A novel inhibitor of apoptosis protein (IAPs) from Crassostrea gigas is involved in anti-apoptosis and innate defense role under Vibrio alginolyticus stimulation

Apoptosis is an essential biological process in vertebrates and invertebrates for the development and maintenance of homeostasis. Inhibition of apoptosis can help some pathogens survive in host cells and escape from immune surveillance. Importantly, it also plays an important role in immune signaling regulation from insects to mammals. In this study, we identified a new inhibitor of the apoptosis protein gene (IAP), CgIAP3 from the Pacific oyster C. gigas, which contained one BIR domain and one RING domain. Blast analysis showed that CgIAP3 share the highest sequence identity of 65.68% with C. virginica IAP8, and clustered with other shellfish IAP in the phylogenetic tree, indicating that CgIAP3 belonged to a member of the IAPs family of shellfish. Homology comparison showed that the BIR domain of CgIAP3 was highly conserved with the BIR3 domain of human IAP. The tissue distribution of CgIAP3 in healthy C. gigas showed that CgIAP3 is ubiquitously expressed in all analyzed tissues, with the highest level of expression in the gills and digestive gland than the adductor muscle and was rapidly up-regulated after V. alginolyticus stimulation. Moreover, cell experiments showed CgIAP3 could inhibit apoptosis by maintaining cell morphology and cell viability. The result of subcellular localization showed that CgIAP3 is widely distributed in cytoplasm and nucleus and only expressed in A549 cells with damaged nucleus. Taken together, we speculated that CgIAP3 might be involved in the innate immune process of the Pacific oyster against V. alginolyticus through maintaining host cell morphology and viability.