Single-Cell Transcriptomic Profiling Uncovers a Metastasis-Associated MUCL3+ Signet-Ring Cell Subpopulation in Gastric Cancer

Background: Gastric signet-ring cell carcinoma (GSRCC) is an aggressive gastric cancer subtype with abundant mucin production and high metastatic propensity. However, scarcity of specific biomarkers has impeded clinical diagnosis and mechanistic research. This study systematically compares GSRCC and gastric adenocarcinoma (AC) to identify biomarkers and elucidate molecular basis of GSRCC’s aggressive behavior. Methods: We performed single-cell RNA sequencing (scRNA-seq) on surgically resected primary GC tissues, validating our findings using public datasets and functional experiments. Results: We identified expansion of a mucin-secreting epithelial subcluster (Mucous_muc5ac) in GSRCC, characterized by high MUC5AC, TFF1, and other prognosis-associated genes. Within this population, a MUCL3+ subpopulation (Cluster 1) spatially corresponded with classic signet-ring morphology, validating MUCL3 as a specific marker for these cells. Multi-omics analysis revealed that MUCL3+ signet-ring cells exhibit genomic instability, dedifferentiation, and enrichment of TNF-α/NF-κB, TGF-β/EMT, and hypoxia pathways, with elevated metastasis/angiogenesis gene scores and high TFF1 expression. Functional validation confirmed that TFF1 was associated with increased gastric cancer cell migration. Conclusions: Our study characterizes the MUCL3+ signet-ring cell subpopulation, highlighting the diagnostic utility of MUCL3 and suggesting TFF1 as a candidate for further investigation. These findings establish a foundation for advancing precision diagnosis and mechanistic understanding of GSRCC.