Engagement of the T lymphocyte antigen receptor regulates association of son‐of‐sevenless homologues with the SH3 domain of phospholipase Cγ1

• Published in: European journal of immunology Vol. 30; no. 8; pp. 2378 - 2387
• Main Authors: Scholler, John K., Perez‐Villar, Juan J., O'Day, Kathleen, Kanner, Steven B.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag GmbH 2000
• Subjects: Cellular activation; Phospholipase Cγ1; SH3; Signal transduction; T lymphocyte
• ISSN: 0014-2980; 1521-4141
• DOI: 10.1002/1521-4141(2000)30:8<2378::AID-IMMU2378>3.0.CO;2-E

One mechanism for transducing signals downstream of lymphocyte receptor activation involves the stable association between signaling proteins. To identify protein ligands of the signal activator phospholipase Cγ1 (PLCγ1), we screened T cell cDNA libraries with the PLCγ1‐SH3 domain by the yeast two‐hybrid assay. We observed association between the PLCγ1‐SH3 domain and the human Ras guanine nucleotide exchange factor son‐of‐sevenless‐2 (hSos2) through a proline‐rich domain interaction. Stable and abundant hSos2 / PLCγ1 and hSos1 / PLCγ1 complexes were observed in unstimulated T cells. The interaction between these enzymes was augmented following engagement of the T cell antigen receptor (TCR / CD3). The kinetics of protein complex enhancement correlated with TCR / CD3‐induced tyrosine phosphorylation of PLCγ1; however, those PLCγ1 molecules in complex with hSos2 were non‐phosphorylated after TCR / CD3 stimulation, in contrast to the phosphorylated PLCγ1 associated with the linker for activation of T cells, LAT. The Grb2 adapter protein was detected in complex with hSos / PLCγ1, suggesting a regulatory role for Grb2. SH3 domains from both Grb2 and PLCγ1, but not RasGAP, bound directly to hSos homologues. The SH2 domain from Grb2 formed an association with the hSos / PLCγ1 complex, which was enhanced following TCR / CD3 ligation. Together, the data suggest a mechanism for the son‐of‐sevenless and PLCγ1 signal transducing enzymes in recruitment to protein complexes with potentially differential signaling consequences in T lymphocytes.