Scallop interferon regulatory factor 1 interacts with myeloid differentiation primary response protein 88 and is crucial for antiviral innate immunity

The interferon regulatory factor (IRF) family comprises transcription factors that are crucial in immune defense, stress response, reproduction, and development. However, the function of IRFs in invertebrates is unclear. Here, the full-length cDNA of an IRF-encoding gene (CfIRF1) in the Zhikong scallop (Chlamys farreri) comprising 2007 bp with an open reading frame of 1053 bp that encoded 350 amino acids was characterized, and its immune function was studied. The CfIRF1 protein contained a typical IRF domain at its N-terminus. CfIRF1 was clustered with other proteins of the IRF1 subfamily, implying that they were closely related. CfIRF1 mRNA transcripts could be detected in all tested scallop tissues, with the highest expression observed in the gills and hepatopancreas. CfIRF1 expression was significantly induced by the polyinosinic-polycytidylic acid and acute viral necrosis virus challenge. CfIRF1 could directly interact with myeloid differentiation primary response protein 88 (MyD88), the key adaptor molecule of the toll-like receptor signaling pathway. CfIRF1 did not interact with scallop IKK1 (IKKα/β family protein), IKK2, IKK3 (IKKε/TBK1 family protein), or with other IRF family proteins (IRF2 or IRF3). However, CfIRF1 interacted with itself to form a homodimer. CfIRF1 could specifically activate the interferon β promoter of mammals and the promoter containing the interferon-stimulated response element (ISRE) in a dose-dependent manner. The truncated form of CfIRF1 had a significantly reduced ISRE activation ability, indicating that structural integrity was crucial for CfIRF1 to function as a transcription factor. Our findings provide insights into the functions of mollusk IRFs in innate immunity. The research results also provide valuable information that enriches the theory of comparative immunology and that can help prevent diseases in scallop farming.