CTLA-4 binding to the lipid kinase phosphatidylinositol 3-kinase in T cells.
CTLA-4 is a T cell antigen that is structurally related to CD28 and serves as a high affinity ligand for the B cell antigen B7-1/2. Unlike CD28, the function of CTLA-4 is unclear, although reports have implicated the antigen in the costimulation of T cells. Recently, phosphatidylinositol 3-kinase (PI 3-kinase) has been implicated in the costimulatory function of CD28 by virtue of its ability to bind to a pYMNM motif within the cytoplasmic tail of the antigen. In this study, we show that CTLA-4 can also associate with PI 3-kinase as detected by lipid kinase analysis and immunoblotting with anti-p85 antiserum. High pressure liquid chromatographic separation of deacylated lipids showed the presence of a peak corresponding to PI-3-P. Anti-CTLA-4 ligation of the receptor induced a significant increase in the levels of precipitable PI 3-kinase activity. Peptide binding studies revealed that the NH2- and COOH-terminal SH2 domains of p85 bind the CTLA-4 cytoplasmic pYVKM motif with an affinity (ID50: 0.6 and 0.04 microM), that is similar to CD28. CTLA-4 binding to PI 3-kinase provides further evidence that CTLA-4 is not an inert counterreceptor, but rather is coupled to an intracellular signaling molecule with the capacity to regulate cell growth.
Schneider
H
H
Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215.
Prasad
K V
KV
Shoelson
S E
SE
Rudd
C E
CE
D000069594:Abatacept; D000595:Amino Acid Sequence; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000378:metabolism*; D060908:CTLA-4 Antigen; D006801:Humans; D018796:Immunoconjugates; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases; D010748:Phosphopeptides / Q000737:chemistry / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011485:Protein Binding; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000201:enzymology*
D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D018796:Immunoconjugates; D010748:Phosphopeptides; D000069594:Abatacept; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor)