title: Tumor necrosis factor-alpha-induced activation of RhoA in airway smooth muscle cells: role in the Ca2+ sensitization of myosin light chain20 phosphorylation.
abstract: Tumor necrosis factor-alpha (TNF), an inflammatory cytokine, has a potentially important role in the pathogenesis of bronchial asthma and may contribute to airway hyper-responsiveness. Recent evidence has revealed that TNF can increase the Ca(2+) sensitivity of agonist-stimulated myosin light chain(20) (MLC(20)) phosphorylation and contractility in guinea pig airway smooth muscle (ASM). In the present study, the potential intracellular pathways responsible for this TNF-induced Ca(2+) sensitization were investigated. In permeabilized cultured guinea pig ASM cells, recombinant human TNF stimulated an increase in Ca(2+)-activated MLC(20) phosphorylation under Ca(2+) "clamp" conditions. This increased MLC(20) phosphorylation was inhibited by preincubation with the Rho-kinase inhibitor Y27632. TNF also increased the proportion of GTP-bound RhoA, as measured using rhotekin Rho-binding domain, in a time course compatible with a role in the TNF-induced Ca(2+) sensitization. In cultured human ASM cells, recombinant human TNF also activated RhoA with a similar time course. In addition, TNF stimulated phosphorylation of the regulatory subunit of the myosin phosphatase, which was inhibited by Y27632. Although human ASM cells expressed both receptor subtypes, TNF-R1 and TNF-R2, the activation of RhoA was predominantly via stimulation of the TNF-R1, although RhoA did not immunoprecipitate with the TNF-R1. In conclusion, the TNF-induced increase in the Ca(2+) sensitivity of MLC(20) phosphorylation is through stimulation of the TNF-R1 receptor and via a RhoA/Rho-kinase pathway leading to inhibition of the myosin light chain phosphatase. This intracellular mechanism may contribute to TNF-induced airway hyper-responsiveness.
authors.affiliation: Department of Biomedical Sciences, Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom.
authors.forename: Irene
authors.initials: I
authors.lastname: Hunter
authors.forename: Hannah J
authors.initials: HJ
authors.lastname: Cobban
authors.forename: Peter
authors.initials: P
authors.lastname: Vandenabeele
authors.forename: David J
authors.initials: DJ
authors.lastname: MacEwan
authors.forename: Graeme F
authors.initials: GF
authors.lastname: Nixon
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D006168:Guinea Pigs; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D018994:Myosin Light Chains / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D014132:Trachea / Q000166:cytology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D018994:Myosin Light Chains; D014409:Tumor Necrosis Factor-alpha; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein; D002118:Calcium