Niemann-Pick C1 Protein Facilitates the Efflux of the Anticancer Drug Daunorubicin from Cells According to a Novel Vesicle-Mediated Pathway

Abstract

Niemann-Pick C1 (NPC1) is a late endosomal/lysosomal membrane protein originally reported on for its role in cholesterol trafficking in mammalian cells. NPC1 has been shown recently to share significant structural homology with a family of prokaryotic permeases and was proposed to play a role in intracellular drug transport; however, the mechanism for this has not been fully understood. We provide evidence here that is consistent with NPC1's involvement in a vesicle-mediated clearance of the anticancer agent daunorubicin from cells. In experiments with human fibroblasts, we demonstrate that lysosomal efflux of daunorubicin, as well as dextran molecules, are significantly reduced in cells with mutated and dysfunctional NPC1 compared with wild-type fibroblasts. Furthermore, we show that NPC1 is implicated in a lysosomal drug sequestration phenotype exhibited by the multidrug-resistant (MDR) human leukemic HL-60 cancer cell line. Evaluations of cholesterol trafficking, NPC1 mRNA levels, and protein expression are all consistent with a loss of NPC1 activity that is associated with the emergence of the MDR phenotype in this cell line. Collectively, this work proposes a novel role for NPC1 in a vesiclemediated pathway responsible for the clearance of drugs from cells and provides an explanation for a drug sequestration phenotype exhibited by the MDR HL-60 cell line.

A Novel Role for α-Tocopherol Transfer Protein (α-TTP) in Protecting against Chloroquine Toxicity

“…For example, the accumulation of a lysosomotropic drug in lysosomes of fibroblasts from NPC1 patients was greater than from normal subjects (28). Substantial amounts of endogenous hydrophobic amines such as sphingosine are concentrated in the lysosomes of liver from mice with NPC disease (26), and Lloyd-Evans et al (32) demonstrated that sphingosine accumulation in lysosomes is an initiating factor in NPC1 disease pathogenesis.…”

Biophysical characterization of MDR breast cancer cell lines reveals the cytoplasm is critical in determining drug sensitivity

“…This may be relevant for MCF-7TaxR where we see a hypopolarised state in spite of the presence of P-gp. The influence of a reduced plasma membrane potential and /or the reduced cytoplasmic conductivity (as [26] and the possibility of altered pH gradients with respect to the parent line [32]. A report by Raghunand et al [33] reported that an acidic pH may enhance microtubular stabilization by paclitaxel [34].…”

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).…”