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 1

Radioresistant GSCs display increased cell-cell adhesion, slower proliferation, and an elevation of stemness properties.

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Radioresistant GSCs display increased cell-cell adhesion, slower prolife...
(A) Clonogenic survival assay for mGS and mGSRR subjected to irradiation (IR) or control without IR. Left: representative images of colonies formed by surviving cells 13 days after a single dose (4 Gy) of irradiation are shown. Right: fraction of surviving cells after radiation doses of 1, 3, or 5 Gy. Scale bar: 10 mm. (B) Survival curves for mice implanted with 1000 tumor cells (mGS or mGSRR) and subjected to whole-brain irradiation consisting of a daily dose of 2 Gy from days 3 to 7 after cell implantation (10 Gy total). Log-rank test. (C) Cell proliferation analysis for mGS and mGSRR after 72 hours. (D) Self-renewal ability of mGS and mGSRR as evaluated by sphere formation assay in soft agar. Scale bar: 10 mm. (E) Western blot showing expression of stem cell marker (Olig2) progressively increases and neural differentiation maker (Tuj1) is decreased following repeated cycles of irradiation in mGS cells. All blots show representative images (n = 3). (F) Representative images of mGS and mGSRR cells stably expressing a fluorescence marker (mCherry) and grown as spheres in neural stem cell medium are shown. Scale bars: 200 μm. (G) Single-cell suspension of mGS and mGSRR cells were cultured for 4 hours, and then the number of nonattached cells determined by differential centrifugation. *P < 0.05, **P < 0.01, ***P < 0.001, 2-tailed Student’s t tests unless otherwise indicated.