Urothelial carcinoma (UC), including upper tract urothelial carcinoma (UTUC) and urinary bladder urothelial carcinoma (UBUC), is a common malignant disease in developed countries. Oncogenic metabolic lesions have been associated with UC development. Methods: Using data mining, a series of studies were performed to study the involvement of SLC14A1 in UC specimens, animal models and UC-derived cell lines. Results: In two cohorts of UTUC (n = 340) and UBUC (n = 295), the SLC14A1 protein level was an independent prognostic factor. Epigenetic silencing contributed to SLC14A1 downregulation in UCs. Total and membranous SLC14A1 played tumor suppressive roles through the inhibition of cell proliferation and metastasis in distinct UC-derived cells and animal models. Functional SLC14A1 prevented the accumulation of arginine and urea, enhanced mitochondrial fusion and aerobic respiration, inhibited glycolysis by altering the expression levels of several related proteins and sensitized arginine-deprivation treatment in ASS1-deficient UC-derived cells. In vitro and in vivo, SLC14A1 inhibited the mTOR signaling pathway and subsequently tumorigenesis, supported by reduced arginine concentrations in vitro. Nuclear SLC14A1 transrepressed HK2 and DEGS1 genes via recruitment of HDAC1 and/or SIN3A to maintain metabolic homeostasis and thereafter impeded tumorigenesis. Conclusion: Clinical associations, animal models and in vitro indications provide solid evidence that the SLC14A1 gene is a novel tumor suppressor in UCs. Total and membranous SLC14A1 prevents urea and arginine accumulation via the mTOR signaling pathway. Nuclear SLC14A1 recruits HDAC1 to transrepress oncometabolite genes.
