The characterization of a novel IRF8-like homolog and its role in the immune modulation of the sea urchin Strongylocentrotus intermedius

Abstract

Interferon regulatory factor (IRF) proteins, functioning as transcription factors, are essential for various animal species' innate immune defense and stress responses. However, further research is required to elucidate the roles of IRF in echinoderms. In this study, a new IRF gene (SiIRF8-like) was obtained from the sea urchin (Strongylocentrotus intermedius). The open reading frame for SiIRF8-like spanned 2004 bp and encoded a protein composed of 667 amino acids. Domain prediction analysis revealed a typical IRF domain at the N-terminus and an IRF3 domain at the C terminus of the SiIRF8-like protein, exhibiting similar amino acid sequences across different species. Phylogenetic analyses indicated that SiIRF8-like proteins were closely related to mollusk IRF8 proteins. Quantitative real-time PCR revealed detectable levels of SiIRF8-like mRNA in all sea urchin tissues examined, with the highest expression observed in coelomocytes. Furthermore, lipopolysaccharide and polyinosinic–polycytidylic acid treatments significantly increased transcript expression levels of SiIRF8-like. Subcellular localization experiments revealed that SiIRF8-like is mainly localized in the nucleus. Additionally, dual-luciferase reporter assays indicated that overexpression of SiIRF8-like in HEK293T cells could specifically activate reporter genes such as interleukin 6, interferon α/β/γ, activating protein 1, and interferon-stimulated response element. Finally, the overexpressed SiIRF8-like could promote the phosphorylation of protein kinases (JNK and Erk1/2). These preliminary findings regarding the immune functions linked to the SiIRF8-like protein offer valuable insights into the innate immunity mechanisms of invertebrate IRFs and provide theoretical support for developing disease-resistant strains of sea urchins.