N-cadherin upregulation mediates adaptive radioresistance in glioblastoma
Satoru Osuka, … , Christopher D. Willey, Erwin G. Van Meir
Satoru Osuka, … , Christopher D. Willey, Erwin G. Van Meir
Published March 15, 2021
Citation Information: J Clin Invest. 2021;131(6):e136098. https://doi.org/10.1172/JCI136098.
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Research Article Oncology

N-cadherin upregulation mediates adaptive radioresistance in glioblastoma

Abstract

Glioblastoma (GBM) is composed of heterogeneous tumor cell populations, including those with stem cell properties, termed glioma stem cells (GSCs). GSCs are innately less radiation sensitive than the tumor bulk and are believed to drive GBM formation and recurrence after repeated irradiation. However, it is unclear how GSCs adapt to escape the toxicity of repeated irradiation used in clinical practice. To identify important mediators of adaptive radioresistance in GBM, we generated radioresistant human and mouse GSCs by exposing them to repeat cycles of irradiation. Surviving subpopulations acquired strong radioresistance in vivo, which was accompanied by a reduction in cell proliferation and an increase in cell-cell adhesion and N-cadherin expression. Increasing N-cadherin expression rendered parental GSCs radioresistant, reduced their proliferation, and increased their stemness and intercellular adhesive properties. Conversely, radioresistant GSCs lost their acquired phenotypes upon CRISPR/Cas9-mediated knockout of N-cadherin. Mechanistically, elevated N-cadherin expression resulted in the accumulation of β-catenin at the cell surface, which suppressed Wnt/β-catenin proliferative signaling, reduced neural differentiation, and protected against apoptosis through Clusterin secretion. N-cadherin upregulation was induced by radiation-induced IGF1 secretion, and the radiation resistance phenotype could be reverted with picropodophyllin, a clinically applicable blood-brain-barrier permeable IGF1 receptor inhibitor, supporting clinical translation.

Authors

Satoru Osuka, Dan Zhu, Zhaobin Zhang, Chaoxi Li, Christian T. Stackhouse, Oltea Sampetrean, Jeffrey J. Olson, G. Yancey Gillespie, Hideyuki Saya, Christopher D. Willey, Erwin G. Van Meir

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Figure 4

Elevated N-cad leads to increased levels of cell-surface β-catenin, resulting in suppression of Wnt/β-catenin–mediated proproliferative and neuronal differentiation signaling.

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Elevated N-cad leads to increased levels of cell-surface β-catenin, resu...
(A) Western blot showing expression changes of several N-cad binding catenins following 6–12 cycles of irradiation (5 Gy) in mGS cells. (B) Fluorescence microscopy shows that β-catenin (green) selectively coaccumulates with N-cad (red) on the cell surface of mGSRR but not mGS cells. Nuclei were counterstained with Hoechst 33342 (blue). Scale bars: 25 μm. (C) Wnt/β-catenin regulated transcriptional activity in mGS and mGSRR cells measured through transient transfection with a luciferase reporter driven by a WT (TOP) or mutant (FOP) TCF binding site. ***P < 0.001, 2-tailed Student’s t test. (D) TOP/FOP ratio showing Wnt/β-catenin activity in parental N-cad–overexpressing and N-cad–KO mGS cells. **P < 0.01, ***P < 0.001, Tukey’s HSD test. (E) Microarray analysis showing that mRNA expression of multiple Wnt target genes is suppressed in mGSRR compared with mGS cells. Each group contains 2 independent replicates (n = 2). (F) qRT/PCR showing that NeuroD1, Ngn1, and Brn3a mRNAs are reduced in mGSRR cells. Two-tailed Student’s t test. (G) Western blot showing expression change of β-catenin (pan and non-phospho), c-Myc, and Tuj1 by N-cad–overexpressing and N-cad–KO mGS cells. All blots show representative images (n = 3 or more).