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Ionizing radiation is known to cause cell apoptosis at high dose range, but little is known about the cellular response to low dose radiation. In this study, we found that conditioned medium harvested from WI-38 lung fibroblasts and H1299 lung adenocarcinoma cells exposed to 0.1Gy to 1Gy could enhance the migration and invasion of unirradiated H1299 cells in both 2D and 3D culturing circumstances. Low dose radiation did not induce apoptosis, but induced senescence in irradiated cells. We next examined the expression of immediately early genes including c-Myc and K-Ras. Although both genes could be up-regulated by low dose radiation, induction of c-Myc was more specific to low dose range (0.5Gy) at transcriptional and translational levels. Knockdown of c-Myc by shRNA could repress the senescence induced by low dose radiation. The conditioned medium of irradiated cells induced migration of unirradiated cells was also repressed by knockdown of c-Myc. The c-Myc inhibitor 10058-F4 could suppress low dose radiation induced cell senescence, and the conditioned medium harvested from irradiated cells pretreated with 10058-F4 also lost the ability to enhance the migration of unirradiated cells. The cytokine array analysis revealed that immunosuppressive monocyte chemoattractant protein-1 increased by low dose radiation could be repressed by 10058-F4. We also showed that 10058-F4 could suppress low dose radiation induced tumor progression in a xenograft tumor model. Taken together, current data suggest that -Myc is involved in low dose radiation induced cell senescence and potent bystander effect to increase the motility of unirradiated cells.

Metastasis is the primary cause of mortality in patients with non-small cell lung cancer (NSCLC). Actin cytoskeletal reorganization is usually accompanied by the epithelial-mesenchymal transition (EMT)-induced invasion and metastasis of cancer cells. In the present study, expression levels of the actin-associated protein cofilin-1 and of the pivotal EMT molecule Twist-1 were determined in NSCLC tissues. Using lung cancer tissue arrays, the identification of 67.4% of tissue spots that exhibited reciprocal levels of cofilin-1 and Twist-1 was achieved by immunohistochemical (IHC) staining. This reciprocal expression pattern was also detected in 21 out of 25 clinicopathological NSCLC tissue sections, and in 10 out of 15 NSCLC cell lines. In addition, high levels of cofilin-1 and low levels of Twist-1 accounted for 80 and 71.5% of the reciprocal expression pattern in tissue arrays and clinicopathological tissue samples, respectively. This pattern was also detected in normal lung tissues, stage I and II lung cancer tissues, and adenocarcinoma subtypes of NSCLC tissues. Although cofilin-1 and Twist-1 were expressed inversely, a positive correlation of these two proteins was present in normal lung tissues and lung tumor tissues. Furthermore, enforced expression of cofilin-1 suppressed the expression level of Twist-1 in NSCLC H1299 cells. An on-line Kaplan-Meier survival analytic tool allowed access to a public microarray dataset with a maximum of 1,926 NSCLC samples. The analysis revealed that high expression levels of both cofilin-1 (CFL1) and Twist-1 (TWIST1) genes were associated with decreased survival of NSCLC patients, notably with regard to the adenocarcinoma subtype. The analysis was conducted using the multivariate Cox regression model. Although the reciprocal association of the expression levels of cofilin-1 and Twist-1 with the survival rate of NSCLC patients requires additional information, it may be a significant indicator of the progression of NSCLC.