IL-33 synergistically promotes the proliferation of lung cancer cells in vitro by inducing antibacterial peptide LL-37 and proinflammatory cytokines in macrophages

Lung cancer is the primary cause of cancer-related deaths, and the persistent inflammation is inextricably linked with the lung cancer tumorigenesis. Pro-inflammatory cytokine interleukin-33 (IL-33) is able to serve as a potent modulator of cancer. Mounting evidence indicates IL-33 has significant effect on lung cancer progression by regulating host immune response, but the current opinions about the function and mechanism of IL-33 in lung cancer are still controversial. Meanwhile, antibacterial peptide LL-37 also exerts a momentous effect on immune responses to lung cancer. LL-37 is regarded as versatile, including antimicrobial activities, chemotaxis and immunoregulation. However, the immunomodulatory mechanism of IL-33 and LL-37 in lung cancer remains thoroughly not defined. Here, we determined the secretion of LL-37 was up-regulated in lung cancer serum samples. Similarly, the expression of CRAMP was enhancive in macrophages after co-cultured with lung cancer cells. Moreover, we expounded that IL-33 could up-regulate LL-37 secretion in macrophages, resulting in the massive releases of IL-6 and IL-1β. Additionally, LL-37 cooperated with IL-33 to increase the phosphorylation of p38 MAPK and NF-κB p65 pathways, and augmented IL-6 and IL-1β secretion, which resulting in the proliferation of lung cancer cells in vitro. In conclusion, our study identified that IL-33 aggravated the inflammation of lung cancer by increasing LL-37 expression in macrophages, thereby promoting lung cancer cell proliferation in vitro. It is contributed to our present understanding of the immunomodulatory relationship between pro-inflammatory cytokines and antibacterial peptides in the tumor immune response, and offer a novel perspective for controlling the progress of lung cancer.