Rationale: Downregulation of Cx43 (connexin 43), the major cardiac gap junction protein, is often associated with arrhythmia, dilated cardiomyopathy (DCM), and heart failure. However, the cause of the reduced expression remains elusive. Reinduction of a nuclear RNA-binding protein CELF1 (CUGBP Elav-like family member 1) in the adult heart has been implicated in the cardiac pathogenesis of myotonic dystrophy type 1. However, how elevated CELF1 level leads to cardiac dysfunction, such as conduction defect, DCM, and heart failure, remains unclear.

Objective: We investigated the mechanism of CELF1-mediated Cx43 mRNA degradation and determined whether elevated CELF1 expression is also a shared feature of the DCM heart.

Methods and Results: RNA immunoprecipitation revealed the involvement of CELF1-regulated genes, including Cx43, in controlling contractility and conduction. CELF1 mediated Cx43 mRNA degradation by binding the UG-rich element in the 3′ untranslated region of Cx43. Mutation of the nuclear localization signal in CELF1 abolished the ability to downregulate Cx43 mRNA, so nuclear localization was required for its function. We further identified a 3′ to 5′ exoribonuclease, RRP6 (ribosomal RNA processing protein 6), as a CELF1-interacting protein. The interaction of CELF1 and RRP6 was RNA-independent and nucleus specific. With knockdown of endogenous RRP6, CELF1 failed to downregulate Cx43 mRNA, which suggests that RRP6 was required for CELF1-mediated Cx43 mRNA degradation. In addition, increased CELF1 level accompanied upregulated RRP6, and reduced Cx43 level was detected in mouse models with DCM, including myotonic dystrophy type 1 and CELF1 overexpression models and a myocardial infarction model. Importantly, depletion of CELF1 in the infarcted heart preserved Cx43 mRNA level and ameliorated the cardiac phenotypes of the infarcted heart.

Conclusions: Our results suggest a mechanism for increased CELF1 expression downregulating Cx43 mRNA level and a pathogenic role for elevated CELF1 level in the DCM heart.

原理：主要的心脏间隙连接蛋白Cx43（连接蛋白43）的下调通常与心律不齐，扩张型心肌病（DCM）和心力衰竭有关。但是，表达降低的原因仍然难以捉摸。成年心脏中核RNA结合蛋白CELF1（CUGBP Elav样家族成员1）的还原与1型强直性肌营养不良的心脏发病有关。但是，CELF1水平升高如何导致心脏功能障碍，例如传导缺陷，DCM和心力衰竭尚不清楚。

目的：我们研究了CELF1介导的Cx43 mRNA降解的机制，并确定CELF1表达升高是否也是DCM心脏的共同特征。

方法和结果：RNA免疫沉淀显示受CELF1调控的基因（包括Cx43）参与控制收缩力和传导。CELF1通过结合Cx43的3'非翻译区中富含UG的元件介导的Cx43 mRNA降解。CELF1中核定位信号的突变消除了下调Cx43 mRNA的能力，因此其功能需要核定位。我们进一步确定了3'至5'外切核糖核酸酶RRP6（核糖体RNA加工蛋白6）作为与CELF1相互作用的蛋白。CELF1和RRP6的相互作用是RNA无关的和特定于细胞核的。随着内源性RRP6的敲低，CELF1无法下调Cx43 mRNA，这表明RLF6是CELF1介导的Cx43 mRNA降解所必需的。此外，CELF1水平升高伴随RRP6上调，并在患有DCM的小鼠模型（包括1型强直性营养不良和CELF1过表达模型以及心肌梗塞模型）中检测到Cx43水平降低。重要的是，梗死心脏中CELF1的消耗保留了Cx43 mRNA的水平，并改善了梗死心脏的心脏表型。

结论：我们的结果表明增加CELF1表达的机制下调了Cx43 mRNA水平，并在DCM心脏中引起了CELF1水平升高的致病作用。