Calponin and mitogen-activated protein kinase signaling in differentiated vascular smooth muscle.
Contraction of smooth muscle cells is generally assumed to require Ca2+/calmodulin-dependent phosphorylation of the 20-kDa myosin light chains. However, we report here that in the absence of extracellular calcium, phenylephrine induces a contraction of freshly isolated ferret aorta cells in the absence of increases in intracellular ionized calcium or light chain phosphorylation levels but in the presence of activation of mitogen-activated protein kinase. A protein at 36 kDa co-immunoprecipitated with the mitogen-activated protein kinase and was identified as the actin-binding protein, calponin, by immunoblot. An overlay assay further confirmed an interaction between the kinase and calponin, even though the kinase did not phosphorylate calponin in vitro. Calponin also co-immunoprecipitated from smooth muscle cells with protein kinase C-epsilon. High resolution digital confocal studies indicated that calponin redistributes to the cell membrane during phenylephrine stimulation at a time when mitogen-activated protein kinase and protein kinase C-epsilon are targeted to the plasmalemma. These results suggest a role for calponin as a signaling molecule, possibly an adapter protein, linking the targeting of mitogen-activated protein kinase and protein kinase C-epsilon to the surface membrane.
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Signal Transduction Group, Boston Biomedical Research Institute, Boston, Massachusetts 02114, USA.
Hulvershorn
J
J
Adam
L P
LP
Wang
C A
CA
Morgan
K G
KG
D000818:Animals; D001011:Aorta; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D002454:Cell Differentiation; D005289:Ferrets; D066298:In Vitro Techniques; D007700:Kinetics; D008840:Microfilament Proteins / Q000302:isolation & purification / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000032:analysis; D015398:Signal Transduction; D000096985:Calponins
D002118:Calcium; D002135:Calcium-Binding Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D008840:Microfilament Proteins; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019000:Phosphotyrosine; D000096985:Calponins