Mardakheh, Faraz K. and Auciello, Giulio and Dafforn, Tim R. and Rappoport, Joshua Z. and Heath, John K (2010) Nbr1 Is a Novel Inhibitor of Ligand-Mediated Receptor Tyrosine Kinase Degradation. Molecular and Cellular Biology, 30 (24). pp. 5672-5685.
Identification Number/DOI: doi:10.1128/MCB.00878-10
endocytic trafficking and selective autophagy. However, the exact function of Nbr1 in these contexts has not
been studied in detail. Here we investigated the role of Nbr1 in the trafficking of receptor tyrosine kinases
(RTKs). We report that ectopic Nbr1 expression inhibits the ligand-mediated lysosomal degradation of RTKs,
and this is probably done via the inhibition of receptor internalization. Conversely, the depletion of endogenous
NBR1 enhances RTK degradation. Analyses of truncation mutations demonstrated that the C terminus of
Nbr1 is essential but not sufficient for this activity. Moreover, the C terminus of Nbr1 is essential but not
sufficient for the localization of the protein to late endosomes. We demonstrate that the C terminus of Nbr1
contains a novel membrane-interacting amphipathic -helix, which is essential for the late endocytic localization
of the protein but not for its effect on RTK degradation. Finally, autophagic and late endocytic
localizations of Nbr1 are independent of one another, suggesting that the roles of Nbr1 in each context might
be distinct. Our results define Nbr1 as a negative regulator of ligand-mediated RTK degradation and reveal the
interplay between its various regions for protein localization and function.
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