Characterization of oligomers induced by inverse agonists of CTLA-4.
Although cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) inhibits T cell activation when ligated by B7 molecules on antigen-presenting cells, it can also act as an activating receptor when binding certain soluble recombinant ligands known as inverse agonists. Following ligation with an inverse agonist, we observed CTLA-4 microclusters evenly distributed on the T cell surface over a 60-min period. We have previously shown that the inverse agonist properties of these ligands correlate with their capacity to induce the formation of large CTLA-4 oligomers that are distinctly different from those resulting by CTLA-4 engagement with membrane-bound B7. These oligomers are composed of CTLA-4 molecules expressed on the cell surface and decrease from both the soluble cell lysate and lipid rafts upon cellular fractionation. Formation of these inverse agonist-induced CTLA-4 oligomers does not require an intact actin cytoskeleton. However, modulation of these oligomers was partially blocked upon actin depolymerization. Retention of CTLA-4 oligomers on the cell surface correlated with enhanced T cell signaling. Together, our data further characterize the structural basis of inverse agonist properties for CTLA-4 ligands that may be used in the design and screening of therapeutic biologicals targeting this receptor.
Teft
Wendy A
WA
The FOCIS Centre for Clinical Immunology and Immunotherapeutics, Robarts Research Institute, and the Department of Microbiology and Immunology, The University of Western Ontario, London, Ontario, Canada N6A 5K8.
Madrenas
Joaquín
J
D000199:Actins / Q000378:metabolism; D018033:Antibodies, Bispecific / Q000494:pharmacology*; D015703:Antigens, CD / Q000378:metabolism*; D000954:Antigens, Surface / Q000378:metabolism; D051940:B7-2 Antigen / Q000494:pharmacology*; D060908:CTLA-4 Antigen; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D007135:Immunoglobulin Variable Region / Q000494:pharmacology*; D019169:Jurkat Cells; D021962:Membrane Microdomains / Q000378:metabolism; D013601:T-Lymphocytes / Q000187:drug effects*
D000199:Actins; D018033:Antibodies, Bispecific; D015703:Antigens, CD; D000954:Antigens, Surface; D051940:B7-2 Antigen; C497964:CD86 protein, human; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D007135:Immunoglobulin Variable Region