AID modulates carcinogenesis network via DNA demethylation in bladder urothelial cell carcinoma

Bladder cancer is one of the most common malignant diseases in the urinary system, with poor survival after metastasis. Activation-induced cytidine deaminase (AID), a versatile enzyme involved in antibody diversification, is an oncogenic gene that induces somatic hypermutation and class-switch recombination (CSR). However, the contribution of AID-mediated DNA demethylation to bladder urothelial cell carcinoma (BUCC) remains unclear. Herein, we evaluated the impact on BUCC caused by AID and explored the gene network downstream of AID by using a proteomic approach. Lentiviral vector containing AID-specific shRNA significantly reduced AID expression in T24 and 5637 cells. Silencing AID expression remarkably inhibited tumour malignancies, including cell proliferation, invasion and migration. We used Isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics analysis technology to study the underpinning mechanism in monoclonal T24 cells, with or without AID knockdown. Among the 6452 proteins identified, 99 and 142 proteins in shAICDA-T24 cells were significantly up- or downregulated, respectively (1.2-fold change) compared with the NC-T24 control. After a pipeline of bioinformatics analyses, we identified three tumour-associated factors, namely, matrix metallopeptidase 14 (MMP14), C-X-C motif chemokine ligand 12 and wntless Wnt ligand secretion mediator, which were further confirmed in human BUCC tissues. Nonetheless, only MMP14 was sensitive to the DNA demethylation molecule 5-aza-2'-deoxycytidine (5-azadC; 5 μM), which reversed the inhibition of carcinogenesis by AID silence in T24 and 5637 cells. Overall, AID is an oncogene that mediates tumourigenesis via DNA demethylation. Our findings provide novel insights into the clinical treatment for BUCC.