Endosomal lipid accumulation in NPC1 leads to inhibition of PKC, hypophosphorylation of vimentin and Rab9 entrapment.
BACKGROUND
Within the group of lysosomal storage diseases, NPC1 [NPC (Niemann-Pick type C) 1] disease is a lipidosis characterized by excessive accumulation of free cholesterol as well as gangliosides, glycosphingolipids and fatty acids in the late E/L (endosomal/lysosomal) system (Chen et al., 2005) due to a defect in late endosome lipid egress. We have previously demonstrated that expression of the small GTPase Rab9 in NPC1 cells can rescue the lipid transport block phenotype (Walter et al., 2003), albeit by an undefined mechanism.


RESULTS
To investigate further the mechanism by which Rab9 facilitates lipid movement from late endosomes we sought to identify novel Rab9 binding/interacting proteins. In the present study, we report that Rab9 interacts with the intermediate filament phosphoprotein vimentin and this interaction is altered by lipid accumulation in late endosomes, which results in inhibition of PKC (protein kinase C) and hypophosphorylation of vimentin, leading to late endosome dysfunction. Intermediate filament hypophosphorylation, aggregation and entrapment of Rab9 ultimately leads to transport defects and inhibition of lipid egress from late endosomes.


CONCLUSIONS
These results reveal a previously unappreciated interaction between Rab proteins and intermediate filaments in regulating intracellular lipid transport.
Walter
Marc
M
Department of Genetics and Genomic Sciences, The Mount Sinai School of Medicine, New York, NY 10029, USA.
Chen
Fannie W
FW
Tamari
Farshad
F
Wang
Rong
R
Ioannou
Yiannis A
YA
D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D015870:Gene Expression; D006801:Humans; D007382:Intermediate Filaments / Q000378:metabolism; D050356:Lipid Metabolism; D052556:Niemann-Pick Disease, Type C / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism*; D013110:Sphingosine / Q000494:pharmacology; D014746:Vimentin / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D014746:Vimentin; D002784:Cholesterol; D011493:Protein Kinase C; C079856:RAB9A protein, human; D020691:rab GTP-Binding Proteins; D013110:Sphingosine