Mutations in the zinc finger domain of IKK gamma block the activation of NF-kappa B and the induction of IL-2 in stimulated T lymphocytes

Targeting NF-κB pathway for the therapy of diseases: mechanism and clinical study

NF-κB pathway consists of canonical and non-canonical pathways. The canonical NF-κB is activated by various stimuli, transducing a quick but transient transcriptional activity, to regulate the expression of various proinflammatory genes and also serve as the critical mediator for inflammatory response. Meanwhile, the activation of the non-canonical NF-κB pathway occurs through a handful of TNF receptor superfamily members. Since the activation of this pathway involves protein synthesis, the kinetics of non-canonical NF-κB activation is slow but persistent, in concordance with its biological functions in the development of immune cell and lymphoid organ, immune homeostasis and immune response. The activation of the canonical and non-canonical NF-κB pathway is tightly controlled, highlighting the vital roles of ubiquitination in these pathways. Emerging studies indicate that dysregulated NF-κB activity causes inflammation-related diseases as well as cancers, and NF-κB has been long proposed as the potential target for therapy of diseases. This review attempts to summarize our current knowledge and updates on the mechanisms of NF-κB pathway regulation and the potential therapeutic application of inhibition of NF-κB signaling in cancer and inflammatory diseases.

Cyclosporine nanomicelle eye drop: a novel medication for corneal graft transplantation treatment

Corneal transplantation has been used to treat severe eye disease for decades, but the therapeutic effect of the operation is highly compromised by immunological allograft rejection. To improve the success rate of corneal transplantation, we studied the protective effects of cyclosporine nanomicelle eye drops (CNED) on immune rejection after high-risk corneal transplantation and its underlying mechanisms. The therapeutic effects against immune rejection of both conventional cyclosporine eye drop (CCED) and CNED in different concentrations were assessed and compared using animal models of corneal transplantation. In addition, the expression of nuclear factor-κ-gene binding (NF-κB) as well as its target intracellular adhesion molecule 1 (ICAM-1) in the corneal samples obtained from recipients treated with either CCED or CNED was also screened. The results showed that the CNED displayed significantly better effects at suppressing the immune response induced by corneal transplantation compared to CCED. CNED also significantly down-regulated the NF-κB and ICAM-1 expressions, indicating NF-κB might play an important role in the initiation of an immune response against the allograft. Our study demonstrates CNED may suppress the NF-κB pathway to attenuate the immune response, which highlights the possible therapeutic applications of cyclosporine nanomicelle eye drops in corneal transplantation.

Two-sided ubiquitin binding of NF-κB essential modulator (NEMO) zinc finger unveiled by a mutation associated with anhidrotic ectodermal dysplasia with immunodeficiency syndrome

Hypomorphic mutations in the X-linked human NEMO gene result in various forms of anhidrotic ectodermal dysplasia with immunodeficiency. NEMO function is mediated by two distal ubiquitin binding domains located in the regulatory C-terminal domain of the protein: the coiled-coil 2-leucine zipper (CC2-LZ) domain and the zinc finger (ZF) domain. Here, we investigated the effect of the D406V mutation found in the NEMO ZF of an ectodermal dysplasia with immunodeficiency patients. This point mutation does not impair the folding of NEMO ZF or mono-ubiquitin binding but is sufficient to alter NEMO function, as NEMO-deficient fibroblasts and Jurkat T lymphocytes reconstituted with full-length D406V NEMO lead to partial and strong defects in NF-κB activation, respectively. To further characterize the ubiquitin binding properties of NEMO ZF, we employed di-ubiquitin (di-Ub) chains composed of several different linkages (Lys-48, Lys-63, and linear (Met-1-linked)). We showed that the pathogenic mutation preferentially impairs the interaction with Lys-63 and Met-1-linked di-Ub, which correlates with its ubiquitin binding defect in vivo. Furthermore, sedimentation velocity and gel filtration showed that NEMO ZF, like other NEMO related-ZFs, binds mono-Ub and di-Ub with distinct stoichiometries, indicating the presence of a new Ub site within the NEMO ZF. Extensive mutagenesis was then performed on NEMO ZF and characterization of mutants allowed the proposal of a structural model of NEMO ZF in interaction with a Lys-63 di-Ub chain.

NEMO mutation as a cause of familial occurrence of Behçet's disease in female patients

Behçet's disease is a chronic, relapsing, multisystem inflammatory disease of unknown etiology. Nuclear factor κB (NF-κB) essential modulator (NEMO) that is required for the activation of NF-κB plays an important role in inflammation. To investigate the role of NEMO in the pathogenesis of Behçet's disease, we analyzed NEMO gene and its expression pattern in tissues in a family with Behçet's disease. We found a heterozygous mutation (1217A> T, D406V) in a 6-year-old girl and her mother. Skewed X-chromosome inactivation was not observed in the peripheral blood mononuclear cells as well as in oral and intestinal mucosa of the patients. Accordingly, there was a significant proportion of peripheral blood monocytes that did not produce sufficient intracellular tumor necrosis factor-α with the stimulation of lipopolysaccharide. Heterozygous NEMO mutation is a cause of familial occurrence of Behçet's disease in female patients.

The zinc finger domain of IKKγ (NEMO) protein in health and disease

Inhibitor of κB kinase (IKK) gamma (IKKγ), also known as nuclear factor κB (NF-κB) essential modulator (NEMO), is a component of the IKK complex that is essential for the activation of the NF-κB pathway. The NF-κB pathway plays a major role in the regulation of the expression of genes that are involved in immune response, inflammation, cell adhesion, cell survival and development. As part of the IKK complex, IKKγ plays a regulatory role by linking the complex to upstream signalling molecules. IKKγ contains two coiled-coil regions, a leucine zipper domain and a highly conserved zinc finger domain. Mutations affecting IKKγ have been associated with X-linked hypohidrotic ectodermal dysplasia with immune deficiency (HED-ID), with the majority of these mutations affecting the C-terminal region of the protein where the zinc finger is located. The zinc finger of IKKγ is needed for NF-κB activation in a cell- and stimulus-specific manner. The major mechanism by which the zinc finger plays this role appears to be the recognition of polyubiquitinated upstream signalling intermediates. This assertion reinforces the current notion that ubiquitination plays a major role in mediating protein–protein interactions in the NF-κB signalling pathway. Because the zinc finger domain of IKKγ is very likely involved in mediating interactions with ubiquitinated proteins, investigations that look for upstream activators or inhibitors of the IKK complex that bind to and interact with the zinc finger of IKKγ are required to gain a better insight into the exact roles of this domain and into the pathogenesis of HED-ID.

Zinc in innate and adaptive tumor immunity

Zinc is important. It is the second most abundant trace metal with 2-4 grams in humans. It is an essential trace element, critical for cell growth, development and differentiation, DNA synthesis, RNA transcription, cell division, and cell activation. Zinc deficiency has adverse consequences during embryogenesis and early childhood development, particularly on immune functioning. It is essential in members of all enzyme classes, including over 300 signaling molecules and transcription factors. Free zinc in immune and tumor cells is regulated by 14 distinct zinc importers (ZIP) and transporters (ZNT1-8). Zinc depletion induces cell death via apoptosis (or necrosis if apoptotic pathways are blocked) while sufficient zinc levels allows maintenance of autophagy. Cancer cells have upregulated zinc importers, and frequently increased zinc levels, which allow them to survive. Based on this novel synthesis, approaches which locally regulate zinc levels to promote survival of immune cells and/or induce tumor apoptosis are in order.

Vitamin D does not modulate NF-kappaB activity in Jurkat T cells

The active form of vitamin D, 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)], has been reported to influence the functioning of the immune system by targeting the activities of cellular signaling pathways, in addition to its direct genomic effects. One of the signaling pathways reported to be targeted by vitamin D is the NF-kappaB pathway, which is highly active in most immune cell types, including T cells. However, the effects of vitamin D on the NF-kappaB pathway in T cells are not fully understood. Therefore, we examined the effects of 1alpha,25(OH)(2)D(3) on the NF-kappaB pathway in the Jurkat cell line, a human T cell line that constitutively expresses endogenous vitamin D receptor. We found that 1alpha,25(OH)(2)D(3) does not inhibit the induction of IkappaBalpha degradation and the expression of an NF-kappaB-dependent reporter gene in Jurkat cells following treatment with PMA/ionomycin. Also, 1alpha,25(OH)(2)D(3) did not suppress the activation of NF-kappaB by TNFalpha or PHA. Furthermore, we demonstrate that 1alpha,25(OH)(2)D(3) does not block the induction of CD69, which is an NF-kappaB target gene and an early T cell activation marker. Therefore, we conclude that vitamin D does not modulate the activity of the NF-kappaB pathway in Jurkat cells.