Calponin phosphorylation

IX. ABSENCE OF CALPONIN PHOSPHORYLATION DURING SMOOTH MUSCLE CONTRACTION... 

Barany M, Barany K (1993a) Dissociation of relaxation and myosin light chain phosphorylation in porcine uterine muscle. Arch Biochem Biophys 305 202-204 Barany M, Barany K (1993b) Calponin phosphorylation does not accompany contraction of various smooth muscles. Biochim Biophys Acta 1179 229-233 Barany K, Barany M (1996a) Myosin light chains. In Bdrany M (ed) Biochemistry of smooth muscle contraction. Academic Press, New York, pp 21-35 Barany K, Barany M (1996b) Protein phosphorylation during contraction and relaxation. In Barany M (ed) Biochemistry of smooth muscle contraction. Academic Press, New York, pp 321-339... 

Gerthoffer WT, Murphy RA (1983) Ca , myosin phosphorylation, and relaxation of arterial smooth muscle. Am J Physiol 245 C271-C277 Gerthoffer WT, Pohl J (1994) Caldesmon and calponin phosphorylation in regulation of smooth muscle contraction. Can J Physiol Pharmacol 72 1410-1414 Gerthoffer WT, Trevethick MA, Murphy RA (1984) Myosin phosphorylation and cyclic adenosine 3, 5 -monophosphate in relaxation of arterial smooth muscle by vasodilators. Circ Res 54 83-89... 

Winder SJ, Allen EG, Fraser ED, Kang HM, Kargacin GJ, Walsh MP (1993) Calponin phosphorylation in vitro and in intact muscle. Biochem J 296 827-836 Winder SJ, Pato MD, Walsh MP (1992) Purification and characterization of calponin phosphatase from smooth muscle. Effect of dephosphorylation on calponin function. Biochem J 286 197-203... 

In skeletal muscle, disinhibition of actin is necessary for contraction to occur, and control of contraction is said to be actin-linked. In smooth muscle, phosphorylation of myosin light chains (MLCs) is required for contraction. Several mechanisms alter MLC phosphorylation, and so in smooth muscle, control of contraction is primarily myosin-linked. Three control proteins have been identified in smooth muscle myosin light chain kinase (MLCK) caldesmon (CaD) and calponin (CaP). Figure 21-14... 

Calponin is another polypeptide monomer (M.W. 32,000) that can inhibit actin-activated myosin ATPase activity. In contrast to CaD, CaP exerts its effect in the absence of tropomyosin and completely inhibits motility in a 2/3 ratio with actin. CaP inhibits myosin binding to actin, but does so by reducing the affinity of actin for myosin rather than competing for the same site. CaP can be phosphorylated by PKC and CaMKII, both of which reverse CaP s inhibitory activity. As with caldesmon, many questions remain. The ratio of CaP to actin actually observed in smooth muscle is in the range 1 10 to 1 16, far from the 2/3 ratio found to produce near-complete inhibition of motility. Therefore, the importance of CaP and its regulation by phosphorylation is still debatable. 

To account for activation of arterial smooth muscle independently of LC20 phosphorylation, attention has been focused on the possible roles of the thin filament-associated regulatory proteins, caldesmon and calponin. Both proteins have been localized in the actomyosin domain of the smooth muscle cell and both have been shown to inhibit actin-activated myosin ATPase by interacting with F-actin, tropomyosin, and/or myosin (Clark et al., 1986 Takahashi et al.,... 

The second aspect of the force-RLC phosphorylation relation that suggests additional regulation is illustrated by alterations in the slope of the relation (Fig. 1, lower right). Alterations in isometric force at fixed values of RLC phosphorylation are probably the strongest evidence for the in vivo operation of thin filament regulation. Smooth muscle contains two thin filament proteins, caldesmon and calponin, that inhibit actin-activated MgATPase activity of phosphorylated myosin. This inhibitory activity is reversed by the binding of Ca +ZCaM or by phosphorylation, and thus CD and CP may modulate the RLC phosphorylation... 

Takeuchi K, Takahashi K, Abe M, Nishida W, Hiwada K, Nabeya T, MaruyamaK (1991) Co-localization of immunoreactive forms of calponin with actin cytoskeleton in platelets, fibroblasts, and vascular smooth muscle. J Biochem 109 311316 Tang D, Mehta D, Gunst SJ (1999). Mechano-sensitive tyrosine phosphorylation of paxUlin and focal adhesion kinase in tracheal smooth muscle. Am I Physiol In press, 1999. 

Gimona M, Small JV (1996) Calponin. In Barany M (ed) The biochemistry of smooth muscle contraction. Academic Press pp 91-103 Gimona M, Sparrow MP, Strasser P, Herzog M, Small JV (1992) Calponin and SM 22 isoforms in avian and mammalian smooth muscle. Absence of phosphorylation in vivo. Eur J Biochem 205 1067-1075... 

Itoh T, Suzuki A, Watanabe Y, Mino T, Naka M, Tanaka T (1995) A calponin peptide enhances Ca " sensitivity of smooth muscle contraction without affecting myosin light chain phosphorylation. J Biol Chem 270 20400-20403... 

Mino T, Yuasa U, Naka M, Tanaka T (1995) Phosphorylation of calponin mediated by protein kinase C in association with contraction in porcine coronary artery. Biochem Biophys Res Commun 208 397-404... 

Nieznanski K, Sobieszek A (1997) Telokin (kinase-related protein) modulates the oligomeric state of smooth-muscle myosin light-chain kinase and its interaction with myosin filaments. Biochem J 322 65-71 Nishida W, Abe M, Takahashi K, Hiwada K (1990) Do thin filaments of smooth muscle contain calponin A new method for the preparation. FEBS Lett 268 165-168 Nishikawa M, de LaneroUe P, Lincoln TM, Adelstein RS (1984) Phosphorylation of mammalian myosin light chain kinases by the catalytic subunit of cyclic AMP-dependent protein kinase and by cyclic GMP-dependent protein kinase. J Biol Chem 259 8429-8436... 

Nixon GF, lizuka K, Haystead CM, Haystead TA, Somlyo AP, Somlyo AV (1995) Phosphorylation of caldesmon by mitogen-activated protein kinase with no effect on Ca sensitivity in rabbit smooth muscle. J Physiol (Lond) 487 283-289 Noda S, Ito M, Watanabe S, Takahashi K, Maruyama K (1992) Conformational changes of actin induced by calponin. Biochem Biophys Res Commun 1992 May 29 185(l) 481-487... 

Winder SJ, Walsh MP (1990) Smooth muscle calponin. Inhibition of actomyosin MgATPase and regulation by phosphorylation. J Biol Chem 265 10148-10155 Winder SJ, Walsh MP (1993) Calponin thin filament-linked regulation of smooth muscle contraction. Cell Signal 5 677-686 Winder SJ, Walsh MP (1996) Calponin. Curr Top Cell Regul 1996 34 33-61 Wingard CJ, Paul RJ, Murphy RA (1994) Dependence of ATP consumption on crossbridge phosphorylation in swine carotid smooth muscle. J Physiol (Lond) 481 111-117... 

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