Ribosomal S6 protein kinase 4 promotes radioresistance in esophageal squamous cell carcinoma
Ming-Yang Li, … , Jian Zhang, Zhe Wang
Ming-Yang Li, … , Jian Zhang, Zhe Wang
Published May 12, 2020
Citation Information: J Clin Invest. 2020;130(8):4301-4319. https://doi.org/10.1172/JCI134930.
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Research Article Oncology

Ribosomal S6 protein kinase 4 promotes radioresistance in esophageal squamous cell carcinoma

Abstract

Esophageal squamous cell carcinoma (ESCC) is one of the most aggressive cancers and is highly resistant to current treatments. ESCC harbors a subpopulation of cells exhibiting cancer stem-like cell (CSC) properties that contribute to therapeutic resistance including radioresistance, but the molecular mechanisms in ESCC CSCs are currently unknown. Here, we report that ribosomal S6 protein kinase 4 (RSK4) plays a pivotal role in promoting CSC properties and radioresistance in ESCC. RSK4 was highly expressed in ESCC CSCs and associated with radioresistance and poor survival in patients with ESCC. RSK4 was found to be a direct downstream transcriptional target of ΔNp63α, the main p63 isoform, which is frequently amplified in ESCC. RSK4 activated the β-catenin signaling pathway through direct phosphorylation of GSK-3β at Ser9. Pharmacologic inhibition of RSK4 effectively reduced CSC properties and improved radiosensitivity in both nude mouse and patient-derived xenograft models. Collectively, our results strongly suggest that the ΔNp63α/RSK4/GSK-3β axis plays a key role in driving CSC properties and radioresistance in ESCC, indicating that RSK4 is a promising therapeutic target for ESCC treatment.

Authors

Ming-Yang Li, Lin-Ni Fan, Dong-Hui Han, Zhou Yu, Jing Ma, Yi-Xiong Liu, Pei-Feng Li, Dan-Hui Zhao, Jia Chai, Lei Jiang, Shi-Liang Li, Juan-Juan Xiao, Qiu-Hong Duan, Jing Ye, Mei Shi, Yong-Zhan Nie, Kai-Chun Wu, Dezhong Joshua Liao, Yu Shi, Yan Wang, Qing-Guo Yan, Shuang-Ping Guo, Xiu-Wu Bian, Feng Zhu, Jian Zhang, Zhe Wang

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Figure 8

Disruption of the RSK4 pathway reduces CSC properties and improves the radiosensitivity of ESCC.

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Disruption of the RSK4 pathway reduces CSC properties and improves the r...
(A and B) Sphere formation assay (A) and flow cytometric analysis (B) of TE10 cells treated with BI-D1870 (10 μM), RSK4 knockdown, or both (n = 3 independent experiments). (C) Immunoblot analyses of BMI-1, NANOG, ABCG2, OCT4, SOX2, and CD271 in TE10 cells with the indicated treatments. (D) Immunoblot analyses of β-catenin, p–β-catenin (Ser33/37/Thr41, inactive state), p–GSK-3β (Ser9), GSK-3β, MYC, CD44, and TCF1 in TE10 cells with the indicated treatments. (E) Cell viability assay of TE10 cells treated with BI-D1870 (10 μM) for 12 hours, IR (10 Gy), or both (n = 3 independent experiments). (F) FACS analyses of apoptosis of TE10 cells treated with BI-D1870 (10 μM) for 12 hours, IR (10 Gy), or both (n = 3 independent experiments). (G) Western blot analysis of phosphorylated and total amounts of the checkpoint proteins ATM and CHK2 from TE10 cells treated with or without BI-D1870 (10 μM) before treatment (–) and 1 hour after 10 Gy IR (+). (H) Immunofluorescence staining of γ-H2AX in TE10 cells with the indicated treatments (n = 3 independent experiments). Scale bar: 100 μm. (I) ESCC-derived xenografts in mice treated with vehicle control, BI-D1870 (50 mg/kg/day, i.p. injection), and/or IR (5 Gy, twice). The growth curve of tumor size and average tumor weight are presented (n = 5 mice each). Data represent the mean ± SD. *P < 0.05 and **P < 0.01. Differences were tested using 1-way ANOVA with Tukey’s post hoc test (A, B, E, F, H, and I).