Mechanisms of mitogen-activated protein kinase inhibition by parathyroid hormone in osteoblast-like cells.
Parathyroid hormone (PTH) dose dependently inhibits growth factor- and stress-induced osteoblast proliferation via inactivating mitogen-activated protein kinase (MAPK) signaling pathways. Osteoblasts have recently been shown to express MAPK phosphatase (MKP)-1, a dual-specific phosphatase inactivator of MAPK. Investigated was the role of MKPs in the PTH-induced attenuation of MAPK and Jun N-terminal kinase (JNK) signaling in osteoblast-like UMR106-01 cells. PTH induced a persistent inhibition of p42/44 MAPK and JNK phosphorylation starting at 10 min of incubation and lasting for at least 2 h. Actinomycin D affected both p42/44 MAPK and JNK dephosphorylation by PTH, suggesting a transcription-dependent mechanism of action. PTH rapidly and transiently induced expression of MKP-1. MKP-1 mRNA was already elevated after 10 min of 10(-7) M PTH incubation, reached maximal expression after 30 to 60 min, and remained elevated after 4 h. MKP-1 protein was also upregulated within 30 to 60 min of PTH administration. The protein kinase A inhibitor H89 partly reduced PTH-induced MKP-1 expression, but the protein kinase C inhibitor bisindolylmaleimide had no effect, suggesting that PTH induces MKP-1 mainly via the protein kinase A pathway. MKP-2 mRNA was downregulated after 2 h after an early period of induction, and MKP-3 mRNA was immediately reduced. Ro 318-220 did not affect PTH-induced MAPK inactivation but effectively blocked JNK dephosphorylation. The time course of PTH-induced MKP-1 protein expression closely correlated with JNK dephosphorylation. PTH attenuates the stress-induced JNK signaling pathway in osteoblasts via induction of MKP-1 synthesis but inhibits the p42/44 MAPK pathway mainly via transcription-independent mechanisms.
Hömme
Meike
M
University Children's Hospital, Division of Pediatric Nephrology, University of Heidelberg, Germany. meike_hoemme@med.uni-heidelberg.de <meike_hoemme@med.uni-heidelberg.de>
Schmitt
Claus P
CP
Mehls
Otto
O
Schaefer
Franz
F
D000818:Animals; D018797:Cell Cycle Proteins / Q000096:biosynthesis; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D003609:Dactinomycin / Q000494:pharmacology; D054638:Dual Specificity Phosphatase 1; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D017874:Immediate-Early Proteins / Q000096:biosynthesis; D007211:Indoles / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors*; D010006:Osteoblasts / Q000201:enzymology*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000096:biosynthesis; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D054645:Protein Phosphatase 1; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D013997:Time Factors
D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D017874:Immediate-Early Proteins; D007211:Indoles; D010281:Parathyroid Hormone; D011500:Protein Synthesis Inhibitors; D011994:Recombinant Proteins; D003609:Dactinomycin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; C517019:DUSP1 protein, human; D054638:Dual Specificity Phosphatase 1; C517021:Dusp1 protein, rat; D017027:Protein Tyrosine Phosphatases; C064758:Ro 31-8220