Ionizing Radiation Promotes Epithelial-Mesenchymal Transition Phenotype and Stem Cell Marker in The Lung adenocarcinoma: In Vitro and Bioinformatic Studies

Ionizing radiation (IR) is one of the major therapeutic approaches in the non-small cell lung cancer (NSCLC); however, it can paradoxically result in cancer progression likely through promoting epithelial-mesenchymal transition (EMT) and the cancer stem cell phenotype. Therefore, we aimed to determine whether IR promote EMT/CSC and to investigate the clinical relevance of EMT/CSC hallmark genes.

In this experimental and bioinformatic study, A549 cell line was irradiated with a high dosage (6 Gy) or a fractionated regimen (2 Gy/day for 15 fractions). The EMT-related features, including cellular morphology, migratory and invasive capacities were evaluated using scratch assay and transwell migration/invasion assays. The mRNA levels of EMT-related genes (CDH1, CDH2, SNAI1 and TWIST1), stemness-related markers (CD44, PROM1, and ALDH1A1) and the CDH2/CDH1 ratio were evaluated via real-time polymerase chain reaction (PCR). The clinical significance of these genes was assessed in the lung adenocarcinoma (LUAD) samples using online databases.

Irradiation resulted in a dramatic elongation of cell shape and enhanced invasion and migration capabilities. These EMT-like alterations were accompanied with enhanced levels of SNAI1, CDH2, TWIST1, CD44, PROM1, and ALDH1A1 as well as an enhanced CDH2/CDH1 ratio. TCGA analysis revealed that, TWIST1, CDH1, PROM1 and CDH2 were upregulated; whereas, CD44, SNAI1 and ALDH1A1 were downregulated. Additionally, correlations between SNAI1-TWIST1, CDH2- TWIST1, CDH2-SNAI1, and ALDH1A1-PROM1 was positive. Kaplan-Meier survival analysis identified lower expression of CDH1, PROM1 and ALDH1A1 and increased expression of CDH2, SNAI1, and TWIST1 as well as CDH2/CDH1 ratio predict overall survival. Additionally, downregulation of ALDH1A1 and upregulation of CDH2, SNAI1 and TWIST1 could predict a shorter first progression.

Altogether, these findings demonstrated that IR promotes EMT phenotype and stem cell markers in A549 cell line and these genes could function as diagnostic or prognostic indicators in LUAD samples.