NF-κB functions as a molecular link between tumor cells and Th1/Tc1 T cells in the tumor microenvironment to exert radiation-mediated tumor suppression
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Priscilla S. Simon1,4,6, Kankana Bardhan1, May R. Chen1, Amy V. Paschall1,4,6, Chunwan Lu1,6, Roni J. Bollag4, Feng-Chong Kong2,4, JianYue Jin2,4, Feng-Ming Kong2,4, Jennifer L. Waller3, Raphael E. Pollock5 and Kebin Liu1,4,6
1 Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA, USA
2 Radiation Oncology, Medical College of Georgia, Augusta, GA, USA
3 Biostatistics and Epidemiology, Medical College of Georgia, Augusta, GA, USA
4 Cancer Center, Georgia Regents University, Augusta, GA, USA
5 Ohio State University Medical Center, Columbia, OH, USA
6 Charlie Norwood VA Medical Center, Augusta, GA, USA
Kebin Liu, email:
Keywords: NF-κB, radiation, TNFα, cytotoxic T lymphocyte, Smac mimetic
Received: December 28, 2015 Accepted: February 28, 2016 Published: March 21, 2016
Radiation modulates both tumor cells and immune cells in the tumor microenvironment to exert its anti-tumor activity; however, the molecular connection between tumor cells and immune cells that mediates radiation-exerted tumor suppression activity in the tumor microenvironment is largely unknown. We report here that radiation induces rapid activation of the p65/p50 and p50/p50 NF-κB complexes in human soft tissue sarcoma (STS) cells. Radiation-activated p65/p50 and p50/p50 bind to the TNFα promoter to activate its transcription in STS cells. Radiation-induced TNFα induces tumor cell death in an autocrine manner. A sublethal dose of Smac mimetic BV6 induces cIAP1 and cIAP2 degradation to increase tumor cell sensitivity to radiation-induced cell death in vitro and to enhance radiation-mediated suppression of STS xenografts in vivo. Inhibition of caspases, RIP1, or RIP3 blocks radiation/TNFα-induced cell death, whereas inhibition of RIP1 blocks TNFα-induced caspase activation, suggesting that caspases and RIP1 act sequentially to mediate the non-compensatory cell death pathways. Furthermore, we determined in a syngeneic sarcoma mouse model that radiation up-regulates IRF3, IFNβ, and the T cell chemokines CCL2 and CCL5 in the tumor microenvironment, which are associated with activation and increased infiltration of Th1/Tc1 T cells in the tumor microenvironment. Moreover, tumor-infiltrating T cells are in their active form since both the perforin and FasL pathways are activated in irradiated tumor tissues. Consequently, combined BV6 and radiation completely suppressed tumor growth in vivo. Therefore, radiation-induced NF-κB functions as a molecular link between tumor cells and immune cells in the tumor microenvironment for radiation-mediated tumor suppression.
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