The antiapoptotic protein HAX-1 mediates half of phospholamban's inhibitory activity on calcium cycling and contractility in the heart
The antiapoptotic protein HAX-1 mediates half of phospholamban's inhibitory activity on calcium cycling and contractility in the heart
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DOI：
10.1074/jbc.ra117.000128
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发表时间：
2018-01-05
影响因子：
4.8
通讯作者：
Kranias, Evangelia G.
中科院分区：
文献类型：
--
作者：
Bidwell, Philip A.;Haghighi, Kobra;Kranias, Evangelia G.
抗凋亡蛋白HAX-1（HS相关蛋白X-1）定位于心脏中的肌浆网（SR），并与小膜蛋白受磷蛋白（PLN）相互作用，抑制心脏肌浆网/内质网钙ATP酶2a（SERCA 2a）调节整体钙处理和心肌收缩性。然而，由于整体HAX-1缺失导致早期致死，内源性HAX-1对PLN对钙循环的抑制活性有多大贡献尚不清楚。因此，我们产生了心脏特异性和诱导型基因敲除小鼠模型。HAX-1消融在成人心脏显著增加收缩参数和钙动力学，与SR钙负荷增加。这些变化发生时，SERCA 2a、PLN和ryanodine受体的蛋白表达或PLN磷酸化状态没有任何变化。HAX-1耗竭心脏中增强的钙循环通过SERCA 2a的钙亲和力增加和PLN-SERCA 2a结合减少介导。HAX-1缺失诱导的刺激作用与PLN消融引起的刺激作用的比较表明，HAX-1介导了心脏中约50%的PLN相关抑制作用。用正性肌力和负性肌力剂异丙肾上腺素刺激消除了野生型、HAX-1缺陷型和PLN缺陷型心脏之间的差异，最大刺激收缩和钙动力学参数在这三组之间相似。此外，PLN在HAX-1-null心肌细胞中的过表达没有引起任何抑制作用，表明HAX-1可能限制PLN活性。这些发现表明，HAX-1是PLN的抑制活性的主要介质和心脏中SR钙循环和收缩性的关键守门人。
The antiapoptotic protein HAX-1 (HS-associated protein X-1) localizes to sarcoplasmic reticulum (SR) in the heart and interacts with the small membrane protein phospholamban (PLN), inhibiting the cardiac sarco/endoplasmic reticulum calcium ATPase 2a (SERCA2a) in the regulation of overall calcium handling and heart muscle contractility. However, because global HAX-1 deletion causes early lethality, how much endogenous HAX-1 contributes to PLN's inhibitory activity on calcium cycling is unknown. We therefore generated a cardiac-specific and inducible knock-out mouse model. HAX-1 ablation in the adult heart significantly increased contractile parameters and calcium kinetics, associated with increased SR calcium load. These changes occurred without any changes in the protein expression of SERCA2a, PLN, and ryanodine receptor or in the PLN phosphorylation status. The enhanced calcium cycling in the HAX-1-depleted heart was mediated through increases in the calcium affinity of SERCA2a and reduced PLN-SERCA2a binding. Comparison of the HAX-1 deletion-induced stimulatory effects with those elicited by PLN ablation indicated that HAX-1 mediates approximate to 50% of the PLN-associated inhibitory effects in the heart. Stimulation with the inotropic and lusitropic agent isoproterenol eliminated the differences among wild-type, HAX-1-deficient, and PLN-deficient hearts, and maximally stimulated contractile and calcium kinetic parameters were similar among these three groups. Furthermore, PLN overexpression in the HAX-1-null cardiomyocytes did not elicit any inhibitory effects, indicating that HAX-1 may limit PLN activity. These findings suggest that HAX-1 is a major mediator of PLN's inhibitory activity and a critical gatekeeper of SR calcium cycling and contractility in the heart.