Rodriguez Patricia, Mitton Bryan, Nicolaou Persoulla, Chen Guoli, Kranias Evangelia G
Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0575, USA.
Am J Physiol Heart Circ Physiol. 2007 Jul;293(1):H762-9. doi: 10.1152/ajpheart.00104.2007. Epub 2007 Apr 6.
The depressed function of failing hearts has been partially attributed to increased protein phosphatase-1 through its impaired regulation by inhibitor-1. Phosphorylation of inhibitor-1 at Thr35 by PKA results in potent inhibition of protein phosphatase-1 activity, while phosphorylation at Ser67 or Thr75 by PKC attenuates the inhibitory activity. To examine the functional role of dual-site (Ser67, Thr75) phosphorylation of inhibitor-1 by PKC, the constitutively phosphorylated Ser67 (S67D) and/or Thr75 (T75D) human inhibitor-1 forms were expressed in adult cardiomyocytes. Expression of either single or double phosphorylated inhibitor-1 was associated with similar decreases in cardiac contractility, indicating that maximal inhibition can be elicited by each of these sites alone and that their inhibitory effects are not additive. Notably, activation of the cAMP pathway could only partially reverse the depressed contractile parameters. Accordingly, protein phosphatase-1 activity remained elevated, phosphorylation of phospholamban at Ser16 was decreased, and the EC(50) values of the sarcoplasmic reticulum calcium transport system were higher compared with controls. Thus phosphorylation of Ser67 and/or Thr75 in inhibitor-1 may mitigate the stimulatory effects of the cAMP pathway, resulting in compromised cardiac function.
衰竭心脏功能的降低部分归因于蛋白磷酸酶-1增加，这是由于其受抑制因子-1的调节受损所致。蛋白激酶A（PKA）使抑制因子-1的苏氨酸35位点磷酸化，可有效抑制蛋白磷酸酶-1的活性，而蛋白激酶C（PKC）使抑制因子-1的丝氨酸67或苏氨酸75位点磷酸化，则会减弱其抑制活性。为了研究PKC对抑制因子-1双位点（丝氨酸67、苏氨酸75）磷酸化的功能作用，将组成型磷酸化的丝氨酸67（S67D）和/或苏氨酸75（T75D）人抑制因子-1形式在成年心肌细胞中表达。单磷酸化或双磷酸化抑制因子-1的表达均与心脏收缩力的类似降低相关，这表明这些位点中的每一个单独都可引发最大抑制作用，且它们的抑制作用并非相加的。值得注意的是，环磷酸腺苷（cAMP）途径的激活只能部分逆转降低的收缩参数。因此，蛋白磷酸酶-1的活性仍然升高；受磷蛋白在丝氨酸16位点的磷酸化减少；与对照组相比，肌浆网钙转运系统的半数有效浓度（EC50）值更高。因此，抑制因子-1中丝氨酸67和/或苏氨酸75位点的磷酸化可能会减轻cAMP途径的刺激作用，从而导致心脏功能受损。
