A scallop IκB protein involved in innate immunity acts as a key regulator of NF-κB

Chlamys farreri, a commercially important bivalve mollusk, is extensively cultivated in China. In recent years, the frequent occurrence of diseases has led to significant mortality in scallop farms. Despite this, our understanding of scallop's innate immune mechanisms remains limited. The NF-kappa B signaling pathway plays a crucial role in various biological processes, including cellular, developmental, and immune defense mechanisms. Inhibitors of NF-kappa B (I kappa B) proteins block the nuclear localization and DNA binding of NF-kappa B, thereby inhibiting its activity. However, the role of these proteins in invertebrates is not well understood. In this study, we identified a new homolog of the I kappa B gene in C. farreri, named CfI kappa B1. The open reading frame of CfI kappa B1 spans 1089 bp, encoding 362 amino acids. Through sequence comparison and phylogenetic analysis, CfI kappa B1 was classified as a member of the invertebrate I kappa B family. Quantitative real-time PCR revealed that CfI kappa B1 transcripts are present in all examined tissues, with the highest expression observed in hemocytes. Expression levels were significantly upregulated following exposure to lipopolysaccharide, peptidoglycan, and polyinosinic:polycytidylic acid. Coimmunoprecipitation studies confirmed that CfI kappa B1 interacts with NF-kappa B family proteins CfRel-1 and CfRel. Dual-luciferase reporter assays demonstrated that CfI kappa B1 inhibits CfRel-dependent activation of NF-kappa B, ISRE, IFN beta, and AP-1. These findings suggest that CfI kappa B1 plays a crucial role in regulating NF-kappa B activity, which is integral to the innate immunity of C. farreri. This research enhances our understanding of the innate immune system in invertebrates and provides a theoretical basis for developing disease-resistant scallops at the molecular level.