CELF1 Mediates Connexin 43 mRNA Degradation in Dilated Cardiomyopathy.

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.

Salvia miltiorrhiza Extract and Individual Synthesized Component Derivatives Induce Activating-Transcription-Factor-3-Mediated Anti-Obesity Effects and Attenuate Obesity-Induced Metabolic Disorder by Suppressing C/EBPα in High-Fat-Induced Obese Mice.

Pharmacological studies indicate that Salvia miltiorrhiza extract (SME) can improve cardiac and blood vessel function. However, there is limited knowledge regarding the effects (exerted through epigenetic regulation) of SME and newly derived single compounds, with the exception of tanshinone IIA and IB, on obesity-induced metabolic disorders. In this study, we administered SME or dimethyl sulfoxide (DMSO) as controls to male C57BL/J6 mice after they were fed a high-fat diet (HFD) for 4 weeks. SME treatment significantly reduced body weight, fasting plasma glucose, triglyceride levels, insulin resistance, and adipogenesis/lipogenesis gene expression in treated mice compared with controls. Transcriptome array analysis revealed that the expression of numerous transcriptional factors, including activating transcription factor 3 (ATF3) and C/EBPα homologous protein (CHOP), was significantly higher in the SME group. ST32db, a novel synthetic derivative similar in structure to compounds from S. miltiorrhiza extract, ameliorates obesity and obesity-induced metabolic syndrome in HFD-fed wild-type mice but not ATF3-/- mice. ST32db treatment of 3T3-L1 adipocytes suppresses lipogenesis/adipogenesis through the ATF3 pathway to directly inhibit C/EBPα expression and indirectly inhibit the CHOP pathway. Overall, ST32db, a single compound modified from S. miltiorrhiza extract, has anti-obesity effects through ATF3-mediated C/EBPα downregulation and the CHOP pathway. Thus, SME and ST32db may reduce obesity and diabetes in mice, indicating the potential of both SME and ST32db as therapeutic drugs for the treatment of obesity-induced metabolic syndrome.

Hyperpolyploidization of hepatocyte initiates preneoplastic lesion formation in the liver.

Hepatocellular carcinoma (HCC) is the most predominant primary malignancy in the liver. Genotoxic and genetic models have revealed that HCC cells are derived from hepatocytes, but where the critical region for tumor foci emergence is and how this transformation occurs are still unclear. Here, hyperpolyploidization of hepatocytes around the centrilobular (CL) region is demonstrated to be closely linked with the development of HCC cells after diethylnitrosamine treatment. We identify the CL region as a dominant lobule for accumulation of hyperpolyploid hepatocytes and preneoplastic tumor foci formation. We also demonstrate that upregulation of Aurkb plays a critical role in promoting hyperpolyploidization. Increase of AURKB phosphorylation is detected on the midbody during cytokinesis, causing abscission failure and hyperpolyploidization. Pharmacological inhibition of AURKB dramatically reduces nucleus size and tumor foci number surrounding the CL region in diethylnitrosamine-treated liver. Our work reveals an intimate molecular link between pathological hyperpolyploidy of CL hepatocytes and transformation into HCC cells.