Suxia Liu

The TIPE (TNFAIP8) family in inflammation, immunity, and cancer.

Tumor necrosis factor (TNF)-alpha-induced protein 8 (TNFAIP8 or TIPE) family are recently identified proteins which are important for maintaining immune homeostasis. The mammalian TNFAIP8 family consists of four members: TNFAIP8, the first identified member of this family, TNFAIP8L1 (TNF-alpha-induced protein 8-like 1, TIPE1), TIPE2, and TIPE3, which share high degrees of sequence homology and involve in proliferation, inflammation, and cell death. Among the members, TNFAIP8 is considered to be associated with carcinogenesis, TIPE2 is an essential negative regulator of both innate and adaptive immunity and the depletion of TIPE2 would cause serve inflammatory disease. Whereas, little is known about TIPE1 and TIPE3.

Roles of TIPE2 in hepatitis B virus-induced hepatic inflammation in humans and mice.

Hepatitis B virus (HBV)-induced hepatic inflammation afflicts hundreds of millions of people worldwide and is a leading cause of hepatic cancer. While the deleterious effect of the chronic hepatitis is well recognized, the molecular mechanisms underlying the pathogenesis of HBV-induced hepatic inflammation are not well understood. We report here that the tumor necrosis factor-alpha-induced protein-8 like-2 (TIPE2 or TNFAIP8L2), a newly identified regulator of immune receptor signaling, plays an important role in controlling HBV-induced hepatitis. Patients with chronic hepatitis B had significantly reduced levels of TIPE2 expression in their peripheral blood mononuclear cells (PBMCs) as compared to healthy individuals. The TIPE2 expression negatively correlated with the blood levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and total bilirubin (Tbil) as well as the HBV load of the patients. Importantly, using a murine model of HBV-induced hepatitis, we found that TIPE2-deficient mice developed significantly more severe hepatic inflammation than wild type mice. These results indicate that TIPE2 plays an important role in taming HBV-induced hepatic inflammation.

Expression of Human TIM‐1 and TIM‐3 on Lymphocytes from Systemic Lupus Erythematosus Patients

The T‐cell immunoglobulin‐ and mucin‐domain‐containing molecules (TIMs) comprise a new family of cell surface molecules expressed on T cells. TIM‐3 is expressed on T helper type 1 (Th1) cells and implicated in the pathogenesis of Th1‐driven auto‐ and allo‐immune diseases. TIM‐1 is suggested to act as a co‐stimulatory molecule for all T cells, but with potentially stronger effects on Th2 than Th1 cells and is associated with Th2‐related immune diseases. However, the TIM molecules have not been investigated in the systemic lupus erythematosus (SLE). In this study, we examined the expression of TIM‐1 and TIM‐3 on peripheral blood mononuclear cells from SLE patients using quantitative real‐time RT‐PCR. An increased TIM‐1 expression was detected in SLE patients, which correlates with interleukin‐10 expression. We also found that there was a significant increase in the expression of TIM‐1 in SLE patients with quite active disease (SLE disease activity index > 6), indicating that TIM‐1 expression might be related to active clinical phases. In contrast, TIM‐3 expression remained normal in SLE patients with low statistical power (34.89%). However, the expression of TIM‐3 ligand, galectin‐9 increased in SLE patients indicating an enhanced engagement of TIM‐3 with its ligand in SLE, which may result in a decreased regulatory T‐cell function as shown by the decreased expression of FoxP3 and TGF‐β1 in SLE. These data suggest that TIM‐1 and TIM‐3/TIM‐3L are involved in the pathogenesis of SLE.

Tissue-specific expression of TIPE2 provides insights into its function

Tumor necrosis factor-alpha-induced protein-8 like-2 (TNFAIP8L2, TIPE2) is a newly discovered negative regulator of innate immunity and cellular immunity. TIPE2 deficiency in mice causes fetal inflammatory diseases and TIPE2 downregulation in humans is associated with systemic autoimmunity. However, TIPE2 deficiency leads to a selective defect in humoral immunity. Due to the lack of a suitable antibody, the nature of cells and tissues that express TIPE2 protein has not been determined. In this study, we generated a highly specific antibody to TIPE2 and examined TIPE2 expression in various murine tissues by immunohistochemistry and RT-PCR. We found that TIPE2 was a cytoplasmic protein expressed preferentially in lymphoid tissues and a small group of non-lymphoid tissues. Within the lymphoid compartment, T cells appear to express high level of TIPE2 protein, while B cells and B cell zones of lymphoid organs were devoid of TIPE2. Within most of the non-lymphoid tissues, TIPE2 was not detected. However, several endocrine tissues and skeletal muscle expressed detectable TIPE2 protein and mRNA. Furthermore, high levels of TIPE2 were detected in monocyte/macrophage derived cell lines and ovarian adenocarcinoma cells, but not detectable or weakly expressed in most human carcinoma cell lines. These results indicate that TIPE2 may perform tissue-specific functions in both lymphoid and non-lymphoid compartments. They may also explain why TIPE2 deficiency enhanced cellular but not humoral immunity.

TIPE2, a novel regulator of immunity, protects against experimental stroke

Background: TIPE2, a newly identified protein, is essential for maintaining immune homeostasis. Results: Genetic ablation of the Tipe2 gene significantly increased the cerebral volume of infarction and neurological dysfunction in experimental stroke. Conclusion: TIPE2 is involved in the pathogenesis of stroke. Significance: TIPE2 plays an essential role in a signal transduction pathway that links the inflammatory immune response to specific conditions after cerebral ischemia. The inflammatory responses accompanying stroke are recognized to contribute to secondary ischemic injury. TIPE2 is a very recently identified negative regulator of inflammation that maintains immune homeostasis. However, it is unknown whether TIPE2 is expressed in the brain and contributes to the regulation of cerebral diseases. In this study, we explored the potential roles of TIPE2 in cerebral ischemia/reperfusion injury. TIPE2−/− mice were used to assess whether TIPE2 provides neuroprotection following cerebral ischemia/reperfusion induced by middle cerebral artery occlusion (MCAO), and in vitro primary cerebral cell cultures were used to investigate the expression and regulation of TIPE2. Our results show that genetic ablation of the Tipe2 gene significantly increased the cerebral volume of infarction and neurological dysfunction in mice subjected to MCAO. Flow cytometric analysis revealed more infiltrating macrophages, neutrophils, and lymphocytes in the ischemic hemisphere of TIPE2−/− mice. The responses to inflammatory cytokines and chemokines were significantly increased in TIPE2−/− mouse brain after MCAO. We further observed that TIPE2 was highly induced in WT mice after cerebral ischemia and was expressed mainly in microglia/macrophages, but not in neurons and astrocytes. Finally, we found that regulation of TIPE2 expression was associated with NADPH oxidase activity. These findings demonstrate, for the first time, that TIPE2 is involved in the pathogenesis of stroke and suggest that TIPE2 plays an essential role in a signal transduction pathway that links the inflammatory immune response to specific conditions after cerebral ischemia. Targeting TIPE2 may be a new therapeutic strategy for stroke treatment.

Acquisition of anoikis resistance reveals a synoikis-like survival style in BEL7402 hepatoma cells.

Resistance to anoikis is a hallmark of human malignancies. Our results showed that hepatoma cells resisted anoikis by non-proliferation, non-apoptosis and cell cycle arrest which were termed synoikis-like. These synoikis-like cells are more resistant to extracellular stimuli and could spontaneously attach and proliferate again under suitable conditions, which indicate a reversible property of these cells. Microarray expression profile reveals the change of molecules involved in the synoikis-like hepatoma cells and our data indicated that ANGPTL4 contributed to anoikis resistance of hepatoma cells. These results demonstrated that hepatoma cells might resist anoikis through a synoikis-like survival style, which may facilitate tumor metastasis.

TIPE2 negatively regulates inflammation by switching arginine metabolism from nitric oxide synthase to arginase.

TIPE2, the tumor necrosis factor (TNF)-alpha-induced protein 8-like 2 (TNFAIP8L2), plays an essential role in maintaining immune homeostasis. It is highly expressed in macrophages and negatively regulates inflammation through inhibiting Toll-like receptor signaling. In this paper, we utilized RAW264.7 cells stably transfected with a TIPE2 expression plasmid, as well as TIPE2-deficient macrophages to study the roles of TIPE2 in LPS-induced nitric oxide (NO) and urea production. The results showed that TIPE2-deficiency significantly upregulated the levels of iNOS expression and NO production in LPS-stimulated macrophages, but decreased mRNA levels of arginase I and urea production. However, TIPE2 overexpression in macrophages was capable of downregulating protein levels of LPS-induced iNOS and NO, but generated greater levels of arginase I and urea production. Furthermore, TIPE2−/− mice had higher iNOS protein levels in lung and liver and higher plasma NO concentrations, but lower levels of liver arginase I compared to LPS-treated WT controls. Interestingly, significant increases in IκB degradation and phosphorylation of JNK, p38, and IκB were observed in TIPE2-deficient macrophages following LPS challenge. These results strongly suggest that TIPE2 plays an important role in shifting L-arginase metabolism from production of NO to urea, during host inflammatory response.

Enhanced Atherosclerosis in TIPE2-Deficient Mice Is Associated with Increased Macrophage Responses to Oxidized Low-Density Lipoprotein

Atherosclerosis has been widely recognized as an inflammatory disease of the arterial wall in which macrophages play a major role. Yet, how macrophage-mediated pathology is regulated during atherosclerosis is poorly understood. TNF-α–induced protein 8–like 2 (TIPE2, also known as TNFAIP8L2) is highly expressed in resting macrophages and can negatively regulate inflammation through inhibiting immune receptor signaling. We report in this article that TIPE2 plays a crucial atheroprotective role likely by regulating macrophage responses to oxidized low-density lipoprotein (ox-LDL). TIPE2-deficient macrophages treated with ox-LDL produced more oxidative stress and proinflammatory cytokines, and exhibited heightened activation of the JNK, NF-κB, and p38 signaling pathways. As a consequence, TIPE2 deficiency in bone marrow–derived cells exacerbated atherosclerosis development in Ldlr−/− mice fed a high-fat diet. Importantly, ox-LDL markedly downregulated TIPE2 mRNA and protein levels in macrophages, suggesting that ox-LDL mediates atherosclerosis by TIPE2 inhibition. These results indicate that TIPE2 is a new inhibitor of atherosclerosis and a potential drug target for treating the disease.

TIPE2 deficiency accelerates neointima formation by downregulating smooth muscle cell differentiation.

Phenotypic switching of vascular smooth muscle cells (VSMCs) is known to play a key role in the development of atherosclerosis. However, the mechanisms that mediate VSMC phenotypic switching are unclear. We report here that TIPE2, the tumor necrosis factor (TNF) α-induced protein 8-like 2 (TNFAIP8L2), plays an atheroprotective role by regulating phenotypic switching of VSMCs in response to oxidized low-density lipoprotein (ox-LDL) stimuli. TIPE2-deficient VSMCs treated with ox-LDL expressed lower levels of contractile proteins such as SMαA, SM-MHC and calponin, whereas the proliferation, migration and the synthetic capacity for growth factors and cytokines were increased remarkably. Furthermore, TIPE2 inhibited VSMCs proliferation by preventing G1/S phase transition. Interestingly, these effects of TIPE2 on VSMCs were dependent on P38 and ERK1/2 kinase signals. As a result, neointima formation was accelerated in the carotid arteries of TIPE2-deficient mice. These results indicate that TIPE2 is a potential inhibitor of atherosclerosis.

The expression of TIPE1 in murine tissues and human cell lines

Members of the tumor necrosis factor-alpha-induced protein-8 (TNFAIP8 or TIPE) family play important roles in immune homeostasis and cancer. TIPE1 (TNFAIP8-like 1) is a new member of the TIPE family that may regulate cell death. However, due to the lack of a suitable antibody, the nature of cells and tissues that express TIPE1 protein has not been determined. In this study, we generated a highly specific antibody to TIPE1 and examined TIPE1 expression in various murine tissues and human cell lines by immunohistochemistry, reverse transcription real-time PCR, and Western blot. We found that TIPE1 protein was detected in a wide variety of tissues in C57BL/6 mice, such as neurons in brain, hepatocytes, germ cells of female and male reproductive organs, muscular tissues, and a variety of cells of the epithelial origin, particularly those with secretory functions. TIPE1 protein was not expressed in mature T or B lymphocytes, but detectable in human B lymphoblast cell line HMy2.CIR and murine T cell line EL4. Furthermore, high levels of TIPE1 mRNA were detected in most human carcinoma cell lines, especially in cells transformed with viral genomes. These results indicate that TIPE1 may perform functions in cell secretion and carcinogenesis, but not in immunity.