Impact of the mitogen-activated protein kinase pathway on parathyroid hormone-related protein actions in osteoblasts.
Parathyroid hormone-related protein (PTHrP) regulates proliferation and differentiation of osteoblastic cells via binding to the parathyroid hormone receptor (PTH-1R). The cAMP-dependent protein kinase A pathway governs the majority of these effects, but recent evidence also implicates the MAPK pathway. MC3T3-E1 subclone 4 cells (MC4) were treated with the MAPK inhibitor U0126 and PTHrP. In differentiated MC4 cells, osteocalcin and bone sialoprotein gene expression were both down-regulated by PTHrP and also by inhibition of the MAPK pathway. PTHrP-mediated down-regulation of PTH-1R mRNA and up-regulation of c-fos mRNA were MAPK-independent, whereas PTHrP stimulation of fra-2 and interleukin-6 (IL-6) mRNA was MAPK-dependent. Luciferase promoter assays revealed that regulation of IL-6 involved the cAMP-dependent protein kinase A and MAPK pathways with a potential minor role of the protein kinase C pathway, and a promoter region containing an activator protein-1 site was necessary for PTHrP-induced IL-6 gene transcription. An alternative pathway, through cAMP/Epac/Rap1/MAPK, mediated ERK phosphorylation but was not sufficient for IL-6 promoter activation. Phosphorylation of the transcription factor CREB was also necessary but not sufficient for PTHrP-mediated IL-6 promoter activity. Most interesting, a bidirectional effect was found with PTHrP increasing phosphorylated ERK in undifferentiated MC4 cells but decreasing phosphorylated ERK in differentiated cells. These data indicate that inactivation of the MAPK pathway shows differential regulation of PTHrP-stimulated activator protein-1 members, blocks PTHrP-stimulated IL-6, and synergistically down-regulates certain osteoblastic markers associated with differentiation. These novel findings indicate that the MAPK pathway plays a selective but important role in the actions of PTHrP.
Chen
Chen
C
Department of Periodontics Prevention Geriatrics, University of Michigan, Ann Arbor, Michigan 48109, USA.
Koh
Amy J
AJ
Datta
Nabanita S
NS
Zhang
Jian
J
Keller
Evan T
ET
Xiao
Guozhi
G
Franceschi
Renny T
RT
D'Silva
Nisha J
NJ
McCauley
Laurie K
LK
D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051921:Fos-Related Antigen-2; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006801:Humans; D058574:Integrin-Binding Sialoprotein; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D015675:Osteocalcin / Q000235:genetics / Q000378:metabolism; D044162:Parathyroid Hormone-Related Protein / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000235:genetics / Q000378:metabolism; D012795:Sialoglycoproteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
D002070:Butadienes; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C482601:Epac protein, mouse; C497872:FOSL2 protein, human; D051921:Fos-Related Antigen-2; D020662:Guanine Nucleotide Exchange Factors; C546871:IBSP protein, human; C546872:Ibsp protein, mouse; D058574:Integrin-Binding Sialoprotein; D015850:Interleukin-6; D009570:Nitriles; D044162:Parathyroid Hormone-Related Protein; D016760:Proto-Oncogene Proteins c-fos; D044168:Receptor, Parathyroid Hormone, Type 1; D012795:Sialoglycoproteins; D014157:Transcription Factors; C113580:U 0126; D015675:Osteocalcin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D020827:rap1 GTP-Binding Proteins