Activation of cutaneous protein kinase C alpha induces keratinocyte apoptosis and intraepidermal inflammation by independent signaling pathways

Mechanistic Investigation of WWOX Function in NF-kB-Induced Skin Inflammation in Psoriasis

Psoriasis is a chronic inflammatory skin disease characterized by epidermal hyperproliferation, aberrant differentiation of keratinocytes, and dysregulated immune responses. WW domain-containing oxidoreductase (WWOX) is a non-classical tumor suppressor gene that regulates multiple cellular processes, including proliferation, apoptosis, and migration. This study aimed to explore the possible role of WWOX in the pathogenesis of psoriasis. Immunohistochemical analysis showed that the expression of WWOX was increased in epidermal keratinocytes of both human psoriatic lesions and imiquimod-induced mice psoriatic model. Immortalized human epidermal keratinocytes were transduced with a recombinant adenovirus expressing microRNA specific for WWOX to downregulate its expression. Inflammatory responses were detected using Western blotting, real-time quantitative reverse transcription polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay. In human epidermal keratinocytes, WWOX knockdown reduced nuclear factor-kappa B signaling and levels of proinflammatory cytokines induced by polyinosinic: polycytidylic acid [(poly(I:C)] in vitro. Furthermore, calcium chelator and protein kinase C (PKC) inhibitors significantly reduced poly(I:C)-induced inflammatory reactions. WWOX plays a role in the inflammatory reaction of epidermal keratinocytes by regulating calcium and PKC signaling. Targeting WWOX could be a novel therapeutic approach for psoriasis in the future.

Keratin 17- and PKCα-dependent transient amplification of neutrophil influx after repeated stress to the skin

Neutrophils contribute to the pathogenesis of chronic inflammatory skin diseases. Little is known about the source and identity of the signals mediating their recruitment in inflamed skin. We used the phorbol ester TPA and UVB, alone or in combination, to induce sterile inflammation in mouse skin and assess whether keratinocyte-derived signals impact neutrophil recruitment. A single TPA treatment results in a neutrophil influx in the dermis that peaks at 12h and resolves within 24h. A second TPA treatment or a UVB challenge, when applied at 24h but not 48h later, accelerates, amplifies, and prolongs neutrophil infiltration. This transient amplification response (TAR) is mediated by local signals in inflamed skin, can be recapitulated in ex vivo culture, and involves the K17-dependent sustainment of protein kinase Cα (PKCα) activity and release of neutrophil chemoattractants by stressed keratinocytes. We show that K17 binds RACK1, a scaffold essential for PKCα activity. Finally, analyses of RNAseq data reveal the presence of a transcriptomic signature consistent with TAR and PKCα activation in chronic inflammatory skin diseases. These findings uncover a novel, transient, and keratin-dependent mechanism that amplifies neutrophil recruitment to the skin under stress, with direct implications for inflammatory skin disorders.

Cilt Kanserlerinin Ayırıcı Tanısında İnflamatuar Belirteçlerin Yeri

Aim: The purpose of this study was to evaluate the role of WBC count, NLR, LMR, PLR, Systemic immune-inflammation index (SII) [(platelet count X neutrophil count) \ lymphocyte count] and platelet count (Plt)×NLR in the differential diagnosis of basal cell carcinoma, squamous cell carcinoma, and malignant melanoma and to determine the effect of tumor type, prediction of lymph node metastasis at initial diagnosis and location on these inflammatory markers. Material and Method: Patients who underwent surgery for basal cell carcinoma, squamous cell carcinoma, or malignant melanoma were retrospectively screened. NLR, LMR, PLR, SII and Plt×NLR were calculated. Relationships between tumor type, prediction of lymph node metastasis at initial diagnosis, tumor localization and the inflammatory and hematological parameters of interest were investigated. Tumor location was classified as head and neck and others. Results: A total of 257 patients were included in the study. No statistically significant differences in WBC, NLR, PLR, LMR, SII or Plt×NLR were detected according to tumor location. The patients with squamous cell carcinoma had higher NLR, PRL, SII and Plt×NLR values than those with basal cell carcinoma. The risk of lymph node metastasis at the time of initial diagnosis was 10.3 times higher in patients with PLR levels of 180.7 and higher. The risk of lymph node metastasis detected at initial diagnosis was 8.9 times higher in patients with Plt×NLR of 747 and higher. The risk of lymph node metastasis detected at initial diagnosis was 7.1 times higher in patients with SII of 414 and higher. Conclusion: Inflammatory markers seem to be useful in the differential diagnosis of skin cancers and determined the risk of lymph node metastasis. However, it does not differ according to tumor localization.

Role of mTOR Signaling Cascade in Epidermal Morphogenesis and Skin Barrier Formation

Simple Summary

The skin epidermis is a stratified multilayered epithelium that provides a life-sustaining protective and defensive barrier for our body. The barrier machinery is established and maintained through a tightly regulated keratinocyte differentiation program. Under normal conditions, the basal layer keratinocytes undergo active proliferation and migration upward, differentiating into the suprabasal layer cells. Perturbation of the epidermal differentiation program often results in skin barrier defects and inflammatory skin disorders. The protein kinase mechanistic target of rapamycin (mTOR) is the central hub of cell growth, metabolism and nutrient signaling. Over the past several years, we and others using transgenic mouse models have unraveled that mTOR signaling is critical for epidermal differentiation and barrier formation. On the other hand, there is increasing evidence that disturbed activation of mTOR signaling is significantly implicated in the development of various skin diseases. In this review, we focus on the formation of skin barrier and discuss the current understanding on how mTOR signaling networks, including upstream inputs, kinases and downstream effectors, regulate epidermal differentiation and skin barrier formation. We hope this review will help us better understand the metabolic signaling in the epidermis, which may open new vistas for epidermal barrier defect-associated disease therapy.

Abstract

The skin epidermis, with its capacity for lifelong self-renewal and rapid repairing response upon injury, must maintain an active status in metabolism. Mechanistic target of rapamycin (mTOR) signaling is a central controller of cellular growth and metabolism that coordinates diverse physiological and pathological processes in a variety of tissues and organs. Recent evidence with genetic mouse models highlights an essential role of the mTOR signaling network in epidermal morphogenesis and barrier formation. In this review, we focus on the recent advances in understanding how mTOR signaling networks, including upstream inputs, kinases and downstream effectors, regulate epidermal morphogenesis and skin barrier formation. Understanding the details of the metabolic signaling will be critical for the development of novel pharmacological approaches to promote skin barrier regeneration and to treat epidermal barrier defect-associated diseases.

The complexities of PKCα signaling in cancer

Protein kinase C α (PKCα) is a ubiquitously expressed member of the PKC family of serine/threonine kinases with diverse functions in normal and neoplastic cells. Early studies identified anti-proliferative and differentiation-inducing functions for PKCα in some normal tissues (e.g., regenerating epithelia) and pro-proliferative effects in others (e.g., cells of the hematopoietic system, smooth muscle cells). Additional well documented roles of PKCα signaling in normal cells include regulation of the cytoskeleton, cell adhesion, and cell migration, and PKCα can function as a survival factor in many contexts. While a majority of tumors lose expression of PKCα, others display aberrant overexpression of the enzyme. Cancer-related mutations in PKCα are uncommon, but rare examples of driver mutations have been detected in certain cancer types (e. g., choroid gliomas). Here we review the role of PKCα in various cancers, describe mechanisms by which PKCα affects cancer-related cell functions, and discuss how the diverse functions of PKCα contribute to tumor suppressive and tumor promoting activities of the enzyme. We end the discussion by addressing mutations and expression of PKCα in tumors and the clinical relevance of these findings.

Apoptosis in epithelial cells and its correlation with leukocyte accumulation in lamellar tissue from horses subjected to experimental sepsis-associated laminitis

Inflammation and apoptosis in the hoof lamellar interface both contribute to the early stages of sepsis-associated laminitis, but it is not clear whether apoptosis is occurring before the onset of inflammation or is being provoked by inflammation. Apoptosis and inflammation were therefore measured in lamellar tissues obtained at different time points throughout the early stages of experimentally induced laminitis. Apoptotic cells and leukocyte were enumerated in archived paraffin embedded lamellar tissue samples from previous experiments in which acute laminitis was induced using Black Walnut Extract (BWE) or starch (CHO). BWE-derived samples from 20 horses were allocated into four groups: Control (CON = 5); Early Time Point (ETP, 1.5 h after induction, n = 5); Developmental Time Point (DTP, 3-4 h after induction, n = 5); Obel Grade 1 (OG1, Onset of Lameness, n = 5). CHO-derived samples from 25 horses were allocated into four groups: CON (n = 8); DTP (10-12 h after induction, n = 6); OG 1 (n = 6); Obel 3 (OG3, lameness progression, n = 5). Apoptotic cells were enumerated using a horse validated TUNEL technique. Compared to controls, significant increases in apoptotic cell counts were not detected in lamellar epithelial cells during the developmental phase or at the onset of lameness during laminitis induction. A negative correlation between apoptosis and leukocyte infiltration was detected in the BWE model (P < 0.05). In conclusion, apoptosis does not play an important role in the initial stages of sepsis-related laminitis.

MHC II-PI3K/Akt/mTOR Signaling Pathway Regulates Intestinal Immune Response Induced by Soy Glycinin in Hybrid Grouper: Protective Effects of Sodium Butyrate

Soy glycinin (11S) is involved in immune regulation. As an additive, sodium butyrate (SB) can relieve inflammation caused by 11S. To further delve into the mechanisms. A diet containing 50% fishmeal was the control group (FM group), and the experimental groups consisted of the FM group baseline plus 2% glycinin (GL group), 8% glycinin (GH group), and 8% glycinin + 0.13% sodium butyrate (GH-SB group). The specific growth ratio (SGR), feed utilization, and density of distal intestinal (DI) type II mucous cells were increased in the GL group. In the serum, IFN-γ was significantly upregulated in the GL group, and IgG and IL-1β were upregulated in the GH group. IgG, IL-1β, and TNF-α in the GH-SB group were significantly downregulated compared to those in the GH group. The mRNA levels of mTOR C1, mTOR C2, and Deptor were upregulated in the GL, GH, and GH-SB groups in the DI compared with those in the FM group, while the mRNA levels of mTOR C1 and Deptor in the GH group were higher than those in the GL and GH-SB groups. 4E-BP1, RICTOR, PRR5, MHC II, and CD4 were upregulated in the GH group. TSC1, mLST8, and NFY mRNA levels in the GL and GH-SB groups were upregulated compared with those in the FM and GH groups. Western blotting showed P-PI3KSer294/T-PI3K, P-AktSer473/T-Akt, and P-mTORSer2448/T-mTOR were upregulated in the GH group. Collectively, our results demonstrate that low-dose 11S could improve serum immune by secreting IFN-γ. The overexpression of IgG and IL-1β is the reason that high-dose 11S reduces serum immune function, and supplementing SB can suppress this overexpression. Low-dose 11S can block the relationship between PI3K and mTOR C2. It can also inhibit the expression of 4E-BP1 through mTOR C1. High-dose 11S upregulates 4E-BP2 through mTOR C1, aggravating intestinal inflammation. SB could relieve inflammation by blocking PI3K/mTOR C2 and inhibiting 4E-BP2. Generally speaking, the hybrid grouper obtained different serum and DI immune responses under different doses of 11S, and these responses were ultimately manifested in growth performance. SB can effectively enhance serum immunity and relieve intestinal inflammation caused by high dose 11S.

Equivocal, explicit and emergent actions of PKC isoforms in cancer

The maturing mutational landscape of cancer genomes, the development and application of clinical interventions and evolving insights into tumour-associated functions reveal unexpected features of the protein kinase C (PKC) family of serine/threonine protein kinases. These advances include recent work showing gain or loss-of-function mutations relating to driver or bystander roles, how conformational constraints and plasticity impact this class of proteins and how emergent cancer-associated properties may offer opportunities for intervention. The profound impact of the tumour microenvironment, reflected in the efficacy of immune checkpoint interventions, further prompts to incorporate PKC family actions and interventions in this ecosystem, informed by insights into the control of stromal and immune cell functions. Drugging PKC isoforms has offered much promise, but when and how is not obvious.

Photocarcinogenesis

Purpose of Review

Skin cancers account for more than 40% of all cancers in the USA and continue to rise in incidence. It is prudent to understand the current burden and pathogenesis of photocarcinogenesis and preventive measures.

Recent Findings

Insights into recently discovered mechanisms have paved way for potential targets for prevention and therapeutics. Nicotinamide has shown promising results as an oral chemopreventive agent. UVB affects the DHODH pathway of pyrimidine synthesis via STAT 3. DHODH inhibition by leflunomide may be a potential targeted chemoprevention strategy. A photolyase containing sunscreen, which repairs UV-damaged DNA, effectively reduced new precancerous lesions. Several antioxidants and anti-inflammatory agents including many phytochemicals ameliorate the process of photocarcinogenesis in preclinical and clinical studies, e.g., green tea polyphenols, Polypodium leucotomos extract, and Timosaponin A III. Diet can potentially affect skin cancer risk by its ability to modify oxidative stress and cell signaling pathways.

Summary

Photocarcinogenesis is a multi-step process. An in-depth understanding is instrumental in development of novel agents for prevention and treatment of skin cancers.

Topical Application of a Dual ABC Transporter Substrate and NF-κB Inhibitor Blocks Multiple Sources of Cutaneous Inflammation in Mouse Skin

Among the molecular signals underlying cutaneous inflammation is the transcription complex NF-κB, its upstream modulators, and cytokines and chemokines that are the downstream proinflammatory effectors. Central to NF-κB activation is IκB kinase (IKK), which phosphorylates IκBα, releasing NF-κB to the nucleus. In a screening of a kinase inhibitor library, we identified two IKK inhibitors that were high-affinity substrates for p-glycoprotein (ABCB1), the multidrug resistance protein known to facilitate transdermal drug delivery. ACHP (2-amino-6-[2-(cyclopropylmethoxy)-6-hydroxyphenyl]-4-(4-piperidinyl)-3-pyridinecarbonitrile) and IKK 16 prevented both nuclear translocation of NF-κB and activation of a NF-κB reporter and reduced the induction of cytokine and chemokine transcripts in human or mouse keratinocytes by IL-1α, tumor necrosis factor-α, and phorbol myristate acetate. ACHP, but not IKK 16, was nontoxic to mouse or human keratinocytes at any dose tested. In mice, topical ACHP prevented the cutaneous inflammation induced by topical phorbol myristate acetate or imiquimod, reduced the inflammation from erythema doses of artificial sunlight, and lowered the tumor incidence of mice treated with 7,12-dimethyl benzanthracene when applied before phorbol myristate acetate. Topical ACHP also reduced the NF-κB and IL-17 inflammatory signature after multiple doses of imiquimod. Thus, ACHP and IKK 16 hit their NF-κB target in mouse and human keratinocytes, and ACHP is an effective topical nonsteroidal anti-inflammatory in mice.

Autoantibody Signaling in Pemphigus Vulgaris: Development of an Integrated Model

Pemphigus vulgaris (PV) is an autoimmune skin blistering disease effecting both cutaneous and mucosal epithelia. Blister formation in PV is known to result from the binding of autoantibodies (autoAbs) to keratinocyte antigens. The primary antigenic targets of pathogenic autoAbs are known to be desmoglein 3, and to a lesser extent, desmoglein 1, cadherin family proteins that partially comprise the desmosome, a protein structure responsible for maintaining cell adhesion, although additional autoAbs, whose role in blister formation is still unclear, are also known to be present in PV patients. Nevertheless, there remain large gaps in knowledge concerning the precise mechanisms through which autoAb binding induces blister formation. Consequently, the primary therapeutic interventions for PV focus on systemic immunosuppression, whose side effects represent a significant health risk to patients. In an effort to identify novel, disease-specific therapeutic targets, a multitude of studies attempting to elucidate the pathogenic mechanisms downstream of autoAb binding, have led to significant advancements in the understanding of autoAb-mediated blister formation. Despite this enhanced characterization of disease processes, a satisfactory explanation of autoAb-induced acantholysis still does not exist. Here, we carefully review the literature investigating the pathogenic disease mechanisms in PV and, taking into account the full scope of results from these studies, provide a novel, comprehensive theory of blister formation in PV.

Debromoaplysiatoxin as the Causative Agent of Dermatitis in a Dog after Exposure to Freshwater in California

Contamination of recreational waters with cyanobacterial toxins continues to increase and presents a risk to animals and humans. Although cases of acute hepato- and neurotoxicoses in dogs following cyanotoxin exposure exist, no reports of skin-related reactions in dogs exist. A 5-year-old female spayed 34 kg Bracco Italiano was initially presented for rapid onset of severe pruritus and urticaria. Marked excoriation and erythema were noted over the chest and neck, while urticaria was noted in the inguinal regions and ventral abdomen. Initial basic dermatology work-up excluded parasitic, fungal, and bacterial organisms. Due to the severity and progression of urticaria, the dog received IV dexamethasone and IM diphenhydramine. Improvement of the urticaria and the dog’s clinical status was noted over the next 45 min. Assessment of the dog’s environment revealed access to a lake on the property with visible algal bloom. Water from the lake was submitted for toxicology testing and revealed the presence of debromoaplysiatoxin. Access to the lake was discontinued and follow-up evaluation over the next few weeks revealed a complete resolution of the skin irritation. To the authors’ knowledge, this is the first case report of debromoaplysiatoxin exposure in a dog after swimming in cyanobacteria-contaminated water. Veterinarians should recognize the potential harm that contaminated waters may cause in terms of dermal, hepatic, and neurological conditions. In addition, more prudent oversight of contaminated recreational waters is recommended for animals and humans to prevent adverse events and intoxications.

A novel DLX3-PKC integrated signaling network drives keratinocyte differentiation

Epidermal homeostasis relies on a well-defined transcriptional control of keratinocyte proliferation and differentiation, which is critical to prevent skin diseases such as atopic dermatitis, psoriasis or cancer. We have recently shown that the homeobox transcription factor DLX3 and the tumor suppressor p53 co-regulate cell cycle-related signaling and that this mechanism is functionally involved in cutaneous squamous cell carcinoma development. Here we show that DLX3 expression and its downstream signaling depend on protein kinase C α (PKCα) activity in skin. We found that following 12-O-tetradecanoyl-phorbol-13-acetate (TPA) topical treatment, DLX3 expression is significantly upregulated in the epidermis and keratinocytes from mice overexpressing PKCα by transgenic targeting (K5-PKCα), resulting in cell cycle block and terminal differentiation. Epidermis lacking DLX3 (DLX3cKO), which is linked to the development of a DLX3-dependent epidermal hyperplasia with hyperkeratosis and dermal leukocyte recruitment, displays enhanced PKCα activation, suggesting a feedback regulation of DLX3 and PKCα. Of particular significance, transcriptional activation of epidermal barrier, antimicrobial peptide and cytokine genes is significantly increased in DLX3cKO skin and further increased by TPA-dependent PKC activation. Furthermore, when inhibiting PKC activity, we show that epidermal thickness, keratinocyte proliferation and inflammatory cell infiltration are reduced and the PKC-DLX3-dependent gene expression signature is normalized. Independently of PKC, DLX3 expression specifically modulates regulatory networks such as Wnt signaling, phosphatase activity and cell adhesion. Chromatin immunoprecipitation sequencing analysis of primary suprabasal keratinocytes showed binding of DLX3 to the proximal promoter regions of genes associated with cell cycle regulation, and of structural proteins and transcription factors involved in epidermal differentiation. These results indicate that Dlx3 potentially regulates a set of crucial genes necessary during the epidermal differentiation process. Altogether, we demonstrate the existence of a robust DLX3–PKCα signaling pathway in keratinocytes that is crucial to epidermal differentiation control and cutaneous homeostasis.

MET signaling in keratinocytes activates EGFR and initiates squamous carcinogenesis

The receptor tyrosine kinase MET is abundant in many human squamous cell carcinomas (SCCs), but its functional significance in tumorigenesis is not clear. We found that the incidence of carcinogen-induced skin squamous tumors was substantially increased in transgenic MT-HGF (mouse metallothionein-hepatocyte growth factor) mice, which have increased abundance of the MET ligand HGF. Squamous tumors also erupted spontaneously on the skin of MT-HGF mice that were promoted by wounding or the application of 12-O-tetradecanoylphorbol 13-acetate, an activator of protein kinase C. Carcinogen-initiated tumors had Ras mutations, but spontaneous tumors did not. Cultured keratinocytes from MT-HGF mice and oncogenic RAS-transduced keratinocytes shared phenotypic and biochemical features of initiation that were dependent on autocrine activation of epidermal growth factor receptor (EGFR) through increased synthesis and release of EGFR ligands, which was mediated by the kinase SRC, the pseudoproteases iRhom1 and iRhom2, and the metallopeptidase ADAM17. Pharmacological inhibition of EGFR caused the regression of MT-HGF squamous tumors that developed spontaneously in orthografts of MT-HGF keratinocytes combined with dermal fibroblasts and implanted onto syngeneic mice. The global gene expression profile in MET-transformed keratinocytes was highly concordant with that in RAS-transformed keratinocytes, and a core RAS/MET coexpression network was activated in precancerous and cancerous human skin lesions. Tissue arrays revealed that many human skin SCCs have abundant HGF at both the transcript and protein levels. Thus, through the activation of EGFR, MET activation parallels a RAS pathway to contribute to human and mouse cutaneous cancers.

Lysophospholipid Receptors, as Novel Conditional Danger Receptors and Homeostatic Receptors Modulate Inflammation-Novel Paradigm and Therapeutic Potential

There are limitations in the current classification of danger-associated molecular patterns (DAMP) receptors. To overcome these limitations, we propose a new paradigm by using endogenous metabolites lysophospholipids (LPLs) as a prototype. By utilizing a data mining method we pioneered, we made the following findings: (1) endogenous metabolites such as LPLs at basal level have physiological functions; (2) under sterile inflammation, expression of some LPLs is elevated. These LPLs act as conditional DAMPs or anti-inflammatory homeostasis-associated molecular pattern molecules (HAMPs) for regulating the progression of inflammation or inhibition of inflammation, respectively; (3) receptors for conditional DAMPs and HAMPs are differentially expressed in human and mouse tissues; and (4) complex signaling mechanism exists between pro-inflammatory mediators and classical DAMPs that regulate the expression of conditional DAMPs and HAMPs. This novel insight will facilitate identification of novel conditional DAMPs and HAMPs, thus promote development of new therapeutic targets to treat inflammatory disorders.

Aberrant Expression of proPTPRN2 in Cancer Cells Confers Resistance to Apoptosis

The protein tyrosine phosphatase receptor PTPRN2 is expressed predominantly in endocrine and neuronal cells, where it functions in exocytosis. We found that its immature isoform proPTPRN2 is overexpressed in various cancers, including breast cancer. High proPTPRN2 expression was associated strongly with lymph node-positive breast cancer and poor clinical outcome. Loss of proPTPRN2 in breast cancer cells promoted apoptosis and blocked tumor formation in mice, whereas enforced expression of proPTPRN2 in nontransformed human mammary epithelial cells exerted a converse effect. Mechanistic investigations suggested that ProPTPRN2 elicited these effects through direct interaction with TRAF2, a hub scaffold protein for multiple kinase cascades, including ones that activate NF-κB. Overall, our results suggest PTPRN2 as a novel candidate biomarker and therapeutic target in breast cancer.

Src is activated by the nuclear receptor peroxisome proliferator-activated receptor β/δ in ultraviolet radiation-induced skin cancer

Although non-melanoma skin cancer (NMSC) is the most common human cancer and its incidence continues to rise worldwide, the mechanisms underlying its development remain incompletely understood. Here, we unveil a cascade of events involving peroxisome proliferator-activated receptor (PPAR) β/δ and the oncogene Src, which promotes the development of ultraviolet (UV)-induced skin cancer in mice. UV-induced PPARβ/δ activity, which directly stimulated Src expression, increased Src kinase activity and enhanced the EGFR/Erk1/2 signalling pathway, resulting in increased epithelial-to-mesenchymal transition (EMT) marker expression. Consistent with these observations, PPARβ/δ-null mice developed fewer and smaller skin tumours, and a PPARβ/δ antagonist prevented UV-dependent Src stimulation. Furthermore, the expression of PPARβ/δ positively correlated with the expression of SRC and EMT markers in human skin squamous cell carcinoma (SCC), and critically, linear models applied to several human epithelial cancers revealed an interaction between PPARβ/δ and SRC and TGFβ1 transcriptional levels. Taken together, these observations motivate the future evaluation of PPARβ/δ modulators to attenuate the development of several epithelial cancers.

Genetically Modified Mice as a Tool to Study Inflammatory Skin Diseases

Although mice have a long tradition as models for human skin diseases, they have recently received increasingly more attention. This is because of the rapid advancement of genetic engineering methods which made it possible to create mice with precisely defined genetic changes. Many of these mice develop impressive and sometimes unexpected, puzzling phenotypes. Their interpretation is a major challenge to the basic researcher and can often be ameliorated by the input of an experienced dermatologist. Together with recent examples of genetically modified mouse models of inflammatory skin diseases we give a short overview of the methods used to generate such mice, describe possible ways to analyse them, and discuss problems that arise in the interpretation of the findings.

Single-molecule studies reveal a hidden key step in the activation mechanism of membrane-bound protein kinase C-α

Protein kinase C-α (PKCα) is a member of the conventional family of protein kinase C isoforms (cPKCs) that regulate diverse cellular signaling pathways, share a common activation mechanism, and are linked to multiple pathologies. The cPKC domain structure is modular, consisting of an N-terminal pseudosubstrate peptide, two inhibitory domains (C1A and C1B), a targeting domain (C2), and a kinase domain. Mature, cytoplasmic cPKCs are inactive until they are switched on by a multistep activation reaction that occurs largely on the plasma membrane surface. Often, this activation begins with a cytoplasmic Ca²⁺ signal that triggers C2 domain targeting to the plasma membrane where it binds phosphatidylserine (PS) and phosphatidylinositol 4,5-bisphosphate (PIP₂). Subsequently, the appearance of the signaling lipid diacylglycerol (DAG) activates the membrane-bound enzyme by recruiting the inhibitory pseudosubstrate and one or both C1 domains away from the kinase domain. To further investigate this mechanism, this study has utilized single-molecule total internal reflection fluorescence microscopy (TIRFM) to quantitate the binding and lateral diffusion of full-length PKCα and fragments missing specific domain(s) on supported lipid bilayers. Lipid binding events, and events during which additional protein is inserted into the bilayer, were detected by their effects on the equilibrium bound particle density and the two-dimensional diffusion rate. In addition to the previously proposed activation steps, the findings reveal a major, undescribed, kinase-inactive intermediate. On bilayers containing PS or PS and PIP₂, full-length PKCα first docks to the membrane via its C2 domain, and then its C1A domain embeds itself in the bilayer even before DAG appears. The resulting pre-DAG intermediate with membrane-bound C1A and C2 domains is the predominant state of PKCα while it awaits the DAG signal. The newly detected, membrane-embedded C1A domain of this pre-DAG intermediate confers multiple useful features, including enhanced membrane affinity and longer bound state lifetime. The findings also identify the key molecular step in kinase activation: because C1A is already membrane-embedded in the kinase off state, recruitment of C1B to the bilayer by DAG or phorbol ester is the key regulatory event that stabilizes the kinase on state. More broadly, this study illustrates the power of single-molecule methods in elucidating the activation mechanisms and hidden regulatory states of membrane-bound signaling proteins.

Molecular mechanisms of mouse skin tumor promotion

Multiple molecular mechanisms are involved in the promotion of skin carcinogenesis. Induction of sustained proliferation and epidermal hyperplasia by direct activation of mitotic signaling pathways or indirectly in response to chronic wounding and/or inflammation, or due to a block in terminal differentiation or resistance to apoptosis is necessary to allow clonal expansion of initiated cells with DNA mutations to form skin tumors. The mitotic pathways include activation of epidermal growth factor receptor and Ras/Raf/mitogen-activated protein kinase signaling. Chronic inflammation results in inflammatory cell secretion of growth factors and cytokines such as tumor necrosis factor-α and interleukins, as well as production of reactive oxygen species, all of which can stimulate proliferation. Persistent activation of these pathways leads to tumor promotion.

VEGF-C and VEGF-D blockade inhibits inflammatory skin carcinogenesis

VEGF-C and VEGF-D were identified as lymphangiogenic growth factors and later shown to promote tumor metastasis, but their effects on carcinogenesis are poorly understood. Here, we have studied the effects of VEGF-C and VEGF-D on tumor development in the murine multistep chemical carcinogenesis model of squamous cell carcinoma by using a soluble VEGF-C/VEGF-D inhibitor. After topical treatment with a tumor initiator and repeated tumor promoter applications, transgenic mice expressing a soluble VEGF-C/VEGF-D receptor (sVEGFR-3) in the skin developed significantly fewer squamous cell tumors with a delayed onset when compared with wild-type mice or mice expressing sVEGFR-3 lacking the ligand-binding site. Epidermal proliferation was reduced in the carcinogen-treated transgenic skin, whereas epidermal keratinocyte proliferation in vitro was not affected by VEGF-C or VEGF-D, indicating indirect effects of sVEGFR-3 expression. Importantly, transgenic mouse skin was less sensitive to tumor promoter-induced inflammation, with reduced angiogenesis and blood vessel leakage. Cutaneous leukocytes, especially macrophages, were reduced in transgenic skin without major changes in macrophage polarization or blood monocyte numbers. Several macrophage-associated cytokines were also reduced in transgenic papillomas, although the dermal macrophages themselves did not express VEGFR-3. These findings indicate that VEGF-C/VEGF-D are involved in shaping the inflammatory tumor microenvironment that regulates early tumor progression. Our results support the use of VEGF-C/VEGF-D-blocking agents not only to inhibit metastatic progression, but also during the early stages of tumor growth.

CD8(+) T cells mediate RAS-induced psoriasis-like skin inflammation through IFN-γ

The RAS signaling pathway is constitutively activated in psoriatic keratinocytes. We expressed activated H-RAS^V12G in suprabasal keratinocytes of adult mice and observed rapid development of a psoriasis-like skin phenotype characterized by basal keratinocyte hyperproliferation, acanthosis, hyperkeratosis, intraepidermal neutrophil microabscesses and increased Th1/Th17 and Tc1/Tc17 skin infiltration. The majority of skin infiltrating CD8⁺ T cells co-expressed IFN-γ and IL-17A. When RAS was expressed on a Rag1−/− background, microabscess formation, iNOS expression and keratinocyte hyperproliferation were suppressed. Depletion of CD8⁺ but not CD4⁺ T cells reduced cutaneous and systemic inflammation, the RAS-induced increase in cutaneous Th17 and IL-17⁺ γΔ T cells, and epidermal hyperproliferation to levels similar to a Rag1−/− background. Reconstitution of Rag1−/− inducible RAS mice with purified CD8⁺ T cells restored microabscess formation and epidermal hyperproliferation. Neutralization of IFN-γ but not IL-17A in CD8⁺ T cell reconstituted Rag1−/− mice expressing RAS blocked CD8-mediated skin inflammation, iNOS expression and keratinocyte hyperproliferation. These results show for that CD8⁺ T cells can orchestrate skin inflammation with psoriasis-like pathology in response to constitutive RAS activation in keratinocytes, and this is primarily mediated through IFN-γ.

IL-1R-MyD88 signaling in keratinocyte transformation and carcinogenesis

Constitutively active RAS plays a central role in the development of human cancer and is sufficient to induce tumors in two-stage skin carcinogenesis. RAS-mediated tumor formation is commonly associated with up-regulation of cytokines and chemokines that mediate an inflammatory response considered relevant to oncogenesis. In this study, we report that mice lacking IL-1R or MyD88 are less sensitive to topical skin carcinogenesis than their respective wild-type (WT) controls. MyD88(-/-) or IL-1R(-/-) keratinocytes expressing oncogenic RAS are hyperproliferative and fail to up-regulate proinflammatory genes or down-regulate differentiation markers characteristic of RAS-expressing WT keratinocytes. Although RAS-expressing MyD88(-/-) keratinocytes form only a few small tumors in orthotopic grafts, IL-1R-deficient RAS-expressing keratinocytes retain the ability to form tumors in orthotopic grafts. Using both genetic and pharmacological approaches, we find that the differentiation and proinflammatory effects of oncogenic RAS in keratinocytes require the establishment of an autocrine loop through IL-1α, IL-1R, and MyD88 leading to phosphorylation of IκBα and NF-κB activation. Blocking IL-1α-mediated NF-κB activation in RAS-expressing WT keratinocytes reverses the differentiation defect and inhibits proinflammatory gene expression. Collectively, these results demonstrate that MyD88 exerts a cell-intrinsic function in RAS-mediated transformation of keratinocytes.

Phospholipase Cɛ has a crucial role in ultraviolet B-induced neutrophil-associated skin inflammation by regulating the expression of CXCL1/KC

Phospholipase C (PLC) ɛ is a phosphoinositide-specific PLC regulated by small GTPases including Ras and Rap. We previously demonstrated that PLCɛ has an important role in the development of phorbol ester-induced skin inflammation. In this study, we investigated the role of PLCɛ in ultraviolet (UV) B-induced acute inflammatory reactions in the skin. Wild-type (PLCɛ+/+) and PLCɛ gene knockout (PLCɛ⁻/⁻) mice were irradiated with a single dose of UVB at 1, 2.5, and 10 kJ/m² on the dorsal area of the skin, and inflammatory reactions in the skin were histologically evaluated up to 168 h after irradiation. In PLCɛ+/+ mice, irradiation with 1 and 2.5 kJ/m² UVB resulted in dose-dependent neutrophil infiltration in the epidermis at 24 and 48 h after irradiation. When mice were irradiated with 10 kJ/m² of UVB, most mice developed skin ulcers by 48 h and these ulcers became more severe at 168 h. In PLCɛ⁻/⁻ mice, UVB (1 or 2.5 kJ/m²)-induced neutrophil infiltration was markedly suppressed compared with PLCɛ+/+ mice. The suppression of neutrophil infiltration in PLCɛ⁻/⁻ mice was accompanied by attenuation of UVB-induced production of CXCL1/keratinocyte-derived chemokine (KC), a potent chemokine for neutrophils, in the whole skin. Cultured epidermal keratinocytes and dermal fibroblasts produced CXCL1/KC in a PLCɛ-dependent manner after UVB irradiation, and the UVB-induced upregulation of CXCL1/KC in these cells was significantly abolished by a PLC inhibitor. Furthermore, UVB-induced epidermal thickening was noticeably reduced in the skin of PLCɛ⁻/⁻ mice. These results indicate that PLCɛ has a crucial role in UVB-induced acute inflammatory reactions such as neutrophil infiltration and epidermal thickening by at least in part regulating the expression of CXCL1/KC in skin cells such as keratinocytes and fibroblasts.

The synthetic bryostatin analog Merle 23 dissects distinct mechanisms of bryostatin activity in the LNCaP human prostate cancer cell line

Bryostatin 1 has attracted considerable attention both as a cancer chemotherapeutic agent and for its unique activity. Although it functions, like phorbol esters, as a potent protein kinase C (PKC) activator, it paradoxically antagonizes many phorbol ester responses in cells. Because of its complex structure, little is known of its structure-function relations. Merle 23 is a synthetic derivative, differing from bryostatin 1 at only four positions. However, in U-937 human leukemia cells, Merle 23 behaves like a phorbol ester and not like bryostatin 1. Here, we characterize the behavior of Merle 23 in the human prostate cancer cell line LNCaP. In this system, bryostatin 1 and phorbol ester have contrasting activities, with the phorbol ester but not bryostatin 1 blocking cell proliferation or tumor necrosis factor alpha secretion, among other responses. We show that Merle 23 displays a highly complex pattern of activity in this system. Depending on the specific biological response or mechanistic change, it was bryostatin-like, phorbol ester-like, intermediate in its behavior, or more effective than either. The pattern of response, moreover, varied depending on the conditions. We conclude that the newly emerging bryostatin derivatives such as Merle 23 provide powerful tools to dissect subsets of bryostatin mechanism and response.

Enhancement of ultraviolet B-induced skin tumor development in phospholipase Cε-knockout mice is associated with decreased cell death

Phospholipase C (PLC) ε is a phosphoinositide-specific PLC regulated by small guanosine triphosphatases including Ras and Rap. Our previous studies revealed that PLCε gene-knockout (PLCε(-/-)) mice exhibit marked resistance to tumor formation in two-stage skin chemical carcinogenesis using 7,12-dimethylbenz(a)anthracene as an initiator and 12-O-tetradecanoylphorbol-13-acetate as a promoter. In this model, PLCε functions in tumor promotion through augmentation of 12-O-tetradecanoylphorbol-13-acetate-induced inflammation. In this study, we have further assessed the role of PLCε in tumorigenesis using a mouse model of ultraviolet (UV) B-induced skin tumor development. We irradiated PLCε(+/+), PLCε(+/-) or PLCε(-/-) mice with doses of UVB increasing from 1 to 10 kJ/m(2) three times a week for a total of 25 weeks and observed tumor formation for up to 50 weeks. In sharp contrast to the results from the two-stage chemical carcinogenesis study, PLCε(-/-) mice developed a large number of neoplasms including malignant tumors, whereas PLCε(+/+) and PLCε(+/-) mice developed a relatively small number of benign tumors. However, UVB-induced skin inflammation was greatly suppressed in PLCε(-/-) mice, as observed with 12-O-tetradecanoylphorbol-13-acetate-induced inflammation, implying that PLCε's role in the suppression of UVB-induced tumorigenesis is not mediated by inflammation. Studies of the tumor initiation stage revealed that UVB-induced cell death in the skin was markedly suppressed in PLCε(-/-)mice. Our findings identify a novel function for PLCε as a critical molecule regulating UVB-induced cell death and suggest that resistance to UVB-induced cell death conferred by the absence of PLCε is closely related to the higher incidence of skin tumor formation.

Altered morphology and function of the lacrimal functional unit in protein kinase C{alpha} knockout mice

PURPOSE

Protein kinase C (PKC) α plays a major role in the parasympathetic neural stimulation of lacrimal gland (LG) secretion. It also has been reported to have antiapoptotic properties and to promote cell survival. Therefore, the hypothesis for the present study was that PKCα knockout ((-/-)) mice have impaired ocular surface-lacrimal gland signaling, rendering them susceptible to desiccating stress and impaired corneal epithelial wound healing. In this study, the lacrimal function unit (LFU) and the stressed wound-healing response were examined in PKCα(-/-) mice.

METHODS

In PKCα(+/+) control mice and PKCα(-/-) mice, tear production, osmolarity, and clearance rate were evaluated before and after experimental desiccating stress. Histology and immunofluorescent staining of PKC and epidermal growth factor were performed in tissues of the LFU. Cornified envelope (CE) precursor protein expression and cell proliferation were evaluated. The time course of healing and degree of neutrophil infiltration was evaluated after corneal epithelial wounding.

RESULTS

Compared with the PKCα(+/+) mice, the PKCα(-/-) mice were noted to have significantly increased lacrimal gland weight, with enlarged, carbohydrate-rich, PAS-positive acinar cells; increased corneal epithelia permeability, with reduced CE expression; and larger conjunctival epithelial goblet cells. The PKCα(-/-) mice showed more rapid corneal epithelial healing, with less neutrophil infiltration and fewer proliferating cells than did the PKCα(+/+) mice.

CONCLUSIONS

The PKCα(-/-) mice showed lower tear production, which appeared to be caused by impaired secretion by the LG and conjunctival goblet cells. Despite their altered tear dynamics, the PKCα(-/-) mice demonstrated more rapid corneal epithelial wound healing, perhaps due to decreased neutrophil infiltration.

RIP4 regulates epidermal differentiation and cutaneous inflammation

The receptor-interacting protein (RIP) family kinase RIP4 interacts with protein kinase C (PKC) isoforms and is implicated in PKC-dependent signaling pathways. RIP4(-/-) mice die at birth with epidermal differentiation defects, causing fusions of all external orifices and loss of the esophageal lumen. To further understand RIP4 function in the skin, we generated transgenic mice with epidermal-specific expression of RIP4 using the human keratin-14 promoter (K14-RIP4). The K14-RIP4 transgene rescued the epidermal phenotype of RIP4(-/-) mice, showing that RIP4 acts autonomously in the epidermis to regulate differentiation. Although RIP4(-/-) mice share many phenotypic similarities with inhibitor kappaB kinase (IKK)alpha(-/-) mice and stratifin repeated epilation (Sfn(Er/Er)) mice, the K14-RIP4 transgene failed to promote epidermal differentiation in these mutant backgrounds. Unexpectedly, topical treatment of K14-RIP4 mice with 12-O-tetradecanoylphorbol-13-acetate (TPA) induced dramatic, neutrophilic inflammation, an effect that was independent of tumor necrosis factor type 1 receptor (TNFR1/p55) function. Despite their enhanced sensitivity to TPA, K14-RIP4 mice did not have an altered frequency of tumor formation in TPA-promoted skin cancer initiated with 7,12-dimethylbenz[a]anthracene (DMBA). These data suggest that RIP4 functions in the epidermis through PKC-specific signaling pathways to regulate differentiation and inflammation.

Regulation of epithelial-mesenchymal IL-1 signaling by PPARbeta/delta is essential for skin homeostasis and wound healing

Skin morphogenesis, maintenance, and healing after wounding require complex epithelial–mesenchymal interactions. In this study, we show that for skin homeostasis, interleukin-1 (IL-1) produced by keratinocytes activates peroxisome proliferator–activated receptor β/δ (PPARβ/δ) expression in underlying fibroblasts, which in turn inhibits the mitotic activity of keratinocytes via inhibition of the IL-1 signaling pathway. In fact, PPARβ/δ stimulates production of the secreted IL-1 receptor antagonist, which leads to an autocrine decrease in IL-1 signaling pathways and consequently decreases production of secreted mitogenic factors by the fibroblasts. This fibroblast PPARβ/δ regulation of the IL-1 signaling is required for proper wound healing and can regulate tumor as well as normal human keratinocyte cell proliferation. Together, these findings provide evidence for a novel homeostatic control of keratinocyte proliferation and differentiation mediated via PPARβ/δ regulation in dermal fibroblasts of IL-1 signaling. Given the ubiquitous expression of PPARβ/δ, other epithelial–mesenchymal interactions may also be regulated in a similar manner.

Inducible cutaneous inflammation reveals a protumorigenic role for keratinocyte CXCR2 in skin carcinogenesis

Transgenic mice that overexpress PKCalpha in the epidermis (K5-PKCalpha mice) exhibit acute CXCR2-mediated intraepidermal neutrophilic inflammation and a strong epidermal hyperplasia in response to application of 12-O-tetradecanoylphorbol-13-acetate (TPA). We now show that hyperplasia is independent of infiltrating neutrophils. Furthermore, when K5-PKCalpha mice were initiated with 7,12-dimethylbenz(a)anthracene (DMBA) and promoted with a low dose of TPA, 58% of K5-PKCalpha mice developed skin papillomas that progressed to carcinoma, whereas wild-type mice did not develop tumors. We confirmed that CXCR2 is expressed by keratinocytes and showed that transformation by oncogenic ras (a hallmark of DMBA initiation) or TPA exposure induced all CXCR2 ligands. Ras induction of CXCR2 ligands was mediated by autocrine activation of epidermal growth factor receptor and nuclear factor-kappaB, and potentiated by PKCalpha. Oncogenic ras also induced CXCR2 ligands in keratinocytes genetically ablated for CXCR2. However, ras transformed CXCR2 null keratinocytes formed only small skin tumors in orthotopic skin grafts to CXCR2 intact hosts, whereas transformed wild-type keratinocytes produced large tumors. In vitro, CXCR2 was essential for CXCR2 ligand-stimulated migration of ras-transformed keratinocytes and for ligand activation of the extracellular signal-regulated kinase (ERK) and Akt pathways. Both migration and activation of ERK and Akt were restored by CXCR2 reconstitution of CXCR2 null keratinocytes. Thus, activation of CXCR2 on ras-transformed keratinocytes has both promigratory and protumorigenic functions. The up-regulation of CXCR2 ligands after initiation by oncogenic ras and promotion with TPA in the mouse skin model provides a mechanism to stimulate migration by both autocrine and paracrine pathways and contribute to tumor development.

The PKC inhibitor AEB071 may be a therapeutic option for psoriasis

PKC isoforms tau, alpha, and beta play fundamental roles in the activation of T cells and other immune cell functions. Here we show that the PKC inhibitor AEB071 both abolishes the production of several cytokines by activated human T cells, keratinocytes, and macrophages in vitro and inhibits an acute allergic contact dermatitis response in rats. To translate these findings into humans, single and multiple ascending oral doses of AEB071 were administered to healthy volunteers and patients with psoriasis, respectively. AEB071 was well tolerated with no clinically relevant laboratory abnormalities. Ex vivo stimulation of lymphocytes from subjects exposed to single doses of AEB071 resulted in a dose-dependent inhibition of both lymphocyte proliferation and IL2 mRNA expression. Clinical severity of psoriasis was reduced up to 69% compared with baseline after 2 weeks of treatment, as measured by the Psoriasis Area Severity Index (PASI) score. The improvement in psoriasis patients was accompanied by histological improvement of skin lesions and may be partially explained by a substantial reduction of p40+ dermal cells, which are known to mediate psoriasis. These data suggest that AEB071 could be an effective novel treatment regimen for psoriasis and other autoimmune diseases, and that AEB071 warrants long-term studies to establish safety and efficacy.

The Role of the NF-kappaB Transcriptome and Proteome as Biomarkers in Human Head and Neck Squamous Cell Carcinomas

NF-kappaB is a family of signal activated transcription factors comprised of hetero- or homo-dimers from 5 different subunits, NF-kappaB1, NF-kappaB2, RELA, cREL and RELB. NF-kappaBs normally are transiently activated in response to infection or injury, but in cancers are aberrantly activated, regulating a transcriptome of hundreds of genes and corresponding proteome that promote pathogenesis and therapeutic resistance. In head and neck squamous cell carcinomas, an important role of NF-kappaB in regulation of the altered transcriptome and proteome has been established, providing a catalog of activating and target genes and proteins that may be useful as biomarkers of alterations in this pathway for this and other cancers. An emerging appreciation that NF-kappaB and other signal pathways form an altered regulatory network highlights the need to use biomarkers and combine targeted agents for personalized therapy of cancer.

Systems biology-defined NF-kappaB regulons, interacting signal pathways and networks are implicated in the malignant phenotype of head and neck cancer cell lines differing in p53 status

BACKGROUND

Aberrant activation of the nuclear factor kappaB (NF-kappaB) pathway has been previously implicated as a crucial signal promoting tumorigenesis. However, how NF-kappaB acts as a key regulatory node to modulate global gene expression, and contributes to the malignant heterogeneity of head and neck cancer, is not well understood.

RESULTS

To address this question, we used a newly developed computational strategy, COGRIM (Clustering Of Gene Regulons using Integrated Modeling), to identify NF-kappaB regulons (a set of genes under regulation of the same transcription factor) for 1,265 genes differentially expressed by head and neck cancer cell lines differing in p53 status. There were 748 NF-kappaB targets predicted and individually annotated for RELA, NFkappaB1 or cREL regulation, and a prevalence of RELA related genes was observed in over-expressed clusters in a tumor subset. Using Ingenuity Pathway Analysis, the NF-kappaB targets were reverse-engineered into annotated signature networks and pathways, revealing relationships broadly altered in cancer lines (activated proinflammatory and down-regulated Wnt/beta-catenin and transforming growth factor-beta pathways), or specifically defective in cancer subsets (growth factors, cytokines, integrins, receptors and intermediate kinases). Representatives of predicted NF-kappaB target genes were experimentally validated through modulation by tumor necrosis factor-alpha or small interfering RNA for RELA or NFkappaB1.

CONCLUSION

NF-kappaB globally regulates diverse gene programs that are organized in signal networks and pathways differing in cancer subsets with distinct p53 status. The concerted alterations in gene expression patterns reflect cross-talk among NF-kappaB and other pathways, which may provide a basis for molecular classifications and targeted therapeutics for heterogeneous subsets of head and neck or other cancers.

HIF-1alpha regulates epithelial inflammation by cell autonomous NFkappaB activation and paracrine stromal remodeling

Hypoxia inducible factor-1 (HIF-1) is a master regulatory transcription factor controlling multiple cell-autonomous and non-cell-autonomous processes, such as metabolism, angiogenesis, matrix invasion, and cancer metastasis. Here we used a new line of transgenic mice with constitutive gain of HIF-1 function in basal keratinocytes and demonstrated a signaling pathway from HIF-1 to nuclear factor kappa B (NFkappaB) activation to enhanced epithelial chemokine and cytokine elaboration. This pathway was responsible for a phenotypically silent accumulation of stromal inflammatory cells and a marked inflammatory hypersensitivity to a single 12-O-tetradecanoylphorbol-13-acetate (TPA) challenge. HIF-1-induced NFkappaB activation was composed of 2 elements, IkappaB hyperphosphorylation and phosphorylation of Ser276 on p65, enhancing p65 nuclear localization and transcriptional activity, respectively. NFkappaB transcriptional targets macrophage inflammatory protein-2 (MIP-2/CXCL2/3), keratinocyte chemokine (KC/CXCL1), and tumor necrosis factor [alfa] (TNFalpha) were constitutively up-regulated and further increased after TPA challenge both in cultured keratinocytes and in transgenic mice. Whole animal KC, MIP-2, or TNFalpha immunodepletion each abrogated TPA-induced inflammation, whereas blockade of either VEGF or placenta growth factor (PlGF) signaling did not affect transgenic inflammatory hyper-responsiveness. Thus, epithelial HIF-1 gain of function remodels the local environment by cell-autonomous NFkappaB-mediated chemokine and cytokine secretion, which may be another mechanism by which HIF-1 facilitates either inflammatory diseases or malignant progression.

Multiple PKCdelta tyrosine residues are required for PKCdelta-dependent activation of involucrin expression--a key role of PKCdelta-Y311

Protein kinase C-delta (PKCdelta) is a key regulator of human involucrin (hINV) gene expression and is regulated by tyrosine phosphorylation. However, a comprehensive analysis of the requirement for individual PKCdelta tyrosine residues is lacking. We show that multiple tyrosine residues influence the ability of PKCdelta to increase hINV gene expression. Mutation of individual PKCdelta tyrosine residues 52, 64, 155, 187, or 565 does not reduce the ability of PKCdelta to increase hINV promoter activity; however, simultaneous mutation of these five tyrosines markedly reduces activity. Moreover, restoration of any one of these residues results in nearly full activity restoration. It is significant that phosphorylation of PKCdelta-Y(311) is reduced in the five-tyrosine mutant and that mutation of Y(311) results in reduced PKCdelta activity comparable to that observed in the five-tyrosine mutant. Restoration of any one of the tyrosine residues in the five-tyrosine mutant restores Y(311) phosphorylation and biological activity. In addition, reduced phosphorylation of endogenous PKCdelta-Y(311) is associated with reduced biological activity. These findings indicate that PKCdelta activity requires Y(311) and a second tyrosine residue; however, any one of the several tyrosine residues can serve in the secondary role.

Topical N-acetyl-S-farnesyl-L-cysteine inhibits mouse skin inflammation, and unlike dexamethasone, its effects are restricted to the application site

N-acetyl-S-farnesyl-L-cysteine (AFC), a modulator of G protein and G-protein coupled receptor signaling, inhibits neutrophil chemotaxis and other inflammatory responses in cell-based assays. Here, we show topical AFC inhibits in vivo acute inflammation induced by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and arachidonic acid using the mouse ear model of inflammation. AFC inhibits edema, as measured by ear weight, and also inhibits neutrophil infiltration as assayed by direct counting in histological sections and by measuring myeloperoxidase (MPO) activity as a neutrophil marker. In addition, AFC inhibits in vivo allergic contact dermatitis in a mouse model utilizing sensitization followed by a subsequent challenge with 2,4-dinitrofluorobenzene. Unlike the established anti-inflammatories dexamethasone and indomethacin, AFC's action was restricted to the site of application. In this mouse model, both dexamethasone and indomethacin inhibited TPA-induced edema and MPO activity in the vehicle-treated, contralateral ear. AFC showed no contralateral ear inhibition for either of these end points. A marginally significant decrease due to AFC treatment was seen in TPA-induced epidermal hyperplasia at 24 hours. This was much less than the 90% inhibition of neutrophil infiltration, suggesting that AFC does not act by directly inhibiting protein kinase C.

Protein kinase C family: on the crossroads of cell signaling in skin and tumor epithelium

The protein kinase C (PKC) family represents a large group of phospholipid dependent enzymes catalyzing the covalent transfer of phosphate from ATP to serine and threonine residues of proteins. Phosphorylation of the substrate proteins induces a conformational change resulting in modification of their functional properties. The PKC family consists of at least ten members, divided into three subgroups: classical PKCs (alpha, betaI, betaII, gamma), novel PKCs (delta, epsilon, eta, theta), and atypical PKCs (zeta, iota/lambda). The specific cofactor requirements, tissue distribution, and cellular compartmentalization suggest differential functions and fine tuning of specific signaling cascades for each isoform. Thus, specific stimuli can lead to differential responses via isoform specific PKC signaling regulated by their expression, localization, and phosphorylation status in particular biological settings. PKC isoforms are activated by a variety of extracellular signals and, in turn, modify the activities of cellular proteins including receptors, enzymes, cytoskeletal proteins, and transcription factors. Accordingly, the PKC family plays a central role in cellular signal processing. Accumulating data suggest that various PKC isoforms participate in the regulation of cell proliferation, differentiation, survival and death. These findings have enabled identification of abnormalities in PKC isoform function, as they occur in several cancers. Specifically, the initiation of squamous cell carcinoma formation and progression to the malignant phenotype was found to be associated with distinct changes in PKC expression, activation, distribution, and phosphorylation. These studies were recently further extended to transgenic and knockout animals, which allowed a more direct analysis of individual PKC functions. Accordingly, this review is focused on the involvement of PKC in physiology and pathology of the skin.

Beyond steric hindrance: the role of adhesion signaling pathways in the pathogenesis of pemphigus

Epidermal cell adhesion depends on the intercellular interactions of transmembrane cadherin glycoproteins, which form the basis of adherens junctions and desmosomes. Pemphigus is a blistering disease of the skin and mucous membranes characterized by autoantibodies against the cell surface desmosomal cadherins, desmoglein (Dsg) 3 and Dsg1. An unanswered question in pemphigus pathophysiology is the mechanism of acantholysis, or loss of keratinocyte cell adhesion. One longstanding theory for pemphigus pathogenesis is the concept of steric hindrance, in which pathogenic pemphigus autoantibodies cause loss of intercellular adhesion by directly interfering with desmosomal cadherin trans-interactions. However, several recent studies have demonstrated that modulation of p38MAPK, Rho family GTPase, c-myc, protein kinase C, and phospholipase C signaling pathways prevents keratinocyte dissociation induced by pemphigus autoantibodies. As it is unlikely that desmosomal signaling would occur only in response to pemphigus autoantibodies, these studies suggest that numerous different signaling molecules may play a role in desmosomal homeostasis. Many of these same signaling pathways regulate classical cadherins in adherens junctions. Given the recent discovery of bidirectional crosstalk between adherens junctions and desmosomes, it would be valuable to understand how signaling pathways implicated in pemphigus pathogenesis may be involved in more general mechanisms of desmosome and adherens junction regulation. In this review, we will summarize the evidence supporting a role for steric hindrance and signaling mechanisms in the pathogenesis of pemphigus acantholysis and discuss potential analogues in the classical cadherin literature.

Histological and proteomic analysis of reversible H-RasV12G expression in transgenic mouse skin

We have used a two-transgene tetracycline system to reversibly express oncogenic H-Ras(V12G) in mouse skin and primary keratinocytes culture using the bovine keratin 5 promoter. Induction of H-Ras(V12G) expression in skin at 30 days after birth causes epidermal basal cell hyperplasia, an eruption of keratinous cysts and loss of hair follicles by 3 weeks. Subsequent H-Ras(V12G) de-induction for 3 days results in massive apoptosis in the non-H-Ras(V12G)-expressing stroma as well as in the suprabasal cells of the epidermis. Several procaspases such as CASP3, 1alpha, 5 and 12 disappeared, whereas the pro-apoptotic proteins AIF, Bax and Fas ligand were induced in H-Ras(V12G) de-induction skin. This process is followed by a wave of cell division at 14 days as hair follicles regrew, returning to near normal histology and skin appearance by 30 days. Using Kinetworkstrade mark multi-immunoblotting screens, the phosphorylation status of 37 proteins and expression levels of 75 protein kinases in the skin were determined in three samples: (i) wild-type skin, (ii) hyperplastic H-Ras(V12G)-expressing skin and (iii) skin where H-Ras(V12G) expression was suppressed for 7 days. Following H-Ras(V12G) induction, 16 kinases were increased over 2-fold, and 2 kinases were reduced over 50%. This included increased phosphorylation of both known downstream H-Ras(V12G) targets and unknown H-Ras(V12G) targets. After H-Ras(V12G) suppression, many but not all protein changes were reversed. These results from skin and primary keratinocytes are organized to reflect the molecular events that cause the histological changes observed. These proteomic changes identify markers that may mediate the oncogenic addiction paradigm.

Lack of phospholipase C-δ1 induces skin inflammation

Phospholipase C (PLC) is a key enzyme in phosphoinositide signaling. We previously generated PLC-delta1 knockout (KO) mice and found that these mice showed remarkable hair loss caused by abnormalities in hair follicle structures. Here we show that the skin of PLC-delta1 KO mice displays typical inflammatory phenotypes, including increased dermal cellularity, leukocyte infiltration, and expression of pro-inflammatory cytokines. In addition, exogenously expressed PLC-delta1 attenuates lipopolysaccharide-induced expression of IL-1beta, a pro-inflammatory cytokine, in an enzymatic activity-dependent manner. Furthermore, suppression of skin inflammation by anti-inflammatory reagents cured the epidermal hyperplasia in PLC-delta1 KO mice. Taken together, these results indicate that lack of PLC-delta1 induces skin inflammation and that the epidermal hyperplasia in PLC-delta1 KO mice is caused by skin inflammation. Our results also suggest that PLC-delta1 regulates homeostasis of the immune system in skin.

Transgenic overexpression of RasGRP1 in mouse epidermis results in spontaneous tumors of the skin

RasGRP1 is a guanine nucleotide exchange factor for Ras and a receptor of the second messenger diacylglycerol and its ultrapotent analogues, the phorbol esters. We have recently shown expression of RasGRP1 in the epidermal keratinocytes where it can mediate Ras activation in response to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate, a well-known mouse skin tumor promoter. To explore the participation of RasGRP1 in skin carcinogenesis, we targeted the overexpression of RasGRP1 to basal epidermal keratinocytes using the keratin 5 promoter. These transgenic mice were viable and indistinguishable from their littermates, with normal differentiation and skin architecture. However, a percentage of the adult transgenic population developed spontaneous skin tumors, mainly squamous cell papillomas. The transgene was detected in the tumors as well as in primary keratinocytes isolated from transgenic mice. The transgenic keratinocytes also displayed elevated levels of active, GTP-loaded Ras compared with the levels observed in keratinocytes derived from wild-type littermates. We noticed a correlation between tumor incidence and wounding, which suggests that RasGRP1 overexpression may confer sensitivity to promotional stimuli, like wound repair mechanisms. Interestingly, we also found elevated levels of granulocyte colony-stimulating factor in conditioned media derived from transgenic keratinocytes subjected to in vitro wounding. Taken together, these data are the first to provide evidence of a novel role for RasGRP1 in skin carcinogenesis and suggest that RasGRP1 may participate in tumorigenesis through modulation of Ras and autocrine pathways.

The effect of plant phenols on the expression and activity of phorbol ester-induced PKC in mouse epidermis

Protein kinase C (PKC) is thought to be a major intracellular receptor for the mouse skin tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). The diversity of PKC isoforms, and their central role in many signaling pathways, makes them important targets for potential chemopreventive agents. Our earlier studies showed that the plant phenols protocatechuic acid, chlorogenic acid and tannic acid alter the activity of enzymes involved in carcinogen activation, inhibit the formation of polycyclic aromatic hydrocarbon (PAH)-DNA adducts in mouse epidermis and decrease the level of lipid peroxidation in the epidermal microsomes. In the present study the effects of protocatechuic acid, chlorogenic acid and tannic acid on TPA-stimulated PKC isozymes alpha, beta(1), beta(2), gamma and zeta activity, and their distribution in mouse epidermis, was examined. The application of these phenolics 15 min before a single dose (3.4 nmol) of TPA resulted in significant inhibition of PKC translocation and a subsequent decrease in classical and novel/atypical PKC isoforms in comparison to a group of mice treated with TPA alone. The most potent inhibitor of PKC translocation and activity was tannic acid. This compound increased the levels of PKCalpha, beta(1), beta(2) in the cytosolic fraction by between 127% and 492% in comparison with TPA treated group of mice. Tannic acid decreased the activities of all three PKC classes by approximately 94% in the membrane fraction in comparison with the TPA treated group of animals. The effect of protocatechuic and chlorogenic acids on the distribution and activity of PKC isozymes was moderate. These compounds mostly affected translocation of PKCalpha and subsequently the activity of classical PKC. The enzyme activity in the particulate fraction was reduced by 59% and 43% in comparison with the TPA group, respectively. Thus, the results of these studies suggest that the subcellular distribution of PKC isoforms, and the activity of PKCs, can be modulated by plant phenolic acids, particularly tannic acid, and that such actions represent a part of the anti-promotional activity of these substances in mouse epidermis.

CXCR2 ligands and G-CSF mediate PKCalpha-induced intraepidermal inflammation

Transgenic mice overexpressing PKCalpha in the epidermis (K5-PKCalpha mice) exhibit an inducible severe intraepidermal neutrophilic inflammation and systemic neutrophilia when PKCalpha is activated by topical 12-O-tetradecanoylphorbol-13-acetate (TPA). This inducible model of cutaneous inflammation was used to define mediators of skin inflammation that may have clinical relevance. Activation of cutaneous PKCalpha increased the production of the chemotactic factors cytokine-induced neutrophil chemoattractant (KC) and macrophage inflammatory protein 2 (MIP-2) in murine plasma. TPA treatment of cultured K5-PKCalpha keratinocytes also released KC and MIP-2 into culture supernatants through an NF-kappaB-dependent pathway. MIP-2 and KC mediated the infiltration of neutrophils into the epidermis, since this was prevented by ablating CXCR2 in K5-PKCalpha mice or administering neutralizing antibodies against KC or MIP-2. The neutrophilia resulted from PKCalpha-mediated upregulation of cutaneous G-CSF released into the plasma independent of CXCR2. These responses could be inhibited by topical treatment with a PKCalpha-selective inhibitor. Inhibiting PKCalpha also reduced the basal and TNF-alpha- or TPA-induced expression of CXCL8 in cultured psoriatic keratinocytes, suggesting that PKCalpha activity may contribute to psoriatic inflammation. Thus, skin can be the source of circulating factors that have both local and systemic consequences, and these factors, their receptors, and possibly PKCalpha could be therapeutic targets for inhibition of cutaneous inflammation.

Inflammation in epithelial skin tumours: old stories and new ideas

The essential contribution of inflammation to tumour development and progression has gained increasing acceptance. For epithelial skin cancer, the observation that tumours arise in sites of chronic irritation and inflammation dates back to 1828 and has stimulated a whole field of research. Chemically-induced mouse skin tumours requiring inflammatory agents such as 12-O-tetradecanoylphorbol 13-acetate (TPA) for tumour-promotion have greatly contributed to our understanding of multi-stage carcinogenesis and have given important insights into the functional interaction between inflammatory micro-environment and epithelial tumour, especially when used in combination with transgenic animals. Data from these and additional new model systems clearly emphasise that the tumour-promoting micro-environment is indispensable for tumour formation and progression. It strongly resembles the wound and is largely orchestrated by inflammatory cells allowing tumour cells to co-opt signalling molecules of the innate immune system to promote their growth, invasion and metastasis. Consequently, anti-inflammatory drugs are of great clinical interest in prevention and treatment of epithelial skin cancers.