A partial catalog of proteins secreted by epidermal keratinocytes in culture

Synchronous activation of ERK and phosphatidylinositol 3-kinase pathways is required for collagen and extracellular matrix production in keloids

Keloid fibroproliferation appears to be influenced by epithelial-mesenchymal interactions between keloid keratinocytes (KKs) and keloid fibroblasts (KFs). Keloid and normal fibroblasts exhibit accelerated proliferation and collagen I and III production in co-culture with KKs compared with single cell culture or co-culture with normal keratinocytes. ERK and phosphatidylinositol 3-kinase (PI3K) pathway activation has been observed in excessively proliferating KFs in co-culture with KKs. We hypothesized that ERK and PI3K pathways might be involved in collagen and extracellular matrix production in KFs. To test our hypothesis, four samples of KFs were co-cultured in defined serum-free medium with KKs for 2-5 days. KF cell lysate was subjected to Western blot analysis. Compared with KF single cell culture, phospho-ERK1/2 and downstream phospho-Elk-1 showed up-regulation in the co-culture groups, as did phospho-PI3K and phospho-Akt-1, indicating ERK and PI3K pathway activation. Western blotting of the conditioned medium demonstrated increased collagen I-III, laminin beta2, and fibronectin levels. Addition of the MEK1/2-specific inhibitor U0126 or the PI3K-specific inhibitor LY294002 (but not p38 kinase and JNK inhibitors) completely nullified collagen I-III production and significantly decreased laminin beta2 and fibronectin secretion. In the presence of the MEK1/2 or PI3K inhibitor, fibronectin demonstrated changes in molecular mass reflected by faster in-gel migration. These data strongly suggest that synchronous activation of both the ERK and PI3K pathways is essential for collagen I-III and laminin beta2 production. These pathways additionally appear to affect the side chain attachments of fibronectin. Modulation of these pathways may suggest a direction for keloid therapy.

Gene expression profile of tissue engineered skin subjected to acute barrier disruption

The main function of the skin is to protect the body from infection, dehydration, and other environmental insults by creating an impermeable barrier of cornified cell layers, the stratum corneum. In contrast to cells in culture, tissue-engineered skin equivalents contain well-developed basal, spinous, granular, and cornified cell layers providing an excellent model to study the tissue response to barrier disruption. After 7 d of culture at the air-liquid interface the barrier of the tissues was disrupted by short exposure to acetone and the global gene expression profile of the tissues was evaluated using DNA microarrays. We found that tissue-engineered skin responds to barrier disruption by a two-wave dynamic response. Early on, the cells upregulate signal transducing, stress, proliferation, and inflammation genes to protect the tissue and possibly to communicate the damage to the immune system and neighboring tissues. At later times, pro-inflammatory cytokines and some growth-related genes are significantly reduced but enzymes that participate in lipid synthesis increase, suggesting that the epidermal cells attempt to restore the lost barrier. Quantitative immunostaining for the proliferation antigen Ki67 revealed that barrier disruption by acetone increased proliferation by 4-fold in agreement with the microarray data and previous in vivo studies. Our work suggests that functional genomics may be used in tissue engineering to understand tissue development, wound regeneration, and response to environmental stimuli. A better understanding of engineered tissues at the molecular level may facilitate their application in the clinic and as biosensors for toxicologic testing.

S100 protein subcellular localization during epidermal differentiation and psoriasis

S100 proteins are calcium-activated signaling proteins that interact with target proteins to modulate biological processes. Our present studies compare the level of expression, and cellular localization of S100A7, S100A8, S100A9, S100A10, and S100A11 in normal and psoriatic epidermis. S100A7 and S100A11 are present in the basal and spinous layers in normal epidermis. These proteins appear in the nucleus and cytoplasm in basal cells but are associated with the plasma membrane in spinous cells. S100A10 is present in basal and spinous cells, in the cytoplasm, and is associated with the plasma membrane. S100A8 and S100A9 are absent or are expressed at minimal levels in normal epidermis. In involved psoriatic tissue, S100A10 and S100A11 levels remain unchanged, whereas, S100A7, S100A8, and S100A9 are markedly overexpressed. The pattern of expression and subcellular localization of S100A7 is similar in normal and psoriatic tissue. S100A8 and S100A9 are strongly expressed in the basal and spinous layers in psoriasis-involved tissue. In addition, we demonstrate that S100A7, S100A10, and S100A11 are incorporated into detergent and reducing agent-resistant multimers, suggesting that they are in vivo transglutaminase substrates. S100A8 and S100A9 did not form these larger complexes. These results indicate that S100 proteins localize to the plasma membrane in differentiated keratinocytes, suggesting a role in regulating calcium-dependent, membrane-associated events. These studies also indicate, as reported previously, that S100A7, S100A8, and S100A9 expression is markedly altered in psoriasis, suggesting a role for these proteins in disease pathogenesis.

Role of IGF system of mitogens in the induction of fibroblast proliferation by keloid-derived keratinocytes in vitro

Keloids are proliferative dermal growths representing a pathological wound-healing response. We report high proliferation rates in normal (NF) and keloid-derived fibroblasts (KF) cocultured with keloid-derived keratinocytes (KK). IGF binding protein (IGFBP)-3 mRNA and secreted IGFBP-3 in conditioned media were increased in NF cocultured with KK compared with NF but markedly reduced in KF cocultured with KK or normal keratinocytes (NK). IGFBP-2 and IGFBP-4 mRNA levels were elevated, whereas IGFBP-5 mRNA was decreased in KF cocultured with KK or NK. Significant increases in IGFBP-2 and -4 mRNA in KF cocultured with KK did not correlate with protein secretion. Downstream IGF signaling cascade components, phospho-Raf, phospho-MEK1/2, phospho-MAPK, PI-3 kinase, phospho-Akt, and phospho-Elk-1, were elevated in KF cocultured with KK. Addition of recombinant human IGFBP-3 or antibodies against IGF-I or IGF-IR significantly inhibited proliferation of KF. The bioavailability of IGF-I may be related to the levels of IGFBP-3 produced, which in turn influences KF proliferation, suggesting that modulation of IGF-I, IGF-IR, and IGFBP-3, individually or in combination, may represent novel approaches to the treatment of keloids.

Cysteine peptidases of mammals: their biological roles and potential effects in the oral cavity and other tissues in health and disease

Cysteine peptidases (CPs) are phylogenetically ubiquitous enzymes that can be classified into clans of evolutionarily independent proteins based on the structural organization of the active site. In mammals, two of the major clans represented in the genome are: the CA clan, whose members share a structure and evolutionary history with papain; and the CD clan, which includes the legumains and caspases. This review focuses on the properties of these enzymes, with an emphasis on their potential roles in the oral cavity. The human genome encodes at least (but possibly no more than) 11 distinct enzymes, called cathepsins, that are members of the papain family C1A. Ten of these are present in rodents, which also carry additional genes encoding other cathepsins and cathepsin-like proteins. Human cathepsins are best known from the ubiquitously expressed lysosomal cathepsins B, H, and L, and dipeptidyl peptidase I (DPP I), which until recently were considered to mediate primarily "housekeeping" functions in the cell. However, mutations in DPP I have now been shown to underlie Papillon-Lefevre syndrome and pre-pubertal periodontitis. Other cathepsins are involved in tissue-specific functions such as bone remodeling, but relatively little is known about the functions of several recently discovered enzymes. Collectively, CPs participate in multiple host systems that are active in health and in disease. They are involved in tissue remodeling and turnover of the extracellular matrix, immune system function, and modulation and alteration of cell function. Intracellularly, CPs function in diverse processes including normal protein turnover, antigen and proprotein processing, and apoptosis. Extracellularly, they can contribute directly to the degradation of foreign proteins and the extracellular matrix. However, CPs can also participate in proteolytic cascades that amplify the degradative capacity, potentially leading to pathological damage, and facilitating the penetration of tissues by cancer cells. We know relatively little regarding the role of human CPs in the oral cavity in health or disease. Most studies to date have focused on the potential use of the lysosomal enzymes as markers for periodontal disease activity. Human saliva contains high levels of cystatins, which are potent CP inhibitors. Although these proteins are presumed to serve a protective function, their in vivo targets are unknown, and it remains to be discovered whether they serve to control any human CP activity.

Immobilization-related hypercalcemia after renal failure in burn injury

OBJECTIVE

To describe a patient with hypercalcemia presumably due to immobilization in the setting of burn injury and acute renal failure.

METHODS

We present a case report of a man who sustained a severe burn injury and then had renal failure and hypercalcemia. An additional series of patients with burns and immobilization was assessed for the presence of hypercalcemia.

RESULTS

In a 43-year-old man with burns on 65% of his body surface area, acute renal failure developed. Renal function failed to return, and he continued to require hemodialysis. Because of the severity and extensiveness of his burns, he remained immobilized. Serum calcium levels were low during the early part of the hospitalization. On the 57th day, generalized tonic-clonic seizures developed, and he was found to have a high ionized calcium level (1.41 mmol/L). Low values were recorded for intact parathyroid hormone (2 pg/mL), 25-hydroxyvitamin D (5 ng/mL), and 1,25-dihydroxyvitamin D (4 pg/mL). Persistent and recurrent hypercalcemia eventually responded to pamidronate and calcitonin. Other than immobilization, we could identify no predisposing factors such as confounding illnesses or medications that could have caused the hypercalcemia. A review of serum ionized calcium levels in 50 consecutive patients admitted to a burn unit and immobilized for at least 20 days failed to reveal any episodes of persistent hypercalcemia.

CONCLUSION

In our patient with burns and renal failure, symptomatic hypercalcemia was most likely attributable to prolonged immobilization. As patients with catastrophic illnesses survive for longer periods, additional problems such as hypercalcemia from immobilization may occur.

A partial transcriptome of human epidermis

Serial analysis of gene expression (SAGE) is a powerful technique for global expression profiling without prior knowledge of the genes of interest. We carried out SAGE analysis of purified keratinocytes derived from human skin biopsy specimens, resulting in a partial transcriptome of human epidermis. We identified 7645 unique SAGE tags with quantitative information from 15,131 collected SAGE tags obtained from approximately 3 x 10(6) epidermal cells. This catalog contains a large number of genes that were not previously known to be expressed by human epidermis. Comparison with the databases of all known human SAGE tags allowed us to identify a number of keratinocyte-specific tags that putatively correspond to formerly unknown genes. Surprisingly, human epidermal keratinocytes in vivo show relatively low expression levels of genes typically associated with epidermal differentiation, whereas the expression levels of housekeeping genes are considerably higher than in cultured keratinocytes. This study provides a first step toward a transcriptome of human epidermis and, as such, harbors a wealth of information to identify genes involved in skin function, and candidate genes for genetic skin disorders.

Skin as a potential organ for ectopic monoclonal antibody production

The therapeutic potential of monoclonal antibodies for treating a variety of severe or life-threatening diseases is high. Although intravenous infusion appears the simplest and most obvious mode of administration, it is not applicable to many long-term treatments. It might be advantageously replaced by gene/cell therapies, however, rendering treatments cost-effective and eliminating the short- and long-term side-effects associated with injection of massive doses of antibodies. We have tested whether skin can potentially be used as an organ for production and systemic delivery of ectopic antibodies. Normal human primary keratinocytes were shown to be capable of synthesis and secretion of a model monoclonal antibody directed against human thyroglobulin upon retroviral gene transduction in vitro. Neo- epidermis reconstructed in vitro, either in cell culture inserts or on dermal substrates, from such modified keratinocytes also produced the monoclonal antibody. Interestingly, the latter could cross the epidermis basal layer and be released in culture fluids. Finally, grafting of epidermis reconstituted in vitro on dermal substrates to SCID mice permitted sustained monoclonal antibody delivery into the bloodstream to be achieved. Our data thus show that genetically engineered keratinocytes can potentially be used for genetic antibody-based immunotherapies. They also indicate that proteins as big as 150 kDa, after release by engineered keratinocytes into skin intercellular spaces, can migrate to the general circulation, which is potentially important for a number of other gene-based therapies.

The Ca2+-binding proteins S100A8 and S100A9 are encoded by novel injury-regulated genes

To gain insight into the molecular mechanisms underlying cutaneous wound repair, we performed a large scale screen to identify novel injury-regulated genes. Here we show a strong up-regulation of the RNA and protein levels of the two Ca(2+)-binding proteins S100A8 and S100A9 in the hyperthickened epidermis of acute murine and human wounds and of human ulcers. Furthermore, both genes were expressed by inflammatory cells in the wound. The increased expression of S100A8 and S100A9 in wound keratinocytes is most likely related to the activated state of the keratinocytes and not secondary to the inflammation of the skin, since we also found up-regulation of S100A8 and S100A9 in the epidermis of activin-overexpressing mice, which develop a hyperproliferative and abnormally differentiated epidermis in the absence of inflammation. Furthermore, S100A8 and S100A9 expression was found to be associated with partially differentiated keratinocytes in vitro. Using confocal microscopy, both proteins were shown to be at least partially associated with the keratin cytoskeleton. In addition, cultured keratinocytes efficiently secreted the S100A8/A9 dimer. These results together with previously published data suggest that S100A8 and S100A9 are novel players in wound repair, where they might be involved in the reorganization of the keratin cytoskeleton in the wounded epidermis, in the chemoattraction of inflammatory cells, and/or in the defense against microorganisms.

Purification and partial amino acid sequence of proteins from human epidermal keratinocyte conditioned medium

Keratinocytes are the main cell type of the epidermis. They secrete a variety of proteins and peptides that have diverse roles in epidermal physiology. In this report, we present purification and partial amino acid sequence of LEKTI, a serine proteinase inhibitor, and DAN (NO3) zinc-finger protein, a tumor suppressor protein of neuroblastoma, from human keratinocyte conditioned medium. Epidermal keratinocytes were isolated from human foreskin and serially passaged in a defined medium (MSBM). At confluence of the fourth passage, MSBM medium was replaced with protein-free Dulbecco's modified Eagle medium/F12 (DMEM:F12) 3:1 base medium and collected every 24 h for 4 days. Medium was pooled and concentrated using a stirred cell concentrator. Concentrated medium was diluted 1:1 in 50 mM sodium phosphate, pH 8 buffer, and loaded onto a preparative heparin affinity column. Proteins/peptides were purified from heparin column passthrough by the combination of preparative and analytical FPLC-based gel filtration chromatography and reversed-phase HPLC. Samples electroblotted onto a PVDF support were sequenced by Edman degradation in a gas-phase sequencing system.

Investigation of the influence of keloid-derived keratinocytes on fibroblast growth and proliferation in vitro

Keloids are disfiguring, proliferative scars that represent a pathological response to cutaneous injury. The overabundant extracellular matrix formation, largely from collagen deposition, is characteristic of these lesions and has led to investigations into the role of the fibroblast in its pathogenesis. Curiously, the role of the epidermis in extracellular matrix collagen deposition of normal skin has been established, but a similar hypothesis in keloids has not been investigated. The aim of this study was to investigate the influence of keloid epithelial keratinocytes on the growth and proliferation of normal fibroblasts in an in vitro serum-free co-culture system. A permeable membrane separated two chambers; the upper chamber contained a fully differentiated stratified epithelium derived from the skin of excised earlobe keloid specimens, whereas the lower chamber contained a monolayer of normal or keloid fibroblasts. Both cell types were nourished by serum-free medium from the lower chamber. Epithelial keratinocytes from five separate earlobe keloid specimens were investigated. Four sets of quadruplicates were performed for each specimen co-cultured with normal fibroblasts or keloid-derived fibroblasts. Controls consisted of (1) normal keratinocytes co-cultured with normal fibroblasts, and (2) fibroblasts grown in serum-free media in the absence of keratinocytes in the upper chamber. Fibroblasts were indirectly quantified by 3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay, with results confirmed by DNA content measurement, at days 1 and 5 after the co- culture initiation.Significantly, increased proliferation was seen in fibroblasts co-cultured with keloid keratinocytes, as compared with the normal keratinocyte controls at day 5 (analysis of variance, p < 0.001). These results strongly suggest that the overlying epidermal keratinocytes of the keloid may have an important, previously unappreciated role in keloid pathogenesis using paracrine or epithelial-mesenchymal signaling.

Serial analysis of gene expression in differentiated cultures of human epidermal keratinocytes

Keratinocyte gene expression was surveyed more comprehensively than before, by means of serial analysis of gene expression. A total of 25,694 tags derived from expressed mRNA, were analyzed in a model for normal differentiation and in a model where cultured keratinocytes were stimulated for a prolonged period of time with tumor necrosis factor-alpha, thus mimicking aberrant differentiation in the context of cutaneous inflammation. Serial analysis of gene expression revealed many transcripts derived from unknown genes and a large number of genes that are not known to be expressed in keratinocytes; furthermore, these data provide quantitative information about the relative abundance of transcripts, allowing the identification of differentially expressed genes. A major part of the identified transcripts accounted for genes involved in energy metabolism and protein synthesis. A large proportion of all transcripts (6%) corresponded to genes associated with terminal differentiation and barrier formation. Another highly expressed functional group of genes (2% of all transcripts) corresponded to proteins involved in host protection such as antimicrobial proteins and proteinase inhibitors. Three of these genes were not known to be expressed in keratinocytes, and some were upregulated after prolonged tumor necrosis factor-alpha exposure. Our data on expressed genes in keratinocytes are consistent with the known function of human epidermis, and provide a first step to generate a transcriptome of human keratinocytes.

Development of a skin-based metabolic sink for phenylalanine by overexpression of phenylalanine hydroxylase and GTP cyclohydrolase in primary human keratinocytes

Phenylketonuria, PKU, is caused by deficiency of phenylalanine hydroxylase (PAH) resulting in increased levels of phenylalanine in body fluids. PAH requires the non-protein cofactor BH4 and the rate-limiting step in the synthesis of BH4 is GTP cyclohydrolase I (GTP-CH). Here we show that overexpression of the two enzymes PAH and GTP-CH in primary human keratinocytes leads to high levels of phenylalanine clearance without BH4 supplementation. Integration of multiple PAH and GTP-CH transgenes were achieved after optimized retroviral transduction. Phenylalanine clearance was measured ex vivo in primary human keratinocytes cotransduced with PAH and GTP-CH (more than 370 nmol/24 h/106 cells), a level exceeding that of a human liver cell line (HepG2 cells). Cells overexpressing either one of the enzymes alone did not clear significant amounts of phenylalanine. Transfer of the two genes into the same cell was not necessary, since cocultivation of cells transduced separately with PAH and GTP-CH also resulted in phenylalanine clearance. Thus the experiments indicate metabolic cooperation between cells overexpressing PAH and cells overexpressing GTP-CH, possibly due to intercellular transport of synthesized BH4.

Regulated cutaneous gene delivery: the skin as a bioreactor

Epidermal keratinocytes can secrete polypeptides into the bloodstream, and they can be easily expanded in culture and genetically modified. It is thus possible to use epidermal keratinocytes for the systemic delivery of transgene products. Here we review the development of epidermal secretory systems, from cultured keratinocytes to skin grafts and transgenic mouse models. We also discuss a gene-switch approach for regulated cutaneous gene delivery.

Comparative in vitro cytotoxicity of ethyl acrylate and tripropylene glycol diacrylate to normal human skin and lung cells

The potential for occupational exposure to the esters of acrylic acid (acrylates) is considerable, and, thus, requires a greater understanding of the their toxicity. Confluent (70-90%) cultures of normal human epidermal keratinocytes (NHEK), dermal fibroblasts (NHDF). or bronchial epithelium (NHBE) were exposed to the monofunctional ethyl acrylate (EA), the multifunctional tripropylene glycol diacrylate (TPGDA), or TPGDA monomer in a radiation curable lacquer (Lacquer A) at equimolar dosages in order to determine human in vitro cytotoxicity. Viability of the cells after 2-24-h exposure to the representative monofunctional or multifunctional acrylate or solvent control was used to calculate an index of acute cytotoxicity (50% inhibitory dose; ID50) and to determine the shape of the dose-response curves. TPGDA, Lacquer A, and EA were equally cytotoxic (ID50 is approximately equal to 0.1 micromol/cm2) to NHEK at equimolar doses. TPGDA or Lacquer A were more cytotoxic (is approximately equal to 100X) to NHDF or NHBE than EA. Sequential exposure of UV(A) and TPGDA to NHEK indicate the potential for a synergistic cytotoxic response. These findings are consistent with observed decreases in free sulfhydryl groups (e.g., glutathione or cysteine) that parallel the dose-response-related decreases in viability. logether, these data suggest possible differences in toxicity between the monofunctional EA and multifunctional TPGDA to NHEK, NHDF. or NHBE, possibly due to the difference in the number of functional acrylate groups and/or physicochemical differences (e.g., vapor pressure) between the acrylates investigated.

Human bronchoalveolar lavage fluid protein two-dimensional database: study of interstitial lung diseases

Recently, we published an analytical two-dimensional electrophoresis (2-DE) protein map of human bronchoalveolar lavage fluid (BALF) using a pool of BALFs from various patients. In this report, the effect of lung disorders on the protein composition of the lung epithelial lining fluid was investigated by 2-DE of BALFs from individual patients with well-defined interstitial lung diseases: sarcoidosis, idiopathic pulmonary fibrosis (IPF) and hypersensitivity pneumonitis (HP), using improved experimental conditions. On these gels, about 600-1000 stained protein spots could be identified in a BALF sample containing 25 microg of protein, and our original human BALF protein database has, therefore, been considerably extended. Altogether, 429 protein spots corresponding to 66 different proteins (including isoforms, protein subunits and fragments) were identified by microsequence analysis and by matching with a human blood plasma 2-DE protein map available in the SWISS-2DPAGE database. A human 2-DE BALF database was established and is available on the World Wide Web (http://www.umh.ac.be/-biochim/proteomic.htm+ ++). The significance of the modifications observed between the different lung pathologies is discussed with the aim of understanding the mechanistic bases of lung disease pathogenesis and finding new potential lung markers of disorders.