Caldesmon inhibition

Chalovich JM, Cornelius P, Benson CE (1987) Caldesmon inhibits skeletal actomyosin subfragment-1 ATPase activity and the binding of myosin subfragment-1 to actin. J Biol Chem 262 57115716... 

Horiuchi KY, Chacko S (1989) Caldesmon inhibits the cooperative turning-on of the smooth muscle heavy meromyosin by tropomyosin-actin. Biochemistry 28 9111-9116... 

Marston S (1988) Aorta caldesmon inhibits actin activation of thiophosphorylated heavy meromyosin Mg -ATPase activity by slowing the rate of product release. FEES Lett 238 147-150... 

Helfman, D. M., Levy, E. T, Berthier, C., Shtutman, M., Riveline, D., Grosheva, L, Lachish-Zalait, A., Elbaum, M. and Bershadsky, A. D. Caldesmon inhibits nonmuscle cell contractility and interferes with the formation of focal adhesions. Mol Biol Cell 10, 3097-3112,1999. 

In in vitro experiments, caldesmon can inhibit the activation of myosin by actin and this inhibition can be reversed by calmodulin. Thus, there is a potentiality for... 

Ngai, P.K. Walsh, M.P. Inhibition of smooth muscle actin-activated myosin Mg -ATPase activity by caldesmon. J. Biol. Chem., 259, 13656-13659 (1984)... 

Apart from the phosphorylation theory, other regulatory mechanisms have also been suggested for smooth muscle contraction. A thin-filament protein that has been proposed as a regulatory component is caldesmon [102], Purified caldesmon is a potent inhibitor of actin-tropomyosin interaction with myosin. The mechanisms by which calcium removes this inhibition are controversial. Furthermore, phosphorylation of caldesmon by a caldesmon kinase in vitro has also been implicated in this... 

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. 

Caldesmon is a cytoplasmic protein with two isoform classes, one of which is found predominantly in smooth muscle cells and other cell types with partial myogenic differentiation. High-molecular-weight isoforms with molecular weights between 89 and 93 kD are capable of binding to actin, tropomyosin, calmodulin, myosin, and phospholipids, and they function to counteract actin-tropomyosin-activated myosin adenosine triphosphatase (ATPase). As such, they are mediators for the inhibition of calcium-dependent smooth muscle contraction." ... 

Possible caldesmon-induced movement of tropomyosin away from this site or competition with tropomyosin for the site may prevent potentiation from occurring. The work of Chacko and associates (Horiuchi and Chacko, 1989 Horiuchi et al., 1991), in fact, implies that caldesmon may modulate the magnitude of tropomyosin activation, and therefore may control actomyosin ATPase by inhibiting tropomyosin potentiation. This view would explain how a single caldesmon molecule could influence the reactivity of many actin molecules along thin filaments. Such a mechanism of modulation implies that caldesmon may fine-tune contractile activity but not act as an on-off switch per se. This view also fits with results of the elegant experiments of Fay and his collaborators (Itoh et al., 1989), who showed that myosin phosphoryla-... 

The basis of the proposed regulatory function of caldesmon is its ability to inhibit the interaction of myosin with the thin filament. A prerequisite for this is that CD binds to actin. In the native thin filament, TM is also present, and it is found that the presence of TM has effects on CD binding to actin and a very pro-... 

At present, the exact biological function of this protein is not known. When tested for its ability to reverse caldesmon s inhibition of the actin-activated myosin ATPase activity, 12-kDa CaBP had no significant effect on the ATPase activity when the mole ratio of 12-kDa... 

When purified CaD binds to actin-tropomyosin, it inhibits actomyosin ATPase activity. CaM in the presence of Ca + can reverse caldesmon s inhibition of the actin-activated myosin ATPase. However, the affinity of CaM for CaD is rather low (Kgg = 1Q6 M i), with the result that a large molar excess of CaM ( 25-fold) at 25°C in 60 mM KCl is required to reverse caldesmon s inhibition (Pritchard and Mar-ston, 1989 Shirinsky et al, 1988). On the other hand, CaT in the presence of 0.2 mM Ca + is very effective in releasing caldesmon s inhibition at 25°C. Complete recovery in the ATPase rate is achieved when 1 mol of CaT is added per mol of CaD (Mani etal, 1992). In fact, most of the inhibition was released (—90%) by the time... 

Caltropin, which is modulated by Ca2+, binds to CaD in a Ca2+-dependent manner with high affinity. It is also very potent in regulating caldesmon s inhibition in a calcium-dependent manner and could conceivably be the Ca + factor that regulates CaD in smooth muscle. 

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.,... 

Caldesmon has also been shown to inhibit tension development in chemically permeabilized gizzard smooth muscle (Pfitzer etal., 1993). Furthermore, inhibition of caldesmon/F-actin interaction in permeabilized VSM resulted in contractile force generation independently of changes in [Ca +J, supporting the concept that caldesmon may function as a regulator in situ independently of LC20 phosphorylation (Katsuyama et al., 1992). Both caldesmon (Adam et al.,... 

FIGURE 4 Schematic depicting the potential roles for MAPK in contractile versus proliferative (or cultured) smooth muscle. MAPK is activated in response to stimulation by growth factors, stretch, and pharmacological agents. This process can be inhibited by cAMP and cAMP-dependent protein kinase. Once activated, MAPK phos-phorylates a number of intracellular proteins (both cytoplasmic and nuclear) that result in an alteration of growth and proliferation in cultured cells. In contractile smooth muscle, MAPK phosphorylation of caldesmon may lead to alterations in muscle contractility or actin filament structure. 

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