Phosphorylation by casein kinase II alters the biological activity of calmodulin

Abstract

Calmodulin is the major intracellular Ca(2+)-binding protein, providing Ca(2+)-dependent regulation of numerous intracellular enzymes. The phosphorylation of calmodulin may provide an additional mechanism for modulating its function as a signal transducer. Phosphocalmodulin has been identified in tissues and cells, and calmodulin is phosphorylated both in vitro and in intact cells by various enzymes. Phosphorylation of calmodulin on serine/threonine residues by casein kinase II decreases its ability to activate both myosin-light-chain kinase and cyclic nucleotide phosphodiesterase. For myosin-light-chain kinase the primary effect is an inhibition of the Vmax. of the reaction, with no apparent change in the concentration at which half-maximal velocity is attained (K0.5) for either Ca2+ or calmodulin. In contrast, for phosphodiesterase, phosphorylation of calmodulin significantly increases the K0.5 for calmodulin without noticeably altering the Vmax. or the K0.5 for Ca2+. The higher the stoichiometry of phosphorylation of calmodulin, the greater the inhibition of calmodulin-stimulated activity for both enzymes. Therefore the phosphorylation of calmodulin by casein kinase II appears to provide a Ca(2+)-independent mechanism whereby calmodulin regulates at least two important target enzymes, myosin-light-chain kinase and cyclic nucleotide phosphodiesterase.

Calmodulin phosphorylation and modulation of endothelial nitric oxide synthase catalysis

“…This result is in agreement with our prior results that used other CaM-dependent enzymes to demonstrate that phosphorylation of CaM does not change the protein's affinity for calcium (24).…”

Phosphorylation of Calmodulin by the Epidermal‐growth‐factor‐receptor Tyrosine Kinase

“…In support of this, it has been shown that phosphorylation of calmodulin by casein kinase-2 (an insulin-sensitive and EGF-sensitive serinehhreonine kinase) alters the biological activity of calmodulin by decreasing the activation of two calmodulin-dependent enzymes, myosinlight chain kinase and cyclic-nucleotide phosphodiesterase (Sacks et al, 1992a). Additionaly, phosphorylation of calmodulin in Tyr99 by the insulin receptor decreases the action of calmodulin antagonists on the type-I cyclic-nucleotide phosphodiesterase, although it does not affect the calmodulin dependency of this enzyme (Saville and Houslay, 1994).…”

“…Recently we have demonstrated that the epidermal growth factor (EGF) receptor can be isolated by calmodulin-affinity chromatography, and that calmodulin inhibits its tyrosine lunase activity (San JosC et al, 1992). Calmodulin, therefore, could potentially play a regulatory role in the EGF-mediated mitogenic-signal pathway.Calmodulin has been shown to be a substrate for several different protein kinases (Plancke and Lazarides, 1983 ;Hiiring et al, 1985;Fukami et al, 1985;Graves et al, 1986;Lin et al, 1986;Nakajo et al, 1986Nakajo et al, , 1988Meggio et al, 1987Meggio et al, , 1992Kubo and Strott, 1988;Sacks and McDonald, 1988;Laurino et al, 1988; Sacks et al, 1989aSacks et al, , 1992aSan JosC et al, 1992;Benguria et al, 1993;Saville and Houslay, 1994). Since this phosphorylation process occurs in intact …”

Analysis of Phosphorylation and Mutation of Tyrosine Residues of Calmodulin on Its Activation of the Erythrocyte Ca2+‐transporting ATPase

“…Moreover, calmodulin phosphorylation is regulated in vivo by insulin (Colca et al, 1987;Sacks et al, 1992a;Joyal and Sacks, 1994), which sigiiificantly enhances phosphate incorporation at serine, threonine and tyrosine residues (Sacks et al, 1992a). The interaction between calmodulin and several calmodulin-dependent enzymes has been studied in detail in vitro using purified components (Cohen and Klee, 1988).…”

“…Phosphorylation is a cotnmon mechanism for the regulation of intracellular signalling and calmodulin is known to be phosphorylated in vitro by several protein kinases. The best characterized of these are casein kinase 11 (Nakajo et al, 1986;Sacks et al, 1992a) and the insulin-receptor kinase (Graves et al, 1986;Sacks and McDonald, 1988;Sacks et al, 1989). The sites phosphorylated on callmodulin are Thr79 (14%), Ser8l(SO%), Serl01(25%) and Thrl17 (1 1 %) by casein kinase 11 (values in parentheses are the relative amounts of phosphorylation at each site, expressed as percentage of total '2P incorporation; Sacks et al, 1992a) and both tyrosine residues, namely Tyr99 and Tyr138, by the insulin-receptor kinase (Joyal and Sacks, 1994;Williams et al, 1994).…”