A New Pathway Promotes Adaptation of Human Glioblastoma Cells to Glucose Starvation.

Alberto Azzalin,Katia Basello,Lorenzo Magrassi,Eloisa Arbustini,Pierluigi Mauri,Francesca Brambilla,Attilio Speciani,Paola Bezzi

doi:10.3390/cells9051249

Abstract

Adaptation of glioblastoma to caloric restriction induces compensatory changes in tumor metabolism that are incompletely known. Here we show that in human glioblastoma cells maintained in exhausted medium, SHC adaptor protein 3 (SHC3) increases due to down-regulation of SHC3 protein degradation. This effect is reversed by glucose addition and is not present in normal astrocytes. Increased SHC3 levels are associated to increased glucose uptake mediated by changes in membrane trafficking of glucose transporters of the solute carrier 2A superfamily (GLUT/SLC2A). We found that the effects on vesicle trafficking are mediated by SHC3 interactions with adaptor protein complex 1 and 2 (AP), BMP-2-inducible protein kinase and a fraction of poly ADP-ribose polymerase 1 (PARP1) associated to vesicles containing GLUT/SLC2As. In glioblastoma cells, PARP1 inhibitor veliparib mimics glucose starvation in enhancing glucose uptake. Furthermore, cytosol extracted from glioblastoma cells inhibits PARP1 enzymatic activity in vitro while immunodepletion of SHC3 from the cytosol significantly relieves this inhibition. The identification of a new pathway controlling glucose uptake in high grade gliomas represents an opportunity for repositioning existing drugs and designing new ones.

Highlights

Enhanced glucose metabolism in glioblastoma, as demonstrated in vivo by positron emission tomography, is associated with poor patient survival [1]
We confirmed that p52SHC3 and p64SHC3, the two major protein isoforms encoded by the human SHC adaptor protein 3 (SHC3) gene, were higher in multicellular tumor spheroids (MTS) [21] (Figure 1B,C) while the levels of the protein isoforms of the closely related gene SHC1 were not increased (Figure 1B)
GLUT3 or GLUT4 cDNA fused to the enhanced green fluorescent protein gene, and we evaluated in U-87 MG and Hu197 the dynamic of the vesicles containing these proteins by total internal reflection fluorescence (TIRF) under normal and glucose deprived conditions or with and without transfection of a plasmid encoding p52SHC3

Summary

Introduction

Enhanced glucose metabolism in glioblastoma, as demonstrated in vivo by positron emission tomography, is associated with poor patient survival [1]. In high-grade gliomas, enhanced glucose uptake through glucose transporters is important for brain tumor initiating cell growth and survival [5] and it is essential for survival of the mesenchymal subtype of glioblastoma [6]. Maintaining an adequate level of glucose inside the cell is vital for glioblastoma cell growth and survival. Glucose uptake in glioblastoma cells is tightly regulated and depends mainly on transporters of the GLUT/SLC2A superfamily [9,10,11]. Inhibition of the GLUT/SLC2As present on the membrane of glioblastoma cells reduces growth and enhances the effect of chemotherapy both in vitro and in vivo [11]

Methods

Results

Discussion

Conclusion