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Signal transduction in T lymphocytes using a conditional allele of Sos
L J Holsinger1, D M Spencer, D J Austin
1Howard Hughes Medical Institute, Stanford University School of Medicine, CA 94305, USA.
Abstract:
While Ras activation has been shown to play an important role in signal transduction by the T-lymphocyte antigen receptor, the mechanism of its activation in T cells is unclear. Membrane localization of the guanine nucleotide exchange factor Sos, but not Vav or Dbl, was sufficient for Ras-mediated signaling in T lymphocytes. Activation of Sos appears to involve membrane recruitment and not allosteric changes, because interaction of Sos with the linking molecule Grb-2 was not required for Ras activation. To extend this analysis, we constructed a modified Sos that could be localized to the membrane inducibly by using a rationally designed chemical inducer of dimerization, FK1012. The role of Grb-2 in signaling was mimicked with this technique, which induced the association of a modified Sos with the membrane, resulting in rapid activation of Ras-induced signaling. In contrast, inducible localization of Grb-2 to the membrane did not activate signaling and suggests that the interaction of Grb-2 with Sos in T cells is subject to regulation. This conditional allele of Sos demonstrates that membrane localization of Sos is sufficient for Ras activation in T cells and indicates that the role of Grb-2 is to realize the biologic advantages of linker-mediated dimerization: enhanced specificity and favorable kinetics for signaling. This method of generating conditional alleles may also be useful in dissecting other signal transduction pathways regulated by protein localization or protein-protein interactions.
Insights
Membrane localization of Son of Sevenless (Sos) is sufficient for Ras activation in T cells. This finding clarifies Ras signaling mechanisms and offers a new method for studying T-cell signal transduction pathways.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Ras activation is crucial for T-lymphocyte antigen receptor signal transduction.
- The precise mechanism of Ras activation in T cells remains unclear.
- Membrane localization of guanine nucleotide exchange factors (GEFs) is implicated in Ras signaling.
Purpose of the Study:
- To elucidate the mechanism of Ras activation in T cells.
- To determine if membrane localization of Sos is sufficient for Ras activation.
- To investigate the role of Grb-2 in Sos-mediated Ras signaling.
Main Methods:
- Constructed a modified Sos protein for inducible membrane localization using FK1012.
- Utilized a chemical inducer of dimerization (FK1012) to control Sos localization.
- Assessed Ras activation upon inducible membrane recruitment of Sos and Grb-2.
Main Results:
- Inducible membrane localization of Sos was sufficient to activate Ras-mediated signaling in T lymphocytes.
- Interaction with Grb-2 was not required for Ras activation, suggesting membrane recruitment is key.
- Inducible membrane localization of Grb-2 alone did not activate signaling, indicating regulation of Grb-2/Sos interaction.
- Conditional Sos allele demonstrated that membrane localization is sufficient for Ras activation.
Conclusions:
- Membrane localization of Sos is sufficient for Ras activation in T cells.
- Grb-2's role in signaling involves enhancing specificity and kinetics of linker-mediated dimerization.
- The developed conditional allele system is a valuable tool for dissecting other signaling pathways regulated by protein localization or interactions.