title: Egr-1 mRNA induction by medium flow involves mRNA stabilization and is enhanced by the p38 inhibitor SB203580 in osteoblast-like cells.
abstract: OBJECTIVE
  Mechanical stimuli are important for maintaining organ structure and tissue function. To elucidate signalling pathways activated by mechanical stimuli, the contribution of mRNA stabilization to induction of egr-1 mRNA by medium flow was examined and the mechanisms responsible for stabilization were analysed. An early-response gene that encodes a transcription factor, egr-1, activates transcription of several genes in response to mechanical stimuli, and was therefore selected to resolve how early-induced signals are integrated and connected to subsequent response.
  
  
  METHODS
  Mouse osteoblast-like MC3T3E1 cells were stably transfected with the chloramphenicol acetyltransferase (CAT) gene linked to the egr-1 promoter, and inductions of endogenous egr-1 and transfected CAT mRNA following medium flow were compared using real-time reverse transcriptase PCR. The mechanism of induction was examined using a transcription inhibitor and mitogen-activated protein (MAP) kinase inhibitors. Activation of MAP kinases by medium flow was investigated using western blotting.
  
  
  RESULTS
  Induction of egr-1 mRNA by medium flow was twofold higher than CAT mRNA induction. Induction of egr-1 mRNA was also observed in cells pre-treated with transcription inhibitor. The p38 inhibitor SB203580 enhanced induction of egr-1 mRNA by medium flow. Extracellular signal regulated kinase (ERK), p38 and c-Jun N-terminal kinase (JNK) were activated by medium flow.
  
  
  CONCLUSIONS
  A considerable part of egr-1 mRNA induction by medium flow may be due to mRNA stabilization. The p38 inhibitor SB203580 enhances induction.
authors.affiliation: Division of Advanced Molecular Medicine, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan. oga.mph@mri.tmd.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Ogata
mesh_terms: D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D002070:Butadienes / Q000494:pharmacology; D002478:Cells, Cultured; D051766:Early Growth Response Protein 1 / Q000096:biosynthesis* / Q000235:genetics; D004789:Enzyme Activation / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology*; D048670:MAP Kinase Kinase 4 / Q000037:antagonists & inhibitors / Q000378:metabolism; D040542:Mechanotransduction, Cellular / Q000502:physiology; D051379:Mice; D009570:Nitriles / Q000494:pharmacology; D010006:Osteoblasts / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D011401:Promoter Regions, Genetic; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011725:Pyridines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D000873:Anthracenes; D002070:Butadienes; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D007093:Imidazoles; D009570:Nitriles; D047428:Protein Kinase Inhibitors; D011725:Pyridines; D012333:RNA, Messenger; C113580:U 0126; C432165:pyrazolanthrone; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; C093642:SB 203580