Niemann-Pick C1 Functions in Regulating Lysosomal Amine Content

Abstract

Mutations in the late endosomal/lysosomal membrane protein Niemann-Pick C1 (NPC1) are known to cause a generalized block in retrograde vesicle-mediated transport, resulting in the hyper-accumulation of multiple lysosomal cargos. An important, yet often overlooked, category of lysosomal cargo includes the vast array of small molecular weight amine-containing molecules that are substrates for ion trapping in the highly acidic organelle lumen. We show here that the introduction of aminecontaining molecules in lysosomes can significantly stimulate NPC1-mediated late endosome/lysosome fusion, and subsequently the secretion of lysosomal cargo. To illustrate the physiological importance of this NPC1-mediated transport pathway, we show that NPC1-deficient cells are more susceptible to the toxic effects of a lysosomotropic polyamine metabolite 3-aminopropanal. Moreover, NPC fibroblasts are shown to have higher levels of polyamine oxidase, an enzyme involved in the formation of 3-aminopropanal. Collectively, these findings provide strong support for a novel functional role for NPC1 and may also provide clues toward understanding NPC disease progression.

Mechanisms of Amine Accumulation in, and Egress from, Lysosomes

“…The kinetics of lysosomal [ 3 H]-dextran release from normal human foreskin fibroblasts (CRL-2076, Coriell) and human foreskin fibroblasts with nonfunctional Niemann–Pick C1 (NPC1; denoted NPC1 −/− , GM03123, Coriell) were obtained from previously published work [22]. Modeling of kinetic data was performed using SAAMII, version 1.1 (Seattle, WA, USA) for Microsoft Windows.…”

“…We have recently performed immunofluorescence analysis on human foreskin fibroblasts and found that amine-induced vacuoles co-localize with the late-endosomal- and lysosomal-resident proteins, namely the mannose 6-phosphate receptor and LAMP-1, respectively. We did not observe any co-localization of vacuoles with the Golgi-specific protein GM130 or the early-endosome-specific protein EEA1 (Figure 4) [22]. …”

Di-22:6-bis(monoacylglycerol)phosphate: A clinical biomarker of drug-induced phospholipidosis for drug development and safety assessment

“…It is also established that some CADs (e.g. U18666A and imipramine) inhibit the function of NPC1 (Kaufmann and Krise, 2008). DIPL can lead to the miss-targeting of enzymes through the mannose-6-phosphate (M6PR/IGF2) receptor pathway (Ikeda et al, 2008;Mesens et al, 2012, Reaves et al, 2000 and autophagic dysfunction (Morissette et al, 2009).…”

Deficiency of Niemann-Pick Type C-1 Protein Impairs Release of Human Immunodeficiency Virus Type 1 and Results in Gag Accumulation in Late Endosomal/Lysosomal Compartments

“…While the complete physiological function of NPC1 is still unclear, NPC1 does share homology with the resistance-nodulation-division family of prokaryotic permeases and may function as a transmembrane efflux pump to transport cargos in LEs (9,75). Other studies suggest that NPC1 might also function in vesicle-mediated pathways for cargo transportation from LEs to other intracellular sites (21,33). Recent studies by Infante et al have propelled forward our understanding of how NPC1 works together with NPC2, also known to bind cholesterol, to support cholesterol efflux from the LE (32).…”