PKC-MEDIATED REDISTRIBUTION OF MITOGEN-ACTIVATED PROTEIN-KINASE DURING SMOOTH-MUSCLE CELL ACTIVATION

Protein kinase C (PKC) translocates from the cytosol to the surface me mbrane at the time it mediates agonist-induced contraction of ferret v ascular smooth muscle cells (R. A. Khalil and K. G. Morgan. J. Physiol . Lond. 455: 585-599, 1992). However, no direct communication between membrane-associated PKC and the contractile filaments has been identif ied. Mitogen-activated protein (MAP) kinase is a substrate for PKC and is also capable of phosphorylating the actin-binding protein caldesmo n at sites phosphorylated during smooth muscle contraction in vivo (L. P. Adam, C. J. Gapinski, and D. R. Hathaway. FEBS Lett. 302: 223-226, 1992). In the present study, the hypothesis that PKC and MAP kinase a re involved in a signal-transduction cascade leading to smooth muscle contraction was tested. Immunofluorescence and digital-imaging microsc opy were used to localize the epsilon-PKC isoform and MAP kinase durin g phenylephrine-induced Ca2+-independent activation of ferret aorta ce lls. We report that maintained phenylephrine-induced translocation of cytosolic PKC to the surface membrane is associated with transient red istribution of cytosolic MAP kinase to the surface membrane before cel l contraction. Coincident with cell contraction, MAP kinase undergoes a second redistribution away from the plasmalemma and toward the vicin ity of contractile filaments. Redistribution of MAP kinase is not stim ulated by Ca2+ but is completely prevented by PKC inhibitors. The tran sient Ca2+-independent but PKC-dependent redistribution of MAP kinase points to MAP kinase as a missing link in the signal-transduction casc ade between membrane-bound PKC and smooth muscle activation.