Tan Wei-Qi, Wang Jian-Xun, Lin Zhi-Qiang, Li Yan-Rui, Lin Yu, Li Pei-Feng
Division of Cardiovascular Research, National Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, China.
Circulation. 2008 Nov 25;118(22):2268-76. doi: 10.1161/CIRCULATIONAHA.107.750869. Epub 2008 Nov 10.
Apoptosis repressor with caspase recruitment domain (ARC) is abundantly expressed in cardiomyocytes. Protein kinase CK2 can phosphorylate ARC at threonine-149, thereby enabling ARC to antagonize apoptosis. ARC phosphorylation occurs in a constitutive manner. Nevertheless, cardiomyocytes still undergo apoptosis that is related to cardiac diseases such as myocardial infarction and heart failure. Whether the occurrence of apoptosis is related to the loss of protection by ARC under pathological conditions remains unknown.
ARC phosphorylation levels are decreased in cardiomyocytes treated with isoproterenol or aldosterone. We explored the molecular mechanism by which ARC phosphorylation levels are decreased. Our results reveal that either direct incubation or coexpression with calcineurin leads to a decrease in ARC phosphorylation levels. Inhibition of calcineurin can attenuate the reduction in ARC phosphorylation levels on treatment with isoproterenol or aldosterone. These data indicate that the reduction in ARC phosphorylation levels is related to its dephosphorylation by calcineurin. Our results further reveal that ARC can prevent isoproterenol- and aldosterone-induced apoptosis, but this function depends on its phosphorylation status. Isoproterenol and aldosterone upregulate Fas ligand expression, and Fas ligand and caspase-8 are required for isoproterenol and aldosterone to induce apoptosis. However, phosphorylated but not dephosphorylated ARC is able to inhibit caspase-8-mediated apoptosis. Phosphorylated ARC exerts its effects against caspase-8 by directly associating with procaspase-8 and inhibiting its interaction with Fas-associated protein with death domain.
Our study identifies a novel cardiac apoptotic pathway in which ARC is dephosphorylated by calcineurin. This pathway could be a component in the cardiac apoptotic machinery.
含半胱天冬酶募集结构域的凋亡抑制蛋白（ARC）在心肌细胞中大量表达。蛋白激酶CK2可使ARC的苏氨酸-149位点磷酸化，从而使ARC能够拮抗细胞凋亡。ARC磷酸化以组成型方式发生。然而，心肌细胞仍会发生与诸如心肌梗死和心力衰竭等心脏疾病相关的细胞凋亡。在病理条件下细胞凋亡的发生是否与ARC保护作用的丧失有关仍不清楚。
用异丙肾上腺素或醛固酮处理的心肌细胞中ARC磷酸化水平降低。我们探究了ARC磷酸化水平降低的分子机制。我们的结果显示，直接孵育或与钙调神经磷酸酶共表达均会导致ARC磷酸化水平降低。抑制钙调神经磷酸酶可减弱异丙肾上腺素或醛固酮处理后ARC磷酸化水平的降低。这些数据表明，ARC磷酸化水平的降低与其被钙调神经磷酸酶去磷酸化有关。我们的结果进一步显示，ARC可预防异丙肾上腺素和醛固酮诱导的细胞凋亡，但该功能取决于其磷酸化状态。异丙肾上腺素和醛固酮上调Fas配体表达，并且异丙肾上腺素和醛固酮诱导细胞凋亡需要Fas配体和半胱天冬酶-8。然而，磷酸化而非去磷酸化的ARC能够抑制半胱天冬酶-8介导的细胞凋亡。磷酸化的ARC通过直接与半胱天冬酶原-8结合并抑制其与死亡结构域相关蛋白的相互作用来发挥其对半胱天冬酶-8的作用。
我们的研究确定了一种新的心脏凋亡途径，其中ARC被钙调神经磷酸酶去磷酸化。该途径可能是心脏凋亡机制的一个组成部分。
