Regulation of Epidermal Growth Factor Receptor Signaling by cbl-b
Uniformed Services University Of The Health Sciences Bethesda United States
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Negative regulation of the Epidermal Growth Factor Receptor EGFR signaling is essential to proper regulation of cellular function. Genetic evidence from C. elegans and Drosophila melanogaster has demonstrated that cbl proteins are negative regulators of the EGFR in these organisms. To determine the role of mammalian cbl proteins in EGFR signaling. stable clones overexpressing cbl-b were created in two cell lines which have distinct biological responses to EGFR activation. In the 3.2DIEGFR murine hematopoetic cell line. overexpression of cbl-b inhibits Epidermal Growth Factor-induced EGF proliferation. In the MDA-MB-468 human breast cancer cell line. EGFR activation induces apoptosis. Overexpression of cbl-b in these cells inhibits EGF-induced apoptosis. These data demonstrate that the mammalian cbl-b protein. like the C. elegans and Drosophila homologs. inhibits EGFR function. The molecular basis of this inhibition was studied in these two model systems. cbl-b is phosphorylated and recruited to the EGFR upon activation. In both cell lines. activation of the EGFR and activation of multiple downstream pathways have a shortened duration of signaling when cbl-b is overexpressed. Further biochemical analysis demonstrated that cbl-b increased activation-induced downregulation of the EGFR by enhancing EGFR ubiquitination and EGFR degradation. Specific inhibitors of either lysosomal or proteasomal proteases blocked cbl-b mediated EGFR degradation. Further analysis of cbl-b expression after cells are stimulated with EGF demonstrated that cbl-b is coordinately degraded along with the EGFR. Both EGFR and cbl-b downregulation requires an intact Tyrosine Kinase Binding and RING finger domain of the cbl-b protein. Additionally. binding of cbl-b to the EGFR is required for either protein to undergo EGF-induced degradation. Other proteins which are recruited to the activated EGFR complex are also coordinately degraded with the EGFR and cbl-b.
- Anatomy and Physiology