Molecular and functional identification of a LC3C homolog in large yellow croaker (Larimichthys crocea)

Autophagy is a conserved cellular process in response to stress that sustains normal cell growth by degrading and recycling unnecessary cytosolic components in autophagosomes and autolysosomes. Microtubule-associated protein 1-light chain 3, MAP1LC3 or LC3, is a major autophagosome component and reliable autophagy marker. In humans, there exist three LC3 orthologues, LC3A, LC3B, and LC3C. To date, only two types of LC3 orthologues, LC3A and LC3B, have been recognized in fish species. This study identified a LC3C (LcLC3C) gene in the large yellow croaker (Larimichthys crocea). The deduced LcLC3C protein possesses conserved characteristic domains, including a GABARAP domain, a C-terminal glycine residue, Atg7 binding site, tubulin binding site, and a lipid site. The LcLC3C gene was constitutively expressed in all examined tissues, and in primary head kidney macrophages (PKM), primary head kidney lymphocytes (PKL), primary head kidney granulocytes (PKG), and large yellow croaker head kidney (LYCK) cell line. After stimulation by poly (I:C), a viral dsRNA mimic, and Vibrio alginolyticus, the mRNA levels of the LcLC3C were downregulated in the head kidney and spleen. Subcellular location indicated that LcLC3C was evenly distributed in the cytoplasm and nucleus of both LYCK cells and epithelioma papulosum cyprini (EPC) cells. Overexpression of LcLC3C in EPC cells promoted the replication of spring viremia of carp virus (SVCV), and its overexpression in both LYCK cells and EPC cells downregulated type I IFN response, suggesting that LcLC3C may promote the replication of virus by negatively regulating type I IFN response. Consequently, our findings enhance the comprehension of the role played by the LC3C homolog in fish.