Identification of RRM2 as a key regulator of malignant epithelial cells in gastric cancer through single‑cell transcriptomics.

Gastric cancer (GC) is one of the most prevalent and life‑threatening malignancies of the digestive tract worldwide. Ribonucleotide reductase regulatory subunit M2 (RRM2), a rate‑limiting subunit in deoxyribonucleotide synthesis, is overexpressed and is associated with a poor prognosis in various solid tumors. However, its functional role and mechanisms in GC‑specific malignant epithelial cell populations remain unclear. Single‑cell transcriptomic data from GC and adjacent normal tissues were analyzed. Key malignant epithelial cell populations were identified using inferCNV, pseudotime trajectory analysis, and weighted gene co‑expression network analysis. RRM2 was identified as a core gene by integrating data from TCGA‑STAD, GSE66229, and GSE84433 datasets and analyzing its clinical relevance. To evaluate the biological effects of RRM2, functional assays, including colony formation, apoptosis, Transwell migration, and wound healing assays, were performed using AGS and HGC‑27 GC cells with RRM2 knockdown. DNA damage was assessed using the alkaline comet assay and phosphorylated histone H2AX (γH2AX) immunofluorescence, and the expression of DNA damage repair‑related proteins [including γH2AX, phosphorylated tumor protein p53 (p‑p53), RAD51 recombinase (RAD51), poly(ADP‑ribose) polymerase 1 (PARP‑1), and X‑ray repair cross‑complementing protein 1 (XRCC1)] was examined using western blotting. Through analysis of gastric epithelial cell populations, a major malignant epithelial effector population in GC was identified, enriched in cells with active DNA replication and repair. Differentially expressed genes specific to this population were intersected with prognostic genes from GEO GC datasets, resulting in the identification of RRM2 as a key effector gene. Transcriptomic analysis revealed that high RRM2 expression was associated with an active immune microenvironment. Functional assays showed that RRM2 knockdown significantly inhibited GC cell proliferation and migration while promoting apoptosis. In addition, RRM2 knockdown exacerbated DNA damage, upregulated p‑p53, and downregulated RAD51, with no significant effects on PARP‑1 or XRCC1 expression. Collectively, RRM2 was shown to be a crucial regulator of the malignant phenotype of gastric epithelial cells. It promoted GC cell proliferation, invasion, and migration and modulated DNA damage and homologous recombination repair. In addition, RRM2 influenced the tumor immune microenvironment, highlighting its potential as a driver of malignant progression and a promising target for immunotherapy in GC.