title: Parathyroid hormone inhibits phosphorylation of mitogen-activated protein kinase (MAPK) ERK1/2 through inhibition of c-Raf and activation of MKP-1 in osteoblastic cells.
abstract: Parathyroid hormone (PTH) regulation of mitogen-activated protein kinases (MAPK) ERK1/2 contributes to PTH regulation of osteoblast growth and apoptosis. We investigated the mechanisms by which PTH inhibits ERK1/2 activity in osteoblastic UMR 106-01 cells. Treatment with PTH significantly inhibited phosphorylated ERK1/2 between 5 and 60 min. Transient transfection of cells with a cDNA encoding MAPK phosphatase-1 (MKP-1) resulted in 30-40% inhibition of pERK1/2; however MKP-1 protein levels were only significantly stimulated by PTH after 30 mins, suggesting another mechanism for the early phase of pERK1/2 inhibition. The active upstream kinase c-Raf phosphorylation at serine 338 (ser(338)) was significantly inhibited by PTH treatment within 5 min and transfection of the cells with constitutively-active c-Raf blocked PTH inhibition of pERK1/2. Inhibition of pERK1/2 and phosphor-c-Raf were seen when cells were treated with PTH(1-34) or PTH(1-31) analogues that stimulate cAMP, but not with PTH(3-34), PTH(7-34) or PTH(18-48) that do not stimulate cAMP. Stimulation of the cells with forskolin or 8BrcAMP also inhibited pERK1/2 and c-Raf.p338. Our results suggest that rapid PTH inhibition of ERK1/2 activity is mediated by PKA dependent inhibition of c-Raf activity and that stimulation of MKP-1 may contribute to maintaining pERK1/2 inhibition over prolonged time.
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, 1 King's College Circle, Room 4342, Toronto, Ontario, Canada M5S 1A8, Canada.
authors.forename: Lick Pui
authors.initials: LP
authors.lastname: Lai
authors.forename: Jane
authors.initials: J
authors.lastname: Mitchell
mesh_terms: D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D054638:Dual Specificity Phosphatase 1 / Q000378:metabolism*; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D010006:Osteoblasts / Q000187:drug effects / Q000201:enzymology*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013997:Time Factors
chemical_list: D010281:Parathyroid Hormone; D000242:Cyclic AMP; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D054638:Dual Specificity Phosphatase 1