Phosphorylation of Ser(16) alone in T17A mutant PLB resulted in mechanical and Ca(2+) kinetic responses to isoproterenol similar to wild-type myocytes, mediating maximal cardiac responses.
Does Ser16 phosphorylation in phospholamban mediate maximal cardiac responses to beta-agonists independently of Thr17?
Ser16 phosphorylation in phospholamban is sufficient to mediate maximal cardiac mechanical and calcium kinetic responses to beta-adrenergic stimulation, independent of Thr17 phosphorylation.
Phospholamban (PLB) can be phosphorylated at Ser(16) by cyclic AMP-dependent protein kinase and at Thr(17) by Ca(2+)-calmodulin-dependent protein kinase during beta-agonist stimulation. A previous study indicated that mutation of S16A in PLB resulted in lack of Thr(17) phosphorylation and attenuation of the beta-agonist stimulatory effects in perfused mouse hearts. To further delineate the functional interplay between dual-site PLB phosphorylation, we generated transgenic mice expressing the T17A mutant PLB in the cardiac compartment of the null background. Lines expressing similar levels of T17A mutant, S16A mutant, or wild-type PLB in the null background were characterized in parallel. Cardiac myocyte basal mechanics and Ca(2+) kinetics were similar among the three groups. Isoproterenol stimulation was associated with phosphorylation of both Ser(16) and Thr(17) in wild-type PLB and Ser(16) phosphorylation in T17A mutant PLB, whereas there was no detectable phosphorylation of S16A mutant PLB. Phosphorylation of Ser(16) alone in T17A mutant PLB resulted in responses of the mechanical and Ca(2+) kinetic parameters to isoproterenol similar to those in wild-type myocytes, which exhibited dual-site PLB phosphorylation. However, those parameters were significantly attenuated in the S16A mutant myocytes. Thus, Ser(16) in PLB can be phosphorylated independently of Thr(17) in vivo, and phosphorylation of Ser(16) is sufficient for mediating the maximal cardiac responses to beta-adrenergic stimulation.
Chu et al. (2000) studied Cardiac myocyte mechanics and Ca(2+) kinetics. Isoproterenol vs. Wild-type PLB and S16A mutant PLB was evaluated on Cardiac myocyte mechanical and Ca(2+) kinetic parameters. Phosphorylation of Ser(16) alone in T17A mutant PLB resulted in mechanical and Ca(2+) kinetic responses to isoproterenol similar to wild-type myocytes, mediating maximal cardiac responses.