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CTSL-2 upon specifically recognizing Vibrio splendidus directly cleaves complement C3 to promote the bacterial phagocytosis and degradation in oyster

Year: 2025

Type: article

Abstract: Cathepsin L (CTSL) as a cysteine cathepsin protease mediates complement C3 cleavage and pathogen degradation. In the present study, a CTSL homolog was identified from Crassostrea gigas (designated as Cg CTSL-2). Its mRNA expression increased significantly in hemocytes after Vibrio splendidus stimulation. The activity of r Cg CTSL-2 was induced after incubation with LPS or V. splendidus in Ca 2+ -dependent manner. r Cg CTSL-2 could specifically bound V. splendidus in Ca 2+ -dependent manner. The co-localization of r Cg CTSL-2 and V. splendidus was observed in cell-free hemolymph. Upon binding V. splendidus , Cg CTSL-2 interacted with Cg C3 in cell-free hemolymph and hemocytes. Cg C3 fragments in Cg CTSL-2-RNAi oysters and full length Cg C3 in r Cg CTSL-2-treated oysters were both reduced in cell-free hemolymph, respectively. Cg C3 fragments were accumulated in Cg CTSL-2-RNAi or r Cg CTSL-2-treated oysters. The co-localizations of V. splendidus , Cg C3, Cg CD18, Cg CTSL-2 and lysosomes were observed in hemocytes. These results suggested that Cg CTSL-2 upon binding V. splendidus directly interacted with Cg C3 to lead to Cg C3 cleavage and then Cg C3 fragments coated on V. splendidus were mediated by Cg CD18 into CTSL-2-lysosome pathway.

Source: Cell Communication and Signaling

DOI: 10.1186/s12964-025-02205-z