Activation of the IL-4/STAT6 Signaling Pathway Promotes Lung Cancer Progression by Increasing M2 Myeloid Cells

Abstract

Emerging evidence shows that signal transducer and activator of transcription 6 (STAT6) plays critical roles in tumor development. We previously found high-level expression of STAT6 in human lung adenocarcinoma and squamous cell carcinoma, specifically in infiltrated immune cells located in the lung interstitium. Nevertheless, the role of STAT6 signaling in lung carcinogenesis and lung cancer proliferation and its underlying mechanisms remain unclear. This study aimed to investigate the role of STAT6 and the interaction between STAT6 and the tumor microenvironment in pulmonary tumorigenesis. We established a murine model of primary lung carcinogenesis in STAT6-deficient (STAT6−/−) and STAT6 wild-type (WT) BALB/c mice using the carcinogen urethane. Two-month-old male mice were intraperitoneally injected with urethane (1 g/kg) dissolved in phosphate buffered saline (PBS). Primary tumors were monitored in vivo by positron emission tomography scanning. At 4, 6, and 9 months after urethane injection, lung tumors were harvested from the STAT6−/− and WT mice for analysis. Small interfering RNA was used to downregulate the expression of STAT6 in tumor cells. Fluorescence activated cell sorting analysis was used to analyze fluorescence-conjugated cell markers. Transwell assays were used in coculturing experiments. STAT6 protein expression was detected by Western blotting, immunohistochemistry, and immunofluorescence. STAT6 mRNA expression was detected by quantitative real time-polymerase chain reaction. Cell Counting Kit-8 and colony formation assays were performed to evaluate cell proliferation. We detected high expression of STAT6 in CD11b+ cells of lung carcinoma. Our results indicate that STAT6 deficiency inhibits carcinogen-induced tumor growth and improves prognosis. STAT6 deficiency also decreased the mobilization and differentiation of CD11b+ cells. STAT6 deficiency in CD11b+ cells but not tumor cells decreased interleukin (IL)-4 secretion and the differentiation of CD11b+ cells into M2 macrophage cells. In conclusion, our findings indicate that IL-4/STAT6 signaling in CD11b+ cells promotes lung cancer progression by triggering an IL-4 positive feedback loop and increasing M2 myeloid cells. STAT6 may be a new therapeutic target for the prevention and treatment of lung cancer.

Differentiation and Regulation of TH Cells: A Balancing Act for Cancer Immunotherapy

“…Binding of IL-4 to IL-4 receptors on immune cells leads to STAT6 phosphorylation, nuclear translocation, and expression of GATA3 transcription factor, resulting in T H 2 cytokine secretion and eventual tumor growth and metastasis ( 26 , 27 ). In studies ranging from lymphoma, melanoma, colorectal, breast, and lung cancer, STAT6 is overexpressed within the tumor microenvironment (TME) as an immunosuppressive signal to promote the function of M2 macrophages to assist in tumor growth and inflammation ( 28 ). To prevent dominance over each other, IL-12 expression from T H 1 cells inhibits the differentiation of T H 2 cells, while IL-4 inhibits T H 1 differentiation ( 29 ).…”

“…In the context of pro-tumorigenic immune response in the TME, T H 2 response has been viewed as controversial, due to their possible role in tumorigenesis, along with another CD4 + T H cell subset, T H 17 cells. T H 2 cells are responsible for the increase in population of tumor infiltrating M2 macrophages and eosinophils in the TME, via their expression of IL-5 and IL-13, which regulate TGF-β secretion and immunosuppressive responses ( 28 ). T H 2-induced tumorigenesis is further driven by their expression of IL-7, which can act as a pro-angiogenic factor, resulting in leaky vasculature and allowing the tumor microenvironment to expand and migratory tumor cells to enter the surrounding tissue ( 134 ).…”

Involvement of IL-4, IL-13 and Their Receptors in Pancreatic Cancer

“…The proline-rich box regions in the intracellular domain of the receptors thereby mediate association with the JAKs instead of exhibiting an intrinsic kinase activity [ 73 ]. Signal transducer and activator of transcription (STAT)6 [ 74 ], insulin receptor substrate (IRS)/phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) [ 75 ], IRS/extracellular signal-regulated kinase (ERK) [ 41 ], and the mechanistic target of rapamycin (mTOR) [ 62 ] are supposed to be the main downstream signaling pathways [ 52 , 76 ]. In addition, IL-13 appears to play its own distinct role in cancer cells through binding to IL-13Rα2 with high affinity [ 77 ] and mediating invasion and metastasis via IL-13Rα2, ERK/activator protein 1 (AP-1) signaling, and matrix metalloproteinases (MMPs) pathways [ 78 ].…”

Use of STAT6 Phosphorylation Inhibitor and Trimethylglycine as New Adjuvant Therapies for 5-Fluorouracil in Colitis-Associated Tumorigenesis

“…The monocytes appear to be recruited throughout tumor progression, including during the early stages of tumor growth where they differentiate into macrophages. Previous reports indicate that STAT6 plays a role in macrophage polarization that could lead to carcinogenesis and cancer progression [58]. We evaluated the circulating CD11b + Ly6C hi monocytic population in our assays, and AS+5-FU therapy induced a decreased percentage of CD11b + Ly6C hi circulating cells, indicating that STAT6 inhibition is a possible target for decreasing an immunological population that may favor resistance to 5-FU.…”