A Caspase-2 involves in regulating LPS-induced haemocyte apoptosis of oyster Crassostrea gigas.

Caspase-2 is an evolutionary conserved cysteine protease that plays multifaceted roles in the DNA damage response, cell cycle regulation, and apoptosis. In the present study, a caspase-2 (designed as CgCaspase-2) from the Pacific oyster Crassostrea gigas was functionally characterized as an important mediator of LPS-induced haemocyte apoptosis. After LPS stimulation, the mRNA expression level of CgCaspase-2 in haemocytes significantly up-regulated, and its protein was translocated from the cytoplasm to nucleus. Transfection of CgCaspase-2 significantly enhanced the apoptosis rate of HEK293T cells. After injection of specific siRNA of CgCaspase-2, the apoptosis rate of haemocytes in CgCaspase-2-RNAi oyster was significantly decreased after LPS stimulation. The down-stream caspases, including CgCaspase-7, CgCaspase-8, CgCaspase-9 were significantly down-regulated in CgCaspase-2-RNAi oysters. Moreover, mRNA expression levels of the pro-apoptotic protein CgBAX and the apoptosis inducing factor CgAIF were also significantly down-regulated in CgCaspase-2-RNAi oysters. These results collectively indicate that CgCaspase-2 is a conserved caspase family member that plays a crucial role in haemocyte apoptosis during the immune response of oysters.