Modulation of Ca2+-induced Ca2+ release by ubiquitin protein ligase E3 component n-recognin UBR3 and 6 in cardiac myocytes.

Ca2+-induced Ca2+ release (CICR) from sarcoplasmic reticulum is a finely tuned process responsible for cardiac excitation and contraction. The ubiquitin-proteasome system (UPS) as a major degradative system plays a crucial role in the maintenance of Ca2+ homeostasis. The E3 component N-recognin (UBR) subfamily is a part of the UPS; however, the role of UBR in regulating cardiac CICR is unknown. In the present study, we found that among the UBR family, single knockdown of UBR3 or UBR6 significantly elevated the amplitude of sarcoplasmic reticulum Ca2+ release without affecting Ca2+ transient decay time in neonatal rat ventricular myocytes. The protein expression of alpha 1 C subunit of L-type voltage-dependent Ca2+ channel (Cav1.2) was increased after UBR3/6 knockdown, whereas the protein levels of RyR2, SERCA2a, and PLB remained unchanged. In line with the increase in Cav1.2 proteins, the UBR3/6 knockdown enhanced the current of Cav1.2 channels. Furthermore, the increase in Cav1.2 proteins caused by UBR3/6 reduction was not counteracted by a protein biosynthesis inhibitor, cycloheximide, suggesting a degradative regulation of UBR3/6 on Cav1.2 channels. Our results indicate that UBR3/6 modulates cardiac CICR via targeting Cav1.2 protein degradation.

Low expression of lncRNA-GAS5 is implicated in human primary varicose great saphenous veins.

The cellular mechanisms of primary varicose great saphenous veins (GSVs) involve inflammation, apoptosis, and proliferation of local cells and extracellular matrix degradation. Long non-coding RNAs (lncRNAs) play important roles in these cellular processes; however, which and how lncRNAs related to these mechanisms take effect on GSVs remain unclear. By screening lncRNAs that might experience changes in GSV varicosities, we selected the lower expressed lncRNA-GAS5 (growth arrest specific transcript 5) for functional assessments. Silencing of lncRNA-GAS5 promoted cell proliferation and migration, and cell cycle of the human saphenous vein smooth muscle cells (HSVSMCs), whereas overexpressing it inhibited these cellular behaviors and reduced apoptosis of HSVSMCs. RNA pull-down experiment revealed a direct bind of lncRNA-GAS5 to a Ca2+-dependent RNA-binding protein, Annexin A2. Further experiments showed that silencing of Annexin A2 reduced the HSVSMCs proliferation and vice versa. In the context of lncRNA-GAS5 knockdown, silencing of Annexin A2 reduced the proliferation of HSVSMCs while overexpression of Annexin A2 increased the proliferation. Thus, the low expression of lncRNA-GAS5 may facilitate HSVSMCs proliferation and migration through Annexin A2 and thereby the pathogenesis of GSV varicosities.

MiR-25 protects cardiomyocytes against oxidative damage by targeting the mitochondrial calcium uniporter.

MicroRNAs (miRNAs) are a class of small non-coding RNAs, whose expression levels vary in different cell types and tissues. Emerging evidence indicates that tissue-specific and -enriched miRNAs are closely associated with cellular development and stress responses in their tissues. MiR-25 has been documented to be abundant in cardiomyocytes, but its function in the heart remains unknown. Here, we report that miR-25 can protect cardiomyocytes against oxidative damage by down-regulating mitochondrial calcium uniporter (MCU). MiR-25 was markedly elevated in response to oxidative stimulation in cardiomyocytes. Further overexpression of miR-25 protected cardiomyocytes against oxidative damage by inactivating the mitochondrial apoptosis pathway. MCU was identified as a potential target of miR-25 by bioinformatical analysis. MCU mRNA level was reversely correlated with miR-25 under the exposure of H2O2, and MCU protein level was largely decreased by miR-25 overexpression. The luciferase reporter assay confirmed that miR-25 bound directly to the 3' untranslated region (UTR) of MCU mRNA. MiR-25 significantly decreased H2O2-induced elevation of mitochondrial Ca2+ concentration, which is likely to be the result of decreased activity of MCU. We conclude that miR-25 targets MCU to protect cardiomyocytes against oxidative damages. This finding provides novel insights into the involvement of miRNAs in oxidative stress in cardiomyocytes.