title: RASopathy-associated CBL germline mutations cause aberrant ubiquitylation and trafficking of EGFR.
abstract: Noonan syndrome, a congenital disorder comprising a characteristic face, short stature, heart defects, learning difficulties, and a predisposition to malignancies, is caused by heterozygous germline mutations in genes encoding components of RAS-MAPK signaling pathways. Mutations in the CBL tumor suppressor gene have been reported in patients with a Noonan syndrome-like phenotype. CBL encodes a multivalent adaptor protein with ubiquitin ligase activity, which promotes ubiquitylation and vesicle-mediated internalization and degradation of the epidermal growth factor (EGF) receptor (EGFR). We investigated the functional consequences of disease-associated CBL amino acid changes p.K382E, p.D390Y, and p.R420Q on ligand-induced EGFR trafficking. Expression of CBL(K382E), CBL(D390Y), or CBL(R420Q) in COS-7 cells resulted in increased levels of surface EGFR and reduced amounts of intracellular EGFR; both consequences indicate ineffective EGFR internalization. Accordingly, receptor-mediated uptake of EGF was decreased. Furthermore, the p.K382E, p.D390Y, and p.R420Q lesions impaired CBL-mediated EGFR ubiquitylation and degradation. Together, these data indicate that pathogenic CBL mutations severely affect vesicle-based EGFR trafficking. Since we detected enhanced ERK phosphorylation in cells expressing mutant CBL, we conclude that aberrant EGFR trafficking contributes to augmented RAS-MAPK signaling, the common trait of Noonan syndrome and related RASopathies. Thus, our data suggest that EGFR trafficking is a novel disease-relevant regulatory level in the RASopathy network.
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Kristina
authors.initials: K
authors.lastname: Brand
authors.forename: Hendrik
authors.initials: H
authors.lastname: Kentsch
authors.forename: Christina
authors.initials: C
authors.lastname: Glashoff
authors.forename: Georg
authors.initials: G
authors.lastname: Rosenberger
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D066246:ErbB Receptors / Q000378:metabolism*; D015870:Gene Expression; D056726:Genetic Association Studies; D018095:Germ-Line Mutation; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D020125:Mutation, Missense; D009634:Noonan Syndrome / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D059748:Proteolysis; D050721:Proto-Oncogene Proteins c-cbl / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D015398:Signal Transduction; D054875:Ubiquitination
chemical_list: D050721:Proto-Oncogene Proteins c-cbl; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases; D016283:Proto-Oncogene Proteins p21(ras)
keywords: CBL; EGFR trafficking; Noonan syndrome; RASopathies; c-Cbl