Program in Molecular Medicine
*Adaptor Proteins, Signal Transducing; Amino Acid Sequence; Animals; Base Sequence; Binding Sites; Caenorhabditis elegans; DNA Primers; DNA, Complementary; Drosophila melanogaster; GRB2 Adaptor Protein; Humans; Molecular Sequence Data; Photoreceptors, Invertebrate; Protein Binding; Proteins; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-cbl; Proto-Oncogenes; Receptor, Epidermal Growth Factor; Sequence Homology, Amino Acid; *Ubiquitin-Protein Ligases; src Homology Domains
Life Sciences | Medicine and Health Sciences
The human proto-oncogene product c-Cbl and a similar protein in Caenorhabditis elegans (Sli-1) contain a proline-rich COOH-terminal region that binds Src homology 3 (SH3) domains of proteins such as the adapter Grb2. Cb1-Grb2 complexes can be recruited to tyrosine-phosphorylated epidermal growth factor (EGF) receptors through the SH2 domain of Grb2. Here we identify by molecular cloning a Drosophila cDNA encoding a protein (Drosophila Cbl [D-Cbl]) that shows high sequence similarity to the N-terminal region of human c-Cbl but lacks proline-rich sequences and fails to bind Grb2. Nonetheless, in COS-1 cells, expression of hemagglutinin epitope-tagged D-Cbl results in its coimmunoprecipitation with EGF receptors in response to EGF. EGF also caused tyrosine phosphorylation of D-Cbl in such cells, but no association of phosphatidylinositol 3-kinase was detected in assays using anti-p85 antibody. A point mutation in D-Cbl (G305E) that suppresses the negative regulation of LET-23 by the Cbl homolog Sli-1 in C. elegans prevented tyrosine phosphorylation of D-Cbl as well as binding to the liganded EGF receptor in COS-1 cells. Colocalization of EGF receptors with both endogenous c-Cbl or expressed D-Cbl in endosomes of EGF-treated COS-1 cells is also demonstrated by immunofluorescence microscopy. In lysates of adult transgenic Drosophila melanogaster, GST-DCbl binds to the tyrosine-phosphorylated 150-kDa torso-DER chimeric receptor. Expression of D-Cbl directed by the sevenless enhancer in intact Drosophila compromises severely the development of the R7 photoreceptor neuron. These data suggest that despite the lack of Grb2 binding sites, D-Cbl functions as a negative regulator of receptor tyrosine kinase signaling in the Drosophila eye by a mechanism that involves its association with EGF receptors or other tyrosine kinases.
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Citation: Mol Cell Biol. 1997 Apr;17(4):2217-25.
Molecular and cellular biology
Meisner, Herman; Daga, Andrea; Buxton, Joanne M.; Fernandez, Belen; Chawla, Anil; Banerjee, Utpal; and Czech, Michael P., "Interactions of Drosophila Cbl with epidermal growth factor receptors and role of Cbl in R7 photoreceptor cell development" (1997). Open Access Articles. 1452.