J. Biol. Chem., Vol. 267, Issue 32, 22853-22859, Nov, 1992
Phosphorylation of smooth muscle caldesmon by mitogen-activated protein (MAP) kinase and expression of MAP kinase in differentiated smooth muscle cells
TJ Childs, MH Watson, JS Sanghera, DL Campbell, SL Pelech and AS Mak
Department of Biochemistry, Queen's University, Kingston, Ontario, Canada.
Smooth muscle caldesmon was phosphorylated in vitro by sea star p44mpk up
to 2.0 mol of phosphate/mol of protein at both Ser and Thr residues. The
phosphorylation sites were contained mainly in the COOH-terminal 10- kDa
cyanogen bromide fragment which houses the binding sites for calmodulin,
tropomyosin, and F-actin. Tryptic peptide maps of 32P- labeled caldesmon by
p44mpk and p34cdc2 showed that while both enzymes recognized similar sites
of phosphorylation, they have different preferred sites. Phosphorylation of
caldesmon attenuated slightly its interaction with actin and had no effect
on its binding to calmodulin and tropomyosin. Smooth muscle cell extracts
from chicken gizzard and rat aorta contained 42- and 44-kDa proteins,
respectively, which were cross-reactive with an antibody to sea star
p44mpk. Immunoprecipitates from gizzard and aorta cell extracts, generated
with the p44mpk antibody, possessed kinase activities toward myelin basic
protein as well as caldesmon. These results suggest that MAP kinase may
have functions in the differentiated smooth muscle cells distinct from
those involved in the cell cycle.
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