Abstract
Abstract Immunotherapy for cancer treatment is achieved through the activation of competent immune effector cells and the inhibition of immunosuppressive cells, such as myeloid-derived suppressor cells (MDSCs). While MDSCs have been shown to contribute to breast cancer development, the mechanism underlying MDSCs-mediated immunosuppression is unclear. We have identified a poorly differentiated MDSC subset in breast cancer suppressing T-cell function through signal transducer and activator of transcription (STAT) 3-dependent indoleamine 2,3 dioxygenase (IDO) up-regulation. Here we investigated the mechanisms underlying aberrant expression of IDO in MDSCs. MDSCs were induced by co-culturing human CD33+ myeloid progenitors with MDA-MB-231 breast cancer cells. Increased STAT3 activation in MDSCs was correlated with activation of the noncanonical nuclear factor-κB (NF-κB) pathway, including increased NF-κB-inducing kinase (NIK) protein level, phosphorylation of cytoplasmic inhibitor of NF-κB kinase (IKK) α and p100, and RelB-p52 nuclear translocation. Blocking STAT3 activation with the small molecule inhibitor JSI-124 significantly inhibited the accumulation of NIK and IDO expression in MDSCs. Knock-down of NIK in MDSCs suppressed IDO expression, but not STAT3 activation. RelB-p52 dimers were found to directly bind to the IDO promoter, leading to IDO expression in MDSCs. IL-6 was found to stimulate STAT3-dependent, NF-κB-mediated IDO up-regulation in MDSCs. Furthermore, significant positive correlation between the numbers of pSTAT3+ MDSCs, IDO+ MDSCs, and NIK+ MDSCs was observed in human breast cancers. These results demonstrate a STAT3-NF-κB-IDO pathway in breast cancer-derived MDSCs, which provides insight into understanding immunosuppressive mechanisms of MDSCs in breast cancer. Citation Format: Jinpu Yu, Yue Wang, Hui Li, Xiubao Ren. Noncanonical NF-κB activation mediates STAT3-stimulated IDO up-regulation in myeloid-derived suppressor cells in breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2353. doi:10.1158/1538-7445.AM2015-2353
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