The novel gene TRIM44L from orange-spotted grouper negatively regulates the interferon response

Accumulated evidence suggests that some of the tripartite motif (TRIM) -family proteins function as critical regulators of carcinogenesis, immunity, and antiviral functions. TRIM44 is an atypical TRIM family protein that lacks the entire RING domain and has been demonstrated to play a crucial role in cancer and viral infection. To our knowledge, the role of TRIM44 in fish still remains largely unknown. Here, we cloned and characterized a novel TRIM44-like gene from orange spotted grouper (EcTRIM44L). Sequence analysis indicated that EcTRIM44L encoded a 393 amino acid peptide, which shared 81.44% and 51.02% identity with large yellow croaker (Larimichthys crocea) and zebrafish (Danio rerio), respectively. However, EcTRIM44L only exhibited 24.69% identity with the TRIM44 protein of humans (Homo sapiens). Moreover, EcTRIM44L contained two conserved domains, including a B-Box domain and a coiled-coil domain, but not a RING domain. Using fluorescence microscopy, we observed green fluorescence in the cytoplasm of the EcTRIM44L-EGFP transfected grouper spleen (GS) cells. As the infection proceeded, EcTRIM44L transcription was significantly up-regulated in red-spotted grouper nervous necrosis virus (RGNNV) infection, suggesting that EcTRIM44L might be involved in fish virus infections. The in vitro overexpression of EcTRIM44L significantly enhanced RGNNV replication, as demonstrated by the accelerated cytopathic effect (CPE) progression induced by RGNNV, as well as the increased expression of coat protein (CP) and RNA-dependent RNA polymerase (RdRp). The overexpression of EcTRIM44L significantly decreased the level of interferon (IFN) related signaling molecules and pro-inflammatory cytokine expression, suggesting that EcTRIM44L affected virus replication by negatively regulating the IFN response. In addition, the melanoma differentiation-associated protein 5 (MDA5) and mitochondrial antiviral-signaling protein (MAVS), but not mediator of IRF3 activation (MITA)-evoked IFN response was negatively regulated by EcTRIM44L. Together, for the first time, our results indicate that EcTRIM44L negatively regulates the interferon response against grouper RNA virus infection.