Shen W, Chang A, Wang J, Zhou W, Gao R, Li J, Xu Y, Luo X, Xiang R, Luo N, Stupack D G
Department of Immunology, School of Medicine, Nankai University, Tianjin, China.
Department of Reproductive Medicine, San Diego School of Medicine, University of California, San Diego, San Diego, CA, USA.
Oncogenesis. 2015 Oct 26;4(10):e173. doi: 10.1038/oncsis.2015.30.
TIFA (TNF receptor associated factor (TRAF)-interacting protein with a Forkhead-associated (FHA) domain), also called T2BP, was first identified using a yeast two-hybrid screening. TIFA contains a FHA domain, which directly binds phosphothreonine and phosphoserine, and a consensus TRAF6-binding motif. TIFA-mediated oligomerization and poly-ubiquitinylation of TRAF6 mediates signaling downstream of the Tumor necrosis factor alpha receptor 1 (TNFaR-I) and interleukin-1/Toll-like receptor 4 (TLR4) pathways. Examining TIFA expression in hepatocellular carcinoma (HCC) tissues microarrays, we noted marked decreases TIFA reactivity in tumor versus control samples. In agreement, we found that HCC cell lines show reduced TIFA expression levels versus normal liver controls. Reconstituting TIFA expression in HCC cell lines promoted two independent apoptosis signaling pathways: the induction of p53 and cell cycle arrest, and the activation of caspase-8 and caspase-3. In contrast, the expression of a non-oligomerizing mutant of TIFA impacted cells minimally, and suppression of TIFA expression protected cells from apoptosis. Mice bearing TIFA overexpression hepatocellular xenografts develop smaller tumors versus TIFA mutant tumors; terminal deoxynucleotidyl transferase dUTP nick end labeling staining demonstrates increased cell apoptosis, and decreased proliferation, reflecting cell cycle arrest. Interestingly, p53 has a greater role in decreased proliferation than cell death, as it appeared dispensable for TIFA-induced cell killing. The findings demonstrate a novel suppressive role of TIFA in HCC progression via promotion of cell death independent of p53.
TIFA（含叉头相关（FHA）结构域的肿瘤坏死因子受体相关因子（TRAF）相互作用蛋白），也称为T2BP，最初是通过酵母双杂交筛选鉴定出来的。TIFA含有一个FHA结构域，可直接结合磷酸苏氨酸和磷酸丝氨酸，以及一个共有TRAF6结合基序。TIFA介导的TRAF6寡聚化和多聚泛素化介导肿瘤坏死因子α受体1（TNFαR - I）和白细胞介素 - 1/ Toll样受体4（TLR4）信号通路的下游信号传导。在肝细胞癌（HCC）组织微阵列中检测TIFA表达时，我们注意到与对照样本相比，肿瘤样本中TIFA反应性显著降低。与此一致的是，我们发现HCC细胞系与正常肝脏对照相比，TIFA表达水平降低。在HCC细胞系中重建TIFA表达可促进两条独立的凋亡信号通路：p53的诱导和细胞周期停滞，以及半胱天冬酶 - 8和半胱天冬酶 - 3的激活。相比之下，TIFA的非寡聚化突变体的表达对细胞影响极小，而抑制TIFA表达可保护细胞免于凋亡。携带TIFA过表达肝细胞异种移植物的小鼠与TIFA突变体肿瘤相比，肿瘤生长较小；末端脱氧核苷酸转移酶dUTP缺口末端标记染色显示细胞凋亡增加，增殖减少，反映细胞周期停滞。有趣的是，p53在增殖减少方面比细胞死亡发挥更大作用，因为它似乎对TIFA诱导的细胞杀伤是可有可无的。这些发现证明了TIFA通过促进独立于p53的细胞死亡在HCC进展中发挥新的抑制作用。
