The suppression of thoc1 in cancer cell apoptosis mediated by activated macrophages is nitric oxide-dependent

Abstract

Activation of Toll-like receptor 4 (TLR4) triggers both innate and adaptive immunity. We previously identified a synthetic glycolipid, CCL-34, which can induce anticancer immunity in a TLR4-dependent manner. In the present study, we demonstrated the involvement of THO complex 1 (thoc1) in the CCL-34-induced anticancer mechanism. The expression of thoc1 was suppressed in bladder cancer cells (MBT-2) co-cultured with CCL-34-activated macrophages, whereas treatment with an iNOS inhibitor could restore the expression of thoc1. Direct treatment of MBT-2 cells with an NO donor also repressed thoc1 expression. Importantly, the thoc1-overexpressing MBT-2 cells (MBT/thoc1) exhibited greater resistance than the MBT-2 cells to cytotoxicity induced by the NO donor or the CCL-34-activated macrophages. In addition, treatments with CCL-34-activated macrophages or the NO donor resulted in the suppression of thoc1 promoter activity in MBT-2 cells, and mutations in the antioxidant response element (ARE) of the thoc1 promoter abolished the repression induced by these treatments. Furthermore, NO treatment increased the expression and nuclear localization of nuclear factor E2-related factor 2 (Nrf2) in MBT-2 cells. Overexpression of Nrf2 suppressed thoc1 promoter activity in an ARE-dependent manner, and knock-down of nrf2 reversed the suppression. Notably, Bcl-2 expression was suppressed in MBT-2 cells, but not in MBT-2/thoc1 cells, treated with CCL-34-activated macrophages or the NO donor. In summary, our results demonstrate that NO-mediated thoc1 downregulation, via Nrf2, is a key step in the cancer cell apoptosis induced by CCL-34-treated macrophages and that downregulated thoc1 could lead to Bcl-2 downregulation and subsequent cancer cell apoptosis.