JAB1 determines the response of rheumatoid arthritis synovial fibroblasts to tumor necrosis factor-alpha

Regulatory mechanisms and therapeutic potential of JAB1 in neurological development and disorders

c-Jun activation domain binding protein-1 (JAB1) is a multifunctional regulator that plays vital roles in diverse cellular processes. It regulates AP-1 transcriptional activity and also acts as the fifth component of the COP9 signalosome complex. While JAB1 is considered an oncoprotein that triggers tumor development, recent studies have shown that it also functions in neurological development and disorders. In this review, we summarize the general features of the JAB1 gene and protein, and present recent updates on the regulation of JAB1 expression. Moreover, we also highlight the functional roles and regulatory mechanisms of JAB1 in neurodevelopmental processes such as neuronal differentiation, synaptic morphogenesis, myelination, and hair cell development and in the pathogenesis of some neurological disorders such as Alzheimer's disease, multiple sclerosis, neuropathic pain, and peripheral nerve injury. Furthermore, current challenges and prospects are discussed, including updates on drug development targeting JAB1.

IKK-Mediated Regulation of the COP9 Signalosome via Phosphorylation of CSN5

The COP9 signalosome (CSN) is an evolutionarily conserved multisubunit protein complex, which controls protein degradation through deneddylation and inactivation of cullin-RING ubiquitin E3 ligases (CRLs). Recently, the CSN complex has been linked to the NF-κB signaling pathway due to its association with the IKK complex. However, how the CSN complex is regulated in this signaling pathway remains unclear. Here, we have carried out biochemical experiments and confirmed the interaction between the CSN and IKK complexes. In addition, we have determined that overexpression of IKKα or IKKβ leads to enhanced phosphorylation of CSN5, the catalytic subunit for CSN deneddylase activity. Mutational analyses have revealed that phosphorylation at serine 201 and threonine 205 of CSN5 impairs CSN-mediated deneddylation activity in vitro. Interestingly, TNF-α treatment not only enhances the interaction between CSN and IKK but also induces an IKK-dependent phosphorylation of CSN5 at serine 201, linking CSN to TNF-α signaling through IKK. Moreover, TNF-α treatment affects the CSN interaction network globally, especially the associations of CSN with the proteasome complex, eukaryotic translation initiation factor complex, and CRL components. Collectively, our results provide new insights into IKK-mediated regulation of CSN associated with the NF-κB signaling pathway.

Redox-sensitive transcription factors play a significant role in the development of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease which is associated with significant morbidity. Redox sensitive transcription factors including NF-κB, HIF, AP-1, and Nrf2 are intimately involved in the pathogenesis of RA. The treatment of this disease is limited by the elusive nature of the pathogenesis of RA. NF-κB is crucial for the maturation of immune cells as well as production of TNFα and MMPs, which escalate RA. HIF is essential for activation of inflammatory cells, angiogenesis and pannus formation in RA. AP-1 regulates cytokine and MMP production as well as synovial hyperplasia which are key processes in RA. Nrf2 is involved with chondrogenesis, osteoblastogenesis, prostaglandin secretion and ROS production in RA. Targeting two or more of these transcription factors may result in increased efficacy than either therapy in isolation. This review will highlight the control specific mediators on these transcription factors, the subsequent effect of these transcription factors once activated, and then mesh this with the pathogenesis of RA. The elucidation of key transcription factor regulation in the pathogenesis of RA may highlight the novel therapy interventions which may prove to have a greater efficacy than those therapies currently available.

1, 25-dihydroxy-vitamin D3 with tumor necrosis factor-alpha protects against rheumatoid arthritis by promoting p53 acetylation-mediated apoptosis via Sirt1 in synoviocytes

Impaired apoptosis of fibroblast-like synoviocytes (FLSs) causes synovial hyperplasia, facilitating destruction of cartilage and bone in rheumatoid arthritis (RA). Tumor necrosis factor (TNF)-α, a dominant inflammatory mediator in RA pathogenesis, promotes progression of RA symptoms. Prevalence of 1, 25-dihydroxy-vitamin D₃ (hereafter termed VD) deficiency is 30-63% in patients with RA. Whether VD leads to apoptosis or enhances TNF-α-mediated apoptosis in FLSs to ameliorate RA is unclear. To determine this, 10-week-old CYP27B1-deficient (CYP27B1^-/-) mice with collagen-induced arthritis (CIA) were intraperitoneally treated with 1 μg/kg VD every other day for 9 weeks. RA phenotypes were compared between vehicle-treated CYP27B1^-/- and wild-type CIA mice. Human rheumatoid FLS-MH7A cells were treated with Dulbecco's modified Eagle's medium (DMEM) without fetal bovine serum (FBS) for 24 h, then with different concentrations of VD and TNF-α, human vitamin D receptor (VDR) siRNA or the p53 pro-apoptotic inhibitor pifithrin-α. Apoptosis and p53 pro-apoptotic signaling were analyzed. The 19-week-old vehicle-treated CYP27B1^-/- CIA mice had increased cumulative arthritis scores and levels of serous rheumatoid factors and C-reactive protein. They had exacerbated articular cartilage and bone destruction, joint space narrowing, joint stiffness, deformity and dysfunction, synovitis and TNF-α secretion, FLS hyperplasia with increased proliferation and decreased apoptosis compared to CIA mice. These RA phenotypes that were aggravated in CIA mice by CYP27B1 deficiency were largely rescued by VD treatment. In vitro, VD with TNF-α treatment upregulated p53 acetylation-mediated apoptosis in MH7A cells by promoting Sirt1 translocation from the nucleus to the cytoplasm. These findings indicated that VD with TNF-α protected against RA by promoting apoptosis of FLSs. The results indicated that clinical administration of VD could be a specific therapy to promote FLS apoptosis and prevent RA progression.

The Role of the Transcriptional Regulation of Stromal Cells in Chronic Inflammation

Chronic inflammation is a common process connecting pathologies that vary in their etiology and pathogenesis such as cancer, autoimmune diseases, and infections. The response of the immune system to tissue damage involves a carefully choreographed series of cellular interactions between immune and non-immune cells. In recent years, it has become clear that stromal resident cells have an essential role perpetuating the inflammatory environment and dictating in many cases the outcome of inflammatory based pathologies. Signal transduction pathways remain the main focus of study to understand how stimuli contribute to perpetuating the inflammatory response, mainly due to their potential role as therapeutic targets. However, molecular events orchestrated in the nucleus by transcription factors add additional levels of complexity and may be equally important for understanding the phenotypic differences of activated stromal components during the chronic inflammatory process. In this review, we focus on the contribution of transcription factors to the selective regulation of inducible proinflammatory genes, with special attention given to the regulation of the stromal fibroblastic cell function and response.

Celastrol induced DNA damage, cell cycle arrest, and apoptosis in human rheumatoid fibroblast-like synovial cells

Celastrol is one of the principal active ingredients of Tripterygium wilfordii Hook.f., a toxic Chinese medical herb traditionally prescribed for controlling pain and inhibiting inflammation in various chronic inflammatory diseases, including rheumatoid arthritis (RA). Resistance to apoptosis of fibroblast-like synoviocytes is considered a major characteristic of RA. In this study, we test celastrol's cytotoxic effect and potential mechanisms in human rheumatoid synovial fibroblasts (RA-FLS). In the cytotoxic assay, we found that celastrol dose-dependently decreased RA-FLS viability and increased LDH release. The apoptotic nuclear morphology was observed after celastrol treatment as determined by DAPI fluorescence staining. Flow cytometry analysis with PI and Annexin V revealed that celastrol induced RA-FLS cell cycle arrest in the G2/M phase and apoptosis. Furthermore, celastrol dramatically increased expression of Bax/Bcl-2, proteolytic cleavage of Caspase-3, -9, PARP, and decreased expression of FasR. In addition, celastrol treatment resulted in DNA damage. Collectively, we concluded that celastrol inhibits RA-FLS proliferation by inducing DNA damage, cell cycle arrest, and apoptosis in vitro, which might provide data for its application in RA treatment.

Role of Apo2L/TRAIL in immunity: Applications to rheumatoid arthritis

Rheumatoid arthritis (RA) is the most common inflammatory disease of the musculoskeletal system primarily affecting the joints. It is characterized by massive synovial hyperplasia and subsequent destruction of articular cartilage and bone. Although various aspects in the pathogenesis of RA remain unclear, genetic, environmental and of course immunological factors have been involved. Defects in apoptosis seem to play a role in both initiation and perpetuation of RA. Apo2 ligand/ tumor necrosis factor (TNF) related apoptosis-inducing ligand (Apo2L/TRAIL) is a cytokine that belongs to the TNF superfamily capable of inducing apoptosis on tumor cells through activation of the extrinsic pathway. Besides this function, like other members of the TNF superfamily, Apo2L/TRAIL has been shown to exert important functions in the regulation of the immune system. Concerning pathological conditions, the Apo2L/TRAIL signaling pathway plays an important role in the response to infections, in immune surveillance against tumors and in autoimmune diseases such as RA. Furthermore, its implication in suppression of autoimmunity suggests that Apo2L/TRAIL has potential as therapeutic agent not only in cancer but also in autoimmune diseases. In fact, Apo2L/TRAIL-based therapies have been shown effective in various animal models of RA. This review summarizes the current knowledge on the biology of Apo2L/TRAIL and its role in RA.

Psoriasin (S100A7) is a positive regulator of survival and invasion of prostate cancer cells

OBJECTIVES

Psoriasin, also known as S100A7 and first identified as a protein highly expressed in psoriatic lesions, is a calcium binding protein that has been indicated in various malignancies. The current study aimed to examine the implication of psoriasin in prostate cancer (CaP), particularly its impact on functions of CaP cells.

MATERIALS AND METHODS

Expression of psoriasin was examined in a variety of prostatic cell lines and human CaP tissues using reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. Knockdown and overexpression of psoriasin in CaP cells was performed using specifically constructed plasmids, which either had an anti-psoriasin ribozyme transgene or the full-length human S100A7 coding sequence. The effects of manipulating psoriasin expression on cellular functions of CaP cells were assessed using in vitro assays.

RESULTS

Psoriasin was expressed in prostate epithelia and cancer cells. Elevated expression of psoriasin was evident in CaP from its IHC staining in CaP frozen specimens. Psoriasin promoted cell survival under serum starvation. Its expression was inversely correlated with cell-matrix adhesion. Psoriasin increased invasiveness of PC-3 cells via a regulation of matrix metalproteinases (MMPs).

CONCLUSIONS

Aberrant expression of psoriasin is implicated in CaP. Its expression in CaP cells is associated with cell survival, adhesion, and in vitro invasion, which is via the regulation of MMPs.

Preclinical efficacy of sodium narcistatin to reduce inflammation and joint destruction in rats with adjuvant-induced arthritis

Current therapies for the treatment of rheumatoid arthritis (RA) do not work for all patients, can lose efficacy over time, and can have significant side effects. The discovery of new, effective therapies for RA remains an unmet medical need. The Amaryllidaceae isocarbostyril narciclasine was previously shown to prophylactically reduce paw swelling in rats with adjuvant-induced arthritis (AA). In this study, the efficacy of sodium narcistatin (SNS), a water-soluble cyclic phosphate pro-drug of narciclasine, was assessed in AA rats for anti-inflammatory and bone-sparing properties after disease onset. AA rats were given daily intraperitoneal injections of SNS (1.75, 3.5, or 5 mg/kg/day, in 500 μl sterile endotoxin-free saline) or saline from disease onset through severe disease stages. Footpad widths and radiographic scoring were used as indicators of inflammation and joint destruction, respectively. Ex vivo cytokine production by peripheral blood mononuclear cells (PMBC), splenocytes, and draining lymph node (DLN) cells were determined using ELISAs. SNS treatment dose-dependently reduced joint inflammation (~70%) and bone loss (~50%) compared with AA controls. SNS treatment also reduced spleen weight (without affecting body weight), pro-inflammatory cytokine production by PMBC, splenocytes, and DLN cells, and site-dependently altered T-helper (Th)1-/Th2-type and anti-inflammatory cytokine profiles. SNS dramatically reduces inflammation and has bone-sparing properties, possibly by reducing immune cell pro-inflammatory cytokine production. Our findings support the development of SNS as a therapeutic for RA.

Treatment of brain inflammatory diseases by delivering exosome encapsulated anti-inflammatory drugs from the nasal region to the brain

In this study, exosomes used to encapsulate curcumin (Exo-cur) or a signal transducer and activator of transcription 3 (Stat3) inhibitor, i.e., JSI124 (Exo-JSI124) were delivered noninvasively to microglia cells via an intranasal route. The results generated from three inflammation-mediated disease models, i.e., a lipopolysaccharide (LPS)-induced brain inflammation model, experimental autoimmune encephalitis and a GL26 brain tumor model, showed that mice treated intranasally with Exo-cur or Exo-JSI124 are protected from LPS-induced brain inflammation, the progression of myelin oligodendrocyte glycoprotein (MOG) peptide induced experimental autoimmune encephalomyelitis (EAE), and had significantly delayed brain tumor growth in the GL26 tumor model. Intranasal administration of Exo-cur or Exo-JSI124 led to rapid delivery of exosome encapsulated drug to the brain that was selectively taken up by microglial cells, and subsequently induced apoptosis of microglial cells. Our results demonstrate that this strategy may provide a noninvasive and novel therapeutic approach for treating brain inflammatory-related diseases.

Plant homologue constitutive photomorphogenesis 9 (COP9) signalosome subunit CSN5 regulates innate immune responses in macrophages

COP9 plays a role in plant innate immunity. The role of COP9 in mammalian innate immune responses is unknown. Here, we show that the COP9 signalosome subunit 5 (CSN5) is required for activation of proinflammatory kinases p38 and Erk and for down-regulation of the expression of genes regulated by nuclear factor E2-related factor 2. Mice with myeloid-specific CSN5 deficiency have lower mortality in polymicrobial sepsis. CSN5 is required for both Toll-like receptor (TLR) and reactive oxygen species-mediated deneddylation of Cul3, which is essential for Cul3/Keap1-mediated degradation of nuclear factor E2-related factor 2. On the basis of our results COP9 subunit CSN5 is considered to be an essential component of mammalian innate immunity.

JAB1/CSN5: a new player in cell cycle control and cancer

c-Jun activation domain-binding protein-1 (Jab1) acts as a modulator of intracellular signaling and affects cellular proliferation and apoptosis, through its existence as a monomer or as the fifth component of the constitutive photomorphogenic-9 signalosome (CSN5). Jab1/CSN5 is involved in transcription factor specificity, deneddylation of NEDD8, and nuclear-to-cytoplasmic shuttling of key molecules. Jab1/CSN5 activities positively and negatively affect a number of pathways, including integrin signaling, cell cycle control, and apoptosis. Also, more recent studies have demonstrated the intriguing roles of Jab1/CSN5 in regulating genomic instability and DNA repair. The effects of Jab1/CSN5's multiple protein interactions are generally oncogenic in nature, and overexpression of Jab1/CSN5 in cancer provides evidence that it is involved in the tumorigenic process. In this review, we highlight our current knowledge of Jab1/CSN5 function and the recent discoveries in dissecting the Jab1 signaling pathway. Further, we also discuss the regulation of Jab1/CSN5 in cancers and its potential as a therapeutic target.

Control of NF-kappaB activation by the COP9 signalosome

The transcription factor NF-kappaB (nuclear factor kappaB) exerts crucial functions in the regulation of innate and adaptive immune responses, wound healing and tissue maintenance and in the development of immune cells. Tight control of NF-kappaB is essential for an efficient defence against pathogens and environmental stress to protect organisms from inflammatory diseases including cancer. An involvement of the CSN (COP9 signalosome) in the regulation of NF-kappaB has been discovered recently. The CSN is a conserved multiprotein complex, which mainly functions in the control of proteolysis. Here, we review recent observations indicating important roles of the CSN in the control of NF-kappaB in innate immunity, as well as T-cell activation and maturation.

Crosstalk between the NF-kappaB activating IKK-complex and the CSN signalosome

A great variety of signalling pathways regulating inflammation, cell development and cell survival require NF-κB transcription factors, which are normally inactive due to binding to inhibitors, such as IκBα. The canonical activation pathway of NF-κB is initiated by phosphorylation of the inhibitor by an IκB kinase (IKK) complex triggering ubiquitination of IκB molecules by SCF-type E3-ligase complexes and rapid degradation by 26S-proteasomes. The ubiquitination machinery is regulated by the COP9 signalosome (CSN). We show that IκB kinases interact with the CSN-complex, as well as the SCF-ubiquitination machinery, providing an explanation for the rapid signalling-induced ubiquitination and degradation of IκBα. Furthermore, we reveal that IKK’s phosphorylate not only IκBα, but also the CSN-subunit Csn5/JAB1 (c-Jun activation domain binding protein-1) and that IKK2 influences ubiquitination of Csn5/JAB1. Our observations imply that the CSN complex acts as an inhibitor of constitutive NF-κB activity in non-activated cells. Knock-down of Csn5/JAB1 clearly enhanced basal NF-κB activity and improved cell survival under stress. The inhibitory effect of Csn5/JAB1 requires a functional MPN⁺ metalloprotease domain, which is responsible for cleaving ubiquitin-like Nedd8-modifications. Upon activation of cells with tumour necrosis factor-α, the CSN complex dissociates from IKK’s allowing full and rapid activation of the NF-κB pathway by the concerted action of interacting protein complexes.

Cell death in rheumatoid arthritis

Apoptosis plays a pivotal role in tissue homoeostasis both under physiological and pathological conditions and several studies have shown that some characteristic changes in the composition and structure of the inflamed synovial membrane in rheumatoid arthritis (RA) are linked to an altered apoptotic response of synovial cells. As a result, a hyperplastic synovial tissue is generated that mediates the progressive destruction of articular cartilage and bone. In addition to inflammatory cells, these changes most prominently affect resident fibroblast-like cells that have been demonstrated to be of utmost importance for joint destruction. Once activated, these cells pass through prominent molecular changes resulting in an aggressive, invasive behaviour. Research of the past years has identified different mechanisms that prevent synovial cells in RA from apoptosis. They include changes in the mitochondrial pathway as well as altered expression of downstream modulators of death receptors and transcriptional regulators such as NFkappaB. This review summarises our recent progress in understanding aberrant apoptosis in the RA synovial membrane and points to possibilities of intervening specifically with this aspect of the pathogenesis of RA.

COP9-associated CSN5 regulates exosomal protein deubiquitination and sorting

Ubiquitinated endosomal proteins that are deposited into the lumens of multivesicular bodies are either sorted for lysosomal-mediated degradation or secreted as exosomes into the extracellular milieu. The mechanisms that underlie the sorting of cellular cargo proteins are currently unknown. In this study, we show that the COP9 signalosome (CSN)-associated protein CSN5 quantitatively regulated proteins that were sorted into exosomes. Western blot analysis of exosomal proteins indicated that small interfering (si)RNA knockdown of CSN5 results in increased levels of both ubiquitinated and non-ubiquitinated exosomal proteins, including heat shock protein 70, in comparison with exosomes isolated from the supernatants of 293 cells transfected with scrambled siRNA. Furthermore, 293 cells transfected with JAB1/MPN/Mov34 metalloenzyme domain-deleted CSN5 produced exosomes with higher levels of ubiquitinated heat shock protein 70, which did not affect non-ubiquitinated heat shock protein 70 levels. The loss of COP9-associated deubiquitin activity of CSN5 also led to the enhancement of HIV Gag that was sorted into exosomes as well as the promotion of HIV-1 release, suggesting that COP9-associated CSN5 regulates the sorting of a number of exosomal proteins in both a CSN5 JAB1/MPN/Mov34 metalloenzyme domain-dependent and -independent manner. We propose that COP9-associated CSN5 regulates exosomal protein sorting in both a deubiquitinating activity-dependent and -independent manner, which is contrary to the current idea of ubiquitin-dependent sorting of proteins to exosomes.

Developments in the synovial biology field 2006

Synovial pathophysiology is a complex and synergistic interplay of different cell populations with tissue components, mediated by a variety of signaling mechanisms. All of these mechanisms drive the affected joint into inflammation and drive the subsequent destruction of cartilage and bone. Each cell type contributes significantly to the initiation and perpetuation of this deleterious concert, especially in rheumatoid arthritis. Rheumatoid arthritis synovial fibroblasts and macrophages, both cell types with pivotal roles in inflammation and destruction, but also T cells and B cells are crucial for complex network in the inflamed synovium. An even more complex cellular crosstalk between these key players maintains a process of chronic inflammation. As outlined in the present review, in the past year substantial progress has been made to elucidate further details of the rich pathophysiology of rheumatoid arthritis, which may also facilitate the identification of novel targets for future therapeutic strategies.