title: Dual degradation mechanisms ensure disposal of NHE6 mutant protein associated with neurological disease.
abstract: Clinical features characterizing Angelman syndrome, previously shown to be caused by disruption of UBE3A, were recently also described in neurologically disabled patients with mutations in SLC9A6, which encodes the Na(+)/H(+) exchanger NHE6. In the present work we have focused on NHE6Delta255-256, the protein product of a specific 6-bp patient deletion in SLC9A6. To resolve the molecular mechanism causing the cellular dysfunction associated with this mutant, we have characterized its intracellular behaviour in comparison to wild type NHE6. Our study demonstrates that NHE6Delta255-256 is much less stable than the wild type protein. Whereas wild type NHE6 is transported to the plasma membrane and early endosomes and remains stable, NHE6Delta255-256 is degraded via two independent pathways mediated by proteasomes and lysosomes, respectively. Depletion of NHE6 had no detectable effect on endosomal pH, but co-depletion of NHE6 and the closely related NHE9 caused enhanced acidification of early endosomes. Our results suggest that NHE6 participates in regulation of endosomal pH and provides a cellular basis for understanding the loss of NHE6 function leading to a neurological phenotype resembling Angelman syndrome.
authors.affiliation: Centre for Cancer Biomedicine, University of Oslo, Montebello, N-0310 Oslo, Norway.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Roxrud
authors.forename: Camilla
authors.initials: C
authors.lastname: Raiborg
authors.forename: Gregor D
authors.initials: GD
authors.lastname: Gilfillan
authors.forename: Petter
authors.initials: P
authors.lastname: Strømme
authors.forename: Harald
authors.initials: H
authors.lastname: Stenmark
mesh_terms: D017204:Angelman Syndrome / Q000235:genetics*; D002884:Chromosomes, Human, Pair 15; D017931:DNA Primers; D011992:Endosomes / Q000502:physiology; D005260:Female; D006367:HeLa Cells / Q000166:cytology / Q000502:physiology; D006801:Humans; D008607:Intellectual Disability / Q000235:genetics; D008297:Male; D018613:Microscopy, Confocal; D009154:Mutation; D009422:Nervous System Diseases / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D017384:Sequence Deletion; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism
chemical_list: D017931:DNA Primers; C445316:SLC9A6 protein, human; D017923:Sodium-Hydrogen Exchangers