TGF-beta1 increases proliferation of airway smooth muscle cells by phosphorylation of map kinases.
BACKGROUND
Airway remodeling in asthma is the result of increased expression of connective tissue proteins, airway smooth muscle cell (ASMC) hyperplasia and hypertrophy. TGF-beta1 has been found to increase ASMC proliferation. The activation of mitogen-activated protein kinases (MAPKs), p38, ERK, and JNK, is critical to the signal transduction associated with cell proliferation. In the present study, we determined the role of phosphorylated MAPKs in TGF-beta1 induced ASMC proliferation.


METHODS
Confluent and growth-arrested bovine ASMCs were treated with TGF-beta1. Proliferation was measured by [3H]-thymidine incorporation and cell counting. Expressions of phosphorylated p38, ERK1/2, and JNK were determined by Western analysis.


RESULTS
In a concentration-dependent manner, TGF-beta1 increased [3H]-thymidine incorporation and cell number of ASMCs. TGF-beta1 also enhanced serum-induced ASMC proliferation. Although ASMCs cultured with TGF-beta1 had a significant increase in phosphorylated p38, ERK1/2, and JNK, the maximal phosphorylation of each MAPK had a varied onset after incubation with TGF-beta1. TGF-beta1 induced DNA synthesis was inhibited by SB 203580 or PD 98059, selective inhibitors of p38 and MAP kinase kinase (MEK), respectively. Antibodies against EGF, FGF-2, IGF-I, and PDGF did not inhibit the TGF-beta1 induced DNA synthesis.


CONCLUSIONS
Our data indicate that ASMCs proliferate in response to TGF-beta1, which is mediated by phosphorylation of p38 and ERK1/2. These findings suggest that TGF-beta1 which is expressed in airways of asthmatics may contribute to irreversible airway remodeling by enhancing ASMC proliferation.
Chen
Gang
G
Division of Respiratory Medicine, Department of Medicine, The University of British Columbia, The Vancouver Coastal Health Research Institute, Vancouver, BC V6H 3Z6, Canada. gang.chen@vch.ca
Khalil
Nasreen
N
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001249:Asthma / Q000378:metabolism; D001798:Blood Proteins / Q000494:pharmacology; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004357:Drug Synergism; D004815:Epidermal Growth Factor / Q000276:immunology / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000276:immunology / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000276:immunology / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000276:immunology / Q000378:metabolism; D014132:Trachea / Q000166:cytology*; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000906:Antibodies; D001798:Blood Proteins; D010982:Platelet-Derived Growth Factor; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D016222:Fibroblast Growth Factor 2; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases