Egr-1 mRNA induction by medium flow involves mRNA stabilization and is enhanced by the p38 inhibitor SB203580 in osteoblast-like cells.
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.
Ogata
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Division of Advanced Molecular Medicine, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan. oga.mph@mri.tmd.ac.jp
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
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