Pathophysiological Role of TIFA in the Regulation of Inflammation

Nuclear factor-κB (NF-κB) controls various aspects of immune responses and regulates cell survival, proliferation, and differentiation. In light of its functional diversity, dysregulation of NF-κB has been linked to a variety of diseases. Our previous study demonstrated that Thr9 phosphorylation-dependent oligomerization of TRAF-interacting protein with a FHA domain (TIFA) triggers the activation of NF-κB. In addition, we investigated the involvement of the kinase in PI3K-Akt signaling pathway is response for the Thr9 phosphorylation. In this study, we identified that Aurora A is an essential kinase for the Thr9 phosphorylation of TIFA, and that TIFA functionally mediates the Aurora A-driven NF-κB survival pathway in acute myeloid leukemia (AML). We found that TIFA protein is overexpressed concurrently with Aurora A and NF-κB signaling factors in de novo AML patients relative to healthy individuals, which is also correlated with the poor prognosis of patients. In addition, TIFA inhibition perturbs leukemic cytokine secretion, significantly enhances chemotoxicity, and potentiates the clearance of leukemic myeloblasts in a xenograft model. These results collectively demonstrate that TIFA may support AML progression, and that targeting TIFA can enhance therapeutic efficacies in the treatment of AML. In accord, we showed that TIFA protein is also overexpressed in hepatocellular carcinoma (HCC) lines and patient cells relative to normal ones. Higher TIFA expression showed significantly shorter disease free survival (DFS) than those with lower TIFA expression in HCC patients. This may correlate with TIFA directed epithelial-mesenchymal transition (EMT) signaling as the molecular mechanism underlying tumor invasion and metastasis in HCC. We also found that silencing of TIFA specifically reduces viability, enhances the chemotoxicity, and retards the migration and invasion abilities of HCC lines. These results may propose TIFA as a novel therapeutic target in the treatment of HCC. On the other hand, toll-like receptor-mediated NF-κB activation is a major innate immune response in vascular endothelial cells (ECs) in response to pro-oxidative and inflammatory stimuli. We identified TIFA as a novel regulator of both priming (Signal 1) and activating (Signal 2) signals of NOD-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome in ECs. Oxidative and inflammatory stresses such as atheroprone flow and oxidized-LDL induce and activate TIFA. Induction of TIFA is required for the transcriptional activation of inflammatory cytokines and inflammasome components which is considered Signal 1. Additionally, Akt-enhanced phosphorylation of TIFA Thr9 promotes the assembly of NLRP3 inflammasome which is considered Signal 2 of inflammasome activation. The results suggest that TIFA is a crucial mediator in the endothelial innate immune response by potentiating and amplifying NLRP3 inflammasome via augmenting Signal 1 and 2. This newly defined mechanism has important translational implications, particularly toward the inflammatory responses in mammalian cells. The overall results obtained in this study are expected to not only decipher the detailed molecular mechanism within TNF and NF-κB axis, but also provide a potential therapeutic target in the treatment of immune disorders and cancers.