Repeated Irradiation with γ-Ray Induces Cancer Stemness through TGF-β-DLX2 Signaling in the A549 Human Lung Cancer Cell Line.

Hae-Ran Park,Uhee Jung,Jee-Young Kim,In-Gyu Kim,Yeo-Jin Choi

doi:10.3390/ijms22084284

Hae-Ran Park, Uhee Jung + Show 3 more

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https://doi.org/10.3390/ijms22084284

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Abstract

Cancer stem cells (CSCs) play an important role in cancer recurrence and metastasis. It is suggested that the CSC properties in heterogeneous cancer cells can be induced by ionizing radiation (IR). This study investigated the role of DLX2 in the radioresistance and CSC properties induced by IR in NSCLC cancer cells. Here, A549 cells were exposed to fractionated irradiation at a cumulative dose of 52 Gy (4 Gy × 13 times) for a generation of radioresistant cells. After fractionated irradiation, surviving A549 cells exhibited resistance to IR and enhanced expression of various cancer stem cell markers. They also showed upregulation of mesenchymal molecular markers and downregulation of epithelial molecular markers, correlating with an increase in the migration and invasion. Fractionated irradiation triggered the secretion of TGF-β1 and DLX2 expression. Interestingly, the increased DLX2 following fractionated irradiation seemed to induce the expression of the gene for the EGFR-ligand betacellulin via Smad2/3 signaling. To contrast, DLX2 knockdown dramatically decreased the expression of CSC markers, migration, and proliferation. Moreover, A549 cells expressing DLX2 shRNA formed tumors with a significantly smaller volume compared to those expressing control shDNA in a mouse xenograft assay. These results suggest that DLX2 overexpression in surviving NSCLC cancer cells after fractionated IR exposure is involved in the cancer stemness, radioresistance, EMT, tumor survival, and tumorigenic capability.

Highlights

IntroductionDuring radiotherapy for cancer, repeated and fractionated irradiation at a low dose reduces adverse effects, and allows damaged normal cells to recover [1]
Radiotherapy is a double-edged sword: Ionizing radiation (IR) is used as a standard treatment for lung cancer patients, its therapeutic efficacy is limited due to the tumor recurrence and metastasis and the induction of damages in normal tissues
We demonstrated that repeated irradiation of A549 NSCLC cells led to acquiring radioresistance and inducing the expression of cancer stem cells (CSCs)-related markers such as CD44, OCT4, SOX2, LIF, Snail, MMP2, and MMP7

Summary

Introduction

During radiotherapy for cancer, repeated and fractionated irradiation at a low dose reduces adverse effects, and allows damaged normal cells to recover [1]. Several studies have suggested that this conventional radiotherapy eventually can lead to tumor recurrence and metastasis [2,3,4]. According to several recent studies, cancer stem cells (CSCs) are considered responsible for tumor relapse, metastasis, and resistance to IR and anti-cancer drugs [5,6,7,8,9]. Representative CSC markers have been suggested, such as Oct, Sox, Snail, CD44, CD133, CD166, and aldehyde dehydrogenase (ALDH) in human cancer [16,17,18,19,20,21,22]

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