The researchers, led by investigators at Nanjing Medical University, began by building a single-cell transcriptomic atlas spanning the disease continuum. They collected tissue from five patients undergoing gastrectomy for intestinal-type gastric cancer, sampling not only the tumors themselves but also matched intestinal metaplasia lesions near the tumor margin and non-atrophic gastritis tissue farther away. After rigorous quality control, the dataset comprised 55,785 individual cells from 13 specimens, which the team sorted into nine major cell types, including epithelial cells, malignant cells, T cells, B cells, plasma cells, myeloid cells, mast cells, fibroblasts, and endothelial cells. The composition shifted tellingly across disease stages: as lesions progressed, the fractions of myeloid cells, endothelial cells, and fibroblasts expanded, while malignant epithelial cells came to dominate the tumor samples.

Within the epithelial compartment, the team re-clustered more than 34,000 cells into eight subtypes, ranging from chief and parietal cells, which dwindled as disease advanced, to tumor cells, which appeared only in cancerous tissue. The pivotal move came from pseudotime trajectory analysis, a computational technique that orders cells along an inferred developmental path based on their gene expression. The trajectory originated in neck cells and flowed toward enterocytes, the absorptive cells characteristic of intestinal metaplasia. One enterocyte population, which the researchers designated Enterocytes-S3, sat squarely between earlier epithelial states and the malignant cells along this trajectory, and tumor cells were heavily enriched in the same transcriptional state. To corroborate this intermediate identity, the team scored each cell against a published signature of incomplete intestinal metaplasia. The score climbed steadily from neck cells through successive enterocyte states, peaked in Enterocytes-S3, and then fell in cancer cells, exactly the pattern expected of a waystation on the road to malignancy.

What makes Enterocytes-S3 dangerous, the data suggest, is its cell-cycle program. Weighted gene co-expression network analysis identified 25 gene modules across the epithelial subtypes, and one of them, Module 4, was strongly upregulated in Enterocytes-S3 and enriched for genes governing mitotic nuclear division and mitotic cell-cycle phase transitions. The subpopulation also showed elevated activity of the G2/M checkpoint and E2F target gene sets, hallmarks of cells primed to proliferate. In short, this transitional population was not merely drifting toward a cancer-like identity; it was rewiring its division machinery, acquiring the proliferative momentum that tumors require.

To find the conductor of that rewiring, the researchers scored bulk transcriptomes from The Cancer Genome Atlas stomach adenocarcinoma cohort against the Enterocytes-S3 signature. PTTG1 emerged as the most significantly upregulated gene in tumors with high signature scores. The finding held up across multiple independent datasets, including the Asian Cancer Research Group cohort and the team’s own in-house transcriptomic data, with paired analyses confirming that PTTG1 expression was elevated in intestinal-type gastric cancer relative to matched normal mucosa. Pseudotime analysis showed the gene’s expression rising progressively from enterocytes toward malignant cells, and immunohistochemistry on a tissue microarray of 88 evaluable paired samples told the same story at the protein level: strong nuclear PTTG1 staining in tumors, weak or absent staining in adjacent normal tissue, and significantly higher levels in intestinal-type than in diffuse-type gastric cancer.

PTTG1 is no stranger to oncology. Originally discovered in rat pituitary tumor cells, the gene encodes securin, an inhibitor that prevents sister chromatids from separating until mitosis is properly timed, thereby safeguarding genomic integrity. It is barely expressed in most normal tissues apart from the testis, yet it is markedly overexpressed in hepatocellular, breast, lung, colon, testicular, and ovarian cancers, where it has been linked to proliferation, invasion, and metastasis through pathways ranging from PI3K/AKT to Wnt/beta-catenin and MAPK signaling. What the new study adds is a specific, mechanistic account of how PTTG1 reprograms the cell cycle in gastric epithelium, and evidence that its activity tracks the premalignant-to-malignant transition in a subtype-specific manner.

The functional experiments were decisive. When the team silenced PTTG1 in MKN1 and MKN7 gastric cancer cell lines using small interfering RNAs, proliferation measured by CCK-8 and EdU assays dropped significantly, and Transwell assays showed reduced migration and invasion. RNA sequencing of the knockdown cells revealed widespread downregulation of cell-cycle genes, with gene set enrichment analysis pinpointing the G2/M checkpoint pathway. Flow cytometry then delivered a subtle but important insight: PTTG1 depletion reduced the proportion of cells in G2 phase and increased the G1 fraction, indicating impaired progression through the G2/M transition rather than a classical arrest at the checkpoint. Western blotting confirmed the molecular signature of stalled mitotic entry, with Cyclin B1 and phosphorylated CDK1 both diminished, while levels of gamma-H2AX, a marker of DNA double-strand breaks, rose sharply, and immunofluorescence showed increased gamma-H2AX foci in the nuclei of PTTG1-deficient cells.

Digging deeper, the researchers traced a regulatory axis from PTTG1 to the machinery of mitosis. Knockdown reduced the expression of E2F1, a transcription factor known to bind directly the promoter of the CCNB1 gene, which encodes Cyclin B1. Using CUT&RUN-qPCR, a technique that maps where a protein sits on chromatin, the team showed that E2F1 occupied the CCNB1 promoter in control cells but that this occupancy fell markedly after PTTG1 silencing, accompanied by reduced CCNB1 messenger RNA. The model that emerges is one in which PTTG1 sustains E2F1-dependent transcription of Cyclin B1, thereby licensing the G2-to-M transition, while simultaneously helping to coordinate cell-cycle progression with DNA damage responses. The precise mechanism by which PTTG1 controls E2F1 remains an open question the authors acknowledge.

Two model systems extended the story beyond cell lines. In human paracancerous gastric organoids derived from intestinal-type gastric cancer patients, lentiviral overexpression of PTTG1 produced organoids that grew significantly larger than controls by days 6, 10, and 12 of culture, with more Ki67-positive proliferating cells and elevated Cyclin B1, much of it in the nucleus, a location associated with mitotic commitment. Strikingly, the overexpressing organoids also stained more intensely with Alcian blue and produced more MUC2, a goblet-cell mucin characteristic of intestinal metaplasia, suggesting that PTTG1 can push gastric epithelium toward an intestinal, mucin-producing identity. In the opposite direction, stable PTTG1 knockdown in MKN1 cells injected subcutaneously into nude mice markedly suppressed tumor growth, with smaller volumes and lower weights at the experimental endpoint, reduced Ki67 and Cyclin B1 staining, and altered AB-PAS mucin staining that, however, was not accompanied by a change in MUC2 expression, hinting that PTTG1’s effects on mucin phenotypes depend on the biological context.

The study is candid about its limits. Tissue dissociation erases the spatial geography of the gastric gland, the cross-sectional sampling of five patients cannot fully capture the temporal dynamics of a cascade that unfolds over years, and the cohort was too small to assess sex-associated differences. The tumor-initiating potential of Enterocytes-S3 remains to be proven, and more physiologically relevant culture systems will be needed to settle the mucin question. Notably, PTTG1 expression showed no significant association with overall survival in the TCGA or ACRG cohorts, suggesting the gene functions as an engine of tumor-intrinsic biology rather than an independent prognostic marker. Even so, by placing a chromosome-segregation guardian at the hinge between intestinal metaplasia and carcinoma, the work offers the clearest single-cell-resolved view yet of how the Correa cascade accelerates, and it flags PTTG1, and the G2/M checkpoint it commands, as a target worth pursuing in the fight against intestinal-type gastric cancer.

Subject of Research: The role of PTTG1 in G2/M checkpoint-mediated cell-cycle reprogramming during intestinal-type gastric cancer progression

Article Title: PTTG1 drives intestinal-type gastric cancer progression via G2/M checkpoint-mediated cell-cycle reprogramming

Article References: Hu, C., Bian, L., Luo, L., Zheng, Z., Chen, Y., Gao, X., Li, F., Yang, D., Liu, Y., Li, G., Xu, H., Yan, C., & Jin, G. (2026). PTTG1 drives intestinal-type gastric cancer progression via G2/M checkpoint-mediated cell-cycle reprogramming. iScience, 29(11), Article 117742. https://doi.org/10.1016/j.isci.2026.117742

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117742

Keywords: gastric cancer, PTTG1, securin, G2/M checkpoint, single-cell RNA sequencing, intestinal metaplasia, Correa cascade, Cyclin B1, E2F1, organoids, xenograft, cell cycle