Glucosamine prevents polarization of cytotoxic granules in NK-92 cells by disturbing FOXO1/ERK/paxillin phosphorylation.

Janja Božič,Veronika Stoka,Iztok Dolenc,Salvatore Papa

doi:10.1371/journal.pone.0200757

Janja Božič, Veronika Stoka + Show 2 more

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https://doi.org/10.1371/journal.pone.0200757

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Abstract

Glucosamine (GlcN) is a naturally occurring derivative of glucose and an over-the-counter food additive. However, the mechanism underlying GlcN action on cells is unknown. In this study, we investigated the effect of GlcN on natural killer (NK) cells. We demonstrate that GlcN affects NK-92 cell cytotoxicity by altering the distribution of cathepsin C, a cysteine protease required for granzyme processing in cytotoxic granules. The relocation of cathepsin C due to GlcN was shown to be accompanied by a decrease in the intracellular enzyme activity and its extracellular secretion. Similarly, the relocation of endosomal aspartic cathepsin E was observed. Furthermore, we elucidated that repositioning of cathepsin C is a consequence of altered signaling pathways of cytotoxic granule movement. The inhibition of phosphorylation upstream and downstream of ERK by GlcN disturbed the polarized release of cytotoxic vesicles. Considerable changes in the ERK phosphorylation dynamics, but not in those of p38 kinase or JNK, were observed in the IL2-activated NK-92 cells. We found decreased phosphorylation of the transcription factor FOXO1 and simultaneous prolonged phosphorylation of ERK as well as its nuclear translocation. Additionally, a protein downstream of the ERK phosphorylation cascade, paxillin, was less phosphorylated, resulting in a diffuse distribution of cytotoxic granules. Taken together, our results suggest that dietary GlcN affects signaling pathway activation of NK-92 immune cells.

Highlights

Glucosamine (GlcN; 2-amino-2-deoxy-D-glucose) is a dietary supplement often used by patients with osteoarthritis
We examined the effects of GlcN and GlcNAc concentrations ranging from 0.1 to 10 mM, on the natural killer (NK)-92 cell cytotoxicity against K562 cells (Fig 1A), and observed that GlcN treatment led to decrease in the NK cell cytotoxicity in a dose-dependent manner
The cytotoxicity of NK-92 cells against the target cells was restored after removing GlcN from the medium (Fig 1B)

Summary

Introduction

Glucosamine (GlcN; 2-amino-2-deoxy-D-glucose) is a dietary supplement often used by patients with osteoarthritis. Clinical studies to date have not provided any evidence of its effectiveness in the treatment of hip and/or knee osteoarthritis [1]. GlcN does not affect fasting blood glucose levels, glucose metabolism, or insulin sensitivity at any oral dose level in healthy individuals [2], while its intestinal absorption allows it to reach high cellular concentrations [3]. Comparison of orally and intravenously administered GlcN showed that its oral ingestion leads to only four times lower bioavailability of this compound because a considerable fraction of GlcN undergoes first-pass metabolism in the liver [3]. GlcN enters cells through glucose transporter GLUT2, which has a much higher affinity for GlcN than for glucose [4].

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