Molecular characterization of a cathepsin L1 highly expressed in phagocytes of pacific oyster Crassostrea gigas. (December 2018)

• Record Type: Journal Article
• Authors: Lv, Zhao; Qiu, Limei; Liu, Zhaoqun; Wang, Weilin; Chen, Hao; Jia, Yunke; Jia, Zhihao; Jiang, Shuai; Wang, Lingling; Song, Linsheng
• Is Part Of: Developmental and comparative immunology. Volume 89(2018)
• Page Start: 152
• Page End: 162
• Publication Date: 2018-12
• Subjects: Crassostrea gigas -- Phagocyte-highly expressed -- Cathepsin L1 -- Proteolytic activity -- Molecular marker; Immunology -- Periodicals; Developmental immunology -- Periodicals; 616.079
• DOI: 10.1016/j.dci.2018.08.014
• Languages: English
• ISSNs: 0145-305X

Abstract

Abstract: Cathepsin L1 (CTSL1) is a lysosomal cysteine protease with a papain-like structure. It is known to be implicated in multiple processes of immune response against pathogen infection based on the proteolytic activity. In the present study, a CTSL1 homologue (designated as Cg CTSL1) was identified from Crassostrea gigas . It contained a typically single Pept_C1 domain with three conserved catalytically essential residues (Gln 25, His 135 and Asn 178 ). The mRNA of Cg CTSL1 was ubiquitously expressed in oyster tissues with the highest expression level in important immune tissues such as gill and hemocytes. Cg CTSL1 proteins were mainly detected in gill and hepatopancreas by immunohistochemistry. Recombinant Cg CTSL1 (r Cg CTSL1) exhibited proteolytic activity to cleave the substrate Ac-FR-amino-4-trifluoromethyl coumarin (AFC) in a dose-dependent manner, and the inhibitor could reduce its proteolytic activity. After the interference of Cg CTSL1 mRNA, the proteolytic activity of oyster hemocytes was significantly down-regulated with the released AFC fluorescence value decreasing from 375.84 to 179.21 ( p < 0.05). Flow cytometry analysis revealed that the expression of Cg CTSL1 protein was higher in phagocytes with the mean fluorescence intensity (MFI) value of 21, 187 (4.13-fold, p < 0.01) compared to the MFI value of 5, 130 in non-phagocytic hemocytes. The further confocal analysis demonstrated that the actively phagocytic hemocytes with green bead signals were co-localized with stronger Cg CTSL1 positive signals. The mRNA expression levels of Cg CTSL1 in phagocyte-like sub-populations of granulocytes and semi-granulocytes were 298.12-fold ( p < 0.01) and 2.75-fold ( p < 0.01) of that in agranulocytes, respectively. Western blotting analysis of the hemocyte proteins revealed that Cg CTSL1 was relatively abundant in granulocytes and semi-granulocytes compared to that in agranulocytes. These results collectively suggested that Cg CTSL1, a CTSL1 homologue highly expressed in phagocyte-like hemocytes, was possibly involved in cellular immune response dependent on its conserved proteolytic activity, which might provide clues for the divergence between phagocytes and non-phagocytic hemocytes as well as the identification of promising molecular markers for phagocytes in oyster C. gigas . Highlights: A lysosomal cysteine protease cathepsin L1 was identified from Crassostrea gigas. In vitro, r Cg CTSL1 exhibited proteolytic activity in a dose-dependent manner. The proteolytic activity of oyster hemocytes was significantly decreased after the interference of Cg CTSL1 mRNA. Transcripts and proteins of Cg CTSL1 were highly expressed in actively phagocytic hemocytes. The higher content of Cg CTSL1 contributed to the higher proteolytic activity in granulocytes.