The cytoplasmic and the transmembrane domains are not sufficient for class I MHC signal transduction.
Class I MHC molecules deliver activation signals to T cells. To analyze the role of the cytoplasmic and the transmembrane (TM) domains of class I MHC molecules in T cell activation, Jurkat cells were transfected with genes for truncated class I MHC molecules which had only four intracytoplasmic amino acids and no potential phosphorylation sites or native molecules or both. Cross-linking either the native or the truncated molecules induced IL-2 production even under limiting stimulation conditions of low engagement of the stimulating mAb. Moreover, direct comparison of transfected truncated and native class I MHC molecules expressed on the same cell revealed significant stimulation induced by cross-linking the truncated molecules, despite low expression. In addition, truncated class I MHC molecules were as able to synergize with CD3, CD2, or CD28 initiated IL-2 production as native molecules. In further experiments, hybrid constructs made of the extracellular portion of the murine CD8 alpha chain and of the TM and the intracytoplasmic domains of H-2Kk class I MHC molecule were transfected into Jurkat T cells. The expression of the transfected hybrid molecules was comparable to that of the native HLA-B7 molecules. Cross-linking the intact monomorphic HLA-A,B,C epitope or the polymorphic HLA-B7 epitope induced IL-2 production upon costimulation with PMA. In contrast, cross-linking the hybrid molecules generated neither an increase in intracellular calcium concentration ([Ca2+]i) nor stimulated IL-2 production. By contrast, cross-linking intact murine class I MHC molecules induced [Ca2+]i, signal and IL-2 production in transfected Jurkat cells. The data therefore indicate that unlike many other signaling molecules, signaling via class I MHC molecules does not involve the cytoplasmic and the TM portions of the molecule, but rather class I MHC signal transduction is likely to be mediated by the extracellular domain of the molecule.
Gur
H
H
The Harold C. Simmons Arthritis Research Center and The Division of Rheumatic Diseases, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, 75235, USA.
Geppert
T D
TD
Wacholtz
M C
MC
Lipsky
P E
PE
D000818:Animals; D015703:Antigens, CD; D016827:CD8 Antigens / Q000235:genetics / Q000276:immunology; D020013:Calcium Signaling; D006183:H-2 Antigens / Q000235:genetics / Q000276:immunology; D006680:HLA Antigens / Q000235:genetics / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007152:Immunologic Capping; D007376:Interleukin-2 / Q000096:biosynthesis; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D008285:Major Histocompatibility Complex; D051379:Mice; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology