Sustained activation of the extracellular signal-regulated kinase pathway is required for extracellular calcium stimulation of human osteoblast proliferation.
Elevated levels of [Ca(2+)](o) in bone milieu as a result of the resorptive action of osteoclasts are implicated in promoting proliferation and migration of osteoblasts during bone remodeling. However, mitogenic effects of [Ca(2+)](o) have only been shown in some, but not all, clonal osteoblast-like cells, and the molecular mechanisms underlying [Ca(2+)](o)-induced mitogenic signaling are largely unknown. In this study we demonstrated for the first time that [Ca(2+)](o) stimulated proliferation of primary human osteoblasts and selectively activated extracellular signal-regulated kinases (ERKs). Neither p38 mitogen-activated protein (MAP) kinase nor stress-activated protein kinase was activated by [Ca(2+)](o). Treatment of human osteoblasts with a MAP kinase kinase inhibitor, PD98059, impaired both basal and [Ca(2+)](o)-stimulated phosphorylation of ERKs and also reduced both basal and [Ca(2+)](o)-stimulated proliferation. [Ca(2+)](o) treatment resulted in two distinctive phases of ERK activation: an acute phase and a sustained phase. An inhibition time course revealed that it was the sustained phase, not the acute phase, that was critical for [Ca(2+)](o)-stimulated osteoblast proliferation. Our results demonstrate that mitogenic responsiveness to [Ca(2+)](o) is present in primary human osteoblasts and is mediated via prolonged activation of the MAP kinase kinase/ERK signal pathway.
Huang
Z
Z
Renal Division and the Division of Bone and Mineral Diseases, Department of Medicine, Washington University, School of Medicine, St. Louis, Missouri 63110, USA. zhuang@im.wustl.edu
Cheng
S L
SL
Slatopolsky
E
E
D016475:3T3 Cells; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009355:Neomycin / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D013936:Thymidine / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
D002413:Cations, Divalent; D004791:Enzyme Inhibitors; D005419:Flavonoids; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D009355:Neomycin; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D002118:Calcium; D013936:Thymidine