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T Cell Receptor-dependent Tyrosine Phosphorylation of β2-Chimaerin Modulates Its Rac-GAP Function in T Cells*S⃞

By María Siliceo and Isabel Mérida


The actin cytoskeleton has an important role in the organization and function of the immune synapse during antigen recognition. Dynamic rearrangement of the actin cytoskeleton in response to T cell receptor (TCR) triggering requires the coordinated activation of Rho family GTPases that cycle between active and inactive conformations. This is controlled by GTPase-activating proteins (GAP), which regulate inactivation of Rho GTPases, and guanine exchange factors, which mediate their activation. Whereas much attention has centered on guanine exchange factors for Rho GTPases in T cell activation, the identity and functional roles of the GAP in this process are largely unknown. We previously reported β2-chimaerin as a diacylglycerol-regulated Rac-GAP that is expressed in T cells. We now demonstrate Lck-dependent phosphorylation of β2-chimaerin in response to TCR triggering. We identify Tyr-153 as the Lck-dependent phosphorylation residue and show that its phosphorylation negatively regulates membrane stabilization of β2-chimaerin, decreasing its GAP activity to Rac. This study establishes the existence of TCR-dependent regulation of β2-chimaerin and identifies a novel mechanism for its inactivation

Topics: Mechanisms of Signal Transduction
Publisher: American Society for Biochemistry and Molecular Biology
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Provided by: PubMed Central
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