BAG2 mediates coelomocyte apoptosis in Vibrio splendidus challenged sea cucumber Apostichopus japonicus

MicroRNAs (miRNAs) are closely related to the occurrence, development, and immune response of diseases. BCL2-associated athanogene 2 (BAG2) is a member of the BAG family that functions in diverse cellular processes, including cell death, differentiation, and cell division. In this study, we cloned the cDNA full-length of sea cucumber (Apostichopus japonicus) BAG2 (AjBAG2) and confirmed it is an anti-apoptotic protein in vitro and in vivo during Vibrio splendidus infection. Moreover, we identified a perfect complementarity between miR-375 and the 3'-untranslated region (UTR) sequence of AjBAG2. The miR-375 expression decreased the luciferase activity dose-dependently when co-transfected with the AjBAG2 3'-UTR-luciferase reporter containing the miR-375 target site in epithelioma papulosum cyprini (EPC) cells. This inhibition was partially recovered by a miR-375 specific inhibitor. The mRNA and protein levels of AjBAG2 were opposite to that of coelomocytes in challenged sea cucumber when treated with miR-375 mimics or inhibitors. Additionally, miR-375 expression induced coelomocytes apoptosis and blocked the anti-apoptotic activity of AjBAG2. Our data demonstrated that AjBAG2 is an anti-apoptotic protein during V. splendidus infection and this function can be inhibited by miR-375 in sea cucumbers.