Functional characterization of two Caspase-1 transcripts that associated with ASC and NLRC3 in apoptosis and inflammatory response in large yellow croaker Larimichthys crocea

As a member of the inflammatory caspases, Caspase-1 can increase the host inflammatory response against pathogen invasion and also function dominantly in apoptosis. In this study, we cloned and obtained two transcripts of Caspase-1 in large yellow croaker (Larimichthys crocea), namely Lc-Caspase-1_tv1 and Lc-Caspase-1_tv2. The ORF of Lc-Caspase-1_tv1 is 1239 bp, whereas Lc-Caspase-1_tv2 is 1167 bp in length, encoding a protein of 412 and 388 aa, and both of which contains a CARD and a CASc domain. Subcellular localization analysis showed that Lc-Caspase-1_tv1 and Lc-Caspase-1_tv2 are both cytoplasmically localized, and were widely expressed in the tested tissues/organs, with the highest expression level of Lc-Caspase-1_tv1 and Lc-Caspase-1_tv2 detected in the muscle and intestine, respectively. The expression of Lc-Caspase-1_tv1 and Lc-Caspase-1_tv2 was markedly induced by poly I:C, LPS, PGN stimulation, and Pseudomonas plecoglossicida infection. In addition, overexpression of Lc-Caspase-1_tv1 and Lc-Caspase-1_tv2 significantly induced apoptosis, and the co-expression of Lc-Caspase-1_tv2 but not Lc-Caspase-1_tv1 with Lc-ASC could significantly enhanced the apoptosis, whereas the co-expression of the Caspase-1 transcripts with Lc-NLRC3 could significantly abolished the apoptosis that mediated by Lc-NLRC3. Furthermore, both Lc-Caspase-1_tv1 and Lc-Caspase-1_tv2 could form protein complexes with Lc-ASC and Lc-NLRC3. The co-expression of Lc-Caspase-1_tv1 with Lc-ASC significantly enhanced the expression levels of IRF3, IRF7, TNF-α, and IFNd, whereas the co-expression of Lc-Caspase-1_tv2 with Lc-ASC significantly enhanced IRF3, Mx, and IFNd expression. Nevertheless, co-expression of the Caspase-1 transcripts with Lc-NLRC3 did not significantly impact expression of these immune-related molecules. These results indicate that Caspase-1 transcripts are essential for apoptosis and immune signaling regulation in teleosts.