BAX, a novel cell pro-apoptotic protein, involved in hemocytes early antiviral immune response in fresh water crayfish, Procambarus clarkii.

Apoptosis plays an important role in various biological processes and acts as a host defending mechanism by which infected cells are eliminated to restrict the virus propagation scale. Bax is a crucial pro-apoptotic protein, which mediates the release of cytochrome c from mitochondrion to cytosol in mammalian. However, its role in invertebrate is still obscure. Here, a novel pro-apoptotic protein gene was identified from hemocytes of red swamp crayfish. There was a Bcl-2 domain in the C-terminus of Pc-Bax, which possessed 497 amino acids residues. And an important transmembrane region existed in the C-terminus of Pc-Bax, which implied that Pc-Bax located in mitochondrial membrane. Besides, Pc-Bax was expressed at a relative high level in hemocytes, and a relative low expression levels in hepatopancreas, gills, and intestine. In hemocytes, Pc-Bax transcript was rapidly up-regulated from 12 h to 36 h after WSSV infection. And there was the same trend for Pc-Bax protein expression level in hemocytes after WSSV infection. Results of qRT-PCR testing for VP28 gene showed WSSV replication was obviously enhanced after Pc-Bax knockdown. Meantime, hemocytes apoptosis was suppressed in Pc-Bax knockdown crayfish after WSSV injection, compared with the dsGFP injection group and normal group. Taken together, these results revealed that crayfish hemocytes apoptosis scale was enhanced to suppress WSSV replication by up-regulating Bax protein expression level after WSSV infection.