Identification and Functional Characterization of Two Executioner Caspases in Crassostrea gigas

Abstract

Caspase-3 and caspase-7 are two key effector caspases that play important roles in apoptotic pathways that maintain normal tissue and organ development and homeostasis. However, little is known about the sequence, structure, activity, and function of effector caspases upon apoptosis in mollusks, especially marine bivalves. In this study, we investigated the possible roles of two executioner caspases in the regulation of apoptosis in the Pacific oyster Crassostrea gigas. A full-length capase-3–like gene named Cgcaspase-3 was cloned from C.gigas cDNA, encoding a predicted protein containing caspase family p20 and p10 domain profiles and a conserved caspase active site motif. Phylogenetic analysis demonstrated that both Cgcaspase-3 and Cgcaspase-1 may function as effector caspases clustered in the invertebrate branch. Although the sequence identities between the two caspases was low, both enzymes possessed executioner caspase activity and were capable of inducing cell death. These results suggested that Cgcaspase-3 and Cgcaspase-1 were two effector caspases in C. gigas. We also observed that nucleus-localized Cgcaspase-3, may function as a caspase-3–like protein and cytoplasm-localized Cgcaspase-1 may function as a caspase-7–like protein. Both Cgcaspase-3 and Cgcaspase-1 mRNA expression increased after larvae settled on the substratum, suggesting that both caspases acted in several tissues or organs that degenerated after oyster larvae settlement. The highest caspase expression levels were observed in the gills indicating that both effector caspases were likely involved in immune or metabolic processes in C. gigas.

Characterization of an inhibitor of apoptosis protein in Crassostrea gigas clarifies its role in apoptosis and immune defense

“…In addition, we also noted that the distribution of CgIAP2 mRNA in different tissues were consistent with that of Cgcaspase-3, described in a previous study (Qu et al, 2014); both proteins had higher mRNA expression levels in gills and the labial palps, and lower expression levels in the gonads, compared to other tissues. The fact that CgIAP2 and Cgcaspase-3 tend to be expressed in the same tissues makes it more likely that CgIAP2 can regulate the activity of effector caspase.…”

The complexity of apoptotic cell death in mollusks: An update

“…Qu et al [103] studied the distribution of Cgcasapse-3 and Cgcaspase-1 in C. gigas in the developmental stages from D-shaped larvae, umbo larvae, and pediveliger larvae to settlement and metamorphosis. This indicates that cytoplasmic substrates cleaved by effector caspases at the settlement and metamorphosis stage occurred at an earlier time point than nuclear substrates.…”

Molecular cloning and characterization of four caspases members in Apostichopus japonicus

“…Moreover, some researches demonstrated that the invariant Cys residue in pentapeptide plays a pivotal role in substrate degradation [39], and conservative caspase family recognizes a core tetrapeptide sequence in their substrates as "P4-P3-P2-P1" to forming a binding pocket [16,40]. In our study, highly conserved residues were all presented in Ajcaspase-2, Ajcaspase-3, and Ajcaspase-6, suggesting that these proteins might have the conservative function of caspase family.…”