New signaling pathway for parathyroid hormone and cyclic AMP action on extracellular-regulated kinase and cell proliferation in bone cells. Checkpoint of modulation by cyclic AMP.
cAMP signaling, activated by extracellular stimuli such as parathyroid hormone, has cell type-specific effects important for cellular proliferation and differentiation in bone cells. Recent evidence of a second enzyme target for cAMP suggests divergent effects on extracellular-regulated kinase (ERK) activity depending on Epac/Rap1/B-Raf signaling. We investigated the molecular mechanism of the dual functionality of cAMP on cell proliferation in clonal bone cell types. MC3T3-E1 and ATDC5, but not MG63, express a 95-kDa isoform of B-Raf. cAMP stimulated Ras-independent and Rap1-dependent ERK phosphorylation and cell proliferation in B-Raf-expressing cells, but inhibited growth in B-Raf-lacking cells. The mitogenic action of cAMP was blocked by the ERK pathway inhibitor PD98059. In B-Raf-transduced MG63 cells, cAMP stimulated ERK activation and cell proliferation. Thus, B-Raf is the dominant molecular switch that permits differential cAMP-dependent regulation of ERK with important implications for cell proliferation in bone cells. These findings might explain the dual functionality of parathyroid hormone on osteoblastic cell proliferation.
Fujita
Takashi
T
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Japan 573-0101. t-fujita@pharm,setsunan
Meguro
Toru
T
Fukuyama
Ryo
R
Nakamuta
Hiromichi
H
Koida
Masao
M
D016475:3T3 Cells; D000818:Animals; D015152:Blotting, Northern; D001842:Bone and Bones / Q000166:cytology*; D002455:Cell Division; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005799:Genes, Dominant; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D008809:Mice, Inbred C3H; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016716:PC12 Cells; D010281:Parathyroid Hormone / Q000378:metabolism*; D010766:Phosphorylation; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D012886:Skull / Q000378:metabolism; D013997:Time Factors; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
D004791:Enzyme Inhibitors; D010281:Parathyroid Hormone; D020033:Protein Isoforms; D012333:RNA, Messenger; D000242:Cyclic AMP; D020928:Mitogen-Activated Protein Kinases; D020827:rap1 GTP-Binding Proteins