Two different forms of human CTLA-4 proteins following peripheral T cell activation.
To study expression of human CTLA-4 in peripheral T cells, we developed a new anti-peptide (anti-CTLA4pB) antibody. Both denatured and native forms of CTLA-4 can be recognized by anti-CTLA4pB antibody. After peripheral T cell activation, we observed that most of CTLA-4 is localized primarily to intracellular compartment rather than to the cell surface. Biochemical study using anti-CTLA4pB antibody was revealed two forms of CTLA-4 on activated peripheral T cells. The majority of CTLA-4 was detected as a 34 kDa moiety in cytosolic fraction under reducing conditions. The presence of a 30 kDa CTLA-4 moiety was observed simultaneously in membrane fraction under reducing condition. The post-induction ratio of cytosolic:membrane-bound forms of CTLA-4 was approximately 50:1. Further analysis was indicated that the 34 kDa moiety in cytosolic fraction is part of a 250 kDa multi-protein complex. Antibodies raised against this complex recognized 54 and 75 kDa proteins together with a 34 kDa form of CTLA-4. In contrast, membrane-bound forms of CTLA-4 were 60 and 120 kDa under non-reducing condition. The molar ratio of 60 and 120 kDa oligomers was approximately 1:1. These results may provide evidence for post-translational modification of human CTLA-4 after T cell activation.
Chun
Taehoon
T
Department of Microbiology and Immunology, School of Medicine, Hanyang University, Haeng-Dang Dong, Sung-Dong Ku, Seoul 133-791, South Korea.
Choi
Hak-Jong
HJ
Chung
Yong-Hoon
YH
D000906:Antibodies / Q000276:immunology; D000918:Antibody Specificity; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D060908:CTLA-4 Antigen; D002462:Cell Membrane / Q000378:metabolism; D019281:Dimerization; D005434:Flow Cytometry; D006801:Humans; D008213:Lymphocyte Activation; D008970:Molecular Weight; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*
D000906:Antibodies; D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D020033:Protein Isoforms