P38 MITOGEN-ACTIVATED PROTEIN-KINASE EXPRESSION AND ACTIVATION IN SMOOTH-MUSCLE

There is relatively little known about expression and activation of p3 8 mitogen-activated protein kinases (MAPKs) through G protein-linked, seven-transmembrane-spanning (STM) receptors in mammalian smooth muscl e. To investigate the role of p38 MAPK in smooth muscle, we cloned and sequenced the p38 MAPK expressed in canine smooth muscles. A full-len gth clone of the canine p38 MAPK expressed in colonic smooth muscle wa s obtained by RT-PCR. The deduced amino acid sequence revealed 99% ide ntity to the human p38 MAPK and differed from the human enzyme in only two conservative substitutions. The deduced molecular mass of the can ine p38 MAPK is 41.2 kDa, with a calculated isoelectric point of 5.41. Canine p38 MAPK was found to be expressed in colonic, tracheal, and v ascular smooth muscles and underwent increased tyrosine phosphorylatio n in response to motor neurotransmitters, acetylcholine (ACh) and neur okinin A (NKA), in colonic smooth muscle. There was an eightfold incre ase in p38 MAPK phosphorylation after a 10-min incubation with ACh and a threefold increase with NKA. We also identified a p38 immunoreactiv e kinase activity isolated from colonic smooth muscle homogenate by Mo no Q chromatography. Partially purified p38 MAPK and activated recombi nant p38 MAPK (Mpk2) phosphorylated both the known p38 MAPK substrate ATF2, as well as porcine stomach h-caldesmon in vitro. The results sug gest that elements of the ''stress-response'' pathway may be coupled t o transcriptional control as well as to cytoskeletal and possibly cont ractile protein phosphorylation in mammalian smooth muscle.