CD6 regulates T-cell responses through activation-dependent recruitment of the positive regulator SLP-76.
Deciphering the role of lymphocyte membrane proteins depends on dissecting the role of a protein in the steady state and on engagement with its ligand. We show that expression of CD6 in T cells limits their responsiveness but that engagement by the physiological ligand CD166 gives costimulation. This costimulatory effect of CD6 is mediated through phosphorylation-dependent binding of a specific tyrosine residue, 662Y, in its cytoplasmic region to the adaptor SLP-76. A direct interaction between SLP-76 and CD6 was shown by binding both to a phosphorylated peptide (equilibrium dissociation constant [K(D)] = 0.5 muM at 37 degrees C) and, using a novel approach, to native phosphorylated CD6. Evidence that CD6 and SLP-76 interact in cells was obtained in coprecipitation experiments with normal human T cells. Analysis of human CD6 mutants in a murine T-cell hybridoma model showed that both costimulation by CD6 and the interaction between CD6 and SLP-76 were dependent on 662Y. The results have implications for regulation by CD6 and the related T-cell surface protein, CD5.
Hassan
Namir J
NJ
Sir William Dunn School of Pathology, South Parks Rd., Oxford, OX1 3RE, United Kingdom.
Simmonds
Stephen J
SJ
Clarkson
Nicholas G
NG
Hanrahan
Sarah
S
Puklavec
Michael J
MJ
Bomb
Martine
M
Barclay
A Neil
AN
Brown
Marion H
MH
D020410:Activated-Leukocyte Cell Adhesion Molecule / Q000276:immunology; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D015703:Antigens, CD / Q000737:chemistry / Q000276:immunology*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000737:chemistry / Q000276:immunology*; D018956:CD5 Antigens / Q000737:chemistry; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis; D019169:Jurkat Cells; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D010455:Peptides / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D013601:T-Lymphocytes / Q000276:immunology*; D018909:src Homology Domains
D020410:Activated-Leukocyte Cell Adhesion Molecule; D048868:Adaptor Proteins, Signal Transducing; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D018956:CD5 Antigens; C062279:CD6 antigen; D007376:Interleukin-2; D010455:Peptides; D010750:Phosphoproteins; C092947:SLP-76 signal Transducing adaptor proteins