Renal cell carcinoma (RCC) is a malignancy in the urinary system originating from the renal tubular epithelium with a high incidence ranking as the sixth and tenth most commonly diagnosed tumor among men and women [1]. There are almost 300,000 new cases and 130,000 deaths caused by RCC each year worldwide. In China, the incidence of RCC has nearly doubled over the past two decades, rising at an average annual rate of 6.5%, and RCC has been recognized as a major public health issue [2]. Clear cell renal cell carcinoma (ccRCC) is the most prevalent histological subtype, accounting for almost 80% to 90% of RCC cases [3]. Although diagnostic methods for ccRCC have been dramatically improved, approximately 15–20% of ccRCC patients are in the advanced stage of ccRCC at primary diagnosis, and 30% eventually relapse after surgery [4]. These patients usually have a worse prognosis due to missing the chance for surgery and the insensitivity of ccRCC patients to radiation or chemotherapy [5]. Moreover, the 5-year survival rate of patients diagnosed at the advanced stage is less than 10% [6]. Currently, sunitinib, as well as several other tyrosine kinase inhibitors (TKIs) and checkpoint inhibitors, such as monoclonal antibodies targeting programmed cell death protein 1 (PD-1) or cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), have benefited patients with metastatic renal cancer. Overall, no effective treatment for advanced ccRCC has been defined [7]. Therefore, there is an urgent need to discover novel clinically applicable biomarkers for early diagnosis and develop more effective treatment strategies for patients with ccRCC.

Sustained proliferative signaling is one of the most critical hallmarks of cancer, and normal cells can evade cell death by acquiring unlimited proliferative potential, eventually leading to tumorigenesis [8]. Mitotic defect accumulation of cells could finally cause chromosomal instability (CIN), a common feature of cancer that can lead to infinite proliferation due to the loss of supervision [9]. Meanwhile, telomeres, which protect the ends of chromosomes, are centrally involved in the capability for unlimited proliferation, and telomere integrity also reflects cell proliferation potential in cancer [10]. Nei endonuclease VIII-like 3 (NEIL3), encoding a protein belonging to the homologous DNA glycosylases and the Fpg/Nei family, has been identified in diverse physiological and pathophysiological processes [11]. NEIL3 was reported to promote the malignant proliferation of tumors by maintaining telomere integrity, clearing oxidative damage, and repairing DNA damage [12], [13]. As previous research noted NEIL3 serves as a prognostic marker and contributes to the carcinogenesis of patients with liver and lung cancer [14], [15]. NEIL3 overexpressed tumors accumulate mutation and chromosomal variations, resulting in worse overall survival in patients with pancreatic adenocarcinoma, lung adenocarcinoma, and lower-grade glioma [16]. Nevertheless, little is known regarding the expression pattern and underlying mechanism of NEIL3 in ccRCC pathogenesis and progression. Therefore, the biological function of NEIL3 in ccRCC proliferation is worthy of further in-depth assessment.

The cyclin D1-Rb-E2F1 axis plays a vital role in regulating cell cycle progression and malignant cell proliferation in several types of cancer [17]. Cyclin D1 was usually overexpressed and served as a pivotal regulatory protein that mediated the G1-S phase transition by forming a cyclin D1-CDKs complex in various tumors. To date, numerous studies have validated cyclin D1 as a proto-oncogene promotes cell proliferation by triggering hyperphosphorylation and deactivation of the tumor suppressor retinoblastoma protein (Rb) and then releasing the E2F1, which transcriptionally activates the down-stream genes that thereby promote the cell proliferation and cell cycle transition in cancers [18]. However, the underlying mechanism of abnormal activation of the cyclin D1-Rb-E2F1 signaling pathway leading to malignant proliferation of ccRCC cells is still poorly understood.

Here, we systematically investigated the expression pattern and potential function of NEIL3 in ccRCC. We found that NEIL3 was highly expressed in ccRCC tissues and cell lines and positively correlated with adverse clinicopathological characteristics and worse clinical outcomes. NEIL3 could serve as an independent diagnostic and prognostic biomarker in ccRCC. Mechanistically, upregulation of NEIL3 expression promoted cell viability, DNA replication, cell cycle progression, and anti-apoptosis capabilities in ccRCC cells. In addition, NEIL3 promoted E2F1 expression through the cyclin D1-Rb-E2F1 pathway, and the upregulation of E2F1 could transcriptionally activate NEIL3 expression by binding with its promoter region, thus forming a feedback loop. Therefore, we suggest that NEIL3 may serve as a promising prognostic marker and represent a valuable potential target for ccRCC diagnosis and treatment.