The regulatory role of Sigmar1 in CVB3-induced myocarditis

Sigma-1 receptor (Sigmar1) is associated with endoplasmic reticulum (ER) stress. This study investigated whether Sigmar1 affect myocarditis progression via Coxsackievirus B3 (CVB3)-caused ER stress. Neonatal mouse cardiomyocytes (NMCs) were transfected with Sigmar1 and/or stress-induced phosphoprotein 1 homology and U-box containing protein 1 (STUB1) overexpression plasmids and exposed to CVB3 for 2 h. E3 ubiquitin ligases binding with Sigmar1 were predicted by Unibrowser. STUB1-Sigmar1 interaction was measured by Co-IP and/or ubiquitination analyses. Lactate dehydrogenase (LDH) release and apoptosis were detected by LDH assay kits and Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick End Labeling (TUNEL) assay. Expressions of Sigmar1, STUB1, glucose regulated protein 78 (GRP78), cysteinyl aspartate specific proteinase 12 (Caspase-12), and C/EBP homologous protein (CHOP) were determined via quantitative real-time polymerase chain reaction (qRT-PCR)/Western blot. After CVB3 infection, STUB1 level was reduced, while Sigmar1 level was enhanced at 12 h and decreased at 48 h. CVB3 increased apoptosis, LDH release, and expressions of GRP78, Caspase-12 and CHOP of NMCs, which were reversed by Sigmar1 overexpression and promoted by STUB1 overexpression. STUB1 degraded Sigmar1 by ubiquitination. STUB1 overexpression and Sigmar1 overexpression mutually counteracted their effects on CVB3-affected NMCs. In conclusion, STUB1-mediated Sigmar1 degradation promotes ER stress in CVB3-induced in-vitro myocarditis.