The ability of Sos1 to oligomerize the adaptor protein LAT is separable from its guanine nucleotide exchange activity in vivo.
The activation of the small guanosine triphosphatase Ras by the guanine nucleotide exchange factor (GEF) Sos1 (Son of Sevenless 1) is a central feature of many receptor-stimulated signaling pathways. In developing T cells (thymocytes), Sos1-dependent activation of extracellular signal-regulated kinase (ERK) is required to stimulate cellular proliferation and differentiation. We showed that in addition to its GEF activity, Sos1 acted as a scaffold to nucleate oligomerization of the T cell adaptor protein LAT (linker for activation of T cells) in vivo. The scaffold function of Sos1 depended on its ability to bind to the adaptor protein Grb2. Furthermore, the GEF activity of Sos1 and the Sos1-dependent oligomerization of LAT were separable functions in vivo. Whereas the GEF activity of Sos1 was required for optimal ERK phosphorylation in response to T cell receptor (TCR) stimulation, the Sos1-dependent oligomerization of LAT was required for maximal TCR-dependent phosphorylation and activation of phospholipase C-γ1 and Ca(2+) signaling. Finally, both of these Sos1 functions were required for early thymocyte proliferation. Whereas transgenic restoration of either the GEF activity or the LAT oligomerization functions of Sos1 alone failed to rescue thymocyte development in Sos1-deficient mice, simultaneous reconstitution of these two signals in the same cell restored normal T cell development. This ability of Sos1 to act both as a RasGEF and as a scaffold to nucleate Grb2-dependent adaptor oligomerization may also occur in other Grb2-dependent pathways, such as those activated by growth factor receptors.
Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Robert L
RL
Kortum
Lakshmi
L
Balagopalan
Clayton P
CP
Alexander
Julie
J
Garcia
John M
JM
Pinski
Robert K
RK
Merrill
Phan H
PH
Nguyen
Wenmei
W
Li
Isha
I
Agarwal
Itoro O
IO
Akpan
Connie L
CL
Sommers
Lawrence E
LE
Samelson
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D020013:Calcium Signaling; D002454:Cell Differentiation; D049109:Cell Proliferation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D051380:GRB2 Adaptor Protein / Q000378:metabolism; D005786:Gene Expression Regulation; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D009711:Nucleotides / Q000737:chemistry; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D020837:SOS1 Protein / Q000235:genetics* / Q000502:physiology*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000166:cytology; D060168:Thymocytes / Q000166:cytology; D019076:Transgenes; D018631:ras Proteins / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; C491734:Lat protein, mouse; D008565:Membrane Proteins; D009711:Nucleotides; D010750:Phosphoproteins; D011948:Receptors, Antigen, T-Cell; D020837:SOS1 Protein; D048049:Extracellular Signal-Regulated MAP Kinases; D018631:ras Proteins