P38 and activating transcription factor-2 involvement in osteoblast osmotic response to elevated extracellular glucose.
Poorly controlled or untreated type I diabetes mellitus is characterized by hyperglycemia and is associated with decreased bone mass and osteoporosis. We have demonstrated that osteoblasts are sensitive to hyperglycemia-associated osmotic stress and respond to elevated extracellular glucose or mannitol by increasing c-jun and collagen I expression. To determine whether MAPKs are involved in this response, MC3T3-E1 osteoblasts were treated with 16.5 mm glucose, mannitol, or contrast dye for 1 h. Immunoblotting of phosphorylated p38 demonstrated activation of p38 MAPK by hyperosmotic stress in vitro and in vivo. Activation peaked at 20 min, remained detectable after 24 h, and was protein kinase C-independent. Activating transcription factor-2 (ATF-2) activation followed the same pattern as phospho-p38. Transactivation of cAMP response element (CRE)- and c-jun promoter (containing a CRE-like element)-reporter constructs increased following hyperosmotic treatment. SB 203580 (a p38 MAPK inhibitor) blocked ATF-2 phosphorylation, CRE transactivation, and c-jun promoter activation. Hyperosmotic activation of collagen I promoter activity was also inhibited by SB 203580, consistent with the involvement of c-jun in collagen I up-regulation. Therefore, we propose that hyperglycemia-induced increases in p38 MAPK activity and ATF-2 phosphorylation contribute to CRE activation and modulation of c-jun and collagen I expression in osteoblasts.
Zayzafoon
Majd
M
Department of Physiology, Michigan State University, East Lansing, Michigan 48824, USA.
Botolin
Sergiu
S
McCabe
Laura R
LR
D016475:3T3 Cells; D051698:Activating Transcription Factor 2; D000818:Animals; D003094:Collagen / Q000235:genetics; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D016758:Genes, jun / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology*; D008353:Mannitol / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009995:Osmosis; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases
D051698:Activating Transcription Factor 2; C497106:Atf2 protein, mouse; D017362:Cyclic AMP Response Element-Binding Protein; D011994:Recombinant Proteins; D014157:Transcription Factors; D008353:Mannitol; D003094:Collagen; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D005947:Glucose