH-related protein receptor gene expression in UMR-106 osteoblast-like cells via a 3',5'-cyclic adenosine monophosphate-dependent, protein kinase A-independent pathway.
Parathyroid hormone (PTH) regulates osteoblast function via a G protein-linked PTH/PTH-related protein (PTHrP) receptor. We have studied the mechanisms of PTH/PTHrP receptor gene repression by PTH in UMR-106 osteoblast-like cells. Inhibition of PTH/PTHrP receptor mRNA expression by rat (r) PTH(1-34) and Insulin-like growth factor-I (IGF-I) at 10(-7)M was significant at 1 h and 3 h, and maximal at 2 h and 6 h. A maximal decrease in receptor mRNA abundance by rPTH(1-34) and IGF-I was maintained for 24 h. Inhibition of receptor gene expression by rPTH(1-34) was mimicked in UMR-106 cells by the addition of forskolin (an adenylyl cyclase activator), or 8-(4-chlorophenylthio)-adenine 3',5'-cyclic monophosphate (8-pCPTcAMP; a cAMP analogue). Although H89, a selective protein kinase A (PKA) inhibitor, completely inhibited PKA activity stimulated by rPTH(1-34), forskolin or 8-pCPTcAMP, suppression of PTH/PTHrP receptor mRNA synthesis induced by these substances in UMR-106 cells was not affected by H89. In primary osteoblast cultures, rPTH(1-34) inhibited synthesis of PTH/PTHrP receptor mRNA irrespective of H89. The down-regulation effect of rPTH(1-34) was also unaltered by PD98059 (an extracellularly regulated kinase 1/2 mitogen-activated protein kinase pathway inhibitor). Pretreatment with cycloheximide, a protein synthesis inhibitor, did not alter the inhibition of PTH/PTHrP receptor mRNA expression by rPTH(1-34), indicating that receptor mRNA suppression does not require new protein synthesis. Transcriptional activation of PTH/PTHrP receptor gene promoter (U3P or U4P)-luciferase constructs was decreased by rPTH(1-34), forskolin and 8-pCPTcAMP irrespective of H89. Thus, PTH transcriptionally down-regulates PTH/PTHrP receptor gene expression in osteoblast-like cells via a cAMP-dependent, PKA-independent pathway.
Kawane
T
T
Department of Biochemistry, Ohu University School of Dentistry, Koriyama 963-8611, Japan.
Mimura
J
J
Yanagawa
T
T
Fujii-Kuriyama
Y
Y
Horiuchi
N
N
D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D003864:Depression, Chemical; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D010006:Osteoblasts / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism / Q000494:pharmacology*; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D018016:Receptors, Parathyroid Hormone / Q000235:genetics*; D015398:Signal Transduction / Q000502:physiology*; D013449:Sulfonamides; D013873:Thionucleotides / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D007546:Isoquinolines; D010281:Parathyroid Hormone; D010446:Peptide Fragments; D012333:RNA, Messenger; D018016:Receptors, Parathyroid Hormone; D013449:Sulfonamides; D013873:Thionucleotides; D005576:Colforsin; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D007334:Insulin-Like Growth Factor I; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide