Contributors to HMGB1 Release by Urothelial Carcinoma Cells in Response to Bacillus Calmette-Guérin

Abstract

Our group previously noted that HMGB1 release by urothelial carcinoma cells occurs as a consequence of bacillus Calmette-Guérin induced nonapoptotic cell death. Additional studies demonstrated that HMGB1 release in response to bacillus Calmette-Guérin is required for the invivo tumor response to bacillus Calmette-Guérin. We evaluated the steps required for HMGB1 release by human urothelial carcinoma cells in response to bacillus Calmette-Guérin exposure. We used the T24 and 253J human urothelial carcinoma cell lines. HMGB1 concentrations in cell culture supernatant with and without bacillus Calmette-Guérin treatment served as the principal end point to assess the role of potentially involved variables. Specific techniques were used to determine the role of α5β1 antigen receptor cross-linking, TLR signaling, inducible nitric oxide synthase expression/nitric oxide production, p21 expression, and bacillus Calmette-Guérin adherence, internalization and viability. Cross-linking of α5β1 integrin or signaling through TLR2/4 did not contribute to HMGB1 release. Optimal HMGB1 release required bacillus Calmette-Guérin adherence and internalization. Bacillus Calmette-Guérin viability correlated with the magnitude of HMGB1 release. Inhibition of oxidative stress and p21 expression in response to bacillus Calmette-Guérin decreased the magnitude of HMGB1 release. Bacillus Calmette-Guérin induced nonapoptotic cell death and HMGB1 release occur as a consequence of a complex multistep process. Understanding the steps and mechanisms involved in the induced HMGB1 release would provide an opportunity for targeted strategies to improve bacillus Calmette-Guérin treatment efficacy.