Role of Rho in Ca(2+)-insensitive contraction and paxillin tyrosine phosphorylation in smooth muscle.
We investigated whether Rho activation is required for Ca(2+)-insensitive paxillin phosphorylation, myosin light chain (MLC) phosphorylation, and contraction in tracheal muscle. Tyrosine-phosphorylated proteins have been implicated in the Ca(2+)-insensitive contractile activation of smooth muscle tissues. The contractile activation of tracheal smooth muscle increases tyrosine phosphorylation of the cytoskeletal proteins paxillin and focal adhesion kinase. Paxillin is implicated in integrin-mediated signal transduction pathways that regulate cytoskeletal organization and cell motility. In fibroblasts and other nonmuscle cells, paxillin tyrosine phosphorylation depends on the activation of Rho and is inhibited by cytochalasin, an inhibitor of actin polymerization. In permeabilized muscle strips, we found that ACh induced Ca(2+)-insensitive contraction, MLC phosphorylation, and paxillin tyrosine phosphorylation. Ca(2+)-insensitive contraction and MLC phosphorylation induced by ACh were inhibited by C3 transferase, an inhibitor of Rho activation; however, C3 transferase did not inhibit paxillin tyrosine phosphorylation. Ca(2+)-insensitive paxillin tyrosine phosphorylation was also not inhibited by the Rho kinase inhibitor Y-27632, by cytochalasin D, or by the inhibition of MLC phosphorylation. We conclude that, in tracheal smooth muscle, Rho mediates Ca(2+)-insensitive contraction and MLC phosphorylation but that Rho is not required for Ca(2+)-insensitive paxillin tyrosine phosphorylation. Paxillin phosphorylation also does not require actomyosin activation, nor is it inhibited by the actin filament capping agent cytochalasin D.
Mehta
D
D
Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46202-5120, USA.
Tang
D D
DD
Wu
M F
MF
Atkinson
S
S
Gunst
S J
SJ
D036002:ADP Ribose Transferases / Q000494:pharmacology; D000818:Animals; D001905:Botulinum Toxins; D003014:Clostridium botulinum; D015638:Cytochalasin D / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000187:drug effects / Q000378:metabolism*; D004285:Dogs; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D051419:Paxillin; D010750:Phosphoproteins / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014132:Trachea / Q000187:drug effects / Q000378:metabolism; D014443:Tyrosine / Q000187:drug effects / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*
D003598:Cytoskeletal Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D051419:Paxillin; D010750:Phosphoproteins; D015638:Cytochalasin D; D014443:Tyrosine; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins; D020741:rho GTP-Binding Proteins