V-ATPase controls tumor growth and autophagy in a Drosophila model of gliomagenesis

Miriam Formica,Alessandra Maria Storaci,Irene Bertolini,Francesca Carminati,Helene Knævelsrud,Valentina Vaira,Thomas Vaccari

doi:10.1080/15548627.2021.1918915

Abstract

ABSTRACT Glioblastoma (GBM), a very aggressive and incurable tumor, often results from constitutive activation of EGFR (epidermal growth factor receptor) and of phosphoinositide 3-kinase (PI3K). To understand the role of autophagy in the pathogenesis of glial tumors in vivo, we used an established Drosophila melanogaster model of glioma based on overexpression in larval glial cells of an active human EGFR and of the PI3K homolog Pi3K92E/Dp110. Interestingly, the resulting hyperplastic glia express high levels of key components of the lysosomal-autophagic compartment, including vacuolar-type H+-ATPase (V-ATPase) subunits and ref(2)P (refractory to Sigma P), the Drosophila homolog of SQSTM1/p62. However, cellular clearance of autophagic cargoes appears inhibited upstream of autophagosome formation. Remarkably, downregulation of subunits of V-ATPase, of Pdk1, or of the Tor (Target of rapamycin) complex 1 (TORC1) component raptor prevents overgrowth and normalize ref(2)P levels. In addition, downregulation of the V-ATPase subunit VhaPPA1-1 reduces Akt and Tor-dependent signaling and restores clearance. Consistent with evidence in flies, neurospheres from patients with high V-ATPase subunit expression show inhibition of autophagy. Altogether, our data suggest that autophagy is repressed during glial tumorigenesis and that V-ATPase and MTORC1 components acting at lysosomes could represent therapeutic targets against GBM.

Highlights

Gliomas, the most common brain malignancy, represent a challenge for therapy because of limited treatment options and of the onset of therapeutic resistance
Upon co-expression of Dp110-CAAX and ΔhEGFR, cells of glial origin make up 70% of the recovered central nervous system (CNS) cells (Fig. 1A)
Larvae carrying gliomas show an extremely altered CNS arrangement, with neurons located in small clusters surrounded by hyperplastic glia (Fig. S1B-B’), and fail to wander or pupariate, eventually dying at third instar (Fig. S1C-C’’)

Summary

Introduction

The most common brain malignancy, represent a challenge for therapy because of limited treatment options and of the onset of therapeutic resistance. In which very little signal of either marker is detected, both proteins strongly colocalize in puncta within glial cells of larvae carrying gliomas (Fig. 1E).

Results

Conclusion