Metastasis is an important factor contributing to poor prognosis in patients with gastric cancer; yet, the molecular mechanism leading to this cell behavior is still not well understood. In this study, we explored the role of cysteine protease inhibitor SN (Cystatin SN, CST1) in promoting gastric cancer metastasis. We hypothesized that CST1 could regulate gastric cancer progression by regulating GPX4 and ferroptosis. Whole transcriptome sequencing suggested that the expression of CST1 was significantly increased in metastatic cancer, and high CST1 expression was correlated with a worse prognosis. Our data further confirmed that the overexpression of CST1 may significantly promote the migration and invasion of gastric cancer cells in vitro and enhance liver, lung, and peritoneal metastasis of gastric cancer in nude mice. Meanwhile, high expression of CST1 promoted the epithelial-mesenchymal transition (EMT) of gastric cancer cells. Mechanistically, a co-immunoprecipitation experiment combined with mass spectrometry analysis confirmed that CST1 could interact with GPX4, a key protein regulating ferroptosis. CST1 relieves GPX4 ubiquitination modification by recruiting OTUB1, improving GPX4 protein stability and reducing intracellular reactive oxygen species (ROS), thereby inhibiting ferroptosis and, in turn, promoting gastric cancer metastasis. Moreover, clinical data suggested that CST1 is significantly increased in peripheral blood and ascites of gastric cancer patients with metastasis; multivariate Cox regression model analysis showed that CST1 was an independent risk factor for the prognosis of gastric cancer patients. Overall, our results elucidated a critical pathway through which high CST1 expression protects gastric cancer cells from undergoing ferroptosis, thus promoting its progression and metastasis. CST1 may be used as a new oncological marker and potential therapeutic target for gastric cancer metastasis.

Despite advances in surgery, radiotherapy and immunotherapy, the mortality rate for gastric cancer remains one of the highest in the world. A large body of evidence has demonstrated that cancer-associated fibroblasts (CAFs), as core members of the stroma, can secrete cytokines, proteins and exosomes to create a tumour microenvironment that is conducive to cancer cell survival. CAFs can also interact with cancer cells to form a complex signalling network, enabling cancer cells to more easily metastasise to other organs and tissues in the body and develop metastatic foci. In this review, we provide an overview of the CAFs concept and activators. We focus on elucidating their effects on immune cells, intratumoural vasculature, extracellular matrix, as well as cancer cell activity, metastatic power and metabolism, and on enhancing the metastatic ability of cancer cells through activation of JAK/STAT, NF/κB and CXCL12/CXCR4. Various therapeutic agents targeting CAFs are also under development and are expected to improve the prognosis of gastric cancer in combination with existing treatment options.

Background: Recent studies suggested that NDUFS1 has an important role in human cancers; however, the effects of NDUFS1 on gastric cancer (GC) are still not fully understood. Methods: We confirmed that NDUFS1 is downregulated in GC cells through western blot immunohistochemistry and bioinformation analysis. The effect of NDUFS1 on GC was studied by CCK-8, colony formation, transwell assay in vitro and Mouse xenograft assay in vivo. Expression and subcellular localization of NDUFS1 and the content of mitochondrial reactive oxygen species (mROS) was observed by confocal reflectance microscopy. Results: Reduced expression of NDUFS1 was found in GC tissues and cell lines. Also, NDUFS1 overexpression inhibited GC cell proliferation, migration, and invasion in vitro as well as growth and metastasis in vivo. Mechanistically, NDUFS1 reduction led to the activation of the mROS-hypoxia-inducible factor 1α (HIF1α) signaling pathway. We further clarified that NDUFS1 reduction upregulated the expression of fibulin 5 (FBLN5), a transcriptional target of HIF1α, through activation of mROS-HIF1α signaling in GC cells. Conclusions: The results of this study indicate that NDUFS1 downregulation promotes GC progression by activating an mROS-HIF1α-FBLN5 signaling pathway.

Numerous aberrant splicing events are implicated in tumor progression, yet comprehensive reports on splicing factors and events associated with peritoneal metastasis in gastric cancer (GCPM) are lacking. In this study, PTBP3 is found to be significantly overexpressed in peritoneal metastatic tissues of gastric cancer compared to primary tumor tissues, and higher PTBP3 expression correlates with poorer prognosis. Using gastric cancer cells and patient‐derived organoids (PDO), the role of PTBP3 in promoting tumor invasion and proliferation is investigated. Mechanistically, through full‐length transcriptome sequencing, PTBP3 mediates exon 4 skipping in its target gene COX11, leading to shorter transcripts that impair COX11 protein function, reducing mitochondrial copper content and enabling tumor cells to evade cuproptosis. Antisense oligonucleotide (ASO) drugs targeting the short COX11 transcripts effectively degrade mRNA, disrupting copper homeostasis. In PDO‐based xenograft models, exogenous copper ionophores combined with ASO drugs induce excessive copper accumulation in mitochondria, triggering proteotoxic stress and cuproptosis. Overall, PTBP3‐mediated exon 4 skipping in COX11 pre‐mRNA is critical for tumor cell survival and progression in GCPM, offering potential therapeutic strategies targeting copper metabolism.

The peritoneum is the most common metastatic site of advanced gastric cancer and is associated with extremely poor prognosis. Endothelial-specific molecule 1 (ESM1) was found to be significantly associated with gastric cancer peritoneal metastasis (GCPM); however, the biological functions and molecular mechanisms of ESM1 in regulating GCPM remain unclear. Herein, we demonstrated that ESM1 expression was significantly upregulated in gastric cancer tissues and positively correlated with platelet endothelial cell adhesion molecule-1 (CD31) levels. Moreover, clinical validation, in in vitro and in vivo experiments, confirmed that ESM1 promoted gastric cancer angiogenesis, eventually promoting gastric cancer peritoneal metastasis. Mechanistically, ESM1 promoted tumor angiogenesis by binding to c-Met on the vascular endothelial cell membrane. In addition, our results confirmed that ESM1 upregulated VEGFA, HIF1α, and MMP9 expression and induced angiogenesis by activating the MAPK/ERK pathway. In conclusion, our findings identified the role of ESM1 in gastric cancer angiogenesis and GCPM, thus providing insights into the diagnosis and treatment of advanced gastric cancer.

The peritoneum is the most common site of metastasis in advanced gastric cancer (GC), and the mechanisms underlying this process of gastric cancer peritoneal metastasis (GCPM) remain largely elusive. Mesothelial-mesenchymal transition (MMT) plays a crucial role in the progression of GCPM. In our current study, the data confirmed that GC-derived exosomes could significantly promote peritoneal metastasis through an MMT-dependent manner in vivo and in vitro. Using RNA-seq, we successfully identified a key circular RNA (circPTBP3). The expression of exosomal circPTBP3 in the plasma of GCPM patients was significantly upregulated and closely correlated with tumor differentiation, depth of invasion, lymphatic invasion, peritoneal metastasis, and TNM stage. Exosomal circPTBP3 thus serves as a reliable diagnostic and prognostic indicator in GCPM patients. Mechanistically, exosomal circPTBP3 could effectively promote the MMT phenotype of mesothelial cells in vitro. Located in the nucleus, circPTPB3 was found to recruit transcription factor AP-2-beta (TFAP2B) to the serum- and glucocorticoid-inducible kinase 1 (SGK1) promoter sites, thereby initiating its transcription in mesothelial cells. These findings suggest that exosomal circPTPB3 functions as a pivotal mediator in facilitating the interplay between GC cells and mesothelial cells, and it provides a promising diagnostic indicator and therapeutic target for GCPM patients.