Circular MTHFD2L RNA-encoded CM-248aa inhibits gastric cancer progression by targeting the SET-PP2A interaction.

The available targeted therapies for gastric cancer (GC) are still limited, so it is important to discover novel molecules as potential treatment options. Proteins or peptides encoded by circular RNAs (circRNAs) are increasingly reported to play essential roles in malignancies. The aim of the present study was to identify an undiscovered protein encoded by circRNA and explore its key role and molecular mechanism in GC progression. CircMTHFD2L (hsa_circ_0069982) was screened and validated as a downregulated circRNA with coding potential. The protein encoded by circMTHFD2L, named CM-248aa, was identified for the first time by immunoprecipitation and mass spectrometry. CM-248aa was significantly downregulated in GC, while its low expression was associated with advanced tumor-node-metastasis (TNM) stage and histopathological grade. Low expression of CM-248aa could be an independent risk factor for poor prognosis. Functionally, CM-248aa, instead of circMTHFD2L suppressed the proliferation and metastasis of GC in vitro and in vivo. Mechanistically, CM-248aa competitively targeted the acidic domain of SET nuclear oncogene (SET) and acted as an endogenous inhibitor of the SET-protein phosphatase 2A interaction to promote dephosphorylation of AKT, extracellular signal-regulated kinase, and P65. Our discovery revealed that CM-248aa could be a potential prognostic biomarker and endogenous therapeutic option for GC.

Circ-E-Cad encodes a protein that promotes the proliferation and migration of gastric cancer via the TGF-ß/Smad/C-E-Cad/PI3K/AKT pathway.

Accumulating studies indicate that circular RNAs (circRNAs) play critical roles in cancer progression. Most of them have been reported to act as microRNA sponges or interact with RNA-binding proteins; however, their full range of functions remains largely unclear. Recently, an increasing number of circRNAs have been found to encode proteins. C-E-Cad, a protein encoded by circular E-cadherin (circ-E-Cad), has been shown to have a great influence in the progression of glioblastoma, but its specific role in gastric cancer (GC) is unclear. Here, we found that both circ-E-Cad and C-E-Cad were upregulated in GC cell lines and GC tissues compared with a human gastric epithelial cell line (GES-1) and normal tissues. Knockdown of circ-E-Cad suppressed GC cell line proliferation and metastasis in vitro and in vivo, whereas overexpression of C-E-Cad had the opposite effects. Immunoblotting revealed that C-E-Cad exerted tumor-promoting functions by regulating the PI3K/AKT pathway. A rescue experiment showed that C-E-Cad but not circ-E-Cad was the executor of protumor biological functions. In addition, we demonstrated that the C-E-Cad expression level could have been increased by the TGF-ß/Smad pathway. In summary, our results indicated that the TGF-ß/Smad pathway could increase the expression of C-E-Cad to regulate GC cell proliferation, migration, and epithelial-mesenchymal transition by affecting PI3K/AKT signaling.

Patient stratification based on urea cycle metabolism for exploration of combination immunotherapy in colon cancer.

BACKGROUND: Owing to the low ratio of patients benefitting from immunotherapy, patient stratification becomes necessary. An accurate patient stratification contributes to therapy for different tumor types. Therefore, this study aimed to subdivide colon cancer patients for improved combination immunotherapy. METHODS: We characterized the patients based on urea cycle metabolism, performed a consensus clustering analysis and constructed a risk model in the cancer genome atlas cohort. Colon cancer patients were further categorized into two tags: clusters, and risk groups, for the exploration of combination immunotherapy. In addition to external validation in the Gene Expression Omnibus datasets, several images of immunohistochemistry were used for further validation. RESULTS: Patient characterization based on urea cycle metabolism was related to immune infiltration. An analysis of consensus clustering and immune infiltration generated a cluster distribution and identified patients in cluster 1 with high immune infiltration levels as hot tumors for immunotherapy. A risk model of seven genes was constructed to subdivide the patients into low- and high-risk groups. Validation was performed using a cohort of 731 colon cancer patients. Patients in cluster 1 had a higher immunophenoscore (IPS) in immune checkpoint inhibitor therapy, and those other risk groups displayed varying sensitivities to potential combination immunotherapeutic agents. Finally, we subdivided the colon cancer patients into four groups to explore combination immunotherapy. Immunohistochemistry analysis showed that protein expression of two genes were upregulated while that of other two genes were downregulated or undetected in cancerous colon tissues. CONCLUSION: Using subdivision to combine chemotherapy with immunotherapy would not only change the dilemma of immunotherapy in not hot tumors, but also promote the proposition of more rational personalized therapy strategies in future.

Gastric cancer immune microenvironment score predicts neoadjuvant chemotherapy efficacy and prognosis.

The efficacy of neoadjuvant chemotherapy (NACT) in patients with advanced gastric cancer (GC) varies greatly. Thus, we aimed to verify the predictive value of tumor-infiltrating immune cells (TIICs) on the treatment response to NACT and the prognosis of patients with advanced GC, and to explore the impact of NACT on the tumor immune microenvironment (TIME). Paired tumor tissues (pre- and post-NACT) from patients with advanced GC were collected for this study. TIICs were assessed using immunohistochemistry staining and analyzed using logistic regression to establish an immune microenvironment score for GC (ISGC score) and predict NACT efficacy. Kaplan-Meier curves were used to evaluate the survival outcome of patients. The results showed that TIME was dramatically heterogeneous between NACT response and nonresponse patients. In the validation cohort, the ISGC score demonstrated good predictive performance for treatment response to NACT. Moreover, high ISGC indicated better long-term survival in patients with advanced GC. Furthermore, tumor-infiltrated T cells (CD3+ and CD8+) and CD11c+ macrophages were significantly increased in the response group, while CD163+ macrophages and FOXP3+ Treg cells were decreased after NACT. However, opposite results were exhibited in the nonresponse group. Finally, we found that the percentage of programmed cell death ligand 1 (PD-L1)-positive tumors was 31% (32/104) pre-NACT and 49% (51/104) post-NACT, and almost all patients with elevated PD-L1 were in the NACT response group. The ISGC model accurately predicted NACT efficacy and classified patients with GC into different survival groups. NACT regulates the TIME in GC, which may provide strategies for personalized immunotherapy.

PMN-MDSCs accumulation induced by CXCL1 promotes CD8+ T cells exhaustion in gastric cancer.

Myeloid-derived suppressor cells (MDSCs) accumulation in multiple tumor is associated with immune checkpoint inhibitors (ICIs) resistance. However, mechanisms of MDSCs in ICIs resistance of gastric cancer (GC) have not been thoroughly explored. In this study, we found that the PMN-MDSCs frequency rather than the M-MDSCs frequency was correlated with the survival of GC patients and CXCL1 induced PMN-MDSCs accumulation in GC. S100A8/A9 heterodimer, a hallmark of MDSCs, upregulated the CXCL1 expression in GC cells through the TLR4/p38 MAPK/NF-κB pathway. Notably, PMN-MDSCs exerted immunosuppressive effect through S100A8/A9. Mechanically, S100A8/A9 led to CD8+ T cells exhaustion including inhibiting CD8+ T cells glycolysis, proliferation and TNF-α and IFN-γ production, which was dependent on TLR4/AKT/mTOR pathway. In tumor-bearing mice, the CXCR2 antagonist SB225002 decreased PMN-MDSCs accumulation, increased CD8+ T cells infiltration in GC and further enhanced anti-tumor efficacy of anti-PD-1. Taken together, our study identified that CXCL1 induced PMN-MDSCs accumulation in GC, and unveiled how PMN-MDSCs promoted CD8+ T cells exhaustion, which may provide a potential therapeutic strategy for GC.