IFN regulatory factor 8 sensitizes soft tissue sarcoma cells to death receptor-initiated apoptosis via repression of FLICE-like protein expression

Dafeng Yang, Suizhao Wang, Craig Brooks, Zheng Dong, Patricia V. Schoenlein, Vijay Kumar, Xinshou Ouyang, Huabao Xiong, Guy Lahat, Andrea Hayes-Jordan, Alexander Lazar, Raphael Pollock, Dina Lev, Kebin Liu*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


IFN regulatory factor 8 (IRF8) has been shown to suppress tumor development at least partly through regulating apoptosis of tumor cells; however, the molecular mechanisms underlying IRF8 regulation of apoptosis are still not fully understood. Here, we showed that disrupting IRF8 function resulted in inhibition of cytochrome c release, caspase-9 and caspase-3 activation, and poly(ADP-ribose) polymerase cleavage in soft tissue sarcoma (STS) cells. Inhibition of the mitochondrion-dependent apoptosis signaling cascade is apparently due to blockage of caspase-8 and Bid activation. Analysis of signaling events upstream of caspase-8 revealed that disrupting IRF8 function dramatically increases FLIP mRNA stability, resulting in increased IRF8 protein level. Furthermore, primary myeloid cells isolated from IRF8-null mice also exhibited increased FLIP protein level, suggesting that IRF8 might be a general repressor of FLIP. Nuclear IRF8 protein was absent in 92% (55 of 60) of human STS specimens, and 99% (59 of 60) of human STS specimens exhibited FLIP expression, suggesting that the nuclear IRF8 protein level is inversely correlated with FLIP level in vivo. Silencing FLIP expression significantly increased human sarcoma cells to both FasL-induced and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, and ectopic expression of IRF8 also significantly increased the sensitivity of these human sarcoma cells to FasL- and TRAIL-induced apoptosis. Taken together, our data suggest that IRF8 mediates FLIP expression level to regulate apoptosis and targeting IRF8 expression is a potentially effective therapeutic strategy to sensitize apoptosis-resistant human STS to apoptosis, thereby possibly overcoming chemoresistance of STS, currently a major obstacle in human STS therapy.

Original languageEnglish
Pages (from-to)1080-1088
Number of pages9
JournalCancer Research
Issue number3
StatePublished - 1 Feb 2009
Externally publishedYes


FundersFunder number
National Cancer InstituteR01CA133085


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