PROTO-ONCOPROTEIN VAV INTERACTS WITH C-CBL IN ACTIVATED THYMOCYTES AND PERIPHERAL T-CELLS

The molecular adapter c-Cbl is rapidly tyrosine phosphorylated followi ng stimulation through the TCR and associates with Src homology domain -a (SH2)/SH3 domain-containing adapters such as Grb2, Crk, and Crk-L, which interact with guanine nucleotide exchange factors specific for t he pas family. This suggests that c-Cbl may link TCR activation to mol ecules that regulate GTP binding proteins. The SH2/SH3-containing prot ein Vav also contains a guanine nucleotide exchange factor domain, and Vav has a crucial role in thymocyte development and activation of per ipheral T cells following stimulation through the TCR, Here we show th at Vav and c-Cbl form inducible molecular complexes in TCR-activated m urine thymocytes and peripheral T cells as well as pervanadate-treated T cells. Vav/c-Cbl interactions are also detectable in freshly isolat ed T cells from gene-targeted mice that lack the T cell-specific inhib itory receptor CTLA-4, in which c-Cbl is hyperphosphorylated on tyrosi ne residues. The interaction between Vav and c-Cbl is directly mediate d via the SH2 domain of Vav and is dependent on tyrosine phosphorylati on of c-Cbl. In addition, we show that the conserved motif Y-699 MTP p resent in c-Cbl is the binding site for the Vav SH2 domain in vitro. T hese data imply that c-Cbl is a molecular adapter that regulates the f unction of Vav in thymocytes and peripheral T cells.