Catalytic activity of the mouse guanine nucleotide exchanger mSOS is activated by Fyn tyrosine protein kinase and the T-cell antigen receptor in T cells.
mSOS, a guanine nucleotide exchange factor, is a positive regulator of Ras. Fyn tyrosine protein kinase is a potential mediator in T-cell antigen receptor signal transduction in subsets of T cells. We investigated the functional and physical interaction between mSOS and Fyn in T-cell hybridoma cells. Stimulation of the T-cell antigen receptor induced the activation of guanine nucleotide exchange activity in mSOS immunoprecipitates. Overexpression of Fyn mutants with an activated kinase mutation and with a Src homology 2 deletion mutation resulted in a stimulation and suppression of the mSOS activity, respectively. The complex formations of Fyn-Shc, Shc-Grb2, and Grb2-mSOS were detected in the activated Fyn-transformed cells, whereas the SH2 deletion mutant of Fyn failed to form a complex with mSOS. Moreover, tyrosine phosphorylation of Shc was induced by the overexpression of the activated Fyn. These findings support the idea that Fyn activates the activity of mSOS bound to Grb2 through tyrosine phosphorylation of Shc. Unlike the current prevailing model, Fyn-induced activation of Ras might involve the stimulation of the catalytic guanine nucleotide exchange activity of mSOS.
Li
B
B
Biological Carcinogenesis and Development Program, National Cancer Institute-Frederick Cancer Research and Development Center, MD 21702-1201, USA.
Subleski
M
M
Fusaki
N
N
Yamamoto
T
T
Copeland
T
T
Princler
G L
GL
Kung
H
H
Kamata
T
T
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D004789:Enzyme Activation; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D015870:Gene Expression; D020662:Guanine Nucleotide Exchange Factors; D007700:Kinetics; D051379:Mice; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D051076:Proto-Oncogene Proteins c-fyn; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D011994:Recombinant Proteins; D017384:Sequence Deletion; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology / Q000378:metabolism*; D014162:Transfection; D020663:ras Guanine Nucleotide Exchange Factors; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; D015852:Eukaryotic Initiation Factor-2; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; D011518:Proto-Oncogene Proteins; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D011948:Receptors, Antigen, T-Cell; D011994:Recombinant Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D011505:Protein-Tyrosine Kinases; C494960:Fyn protein, mouse; D051076:Proto-Oncogene Proteins c-fyn