Calmodulin-dependent Cyclic Nucleotide Phosphodiesterase Research Articles

Inhibition of calmodulin-dependent cyclic nucleotide phosphodiesterase by flunarizine, a calcium-entry blocker

It has been reported that flunarizine, classified as calcium entryblockers, is a potent brain protective drug without any heart depressant effect, contrasting with other drugs in this group. This paper presents evidence that through a competitive antagonism against calmodulin, a major intracellular calcium receptor, flunarizine inhibits the calcium·calmodulin-activated phosphodiesterase activity of bovine brain, but not of heart, whereas other calcium-entry blockers and calmodulin antagonists inhibit to the same extent, the activation of the enzyme from the two sources. It could be suggested that some of pharmacological effects by flunarizine and its differences from other calcium-entry blockers may be explained by its interaction with calmodulin.

Demonstration of bovine brain calmodulin-dependent cyclic nucleotide phosphodiesterase isozymes by monoclonal antibodies.

Calmodulin-dependent cyclic nucleotide phosphodiesterase from bovine brain is found to be composed of two distinct subunits, 60,000- and 63,000-dalton polypeptides. Peptide mapping of the subunits by partial proteolysis demonstrated that the 60-kDa polypeptide is not derived from the 63-kDa species. The interaction of the enzyme with three monoclonal antibodies, A6, C1, and A2, and the analysis of immunocomplexes by sucrose density gradient centrifugation revealed that calmodulin-dependent cyclic nucleotide phosphodiesterase exists in three different forms, i.e. (a) homodiamer of 60-kDa, (b) heterodimer of 60- and 63-kDa, and (c) homodimer of 63-kDa. A6 antibody reacts with both 60- and 63-kDa polypeptides indicating that they are immunologically related. C1 and A2 antibodies react with only 60-kDa polypeptide species. By using C1 Sepharose 4B affinity column chromatography, the 63-kDa homodimer which did not bind to the column (Fraction I) was separated from the 60-kDa polypeptide containing isozymes (the heterodimer and the 60-kDa homodimer) which were retained on the column and later eluted as a mixture (Fraction II). Fraction I, the 63-kDa homodimer enzyme, has higher Vmax toward cGMP as substrate than cAMP whereas the opposite was found with Fraction II. The specific activity of Fraction II enzyme toward cAMP was approximately 500 mumol/min/mg, the highest value ever reported for brain calmodulin-dependent cyclic nucleotide phosphodiesterase preparations.

Heat-stable calmodulin-binding protein in rat testis. Inhibition of calmodulin-stimulated cyclic nucleotide phosphodiesterase activity.

An inhibitor of procine brain calmodulin-dependent cyclic nucleotide phosphodiesterase was purified about 940-fold from rat testis. This inhibitor inhibited the calmodulin-induced activation of the enzyme without affecting its basal activity. The inhibitor activity was counteracted by a high concentration of calmodulin, but was not by a high concentration of Ca2+. The analysis on polyacrylamide disc gel electrophoresis demonstrated that the inhibitor and calmodulin form a complex in the presence of Ca2+ but not in the presence of excess amount of EGTA. This inhibitor also inhibited the calmodulin-induced activation of Ca2+, Mg2+ -ATPase of human erythrocytes. The inhibitor appeared to be a heat-stable protein, since the inhibitor activity was not attenuated by boiling up to 9 min but was completely abolished by tryptic or chymotryptic digestion. The molecular weights of the inhibitor determined by linear polyacrylamide gradient gel electrophoresis under nondenaturing conditions and sodium dodecyl sulfate-polyacrylamide gel electrophoresis were 40,000 and 32,000, respectively. Thus, the inhibitor is suggested to be a calmodulin-binding protein composed of a monomer which has unique properties different from those of other tissues.

Function of calmodulin in mammalian sperm: Presence of a calmodulin-dependent cyclic nucleotide phosphodiesterase associated with demembranated rat caudal epididymal sperm

A calmodulin dependent cyclic nucleotide phosphodiesterase is associated with the head and tailpieces of demembranated rat caudal epididymal sperm. The phosphodiesterase was stimulated two-fold in the presence of Ca 2+, while the simultaneous addition of Ca 2+ and calmodulin resulted in a four-fold increase in activity. Ca 2+ stimulation was abolished if demembranated sperm were extracted with EGTA and was recovered upon the addition of exogenous calmodulin. Micromolar levels of Ca 2+ were required for full stimulation. Trifluoperazine inhibited the Ca 2+ stimulated enzyme in a dose dependent manner (ID 50 = 50 μM) but had no effect on the basal phosphodiesterase activity.

A monoclonal antibody showing cross-reactivity toward three calmodulin-dependent enzymes.

The spleen cells of a Balb/c mouse immunized with purified bovine calmodulin-dependent cyclic nucleotide phosphodiesterase were fused with nonsecreting mouse myeloma cells (P3-X63-Ag8-653). Antibody producing hybridomas were screened by the enzyme-linked immunosorbent assay using purified phosphodiesterase as the antigen. One monoclonal cell line, CR-B1, was found to produce antibodies which showed positive enzyme-linked immunosorbent assay reactions with bovine brain calcineurin and rabbit muscle phosphorylase kinase in addition to phosphodiesterase. The antibody was purified and characterized. It was shown to immunoprecipitate the calmodulin (CaM)-dependent phosphodiesterase and phosphorylase kinase activities but not those of CaM itself, CaM-independent phosphodiesterase and the catalytic unit of cAMP-dependent protein kinase. The immunoprecipitation of phosphodiesterase could be inhibited by calcineurin and phosphorylase kinase. These results suggest that the antibody interacts at a common site on these calmodulin-dependent proteins. The antigenic determinant in phosphodiesterase does not appear to reside in the calmodulin-binding domain of the enzyme since the antibody and phosphodiesterase interaction is not inhibited by calmodulin, and the calmodulin activation of phosphodiesterase is not affected by CR-B1 antibody. It is therefore suggested that the structural similarity among the three calmodulin-dependent proteins extends beyond the calmodulin-binding domains.

Purification and kinetic properties of two soluble forms of calmodulin-dependent cyclic nucleotide phosphodiesterase from rat pancreas.

The calmodulin-dependent cyclic AMP phosphodiesterase and cyclic GMP phosphodiesterase (EC 3.1.4.17) activity of rat pancreas was purified 280-fold by affinity chromatography on calmodulin-Sepharose 4B. It then accounted for 15% of the total cytosol cyclic GMP nucleotide phosphodiesterase activity, in the presence of Ca2+, and represented a minor component of proteins specifically adsorbed by the column. This activity was resolved on a DEAE-Sephacel column into two fractions, termed PI and PII, on the basis of their order of emergence. After this step, PI and PII were purified 5650- and 3700-fold respectively. The molecular weight of PI was 175 000 and that of PII was 116 000, by polyacrylamide-gradient-gel electrophoresis. Both forms of phosphodiesterase could hydrolyse cyclic AMP and cyclic GMP, although PII displayed a higher affinity toward cyclic GMP than toward cyclic AMP. PI and PII exhibited negative homotropic kinetics in the absence of calmodulin. Upon addition of calmodulin, both enzymes displayed Michaelis-Menten kinetics and a 5-9-fold increase in maximal velocity, at physiological concentrations of cyclic GMP and cyclic AMP. When a pancreatic extract freshly purified by affinity chromatography was immediately analysed by high-performance gel-permeation chromatography on a TSK gel G3000 SW column, PII represented as much as 78% of the eluted activity. This percentage decreased to 52% when the sample was stored at 0 degrees C for 20 h before analysis, suggesting that PII, possibly predominant in vivo, was converted into the heavier PI form upon storage.

Ca2+-channel blockers and calmodulin

We examined the interactions among calmodulin (CaM) and Ca2+ -channel blockers with regard to the possible inhibition of two Ca2+-CaM-dependent enzymes, Ca2+-CaM-dependent cyclic nucleotide phosphodiesterase (Ca2+-pde) and myosin light chain kinase(MLCK). Although all the Ca2+-channel blockers tested inhibited Ca2+-PDE, the mode of inhibitory action differed.

Interaction of psychotropic drugs with phospholipids

The interactions of psychotropic drugs with phospholipids, including lysophosphatidylcholine, phosphatidylinositol, and lysophosphatidylserine, were studied using calmodulin-dependent cyclic nucleotide phosphodiesterase partially purified from the cortex of hog brain. All the compounds used inhibited both calmodulin- and phospholipid-stimulated phosphodiesterase activity but not the basal activity. Fluphenazine was confirmed by kinetic analysis to be a competitive inhibitor, with both calmodulin and phospholipid. Using fluphenazine-Sepharose affinity chromatography, it was demonstrated that fluphenazine did not interact with the enzyme. The potencies of antipsychotics such as fluphenazine in inhibiting the various phospholipid-dependent activations decreased in the following order: lysophosphatidylcholine-, phosphatidylinositol-, and lysophosphatidylserine-dependent activation. On the other hand, antidepressant drugs exhibited similar inhibitory potencies towards lysophosphatidylcholine- and phosphatidylinositol-dependent activation. Antipsychotic and antide-pressant drugs appear to have different characteristics with regard to lipid-drug interaction.

Inhibition of bovine brain cyclic nucleotide phosphodiesterase by a proteinaceous factor from Escherichia coli.

An inhibitory factor for Ca2+ and calmodulin-dependent cyclic nucleotide phosphodiesterase of bovine brain was present in the soluble fraction of Escherichia coli. The factor was heat-stable but trypsin sensitive. The activity of brain phosphodiesterase supported by Ca2+ and calmodulin was inhibited by the factor in a dose dependent manner, but the basal activity was not affected. The inhibition of phosphodiesterase induced by the factor could be abolished by adding large amount of calmodulin, but not by increasing concentration of Ca2+. It was suggested that the factor interacted with calmodulin and thereby inhibited the phosphodiesterase. The factor may be a calmodulin-binding protein in E. coli.

Interaction of calmodulin with chromatin associated proteins and myelin basic protien

Chromatin associated proteins such as histone and protamine and myelin basic protein inhibit the activities of calmodulin-dependent cyclic nucleotide phosphodiesterase and myosin light chain kinase supported by Ca 2+ and calmodulin in a dose-dependent manner. The inhibition of these enzymes induced by the proteins is completely abolished by high concentration of calmodulin but not with that of Ca 2+. Kinetic analysis of this inhibition reveals that the proteins inhibit these enzyme activities in a competitive fashion with calmodulin. The proteins bind to calmodulin on a calmodulin coupled-agarose affinity column in the presence of Ca 2+. It is suggested that endogenous basic proteins interact with calmodulin and may modulate intracellular regulation by calmodulin.

Cyclic nucleotide phosphodiesterase of rat pancreatic islets. Effects of Ca2+, calmodulin and trifluoperazine.

Cyclic nucleotide phosphodiesterase activity towards cyclic AMP and cyclic GMP was studied in extracts of rat islets of Langerhans. Biphasic Eadie plots [Eadie (1942) J. Biol. Chem. 146, 85-93] were obtained with either substrate suggesting the presence of both 'high'- and 'low'-Km components. The apparent Km values were 6.2 +/- 0.5 (n = 8) microM and 103.4 +/- 13.5 (6) microM for cyclic AMP and 3.6 +/- 0.3 (12) microM and 61.4 +/- 7.5 (13) microM for cyclic GMP. With cyclic AMP as substrate, phosphodeisterase activity was increased by calmodulin and Ca2+ and decreased by trifluoperazine, a specific inhibitor of calmodulin. With cyclic GMP as substrate, phosphodiesterase activity was decreased by omission of Ca2+ or addition of trifluoperazine. Addition of exogenous calmodulin had no effect on activity. The data suggest that Ca2+ may influence the islet content of cyclic AMP and cyclic GMP via effects on calmodulin-dependent cyclic nucleotide phosphodiesterase(s).

Differential interaction of rabbit skeletal muscle phosphorylase kinase isozymes with calmodulin.

Rabbit skeletal muscle contains two phosphorylase kinase isozymes arising from the two different muscle types, the white and the red muscle (Jennissen, H. P., and Heilmeyer, L. M. G. (1974) FEBS Lett. 42, 77-80). The two phosphorylase kinase isozymes could be separated by affinity chromatography on a calmodulin-Sepharose 4B column. In media containing high concentrations of Ca2+, about 2 mM, both isozymes were bound to the affinity column. When the column was eluted with a buffer containing 0.2 mM Ca2+, the red muscle isozyme was eluted, whereas white muscle isozyme was eluted from the column by an ethylene glycol bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid. The purified white muscle isozyme can be distinguished from the red muscle isozyme by its ability to inhibit calmodulin-dependent cyclic nucleotide phosphodiesterase. The two isozymes are also regulated differently by calmodulin. Both isozymes contain tightly bound calmodulin as a subunit (Cohen, P., Burchell, A., Foulkes, J. G., Cohen, P. T. W., Vanaman, T. C., and Nairn, A. C. (1978) FEBS Lett. 92, 287-293), which renders the enzyme sensitive to Ca2+. Only the white muscle isozyme can be activated by exogenous calmodulin.

Purification and properties of bovine brain calmodulin-dependent cyclic nucleotide phosphodiesterase.

Calmodulin-dependent cyclic nucleotide phosphodiesterase was purified from bovine brain to apparent homogeneity by a new procedure involving DEAE-cellulose, Affi-Gel blue, calmodulin-Sepharose 4B, and Sephadex G-200 column chromatographies. The enzyme was purified more than 3,000-fold from the brain extracts with greater than 12% yield. The purified phosphodiesterase could be activated 10- to 15-fold by calmodulin and Ca2+ to a specific enzyme activity of more than 300 mumol of cAMP hydrolyzed/min/mg of protein. Molecular weight of the enzyme was determined to be 115,800 by the sedimentation equilibirum method or 124,000 from the sedimentation constant and Stokes radius of the protein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the enzyme showed a single protein band with an apparent molecular weight of 58,000. These results suggested that the calmodulin-dependent phosphodiesterase from bovine brain has a subunit structure of alpha2. Molecular weight of the complex of calmodulin and phosphodiesterase was the complex of calmodulin and phosphodiesterase was also calculated from the sedimentation constant and Stokes radius to be 159,000. Since calmodulin has a molecular weight of about 17,000, the result indicated that the stoichiometry of the complex is calmodulin2 alpha2. The catalytic subunit of cylic AMP-dependent protein kinase was found to catalyze the phosphorylation of the purified phosphodiesterase with the incorporation of 2 mol of phosphate/mol of the enzyme.