SHP-1/immunoreceptor tyrosine-based inhibition motif-independent inhibitory signalling through murine natural killer cell receptor Ly-49A in a transfected B-cell line.
Ly-49A is a member of the Ly-49 family of mouse natural killer cell receptors that inhibit cytotoxicity upon recognition of their ligands, the major histocompatibility complex (MHC) class I molecules, on the target cell surface. Although Ly-49A has an immunoreceptor tyrosine-based inhibition motif (ITIM) in its cytoplasmic tail, relatively little is known about the mechanisms underlying its inhibitory function. We report here that antibody-mediated co-ligation of the B-cell receptor (BCR) with the transfected Ly-49A molecule results in abrogation of BCR-induced interleukin-2 (IL-2) secretion and mild reduction in activation of Erk1/2 and p38 mitogen-activated protein (MAP) kinases in the B-cell line A20. Surprisingly, BCR-induced calcium mobilization was unaffected by cross-linking of BCR with Ly-49A. Furthermore, substitution of the single tyrosine residue in ITIM with phenylalanine, did not result in a complete loss of inhibitory function, as measured by BCR-induced IL-2 secretion. Deletion of the N-terminal 37 amino acid peptide, which includes the ITIM, did abrogate the inhibitory activity. Co-immunoprecipitation experiments revealed that, upon induction of tyrosine phosphorylation, Ly-49A recruits tyrosine phosphatase src-homology 2 (SH2) containing tyrosine phosphatases-1 (SHP-1), but not inositol phosphatase src-homology 2 (SH2) containing inositol phosphatase (SHIP), and that the tyrosine residue in the ITIM is critical for this interaction. These results suggest that transfected Ly-49A utilizes two different inhibitory mechanisms in B-cell signalling: ITIM-dependent and ITIM-independent.
Second Department of Internal Medicine, Okayama University Medical School, Okayama, Japan.
K
K
Motoda
M
M
Takata
K
K
Kiura
I
I
Nakamura
M
M
Harada
D000818:Animals; D000950:Antigens, Ly; D001402:B-Lymphocytes / Q000276:immunology*; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000276:immunology*; D047908:Intracellular Signaling Peptides and Proteins; D007694:Killer Cells, Natural / Q000276:immunology*; D037181:Lectins, C-Type; D008213:Lymphocyte Activation / Q000276:immunology; D008565:Membrane Proteins / Q000276:immunology*; D051379:Mice; D010766:Phosphorylation; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000276:immunology*; D017452:Receptors, IgG / Q000276:immunology; D011971:Receptors, Immunologic / Q000276:immunology*; D055630:Receptors, NK Cell Lectin-Like; D015398:Signal Transduction / Q000276:immunology; D014162:Transfection; D014407:Tumor Cells, Cultured; D014443:Tyrosine
D000950:Antigens, Ly; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D037181:Lectins, C-Type; D008565:Membrane Proteins; D017452:Receptors, IgG; D011971:Receptors, Immunologic; D055630:Receptors, NK Cell Lectin-Like; D014443:Tyrosine; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C516725:Ptpn11 protein, mouse; C509248:Ptpn6 protein, mouse; D002118:Calcium