Identification and Functional Analysis of Interleukin-1β in the Chinese Soft-Shelled Turtle Pelodiscus sinensis

Chinese soft-shelled turtle (Pelodiscus sinensis) is commercially cultured in East and Southeast Asia for its nutritional and medicinal values. In this study, we identified interleukin-1β (IL-1β) from Chinese soft-shelled turtle. The full-length cDNA of Pelodiscus sinensis IL-1β (tIL-1β) consists of 1529 base pairs with an 831-base-pair open reading frame, encoding 277 amino acids. The guanine-cytosine (GC) content in the coding sequence and 3' untranslated region of tIL-1β is considerably higher than that of other vertebrates. Its mRNA expression level increased significantly during Aeromonas hydrophila infection. The tIL-1β lacks the typical IL-1β-converting enzyme (ICE) cut site found in mammalian IL-1β, but still could be cleaved by turtle caspase-1. By mutating the potential cleavage sites, we identified aspartic acid (Asp/D) 130 as the ICE cut site in tIL-1β. The peptide truncated at D130 was expressed using the baculovirus expression system; its bioactivity is confirmed by the ability to induce cyclooxygenase-2 (COX-2) and tIL-1β itself in peripheral blood monocytes. In conclusion, we characterized IL-1β from Chinese soft-shelled turtle and identified its D130 as a non-typical ICE cut size.