Identification of glycogene-type and validation of ST3GAL6 as a biomarker predicts clinical outcome and cancer cell invasion in urinary bladder cancer

Background: Urinary bladder cancer (UBC) is one of the most common causes of morbidity and mortality worldwide characterized by a high risk of invasion and metastasis; however, the molecular classification biomarkers and underlying molecular mechanisms for UBC patient stratification on clinical outcome need to be investigated. Methods: A systematic transcriptomic analysis of 185 glycogenes in the public UBC datasets with survival information and clinicopathological parameters were performed using unsupervised hierarchical clustering. The gene signature for glycogene-type classification was identified using Limma package in R language, and correlated to 8 known molecular features by Gene Set Variation Analysis (GSVA). The clinical relevance and function of a glycogene was characterized by immunohistochemistry in UBC patient samples, and quantitative RT-PCR, Western blotting, promoter activity, MAL II blotting, immunofluorescence staining, wound healing, and transwell assays in UBC cells. Results: A 14-glycogene signature for glycogene-type classification was identified. Among them, ST3GAL6, a glycotransferase to transfer sialic acid to 3'-hydroxyl group of a galactose residue, showed a significant negative association with the subtype with luminal feature in UBC patients (n=2,130 in total). Increased ST3GAL6 was positively correlated to tumor stage, grade, and survival in UBCs from public datasets or our cohort (n=52). Transcription factor GATA3, a luminal-specific marker for UBC, was further identified as a direct upstream regulator of ST3GAL6 to negatively regulate its transactivation. ST3GAL6 depletion decreased MAL II level, cell invasion and migration in 5637 and J82 UBC cells. ST3GAL6 could reverse the effects of GATA3 on global sialylation and cell invasion in SW780 cells. Conclusions: Herein, we successfully identified a novel 14-gene signature for glycogene-type classification of UBC patients. ST3GAL6 gene, from this signature, was demonstrated as a potential biomarker for poor outcomes and cell invasion in UBCs.