ZAP-70 and p72syk are signaling response elements through MHC class II molecules.
Ligation of major histocompatibility complex (MHC) class II antigens expressed on antigen-activated human CD4+ T-lymphocytes induces early signal transduction events including the activation of tyrosine kinases, the tyrosine phosphorylation of phospholipase-C gamma 1 and the mobilization of intracellular calcium. Similar responses have been observed in B-cells following stimulation of MHC class II molecules, including the increased production of intracellular cAMP. In this report, we demonstrate that the ZAP-70 tyrosine kinase is a responsive signaling element following cross-linking of HLA-DR in class II+ T-cells, and that the homologous tyrosine kinase p72syk is stimulated in B-cells following ligation of class II antigens. Antibody mediated co-ligation of the T-cell antigen receptor (TCR/CD3) with class II molecules resulted in augmented tyrosine phosphorylation of ZAP-70. Comparable to antibody induced receptor ligation, bacterial superantigen (SEA and SEB) treatment of HLA-DR+ T-cells stimulated ZAP-70 tyrosine phosphorylation, consistent with class II transmembrane signaling by ligation of HLA-DR and V beta in cis. Modulation of the TCR/CD3 led to abrogation of class II induced ZAP-70 tyrosine phosphorylation, but did not result in sequestering of ZAP-70 from the cellular cytoplasm. Hyperphosphorylated ZAP-70 was associated with TCR/CD3 zeta-chain following cross-linking of HLA-DR, suggesting a mechanism for the TCR/CD3-dependence of class II induced signals in alloantigen-activated human T-cells. In both tonsillar B-lymphocytes and B-cell leukemia lines, p72syk was rapidly phosphorylated on tyrosine residues following HLA-DR cross-linking. Tyrosine phosphorylation of p72syk induced through ligation of either the B-cell antigen receptor or class II molecules was potently inhibited by herbimycin A. MHC class II ligation on B-lymphocytes resulted in cell death, which was both qualitatively distinct from Fas-induced apoptosis and partially protected by herbimycin A pretreatment. Thus, ligation of MHC class II molecules expressed on human lymphocytes stimulates the ZAP-70/p72syk family of tyrosine kinases, leading functionally to a tyrosine kinase-dependent pathway of receptor-induced cell death.
Kanner
S B
SB
Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle, Washington, USA.
Grosmaire
L S
LS
Blake
J
J
Schieven
G L
GL
Masewicz
S
S
Odum
N
N
Ledbetter
J A
JA
D015496:CD4-Positive T-Lymphocytes / Q000201:enzymology / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology; D004792:Enzyme Precursors / Q000032:analysis* / Q000737:chemistry / Q000276:immunology; D006684:HLA-DR Antigens / Q000737:chemistry / Q000276:immunology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008213:Lymphocyte Activation; D011505:Protein-Tyrosine Kinases / Q000032:analysis* / Q000737:chemistry / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D015398:Signal Transduction / Q000276:immunology*; D000072377:Syk Kinase; D051746:ZAP-70 Protein-Tyrosine Kinase
D004792:Enzyme Precursors; D006684:HLA-DR Antigens; D047908:Intracellular Signaling Peptides and Proteins; D011948:Receptors, Antigen, T-Cell; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human