Communication between the tyrosine kinase pathway and the myosin
light chain kinase pathway of vascular smooth muscle activation.
Jin, Najia, Rafat A. Siddiqui, Denis English, Rodney A. Rhoades.
Department of Physiology/Biophysics, Indiana University School of
Medicine, Indianapolis, Indiana 46202, and the Bone Marrow
Transplantation Laboratory, Methodist Hospital of Indiana,
Indianapolis, Indiana, 46202
APStracts 3:0098H, 1996.
Two separate signal transduction pathways exist in vascular smooth
muscle; one for cell growth, proliferation and differentiation, and
the other for contraction. While activation of protein tyrosine
kinases is intimately involved in the signaling pathway which induces
cell growth, proliferation, and differentiation, activation of myosin
light chain kinase (MLCK) is an important step in the pathway leading
to smooth muscle contraction. Indirect evidence suggests that
"crosstalk" exists between these two signaling pathways, but
the common intermediates are not well defined. The purpose of this
study was to determine if a vasoconstrictor and a mitogen initiate
crossover signalling between the tyrosine kinase pathway and the MLCK
pathway in vascular smooth muscle. Rat aorta and pulmonary arteries
were isolated and stimulated with either fetal bovine serum or with
phenylephrine in the presence or absence of a tyrosine kinase
inhibitor (genistein) or tyrosine phosphatase inhibitor (sodium
orthovanadate). Isometric force was recorded as a function of time;
myosin light chain phosphorylation, protein tyrosine phosphorylation
and MAP kinase mobility were determined by immunoblotting. The
results demonstrate that fetal calf serum, which contains a variety
of growth factors known to activate tyrosine kinases, induced myosin
light chain phosphorylation and contraction in vascular smooth
muscle. Phenylephrine, a vasoconstrictor known to activate MLCK,
induced tyrosine phosphorylation of a 42 kD protein identified as MAP
kinase. Tyrosine phosphorylation of this protein was inhibited by
genistein and enhanced by vanadate. Genistein significantly inhibited
both serum- and phenylephrine-induced myosin light chain
phosphorylation as well as the serum- and phenylephrine-induced force
generation while sodium orthovanadate (Na3VO4) enhanced these
responses. These data demonstrate interrelationship between
activation of the tyrosine kinase pathway and the MLCK pathway in
vascular smooth muscle. These interactions may influence smooth
muscle contraction and be important in the regulation of smooth
muscle cell proliferation.
Received 20 September 1995; accepted in final form 28 February
1996.
APS Manuscript Number H885-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96