Intratumoral microbiota can affect the development and progression of many types of cancer, including gastric cancer. A better understanding of the precise mechanisms by which microbiota support gastric cancer could lead to improved therapeutic approaches. In this study, we investigated the effect of intratumoral microbiota on the tumor immune microenvironment during gastric cancer malignant progression. Analysis of human gastric cancer tissues with 16S rRNA amplicon sequencing revealed that Fusobacterium nucleatum was significantly enriched in gastric cancer tissues with lymph node metastasis and correlated with a poor prognosis. F. nucleatum infection spontaneously induced chronic gastritis and promoted gastric mucosa dysplasia in mice. Furthermore, gastric cancer cells infected with F. nucleatum showed accelerated growth in immunocompetent mice compared with immunodeficient mice. Single-cell RNA sequencing uncovered that F. nucleatum recruited tumor-associated neutrophils (TAN) to reshape the tumor immune microenvironment. Mechanistically, F. nucleatum invaded gastric cancer cells and activated IL17/NF-κB/RelB signaling, inducing TAN recruitment. F. nucleatum also stimulated TAN differentiation into the protumoral subtype and subsequent promotion of PD-L1 expression, further facilitating gastric cancer immune evasion while also enhancing the efficacy of anti–PD-L1 antibody therapy. Together, these data uncover mechanisms by which F. nucleatum affects gastric cancer immune evasion and immunotherapy efficacy, providing insights for developing effective treatment strategies. Significance: Intratumoral F. nucleatum activates NF-κB signaling to facilitate gastric cancer immune evasion by promoting tumor-associated neutrophil recruitment that sensitizes tumors to immune checkpoint blockade therapy.

Resistance to poly (ADP-ribose) polymerase inhibitors (PARPi) limits the therapeutic efficacy of PARP inhibition in treating breast cancer susceptibility gene 1 (BRCA1)-deficient cancers. Here we reveal that BRCA1 has a dual role in regulating ferroptosis. BRCA1 promotes the transcription of voltage-dependent anion channel 3 (VDAC3) and glutathione peroxidase 4 (GPX4); consequently, BRCA1 deficiency promotes cellular resistance to erastin-induced ferroptosis but sensitizes cancer cells to ferroptosis induced by GPX4 inhibitors (GPX4i). In addition, nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy and defective GPX4 induction unleash potent ferroptosis in BRCA1-deficient cancer cells upon PARPi and GPX4i co-treatment. Finally, we show that xenograft tumors derived from patients with BRCA1-mutant breast cancer with PARPi resistance exhibit decreased GPX4 expression and high sensitivity to PARP and GPX4 co-inhibition. Our results show that BRCA1 deficiency induces a ferroptosis vulnerability to PARP and GPX4 co-inhibition and inform a therapeutic strategy for overcoming PARPi resistance in BRCA1-deficient cancers. Significance: BRCA1 deficiency promotes resistance to erastin-induced ferroptosis via blocking VDAC3 yet renders cancer cells vulnerable to GPX4i-induced ferroptosis via inhibiting GPX4. NCOA4 induction and defective GPX4 further synergizes GPX4i with PARPi to induce ferroptosis in BRCA1-deficient cancers and targeting GPX4 mitigates PARPi resistance in those cancers. See related commentary by Alborzinia and Friedmann Angeli, p. 1372

Background: Methyltransferase 3 (METTL3)‐mediated N6‐methyladenosine (m ⁶ A) RNA modification has been demonstrated to be a potential factor in promoting gastric cancer (GC). METTL3 regulates a series of signaling pathways by modifying various mRNAs. This study aimed to identify novel METTL3‐mediated signaling pathways and explored possible targets for use in the clinical setting of gastric cancer. Methods: To investigate the proliferation and metastatic capacity of GC cell lines with METTL3 knockdown, a xenograft, lung metastasis, and popliteal lymph node metastasis model was used. The m ⁶ A‐modified RNA immunoprecipitation (Me‐RIP) sequence was utilized to explore the target mRNAs of METTL3. Cell counting kit 8 and transwell assays were performed to investigate the promoting function of pre‐B cell leukemia homeobox 1 (PBX1) and GTP cyclohydrolase 1 (GCH1). Western blotting and chromatin immunoprecipitation were employed to confirm the involvement of the METTL3‐PBX1‐GCH1 axis. ELISA and liquid chromatography‐mass spectrometry were used to explore the biological function of tetrahydrobiopterin (BH ₄ ). Results: Knockdown of METTL3 suppressed xenograft tumor growth and lung/lymph node metastasis in vivo. Mechanistically, we found that METTL3 combined with and stabilized PBX1 mRNAs. Chromatin immunoprecipitation (ChIP) and further experiments suggested that PBX1 acted as a transcription factor inducing GCH1 expression. Moreover, the METTL3‐PBX1‐GCH1 axis increased BH ₄ levels in GC cells, thereby promoting tumor progression. Conclusions: This study suggested that METTL3 enzymes promote tumor growth and lung/lymph node metastasis via METTL3‐PBX1‐GCH1 axis increasing BH4 levels in GC.

Gastric cancer (GC) is one of the most lethal malignancies worldwide. Despite extensive efforts to develop novel therapeutic targets, effective drugs for GC remain limited. Recent studies have indicated that Lipocalin (LCN)2 abnormalities significantly impact GC progression; however, its regulatory network remains unclear. Our study investigates the functional role and regulatory mechanism of action of LCN2 in GC progression. We observed a positive correlation between LCN2 expression, lower GC grade, and better prognosis in patients with GC. LCN2 overexpression suppressed GC proliferation and metastasis both in vitro and in vivo. Transcriptome sequencing identified secreted protein acidic and rich in cysteine (SPARC) as a pivotal downstream target of LCN2. Mechanistically, c-Jun acted as a transcription factor inducing SPARC expression, and LCN2 downregulated SPARC by inhibiting the JNK/c-Jun pathway. Moreover, LCN2 bound to its receptor, 24p3R, via autocrine signaling, which directly inhibited JNK phosphorylation and then inhibited the JNK/c-Jun pathway. Finally, analysis of clinical data demonstrated that SPARC expression correlated negatively with lower GC grade and better prognosis, and that LCN2 expression correlated negatively with p-JNK, c-Jun, and SPARC expression in GC. These findings suggest that the LCN2/24p3R/JNK/c-Jun/SPARC axis is crucial in the malignant progression of GC, offering novel prognostic markers and therapeutic targets.

The m6a demethyltransferase ALKBH5 dynamically modulates gene expression and intracellular metabolic molecules by modifying RNA m6a in cancer cells. However, ALKBH5’s function in gastric cancer (GC) has remained controversial. This study demonstrates that ALKBH5 is highly expressed in GC. Silencing ALKBH5 hampers proliferation, and metastatic potential, and induces cell death in GC cells. Through a comprehensive analysis of the transcriptome and m6A sequencing, alterations in certain ALKBH5 target genes, including CHAC1, were identified. ALKBH5’s demethylation effect regulates CHAC1 RNA stability, leading to reduced CHAC1 expression. Moreover, CHAC1 modulates intracellular ROS levels, influencing the chemotherapy sensitivity of gastric cancer. In summary, our study unveils the pivotal role of the ALKBH5-CHAC1-ROS axis and highlights the significance of m6A methylation in gastric cancer.

Immune checkpoint inhibitors (ICIs) therapy has been successfully utilized in the treatment of multiple tumors, but only a fraction of patients with gastric cancer (GC) could greatly benefit from it. A recent study has shown that the tumor microenvironment (TME) can greatly affect the effect of immunotherapy in GC. In this study, we established a novel immune risk signature (IRS) for prognosis and predicting response to ICIs in GC based on the TCGA-STAD dataset. Characterization of the TME was explored and further validated to reveal the underlying survival mechanisms and the potential therapeutic targets of GC. The GC patients were stratified into high- and low-risk groups based on the IRS. Patients in the high-risk group, associated with poorer outcomes, were characterized by significantly higher immune function. Further analysis showed higher T cell immune dysfunction and probability of potential immune escape. In vivo, we detected the expressions of SERPINE1 by the quantitative real-time polymerase chain reaction (qPCR)in tumor tissues and adjacent normal tissues. In vitro, knockdown of SERPINE1 significantly attenuated malignant biological behaviors of tumor cells in GC. Our signature can effectively predict the prognosis and response to immunotherapy in patients with GC.