IL-24 Inhibits Lung Cancer Growth by Suppressing GLI1 and Inducing DNA Damage.

Aberrant expression of GLI1 is responsible for aggressive tumor behavior and survival due to its effects on the DNA damage response (DDR). We investigated whether interleukin (IL)-24, a tumor suppressor, inhibits GLI1 and the associated DDR pathway in human NSCLCs. IL-24 treatment reduces mRNA and protein expression of GLI1 in lung tumor cells, but not in normal cells. GLI1 reporter assay and mRNA studies demonstrated that IL-24 regulates GLI1 at the post-transcriptional level by favoring mRNA degradation. Associated with GLI1 inhibition was marked suppression of the ATM-mediated DDR pathway resulting in increased DNA damage, as evidenced by gamma-H2AX foci and Comet assay. Furthermore, attenuation of GLI1-associated DDR by IL-24 increased caspase-3 and PARP activity, resulting in cancer cell apoptosis. GLI1 inhibition and overexpression confirmed that IL-24-mediated anti-tumor effects involved the GLI-dependent pathway. Finally, we observed that IL-24-mediated alteration in GLI1 is independent of the canonical hedgehog-signaling pathway. Our study provides evidence that IL-24 treatment induces DNA damage, and reduces GLI1 expression and offers an opportunity for testing IL-24-based therapy for inhibiting GLI1 in lung cancer.