Mattiazzi Alicia, Kranias Evangelia G
Facultad de Medicina, Centro de Investigaciones Cardiovasculares, Conicet La Plata-Universidad Nacional de La Plata La Plata, Argentina.
Department of Pharmacology and Cell Biophysics, College of Medicine, University of Cincinnati Cincinnati, OH, USA.
Front Pharmacol. 2014 Jan 27;5:5. doi: 10.3389/fphar.2014.00005. eCollection 2014.
Phospholamban (PLN) is a phosphoprotein in cardiac sarcoplasmic reticulum (SR) that is a reversible regulator of the Ca(2) (+)-ATPase (SERCA2a) activity and cardiac contractility. Dephosphorylated PLN inhibits SERCA2a and PLN phosphorylation, at either Ser(16) by PKA or Thr(17) by Ca(2) (+)-calmodulin-dependent protein kinase (CaMKII), reverses this inhibition. Through this mechanism, PLN is a key modulator of SR Ca(2) (+) uptake, Ca(2) (+) load, contractility, and relaxation. PLN phosphorylation is also the main determinant of β1-adrenergic responses in the heart. Although phosphorylation of Thr(17) by CaMKII contributes to this effect, its role is subordinate to the PKA-dependent increase in cytosolic Ca(2) (+), necessary to activate CaMKII. Furthermore, the effects of PLN and its phosphorylation on cardiac function are subject to additional regulation by its interacting partners, the anti-apoptotic HAX-1 protein and Gm or the anchoring unit of protein phosphatase 1. Regulation of PLN activity by this multimeric complex becomes even more important in pathological conditions, characterized by aberrant Ca(2) (+)-cycling. In this scenario, CaMKII-dependent PLN phosphorylation has been associated with protective effects in both acidosis and ischemia/reperfusion. However, the beneficial effects of increasing SR Ca(2) (+) uptake through PLN phosphorylation may be lost or even become deleterious, when these occur in association with alterations in SR Ca(2) (+) leak. Moreover, a major characteristic in human and experimental heart failure (HF) is depressed SR Ca(2) (+) uptake, associated with decreased SERCA2a levels and dephosphorylation of PLN, leading to decreased SR Ca(2) (+) load and impaired contractility. Thus, the strategy of altering SERCA2a and/or PLN levels or activity to restore perturbed SR Ca(2) (+) uptake is a potential therapeutic tool for HF treatment. We will review here the role of CaMKII-dependent phosphorylation of PLN at Thr(17) on cardiac function under physiological and pathological conditions.
受磷蛋白（PLN）是心肌肌浆网（SR）中的一种磷蛋白，是Ca(2) (+)-ATP酶（SERCA2a）活性和心肌收缩性的可逆调节因子。去磷酸化的PLN抑制SERCA2a，而PLN的磷酸化，无论是蛋白激酶A（PKA）介导的Ser(16)位点磷酸化还是Ca(2) (+)-钙调蛋白依赖性蛋白激酶（CaMKII）介导的Thr(17)位点磷酸化，均可逆转这种抑制作用。通过这一机制，PLN是肌浆网Ca(2) (+)摄取、Ca(2) (+)负荷、收缩性和舒张的关键调节因子。PLN磷酸化也是心脏中β1-肾上腺素能反应的主要决定因素。虽然CaMKII介导的Thr(17)位点磷酸化有助于这一效应，但其作用从属于PKA依赖性的胞质Ca(2) (+)增加，而这是激活CaMKII所必需的。此外，PLN及其磷酸化对心脏功能的影响还受到其相互作用伙伴的额外调节，即抗凋亡蛋白HAX-1和Gm或蛋白磷酸酶1的锚定单位。在以异常Ca(2) (+)循环为特征的病理状态下，这种多聚体复合物对PLN活性的调节变得更加重要。在这种情况下，CaMKII依赖性的PLN磷酸化在酸中毒和缺血/再灌注中均与保护作用相关。然而，当通过PLN磷酸化增加肌浆网Ca(2) (+)摄取与肌浆网Ca(2) (+)泄漏改变同时发生时，其有益作用可能会丧失甚至变得有害。此外，人类和实验性心力衰竭（HF）的一个主要特征是肌浆网Ca(2) (+)摄取降低，这与SERCA2a水平降低和PLN去磷酸化有关，导致肌浆网Ca(2) (+)负荷降低和收缩性受损。因此，改变SERCA2a和/或PLN水平或活性以恢复受扰的肌浆网Ca(2) (+)摄取的策略是治疗HF的一种潜在治疗工具。我们将在此回顾CaMKII依赖性的PLN在Thr(17)位点磷酸化在生理和病理条件下对心脏功能的作用。
