The Cbl RING finger C-terminal flank controls epidermal growth factor receptor fate downstream of receptor ubiquitination.
Evolutionarily conserved sequences of the E3/protein-ubiquitin ligase Cbl regulate epidermal growth factor receptor (EGF-R) signaling and degradation. These sequences encompass Cbl's tyrosine kinase-binding domain, linker region, RING finger (RF), and an uncharacterized flank C-terminal to the RF (residues 420-436). The latter domain, designated the RF tail, extends beyond Cbl's ubiquitin-conjugating enzyme (Ubc)-binding domain and has no known function. We report structure-function studies evaluating the impact of Cbl RF tail truncations on EGF-R fate in HEK 293 cells. All of the truncation mutants exhibit greatly reduced binding to activated EGF-R and lack proline-rich sequences that mediate direct Cbl association with SH3 proteins such as Grb2, yet a subset of mutants collectively enhances EGF-R ubiquitination, downregulation, and degradation. Significantly, EGF-R degradation correlates better with RF tail-dependent degradation of the Cbl substrate Sprouty2 than with EGF-R ubiquitination: expression of the RF tail truncation mutant Cbl 1-433 enhanced EGF-R ubiquitination while impeding Sprouty2 degradation, and Cbl 1-433 failed to enhance EGF-R downregulation or degradation. Our results suggest that EGF-R fate is controlled by a checkpoint downstream of receptor ubiquitination whose regulation by the Cbl RF tail may require Sprouty2 degradation.
Visser
Gina D
GD
Department of Pharmacology, Carver College of Medicine, University of Iowa, 51 Newton Road 2-471 BSB, Iowa City, IA 52242, USA.
Lill
Nancy L
NL
D000595:Amino Acid Sequence; D002478:Cells, Cultured; D017124:Conserved Sequence; D015536:Down-Regulation; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl / Q000235:genetics* / Q000378:metabolism*; D017384:Sequence Deletion; D014443:Tyrosine / Q000378:metabolism; D025801:Ubiquitin
D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011506:Proteins; C485561:SPRY2 protein, human; D025801:Ubiquitin; D014443:Tyrosine; D050721:Proto-Oncogene Proteins c-cbl; D066246:ErbB Receptors; C067419:CBL protein, human