| Objectives:The cytidine deaminase activity of apolipoprotein B mRNA editing enzyme catalytic polypeptide 3B(APOBEC3B/A3B)is one of the important sources of endogenous mutations.Recent studies have found that A3 B is related to the occurrence,development and poor prognosis of tumors.Therefore,this study aims to explore the effect of A3 B on the malignant biological behavior of bladder cancer and its potential mechanism,in order to determine its feasibility as a therapeutic target for bladder cancer.Methods:1.Integrate data from the TCGA and GTEx databases to analyze A3B’s expression in pan-cancer.Investigate differences in A3 B expression between bladder cancer and adjacent tissues in the TCGA database.Additionally,integrate clinical information to determine the relevance and diagnostic value of A3 B expression regarding bladder cancer’s clinical features.2.Paraffin sections of 60 clinical samples were collected.The expression of A3 B in cancer and its neighboring paracancerous tissues was verified by immunohistochemistry.The correlation of A3 B expression with clinical features and A3B’s diagnostic value were analyzed.3.Construct a cellular model overexpressing or interfering with A3 B and investigate its influence on bladder cancer cell proliferation,cell cycle,apoptosis,migration,invasion,and cisplatin chemosensitivity through a variety of cellular functional assays.4.To examine the impact of A3 B expression on xenograft tumor under in vivo conditions,we constructed a subcutaneous xenograft tumor model in nude mice with either overexpression or interference of A3 B.5.Utilizing the TCGA database,we probed into the potential mechanism of A3 B in bladder cancer by assessing its association with somatic mutation,gene expression of DNA repair,and level of tumor immune infiltration.Moreover,by performing gene set enrichment analysis,we detected the pathways that are linked to the functions of A3 B.6.To investigate the impact of A3 B expression on tumor-associated macrophage markers,we co-cultured M0 macrophages with a cell model that overexpressed A3 B.7.Finally,this study investigates the predictive role of A3 B in immunotherapy efficacy by examining the relationship between A3 B expression and immune checkpoint-related genes and tumor mutational burden.Furthermore,the correlation between A3 B expression and the efficacy of anti-PD-L1 therapy was verified in the IMvigor210 cohort of patients with metastatic urothelial carcinoma.Results:1.The results of pan-cancer analysis showed that the expression of A3 B mRNA in cancer tissues was generally higher than that in paracancerous tissues.Similarly,the expression of A3 BmRNA in bladder cancer tissues was significantly higher than that in paracancerous tissues.High expression of A3 B is associated with higher histopathological grade and later clinical stage and has high diagnostic value.2.The immunohistochemical results of clinical samples suggested that A3 B protein was significantly increased in cancer tissues,but the expression of A3 B protein was not significantly related to clinical features.A3 B protein expression also showed good diagnostic value.3.In vitro experiments showed that overexpression of A3 B promoted cell proliferation,migration,and invasion of bladder cancer cells.It also induced cell cycle transition from G0/G1 phase to S phase while inhibiting apoptosis and reducing the sensitivity of bladder cancer cells to cisplatin chemotherapy.Knockdown of A3 B produced the opposite results.4.Subcutaneous tumor transplantation experiments were performed on nude mice.The results indicated that A3 B overexpression enhanced tumor growth and simultaneously reduced tumor cell apoptosis,thereby promoting tumor progression in comparison to the OE-NC group.On the contrary,knocking down A3 B yielded opposite observations.5.The frequency of somatic mutations was higher in the high A3 B expression group.C>T was the most prevalent type of SNP observed in bladder cancer,with missense mutations being the most frequent variant classification and SNPs being the most common type.Gene set enrichment analysis indicated that the group with high A3 B expression was primarily enriched in pathways including the cell cycle,cytokine-cytokine receptor interaction,and inflammatory response.Moreover,the expression levels of A3 B were significantly correlated with several DNA mismatch repair genes and the extent of infiltration of various immune cells.6.In co-culture experiments performed in vitro,bladder cancer cells that overexpressed A3 B were found to promote the markers for M2 tumor-associated macrophages and reduce the markers for M1 tumor-associated macrophages.7.The expression of A3 B correlated significantly with the expression of immune checkpoint-related genes.Furthermore,high A3 B expression is associated with significantly higher tumor mutational burden.A3 B expression was significantly higher in responders to immunotherapy in the IMvigor210 cohort.Conclusions:1.A3 B is highly expressed in bladder cancer tissue,and its high expression is significantly associated with higher tissue pathological grade and later clinical stage,and has a higher diagnostic value.2.In vitro,A3 B can effectively promote bladder cancer cell proliferation,migration,and invasion.At the same time,it encourages the transition of the cell cycle from the G0/G1 phase to the S phase,inhibits apoptosis,reduces the sensitivity of bladder cancer cells to cisplatin chemotherapy,and thus exerts a carcinogenic effect.3.Subcutaneous tumor transplantation in nude mice demonstrate that,in vivo,A3 B is able to enhance tumor proliferation and suppress tumor cell apoptosis,thus promoting tumor progression.4.Patients with high expression of A3 B have a higher frequency of somatic mutations.5.A3 B may regulate pathways such as the cell cycle,cytokines,and inflammatory responses,as well as promote macrophage polarization and infiltration to facilitate the progression of bladder cancer.6.A3 B can serve as a biomarker for predicting the efficacy of immunotherapy. |
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