title: αPIX Is a Trafficking Regulator that Balances Recycling and Degradation of the Epidermal Growth Factor Receptor.
abstract: Endosomal sorting is an essential control mechanism for signaling through the epidermal growth factor receptor (EGFR). We report here that the guanine nucleotide exchange factor αPIX, which modulates the activity of Rho-GTPases, is a potent bimodal regulator of EGFR trafficking. αPIX interacts with the E3 ubiquitin ligase c-Cbl, an enzyme that attaches ubiquitin to EGFR, thereby labelling this tyrosine kinase receptor for lysosomal degradation. We show that EGF stimulation induces αPIX::c-Cbl complex formation. Simultaneously, αPIX and c-Cbl protein levels decrease, which depends on both αPIX binding to c-Cbl and c-Cbl ubiquitin ligase activity. Through interaction αPIX sequesters c-Cbl from EGFR and this results in reduced EGFR ubiquitination and decreased EGFR degradation upon EGF treatment. However, quantitatively more decisive for cellular EGFR distribution than impaired EGFR degradation is a strong stimulating effect of αPIX on EGFR recycling to the cell surface. This function depends on the GIT binding domain of αPIX but not on interaction with c-Cbl or αPIX exchange activity. In summary, our data demonstrate a previously unappreciated function of αPIX as a strong promoter of EGFR recycling. We suggest that the novel recycling regulator αPIX and the degradation factor c-Cbl closely cooperate in the regulation of EGFR trafficking: uncomplexed αPIX and c-Cbl mediate a positive and a negative feedback on EGFR signaling, respectively; αPIX::c-Cbl complex formation, however, results in mutual inhibition, which may reflect a stable condition in the homeostasis of EGF-induced signal flow.
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Fanny
authors.initials: F
authors.lastname: Kortüm
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Frederike Leonie
authors.initials: FL
authors.lastname: Harms
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Natascha
authors.initials: N
authors.lastname: Hennighausen
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Rosenberger
mesh_terms: D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D004815:Epidermal Growth Factor / Q000502:physiology; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D059748:Proteolysis; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism; D064067:Rho Guanine Nucleotide Exchange Factors / Q000502:physiology; D054875:Ubiquitination
chemical_list: C576603:ARHGEF6 protein, human; D064067:Rho Guanine Nucleotide Exchange Factors; D004815:Epidermal Growth Factor; D050721:Proto-Oncogene Proteins c-cbl; C512478:EGFR protein, human; D066246:ErbB Receptors; C067419:CBL protein, human