Targeted knock-in mice expressing mutations of CD28 reveal an essential pathway for costimulation.
Despite extensive study, the role of phosphatidylinositol 3-kinase (PI3-kinase) activation in CD28 function has been highly contentious. To definitively address this question, we generated knock-in mice expressing mutations in two critical domains of the cytoplasmic tail of CD28. Mutation of the proximal tyrosine motif interrupted PI3-kinase binding and prevented CD28-dependent phosphorylation of protein kinase B (PKB)/Akt; however, there was no detectable effect on interleukin-2 (IL-2) secretion, expression of Bcl-X(L), or on T-cell function in vivo. Furthermore, we demonstrate that signaling initiated by the C-terminal proline motif is directly responsible for tyrosine phosphorylation of phosphoinosotide-dependent kinase 1, protein kinase C theta, and glycogen synthase kinase 3beta, as well as contributing to threonine phosphorylation of PKB. T cells mutated in this domain were profoundly impaired in IL-2 secretion, and the mice had marked impairment of humoral responses as well as less severe disease manifestations in experimental allergic encephalomyelitis. These data demonstrate that the distal proline motif initiates a critical nonredundant signaling pathway, whereas direct activation of PI3-kinase by the proximal tyrosine motif of CD28 is not required for normal T-cell function.
Dodson
Lindzy F
LF
Division of Biology and Biomedical Sciences, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Boomer
Jonathan S
JS
Deppong
Christine M
CM
Shah
Dulari D
DD
Sim
Julia
J
Bricker
Traci L
TL
Russell
John H
JH
Green
Jonathan M
JM
D020816:Amino Acid Motifs; D000818:Animals; D018106:CD28 Antigens / Q000235:genetics / Q000276:immunology; D004681:Encephalomyelitis, Autoimmune, Experimental / Q000276:immunology; D004789:Enzyme Activation; D007249:Inflammation / Q000276:immunology; D007376:Interleukin-2 / Q000235:genetics / Q000378:metabolism; D015847:Interleukin-4 / Q000276:immunology / Q000378:metabolism; D008213:Lymphocyte Activation / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013154:Spleen / Q000166:cytology; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology; D051020:bcl-X Protein / Q000378:metabolism
C494812:Bcl2l1 protein, mouse; D018106:CD28 Antigens; D007376:Interleukin-2; D051020:bcl-X Protein; D015847:Interleukin-4; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt