Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL, USA.
Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA.
Cardiovasc Res. 2018 Apr 1;114(5):737-746. doi: 10.1093/cvr/cvy011.
c-jun N-terminal kinase (JNK) is a critical stress response kinase that activates in a wide range of physiological and pathological cellular processes. We recently discovered a pivotal role of JNK in the development of atrial arrhythmias in the aged heart, while cardiac CaMKIIδ, another pro-arrhythmic molecule, was also known to enhance atrial arrhythmogenicity. Here, we aimed to reveal a regulatory role of the stress kinase JNK2 isoform on CaMKIIδ expression.
Activated JNK2 leads to increased CaMKIIδ protein expression in aged human and mouse atria, evidenced from the reversal of CaMKIIδ up-regulation in JNK2 inhibitor treated wild-type aged mice. This JNK2 action in CaMKIIδ expression was further confirmed in HL-1 myocytes co-infected with AdMKK7D-JNK2, but not when co-infected with AdMKK7D-JNK1. JNK2-specific inhibition (either by a JNK2 inhibitor or overexpression of inactivated dominant-negative JNK2 (JNK2dn) completely attenuated JNK activator anisomycin-induced CaMKIIδ up-regulation in HL-1 myocytes, whereas overexpression of JNK1dn did not. Moreover, up-regulated CaMKIIδ mRNA along with substantially increased phosphorylation of JNK downstream transcription factor c-jun [but not activating transcription factor2 (ATF2)] were exhibited in both aged atria (humans and mice) and transiently JNK activated HL-1 myocytes. Cross-linked chromatin-immunoprecipitation assays (XChIP) revealed that both c-jun and ATF2 were bound to the CaMKIIδ promoter, but significantly increased binding of c-jun only occurred in the presence of anisomycin and JNK inhibition alleviated this anisomycin-elevated c-jun binding. Mutated CaMKII consensus c-jun binding sites impaired its promoter activity. Enhanced transcriptional activity of CaMKIIδ by anisomycin was also completely reversed to the baseline by either JNK2 siRNA or c-jun siRNA knockdown.
JNK2 activation up-regulates CaMKIIδ expression in the aged atrium. This JNK2 regulation in CaMKIIδ expression occurs at the transcription level through the JNK downstream transcription factor c-jun. The discovery of this novel molecular mechanism of JNK2-regulated CaMKII expression sheds new light on possible anti-arrhythmia drug development.
c-jun N-末端激酶（JNK）是一种关键的应激反应激酶，它在广泛的生理和病理细胞过程中被激活。我们最近发现 JNK 在老年心脏中的心房性心律失常的发展中起着关键作用，而另一种致心律失常分子心脏 CaMKIIδ 也被认为增强了心房性心律失常的发生。在这里，我们旨在揭示应激激酶 JNK2 同工型对 CaMKIIδ 表达的调节作用。
激活的 JNK2 导致老年人心房中人 CaMKIIδ 蛋白表达增加，这从 JNK2 抑制剂处理的野生型老年小鼠中 CaMKIIδ 上调的逆转中得到了证明。这种 JNK2 在 CaMKIIδ 表达中的作用在共感染 AdMKK7D-JNK2 的 HL-1 心肌细胞中进一步得到了证实，但在共感染 AdMKK7D-JNK1 时则没有。JNK2 特异性抑制（无论是通过 JNK2 抑制剂还是过表达失活的显性负性 JNK2（JNK2dn））完全减弱了 HL-1 心肌细胞中 JNK 激活剂 anisomycin 诱导的 CaMKIIδ 上调，而 JNK1dn 的过表达则没有。此外，在老年心房（人和小鼠）和瞬时 JNK 激活的 HL-1 心肌细胞中，均表现出 CaMKIIδ mRNA 上调，以及 JNK 下游转录因子 c-jun 的磷酸化显著增加[但不是激活转录因子 2（ATF2）]。交联染色质免疫沉淀检测（XChIP）显示，c-jun 和 ATF2 均与 CaMKIIδ 启动子结合，但仅在存在 anisomycin 时 c-jun 的结合显著增加，而 JNK 抑制减轻了这种 anisomycin 升高的 c-jun 结合。CaMKII 共有 c-jun 结合位点的突变损害了其启动子活性。anisomycin 对 CaMKIIδ 转录活性的增强也被 JNK2 siRNA 或 c-jun siRNA 敲低完全逆转至基线。
JNK2 激活可上调老年心房中的 CaMKIIδ 表达。这种 JNK2 在 CaMKIIδ 表达中的调节作用发生在转录水平，通过 JNK 下游转录因子 c-jun 发生。发现 JNK2 调节 CaMKII 表达的这种新分子机制为开发可能的抗心律失常药物提供了新的思路。
