Integrative Analyses of Pyrimidine Salvage Pathway-Related Genes Revealing the Associations Between UPPI and Tumor Microenvironment

Background: The pyrimidine salvage pathway plays a critical role in tumor progression and patient outcomes. The roles of pyrimidine salvage pathway-related genes (PSPGs) in cancer, however, are not fully understood. This study aims to depict the characteristics of PSPGs across various cancers. Methods: An integrative pan-cancer analysis of six PSPGs (CDA, UCK1, UCK2, UCKL1, UPPI, and UPP2) was conducted using TCGA data, single-cell RNA sequencing datasets, and patient samples. Single-cell transcriptome analysis and RT-qPCR were used to validate the relation between UPPI and cytokines. Flow cytometry was performed to validate the role of UPPI in immune checkpoint regulation. The correlation between UPPI and tumor associated neutrophils (TAN) were investigated and validated by single-cell transcriptome analysis and tissue microarrays (TMAs). Results: PSPGs showed low mutation rates but significant copy number variations, particularly amplifications in UCKL1, UPPI, and UCK2 across various cancers. DNA methylation patterns varied, with notable negative correlations between methylation and gene expression in UPPI. PSPGs were broadly up-regulated in multiple cancers, with correlations to clinical staging and prognosis. Proteomic data further confirmed these findings. Functional analysis revealed PSPGs' associations with tumor proliferation, metastasis, and various signaling pathways. UPPI showed strong correlations with the tumor microenvironment (TME), particularly with cytokines, immune checkpoints, and various immune cells. Single-cell transcriptome analysis confirmed these associations, highlighting UPPl's influence on cytokine expression and immune checkpoint regulation. In esophageal squamous cell carcinoma (ESCC), UPPI-high tumor cells were significantly associated with immunosuppressive cells in the TME. Spatial analysis using TMAs revealed that UPP1+ tumor cells were predominantly located at the invasive margin and closely associated with neutrophils, correlating with poorer patient prognosis. Conclusion: Our study depicted the multi-dimensional view of PSPGs in cancer, with a particular focus on UPPl's role in the TME. Targeting UPPI holds promise as a potential strategy for cancer therapy. Keywords: pyrimidine salvage pathways, UPPI, microenvironment