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 5

RSK4 is essential for ΔNp63α-mediated CSC properties and radioresistance of ESCC cells.

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RSK4 is essential for ΔNp63α-mediated CSC properties and radioresistance...
(A) Knockdown of RSK4 abolished ΔNp63α-enhanced sphere formation ability, whereas RSK4 overexpression partially restored the effects of ΔNp63-suppressed sphere formation (n = 3 independent experiments). Scale bars: 100 μm. (B) Flow cytometric analysis of ALDH activity and the proportion of CD90+ cells in ESCC cells from the indicated groups (n = 3 independent experiments). (C) Western blot analysis of ESCC CSC markers in the indicated groups. (D) Clonogenic survival assays of ESCC cells in the indicated groups at IR doses of 0, 3, and 6 Gy (n = 3 independent experiments). (E) Relative caspase-3 activity 24 hours after IR (10 Gy) of ESCC cells in the indicated groups (n = 3 independent experiments). (F) Western blot analysis of phosphorylated and total amounts of the checkpoint proteins ATM and CHK2 from the indicated groups 1 hour after 10 Gy IR. (G) ESCC cells from the indicated groups were treated with 10 Gy IR and recultured under normal conditions for 1 and 6 hours, and then subjected to Western blot analysis with γ-H2AX antibody. 0 h, cells with IR treatment but with no time for DNA repair. Data represent the mean ± SD. **P < 0.01 and ***P < 0.001. Differences were tested using an unpaired, 2-sided Student’s t test (A, B, D, and E).