Cbl-b, a member of the Sli-1/c-Cbl protein family, inhibits Vav-mediated c-Jun N-terminal kinase activation.
We have used the yeast two-hybrid system to identify proteins that interact with Vav, a GDP/GTP exchange factor for the Rac-1 GTPase that plays an important role in cell signaling and oncogenic transformation. This experimental approach resulted in the isolation of Cbl-b, a signal transduction molecule highly related to the mammalian c-cbl proto-oncogene product and to the C. elegans Sli-1 protein, a negative regulator of the EGF-receptor-like Let23 protein. The interaction between Vav and Cbl-b requires the entire SH3-SH2-SH3 carboxy-terminal domain of Vav and a long stretch of proline-rich sequences present in the central region of Cbl-b. Stimulation of quiescent rodent fibroblasts with either epidermal or platelet-derived growth factors induces an increased affinity of Vav for Cbl-b and results in the subsequent formation of a Vav-dependent trimeric complex with the ligand-stimulated tyrosine kinase receptors. During this process, Vav, but not Cbl-b, becomes highly phosphorylated on tyrosine residues. Overexpression of Cbl-b inhibits the signal transduction pathway of Vav that leads to the stimulation of c-Jun N-terminal kinase. By contrast, expression of truncated Cbl-b proteins and of missense mutants analogous to those found in inactive Sli-1 proteins have no detectable effect on Vav activity. These results indicate that Vav and Cbl-b act coordinately in the first steps of tyrosine protein kinase receptor-mediated signaling and suggest that members of the Sli-1/Cbl family are also negative regulators of signal transduction in mammalian cells.
Bustelo
X R
XR
Department of Molecular Oncology, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, New Jersey 08543, USA.
Crespo
P
P
López-Barahona
M
M
Gutkind
J S
JS
Barbacid
M
M
D000818:Animals; D019556:COS Cells; D018797:Cell Cycle Proteins; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D011494:Protein Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D050721:Proto-Oncogene Proteins c-cbl; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav; D011817:Rabbits; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology; D015398:Signal Transduction; D044767:Ubiquitin-Protein Ligases; D020744:rac GTP-Binding Proteins; D018909:src Homology Domains
D018797:Cell Cycle Proteins; D011518:Proto-Oncogene Proteins; D016755:Proto-Oncogene Proteins c-jun; D051567:Proto-Oncogene Proteins c-vav; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D011494:Protein Kinases; D020794:Receptor Protein-Tyrosine Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins