Protein Expression of TNF-α in Psoriatic Skin Is Regulated at a Posttranscriptional Level by MAPK-Activated Protein Kinase 2

Cytokine regulation by MAPK activated kinase 2 in keratinocytes exposed to sulfur mustard

Uncontrolled inflammation contributes to cutaneous damage following exposure to the warfare agent bis(2-chloroethyl) sulfide (sulfur mustard, SM). Activation of the p38 mitogen activated protein kinase (MAPK) precedes SM-induced cytokine secretion in normal human epidermal keratinocytes (NHEKs). This study examined the role of p38-regulated MAPK activated kinase 2 (MK2) during this process. Time course analysis studies using NHEK cells exposed to 200μM SM demonstrated rapid MK2 activation via phosphorylation that occurred within 15 min. p38 activation was necessary for MK2 phosphorylation as determined by studies using the p38 inhibitor SB203580. To compare the role of p38 and MK2 during SM-induced cytokine secretion, small interfering RNA (siRNA) targeting these proteins was utilized. TNF-α, IL-1β, IL-6 and IL-8 secretion was evaluated 24h postexposure, while mRNA changes were quantified after 8h. TNF-α, IL-6 and IL-8 up regulation at the protein and mRNA level was observed following SM exposure. IL-1β secretion was also elevated despite unchanged mRNA levels. p38 knockdown reduced SM-induced secretion of all the cytokines examined, whereas significant reduction in SM-induced cytokine secretion was only observed with TNF-α and IL-6 following MK2 knockdown. Our observations demonstrate potential activation of other p38 targets in addition to MK2 during SM-induced cytokine secretion.

p38 MAPK Signaling in Pemphigus: Implications for Skin Autoimmunity

p38 mitogen activated protein kinase (p38 MAPK) signaling plays a major role in the modulation of immune-mediated inflammatory responses and therefore has been linked with several autoimmune diseases. The extent of the involvement of p38 MAPK in the pathogenesis of autoimmune blistering diseases has started to emerge, but whether it pays a critical role is a matter of debate. The activity of p38 MAPK has been studied in great detail during the loss of keratinocyte cell-cell adhesions and the development of pemphigus vulgaris (PV) and pemphigus foliaceus (PF). These diseases are characterised by autoantibodies targeting desmogleins (Dsg). Whether autoantibody-antigen interactions can trigger signaling pathways (such as p38 MAPK) that are tightly linked to the secretion of inflammatory mediators which may perpetuate inflammation and tissue damage in pemphigus remains unclear. Yet, the ability of p38 MAPK inhibitors to block activation of the proapoptotic proteinase caspase-3 suggests that the induction of apoptosis may be a consequence of p38 MAPK activation during acantholysis in PV. This review discusses the current evidence for the role of p38 MAPK in the pathogenesis of pemphigus. We will also present data relating to the targeting of these cascades as a means of therapeutic intervention.

The Role of Mitogen-Activated Protein Kinase-Activated Protein Kinases (MAPKAPKs) in Inflammation

Mitogen-activated protein kinase (MAPK) pathways are implicated in several cellular processes including proliferation, differentiation, apoptosis, cell survival, cell motility, metabolism, stress response and inflammation. MAPK pathways transmit and convert a plethora of extracellular signals by three consecutive phosphorylation events involving a MAPK kinase kinase, a MAPK kinase, and a MAPK. In turn MAPKs phosphorylate substrates, including other protein kinases referred to as MAPK-activated protein kinases (MAPKAPKs). Eleven mammalian MAPKAPKs have been identified: ribosomal-S6-kinases (RSK1-4), mitogen- and stress-activated kinases (MSK1-2), MAPK-interacting kinases (MNK1-2), MAPKAPK-2 (MK2), MAPKAPK-3 (MK3), and MAPKAPK-5 (MK5). The role of these MAPKAPKs in inflammation will be reviewed.

Delivery systems and local administration routes for therapeutic siRNA

With the increasing number of studies proposing new and optimal delivery strategies for the efficacious silencing of gene-related diseases by the local administration of siRNAs, the present review aims to provide a broad overview of the most important and latest developments of non-viral siRNA delivery systems for local administration. Moreover, the main disease targets for the local delivery of siRNA to specific tissues or organs, including the skin, the lung, the eye, the nervous system, the digestive system and the vagina, were explored.

Skin regenerative potentials of curcumin

Curcumin, an active constituent of the spice turmeric, is well known for its chemopreventive properties and is found to be beneficial in treating various disorders including skin diseases. Curcumin protects skin by quenching free radicals and reducing inflammation through the inhibition of nuclear factor-kappa B. Curcumin also affects other signaling pathways including transforming growth factor-β and mitogen-activated protein kinase pathway. Curcumin also modulates the phase II detoxification enzymes which are crucial in detoxification reactions and for protection against oxidative stress. In the present review, the biological mechanisms of the chemopreventive potential of curcumin in various skin diseases like psoriasis, vitiligo, and melanoma is discussed. The application of curcumin in skin regeneration and wound healing is also elucidated. We also explored the recent innovations and advances involved in the development of transdermal delivery systems to enhance the bioavailability of curcumin, particularly in the skin. Recent clinical trials pertaining to the use of curcumin in skin diseases establishes its benefits and also the need for additional clinical trials in other diseases are discussed.

p38 mitogen-activated protein kinase (p38 MAPK)-mediated autoimmunity: lessons to learn from ANCA vasculitis and pemphigus vulgaris

Evidence is beginning to accumulate that p38 mitogen activated protein kinase (p38 MAPK) signaling pathway plays an important role in the regulation of cellular and humoral autoimmune responses. The exact mechanisms and the degree by which the p38 MAPK pathway participates in the immune-mediated induction of diseases have started to emerge. This review discusses the recent advances in the molecular dissection of the p38 MAPK pathway and the findings generated by reports investigating its role in the pathogenesis of autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and autoimmune hepatitis. Application of newly-developed protocols based on sensitive flow cytometric detection has proven to be a useful tool in the investigation of the phosphorylation of p38 MAPK within different peripheral blood mononuclear cell populations and may help us to better understand the enigmatic role of this signaling cascade in the induction of autoimmunity as well as its role in immunosuppressive-induced remission. Special attention is paid to reported data proposing a specific role for autoantibody-induced activation of p38 MAPK-mediated immunopathology in the pathogenesis of autoimmune blistering diseases and anti-neutrophilic antibody-mediated vasculitides.

Lentiviral vectors for cutaneous RNA managing

Post-transcriptional managing of RNA plays a key role in the intricate network of cellular pathways that regulate our genes. Numerous small RNA species have emerged as crucial regulators of RNA processing and translation. Among these, microRNAs (miRNAs) regulate protein synthesis through specific interactions with target RNAs and are believed to play a role in almost any cellular process and tissue. Skin is no exception, and miRNAs are intensively studied for their role in skin homoeostasis and as potential triggers of disease. For use in skin and many other tissues, therapeutic RNA managing by small RNA technologies is now widely explored. Despite the easy accessibility of skin, the natural barrier properties of skin have challenged genetic intervention studies, and unique tools for studying gene expression and the regulatory role of small RNAs, including miRNAs, in human skin are urgently needed. Human immunodeficiency virus (HIV)-derived lentiviral vectors (LVs) have been established as prominent carriers of foreign genetic cargo. In this review, we describe the use of HIV-derived LVs for efficient gene transfer to skin and establishment of long-term transgene expression in xenotransplanted skin. We outline the status of engineered LVs for delivery of small RNAs and their in vivo applicability for expression of genes and small RNA effectors including small hairpin RNAs, miRNAs and miRNA inhibitors. Current findings suggest that LVs may become key tools in experimental dermatology with particular significance for cutaneous RNA managing and in vivo genetic intervention.

Absence of a human DnaJ protein hTid-1S correlates with aberrant actin cytoskeleton organization in lesional psoriatic skin

The biochemical mechanism by which the human tumorous imaginal disc1(S) (hTid-1(S)) interferes with actin cytoskeleton organization in keratinocytes of human skin epidermis was investigated. We found that hTid-1, specifically hTid-1(S), interacts with MK5, a p38-regulated/activated protein kinase, and inhibits the protein kinase activity of MK5 that phosphorylates heat shock protein HSP27 in cultured HeLa cells. Thus, hTid-1(S) expression inhibits the phosphorylation of HSP27 known to play important roles in F-actin polymerization and actin cytoskeleton organization. The interplay between MK5/HSP27 signaling and hTid-1(S) expression was supported by the inhibition of HSP27 phosphorylation and MK5 activity in HeLa cells in response to hypoxia during which hTid-1(S) expression was down-regulated. We also found that overexpression of hTid-1(S) results in the inhibition of HSP27 phosphorylation, F-actin polymerization, and actin cytoskeleton organization in transduced HaCaT keratinocytes. This study further proposes that the loss of hTid-1(S) expression in the basal layer of skin epidermis correlates with the enhanced HSP27 phosphorylation, keratinocyte hyperproliferation, and excess actin cytoskeleton organization in lesional psoriatic skin.

Understanding the molecular basis of MK2-p38α signaling complex assembly: insights into protein-protein interaction by molecular dynamics and free energy studies

The formation of a p38 MAPK and MAPK-activated protein kinase 2 (MK2) signaling complex is physiologically relevant to cellular responses such as the proinflammatory cytokine production. The interaction between p38α isoform and MK2 is of great importance for this signaling. In this study, molecular dynamics simulation and binding free energy calculation were performed on the MK2-p38α signaling complex to investigate the protein-protein interaction between the two proteins. Dynamic domain motion analyses were performed to analyze the conformational changes between the unbound and bound states of proteins during the interaction. The activation loop, αF-I helices, and loops among α helices in the C-lobe of MK2 are found to be highly flexible and exhibit significant changes upon p38α binding. The results also show that after the binding of p38α, the N- and C-terminal domains of MK2 display an opening and twisting motion centered on the activation loop. The molecular mechanics Poisson-Boltzmann and generalized-Born surface area (MM-PB/GBSA) methods were used to calculate binding free energies between MK2 and p38α. The analysis of the components of binding free energy calculation indicates that the van der Waals interaction and the nonpolar solvation energy provide the driving force for the binding process, while the electrostatic interaction contributes critically to the specificity, rather than to MK2-p38α binding affinity. The contribution of each residue at the interaction interface to the binding affinity of MK2 with p38α was also analyzed by free energy decomposition. Several important residues responsible for the protein-protein interaction were also identified.

The inflammatory response of keratinocytes and its modulation by vitamin D: the role of MAPK signaling pathways

The hormonal form of vitamin D, calcitriol, and its analogs are known for their beneficial effect in the treatment of inflammatory skin disorders. Keratinocytes play a role in epidermal inflammatory responses invoked by breeching of the epidermal barrier, by infectious agents and by infiltrating immune cells. We studied the role of calcitriol in the initiation of keratinocyte inflammatory response by the viral and injury mimic polyinosinic-polycytidylic acid (poly(I:C)) and in its maintenance by tumor-necrosis-factor α (TNFα) and investigated the role of the mitogen-activated protein kinase cascades in these processes and their regulation by calcitriol. The inflammatory response of human HaCaT keratinocytes to poly(I:C) or TNFα was assessed by measuring mRNA levels of 13 inflammation-related molecules by real-time PCR microarray and by in-depth investigation of the regulation of interleukin 8, intercellular-adhesion-molecule 1, and TNFα expression. We found that while calcitriol had only a minor effect on the keratinocyte response to poly(I:C) and a modest effect on the early response (2 h) to TNFα, it markedly attenuated the later response (16-24 h) to TNFα. The expression of CYP27B1, the enzyme responsible for calcitriol production, was marginally increased by poly(I:C) and markedly by TNFα treatment. This pattern suggests that while allowing the initial keratinocyte inflammatory response to proceed, calcitriol contributes to its timely resolution. Using pharmacological inhibitors we found that while the p38 MAPK and the extracellular signal-regulated kinase have only a minor role, c-Jun N-terminal kinase plays a pivotal role in the induction of the pro-inflammatory genes and its modulation by calcitriol.

C-reactive protein induces interleukin-6 and thrombospondin-1 protein and mRNA expression through activation of nuclear factor-ĸB in HK-2 cells

BACKGROUND

Although C-reactive protein (CRP) is significantly increased in patients with diabetic nephropathy, whether CRP exerts direct proinflammatory effects on human renal tubular epithelial cells (HK-2 cells) is still unclear.

METHODS

HK-2 cells were incubated with purified CRP at clinically relevant concentrations (0, 5, 10, 20 and 40 μg/ml). The protein and transcript levels of thrombospondin-1 (TSP-1) and interleukin-6 (IL-6) were determined by ELISA and RT-PCR. Phosphorylation of p38MAPK was investigated through Western blot analysis in HK-2 cells induced by CRP. The activation of nuclear factor-kappa B (NF-κB) was studied via EMSA. A specific p38MAPK inhibitor (SB203580) and an NF-κB inhibitor (PDTC; pyrrolidine dithiocarbamate) were used to analyze the signal transduction in CRP induction. To explore the direct or indirect role of CRP in HK-2 cells, IL-6 or TSP-1 antibodies were used. The expression of IL-6, TSP-1 and transforming growth factor-β(1 )(TGF-β(1)) were determined through Western blot analysis in HK-2 cells.

RESULTS

In HK-2 cells, purified CRP significantly induced protein release and mRNA expression of IL-6 and TSP-1 in a dose- and time-dependent manner. TGF-β(1) protein was overexpressed in HK-2 cells induced by CRP, which cannot be inhibited by IL-6 or TSP-1 antibodies. CRP triggered phosphorylation of p38MAPK and activation of NF-κB-mediated signal transduction. SB203580 (5 μM) and PDTC (50 μM) efficiently suppressed those effects of CRP in HK-2 cells.

CONCLUSIONS

CRP induces IL-6 and TSP-1 protein release and mRNA expression from HK-2 cells via activation of the p38MAPK and NF-κB signaling pathways and TGF-β(1) was highly expressed in HK-2 cells, suggesting that CRP plays an important role in the propagation and prolongation of inflammation in renal fibrosis.

Low-molecular-weight MK2 inhibitors: a tough nut to crack!

The p38 pathway has been at the center of interest for anti-inflammatory drug discovery for many years as it is crucial for the biosynthesis of TNF-α, IL-1β and other mediators. Most of the anti-inflammatory effects of p38 inhibition are mediated through MAPK-activated protein kinase-2 (MK2), a direct downstream target of p38, which makes MK2 a very interesting drug target. Within the last 5 years, several classes of low-molecular-weight MK2 inhibitors were disclosed in the patent and primary literature. Advanced compounds could be optimized to nanomolar potencies and inhibit TNF-α release, as well as the phosphorylation of the MK2 substrate heat-shock protein 27 in cellular assays. This article will review the recent progress in this field and will highlight and discuss the most promising compound series disclosed so far.

Regulation of caspase 14 expression in keratinocytes by inflammatory cytokines--a possible link between reduced skin barrier function and inflammation?

Caspase 14 is a unique member of the cysteinyl aspartate-specific proteinase family. Its expression is confined primarily to cornified epithelium such as the skin. Caspase 14 has been associated with the processing of filaggrin monomers and the development of natural moisturising factors of the skin, and thus, it could be speculated that caspase 14 dysregulation is implicated in the development of an impaired skin barrier function. We have investigated the regulation of caspase 14 transcription in cultured primary keratinocytes following stimulation with a number of factors present in inflamed skin, including T(H)1- and T(H)2-associated cytokines in addition to LPS and peptidoglycan. In particular, we found that T(H)2-associated cytokines reduced the caspase 14 mRNA level significantly. Furthermore, we found that the expression of caspase 14 was reduced in skin biopsies from patients with atopic dermatitis (AD), psoriasis and contact dermatitis, further supporting a role for this kinase in inflammatory skin conditions. Hence, the regulation of caspase 14 levels provides a possible link between impaired skin barrier function and inflammatory reactions in skin diseases such as AD and may offer an explanation to the skin barrier dysfunction in inflamed skin lesions.

Peptide inhibitors of MK2 show promise for inhibition of abdominal adhesions

BACKGROUND

Abdominal adhesions are a common side effect of surgical procedures with complications including infertility, chronic pain, and bowel obstruction, which may lead to the need for surgical lyses of the adhesions. Mitogen-activated protein kinase-activated protein kinase 2 (MK2) has been implicated in several diseases, involving inflammation and fibrosis. Thus, the development of a cell-penetrating peptide (CPP) that modulates MK2 activity may confer therapeutic benefit after abdominal surgery in general and more specifically after bowel anastomosis.

METHODS

This study evaluated the function of a CPP inhibitor of MK2 in human mesothelial cells and in a rat bowel anastomosis model. To determine IC50 and basic specificity, kinase inhibition was performed using a radiometric assay. Enzyme-linked immunoassay (ELISA) was used to evaluate interleukin-6 (IL-6) expression in response to IL-1β and tumor necrosis factor-α (TNF-α) stimulation in vitro to validate MK2 kinase inhibition. Following bowel anastomosis (10 rats for each control and treatment at 4 and 10 d), the rats were evaluated for weight loss, normal healing (colonic burst strength and hydroxyproline content at the anastomosis), and number and density of adhesions.

RESULTS

The IC50 of the MK2 inhibitor peptide (22 μM) was similar to that of the nonspecific small molecule rottlerin (IC50 = 5 μM). The MK2 inhibitor peptide was effective at suppressing IL-1β and TNF-α stimulated IL-6 expression in mesothelial cells. In vivo, the MK2 inhibitor peptide was effective at suppressing both the density and number of adhesions formed as a result of bowel an anastamosis. Importantly, the peptide had no negative effect on normal healing.

CONCLUSIONS

In conclusion, the peptide inhibitor of MK2, MMI-0100, has the potential to significantly reduce inflammation through suppression of inflammatory cytokine expression and showed promise as a therapeutic for abdominal adhesions.

Effects of AIN457, a fully human antibody to interleukin-17A, on psoriasis, rheumatoid arthritis, and uveitis

Interleukin-17A (IL-17A) is elaborated by the T helper 17 (T(H)17) subset of T(H) cells and exhibits potent proinflammatory properties in animal models of autoimmunity, including collagen-induced arthritis, experimental autoimmune encephalomyelitis, and experimental autoimmune uveitis. To determine whether IL-17A mediates human inflammatory diseases, we investigated the efficacy and safety of AIN457, a human antibody to IL-17A, in patients with psoriasis, rheumatoid arthritis, and chronic noninfectious uveitis. Patients with chronic plaque-type psoriasis (n = 36), rheumatoid arthritis (n = 52), or chronic noninfectious uveitis (n = 16) were enrolled in clinical trials to evaluate the effects of neutralizing IL-17A by AIN457 at doses of 3 to 10 mg/kg, given intravenously. We evaluated efficacy by measuring the psoriasis area and severity index (PASI), the American College of Rheumatology 20% response (ACR20) for rheumatoid arthritis, or the number of responders for uveitis, as defined by either vision improvement or reduction in ocular inflammation or corticosteroid dose. AIN457 treatment induced clinically relevant responses of variable magnitude in patients suffering from each of these diverse immune-mediated diseases. Variable response rates may be due to heterogeneity in small patient populations, differential pathogenic roles of IL-17A in these diseases, and the different involvement or activation of IL-17A-producing cells. The rates of adverse events, including infections, were similar in the AIN457 and placebo groups. These results support a role for IL-17A in the pathophysiology of diverse inflammatory diseases including psoriasis, rheumatoid arthritis, and noninfectious uveitis.

Role of neuropeptide, cytokine, and growth factor signaling in complex regional pain syndrome

OBJECTIVE

Complex regional pain syndrome (CRPS) patients exhibit multiorgan pathology and inflammatory changes after limb trauma. The objective of this study was to identify how neuro-cutaneous signaling is facilitated after fracture and examine how this altered signaling contributes to the development of CRPS-like changes in the injured limb.

DESIGN AND METHODS

These studies used a rat tibia fracture model that reliably generates hindpaw warmth, edema, increased spontaneous protein extravasation, allodynia, unweighting, and periarticular bone loss, a symptom complex resembling the vascular, nociceptive, and bone sequelae observed in early CRPS. Substance P (SP)-evoked extravasation responses, EIA and PCR assays, and immunohistochemical techniques were used to evaluate post-fracture up-regulation of neuro-cutaneous inflammatory signaling. A SP NK1 receptor antagonist was used to inhibit CRPS-like changes in the fracture model.

RESULTS

In the rat fracture model the SP-evoked extravasation and edema responses were enhanced. SP NK1 receptor expression also increased in the microvascular endothelial cells in the fracture hindpaw skin, leading us to postulate that NK1 receptor up-regulation mediates the facilitated extravasation and edema responses observed after SP injection. The NK1 receptor antagonist LY303870 reversed hindpaw warmth, edema, increased vascular permeability, allodynia, and unweighting observed after tibia fracture in rats. There was also increased keratinocyte proliferation and NK1 receptor expression in the fracture hindpaw. Similar to the rat fracture model, we have observed increased epidermal thickness and keratinocyte NK1 expression in skin biopsies from CRPS patients. There was an up-regulation of inflammatory cytokine expression in the rat hindpaw skin and in keratinocytes at 4 weeks post-fracture. These inflammatory mediators appear to play a crucial role in the development of pain behavior after fracture, as we have repeatedly demonstrated that inhibition of cytokine, and NGF signaling prevents the allodynia and attenuates unweighting at 4 weeks post-fracture. LY303870 treatment also reversed post-fracture keratinocyte proliferation, suggesting that SP might be acting as an intermediate mediator in the inflammatory cascade by causing the up-regulation of inflammatory proteins that can directly sensitize nociceptors in the skin and joints.

CONCLUSIONS

Collectively, these data suggest that neuro-cutaneous signaling is up-regulated and can mediate inflammatory changes observed in the hindpaw skin of the fracture rat model and in human CRPS skin. Future translational and clinical studies mapping these inflammatory changes may identify novel therapeutic targets for preventing post-traumatic pain from transitioning into chronic CRPS.

A Characterization of the expression of 14-3-3 isoforms in psoriasis, basal cell carcinoma, atopic dermatitis and contact dermatitis

14-3-3 is a highly conserved protein involved in a number of cellular processes including cell signalling, cell cycle regulation and gene transcription. Seven isoforms of the protein have been identified; β, γ, ε, ζ η σ and τ. The expression profile of the various isoforms in skin diseases is unknown. To investigate the expression of the seven 14-3-3 isoforms in involved and uninvolved skin from psoriasis, basal cell carcinoma (BCC), atopic dermatitis and nickel induced allergic contact dermatitis. Punch biopsies from involved and uninvolved skin were analyzed with quantitative reverse transcription-polymerase chain reaction to determine the mRNA expression of the 14-3-3 isoforms. The protein level of 14-3-3 isoforms was measured by Western blot technique in keratome biopsies from patients with psoriasis. Evaluation of dermal and epidermal protein expression was performed by immunofluorescence staining. Increased 14-3-3τ mRNA levels were detected in involved skin from patients with psoriasis, contact dermatitis and BCC. 14-3-3σ mRNA expression was increased in psoriasis and contact dermatitis, but not in BCC. In atopic dermatitis no significant difference between involved and uninvolved skin was found. The expression of the 14-3-3 isoforms was also studied at the protein level in psoriasis. Only 14-3-3τ expression was significantly increased in involved psoriatic skin compared with uninvolved skin. Immunofluorescence staining with 14-3-3τ- and 14-3-3σ-specific antibodies showed localization of both isoforms to the cytoplasm of the keratinocytes in the various skin sections. These results demonstrate a disease specific expression profile of the 14-3-3τ and 14-3-3σ iso-forms.

Regulation of cytokines by small RNAs during skin inflammation

Intercellular signaling by cytokines is a vital feature of the innate immune system. In skin, an inflammatory response is mediated by cytokines and an entwined network of cellular communication between T-cells and epidermal keratinocytes. Dysregulated cytokine production, orchestrated by activated T-cells homing to the skin, is believed to be the main cause of psoriasis, a common inflammatory skin disorder. Cytokines are heavily regulated at the transcriptional level, but emerging evidence suggests that regulatory mechanisms that operate after transcription play a key role in balancing the production of cytokines. Herein, we review the nature of cytokine signaling in psoriasis with particular emphasis on regulation by mRNA destabilizing elements and the potential targeting of cytokine-encoding mRNAs by miRNAs. The proposed linkage between mRNA decay mediated by AU-rich elements and miRNA association is described and discussed as a possible general feature of cytokine regulation in skin. Moreover, we describe the latest attempts to therapeutically target cytokines at the RNA level in psoriasis by exploiting the cellular RNA interference machinery. The applicability of cytokine-encoding mRNAs as future clinical drug targets is evaluated, and advances and obstacles related to topical administration of RNA-based drugs targeting the cytokine circuit in psoriasis are described.

Identifying targets of miR-143 using a SILAC-based proteomic approach

Although the targets of most miRNAs have not been experimentally identified, microRNAs (miRNAs) have begun to be extensively characterized in physiological, developmental and disease-related contexts in recent years. Thus far, mainly computational approaches have been employed to predict potential targets for the large majority of miRNAs. Although miRNAs exert a major influence on the efficiency of translation of their targets in animals, most studies describing experimental identification of miRNA target genes are based on detection of altered mRNA levels. miR-143 is a miRNA involved in tumorigenesis in multiple types of cancer, smooth muscle cell fate and adipocyte differentiation. Only a few miR-143 targets are experimentally verified, so we employed a SILAC-based quantitative proteomic strategy to systematically identify potential targets of miR-143. In total, we identified >1200 proteins from MiaPaCa2 pancreatic cancer cells, of which 93 proteins were downregulated >2-fold in miR-143 mimic transfected cells as compared to controls. Validation of 34 of these candidate targets in luciferase assays showed that 10 of them were likely direct targets of miR-143. Importantly, we also carried out gene expression profiling of the same cells and observed that the majority of the candidate targets identified by proteomics did not show a concomitant decrease in mRNA levels confirming that miRNAs affect the expression of most targets through translational inhibition. Our study clearly demonstrates that quantitative proteomic approaches are important and necessary for identifying miRNA targets.

Identifying targets of miR-143 using a SILAC-based proteomic approach

Although the targets of most miRNAs have not been experimentally identified, microRNAs (miRNAs) have begun to be extensively characterized in physiological, developmental and disease-related contexts in recent years. Thus far, mainly computational approaches have been employed to predict potential targets for the large majority of miRNAs. Although miRNAs exert a major influence on the efficiency of translation of their targets in animals, most studies describing experimental identification of miRNA target genes are based on detection of altered mRNA levels. miR-143 is a miRNA involved in tumorigenesis in multiple types of cancer, smooth muscle cell fate and adipocyte differentiation. Only a few miR-143 targets are experimentally verified, so we employed a SILAC-based quantitative proteomic strategy to systematically identify potential targets of miR-143. In total, we identified >1200 proteins from MiaPaCa2 pancreatic cancer cells, of which 93 proteins were downregulated >2-fold in miR-143 mimic transfected cells as compared to controls. Validation of 34 of these candidate targets in luciferase assays showed that 10 of them were likely direct targets of miR-143. Importantly, we also carried out gene expression profiling of the same cells and observed that the majority of the candidate targets identified by proteomics did not show a concomitant decrease in mRNA levels confirming that miRNAs affect the expression of most targets through translational inhibition. Our study clearly demonstrates that quantitative proteomic approaches are important and necessary for identifying miRNA targets.

TRIF signaling stimulates translation of TNF-alpha mRNA via prolonged activation of MK2

The adapter protein TRIF mediates signal transduction through TLR3 and TLR4, inducing production of type I IFNs and inflammatory cytokines. The present study investigates the mechanisms by which TRIF signaling controls TNF-alpha biosynthesis. We provide evidence that, in LPS-stimulated murine dendritic cells, TRIF stimulates TNF-alpha biosynthesis selectively at the posttranscriptional level by promoting mRNA translation. In the absence of functional TRIF, the production of TNF-alpha protein was severely impaired, whereas TNF-alpha mRNA levels and stability, as well as transcriptional activity of the Tnfa gene, were not affected. Similarly, TRIF was required for production of LPS-induced TNF-alpha protein, but not of mRNA, in bone marrow-derived macrophages. In peritoneal macrophages, however, TRIF was also required for normal induction of TNF-alpha mRNA, suggesting cell type-related functions of TRIF. The influence of TRIF on dendritic cell TNF-alpha production was independent of type I IFNs. TRIF was required for prolonged activation of MAPKs in LPS-stimulated dendritic cells but was dispensable for the activation of NF-kappaB. Inhibition of late p38 activity attenuated LPS-stimulated elevation of TNF-alpha protein but not mRNA levels. The p38 effector kinase MK2 was directly activated through the TRIF pathway of TLR4. Importantly, stimulation of Mk2(-/-) cells through TLR3 or TLR4 severely impaired TNF-alpha protein production but did not affect TNF-alpha mRNA induction. Together, these results indicate that the TRIF signaling pathway promotes TNF-alpha mRNA translation through activation of the protein kinase MK2.

MAPKAPK-2 signaling is critical for cutaneous wound healing

Cutaneous wound healing is a complex process, which is heavily dependent on successful inflammatory action. Mitogen-activated protein kinase (MAPK)-activated protein kinase-2 (MAPKAPK-2 or MK2), a major substrate of p38 MAPK, has been shown to be a major player in multiple inflammatory diseases, but its role in cutaneous wound healing has not yet been explored. In this study, by comparing excisional wounds made on the backs of MK2 knockout (KO) and MK2 wild-type (WT) mice, we found that the kinetics of wound healing are significantly affected by the absence of MK2 (P=0.010 to P<0.001). Histological examination showed a higher level of acanthosis of the migrating wound keratinocyte layer as well as a higher level of collagen deposition in the granulation tissue of the wounds from MK2 WT mice compared with those from MK2 KO mice. Interestingly, although MK2 did not influence macrophage and neutrophil infiltration of the wounds, the expression of many cytokines and chemokines was significantly affected at different days post wounding. Furthermore, the delayed healing rate of wounds in MK2 KO mice can be significantly improved by passive transfer of macrophages with intact MK2. Overall, these results show a critical role for MK2 gene expression in macrophages participating in the process of cutaneous wound healing.

The p38 MAPK regulates IL-24 expression by stabilization of the 3' UTR of IL-24 mRNA

Background

IL-24 (melanoma differentiation-associated gene-7 (mda-7)), a member of the IL-10 cytokine family, possesses the properties of a classical cytokine as well as tumor suppressor effects. The exact role of IL-24 in the immune system has not been defined but studies have indicated a role for IL-24 in inflammatory conditions such as psoriasis. The tumor suppressor effects of IL-24 include inhibition of angiogenesis, sensitization to chemotherapy, and p38 mitogen-activated protein kinase (MAPK)-mediated apoptosis. Current knowledge on the regulation of IL-24 expression is sparse. Previous studies have suggested that mRNA stabilization is of major importance to IL-24 expression. Yet, the mechanisms responsible for the regulation of IL-24 mRNA stability remain unidentified. As p38 MAPK is known to regulate gene expression by interfering with mRNA degradation we examined the role of p38 MAPK in the regulation of IL-24 gene expression in cultured normal human keratinocytes.

Methodology/Principal Findings

In the present study we show that anisomycin- and IL-1β- induced IL-24 expression is strongly dependent on p38 MAPK activation. Studies of IL-24 mRNA stability in anisomycin-treated keratinocytes reveal that the p38 MAPK inhibitor SB 202190 accelerates IL-24 mRNA decay suggesting p38 MAPK to regulate IL-24 expression by mRNA-stabilizing mechanisms. The insertion of the 3′ untranslated region (UTR) of IL-24 mRNA in a tet-off reporter construct induces degradation of the reporter mRNA. The observed mRNA degradation is markedly reduced when a constitutively active mutant of MAPK kinase 6 (MKK6), which selectively activates p38 MAPK, is co-expressed.

Conclusions/Significance

Taken together, we here report p38 MAPK as a regulator of IL-24 expression and determine interference with destabilization mediated by the 3′ UTR of IL-24 mRNA as mode of action. As discussed in the present work these findings have important implications for our understanding of IL-24 as a tumor suppressor protein as well as an immune modulating cytokine.

MK2 regulates the early stages of skin tumor promotion

The association between inflammation and tumorigenesis is well recognized. Mitogen-activated protein kinase-activated protein kinase-2 (MK2) is known to play a pivotal role in inflammatory processes. Here, we studied the effect of MK2-deficiency and tumor necrosis factor (TNF)-alpha-deficiency on skin tumor development in mice using the two-stage chemical carcinogenesis model. We found that MK2(-/-) mice developed significantly fewer skin tumors compared with both TNF-alpha(-/-) and wild-type mice when induced by initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and by promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA). The TPA-induced inflammatory response was reduced in both, TNF-alpha(-/-) mice and MK2(-/-) mice, but most pronounced in TNF-alpha(-/-) mice, indicating that a reduced inflammatory response was not the only explanation for the inhibited tumorigenesis seen in MK2(-/-) mice. Interestingly, increased numbers of apoptotic cells were detected in the epidermis of MK2(-/-) mice compared with TNF-alpha(-/-) and wild-type mice, suggesting an additional role of MK2 in the regulation of apoptosis. This was further supported by: (i) increased levels of the tumor suppressor protein p53 in MK2(-/-) mice after DMBA/TPA treatment compared with controls, (ii) reduced phosphorylation (activation) of the negative p53 regulator, murine double minute 2 in MK2(-)(/-) mouse keratinocytes in vitro and (iii) a significant decrease in the DMBA/TPA induced apoptosis in cultured MK2(-/-) keratinocytes transfected with p53 small interfering RNA. Taken together, these findings demonstrate a dual role of MK2 in the early stages of tumor promotion through regulation of both the inflammatory response and apoptosis of DNA-damaged cells. These results also identify MK2 as a putative target for future skin carcinoma therapy.

Molecular pathophysiology of psoriasis and molecular targets of antipsoriatic therapy

Psoriasis is a chronic inflammatory skin disease characterised by elevated red scaly plaques on specific body sites. Histologically, the plaques are defined by epidermal hyperplasia, epidermal and dermal infiltration by leukocytes, and changes in the dermal microvasculature. Differentiation and activation are disturbed in lesional psoriatic keratinocytes, and the pool of proliferating keratinocytes is increased, which is accompanied by enhanced production of proinflammatory cytokines, adhesion molecules and antimicrobial peptides. These changes in psoriatic keratinocytes are caused by altered expression of genes associated with epidermal differentiation, and by activation of signalling pathways involving signal transducer and activator of transcription 3 (STAT3), type I interferon (IFN) and mitogen-activated protein kinase (MAPK). The number of T cells, and myeloid and plasmacytoid dendritic cells (DCs) is markedly increased in psoriatic lesions. Myeloid DCs produce interleukin (IL)-23, tumour necrosis factor (TNF)-alpha and inducible nitric oxide synthase (iNOS), which are crucial cytokines in the pathogenesis of psoriasis. IL-23 stimulates the secretion of IL-22 by T helper 17 cells, and IL-22 induces epidermal hyperplasia. The crosstalk between keratinocytes and leukocytes via their proinflammatory cytokines creates the vicious circle of chronic skin inflammation seen in psoriasis. This suggests that optimal treatment of psoriasis needs to target pathogenic pathways in both leukocytes and keratinocytes.

The UV response of the skin: a review of the MAPK, NFkappaB and TNFalpha signal transduction pathways

The sun emits different types of ultraviolet (UV) light. Our skin is a natural target of UV radiation which is involved in vitamin D3 production in our body. UV radiation at high doses is an environmental carcinogen which can elicit skin damage as well as inducing skin cancer. It can mediate inflammatory and immunological reactions through activation of receptors, DNA/RNA damage and production of reactive oxygen species. It is also involved in the release of pro-inflammatory cytokines, of which TNFalpha has been implicated in tumorigenic activities. In order to mediate its effects, UV radiation is known to activate multiple signalling cascades such as the p38 MAPK, Jun N-terminal kinase, extracellular signal-regulated kinase 1/2 and NFkappaB pathways in skin cells. The role each of these pathways plays in mediating the release of cytokines such as TNFalpha remains to be fully characterized. Once the function of these pathways is known, this information may provide for the formulation of therapy which will prevent the release of immunosuppressive cytokines resulting in a reduction in skin cancer formation.

The role of mitogen-activated protein kinase-activated protein kinase 2 in the p38/TNF-alpha pathway of systemic and cutaneous inflammation

Mitogen-activated protein kinase-activated protein kinase 2 (MK2) is a downstream molecule of p38, involved in the production of TNF-alpha, a key cytokine, and an established drug target for many inflammatory diseases. We investigated the role of MK2 in skin inflammation to determine its drug target potential. MK2 deficiency significantly decreased plasma TNF-alpha levels after systemic endotoxin application. Deficient mice showed decreased skin edema formation in chronic 2-O-tetradecanoylphorbol-13-acetate (TPA)-induced irritative dermatitis and in subacute 2,4-dinitrofluorobenzene (DNFB)-induced contact hypersensitivity. Surprisingly, MK2 deficiency did not inhibit edema formation in subacute 2,4-dinitrochlorobenzene (DNCB)-induced contact allergy and even increased TNF-alpha and IL-1beta levels as well as granulocyte infiltration in diseased ears. Ear inflammation in this model, however, was inhibited by TNF-alpha neutralization as it was in the subacute DNFB model. MK2 deficiency also did not show anti-inflammatory effects in acute DNFB-induced contact hypersensitivity, whereas the p38 inhibitor, SB203580, ameliorated skin inflammation supporting a pathophysiological role of p38. When evaluating possible mechanisms, we found that TNF-alpha production in MK2-deficient spleen cells was strongly diminished after TLR stimulation but less affected after T-cell receptor stimulation. Our data suggest that MK2, in contrast to its downstream effector molecule, TNF-alpha, has a rather elusive role in T-cell-dependent cutaneous inflammation.

p38(MAPK): stress responses from molecular mechanisms to therapeutics

The p38(MAPK) protein kinases affect a variety of intracellular responses, with well-recognized roles in inflammation, cell-cycle regulation, cell death, development, differentiation, senescence and tumorigenesis. In this review, we examine the regulatory and effector components of this pathway, focusing on their emerging roles in biological processes involved in different pathologies. We summarize how this pathway has been exploited for the development of therapeutics and discuss the potential obstacles of targeting this promiscuous protein kinase pathway for the treatment of different diseases. Furthermore, we discuss how the p38(MAPK) pathway might be best exploited for the development of more effective therapeutics with minimal side effects in a range of specific disease settings.

Angiogenesis drives psoriasis pathogenesis

Psoriasis pathogenesis is closely associated with disease-inducing Th1 and Th17 cells. Yet, several studies suggest that aberrant keratinocyte or endothelial cell signalling significantly contributes to disease manifestation. Histological hallmarks of psoriatic skin include the infiltration of multiple immune cells, keratinocyte proliferation and increased dermal vascularity. Formation of new blood vessels starts with early psoriatic changes and disappears with disease clearance. Several angiogenic mediators like vascular endothelial growth factor, hypoxia-inducible factors, angiopoietins and pro-angiogenic cytokines, such as tumour necrosis factor (TNF), interleukin (IL)-8 and IL-17, are up-regulated in psoriasis development. Contact- and mediator-dependent factors derived from keratinocytes, mast cells and immune cells may contribute to the strong blood vessel formation of psoriasis. New technologies and experimental models provide new insights into the role of angiogenesis in psoriasis pathogenesis. Interestingly, many therapies target not only immune cells, but also protein structures of endothelial cells. Here we summarize the role of pro-angiogenic factors in psoriasis development and discuss angiogenesis as a potential target of novel therapies.

Amelioration of psoriasis by anti-TNF-alpha RNAi in the xenograft transplantation model

Tumor necrosis factor-alpha (TNF-alpha) is upregulated in psoriatic skin and represents a prominent target in psoriasis treatment. The level of TNF-alpha-encoding mRNA, however, is not increased in psoriatic skin, and it remains unclear whether intervention strategies based on RNA interference (RNAi) are therapeutically relevant. To test this hypothesis the present study describes first the in vitro functional screening of a panel of short hairpin RNAs (shRNAs) targeting human TNF-alpha mRNA and, next, the transfer of the most potent TNF-alpha shRNA variant, as assessed in vitro, to human skin in the psoriasis xenograft transplantation model by the use of lentiviral vectors. TNF-alpha shRNA treatment leads to amelioration of the psoriasis phentotype in the model, as documented by reduced epidermal thickness, normalization of the skin morphology, and reduced levels of TNF-alpha mRNA as detected in skin biopsies 3 weeks after a single vector injection of lentiviral vectors encoding TNF-alpha shRNA. Our data show efficient lentiviral gene delivery to psoriatic skin and therapeutic applicability of anti-TNF-alpha shRNAs in human skin. These findings validate TNF-alpha mRNA as a target molecule for a potential persistent RNA-based treatment of psoriasis and establish the use of small RNA effectors as a novel platform for target validation in psoriasis and other skin disorders.

Dose escalation of infliximab therapy in arthritis patients is related to diagnosis and concomitant methotrexate treatment: observational results from the South Swedish Arthritis Treatment Group register

OBJECTIVE

To study frequency of dose escalation in infliximab-treated patients and to identify possible predictors thereof.

METHODS

Patients with chronic arthritis initiating their first course of anti-TNF treatment with infliximab at Lund University Hospital were included in a structured clinical follow-up protocol. Information on diagnosis, drug dosage, disease duration, previous and ongoing DMARDs, treatment start and cessation were prospectively collected during the period March 1999 through February 2007. All patients were started on a dose of 3 mg/kg at time 0, week 2, week 6 and then every eighth week independent of diagnosis and were followed for a period of 2 yrs.

RESULTS

A total of 206 patients were included in the study. Thirty-two of the patients had PsA, 25 had AS and 149 patients had RA. A minor dose escalation, defined as less than doubling of the dosage, was observed for 53, 48 and 42% of the patients with PsA, AS and RA, respectively. The corresponding values for major dose escalation was observed for 19, 8 and 15% of the patients, respectively. Regression analysis showed that patients with a diagnosis of PsA (P = 0.03), longer follow-up period (P < 0.01), and lack of concomitant MTX treatment (P = 0.03) were significantly associated with risk of dose escalation.

CONCLUSION

Dose escalations were performed in 59% of all infliximab-treated patients during the first 2 yrs of treatment. Our data suggest that PsA patients might require higher dosages than RA and AS patients.

Reduced oxazolone-induced skin inflammation in MAPKAP kinase 2 knockout mice

Mitogen-activated protein kinase (MAPK) AP kinase 2 (MK2) is a serine/threonine kinase that is phosphorylated and activated by p38 MAPK. MK2 regulates the expression of various proinflammatory cytokines including TNF-alpha, IL-1beta, IL-6, and IL-8. Recently, MK2 was demonstrated to be activated in lesional psoriatic epidermis. This study investigates for the first time the role of MK2 in skin inflammation using the model of oxazolone-induced acute allergic contact dermatitis in mice. We show that oxazolone treatment leads to increased expression and sustained activation of both p38 MAPK and MK2. The inflammatory response was determined by ear thickness, myeloperoxidase activity, and histology after oxazolone challenge. Pretreatment with the p38 MAPK inhibitor SB202190 and genetic ablation of MK2 inhibit this inflammatory response. In particular, IL-1beta and, to a smaller but significant extent, also TNF-alpha and IFN-gamma expression were decreased in MK2 knockout mice compared with wild-type mice. These results indicate that MK2 is a potential target for the treatment of inflammatory skin diseases.

Characterization of the interleukin-17 isoforms and receptors in lesional psoriatic skin

BACKGROUND

Th17 cells are a lineage of proinflammatory T helper cells producing interleukin (IL)-17. The importance of Th17 cells in inflammation and autoimmunity has now been recognized. The IL-17 cytokine family consists of six isoforms (IL-17A-IL-17F) whereas five members of the IL-17 receptor (IL-17R) family have been identified (IL-17RA-IL-17RE).

OBJECTIVES

To characterize the expression of the IL-17 isoforms and receptors in lesional and nonlesional psoriatic skin. Methods Keratome and punch biopsies taken from patients with psoriasis were examined by enzyme-linked immunosorbent assay and quantitative reverse transcription-polymerase chain reaction in order to measure the IL-17 isoforms and receptors.

RESULTS

We demonstrated significantly increased mRNA expression of IL-17A, IL-17C and IL-17F in psoriatic skin. In contrast, the mRNA expression of IL-17B and IL-17D was significantly decreased in lesional compared with nonlesional skin, while IL-17E mRNA was undetectable. The increased mRNA expression of IL-17A, IL-17C and IL-17F was paralleled by an increased protein accumulation of these cytokines in psoriatic skin. Analysis of the IL-17R mRNA expression revealed significantly impaired mRNA expression of IL-17RB, IL-17RC, IL-17RD and IL-17RE in lesional psoriatic skin, whereas the mRNA expression of IL-17RA was similar in lesional and nonlesional psoriatic skin.

CONCLUSIONS

This study characterizes the mRNA profile of the IL-17 isoforms and receptors in psoriatic skin lesions. Furthermore, we demonstrate for the first time augmented protein levels of IL-17A, IL-17C and IL-17F in psoriatic skin lesions, indicating a possible role for IL-17C in addition to IL-17A and IL-17F in the pathogenesis of psoriasis.

Pentoxifylline attenuates nociceptive sensitization and cytokine expression in a tibia fracture rat model of complex regional pain syndrome

BACKGROUND

Tibia fracture in rats evokes chronic hindpaw warmth, edema, allodynia, and regional osteopenia, a syndrome resembling complex regional pain syndrome (CRPS). Previous studies suggest that the pathogenesis of some of these changes involves an exaggerated regional inflammatory response to injury and we postulated that inflammatory cytokines contribute to the development of CRPS-like changes after fracture.

METHODS

The distal tibia was fractured and the hindlimb casted for 4 weeks. The rats were given drinking water with or without the cytokine inhibitor pentoxifylline (PTX) starting the day before fracture and continuing for 4 weeks, after which time the cast was removed and multiple assays were performed in the hindpaw. PCR and immunoassays were used to evaluate changes in cytokine expression. Bilateral hindpaw thickness, temperature, and nociceptive thresholds were determined, and bone microarchitecture was measured by microcomputed tomography (microCT).

RESULTS

Tibia fracture chronically up-regulated TNFalpha, IL-1beta and IL-6 mRNA and protein levels in hindpaw skin and PTX treatment significantly reduced the mRNA expression and cytokine protein levels for all these cytokines. PTX inhibited the nociceptive sensitization and some vascular changes, but had insignificant effects on most of the bone-related parameters measured in these studies. Immunostaining of hindpaw skin was negative for immunocyte infiltration at 4 weeks post-fracture.

CONCLUSIONS

These results suggest that pro-inflammatory cytokines contribute to the nociceptive and vascular sequelae of fracture and that PTX treatment can reverse these CRPS-like changes.

Reactive oxygen species in tumor necrosis factor-alpha-activated primary human keratinocytes: implications for psoriasis and inflammatory skin disease

The multifunctional cytokine tumor necrosis factor-alpha (TNF-alpha) is known to play an important role in inflammatory and immunological responses in human skin. Although it has been documented that reactive oxygen species (ROS) are involved in TNF-alpha-induced signaling pathways associated with certain inflammatory diseases, their role in TNF-alpha signaling cascades has not been examined in primary human keratinocytes used as a model of inflammatory skin disease and psoriasis. Employing a series of in vitro and in cellulo approaches, we have demonstrated that in primary human keratinocytes (i) TNF-alpha rapidly induces ROS generation, IkappaB degradation, NF-kappaB p65 nuclear translocation, and ultimately production of inflammatory cytokines; (ii) TNF-alpha-induced cytokine production is mediated both by the mammalian target of rapamycin signaling pathway via NF-kappaB activation and by ROS; (iii) TNF-alpha-dependent NF-kappaB activation (that is, IkappaB degradation and NF-kappaB p65 nuclear translocation) is not mediated by ROS; and (iv) a cell-penetrating derivative of the antioxidant enzyme, catalase, as well as taurine and N-acetyl-cysteine attenuate the TNF-alpha-induced production of cytokines. These latter results suggest that catalase and perhaps other antioxidants should be considered as part of a more specific and effective therapy for the treatment of inflammatory skin diseases, including psoriasis.