Fas ligand-induced proinflammatory transcriptional responses in reconstructed human epidermis. Recruitment of the epidermal growth factor receptor and activation of MAP kinases

A systematic review of case-control studies of cytokines in blister fluid and skin tissue of patients with Stevens Johnson syndrome and toxic epidermal necrolysis

Stevens Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are severe cutaneous adverse reactions characterised by keratinocyte apoptosis, necroptosis and epidermal detachment. Several cytokines and cytotoxic proteins have been shown to be elevated in the blood and skin of SJS/TEN sufferers and biologics such as intravenous immune globulin and tumour necrosis factor (TNF)-alpha inhibitors have demonstrated good therapeutic potential. The exact pathogenic model of SJS/TEN however remains elusive. This systematic review aimed to evaluate the case-control studies of cytokines and cytotoxic proteins in the blister fluid and skin of adults with Stevens Johnson syndrome and/or toxic epidermal necrolysis. This review was registered with INPLASY and conducted in accordance with the PRISMA reporting guidelines. Potential bias was assessed using the NIH criteria. Eleven articles describing results from 96 cases and 170 controls were included. Fas, Fas ligand, Interleukin (IL)-8 and B-cell lymphoma (Bcl)-2 were elevated in SJS/TEN blister fluid and skin tissue, compared with healthy controls. IL-2, IL-6, TNF-alpha, tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), interferon-gamma and matrix metalloproteinase-2 were elevated in SJS/TEN blister fluid compared with fluid sampled from lesional controls. Granulysin, IL-33, TGF-beta-1 and IL-13 were elevated in SJS/TEN skin tissue compared with lesional lichen planus tissue, as was IL-13, IFN-gamma, IL-2 and IL-5, when compared with erythema multiforme tissue. A wide array of cytokines and cytotoxic proteins are present at higher concentrations in the blister fluid and skin tissue of SJS/TEN patients compared with healthy and lesional controls. Our findings suggest that these proteins may be pathogenic, as well as possibly markers for diagnosis, disease severity and course. They may also prove to be useful therapeutic targets. More research is needed.

The dual role of the CD95 and CD95L signaling pathway in glioblastoma

Binding of CD95, a cell surface death receptor, to its homologous ligand CD95L, transduces a cascade of downstream signals leading to apoptosis crucial for immune homeostasis and immune surveillance. Although CD95 and CD95L binding classically induces programmed cell death, most tumor cells show resistance to CD95L-induced apoptosis. In some cancers, such as glioblastoma, CD95-CD95L binding can exhibit paradoxical functions that promote tumor growth by inducing inflammation, regulating immune cell homeostasis, and/or promoting cell survival, proliferation, migration, and maintenance of the stemness of cancer cells. In this review, potential mechanisms such as the expression of apoptotic inhibitor proteins, decreased activity of downstream elements, production of nonapoptotic soluble CD95L, and non-apoptotic signals that replace apoptotic signals in cancer cells are summarized. CD95L is also expressed by other types of cells, such as endothelial cells, polymorphonuclear myeloid-derived suppressor cells, cancer-associated fibroblasts, and tumor-associated microglia, and macrophages, which are educated by the tumor microenvironment and can induce apoptosis of tumor-infiltrating lymphocytes, which recognize and kill cancer cells. The dual role of the CD95-CD95L system makes targeted therapy strategies against CD95 or CD95L in glioblastoma difficult and controversial. In this review, we also discuss the current status and perspective of clinical trials on glioblastoma based on the CD95-CD95L signaling pathway.

Therapeutic approaches targeting CD95L/CD95 signaling in cancer and autoimmune diseases

Cell death plays a pivotal role in the maintenance of tissue homeostasis. Key players in the controlled induction of cell death are the Death Receptors (DR). CD95 is a prototypic DR activated by its cognate ligand CD95L triggering programmed cell death. As a consequence, alterations in the CD95/CD95L pathway have been involved in several disease conditions ranging from autoimmune diseases to inflammation and cancer. CD95L-induced cell death has multiple roles in the immune response since it constitutes one of the mechanisms by which cytotoxic lymphocytes kill their targets, but it is also involved in the process of turning off the immune response. Furthermore, beyond the canonical pro-death signals, CD95L, which can be membrane-bound or soluble, also induces non-apoptotic signaling that contributes to its tumor-promoting and pro-inflammatory roles. The intent of this review is to describe the role of CD95/CD95L in the pathophysiology of cancers, autoimmune diseases and chronic inflammation and to discuss recently patented and emerging therapeutic strategies that exploit/block the CD95/CD95L system in these diseases.

[Search for Compounds Regulating TSLP Production]

Thymic stromal lymphopoietin (TSLP) is an epithelial cell-derived immunostimulatory factor, which activates several immune cells such as dendritic cells, T cells, and mast cells. Recently, epithelial cell-derived TSLP has gained immense attention as a cytokine that induces allergic immune responses. Therefore, understanding the regulation of TSLP production is an important step in uncovering the pathophysiology of allergic diseases. Moreover, the compounds that regulate TSLP production can be used as therapeutic drugs for the treatment of allergic diseases. We aim to elucidate the detailed regulation of TSLP production from epithelial cells, and in doing so discovered new regulating factors and an inhibitor of TSLP production. This review article explains the role of TSLP in allergic diseases, its regulation, and our research results.

Cytokines and apoptosis in atopic dermatitis

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease. AD affects 10-20% of children worldwide and persists into adulthood in a minority of cases, affecting approximately 2-3% of the adult population, with an increased prevalence over the past decades in developed countries. Atopy is a genetic tendency to overproduce IgE class antibodies in response to common antigens found in the environment. Concurrence of different atopy such as allergic rhinitis or asthma in children with AD is estimated at 80%. AD is characterized by a vicious cycle of an allergic immune response. The emerging picture of the AD is a complex disorder with barrier dysfunction, immunological, genetic and environmental factors all playing key roles. Patients with severe or persistent disease and their families experience significant impairment in their quality of life, and in addition, AD places a heavy economic burden on society as a whole. Pathogenesis, the role of the epidermal barrier, mechanisms of cells apoptosis, the role of T cells and cytokines in AD are discussed in this article.

Aberrant expression of the UPF1 RNA surveillance gene disturbs keratinocyte homeostasis by stabilizing AREG

The up‑frameshift suppressor 1 homolog (UPF1) RNA surveillance gene is a core element in the nonsense‑mediated RNA decay (NMD) pathway, which impacts a broad spectrum of biological processes in a cell‑specific manner. In the present study, the contribution of the NMD pathway to psoriasis lesions and its moderating effects on the biological processes of keratinocytes was reported. Sanger sequencing for skin scales from two patients with psoriasis identified two mRNA mutations (c.2935_2936insA and c.2030‑2081del) in the UPF1 gene. The somatic mutants produced truncated UPF1 proteins and perturbed the NMD pathway in cells, leading to the upregulation of NMD substrates. As the most abundant epidermal growth factor receptor ligand in keratinocytes, it was concluded that amphiregulin (AREG) mRNA is a natural NMD substrate, that is dependent on its 3' untranslated region sequence. Perturbed NMD modulated keratinocyte homeostasis in an AREG‑dependent but nonidentical manner, which highlighted the unique characteristics of NMD in keratinocytes. By targeting AREG mRNA post‑transcriptionally, the UPF1‑NMD pathway contributed to an imbalance between proliferation on the one hand, and apoptosis and abnormal differentiation, migration and inflammatory response on the other, in keratinocytes, which indicated a role of the NMD pathway in the full development of keratinocyte‑related morbidity and skin diseases.

Activation of invariant natural killer T cells stimulates adipose tissue remodeling via adipocyte death and birth in obesity

In this study, Park et al. set out to elucidate the mechanism by which adipose-resident invariant natural killer T cells (iNKT) cells impact adipose tissue remodeling in obesity. Using in vitro and ex vivo approaches, the authors found that, in obesity, adipose iNKT cells can kill hypertrophic and pro-inflammatory adipocytes via FasL-Fas-dependent apoptosis, thus providing new insight into the role adipose iNKT cells play in promoting healthy adipose tissue remodeling.

In obesity, adipose tissue undergoes dynamic remodeling processes such as adipocyte hypertrophy, hypoxia, immune responses, and adipocyte death. However, whether and how invariant natural killer T (iNKT) cells contribute to adipose tissue remodeling are elusive. In this study, we demonstrate that iNKT cells remove unhealthy adipocytes and stimulate the differentiation of healthy adipocytes. In obese adipose tissue, iNKT cells were abundantly found nearby dead adipocytes. FasL-positive adipose iNKT cells exerted cytotoxic effects to eliminate hypertrophic and pro-inflammatory Fas-positive adipocytes. Furthermore, in vivo adipocyte-lineage tracing mice model showed that activation of iNKT cells by alpha-galactosylceramide promoted adipocyte turnover, eventually leading to potentiation of the insulin-dependent glucose uptake ability in adipose tissue. Collectively, our data propose a novel role of adipose iNKT cells in the regulation of adipocyte turnover in obesity.

Caspase-10 Negatively Regulates Caspase-8-Mediated Cell Death, Switching the Response to CD95L in Favor of NF-κB Activation and Cell Survival

Formation of the death-inducing signaling complex (DISC) initiates extrinsic apoptosis. Caspase-8 and its regulator cFLIP control death signaling by binding to death-receptor-bound FADD. By elucidating the function of the caspase-8 homolog, caspase-10, we discover that caspase-10 negatively regulates caspase-8-mediated cell death. Significantly, we reveal that caspase-10 reduces DISC association and activation of caspase-8. Furthermore, we extend our co-operative/hierarchical binding model of caspase-8/cFLIP and show that caspase-10 does not compete with caspase-8 for binding to FADD. Utilizing caspase-8-knockout cells, we demonstrate that caspase-8 is required upstream of both cFLIP and caspase-10 and that DISC formation critically depends on the scaffold function of caspase-8. We establish that caspase-10 rewires DISC signaling to NF-κB activation/cell survival and demonstrate that the catalytic activity of caspase-10, and caspase-8, is redundant in gene induction. Thus, our data are consistent with a model in which both caspase-10 and cFLIP coordinately regulate CD95L-mediated signaling for death or survival.

EGFR transactivation is involved in TNF-α-induced expression of thymic stromal lymphopoietin in human keratinocyte cell line

BACKGROUND

Thymic stromal lymphopoietin (TSLP) is an epithelial cell-derived cytokine involved in the pathology of inflammatory skin diseases, such as atopic dermatitis and psoriasis. Tumor necrosis factor (TNF)-α, a key cytokine in inflammatory skin diseases, is a known TSLP inducer. TNF-α activates NF-κB and induces transactivation of epidermal growth factor receptor (EGFR) in epithelial cells. However, the detailed mechanism of TSLP induction by TNF-α has remained unclear.

OBJECTIVE

We investigated the involvement of TNF-α-induced EGFR transactivation in TSLP expression.

METHODS

HaCaT cells were stimulated with TNF-α or EGF in the presence or absence of an EGFR kinase inhibitor or other signaling inhibitors. The expression of TSLP mRNA was analyzed by RT-PCR and the phosphorylation level of signal proteins was analyzed by western blot. TSLP promoter and NF-κB transcription activities were analyzed by luciferase assay.

RESULTS

TNF-α-induced TSLP expression was inhibited by the EGFR kinase inhibitor AG1478. While TSLP expression was induced by EGF, it was inhibited by the MEK inhibitor, U0126. Inhibitors of p38 and ADAM proteases suppressed the TNF-α-induced TSLP expression and EGFR phosphorylation, but not the EGF-induced expression.

CONCLUSION

TNF-α-induced EGFR transactivation results in TSLP induction through ERK activation. The activation of p38 and ADAM proteases mediates TNF-α-induced EGFR phosphorylation. These findings suggested that the TNF-α-induced EGFR transactivation pathway could be a target for the treatment of inflammatory skin diseases.

Involvement of Fas/FasL pathway in the murine model of atopic dermatitis

Objective and design

The aim of this study was to elucidate the role of apoptosis mediated through Fas/FasL pathway using the mouse model of atopic dermatitis (AD).

Materials and treatment

AD was induced by epicutaneous application of ovalbumin (OVA) in wild-type C57BL/6, B6. MRL-Faslpr/J (Fas−) and B6Smn.C3-Faslgld/J (FasL−) mouse strains.

Methods

Skin samples were subjected to staining for Fas/FasL expression, M30 epitope and assessment of inflammatory response via immunohistochemical staining. Cytokine and chemokine production was assessed by real-time PCR.

Results

In comparison to wild-type mice, OVA sensitization of Fas- and FasL-deficient mice led to increased epidermal and dermal thickness, collagen deposition and local inflammation consisting of macrophages, neutrophils and CD4+ T cells. Fas- and FasL-deficient mice showed increased total counts of regulatory T cells (Tregs) and IgE levels in blood as well as increased expression of IL-1β, IL-4, IL-5, IL-13 and TGF-1β mRNA in comparison to wild-type mice. On the other hand, expression of CXCL9 and CXCL10, IL-17 mRNAs in the skin samples in Fas- and FasL-deficient mice was decreased.

Conclusions

Our results show that lack of the Fas-induced apoptosis leads to exacerbation of AD characteristics such as Th2 inflammation and dermal thickening. Therefore, Fas receptor can play an important role in AD pathogenesis by controlling development of the local inflammation.

Cell death-independent activities of the death receptors CD95, TRAILR1, and TRAILR2

Since their identification more than 20 years ago, the death receptors CD95, TRAILR1, and TRAILR2 have been intensively studied with respect to their cell death-inducing activities. These receptors, however, can also trigger a variety of cell death-independent cellular responses reaching from the activation of proinflammatory gene transcription programs over the stimulation of proliferation and differentiation to induction of cell migration. The cell death-inducing signaling mechanisms of CD95 and the TRAIL death receptors are well understood. In contrast, despite the increasing recognition of the biological and pathophysiological relevance of the cell death-independent activities of CD95, TRAILR1, and TRAILR2, the corresponding signaling mechanisms are less understood and give no fully coherent picture. This review is focused on the cell death-independent activities of CD95 and the TRAIL death receptors and addresses mainly three questions: (a) how are these receptors linked to noncell death pathways at the molecular level, (b) which factors determine the balance of cell death and cell death-independent activities of CD95 and the TRAIL death receptors at the cellular level, and (c) what are the consequences of the cell death-independent functions of these receptors for their role in cancer and inflammatory diseases.

ADAM10 mediates the house dust mite-induced release of chemokine ligand CCL20 by airway epithelium

BACKGROUND

House dust mite (HDM) acts on the airway epithelium to induce airway inflammation in asthma. We previously showed that the ability of HDM to induce allergic sensitization in mice is related to airway epithelial CCL20 secretion.

OBJECTIVE

As a disintegrin and metalloprotease (ADAM)s have been implicated in chemokine shedding, we sought to determine their involvement in HDM-induced release of chemokines, including CCL20, by airway epithelial cells.

METHODS

We studied the effects of pharmacological ADAM inhibitors as well as ADAM10 and ADAM17 siRNA downregulation on chemokine release using (multiplex) ELISA in supernatants from HDM-exposed human bronchial epithelial 16HBE cells and primary normal human bronchial epithelial cells (NHBE) at 4-24 h.

RESULTS

House dust) mite markedly increased CCL20 levels in both 16HBE and NHBE cells (16-24 h). In 16HBE cells, the HDM-induced increase was observed as early as 4 h upon exposure and the use of specific inhibitors indicated the involvement of ADAM10/17-mediated shedding. siRNA knockdown of ADAM10, but not of ADAM17, significantly reduced the HDM-induced release of CCL20 in both 16HBE and NHBE cells. A similar effect was observed for HDM-induced CCL2, CCL5, and CXCL8 release in NHBE cells. The HDM-induced increase in CCL20 levels was not affected by protein synthesis inhibitor cycloheximide nor protein transport inhibitor monensin, indicating that HDM induces surface shedding of chemokines.

CONCLUSION

Our data show for the first time that ADAM10 activity contributes to HDM-induced shedding of chemokines, including CCL20. The ADAM10/CCL20 axis may be a target for novel therapeutic strategies in asthma.

Fas (CD95) expression in myeloid cells promotes obesity‐induced muscle insulin resistance

Low-grade inflammation in adipose tissue and liver has been implicated in obesity-associated insulin resistance and type 2 diabetes. Yet, the contribution of inflammatory cells to the pathogenesis of skeletal muscle insulin resistance remains elusive. In a large cohort of obese human individuals, blood monocyte Fas (CD95) expression correlated with systemic and skeletal muscle insulin resistance. To test a causal role for myeloid cell Fas expression in the development of skeletal muscle insulin resistance, we generated myeloid/haematopoietic cell-specific Fas-depleted mice. Myeloid/haematopoietic Fas deficiency prevented the development of glucose intolerance in high fat-fed mice, in ob/ob mice, and in mice acutely challenged by LPS. In vivo, ex vivo and in vitro studies demonstrated preservation of muscle insulin responsiveness with no effect on adipose tissue or liver. Studies using neutralizing antibodies demonstrated a role for TNFα as mediator between myeloid Fas and skeletal muscle insulin resistance, supported by significant correlations between monocyte Fas expression and circulating TNFα in humans. In conclusion, our results demonstrate an unanticipated crosstalk between myeloid cells and skeletal muscle in the development of obesity-associated insulin resistance.

Blockade of Fas signaling in breast cancer cells suppresses tumor growth and metastasis via disruption of Fas signaling-initiated cancer-related inflammation

Mechanisms for cancer-related inflammation remain to be fully elucidated. Non-apoptotic functions of Fas signaling have been proposed to play an important role in promoting tumor progression. It has yet to be determined if targeting Fas signaling can control tumor progression through suppression of cancer-related inflammation. In the current study we found that breast cancer cells with constitutive Fas expression were resistant to apoptosis induction by agonistic anti-Fas antibody (Jo2) ligation or Fas ligand cross-linking. Higher expression of Fas in human breast cancer tissue has been significantly correlated with poorer prognosis in breast cancer patients. To determine whether blockade of Fas signaling in breast cancer could suppress tumor progression, we prepared an orthotopic xenograft mouse model with mammary cancer cells 4T1 and found that blockade of Fas signaling in 4T1 cancer cells markedly reduced tumor growth, inhibited tumor metastasis in vivo, and prolonged survival of tumor-bearing mice. Mechanistically, blockade of Fas signaling in cancer cells significantly decreased systemic or local recruitment of myeloid derived suppressor cells (MDSCs) in vivo. Furthermore, blockade of Fas signaling markedly reduced IL-6, prostaglandin E2 production from breast cancer cells by impairing p-p38, and activity of the NFκB pathway. In addition, administration of a COX-2 inhibitor and anti-IL-6 antibody significantly reduced MDSC accumulation in vivo. Therefore, blockade of Fas signaling can suppress breast cancer progression by inhibiting proinflammatory cytokine production and MDSC accumulation, indicating that Fas signaling-initiated cancer-related inflammation in breast cancer cells may be a potential target for treatment of breast cancer.

Differential apoptosis gene expressions of rhabdomyosarcoma cells in response to enterovirus 71 infection

Background

Enterovirus 71 (EV71) infection can induce the apoptosis of infected cells. The aim of this study is to explore the effect of EV71 infection on apoptosis mechanisms in virus-infected human rhabdomyosarcoma (RD) cells.

Methods

The apoptosis of RD cells was examined using annexin V-FITC/PI by flow cytometry and cytokines were detected by ELISA. Cellular RNA was extracted and transcribed to cDNA. PCR array was employed to analyze the expressions of 84 apoptotic genes from EV71-infected RD cells at 8 and 20 h postinfection, respectively. In addition, the expressions of FasL, caspase, AKT2, JNK1/2, c-Jun and NF-κB proteins were detected by western blotting.

Results

Flow cytometry demonstrated that the apoptosis or death of EV71-infected RD cells was increased by 37.1% with a multiplicity of infection (MOI) of 5 at 20 h postinfection. The production of IL-4, IL-10 and TNF-α was enhanced by the subsequent EV71 infection. PCR array revealed significant changes in the expressions of apoptotic genes. Among 84 genes, 42 genes were down-regulated after EV71 infection at 8 h, whereas 32 genes were up-regulated at 20 h postinfection. Moreover, the ligands of TNF superfamily such as FasL, CD40L and TNF-α were significantly up-regulated and enhanced the expressions of apoptosis-related cysteine peptidases, including caspase-10, -8, -7 and -3. In addition, EV71 infection induces the phosphorylation of AKT2, JNK1/2, c-Jun and NF-κB at 20 h postinfection.

Conclusion

PCR array for the determination of apoptosis gene expressions is an informative assay in elucidating biological pathways. During the early stage of EV71 infection, the apoptotic process of RD cells is significantly delayed. EV71 infection can also induce the expressions of FasL, TNF-α and CD40L, which contribute to the apoptosis of RD cells.

Activation of the aryl hydrocarbon receptor sensitises human keratinocytes for CD95L- and TRAIL-induced apoptosis

In this study, we have analysed the apoptotic effects of the ubiquitous environmental toxin benzo[a]pyrene (BP) in HaCaT cells and human keratinocytes. Although prolonged exposure to BP was not cytotoxic on its own, a strong enhancement of CD95 (Fas)-mediated apoptosis was observed with BP at concentrations activating the aryl hydrocarbon receptor (AhR). Importantly, the ultimately mutagenic BP-metabolite, that is, (+)-anti-BP-7,8-diol-9,10-epoxide (BPDE), failed to enhance CD95-mediated cell death, suggesting that the observed pro-apoptotic effect of BP is neither associated with DNA adducts nor DNA-damage related signalling. CD95-induced apoptosis was also enhanced by β-naphtoflavone, a well-known agonist of the AhR that does not induce DNA damage, thus suggesting a crucial role for AhR activation. Consistently, BP failed to sensitise for CD95L-induced apoptosis in AhR knockdown HaCaT cells. Furthermore, inhibition of CYP1A1 and/or 1B1 expression did not affect the pro-apoptotic crosstalk. Exposure to BP did not increase expression of CD95, but led to augmented activation of caspase-8. Enhancement of apoptosis was also observed with the TRAIL death receptors that activate caspase-8 and apoptosis by similar mechanisms as CD95. Together, these observations indicate an interference of AhR signalling with the activity of receptor-associated signalling intermediates that are shared by CD95 and TRAIL receptors. Our data thus suggest that AhR agonists can enhance cytokine-mediated adversity upon dermal exposure.

TSLP expression: cellular sources, triggers, and regulatory mechanisms

Thymic stromal lymphopoietin (TSLP) is an IL-7-like cytokine initially identified in the culture supernatant of a thymic stromal cell line. Highly expressed in the epidermis in skin lesions of atopic dermatitis patients, TSLP was subsequently found to be a critical factor linking responses at interfaces between the body and environment (skin, airway, gut, ocular tissues, and so on) to Th2 responses. Recent studies have revealed that various cell types other than epithelial cells and epidermal keratinocytes (such as mast cells, airway smooth muscle cells, fibroblasts, dendritic cells, trophoblasts, and cancer or cancer-associated cells) also express TSLP. Environmental factors such as Toll-like receptor ligands, a Nod2 ligand, viruses, microbes, allergen sources, helminths, diesel exhaust, cigarette smoke, and chemicals trigger TSLP production. Proinflammatory cytokines, Th2-related cytokines, and IgE also induce or enhance TSLP production, indicating cycles of amplification. Skin barrier injury, increased epidermal endogenous protease activity, and less epidermal Notch signaling, all of which have been reported in atopic dermatitis, and keratinocyte-specific loss of retinoid X receptors and treatment of skin with agonists for vitamin D receptor in mice induce TSLP production, Th2 response, or atopic dermatitis-like inflammation. The transcription factors NF-κB and AP-1, nuclear receptors, single nucleotide polymorphisms, microRNAs, and the peptidyl-proryl isomerase Pin1 regulate TSLP mRNA expression transcriptionally or posttranscriptionally. This review focuses on events upstream of TSLP production, which is critical in allergic diseases and important in other TSLP-related disorders i.e. production sites, cellular sources, environmental and endogenous triggers and regulatory factors, and regulatory mechanisms of gene expression.

Potential for modulation of the fas apoptotic pathway by epidermal growth factor in sarcomas

One important mechanism by which cancer cells parasitize their host is by escaping apoptosis. Thus, selectively facilitating apoptosis is a therapeutic mechanism by which oncotherapy may prove highly advantageous. One major apoptotic pathway is mediated by Fas ligand (FasL). The death-inducing signaling Ccmplex (DISC) and subsequent death-domain aggregations are created when FasL is bound by its receptor thereby enabling programmed cell death. Conceptually, if a better understanding of the Fas pathway can be garnered, an oncoselective prodeath therapeutic approach can be tailored. Herein, we propose that EGF and CTGF play essential roles in the regulation of the Fas apoptotic pathway in sarcomas. Tumor and in vitro data suggest viable cells counter the prodeath signal induced by FasL by activating EGF, which in turn induces prosurvival CTGF. The prosurvival attributes of CTGF ultimately predominate over the death-inducing FasL. Cells destined for elimination inhibit this prosurvival response via a presently undefined pathway. This scenario represents a novel role for EGF and CTGF as regulators of the Fas pathway in sarcomas.

An epidermotypic model of interface dermatitis reveals individual functions of fas ligand and gamma interferon in hypergranulosis, cytoid body formation, and gene expression

Analysis of complex cutaneous reactions using animal models allows for the identification of essential or modulatory participants, that is, cyto- and chemokines or adhesion molecules. However, complex whole animal modeling is bound to obscure some specific contributions of individual players. Mouse models suggest that expression of Fas ligand (FasL) by donor T cells is essential for the cutaneous acute graft-versus-host reaction (aGvHR), a major complication after allogeneic hematopoietic stem cell transplantation. The role of FasL/Fas in human cutaneous GvHR is not known. To understand the mechanisms of cytotoxicity and inflammation in human cutaneous GvHR, we developed an organotypic model using reconstructed human epidermis (RHE) that was exposed to FasL, gamma-interferon (IFNγ), or both. The model recapitulated key histological hallmarks of cutaneous aGvHR, including interface dermatitis, appearance of cytoid bodies, hypergranulosis, and expression of ICAM-1. Cytoid body formation and expression of ICAM-1 were attributable entirely to IFNγ, whereas hypergranulosis was triggered by FasL. Both FasL and IFNγ triggered vacuolar degeneration of keratinocytes. The validity of the RHE model of GvHR was demonstrated by histological correlation with biopsied skin from patients with acute graft-versus-host disease. FasL and IFNγ each elicited potent and specific proinflammatory genomic responses in RHE. Inhibition of caspase activity dramatically augmented the FasL-induced proinflammatory responses, suggesting an "apoptosis-versus-inflammation" antagonism in cutaneous aGvHR and other lichenoid dermatoses.

Fas activation in adipocytes impairs insulin-stimulated glucose uptake by reducing Akt

Fas (CD95) belongs to the superfamily of the tumor necrosis factor (TNF) receptors. Besides its key role in apoptosis, Fas contributes to non-apoptotic pathways such as cell proliferation and inflammation. In 3T3-L1 adipocytes, activation of Fas by Fas ligand decreased insulin-stimulated glucose uptake, without affecting cell viability. This decrease in glucose uptake was accompanied by reduced protein expression and diminished phosphorylation of Akt. Similarly, insulin-stimulated glucose incorporation and protein levels of Akt were increased in isolated adipocytes from Fas deficient mice when compared to wild-type mice. In conclusion, Fas activation in adipocytes decreases Akt expression and thereby impairs insulin sensitivity.

Enhanced contact allergen- and UVB-induced keratinocyte apoptosis in the absence of CD95/Fas/Apo-1

FAS/CD95/Apo-1 is a ubiquitously expressed cell-surface receptor involved in the initiation of programmed cell death. Its function in epidermal keratinocytes has been incompletely defined. Available evidence from in vitro studies points to important roles of Fas in the pathogenesis of contact dermatitis and in keratinocyte apoptosis induced by ultraviolet light. To define functions of Fas in the epidermis in vivo, we have generated mice with epidermis-specific deletion of the fas gene and tested its requirement for 2,4-dinitrofluorobenzene-induced contact dermatitis and for ultraviolet light B (UVB)-induced keratinocyte apoptosis. We report here our unexpected finding that keratinocyte apoptosis induced by both a contact allergen and UVB irradiation was significantly enhanced in Fas-negative epidermis. Expression of Fas by epidermal keratinocytes was neither necessary for the normal development of contact hypersensitivity of the skin, nor required for keratinocyte apoptosis following UVB irradiation. Our study results thus show that in the epidermis in vivo Fas exerts antiapoptotic effects that outweigh its proapoptotic role in contact hypersensitivity responses of the skin and in the tissue response of the epidermis to UVB irradiation.

The role of FasL and Fas in health and disease

The FS7-associated cell surface antigen (Fas, also named CD95, APO-1 or TNFRSF6) attracted considerable interest in the field of apoptosis research since its discovery in 1989. The groups of Shin Yonehara and Peter Krammer were the first reporting extensive apoptotic cell death induction upon treating cells with Fas-specific monoclonal antibodies.1,2 Cloning of Fas3 and its ligand,4,5 FasL (also known as CD178, CD95L or TNFSF6), laid the cornerstone in establishing this receptor-ligand system as a central regulator of apoptosis in mammals. Therapeutic exploitation of FasL-Fas-mediated cytotoxicity was soon an ambitous goal and during the last decade numerous strategies have been developed for its realization. In this chapter, we will briefly introduce essential general aspects of the FasL-Fas system before reviewing its physiological and pathophysiological relevance. Finally, FasL-Fas-related therapeutic tools and concepts will be addressed.

Deletion of Fas in adipocytes relieves adipose tissue inflammation and hepatic manifestations of obesity in mice

Adipose tissue inflammation is linked to the pathogenesis of insulin resistance. In addition to exerting death-promoting effects, the death receptor Fas (also known as CD95) can activate inflammatory pathways in several cell lines and tissues, although little is known about the metabolic consequence of Fas activation in adipose tissue. We therefore sought to investigate the contribution of Fas in adipocytes to obesity-associated metabolic dysregulation. Fas expression was markedly increased in the adipocytes of common genetic and diet-induced mouse models of obesity and insulin resistance, as well as in the adipose tissue of obese and type 2 diabetic patients. Mice with Fas deficiency either in all cells or specifically in adipocytes (the latter are referred to herein as AFasKO mice) were protected from deterioration of glucose homeostasis induced by high-fat diet (HFD). Adipocytes in AFasKO mice were more insulin sensitive than those in wild-type mice, and mRNA levels of proinflammatory factors were reduced in white adipose tissue. Moreover, AFasKO mice were protected against hepatic steatosis and were more insulin sensitive, both at the whole-body level and in the liver. Thus, Fas in adipocytes contributes to adipose tissue inflammation, hepatic steatosis, and insulin resistance induced by obesity and may constitute a potential therapeutic target for the treatment of insulin resistance and type 2 diabetes.

Th17 cytokines stimulate CCL20 expression in keratinocytes in vitro and in vivo: implications for psoriasis pathogenesis

T helper (Th) 17 cells have recently been implicated in psoriasis pathogenesis, but mechanisms of how these cells traffic into inflamed skin are unknown. By immunostaining for interleukin (IL)-17A and IL-22, we show numerous cells present in psoriasis lesions that produce these cytokines. We next found that Th17 cytokines (IL-17A, IL-22, and tumor necrosis factor (TNF)-alpha) markedly increased the expression of CC chemokine ligand (CCL) 20, a CC chemokine receptor (CCR)6 ligand, in human keratinocyte monolayer and raft cultures in a dose- and time-dependent manner. Lastly, we showed in mice that subcutaneous injection with recombinant IL-17A, IL-22, or TNF-alpha led to the upregulation of both CCL20 and CCR6 expression in skin as well as cutaneous T-cell infiltration. Taken together, these data show that Th17 cytokines stimulate CCL20 production in vitro and in vivo, and thus provide a potential explanation of how CCR6-positive Th17 cells maintain their continual presence in psoriasis through a positive chemotactic feedback loop.

The epidermal growth factor receptor: a link between inflammation and liver cancer

Epidemiological studies have established that many tumours occur in association with persistent inflammation. One clear example of inflammation-related cancer is hepatocellular carcinoma (HCC). HCC slowly unfolds on a background of chronic inflammation triggered by exposure to infectious agents (hepatotropic viruses), toxic compounds (ethanol), or metabolic impairment. The molecular links that connect inflammation and cancer are not completely known, but evidence gathered over the past few years is beginning to define the precise mechanisms. A central role for cytokines such as interleukin-6 (IL-6) and IL-1 (alpha and beta) in liver cancer has been established in experimental models. Besides these inflammatory mediators, mounting evidence points to the dysregulation of specific growth and survival-related pathways in HCC development. Among them is the pathway governed by the epidermal growth factor receptor (EGFR), which can be bound and activated by a broad family of ligands. Of special relevance is the fact that the EGFR engages in extensive crosstalk with other signaling pathways, serving as a "signaling hub" for an increasing list of growth factors, cytokines, and inflammatory mediators. In this review, we summarize the most recent evidences supporting a role for the EGFR system in inflammation-related cell signaling, with special emphasis in liver inflammation and HCC. The molecular dissection of the pathways connecting the inflammatory reaction and neoplasia will facilitate the development of novel and more effective antitumor strategies.

Cell death in the skin

The skin is the largest organ of the body and protects the organism against external physical, chemical and biological insults, such as wounding, ultraviolet radiation and micro-organisms. The epidermis is the upper part of the skin that is continuously renewed. The keratinocytes are the major cell type in the epidermis and undergo a specialized form of programmed cell death, called cornification, which is different from classical apoptosis. In keep with this view, several lines of evidence indicate that NF-kB is an important factor providing protection against keratinocyte apoptosis in homeostatic and inflammatory conditions. In contrast, the hair follicle is an epidermal appendage that shows cyclic apoptosis-driven involution, as part of the normal hair cycle. The different cell death programs need to be well orchestrated to maintain skin homeostasis. One of the major environmental insults to the skin is UVB radiation, causing the occurrence of apoptotic sunburn cells. Deregulation of cell death mechanisms in the skin can lead to diseases such as cancer, necrolysis and graft-versus-host disease. Here we review the apoptotic and the anti-apoptotic mechanisms in skin homeostasis and disease.