Defective signaling to Fyn by a T cell antigen receptor lacking the alpha -chain connecting peptide motif.
A key role in the communication between the alphabetaTCR and the CD3/zeta complex is played by a specific motif within the connecting peptide domain of the TCR alpha chain (alpha-CPM). T cell hybridomas expressing an alpha-CPM-mutated TCR show a dramatic impairment in antigen-driven interleukin-2 production. This defect can be complemented by a calcium ionophore, indicating that activation of the calcium pathway is impaired. Several lines of evidence implicate Fyn in the regulation of calcium mobilization, at least in part through the activation of phospholipase Cgamma. Here we have investigated the potential involvement of Fyn in the TCR alpha-CPM signaling defect. Using T cell hybridomas expressing either a wild-type TCR or an alpha-CPM mutant, we show that Fyn fails to be activated by the mutant receptor following SEB binding and fails to generate tyrosine-phosphorylated Pyk2, a member of the focal adhesion kinase family. This defect correlated with an impairment in phospholipase Cgamma phosphorylation. Production of interlukin-2 and activation of the transcription factor NF-AT in response to triggering of the TCR alpha-CPM mutant with SEB were fully restored in the presence of constitutively active Fyn. Hence the signaling defect generated by the TCR alpha-CPM mutation results at least in part from an impaired coupling of the TCR.CD3 complex to Fyn activation.
Ulivieri
C
C
Department of Evolutionary Biology, University of Siena, Via Mattioli 4, 53100 Siena, Italy.
Peter
A
A
Orsini
E
E
Palmer
E
E
Baldari
C T
CT
D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D002352:Carrier Proteins / Q000502:physiology*; D004768:Enterotoxins / Q000494:pharmacology; D051418:Focal Adhesion Kinase 2; D006801:Humans; D006825:Hybridomas; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013601:T-Lymphocytes / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004768:Enterotoxins; C106957:FYB1 protein, human; D007527:Isoenzymes; D016693:Receptors, Antigen, T-Cell, alpha-beta; C031818:enterotoxin B, staphylococcal; D011505:Protein-Tyrosine Kinases; D051418:Focal Adhesion Kinase 2; D010738:Type C Phospholipases; D051966:Phospholipase C gamma