Role of Protein Phosphatase Type 1 in Contractile Functions: Myosin Phosphatase

Protein phosphatase type 1 (PP1) 1The abbreviations used are: PP1, protein phosphatase type 1; cGK, cGMP-dependent kinase; CPI-17, C-kinase-dependent phosphatase inhibitor of 17 kDa; ILK, integrin-linked kinase; LZ, leucine zipper motifs; MLCK, myosin light chain kinase; MP, myosin phosphatase; MYPT, myosin phosphatase target subunit; PKA, cAMP-dependent kinase; PKC, protein kinase C; P-LC20, phosphorylated 20-kDa myosin light chain; P-myosin, phosphorylated myosin; PP1c, catalytic subunit of PP1; ROK, Rho-associated kinase; TIMAP, transforming growth factor-β-inhibited membrane-associated protein; ATPγS, adenosine 5′-3-O-(thio)triphosphate. is involved in a wide range of cell activities (1Cohen P.T.W. J. Cell Sci. 2002; 115: 241-256Crossref PubMed Google Scholar), and even within the more restricted theme of contractile activity in muscle several processes may be considered. Important areas include regulation of ion channels (2Herzig S. Neumann J. Physiol. Rev. 2002; 80: 173-210Crossref Scopus (239) Google Scholar), effect of phospholamban on Ca2+ uptake by the SR (3Asahi M. Nakayama H. Tada M. Otsu K. Trends Cardiovasc. Med. 2003; 13: 152-157Crossref PubMed Scopus (51) Google Scholar), and phosphorylation-dephosphorylation of myosin II. Phosphorylation of myosin light chains (located in the head-neck junction of the myosin molecule) by the Ca2+-calmodulin-dependent MLCK in all muscle types is established (4Kamm K.E. Stull J.T. J. Biol. Chem. 2001; 276: 4527-4530Abstract Full Text Full Text PDF PubMed Scopus (472) Google Scholar). Discovery of MLCK spurred numerous reports on the phosphatases involved. In smooth muscle, phosphorylation of myosin II increases actin-activated ATPase activity and is required for contraction (4Kamm K.E. Stull J.T. J. Biol. Chem. 2001; 276: 4527-4530Abstract Full Text Full Text PDF PubMed Scopus (472) Google Scholar). Much of the earlier work focused on smooth muscle myosin phosphatase (MP). An initial controversy was the type of catalytic subunit involved, i.e. PP1c, PP2Ac, etc. In smooth muscle the majority of MP activity is due to PP1c (5Erdumlautodi F. Ito M. Hartshorne D.J. Barany M. Biochemistry of Smooth Muscle Contraction. Academic Press, San Diego, CA1996: 131-142Crossref Google Scholar), and this finding was extended to include skeletal and cardiac muscle. Three genes encode PP1c: α, γ, and δ (also called β). Five PP1c isoforms are expressed, where α1/α2 and γ1/γ2 are generated by alternative splicing (1Cohen P.T.W. J. Cell Sci. 2002; 115: 241-256Crossref PubMed Google Scholar). To accommodate specific functions of the limited number of PP1c isoforms with the multiple roles of PP1c the concept of target subunits was developed. Over 50 potential target subunits have been identified (1Cohen P.T.W. J. Cell Sci. 2002; 115: 241-256Crossref PubMed Google Scholar) that in complex with PP1c may designate specific substrates, regulate activity, and direct distinct cell localization. This review describes one of the PP1 holoenzymes, namely the myosin phosphatase of muscle. In smooth muscle the role of MP is to dephosphorylate Ser-19 and to a lesser extent Thr-18 in P-LC20. (The PKC site, Thr-9, can also be dephosphorylated by MP.) The current model for smooth muscle MP is based on the gizzard holoenzyme (6Alessi D. MacDougall L.K. Sola M.M. Ikebe M. Cohen P. Eur. J. Biochem. 1992; 210: 1023-1035Crossref PubMed Scopus (331) Google Scholar, 7Hartshorne D.J. Ito M. Erdödi F. J. Muscle Res. Cell Motil. 1998; 19: 325-341Crossref PubMed Scopus (345) Google Scholar). The holoenzyme is a trimer consisting of: a catalytic subunit, PP1cδ; a target subunit of ∼110 kDa; and a smaller subunit of ∼20 kDa (M20). A scheme of the MP holoenzyme is shown in Fig. 1. The function of M20 is not known, and the critical properties of MP can be ascribed to the large subunit, i.e. binding of PP1c and the substrate, P-myosin. Thus, it is termed myosin phosphatase target subunit, MYPT1. (Other terms include M110, myosin binding subunit (MBS), and M130/M133). Initially MYPT1 was cloned from chicken gizzard (M130/M133 (8Shimizu H. Ito M. Miyahara M. Ichikawa K. Okubo S. Konishi T. Naka M. Tanaka T. Hirano K. Hartshorne D.J. Nakano T. J. Biol. Chem. 1994; 269: 30407-30411Abstract Full Text PDF PubMed Google Scholar)) and also from rat aorta (rat3 isoform (9Chen Y.H. Chen M.X. Alessi D.R. Campbell D.G. Shanahan C. Cohen P. Cohen P.T.W. FEBS Lett. 1994; 356: 51-55Crossref PubMed Scopus (128) Google Scholar)). From the initial reports the basic features of the MYPT1 molecule were established. The molecule is hydrophilic, and no extensive hydrophobic patches are found. Plans of human and chicken MYPT1 are shown in Fig. 1. A striking feature of all MYPT isoforms is the presence of N-terminal ankyrin repeats. In MYPT1 each of the 7 or 8 repeats contains ∼33 residues with 20 residues conserved. The 171–197 region is less homologous but shows similarity to ankyrin repeats and was so considered in chicken M130/M133 (8Shimizu H. Ito M. Miyahara M. Ichikawa K. Okubo S. Konishi T. Naka M. Tanaka T. Hirano K. Hartshorne D.J. Nakano T. J. Biol. Chem. 1994; 269: 30407-30411Abstract Full Text PDF PubMed Google Scholar). It is suggested that the conserved sequence for ankyrin repeats is structure-based in that it forms a β-hairpin-helix-loop-helix (β2α2) structure (10Sedgewick S.G. Smerdon S.J. Trends Biochem. Sci. 1999; 24: 311-316Abstract Full Text Full Text PDF PubMed Scopus (664) Google Scholar). Based on several solved structures it is known that both the β-hairpins and the surface of the ankyrin groove (helical bundle) can be involved in binding to target proteins (10Sedgewick S.G. Smerdon S.J. Trends Biochem. Sci. 1999; 24: 311-316Abstract Full Text Full Text PDF PubMed Scopus (664) Google Scholar). Many proteins interact with ankyrin repeats (11Bennett V. Baines A.J. Physiol. Rev. 2001; 81: 1353-1392Crossref PubMed Scopus (795) Google Scholar), and thus the proposed role for these repeats in MYPT1 is to act as an interactive protein platform. Flanking the N-terminal edge of the first ankyrin repeat is the PP1c-binding motif, the "RVXF" (1Cohen P.T.W. J. Cell Sci. 2002; 115: 241-256Crossref PubMed Google Scholar) motif (residues 35–38). Some variation is allowed and a general consensus is (R/K)X1(V/I)X2(F/W), where X1 may be absent or be residues other than large hydrophobes and X2 is any residue except large hydrophobes, phosphoserine and probably aspartic acid (1Cohen P.T.W. J. Cell Sci. 2002; 115: 241-256Crossref PubMed Google Scholar). Residues flanking the motif, N-terminal basic residues, and C-terminal acidic residue(s) may contribute to binding (12Zhao S. Lee E.Y.C. J. Biol. Chem. 1997; 272: 28368-28372Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar). In human MYPT1 the pertinent sequence is 30KRQKTKVKFDD. The RVXF motif is present in many target proteins and even occurs in proteins unlikely to bind PP1c (1Cohen P.T.W. J. Cell Sci. 2002; 115: 241-256Crossref PubMed Google Scholar). This motif interacts with PP1c in a hydrophobic groove involving residues Ile-169, Leu-243, Phe-257, Leu-289, Cys-291, and Phe-293. Important points are that the interaction site for RVXF on PP1c is within the invariant region for all PP1c isoforms (but not conserved in PP2A and PP2B) and that the site is distinct from the catalytic site. Peptides containing the RVXF motif may displace target subunits, but binding of the RVXF motif to PP1c does not directly influence activity (1Cohen P.T.W. J. Cell Sci. 2002; 115: 241-256Crossref PubMed Google Scholar, 13Bollen M. Trends Biochem. Sci. 2001; 26: 426-431Abstract Full Text Full Text PDF PubMed Scopus (256) Google Scholar). In MYPT1 the RVXF motif (KVKF) acts as the primary interaction site (an anchoring site) for PP1cδ, but other interactions are involved (14Tóth A. Kiss E. Herberg F.W. Gergely P. Hartshorne D.J. Erdödi F. Eur. J. Biochem. 2000; 267: 1687-1697Crossref PubMed Scopus (66) Google Scholar). These include residues 1–22, the ankyrin repeats (possibly repeats 5–8, sequence 167–295 (7Hartshorne D.J. Ito M. Erdödi F. J. Muscle Res. Cell Motil. 1998; 19: 325-341Crossref PubMed Scopus (345) Google Scholar)), and a site within the sequence 304–511. Only the interaction with KVKF has high affinity, but the other secondary interactions are important in that they may modify PP1c properties. For example, interaction of PP1c or P-myosin with the N-terminal segment of MYPT1 could activate PP1c. These multiple and hierarchical interactions form a combinatorial control of PP1c (13Bollen M. Trends Biochem. Sci. 2001; 26: 426-431Abstract Full Text Full Text PDF PubMed Scopus (256) Google Scholar), and considering these, it is likely that PP1c is pivoted via the RVXF motif and clasped by the N-terminal sequence of MYPT1 and the ankyrin repeats. Other structural features of MYPT1, including some phosphorylation sites, are shown in Fig. 1. A potentially important feature of MYPT1 as a target subunit is that it is a platform for multiple interactions. The binding of myosin to MYPT1 is an important but controversial point. One view is that P-myosin or P-LC20 binds to the ankyrin repeats, possibly repeats 6–8 (15Hirano K. Phan B.C. Hartshorne D.J. J. Biol. Chem. 1997; 272: 3683-3688Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar). Interaction of the phosphorylated substrate with the catalytic site of PP1c is expected with an added contribution to binding by the ankyrin repeats. Dephosphorylated substrate binds less effectively, and in the presence of ATP only P-myosin or P-LC20 is bound (7Hartshorne D.J. Ito M. Erdödi F. J. Muscle Res. Cell Motil. 1998; 19: 325-341Crossref PubMed Scopus (345) Google Scholar). The opposing view is that dephosphorylated myosin binds to the C-terminal sequence of MYPT1 (excluding the C-terminal 72 residues (16Johnson D. Cohen P. Chen M.X. Chen Y.H. Cohen P.T.W. Eur. J. Biochem. 1997; 244: 931-939Crossref PubMed Scopus (83) Google Scholar) in the chicken isoforms). Binding to both the N-terminal and C-terminal regions of MYPT1 is feasible if P-LC20 (in the myosin S2 region) binds to the N-terminal sites and the rod portion of myosin binds to the C-terminal sites. It was suggested that phosphorylation of Thr-850 (chicken M133) by ROK reduced binding of MYPT1 to myosin (17Velasco G. Armstrong C. Morrice N. Frame S. Cohen P. FEBS Lett. 2002; 527: 101-104Crossref PubMed Scopus (181) Google Scholar). Adducin (α, β, γ (18Amano M. Fukata Y. Kaibuchi K. Exp. Cell Res. 2000; 261: 44-51Crossref PubMed Scopus (454) Google Scholar)) and Tau and MAP2 (19Amano M. Kaneko T. Maeda A. Nakayama M. Ito M. Yamauchi T. Goto H. Fukata Y. Oshiro N. Shinohara A. Iwamatsu A. Kaibuchi K. J. Neurochem. 2003; 87: 780-790Crossref PubMed Scopus (89) Google Scholar) also bind to the ankyrin repeats and are phosphorylated and dephosphorylated by ROK and MP, respectively. Multiple interactions with the ankyrin repeats are expected (11Bennett V. Baines A.J. Physiol. Rev. 2001; 81: 1353-1392Crossref PubMed Scopus (795) Google Scholar), but what is surprising is that the C-terminal half of MYPT1 also interacts with many molecules (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar). M20 binds to the C-terminal region of MYPT1, residues 934–1006 of human MYPT1, in an interaction not involving LZ repeats (15Hirano K. Phan B.C. Hartshorne D.J. J. Biol. Chem. 1997; 272: 3683-3688Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 16Johnson D. Cohen P. Chen M.X. Chen Y.H. Cohen P.T.W. Eur. J. Biochem. 1997; 244: 931-939Crossref PubMed Scopus (83) Google Scholar). M20 also binds to myosin but not PP1c (16Johnson D. Cohen P. Chen M.X. Chen Y.H. Cohen P.T.W. Eur. J. Biochem. 1997; 244: 931-939Crossref PubMed Scopus (83) Google Scholar). GTP-RhoA (but not inactive GDP-RhoA) binds to the C terminus and could represent an alternative docking site for GTP-RhoA in addition to the plasmalemma. Acidic phospholipids target residues 667–1004 of chicken M133 (does not contain LZ sequences) and inhibit PP1c activity (7Hartshorne D.J. Ito M. Erdödi F. J. Muscle Res. Cell Motil. 1998; 19: 325-341Crossref PubMed Scopus (345) Google Scholar). This binding/inhibition of MP activity is reversed on phosphorylation of MYPT1 by PKA. Moesin also binds to MYPT1 via the C-terminal part (18Amano M. Fukata Y. Kaibuchi K. Exp. Cell Res. 2000; 261: 44-51Crossref PubMed Scopus (454) Google Scholar). Other interactions involve the LZ motifs in some isoforms of MYPT1 and include: 1) interaction of the LZ motifs of cGMP-dependent kinase (cGKIα) and MYPT1 (21Surks H.K. Mochizuki N. Kasai Y. Georgescu S.P. Tang K.M. Ito M. Lincoln T.M. Mendelsohn M.E. Science. 1999; 286: 1583-1587Crossref PubMed Scopus (444) Google Scholar); 2) binding of the PDZ2 domain of interleukin-16 precursor proteins to the C-terminal 30 residues of MYPT (22Bannert N. Vollhardt K. Asomuddinov B. Haag M. König H. Norley S. Kurth R. J. Biol. Chem. 2003; 278: 42190-42199Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar); and 3) interaction of a coiled-coil domain in RhoA-interacting protein (expressed in vascular smooth muscle) with the LZ motifs of MYPT1 (23Surks H.K. Richards C.T. Mendelsohn M.E. J. Biol. Chem. 2003; 278: 51484-51493Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar). The many interactions involving MYPT1 suggest several substrates and a possible targeting function in other macromolecular complexes and thus a much broader role in cell function than only dephosphorylation of P-myosin. This complexity may reflect the varied cell localizations observed with MYPT1 on filaments and membranes (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar). In differentiated striated muscle MYPT may have a more restricted isoforms of MYPT1 has the or C for MYPT1, and A or for and TIMAP, and for is on as are generated by alternative splicing of and involve the presence or of and the C-terminal LZ The chicken gizzard MYPT1 isoforms by a (residues of M133 (8Shimizu H. Ito M. Miyahara M. Ichikawa K. Okubo S. Konishi T. Naka M. Tanaka T. Hirano K. Hartshorne D.J. Nakano T. J. Biol. Chem. 1994; 269: 30407-30411Abstract Full Text PDF PubMed Google Scholar)) from a F. J. Physiol. 2000; 278: PubMed Google Scholar). In rat the is more and isoforms are generated F. J. Physiol. 2000; 278: PubMed Google Scholar) from of of this region (in is by a complex to the alternative site J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). In isoforms are generated by alternative splicing of a of this for the MYPT1, and of the a and for the MYPT1 K.M. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). many isoforms of MYPT1 can be generated and to some extent are in a F. J. Physiol. 2000; 278: PubMed Google Scholar, K.M. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). several molecules to MYPT1 have been has the N-terminal ankyrin repeats and the RVXF The C-terminal half is more cloned M. N. H. S. Ichikawa K. J. M. Kaibuchi K. Hartshorne D.J. Nakano T. Ito M. 1998; PubMed Scopus Google Scholar) residues and a isoform was from the of the T. N. J. S. A. H. A. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). These from alternative splicing of each isoform the of or contain C-terminal LZ A of MYPT1 and is shown in Fig. is but several areas are more conserved The N-terminal of and of are distinct both contain the PP1c-binding MYPT1 may be considered a and is in but is in smooth muscle in is M. and M. J. is more restricted with both A and isoforms in skeletal muscle, and and in other T. N. J. S. A. H. A. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). of the MYPT is T. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). This is with in the binds to the isoform and also binds and P-myosin Phosphorylation of by kinase or ROK is required for binding to and of phosphatase activity T. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). has some similarity to 2) but only in N-terminal half Biochem. J. 2001; 356: PubMed Scopus Google Scholar). Other features are shown in Fig. A site is not the activity of with a and P-myosin in to of by MYPT1 with P-myosin. is and in high in and is to and contains the N-terminal conserved and a C-terminal H. K. J. J. Physiol. 2002; PubMed Scopus Google Scholar). It shows high in and of that several homologous to and Biochem. J. 2001; 356: PubMed Scopus Google Scholar, H. K. J. J. Physiol. 2002; PubMed Scopus Google Scholar). binds PP1c via the RVXF motif, and the binding of PP1c and substrate may be by the ankyrin repeats. The C-terminal region is for a regulation or binding of other or to membranes the C the of MYPT is not with MYPT1 and it is possible that substrates other than P-myosin are M20 was cloned from chicken gizzard (9Chen Y.H. Chen M.X. Alessi D.R. Campbell D.G. Shanahan C. Cohen P. Cohen P.T.W. FEBS Lett. 1994; 356: 51-55Crossref PubMed Scopus (128) Google Scholar), and splicing of and residues were K. K. Ito M. Nakano T. T. 1999; PubMed Scopus Google Scholar). Only contains C-terminal LZ of each isoform is K. K. Ito M. Nakano T. T. 1999; PubMed Scopus Google Scholar). of M20 from the G. D. Morrice N. Cohen P. FEBS Lett. 1998; PubMed Scopus Google Scholar), and isoforms of M20 from the and genes involving T. N. J. S. A. H. A. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). M20 was not in or skeletal muscle (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar). The function of M20 is not established. roles (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar) include: of Ca2+ in and cardiac binding to the myosin and a role in The binding of M20 to MYPT1 does not phosphatase activity (7Hartshorne D.J. Ito M. Erdödi F. J. Muscle Res. Cell Motil. 1998; 19: 325-341Crossref PubMed Scopus (345) Google Scholar). that MP activity was but more and have been of MP and in Ca2+ and Ca2+ respectively. are for Ca2+ of MP was to be to via numerous in Physiol. Rev. 2003; PubMed Scopus Google Scholar), and and thus Rho-associated ROK, are important (7Hartshorne D.J. Ito M. Erdödi F. J. Muscle Res. Cell Motil. 1998; 19: 325-341Crossref PubMed Scopus (345) Google Scholar, Physiol. Rev. 2003; PubMed Scopus Google Scholar). are isoforms of ROK and (18Amano M. Fukata Y. Kaibuchi K. Exp. Cell Res. 2000; 261: 44-51Crossref PubMed Scopus (454) Google Scholar) with was from chicken gizzard smooth muscle J. Ito M. Y. Ichikawa K. M. N. K. Iwamatsu A. Kaibuchi K. Hartshorne D.J. Nakano T. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). are several proposed for of MP (7Hartshorne D.J. Ito M. Erdödi F. J. Muscle Res. Cell Motil. 1998; 19: 325-341Crossref PubMed Scopus (345) Google Scholar, M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar), i.e. phosphorylation of phosphorylation of an of the and and of the The first are more Initially it was that of with Ca2+ of MP, and of MYPT1 7Hartshorne D.J. Ito M. Erdödi F. J. Muscle Res. Cell Motil. 1998; 19: 325-341Crossref PubMed Scopus (345) Google and M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar). it was shown that phosphorylation of MYPT1 in human by an kinase gizzard MP ROK was the first known kinase shown to MYPT1 (7Hartshorne D.J. Ito M. Erdödi F. J. Muscle Res. Cell Motil. 1998; 19: 325-341Crossref PubMed Scopus (345) Google Scholar, M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar), and sites, and (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar, Y. Y. Oshiro N. M. T. Ito M. F. M. Kaibuchi K. J. Cell Biol. 1999; PubMed Scopus Google Scholar), and several sites Y. Y. Oshiro N. M. T. Ito M. F. M. Kaibuchi K. J. Cell Biol. 1999; PubMed Scopus Google Scholar) were are known to MYPT1 (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar), many the site. The kinase was identified and termed MYPT1 kinase kinase A. Hartshorne D.J. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar)). Some of these MYPT1 and can also directly Ser-19 and have been in contractile in The of multiple that the site is not known but may represent the of MYPT1, protein or and The for of MP as a of phosphorylation is not The with several substrates is due to a in of MP phosphorylation is unlikely (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar). For of the molecule is expected to interaction of with the PP1c. it be that both and are to that Ser-19 of to also could via of of MYPT1 (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar). It is of residues and in smooth muscle and M. S. F. M. FEBS Lett. 1997; PubMed Scopus Google Scholar). In human aorta a splicing is that sequence by of the (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar). other of PP1, 1 and both the catalytic subunit and PP1 Phosphorylation and the first kinase was PKC and δ isoforms). several ROK, were to Residues are required for of MP and is to dephosphorylation of by MP Y. S. M. M. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). The structure M. E. T. Y. M. D. M. J. Mol. Biol. 2001; PubMed Scopus Google Scholar) that phosphorylation of a that specific of MP by of smooth muscle phosphorylation of that was reduced by both ROK and PKC from T. M. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). or MYPT1 is in regulation of MP is controversial and on the involved. are that MLCK and MP are in than smooth muscle and that is in vascular with muscle M. A. T. J. Physiol. 2001; Scopus Google Scholar). reports have suggested that a role in Ca2+ in smooth M. A. T. J. Physiol. 2001; Scopus Google Scholar, T. M. M. J. Physiol. 2003; Scopus Google Scholar, N. Y. Ikebe M. Biochem. J. 2003; PubMed Scopus Google Scholar). in a in phosphorylation to a of MP activity M. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). other of PP1 are the phosphatase holoenzyme and M. A. 1999; PubMed Scopus Google Scholar)) and protein phosphatase type 1 inhibitor D. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar)). and are high in cardiac muscle. has sequence similarity to and also to the C-terminal domain of T. S. E. M. A. A. Biochem. Res. 2003; PubMed Scopus Google Scholar). be considered in of MP and Ca2+ acid was proposed to the MP subunits (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar, Physiol. Rev. 2003; PubMed Scopus Google Scholar) with the reduced activity of PP1c. An alternative is that acid ROK, of and this MYPT1 or (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar). and acid also activate the ROK Physiol. Rev. 2003; PubMed Scopus Google Scholar). phosphorylation of myosin II is critical for smooth muscle function in the of phosphorylation may to of smooth muscle. of MP via the and the ROK and have been include and (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar, Physiol. Rev. 2003; PubMed Scopus Google Scholar). is known of MP this is with of smooth muscle by increases in and An is the of MP by phosphorylation of MYPT1 (in human to reflect an in binding to P-myosin G. Y. S. H. Hartshorne D.J. F. J. Cell Biol. 1999; PubMed Scopus Google Scholar). The of MP shown in smooth muscle Physiol. Rev. 2003; PubMed Scopus Google Scholar)) by and is not but in this the phosphorylation of MYPT1 by kinase does not activate MP (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar), and thus it is that are involved. One is that and the in is phosphorylated by and and was to (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar, Physiol. Rev. 2003; PubMed Scopus Google Scholar). A with this is that phosphorylation of in was to phosphorylation of was in K. K. J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). The of may be of interaction of phosphorylated with K. K. J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar) phosphorylation of the region of and reduced by T. J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). in not effect a of MP but the extent of of MP by is suggested to interaction of the of MYPT1 and (21Surks H.K. Mochizuki N. Kasai Y. Georgescu S.P. Tang K.M. Ito M. Lincoln T.M. Mendelsohn M.E. Science. 1999; 286: 1583-1587Crossref PubMed Scopus (444) Google Scholar), and only smooth the MYPT1 isoforms cGMP-dependent Ca2+ K.M. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). an protein from the smooth muscle MLCK contains the C-terminal domain of MLCK (20Ito M. Nakano T. Erdödi F. Hartshorne D.J. Mol. Cell. Biochem. 2004; 259: 197-209Crossref PubMed Scopus (382) Google Scholar) and also has been in of smooth muscle Physiol. Rev. 2003; PubMed Scopus Google Scholar). It is high i.e. the as myosin only in smooth muscle. in is phosphorylated by and Physiol. Rev. 2003; PubMed Scopus Google Scholar). also is phosphorylated a protein kinase site, but the in role for this is not known Physiol. Rev. 2003; PubMed Scopus Google Scholar). The by or phosphorylated MP is not established. In striated muscle the target for MP is on the light The that MP in skeletal muscle a subunit than that in smooth muscle was proposed by Cohen and (6Alessi D. MacDougall L.K. Sola M.M. Ikebe M. Cohen P. Eur. J. Biochem. 1992; 210: 1023-1035Crossref PubMed Scopus (331) Google Scholar). This was identified as based on M. N. H. S. Ichikawa K. J. M. Kaibuchi K. Hartshorne D.J. Nakano T. Ito M. 1998; PubMed Scopus Google Scholar), of from skeletal muscle G. D. Morrice N. Cohen P. FEBS Lett. 1998; PubMed Scopus Google Scholar, J. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), and the of the in rat muscle Y. Erdödi F. A. Hartshorne D.J. J. Muscle Res. Cell Motil. 2003; 24: PubMed Scopus Google Scholar). In cardiac muscle, also is the targeting subunit of MP M. N. H. S. Ichikawa K. J. M. Kaibuchi K. Hartshorne D.J. Nakano T. Ito M. 1998; PubMed Scopus Google Scholar). In the cell a from MYPT1 to occurs as the a Y. Erdödi F. A. Hartshorne D.J. J. Muscle Res. Cell Motil. 2003; 24: PubMed Scopus Google Scholar). The function of myosin phosphorylation in striated muscle is not as as in smooth muscle. In phosphorylation of striated muscle myosin increases i.e. an in Ca2+ and is in muscle. It is proposed that phosphorylation of the light chains the myosin to the and increases the from to Stull J.T. J. Physiol. PubMed Google Scholar). This may be a general in all muscle phosphorylation (in muscle) is than the contraction but than phosphatase 1 with Stull J.T. J. Physiol. PubMed Google Scholar)). In cardiac muscle the of myosin phosphorylation and dephosphorylation are of muscle Stull J.T. J. Physiol. PubMed Google Scholar)), and due to myosin phosphorylation thus are more to in rat a was myosin phosphorylation and Stull J.T. J. Physiol. PubMed Google Scholar). a light chain of Ca2+ and structural A. J. H. J. D.G. J. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). A more is that the of myosin phosphorylation may be important in or In of MLCK a in the of Y. Erdödi F. A. Hartshorne D.J. J. Muscle Res. Cell Motil. 2003; 24: PubMed Scopus Google Scholar), and in cardiac MLCK the H. J. S. Med. 2000; PubMed Scopus Google Scholar). In view of the of a of myosin phosphorylation it is likely that striated muscle MP is are no to on MP is of the basic i.e. MYPT1 (in smooth muscle) and several are of MP regulation in smooth muscle are important to both for a of contractile functions and to for many of smooth muscle In striated muscle are no on regulation of bind to MYPT1, and the is that MP is not to P-myosin but has alternative substrates and for is to the roles of the other of the MYPT