Reduced expression of proteolipid protein 2 increases ER stress-induced apoptosis and autophagy in glioblastoma.

Zichao Feng,Xingang Li,Yaotian Hu,Yang Kong,Yulin Zhang,Di Zhang,Wenjie Li,Qichao Qi,Anjing Chen,Frits Thorsen,Bin Huang,Mingzhi Han,Jiwei Wang,Rolf Bjerkvig,Jian Wang,Qing Zhang,Wenjing Zhou,Anbin Chen

doi:10.1111/jcmm.14840

Abstract

Proteolipid protein 2 (PLP2) is an integral ion channel membrane protein of the endoplasmic reticulum. The protein has been shown to be highly expressed in many cancer types, but its importance in glioma progression is poorly understood. Using publicly available datasets (Rembrandt, TCGA and CGGA), we found that the expression of PLP2 was significantly higher in high‐grade gliomas than in low‐grade gliomas. We confirmed these results at the protein level through IHC staining of high‐grade (n = 56) and low‐grade glioma biopsies (n = 16). Kaplan‐Meier analysis demonstrated that increased PLP2 expression was associated with poorer patient survival. In functional experiments, siRNA and shRNA PLP2 knockdown induced ER stress and increased apoptosis and autophagy in U87 and U251 glioma cell lines. Inhibition of autophagy with chloroquine augmented apoptotic cell death in U87‐ and U251‐siPLP2 cells. Finally, intracranial xenografts derived from U87‐ and U251‐shPLP2 cells revealed that loss of PLP2 reduced glioma growth in vivo. Our results therefore indicate that increased PLP2 expression promotes GBM growth and that PLP2 represents a potential future therapeutic target.

Highlights

Gliomas constitute approximately 75% of the malignant primary brain tumours in adults.[1]
Apoptosis and the induction of autophagy, and in particular the crosstalk between these two processes, remain a subject of interest. We show in both clinical samples and cell lines that proteolipid protein 2 (PLP2) is significantly overexpressed in GBMs compared with normal human astrocytes (NHAs) and normal human brain tissue samples
We found that PLP2 knockdown reduces cell proliferation and increases endoplasmic reticulum (ER) stress-induced apoptosis and autophagy via CCAATenhancer-binding protein homologous protein (CHOP), a ubiquitous transcription factor known to have a regulatory role in the crosstalk between autophagy and apoptosis.[20]

Summary

Introduction

Gliomas constitute approximately 75% of the malignant primary brain tumours in adults.[1]. We found that PLP2 knockdown reduces cell proliferation and increases ER stress-induced apoptosis and autophagy via CCAATenhancer-binding protein homologous protein (CHOP), a ubiquitous transcription factor known to have a regulatory role in the crosstalk between autophagy and apoptosis.[20] Our results establish a vital role for PLP2 in promoting GBM growth and as a potential therapeutic target. We performed Western blot analysis to determine PLP2 protein levels in normal human astrocytes (NHA) and human GBM cell lines U87, A172, U251 and T98.

Results

Conclusion