Localization of α-Dystrobrevin in Cajal Bodies and Nucleoli: A New Role for α-Dystrobrevin in the Structure/Stability of the Nucleolus

An Overview of Alternative Splicing Defects Implicated in Myotonic Dystrophy Type I

Myotonic dystrophy type I (DM1) is the most common form of adult muscular dystrophy, caused by expansion of a CTG triplet repeat in the 3′ untranslated region (3′UTR) of the myotonic dystrophy protein kinase (DMPK) gene. The pathological CTG repeats result in protein trapping by expanded transcripts, a decreased DMPK translation and the disruption of the chromatin structure, affecting neighboring genes expression. The muscleblind-like (MBNL) and CUG-BP and ETR-3-like factors (CELF) are two families of tissue-specific regulators of developmentally programmed alternative splicing that act as antagonist regulators of several pre-mRNA targets, including troponin 2 (TNNT2), insulin receptor (INSR), chloride channel 1 (CLCN1) and MBNL2. Sequestration of MBNL proteins and up-regulation of CELF1 are key to DM1 pathology, inducing a spliceopathy that leads to a developmental remodelling of the transcriptome due to an adult-to-foetal splicing switch, which results in the loss of cell function and viability. Moreover, recent studies indicate that additional pathogenic mechanisms may also contribute to disease pathology, including a misregulation of cellular mRNA translation, localization and stability. This review focuses on the cause and effects of MBNL and CELF1 deregulation in DM1, describing the molecular mechanisms underlying alternative splicing misregulation for a deeper understanding of DM1 complexity. To contribute to this analysis, we have prepared a comprehensive list of transcript alterations involved in DM1 pathogenesis, as well as other deregulated mRNA processing pathways implications.

The intracellular domain of β-dystroglycan mediates the nucleolar stress response by suppressing UBF transcriptional activity

β-dystroglycan (β-DG) is a key component of multiprotein complexes in the plasma membrane and nuclear envelope. In addition, β-DG undergoes two successive proteolytic cleavages that result in the liberation of its intracellular domain (ICD) into the cytosol and nucleus. However, stimuli-inducing ICD cleavage and the physiological relevance of this proteolytic fragment are largely unknown. In this study we show for the first time that β-DG ICD is targeted to the nucleolus where it interacts with the nuclear proteins B23 and UBF (central factor of Pol I-mediated rRNA gene transcription) and binds to rDNA promoter regions. Interestingly DG silencing results in reduced B23 and UBF levels and aberrant nucleolar morphology. Furthermore, β-DG ICD cleavage is induced by different nucleolar stressors, including oxidative stress, acidosis, and UV irradiation, which implies its participation in the response to nucleolar stress. Consistent with this idea, overexpression of β-DG elicited mislocalization and decreased levels of UBF and suppression of rRNA expression, which in turn provoked altered ribosome profiling and decreased cell growth. Collectively our data reveal that β-DG ICD acts as negative regulator of rDNA transcription by impeding the transcriptional activity of UBF, as a part of the protective mechanism activated in response to nucleolar stress.

Protective role of microRNA-374 against myocardial ischemia-reperfusion injury in mice following thoracic epidural anesthesia by downregulating dystrobrevin alpha-mediated Notch1 axis

Ischemia-reperfusion (I/R) injury often leads to myocardial apoptosis and necrosis. Studies have demonstrated the role microRNAs (miRs) played in myocardial I/R injury. Thus, we established a myocardial I/R injury model and a thoracic epidural anesthesia (TEA) model in mice to explore whether microRNA-374 (miR-374) affects myocardial I/R injury. We collected myocardial tissues to evaluate whether TEA exerts a protection effect on myocardial tissues. In addition, the levels of miR-374, dystrobrevin alpha (DTNA), and the statue of the Notch1 axis were detected. Subsequently, cardiomyocytes extracted from TEA mice were treated to regulate their levels of miR-374 and DTNA. After that, cell viability, cell cycle distribution, and apoptosis of cardiomyocytes were assessed. This was followed by the detection of the myocardial infarction area. The mice models of myocardial I/R injury were associated with poorly expressed miR-374 and highly expressed DTNA. TEA was found to protect myocardial tissues against myocardial I/R injury by elevating miR-374 and reducing DTNA. Dual-luciferase reporter assay validated that DTNA was the target gene of miR-374. Cardiomyocytes with overexpressed miR-374 were shown to have downregulated DTNA levels and blocked Notch1 axis. Overexpressed miR-374 was also found to promote the viability and inhibit the apoptosis of cardiomyocytes, as well as to increase the number of cells arrested in the S phase. In accordance with this, the myocardial infarction area was decreased with the upregulated miR-347 and downregulated DTNA. Collectively, these results demonstrated that, by inhibiting the activity of DTNA-mediated Notch1 axis, miR-374 could protect against myocardial I/R injury in mice after TEA.