Suppression of the pro-inflammatory NLRP3/interleukin-1ß pathway in macrophages by the thioredoxin reductase inhibitor auranofin.

BACKGROUND: The thioredoxin/thioredoxin reductase system, which is best known for its essential role in antioxidant defense and redox homeostasis, is increasingly implicated in the regulation of multiple cellular signaling pathways. In the present study, we asked if the thioredoxin system in macrophages might regulate toll-like receptor 4 (TLR4)-dependent gene expression and consequent responses. METHODS: Using microarray analysis we analyzed the effect of auranofin, a highly potent and specific inhibitor of thioredoxin reductase, on the transcriptional program activated in J774 macrophages by the TLR4 agonist, lipopolysaccharide (LPS). We used quantitative real-time PCR (qPCR), Western blotting, ELISA and cytotoxicity assays to confirm and extend the microarray results. RESULTS: Global transcriptional profiling revealed that macrophage treatment with auranofin exerted a selective effect on LPS-induced gene expression, suppressing the induction of a small number of genes. Interestingly, among these suppressed genes were three members of the interleukin-1 (IL-1) family of genes, among which IL-1ß was most affected. qPCR analyses confirmed the repressive effects of auranofin on IL-1 genes. In addition, qPCR and Western blot analyses showed that auranofin impaired TLR4-dependent induction of the inflammasome receptor NLRP3, which plays a critical role in IL-1ß processing. Consistent with these findings, inflammasome-dependent release of IL-1ß from stimulated macrophages was suppressed by auranofin as was inflammasome-mediated cell death. CONCLUSIONS: Our findings suggest a regulatory role for the thioredoxin system in macrophage inflammatory signaling. Inhibition of the thioredoxin system in macrophages exerts an anti-inflammatory effect by repressing the activation of the NLRP3/IL-1ß pathway.

Activating Transcription Factor-5 Knockdown Reduces Aggressiveness of Mammary Tumor Cells and Attenuates Mammary Tumor Growth.

Activating transcription factor-5 (ATF5) is an anti-apoptotic factor and has been implicated in enhancing the survival of cancer cells under stress and in regulating the autophagy process. Targeting ATF5 in anticancer therapy may be particularly attractive because of its differential role in cancer cells than in non-transformed cells, thus allowing specificity of the treatment. Using the delivery of short hairpin RNA vectors into the Mvt1 and Met1 cell lines, we tested the role of ATF5 in the development of mammary tumors in vivo and in regulating proliferation and migration of these cells in vitro. In this study, we demonstrate that knockdown of ATF5 (ATF5-KD) in both cell lines results in a decreased tumor volume and weight, as well as in a reduced proliferation rate and migratory potential of the cells. In addition, ATF5-KD led to an increased autophagy flux and a shift in the sub-populations comprising Mvt1 cells from the aggressive CD24-positive cells toward less aggressive CD24-negative cells. Taken together, these findings suggest that ATF5 plays an important role in enhancing mammary tumor cells overall aggressiveness and in promoting mammary tumor growth and emphasize the possible benefit of anti-ATF5 therapy in breast cancer patients, particularly, against tumors characterized with the positive expression of cell surface CD24.

Blocking IL1ß Pathway Following Paclitaxel Chemotherapy Slightly Inhibits Primary Tumor Growth but Promotes Spontaneous Metastasis.

Acquired resistance to therapy is a major obstacle in clinical oncology, and little is known about the contributing mechanisms of the host response to therapy. Here, we show that the proinflammatory cytokine IL1ß is overexpressed in response to paclitaxel chemotherapy in macrophages, subsequently promoting the invasive properties of malignant cells. In accordance, blocking IL1ß, or its receptor, using either genetic or pharmacologic approach, results in slight retardation of primary tumor growth; however, it accelerates metastasis spread. Tumors from mice treated with combined therapy of paclitaxel and the IL1 receptor antagonist anakinra exhibit increased number of M2 macrophages and vessel leakiness when compared with paclitaxel monotherapy-treated mice, indicating a prometastatic role of M2 macrophages in the IL1ß-deprived microenvironment. Taken together, these findings demonstrate the dual effects of blocking the IL1 pathway on tumor growth. Accordingly, treatments using "add-on" drugs to conventional therapy should be investigated in appropriate tumor models consisting of primary tumors and their metastases.