OBJECTIVE: To investigate the role of solute carrier family 12 member A8 (SLC12A8) in regulation of biological behaviors of bladder cancer and the mechanism mediating its effect.
METHODS: The TCGA database was used to analyze SLC12A8 expression in bladder cancer and is correlation with prognosis and clinicopathological characteristics of the patients. In different bladder cancer cell lines, the effects of transient transfection with SLC12A8 siRNA on cell proliferation, invasion and migration ability were examined using CCK-8 assay, Transwell assay and scratch experiment. Gene set enrichment analysis (GSEA) was carried out to analyze pathway enrichment. The correlation of SLC12A8 with the expressions of epithelial-mesenchymal transition (EMT) markers was analyzed using Western blotting. The effect of colivelin on biological behaviors of the cells with SLC12A8 knockdown was assessed using CCK-8 and Transwell assays.
RESULTS: SLC12A8 was highly expressed in bladder cancer (P<0.05) and associated with a poor prognosis and advanced pathological stages of the patients (P<0.05), and could serve as an independent prognostic factor. The bladder cancer cell lines with SLC12A8 knockdown showed significantly attenuated proliferation, invasion and migration capacities (P<0.05). GSEA identified significant gene enrichment in the JAK/STAT signaling pathway (P=0.008). Correlation analysis showed that SLC12A8 expression was negatively correlated with E- cadherin expression (r=-0.167, P<0.001) but positively with N-cadherin (r=0.306, P<0.001) and vimentin (r=0.358, P<0.001) expressions. The bladder cancer cells with SLC12A8 knockdown showed significantly decreased expressions of p-Jak2, p-Stat3, N-cadherin and vimentin proteins with an increased expression of E-cadherin. Treatment with colivelin effectively enhanced proliferation, invasion and migration capacities of the bladder cancer cells with SLC12A8 knockdown (P<0.05).
CONCLUSIONS: SLC12A8 promotes bladder cancer progression by activating the JAK/STAT signaling pathway and its high expression is closely associated with a poor prognosis of the patients.

The solute carrier family has been reported to play critical roles in the progression of several cancers; however, the relationship between solute carrier family 12 member 8 (SLC12A8) and bladder cancer (BC) has not been clearly confirmed. This study explores the prognostic value of SLC12A8 for BC and its correlation with immune cell infiltration. We found that the expression of SLC12A8 mRNA was significantly overexpressed in BC tissues compared with noncancerous tissues in multiple public databases, and the result was validated using real-time PCR and immunohistochemistry (IHC). The Kaplan-Meier method and Cox proportional hazards models were used to evaluate the prognostic value of SLC12A8 for BC. The high expression of SLC12A8 led to a shorter overall survival time and was an unfavorable prognostic biomarker for BC. The mechanisms of SLC12A8 promoting tumorigenesis were investigated by Gene Set Enrichment Analysis (GSEA). Moreover, the correlations of SLC12A8 expression with the tumor-infiltrating immune cells (TICs) in BC were explored using TIMER 2.0 and CIBERSORT. SLC12A8 was associated with CD4+ T cells, dendritic cells, neutrophils, and macrophages infiltration. The expression of SLC12A8 was positively correlated with crucial immune checkpoint molecules. In conclusion, SLC12A8 might be an unfavorable prognostic biomarker in BC related to tumor immune cell infiltration.

Bladder cancer is the most common malignant tumor of the urinary system. The intention of the present research is to explore the prognostic value and biological function of solute carrier family 12 member 8 (SLC12A8) in bladder cancer. The analysis based on the TCGA and ONCOMINE database revealed that the expression of SLC12A8 in bladder cancer was notably increased compared with the normal group. SLC12A8 expression was notably correlated with the age, pathological stage, T-stage, and lymph node metastasis of bladder cancer patients. Moreover, the patients\' overall survival was notably shorter in the high SLC12A8 group. Compared with the control, SLC12A8 upregulation enhanced the proliferative, invasive, and migratory capacities of bladder cancer cells and promoted the expression of epithelial-mesenchymal transition (EMT) protein markers including β-catenin, vimentin, snail, and slug, while reduced the expression of E-cadherin. In the case of downregulated SLC12A8 expression, the proliferative, invasive, and migratory capacities of bladder cancer cells and the expression of EMT protein markers presented the opposite trend. This study demonstrated that SLC12A8 was highly correlated with oncogenesis and progression of bladder cancer, indicating that SLC12A8 may be a meaningful biomarker for initial diagnosis and early treatment of bladder cancer.