MHC‐II on alveolar type‐II (AT‐II) cells is associated with immune tolerance in an inflammatory microenvironment. Recently, we found TNF‐α upregulated MHC‐II in AT‐II in vitro. In this study, we explored whether TNF‐α‐mediated inflammation upregulates MHC‐II on AT‐II cells to trigger Treg expansion in inflammation‐driven lung adenocarcinoma (IDLA). Using urethane‐induced mice IDLA model, we found that IDLA cells mainly arise from AT‐II cells, which are the major source of MHC‐II. Blocking urethane‐induced inflammation by TNF‐α neutralization inhibited tumorigenesis and reversed MHC‐II upregulation on tumor cells of AT‐II cellular origin in IDLA. MHC‐II‐dependent AT‐II cells were isolated from IDLA‐induced Treg expansion. In human LA samples, we found high expression of MHC‐II in tumor cells of AT‐II cellular origin, which was correlated with increased Foxp3+ T cells infiltration as well as CXCR‐2 expression. CXCR‐2 and MHC‐II colocalization was observed in inflamed lung tissue and IDLA cells of AT‐II cellular origin. Furthermore, at the pro‐IDLA inflammatory stage, TNF‐α‐neutralization or CXCR‐2 deficiency inhibited the upregulation of MHC‐II on AT‐II cells in inflamed lung tissue. Thus, tumor cells of AT‐II cellular origin contribute to Treg expansion in an MHC‐II‐dependent manner in TNF‐α‐mediated IDLA. At the pro‐tumor inflammatory stage, TNF‐α‐dependent lung inflammation plays an important role in MHC‐II upregulation on AT‐II cells.

Tumor-associated inflammation plays a critical role in facilitating tumor growth, invasion and metastasis. Our previous study showed Aflatoxin G1 (AFG1) could induce lung adenocarcinoma in mice. Chronic lung inflammation associated with superoxide dismutase (SOD)-2 upregulation was found in the lung carcinogenesis. However, it is unclear whether tumor-associated inflammation mediates SOD-2 to contribute to cell invasion in AFG1-induced lung adenocarcinoma. Here, we found increased SOD-2 expression associated with vimentin, α-SMA, Twist1, and MMP upregulation in AFG1-induced lung adenocarcinoma. Tumor-associated inflammatory microenvironment was also elicited, which may be related to SOD-2 upregulation and EMT in cancer cells. To mimic an AFG1-induced tumor-associated inflammatory microenvironment in vitro, we treated A549 cells and human macrophage THP-1 (MΦ-THP-1) cells with AFG1, TNF-α and/or IL-6 respectively. We found AFG1 did not promote SOD-2 expression and EMT in cancer cells, but enhanced TNF-α and SOD-2 expression in MΦ-THP-1 cells. Furthermore, TNF-α could upregulate SOD-2 expression in A549 cells through NF-κB pathway. Blocking of SOD-2 by siRNA partly inhibited TNF-α-mediated E-cadherin and vimentin alteration, and reversed EMT and cell migration in A549 cells. Thus, we suggest that tumor-associated inflammation mediates SOD-2 upregulation through NF-κB pathway, which may contribute to EMT and cell migration in AFG1-induced lung adenocarcinoma.Introduction.

Aflatoxin G1 (AFG1), a member of the AF family with cytotoxic and carcinogenic properties, could cause DNA damage in alveolar type II (AT‐II) cells and induce lung adenocarcinoma. Recently, we found AFG1 could induce chronic lung inflammation associated with oxidative stress in the protumor stage. Chronic inflammation plays a critical role in cigarette smoke or benzo[a]pyrene‐induced lung tissues damage. However, it is unclear whether and how AFG1‐induced lung inflammation affects DNA damage in AT‐II cells. In this study, we found increased DNA damage and cytochrome P450 (CYP2A13) expression in AFG1‐induced inflamed lung tissues. Furthermore, we treated the mice with a soluble tumor necrosis factor (TNF)‐α receptor and AFG1 and found that TNF‐α neutralization inhibited the AFG1‐induced chronic lung inflammation in vivo, and then reversed the CYP2A13 expression and DNA damage in AT‐II cells. The results suggest that AFG1 induces TNF‐α‐dependent lung inflammation to regulate 2A13 expression and enhance DNA damage in AT‐II cells. Then, we treated the primary mice AT‐II cells and human AT‐II like cells (A549) with AFG1 and TNF‐α and found that TNF‐α enhanced the AFG1‐induced DNA damage in mice AT‐II cells as well as A549 cells in vitro. In AFG1‐exposed A549 cells, TNF‐α‐enhanced DNA damage and apoptosis were reversed by CYP2A13 small interfering RNA. Blocking NF‐κB pathway inhibited the TNF‐α‐enhanced CYP2A13 upregulation and DNA damage confirming that the CYP2A13 upregulation by TNF‐α plays an essential role in the activation of AFG1 under inflammatory conditions. Taken together, our findings suggest that AFG1 induces TNF‐α‐dependent lung inflammation, which upregulates CYP2A13 to promote the metabolic activation of AFG1 and enhance oxidative DNA damage in AT‐II cells.

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