ENOX2 (tNOX)-Associated Stemness in Oral Cancer Cells and Its Clinical Correlation in Head and Neck Tumors

Cancer remains one of the most common causes of death worldwide and imposes enormous social and economic burdens. Human tumor-associated NADH oxidase (ENOX2, also known as tNOX) is a cancer cell-specialized NADH oxidase that is expressed on the membranes of cancer cells. In this study, we investigated the potential role of ENOX2 in regulating stemness properties in oral cancer through a combination of in vitro, in vivo, and bioinformatics approaches. We found that ENOX2 physically interacted with the stem cell transcription factor, SOX2, in co-immunoprecipitation experiments. The expression and activity of ENOX2 were elevated in p53-functional SAS and p53-mutated HSC-3 oral cancer cell spheroids compared with their monolayer counterparts. Consistently, SIRT1, a downstream effector modulated by ENOX2 through NAD⁺ generation, was also upregulated in spheroid cultures. Functional studies further established that ENOX2 overexpression significantly enhanced spheroid formation, self-renewal properties, stem cell marker expression, and PKCδ expression, whereas ENOX2 knockdown produced the opposite effects. In xenograft models, ENOX2-overexpressing oral cancer cell spheroids exhibited enhanced tumorigenicity, while ENOX2-silenced spheroids formed significantly smaller tumors. Complementary analyses of public transcriptomic and proteomic datasets revealed elevated ENOX2 expression in human head and neck tumor tissues compared with adjacent normal tissues. Based on these findings and literature-supported correlations, we propose a putative ENOX2-SIRT1-SOX2 regulatory framework that may contribute to the acquisition and maintenance of stem-like properties of oral cancer cells. While the ENOX2-SOX2 interaction was experimentally validated, the roles of SIRT1 and other downstream components are inferred from bioinformatic analyses and prior studies; thus, this axis represents a hypothetical model that warrants further mechanistic investigation. Collectively, our results identify ENOX2 as a potential regulator of oral cancer stemness and provide a conceptual foundation for future studies aimed at elucidating its downstream pathways and clinical relevance in head and neck tumors.