Dedicated Myosin Light Chain Kinases with Diverse Cellular Functions

Abstract

intracellular calcium concentration myosin light chain kinase regulatory light chain of myosin II fibronectin repeat sequences rich in Phe, Glu, Val, and Lys residues kilobase(s) concentration of Ca2+/calmodulin required for half-maximal activation Ca2+/calmodulin-dependent protein kinase II p21-activated kinase mitogen-activated protein kinase guanosine 5′-3-O-(thio)triphosphate MAPK/extracellular signal-regulated kinase kinase urokinase-type plasminogen activator Cell signaling events that lead to increased [Ca2+]i1in smooth and skeletal muscles activate Ca2+/calmodulin-dependent MLCK. The kinase phosphorylates a specific site on the N terminus of the RLC of the molecular motor myosin II (1Kamm K.E. Stull J.T. Annu. Rev. Pharmacol. Toxicol. 1985; 25: 593-620Crossref PubMed Google Scholar, 2Hartshorne D.J. Johnson L.R. Physiology of the Gastrointestinal Tract. Raven Press, New York1987: 423-482Google Scholar, 3Stull J.T. Lin P.J. Krueger J.K. Trewhella J. Zhi G. Acta Physiol. Scand. 1998; 164: 471-482Crossref PubMed Scopus (68) Google Scholar). RLC phosphorylation is sufficient to initiate contraction in smooth muscle, but in striated muscles, RLC phosphorylation potentiates the force and speed of contractions that are dependent on Ca2+ binding to troponin on actin-containing thin filaments. The only known physiological substrate for MLCK is myosin RLC; thus, it is a dedicated protein kinase. Interest in RLC phosphorylation has increased substantially with recent reports implicating phosphorylation-dependent myosin II activity in many functions of nonmuscle cells. These include cell spreading and migration, neurite growth cone advancement, cytokinesis, cytoskeletal clustering of integrins at focal adhesions, stress fiber formation, platelet shape changes, secretion, transepithelial permeability, and cytoskeletal arrangements that affect ion currents or exchange at the plasma membrane (4Schoenwaelder S.M. Burridge K. Curr. Opin. Cell Biol. 1999; 11: 274-286Crossref PubMed Scopus (651) Google Scholar, 5Bresnick A.R. Curr. Opin. Cell Biol. 1999; 11: 26-33Crossref PubMed Scopus (315) Google Scholar, 6Szaszi K. Kurashima K. Kapus A. Paulsen A. Kaibuchi K. Grinstein S. Orlowski J. J. Biol. Chem. 2000; 275: 28599-28606Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar, 7Aromolaran A.S. Albert A.P. Large W.A. J. Physiol. (Lond.). 2000; 524: 853-863Crossref Scopus (45) Google Scholar, 8Tran Q.-K. Watanabe H. Zhang X.-X. Takahashi T. Ohno R. Cardiovasc. Res. 1999; 44: 623-631Crossref PubMed Scopus (13) Google Scholar). The potential importance of RLC phosphorylation in pathophysiological processes involving cell migration is apparent, but less obvious involvements may include cerebral vasospasm (9Sato M. Tani E. Fujikawa H. Kaibuchi K. Circ. Res. 2000; 87: 195-200Crossref PubMed Scopus (214) Google Scholar), increased endothelial permeability during inflammation (10van Nieuw Amerongen G.P. van Delft S. Vermeer M.A. Collard J.G. van Hinsbergh V.W.M. Circ. Res. 2000; 87: 335-340Crossref PubMed Google Scholar), and asthma (11Ammit A.J. Armour C.L. Black J.L. Am. J. Respir. Crit. Care Med. 2000; 161: 257-263Crossref PubMed Scopus (86) Google Scholar). In vertebrates there are two genes for MLCK (3Stull J.T. Lin P.J. Krueger J.K. Trewhella J. Zhi G. Acta Physiol. Scand. 1998; 164: 471-482Crossref PubMed Scopus (68) Google Scholar). The skeletal muscle MLCK gene encodes a kinase catalytic core and regulatory segment containing autoinhibitory and Ca2+/calmodulin-binding sequences (Fig. 1). The smooth muscle MLCK gene expresses three transcripts in a cell-specific manner due to alternate promoters (12Birukov K.G. Schavocky J.P. Shirinsky V.P. Chibalina M.V. Van Eldik L.J. Watterson D.M. J. Cell. Biochem. 1998; 70: 402-413Crossref PubMed Scopus (50) Google Scholar, 13Watterson D.M. Schavocky J.P. Guo L. Weiss C. Chlenski A. Shirinsky V.P. Van Eldik L.J. Haiech J. J. Cell. Biochem. 1999; 75: 481-491Crossref PubMed Scopus (31) Google Scholar, 14Smith A.F. Bigsby R.M. Word R.A. Herring N.T. Am. J. Physiol. 1998; 274: C1188-C1195Crossref PubMed Google Scholar). Smooth muscle tissues normally have a short form of the kinase containing a catalytic core and regulatory segment that differ in sequence and catalytic specificity from skeletal muscle MLCK (Fig. 1). This kinase also contains three Ig modules, one Fn module as well as a PEVK repeat-rich region and an actin-binding sequence at the N terminus (Fig. 1). The Ig and Fn modules have β sandwich structures whereas the PEVK module is responsible for the titin-dependent elastic properties of striated muscle sarcomeres (15Champagne M.B. Edwards K.A. Erickson H.P. Kiehart D.P. J. Mol. Biol. 2000; 300: 759-777Crossref PubMed Scopus (39) Google Scholar). The functions of these sequences in MLCK are not clear. However, the actin-binding sequence is both necessary and sufficient for high affinity binding in vitro and in vivo (16Lin P. Luby-Phelps K. Stull J.T. J. Biol. Ch