Novel transcript variants of TRAIL show different activities in activation of NF-κB and apoptosis

Identification, characterization and bioactivity of tumor necrosis factor (TNF)-related apoptosis-inducing ligand from Equus caballus

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily and plays multifunctional roles in the immune system. In the present study, a homolog of TRAIL from the Mongolian horse (named ecTRAIL) was identified and characterized. The 870-bp open reading frame encodes a polypeptide of 289 amino acid residues with a predicted molecular weight of 33.47 kDa and pI of 8.47. The genomic structure of ecTRAIL shares a five-exon/six-intron arrangement similar to its orthologs. Multiple alignments show that ecTRAIL is a type II transmembrane protein with a typical transmembrane region, three conserved cysteine residues (Cys56, Cys77, Cys238) and a TNF family signature sequence ([LV]-x-[LIVM]-x(3)-G-[LIVMF]-Y-[LIVMFY](2)-x(2)-[QEKHL]-[LIVMGT]-x-[LIVMFY]). Three-dimensional structure prediction based on the same template revealed that the positional arrangement of the key amino acid residues, Cys238 and Cys230 in ecTRAIL and human TRAIL, respectively, is significantly conserved. Evolutionary analysis suggests that ecTRAIL is most closely related to its ortholog from pigs, with an identity of 83.99%. The solubilizing small ubiquitin-related modifier (SUMO) tag fused recombinant protein SUMO-ecsTRAIL was successfully expressed in E. coli and exhibited binding activity and cytotoxicity to HeLa cells in a cross-species manner in vitro. These results provide a better understanding of TRAILs in mammals and indicate that ecTRAIL may play an important role in the immune response in horses.

The role of the osteoprotegerin/tumor necrosis factor related apoptosis-inducing ligand axis in the pathogenesis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a fatal condition driven by a progressive remodelling of the small pulmonary arteries through sustained vasoconstriction, and vascular cell proliferation. This process causes a substantial reduction in luminal area increasing pulmonary vascular resistance and blood pressure leading to right heart failure. Current medical therapies can alleviate some symptoms and reduce the vasoconstrictive aspects of disease but new treatments are required that target the vascular cell proliferation if we are to develop new therapies. Expression of the tumour necrosis factor related apoptosis-inducing ligand (TRAIL) and osteoprotegerin (OPG) proteins are increased in IPAH. Specifically OPG is increased within the serum of patients with idiopathic pulmonary arterial hypertension (IPAH) and has prognostic utility, and both OPG and TRAIL are increased within pulmonary vascular lesions of patients with IPAH, and are mitogens for pulmonary artery smooth muscle cells in vitro. We have demonstrated that genetic deletion, or antibody blockade of TRAIL prevents, and critically reverses the development of PAH in multiple rodent models. The role OPG plays in this process both through interacting with TRAIL, and indirectly through other mechanisms is currently unclear these but data highlight the critical importance of this pathway in PAH pathogenesis, and its potential for future therapies.

TRAIL deficiency contributes to diabetic nephropathy in fat-fed ApoE-/- mice

Background

We recently demonstrated that TNF-related apoptosis-inducing ligand (TRAIL) is protective of diet-induced diabetes in mice. While TRAIL has been implicated in chronic kidney disease, its role in vivo in diabetic nephropathy is not clear. The present study investigated the role of TRAIL in the pathogenesis of diabetic nephropathy using TRAIL^-/-ApoE^-/- mice.

Methods

TRAIL^-/-ApoE^-/- and ApoE^-/- mice were fed a high fat diet for 20 w. Plasma glucose and insulin levels were assessed over 0, 5, 8 and 20 w. At 20 w, markers of kidney function including creatinine, phosphate, calcium and cystatin C were measured. Changes in mRNA expression of MMPs, TIMP-1, IL-1β and IL-18 were assessed in the kidney. Functional and histological changes in kidneys were examined. Glucose and insulin tolerance tests were performed.

Results

TRAIL^-/-ApoE^-/- mice had significantly increased urine protein, urine protein:creatinine ratio, plasma phosphorous, and plasma cystatin C, with accelerated nephropathy. Histologically, increased extracellular matrix, mesangial expansion and mesangial cell proliferation in the glomeruli were observed. Moreover, TRAIL^-/-ApoE^-/- kidneys displayed loss of the brush border and disorganisation of tubular epithelium, with increased fibrosis. TRAIL-deficient kidneys also had increased expression of MMPs, TIMP-1, PAI-1, IL-1β and IL-18, markers of renal injury and inflammation. Compared with ApoE^-/- mice, TRAIL^-/-ApoE^-/- mice displayed insulin resistance and type-2 diabetic features with reduced renal insulin-receptor expression.

Conclusions

Here, we show that TRAIL-deficiency in ApoE^-/- mice exacerbates nephropathy and insulin resistance. Understanding TRAIL signalling in kidney disease and diabetes, may therefore lead to novel strategies for the treatment of diabetic nephropathy.

On the TRAIL of obesity and diabetes

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been extensively studied for its preferential ability to induce apoptosis of cancer cells. Beyond the cytotoxic capacity of TRAIL, new physiological and pathological roles for TRAIL have been identified, and there is now growing evidence supporting its involvement in the development of obesity and diabetes. This review summarizes the most recent findings associating TRAIL with obesity and diabetes in both humans and experimental settings. We also present and discuss some of the reported controversies behind TRAIL signaling and function. Understanding TRAIL mechanism(s) in vivo and its involvement in disease may lead to novel strategies to combat the growing pandemic of obesity and diabetes worldwide.

Transcriptional regulation of tumour necrosis factor-related apoptosis-inducing ligand

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) has dual functions mediating both apoptosis and survival of cells. This review focusses on the current regulatory factors that control TRAIL transcription. Here, we also highlight the role of distinct transcription factors that co-operate and regulate TRAIL in different pathological states. A better understanding of the molecular signalling pathways of TRAIL-induced cell death and survival in disease may lead to more sophisticated technologies for novel therapeutic targets.

Inhibition of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) reverses experimental pulmonary hypertension

Genetic deletion of TRAIL or antibody blockade prevents the development of pulmonary arterial hypertension and can reverse vascular remodeling in established disease.

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by the progressive narrowing and occlusion of small pulmonary arteries. Current therapies fail to fully reverse this vascular remodeling. Identifying key pathways in disease pathogenesis is therefore required for the development of new-targeted therapeutics. We have previously reported tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) immunoreactivity within pulmonary vascular lesions from patients with idiopathic PAH and animal models. Because TRAIL can induce both endothelial cell apoptosis and smooth muscle cell proliferation in the systemic circulation, we hypothesized that TRAIL is an important mediator in the pathogenesis of PAH. We demonstrate for the first time that TRAIL is a potent stimulus for pulmonary vascular remodeling in human cells and rodent models. Furthermore, antibody blockade or genetic deletion of TRAIL prevents the development of PAH in three independent rodent models. Finally, anti-TRAIL antibody treatment of rodents with established PAH reverses pulmonary vascular remodeling by reducing proliferation and inducing apoptosis, improves hemodynamic indices, and significantly increases survival. These preclinical investigations are the first to demonstrate the importance of TRAIL in PAH pathogenesis and highlight its potential as a novel therapeutic target to direct future translational therapies.

Regulation of the human TRAIL gene

TRAIL is a member of the TNF superfamily that induces tumor-selective cell death by engaging the pro-apoptotic death receptors DR4 and DR5. The antitumor potential of the TRAIL pathway has been targeted by several therapeutic approaches including recombinant TRAIL and TRAIL-receptor agonist antibodies among others. Interest in sensitizing tumor cells to TRAIL-mediated apoptosis has driven investigations of TRAIL-receptor gene regulation, though regulation of the TRAIL gene has been less studied. Physiologically, TRAIL serves as a pro-apoptotic effector molecule in the immune surveillance of cancer that is conditionally expressed by immune cells upon stimulation via an interferon-response element that was identified in early studies of the TRAIL gene promoter. Here, we map the TRAIL gene promoter and review studies of TRAIL gene regulation that involve several modalities of gene regulation including transcription factors, epigenetics, single-nucleotide polymorphisms and functionally distinct isoforms.