Constitutive Clathrin-mediated Endocytosis of CTLA-4 Persists during T Cell Activation

• Published in: The Journal of biological chemistry 2012-03, Vol.287 (12), p.9429-9440
• Main Authors: Qureshi, Omar S., Kaur, Satdip, Hou, Tie Zheng, Jeffery, Louisa E., Poulter, Natalie S., Briggs, Zoe, Kenefeck, Rupert, Willox, Anna K., Royle, Stephen J., Rappoport, Joshua Z., Sansom, David M.
• Format: Article
• Language: English
• Subjects: Animals; CD4-Positive T-Lymphocytes - immunology; CD4-Positive T-Lymphocytes - metabolism; Cell Biology; Cell Membrane - metabolism; Cells, Cultured; CHO Cells; Clathrin - metabolism; Co-stimulation; Cricetinae; CTLA-4; CTLA-4 Antigen - metabolism; Endocytosis; Endosomes - metabolism; Humans; Immunology; Lymphocyte Activation; Protein Transport; Receptor Recycling; T Cell Biology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.304329

CTLA-4 is one of the most important negative regulators of the T cell immune response. However, the subcellular distribution of CTLA-4 is unusual for a receptor that interacts with cell surface transmembrane ligands in that CTLA-4 is rapidly internalized from the plasma membrane. It has been proposed that T cell activation can lead to stabilization of CTLA-4 expression at the cell surface. Here we have analyzed in detail the internalization, recycling, and degradation of CTLA-4. We demonstrate that CTLA-4 is rapidly internalized from the plasma membrane in a clathrin- and dynamin-dependent manner driven by the well characterized YVKM trafficking motif. Furthermore, we show that once internalized, CTLA-4 co-localizes with markers of recycling endosomes and is recycled to the plasma membrane. Although we observed limited co-localization of CTLA-4 with lysosomal markers, CTLA-4 was nonetheless degraded in a manner inhibited by lysosomal blockade. T cell activation stimulated mobilization of CTLA-4, as judged by an increase in cell surface expression; however, this pool of CTLA-4 continued to endocytose and was not stably retained at the cell surface. These data support a model of trafficking whereby CTLA-4 is constitutively internalized in a ligand-independent manner undergoing both recycling and degradation. Stimulation of T cells increases CTLA-4 turnover at the plasma membrane; however, CTLA-4 endocytosis continues and is not stabilized during activation of human T cells. These findings emphasize the importance of clathrin-mediated endocytosis in regulating CTLA-4 trafficking throughout T cell activation. CTLA-4 is an essential regulator of T cell immune responses with unusual intracellular trafficking. Endocytosis of CTLA-4 is continuous with subsequent recycling and degradation. Clathrin-mediated endocytosis of CTLA-4 persists in activated T cells. This alters our understanding of CTLA-4 behavior and, therefore, how it might function.