LUAD, the most common type of malignant tumors, has significant morbidity and mortality rates. Growing scientific research has focused on searching for effective treatment methods and sensitive biomarkers to improve the 5-year survival rate and life quality of LUAD patients. NEIL3, a DNA glycosylase of the BER pathway, repairs telomere oxidative damage and protects telomere integrity in cells with a high proliferative capacity during the S phase, which may explain the advanced T classification in NEIL3 overexpressing patients. In addition, some studies indicated NEIL3 as a cell cycle dependent gene was regulated by BRG1 in breast cancer cells and that NEIL3 overexpression may facilitate distant metastasis in primary melanoma[15, 19]. As mentioned in the literature review, NEIL3 plays a crucial role in preventing autoimmunity and cell proliferation[11, 13]. Here a comprehensive bioinformatics analysis was performed based on gene transcript profiles of LUAD from TCGA and GEO databases. Combined with the IHC-scores of our 406 patients cohort, NEIL3 expression was up-regulated in LUAD tissues and correlated with clinicopathological characteristics, especially advanced clinical stage and large tumor size. Meanwhile, the Cox regression analysis results demonstrated that NEIL3 may serve as an independent prognostic predictor in LUAD patients.
Over the past decade, immunotherapy has been a well-known promising cancer treatment with amazing achievements in treating various refractory malignancies. The pivotal strategy of immunotherapy is to interfere with immune checkpoints expressed in immune cells. Immune cells are a crucial part of the immune microenvironment, including tumor infiltrating lymphocytes (TILs), tumor-associated macrophages (TAM), dendritic cells (DC), and myeloid-derived suppressor cells (MDSCs)[30, 31]. As reported in the immunoediting theory, tumor invasive immune cells (TIICs) play a "double-edged sword" role in the development of cancers. A large number of studies have found the occurrence and development of lung adenocarcinoma not only depends on the lung cancer cells themselves but also is regulated by the tumor-infiltrating immune cells in the lung cancer microenvironment.
Based on the TIMER database review, NEIL3 expression had a significant negative correlation with B cells, CD4+ T cells, and DCs. The ImmuCellAI analysis revealed nTreg, iTreg, and Exhausted T cells were increased in the high NEIL3 expression group, whereas Th17 cells, DCs and CD4+ T cells were decreased. Th17 cells play a contradictory role in tumorigenesis and might be associated with secreting cytokines such as IL-17A, IL-17F, IL-21, and IFN-γ + Th17 cells as well as effector lymphocytes, including Th1, Tc1, and NK cells [33–35]. Treg cells could inhibit the activation of T lymphocytes by secreting cytokines such as IL-4, IL-10, and TGF-β, which regulate the immune function of tumor patients and promote the proliferation of lung cancer cells. Evidence indicates that DCs induced antitumor immunity and inhibit the formation of new blood vessels in tumors in the lung cancer microenvironment . These findings suggest that NEIL3 overexpression could increase the proportion of T regulatory cells and inhibit the antitumor function of Th17 cells and DCs, which predicted a poor OS and advanced clinical stage. Together this evidence demonstrates that NEIL3 plays a pivotal role in the regulation of immune infiltrating cells and could be considered a novel immune-related therapeutic target in LUAD.
Equally important, GSEA analysis showed that the cell cycle and P53 signaling pathway were enriched in cases of high NEIL3 expression. As we all know, cell cycle proteins dysregulations is related to uncontrolled proliferation of a malignant tumor and becomes an attractive target in cancer therapy. This work selected nine prognosis-associated hub genes among 370 genes co-expressed with NEIL3: CCNA2, BUB1B, CDC45, BUB1, CDK1, NCAPG, KIF23, UBE2C and CCNB2 (Table 3, Supplemental Fig. 2). CDK1, a cyclin-dependent kinase, plays an important part in regulating cell cycle progression and reportedly increases cellular proliferation in various cancers if dysregulated. CCNA2 and CCNB2 are cyclin family proteins. CCNA2 was recognized as an effective prognostic marker in prostate, colon, lung, and liver cancers [40, 41]. In line with CCNA2, CCNB2 increased the risk of multiple cancer prognoses such as such as adrenocortical carcinoma, lung cancer, breast cancer, and colorectal adenocarcinoma. Our result showed that NEIL3 and nine hub genes were in a tight co-expressed relationship. Combining the expression levels of the nine hub genes and NEIL3, a 10-gene prognostic signature was constructed to accurately predict the prognostic risk of LUAD patients. Multivariate Cox regression analyses proved that the risk score was an independent prognostic factor correlated with clinical stage and tumor size. Analysis of the test cohort data achieved the same results. In recent years, scholars have performed a great many studies to explore new predictive biomarkers. One type of effective biomarkers was constructed by several prognostic genes through bioinformatics analysis. This 10-gene signature could effectively predict the prognostic risk of LUAD patients and provide a theoretical basis for the development of new targeted therapies.
NEIL3 expression and the 10-gene signature were proven to be independent predictors for LUAD patients using bioinformatics technology in this study. However, identifying NEIL3 in LUAD cell lines, exploring the underlying tumorigenesis mechanism, and designing novel potent selective NEIL3-targeted drugs require further research.