Spotted knifejaw (Oplegnathus punctatus) TARBP2 negatively regulates type I IFN responses to promote RGNNV replication

Trans-Activation-Responsive RNA-Binding Protein (TARBP), a dsRNA-binding protein family member, serves as a hub for regulating gene expression and influencing diverse biological processes. While current research primarily focuses on its cytoplasmic interactions with factors like Dicer, protein kinase RNA-activated (PKR), and PKR activator (PACT), its role in teleost antiviral immunity remains less explored. In this study, we cloned and characterized an ortholog of TARBP2 from spotted knifejaw (Oplegnathus punctatus), designated OpTARBP2. Its open reading frame (ORF) spans 1038 bp, encoding a 345-amino acid protein with a predicted molecular weight of 37.1 kDa. Sequence analysis revealed that OpTARBP2 possesses three conserved dsRNA-binding domains and shares 96.81 % sequence homology with giant grouper (Epinephelus lanceolatus) TARBP2. Expression profiling indicated widespread OpTARBP2 distribution across tissues, with highest levels in the liver and intestine. Fluorescence microscopy confirmed its cytoplasmic localization. Functionally, overexpression of OpTARBP2 in grouper spleen (GS) cells reduced the transcription of pro-inflammatory cytokines and interferon-related genes, and thereby promoting replication of the red-spotted grouper nervous necrosis virus (RGNNV). Furthermore, OpTARBP2 significantly inhibited E. coioides Melanoma differentiation-associated gene 5 (MDA5), Mitochondrial anti viral signaling protein (MAVS), and TANK-Binding Kinase 1 (TBK1)-induced luciferase activity driven by the Interferon-stimulated response elements (ISRE) and NF-κB promoters. Collectively, these results demonstrate that OpTARBP2 enhanced viral replication by negatively regulating type I interferon responses, laying a foundation for understanding the antiviral immune role of TARBP2 in teleosts.