Expression of sialyl-Tn sugar antigen in bladder cancer cells affects response to <i>Bacillus Calmette Guérin</i> (BCG) and to oxidative damage

Abstract

The sialyl-Tn (sTn) antigen is an <i>O</i>-linked carbohydrate chain aberrantly expressed in bladder cancer (BC), whose biosynthesis is mainly controlled by the sialyltransferase ST6GALNAC1. Treatment with <i>Bacillus Calmette-Guérin</i> (BCG) is the most effective adjuvant immunotherapy for superficial BC but one third of the patients fail to respond. A poorly understood correlation between the expression of sTn and BC patient's response to BCG was previously observed. By analyzing tumor tissues, we showed that patients with high ST6GALNAC1 and IL-6 mRNA expression were BCG responders. To investigate the role of sTn in BC cell biology and BCG response, we established the cell lines MCR_sTn and MCR_Nc by retroviral transduction of the BC cell line MCR with the <i>ST6GALNAC1</i> cDNA or with an empty vector, respectively. Compared with MCR_Nc, BCG-stimulated MCR_sTn secreted higher levels of IL-6 and IL-8 and their secretome induced a stronger IL-6, IL-1β, and TNFα secretion by macrophages, suggesting the induction of a stronger inflammatory response. Transcriptomic analysis of MCR_Nc and MCR_sTn revealed that <i>ST6GALNAC1</i>/sTn expression modulates hundreds of genes towards a putative more malignant phenotype and down-regulates several genes maintaining genomic stability. Consistently, MCR_sTn cells displayed higher H₂O₂ sensitivity. In MCR_sTn,, BCG challenge induced an increased expression of several regulatory non coding RNA genes. These results indicate that the expression of <i>ST6GALNAC1</i>/sTn improves the response to BCG therapy by inducing a stronger macrophage response and alters gene expression towards malignancy and genomic instability, increasing the sensitivity of BC cells to the oxidizing agents released by BCG.