ABSTRACT
Src homology 2 (SH2) domain-containing protein tyrosine phosphatase-1 (SHP-1) is a critical inhibitory regulator in T cell-receptor (TCR) signaling. However, the exact molecular mechanism underlying this is poorly defined, largely because the physiological substrates for SHP-1 in T cells remain elusive. In this study, we showed that adaptor protein 3BP2 serves as a binding protein and a physiological substrate of SHP-1. 3BP2 is phosphorylated on tyrosyl residue 448 in response to TCR activation, and the phosphorylation is required for T cell signalling, as indicated by transcriptional activation of nuclear factor activated in T cells (NFAT). Concurrently, phosphorylation of Tyr566 at the C-terminus of SHP-1 causes specific recruitment of 3BP2 to the phosphatase through the SH2 domain of the adaptor protein. This leads to efficient dephosphorylation of 3BP2 and thereby termination of T cell signaling. The study thus defines a novel function of the C-terminal segment of SHP-1 and reveals a new mechanism by which T cell signaling is regulated.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Intracellular Signaling Peptides and Proteins/physiology , Protein Tyrosine Phosphatases/physiology , Receptors, Antigen, T-Cell/metabolism , Signal Transduction/drug effects , src Homology Domains/physiology , Adaptor Proteins, Signal Transducing/genetics , Cells, Cultured , Down-Regulation , Humans , Intracellular Signaling Peptides and Proteins/genetics , Jurkat Cells , Lymphocyte Specific Protein Tyrosine Kinase p56(lck)/metabolism , NFATC Transcription Factors/metabolism , Phosphorylation , Protein Phosphatase 1 , Protein Tyrosine Phosphatase, Non-Receptor Type 6 , Protein Tyrosine Phosphatases/genetics , Two-Hybrid System Techniques , src Homology Domains/drug effectsABSTRACT
PTEN is a tumor suppressor that primarily dephosphorylates phosphatidylinositol 3,4,5-trisphosphate to down-regulate the phosphoinositide 3-kinase/Akt signaling pathway. Although the cellular functions of PTEN as a tumor suppressor have been well characterized, the mechanism by which PTEN activity is modulated by other signal molecules in vivo remains poorly understood. In searching for potential PTEN modulators through protein-protein interaction, we identified the major vault protein (MVP) as a dominant PTEN-binding protein in a yeast two-hybrid screen. MVP is the major structural component of vault, the largest intracellular ribonucleoprotein particle. Co-immunoprecipitation confirmed the interaction between PTEN and MVP in transfected mammalian cells. More importantly, we found that a significant portion of endogenous PTEN associates with vault particles in human HeLa cells. Deletion mutation analysis demonstrated that MVP binds to the C2 domain of PTEN and that PTEN interacts with MVP through its EF hand-like motif. Furthermore, the in vitro binding experiments revealed that the interaction of PTEN with MVP is Ca(2+)-dependent.
