A novel caspase-6 from sea cucumber Holothuria leucospilota: Molecular characterization, expression analysis and apoptosis detection.

In this study, a novel caspase-6 named HLcaspase-6 was identified from sea cucumber Holothuria leucospilota. The full-length cDNA of HLcaspase-6 is 2195 bp in size, containing a 126 bp 5'-untranslated region (UTR), a 1043 bp 3'-UTR and a 1026 bp open reading frame (ORF) encoding a protein of 341 amino acids with a deduced molecular weight of 38.57 kDa. HLcaspase-6 contains the common signatures of the caspase family, including the conserved pentapeptide motif QACRG, as well as the P20 and P10 domains. In addition, HLcaspase-6 contains a short pro-domain. HLcaspase-6 mRNA is ubiquitously expressed in all tissues examined, with the highest transcript level in the intestine, followed by coelomocytes. In in vitro experiments, the expression of HLcaspase-6 mRNA in coelomocytes was significantly up-regulated by lipopolysaccharides (LPS) or polyriboinosinic-polyribocytidylic acid [poly (I:C)] challenge, suggesting that HLcaspase-6 might play important roles in the innate immune defense of sea cucumber against bacterial and viral infections. Moreover, we further confirmed that overexpression of HLcaspase-6 could induce apoptosis and activate the p53 signal pathway.