The protein tyrosine kinase syk activity is reduced by clustering the mast cell function-associated antigen.
The mast cell function-associated antigen (MAFA) is a glycoprotein first identified on the membrane of rat mucosal-type mast cells (RBL-2H3 line). MAFA clustering causes a dose-dependent inhibition of these cells' secretory response to the type I Fcepsilon receptor (FcepsilonRI) stimulus. The inhibition has earlier been shown to take place upstream to the production step of inositol phosphates in the FcepsilonRI coupling cascade. To resolve further the mechanism of action of MAFA, we have investigated the events prior to the activation of phospholipase C. Activities of the non-receptor protein tyrosine kinases Lyn and Syk in untreated cells were compared with those where the FcepsilonRI, MAFA or both were clustered. Syk tyrosine phosphorylation and activation, as well as LAT (linker for activation of T cells) tyrosine phosphorylation, both induced by FcepsilonRI clustering, were found to be reduced upon MAFA clustering. In contrast, the activity of the Src homology domain 2 (SH2)-containing protein tyrosine phosphatase (SHP-2) increased. MAFA clustering also enhanced the co-isolation of SHP-2 and Syk with tyrosine-phosphorylated MAFA in both untreated and FcepsilonRI-stimulated cells. SHP-2 caused a decline in the FcepsilonRI-induced tyrosine phosphorylation of Syk, at least under in vitro conditions. Taken together, these results suggest that one possible mechanism by which MAFA affects the FcepsilonRI stimulation cascade is suppression of Syk activity, i.e. MAFA clustering leads SHP-2 to act on Syk, thereby reducing its tyrosine phosphorylation and its activity.
Xu
R
R
Department of Immunology, The Weizmann Institute of Science, Rehovot, Israel.
Pecht
I
I
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D015536:Down-Regulation; D004789:Enzyme Activation / Q000187:drug effects; D004792:Enzyme Precursors / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D037181:Lectins, C-Type; D046911:Macromolecular Substances; D008407:Mast Cells / Q000201:enzymology* / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding; D021122:Protein Subunits; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D017455:Receptors, IgE / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase; D019061:src-Family Kinases / Q000378:metabolism
D002352:Carrier Proteins; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; C094696:Klrg1 protein, rat; D037181:Lectins, C-Type; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D021122:Protein Subunits; D017455:Receptors, IgE; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606898:Syk protein, rat; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C516727:Ptpn11 protein, rat; C509250:Ptpn6 protein, rat