Cloning, characterization and expression analysis of a caspase-8 like gene from the Hong Kong oyster, Crassostrea hongkongensis

• The cDNA sequence of ChCaspase-8 was first cloned from bivalve, the Hong Kong oyster C. hongkongensis.
• The mRNA transcript of ChCaspase-8 could be detected in all the examined tissues.
• Expression levels of ChCaspase-8 increased with microbial infection.
• ChCaspase-8 is located in the cytoplasm, and activating NF-κB and p53/p21 reporter genes.
• ChCaspase-8 is involved in the molecular mechanisms of immunity and apoptosis.

Apoptosis plays a key role in many biological processes, including homeostasis within the immune system. A family of cysteine proteases, the caspases, constitutes the core of the apoptotic machinery. We have characterized the first bivalve caspase-8 ortholog from the Hong Kong oyster Crassostrea hongkongensis (designated ChCaspase-8). The full-length cDNA is 1945 bp in length encoding a putative protein of 557 amino acids that contains two N-terminal DED domains, and a CASc domain at the C-terminus. ChCaspase-8 is ubiquitously expressed in oysters, with highest expression levels in the gonad and labial palps. Following microbial infection, the expression of ChCaspase-8 increased in hemocytes from 12 to 72 h post-challenge. When expressed in HeLa cells, ChCaspase-8 is located in the cytoplasm, while over-expression of ChCaspase-8 in HEK293T cells activates the transcriptional activities of NF-κB. These results indicate that ChCaspase-8 might play an important role in the immune and apoptotic responses of oysters.