Modulation of murine complement receptor type 2 (CR2/CD21) ectodomain shedding by its cytoplasmic domain

• Published in: Molecular immunology Vol. 45; no. 8; pp. 2127 - 2137
• Main Authors: Hoefer, Melanie M., Aichem, Annette, Knight, Andrew M., Illges, Harald
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2008
• Subjects: Amino Acid Sequence; Animals; Antioxidants - pharmacology; B cell activation; B-Lymphocytes - cytology; B-Lymphocytes - drug effects; B-Lymphocytes - metabolism; Complement receptor 2/CD21; Cytoplasm - drug effects; Cytoplasm - metabolism; Fluorescence; Glutathione; Male; Mice; Mice, Inbred C57BL; Molecular Sequence Data; Mutagenesis, Site-Directed; Pervanadate; Protein Structure, Tertiary; Receptors, Complement 3d - chemistry; Receptors, Complement 3d - metabolism; Sequence Deletion; Shedding; Sulfhydryl Compounds - pharmacology; Time Factors; Vanadates - pharmacology; NAC; MMP; Shedding; Complement receptor 2/CD21; SCR; Pervanadate; PV; B cell activation; GSH; Glutathione
• ISSN: 0161-5890; 1872-9142
• DOI: 10.1016/j.molimm.2007.12.015

Ectodomain shedding is a mechanism that regulates numerous functions of cell surface proteins. The extracellular domain of the human complement receptor 2 (CR2/CD21) is released by proteolytic cleavage as a soluble protein through a variety of stimuli including the thiol antioxidants N-acetylcysteine (NAC) and glutathione (GSH), and the oxidant pervanadate (PV). In addition, PV mimics B cell antigen receptor (BCR) signaling. Here, we show that murine CD21 is shed upon those stimuli and that the cytoplasmic domain is an important modulator for CD21-shedding. B cells expressing a mutant CD21 cytoplasmic domain with only three amino acids (KHR) showed increased CD21-shedding and required lower stimuli concentrations. At lower PV concentrations, wildtype CD21 was up-regulated on the cell surface, whereas at higher PV concentrations the ectodomain was shed. These findings further indicate that GSH and NAC utilize different pathways than PV to activate CD21-shedding. Altogether, as pre-activated B cells express higher CD21 levels than resting mature B cells or fully activated and antigen-experienced B cells, we suggest CD21-shedding to be a mechanism to fine-tune B cell activation.