The tumor promoter, 12-O-tetradecanoylphorbol-13-acetate accelerates keratinocyte differentiation and stimulates growth of an unidentified cell type in cultured human epidermis

Chronotherapy of maxacalcitol on skin inflammation induced by topical 12-O-tetradecanoylphorbol-13-acetate in mice

In general, chronotherapy is desirable for a more effective and/or safe dosage regimen. In this study, a daily rhythm of skin vitamin D receptor (VDR) and chronotherapeutic profiles of maxacalcitol, a vitamin D analogue, were evaluated using mice with skin inflammation induced by topical 12-O-tetradecanoylphorbol-13-acetate (TPA). This study showed that skin nuclear VDR expression in TPA-treated mice has a daily rhythm with the peak at the middle of active period. The effects of maxacalcitol were greater after dosing during early to middle of active period than those after dosing during early to middle of inactive period. These data suggest that chronotherapeutic profiles of maxacalcitol partly depend on the daily rhythm of skin nuclear VDR in TPA-treated mice. Because TPA-treated mice are considered as one of animal models of psoriasis, these animal data might be helpful for establishing chronotherapeutic approach of maxacalcitol in clinical practice.

Identification of C/EBPα as a novel target of the HPV8 E6 protein regulating miR-203 in human keratinocytes

Patients suffering from Epidermodysplasia verruciformis (EV), a rare inherited skin disease, display a particular susceptibility to persistent infection with cutaneous genus beta-human papillomavirus (beta-HPV), such as HPV type 8. They have a high risk to develop non-melanoma skin cancer at sun-exposed sites. In various models evidence is emerging that cutaneous HPV E6 proteins disturb epidermal homeostasis and support carcinogenesis, however, the underlying mechanisms are not fully understood as yet. In this study we demonstrate that microRNA-203 (miR-203), a key regulator of epidermal proliferation and differentiation, is strongly down-regulated in HPV8-positive EV-lesions. We provide evidence that CCAAT/enhancer-binding protein α (C/EBPα), a differentiation-regulating transcription factor and suppressor of UV-induced skin carcinogenesis, directly binds the miR-203 gene within its hairpin region and thereby induces miR-203 transcription. Our data further demonstrate that the HPV8 E6 protein significantly suppresses this novel C/EBPα/mir-203-pathway. As a consequence, the miR-203 target ΔNp63α, a proliferation-inducing transcription factor, is up-regulated, while the differentiation factor involucrin is suppressed. HPV8 E6 specifically down-regulates C/EBPα but not C/EBPβ expression at the transcriptional level. As shown in knock-down experiments, C/EBPα is regulated by the acetyltransferase p300, a well-described target of cutaneous E6 proteins. Notably, p300 bound significantly less to the C/EBPα regulatory region in HPV8 E6 expressing keratinocytes than in control cells as demonstrated by chromatin immunoprecipitation. In situ analysis confirmed congruent suprabasal expression patterns of C/EBPα and miR-203 in non-lesional skin of EV-patients. In HPV8-positive EV-lesions both factors are potently down-regulated in vivo further supporting our in vitro data. In conclusion our study has unraveled a novel p300/C/EBPα/mir-203-dependent mechanism, by which the cutaneous HPV8 E6 protein may expand p63-positive cells in the epidermis of EV-patients and disturbs fundamental keratinocyte functions. This may drive HPV-mediated pathogenesis and may potentially also pave the way for skin carcinogenesis in EV-patients.

Cutaneous genus beta-HPV types infect skin keratinocytes. Their potential role in skin carcinogenesis, particularly in immunosuppressed patients, has become a major field of interest. Patients suffering from the rare genetic disorder Epidermodysplasia verruciformis (EV) are highly susceptible to persistent genus beta-HPV infection and have an increased risk to develop non-melanoma skin cancer at sun-exposed sites. Thus, EV serves as a valuable model disease for studying genus beta-HPV biology. Here, we demonstrate that in human HPV8-infected EV skin lesions, the ‘stemness-repressing’ microRNA-203 is strongly down-regulated. In contrast, cells expressing the miR-203-regulated ‘stemness-maintaining’ factor p63, are highly amplified. Notably, we identified the transcription factor C/EBPα, a well-known suppressor of UV-induced skin carcinogenesis, as a p300-dependent target of the HPV8-encoded E6 oncoprotein and as a critical inducer of miR-203 gene expression. Our data provide evidence for a novel p300/C/EBPα/miR-203-dependent pathway, which links HPV8 infection to the expansion of p63-positive cells in the epidermis of EV-patients. This may contribute to the beta-HPV-induced disturbance of epidermal homeostasis and pave the way for skin carcinogenesis.

Role of the Slug Transcription Factor in Chemically-Induced Skin Cancer

The Slug transcription factor plays an important role in ultraviolet radiation (UVR)-induced skin carcinogenesis, particularly in the epithelial-mesenchymal transition (EMT) occurring during tumor progression. In the present studies, we investigated the role of Slug in two-stage chemical skin carcinogenesis. Slug and the related transcription factor Snail were expressed at high levels in skin tumors induced by 7,12-dimethylbenz[α]anthracene application followed by 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment. TPA-induced transient elevation of Slug and Snail proteins in normal mouse epidermis and studies in Slug transgenic mice indicated that Slug modulates TPA-induced epidermal hyperplasia and cutaneous inflammation. Although Snail family factors have been linked to inflammation via interactions with the cyclooxygenase-2 (COX-2) pathway, a pathway that also plays an important role in skin carcinogenesis, transient TPA induction of Slug and Snail appeared unrelated to COX-2 expression. In cultured human keratinocytes, TPA induced Snail mRNA expression while suppressing Slug expression, and this differential regulation was due specifically to activation of the TPA receptor. These studies show that Slug and Snail exhibit similar patterns of expression during both UVR and chemical skin carcinogenesis, that Slug and Snail can be differentially regulated under some conditions and that in vitro findings may not recapitulate in vivo results.

Cellular differentiation regulator BLIMP1 induces Epstein-Barr virus lytic reactivation in epithelial and B cells by activating transcription from both the R and Z promoters

Epstein-Barr virus (EBV) maintains a lifelong latent infection within a subset of its host's memory B cells, while lytic EBV replication takes place in plasma cells and differentiated epithelial cells. Therefore, cellular transcription factors, such as BLIMP1, that are key mediators of differentiation likely contribute to the EBV latent-to-lytic switch. Previous reports showed that ectopic BLIMP1 expression induces reactivation in some EBV-positive (EBV(+)) B-cell lines and transcription from Zp, with all Z(+) cells in oral hairy leukoplakia being BLIMP1(+). Here, we examined BLIMP1's role in inducing EBV lytic gene expression in numerous EBV(+) epithelial and B-cell lines and activating transcription from Rp. BLIMP1 addition was sufficient to induce reactivation in latently infected epithelial cells derived from gastric cancers, nasopharyngeal carcinomas, and normal oral keratinocytes (NOK) as well as some, but not all B-cell lines. BLIMP1 strongly induced transcription from Rp as well as Zp, with there being three or more synergistically acting BLIMP1-responsive elements (BRE) within Rp. BLIMP1's DNA-binding domain was required for reactivation, but BLIMP1 did not directly bind the nucleotide (nt) -660 Rp BRE. siRNA knockdown of BLIMP1 inhibited 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced lytic reactivation in NOK-Akata cells, cells that can be reactivated by R, but not Z. Thus, we conclude that BLIMP1 expression is both necessary and sufficient to induce EBV lytic replication in many (possibly all) EBV(+) epithelial-cell types, but in only a subset of EBV(+) B-cell types; it does so, at least in part, by strongly activating expression of both EBV immediately early genes, BZLF1 and BRLF1.

IMPORTANCE

This study is the first one to show that the cellular transcription factor BLIMP1, a key player in both epithelial and B-cell differentiation, induces reactivation of the oncogenic herpesvirus Epstein-Barr virus (EBV) out of latency into lytic replication in a variety of cancerous epithelial cell types as well as in some, but not all, B-cell types that contain this virus in a dormant state. The mechanism by which BLIMP1 does so involves strongly turning on expression of both of the immediate early genes of the virus, probably by directly acting upon the promoters as part of protein complexes or indirectly by altering the expression or activities of some cellular transcription factors and signaling pathways. The fact that EBV(+) cancers usually contain mostly undifferentiated cells may be due in part to these cells dying from lytic EBV infection when they differentiate and express wild-type BLIMP1.

Loss of Prkar1a leads to Bcl-2 family protein induction and cachexia in mice

Loss of function mutations in the Prkar1a gene are the cause of most cases of Carney complex disorder. Defects in Prkar1a are thought to cause hyper-activation of PKA signalling, which drives neoplastic transformation, and Prkar1a is therefore considered to be a tumour suppressor. Here we show that loss of Prkar1a in genetically modified mice caused transcriptional activation of several proapoptotic Bcl-2 family members and thereby caused cell death. Interestingly, combined loss of Bim and Prkar1a increased colony formation of fibroblasts in culture and promoted their growth as tumours in immune-deficient mice. Apart from inducing apoptosis, systemic deletion of Prkar1a caused cachexia with muscle loss, macrophage activation and increased lipolysis as well as serum triglyceride levels. Loss of single allele of Prkar1a did not enhance tumour development in a skin cancer model, but surprisingly, when combined with the loss of Bim, caused a significant delay in tumorigenesis and this was associated with upregulation of other BH3-only proteins, PUMA and NOXA. These results show that loss of Prkar1a can only promote tumorigenesis when Prkar1a-mediated apoptosis is somehow countered.

Keratinocytes propagated in serum-free, feeder-free culture conditions fail to form stratified epidermis in a reconstituted skin model

Primary human epidermal stem cells isolated from skin tissues and subsequently expanded in tissue culture are used for human therapeutic use to reconstitute skin on patients and to generate artificial skin in culture for academic and commercial research. Classically, epidermal cells, known as keratinocytes, required fibroblast feeder support and serum-containing media for serial propagation. In alignment with global efforts to remove potential animal contaminants, many serum-free, feeder-free culture methods have been developed that support derivation and growth of these cells in 2-dimensional culture. Here we show that keratinocytes grown continually in serum-free and feeder-free conditions were unable to form into a stratified, mature epidermis in a skin equivalent model. This is not due to loss of cell potential as keratinocytes propagated in serum-free, feeder-free conditions retain their ability to form stratified epidermis when re-introduced to classic serum-containing media. Extracellular calcium supplementation failed to improve epidermis development. In contrast, the addition of serum to commercial, growth media developed for serum-free expansion of keratinocytes facilitated 3-dimensional stratification in our skin equivalent model. Moreover, the addition of heat-inactivated serum improved the epidermis structure and thickness, suggesting that serum contains factors that both aid and inhibit stratification.

Calcium regulation of keratinocyte differentiation

Calcium is the major regulator of keratinocyte differentiation in vivo and in vitro. A calcium gradient within the epidermis promotes the sequential differentiation of keratinocytes as they traverse the different layers of the epidermis to form the permeability barrier of the stratum corneum. Calcium promotes differentiation by both outside-in and inside-out signaling. A number of signaling pathways involved with differentiation are regulated by calcium, including the formation of desmosomes, adherens junctions and tight junctions, which maintain cell-cell adhesion and play an important intracellular signaling role through their activation of various kinases and phospholipases that produce second messengers that regulate intracellular free calcium and PKC activity, critical for the differentiation process. The calcium receptor plays a central role by initiating the intracellular signaling events that drive differentiation in response to extracellular calcium. This review will discuss these mechanisms.

Transforming growth factor beta1 enhances tumor promotion in mouse skin carcinogenesis

Transforming growth factor beta1 (TGFbeta1) expression is elevated by tumor promoters in the mouse skin, but its role in tumor promotion has not been well defined. To investigate this, we have compared TGFbeta1+/+ and +/- mice in a two-stage skin chemical carcinogenesis protocol. Surprisingly, TGFbeta1+/- mice had fewer number and incidence of benign papillomas, reduced epidermal and tumor cell proliferation and reduced epidermal TGFbeta1 and nuclear p-Smad2 localization in response to the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) compared with TGFbeta1+/+ mice. Maximal TPA activation of protein kinase C (PKCalpha) as measured by activity assays and activation of target genes and induction of cornified envelopes correlated with TGFbeta1 gene dosage in keratinocytes and addition of exogenous TGFbeta1 restored the cornification defect in TGFbeta1+/- keratinocytes. Similarly, inhibition of ALK5-suppressed TPA-mediated PKCalpha activation suggesting that physiological levels of TGFbeta1 are required for maximal activation of PKC-dependent mitogenic responses. Paradoxically, the TPA-induced inflammatory response was greater in TGFbeta1+/- skin, but TGFbeta1+/+ papillomas had more tumor infiltrating myeloperoxidase-positive cells and pro-inflammatory gene expression was elevated in v-ras(Ha)-transduced TGFbeta1+/+ but not TGFbeta1+/- keratinocytes. Thus, ras activation switches TGFbeta1 to a pro-inflammatory cytokine. Despite this differential proliferative and inflammatory response to TPA and enhanced papilloma formation in the TGFbeta1+/+ mice, the frequency of malignant conversion was reduced compared with TGFbeta1+/- mice. Therefore, TGFbeta1 promotes benign tumors by modifying tumor promoter-induced cell proliferation and inflammation but retains a suppressive function for malignant conversion.

Protein kinase C-dependent upregulation of miR-203 induces the differentiation of human keratinocytes

Terminal differentiation of keratinocytes is a multistep process that requires a coordinated program of gene expression. We aimed to explore the possible involvement of a previously unreported class of non-coding RNA genes, microRNAs (miRNAs) in keratinocyte differentiation by using miRNA expression profiling. Out of 365 miRNAs tested, 7 showed significant change between keratinocytes cultured in low or high calcium concentration. The highest-ranked upregulated gene was miR-203, whose expression was significantly upregulated in response to calcium and other inducers of keratinocyte differentiation such as 12-O-tetradecanoylphorbol-13-acetate (TPA) and vitamin D(3). Differentiation-induced upregulation of miR-203 expression was blocked by treatment with specific inhibitors of protein kinase C (PKC), GF109203X, and Ro31-8220. Moreover, our results showed that the activator protein-1 (AP-1) proteins c-Jun and JunB regulate miR-203 expression in keratinocytes. In contrast to inducers of keratinocyte differentiation, epidermal growth factor and keratinocyte growth factor suppressed miR-203 expression in keratinocytes below the basal level. Overexpression of miR-203 in keratinocytes resulted in enhanced differentiation, whereas inhibition of miR-203 suppressed calcium-induced terminal differentiation as judged by involucrin expression. These results suggest that upregulation of miR-203 in human keratinocytes is required for their differentiation and is dependent on the activation of the PKC/AP-1 pathway.

Mouse Prkar1a haploinsufficiency leads to an increase in tumors in the Trp53+/- or Rb1+/- backgrounds and chemically induced skin papillomas by dysregulation of the cell cycle and Wnt signaling

PRKAR1A inactivation leads to dysregulated cAMP signaling and Carney complex (CNC) in humans, a syndrome associated with skin, endocrine and other tumors. The CNC phenotype is not easily explained by the ubiquitous cAMP signaling defect; furthermore, Prkar1a(+/-) mice did not develop skin and other CNC tumors. To identify whether a Prkar1a defect is truly a generic but weak tumorigenic signal that depends on tissue-specific or other factors, we investigated Prkar1a(+/-) mice when bred within the Rb1(+/-) or Trp53(+/-) backgrounds, or treated with a two-step skin carcinogenesis protocol. Prkar1a(+/-) Trp53(+/-) mice developed more sarcomas than Trp53(+/-) mice (P < 0.05) and Prkar1a(+/-) Rb1(+/-) mice grew more (and larger) pituitary and thyroid tumors than Rb1(+/-) mice. All mice with double heterozygosity had significantly reduced life-spans compared with their single-heterozygous counterparts. Prkar1a(+/-) mice also developed more papillomas than wild-type animals. A whole-genome transcriptome profiling of tumors produced by all three models identified Wnt signaling as the main pathway activated by abnormal cAMP signaling, along with cell cycle abnormalities; all changes were confirmed by qRT-PCR array and immunohistochemistry. siRNA down-regulation of Ctnnb1, E2f1 or Cdk4 inhibited proliferation of human adrenal cells bearing a PRKAR1A-inactivating mutation and Prkar1a(+/-) mouse embryonic fibroblasts and arrested both cell lines at the G0/G1 phase of the cell cycle. In conclusion, Prkar1a haploinsufficiency is a relatively weak tumorigenic signal that can act synergistically with other tumor suppressor gene defects or chemicals to induce tumors, mostly through Wnt-signaling activation and cell cycle dysregulation, consistent with studies in human neoplasms carrying PRKAR1A defects.

Regulation of calprotectin expression by interleukin-1? and transforming growth factor-? in human gingival keratinocytes

BACKGROUND AND OBJECTIVE

Calprotectin, a heterodimer of S100A8 and S100A9 with antimicrobial properties, is expressed in gingival keratinocytes and plays an important role in innate immunity. Because calprotectin expression is localized in the spinous cell layer of the gingival epithelium, we hypothesized that the expression of calprotectin in keratinocytes is related to the differentiation stage. The aim of the present study was to investigate the relationship between calprotectin expression and keratinocyte differentiation using some factors that regulated its differentiation.

MATERIAL AND METHODS

Normal human gingival keratinocytes were isolated from gingival tissues obtained at the extraction of wisdom teeth, and were cultured in serum-free keratinocyte medium supplemented with interleukin-1alpha or calcium, which promote keratinocyte differentiation, and transforming frowth factor-beta (TGF-beta) or retinoic acid, which suppress its differentiation. The expression of S100A8/A9 mRNA and the production of calprotectin in normal human gingival keratinocytes were examined by northern blotting and enzyme-linked immunosorbent assay, respectively. The expression of cytokeratin 14, involucrin and filaggrin (marker proteins of keratinocyte differentiation) was investigated by immunohistochemical staining, and the DNA-binding activity of CCAAT/enhancer binding protein alpha (C/EBPalpha), a transcription factor, was examined by electrophoretic mobility shift assay.

RESULTS

The expression of S100A8/A9 mRNA and the production of calprotectin were increased by interleukin-1alpha and calcium, but decreased by TGF-beta. RA inhibited the expression of S100A8/A9 and keratinocyte differentiation, which were induced by interleukin-1alpha. C/EBPalpha DNA-binding activity in normal human gingival keratinocytes was enhanced by interleukin-1alpha and calcium, but suppressed by TGF-beta.

CONCLUSION

The present study suggests that calprotectin expression is related to keratinocyte differentiation and that C/EBPalpha is a regulator of calprotectin expression in keratinocytes.

Cell markers and the side population phenotype in ocular surface epithelial stem cell characterization and isolation

The ocular surface is covered by tworapidly renewing and embryologically-related linings, the corneal and conjunctival epithelia. The long-term survival of thesetissues is ultimately dependent on their respective resident stem cells. In the corneal epithelium, the stem cells and their early precursors are exclusively circumscribed to the narrow vasscularize limbal rim that provides epithelial precursor cells to the critically transparent central cornea. Limbal damage causes an interruption of this essential cell supply and allows the invasion of the corneal surface by the conjunctival epithelium, an event that ultimately leads to corneal scarring. The limited supply of immunocompatible tissue is a major hindrance to efforts to develop effective procedures for ocular surface reconstruction. This review describes some of the current work and strategies being developed to achieve the isolation of the limbal stem cell and define its genetic, biochemical, and functional make-up. The study of isolated ocular surface stem cells will foster basic understanding of the environmentalrequisites for their survival and proliferation in a self-replicative mode, leading eventually to advances in therapeutic approaches.

Ocular surface epithelia contain ABCG2-dependent side population cells exhibiting features associated with stem cells

When cell populations are incubated with the DNA-binding dye Hoechst 33342 and subjected to flow cytometry analysis for Hoechst 33342 emissions, active efflux of the dye by the ABCG2/BCRP1 transporter causes certain cells to appear as a segregated cohort, known as a side population (SP). Stem cells from several tissues have been shown to possess the SP phenotype. As the lack of specific surface markers has hindered the isolation and subsequent biochemical characterization of epithelial stem cells this study sought to determine the existence of SP cells and expression of ABCG2 in the epithelia of the ocular surface and evaluate whether such SP cells had features associated with epithelial stem cells. Human and rabbit limbal-corneal and conjunctival epithelial cells were incubated with Hoechst 33342, and analyzed and sorted by flow cytometry. Sorted cells were subjected to several tests to determine whether the isolated SP cells displayed features consistent with the stem cell phenotype. Side populations amounting to <1% of total cells, which were sensitive to the ABCG2-inhibitor fumitremorgin C, were found in the conjunctival and limbal epithelia, but were absent from the stem cell-free corneal epithelium. Immunohistochemistry was used to establish the spatial expression pattern of ABCG2. The antigen was detected in clusters of conjunctival and limbal epithelia basal cells but was not present in the corneal epithelium. SP cells were characterized by extremely low light side scattering and contained a high percentage of cells that: showed slow cycling prior to tissue collection; exhibited an initial delay in proliferation after culturing; and displayed clonogenic capacity and resistance to phorbol-induced differentiation; all features that are consistent with a stem cell phenotype.

Identification of calcium-inducible genes in primary keratinocytes using suppression-subtractive hybridization

Terminal differentiation in epidermal keratinocytes involves major biochemical changes including the expression of many new differentiation-specific genes. To further understand this process, we performed suppression-subtractive hybridization of keratinocytes cultured under high-calcium condition, known to induce differentiation in vitro. We randomly isolated 300 clones representing 90 different genes. By reverse Northern blot analyses, 20 different genes were found to be overexpressed, of which 13 were confirmed as differentially expressed genes during keratinocyte differentiation by Northern blot analysis. Of those, five genes, transglutaminase 1, keratin 6, interleukin-1 receptor antagonist, kallikrein 7, and heat shock protein 27, are known to be up-regulated during epidermal differentiation. Six genes, ferritin-L chain, ribosomal protein S6, tumor-associated calcium signal transducer 2, neuroendocrine secretory protein 55, phosphoserine aminotransferase, and neutrophil gelatinase-associated lipocalin, heretofore were not known to be up-regulated during keratinocyte differentiation. We also identified two novel genes. One of these maps to chromosome 1q21 of the epidermal differentiation complex, and its expression level was strongly increased in differentiating keratinocytes. These differentially expressed genes may provide significant opportunities for further understanding of the epidermal keratinocyte differentiation.

Role of protein kinase C alpha in calcium induced keratinocyte differentiation: defective regulation in squamous cell carcinoma

Calcium induces both involucrin and transglutaminase-K in normal keratinocytes (NHK) but not in squamous carcinoma cell lines (SCC). The protein kinase C (PKC) agonist phorbol myristoyl acetate potentiates and the PKC antagonist Ro31-8220 blocks the ability of calcium to stimulate the involucrin promoter in normal human keratinocytes but not in SCC4. We thus examined the ability of calcium to regulate the levels of five PKC isozymes in NHK and two SCC. In the normal keratinocytes, the levels of PKC [alpha], PKC [delta], PKC [eta], and PKC [zeta] increased over the first one to two weeks in a calcium-and time-dependent manner. PKC [epsilon] decreased in a time-and calcium-dependent fashion over the three-week period. All five isozymes showed little change during culture in SCC4 at any calcium concentration. Calcium and time of culture had partial effects on SCC12B2, a carcinoma that shows partial differentiation characteristics. Since PKC [alpha] is the only calcium responsive PKC isozyme in keratinocytes and most likely to be directly involved in calcium induced differentiation, we evaluated the effect of inhibiting its production with antisense oligonucleotides on calcium-regulated markers of differentiation. We found that the PKC [alpha] specific antisense oligonucleotide blocked calcium stimulated involucrin promoter activity as well as PKC [alpha], involucrin, and transglutaminase protein production, whereas the sense oligonucleotide control did not. We conclude that although a number of PKC isozymes are regulated during calcium-induced differentiation, PKC [alpha] plays a necessary role in mediating calcium-induced differentiation. Failure to regulate PKC [alpha] in SCC4 may underlie at least part of the failure of calcium to promote differentiation in these cells.

Transactivation of involucrin, a marker of differentiation in keratinocytes, by lens epithelium-derived growth factor (LEDGF)

Human involucrin (hINV), first appears in the cytosol of keratinocytes and ultimately cross-linked to membrane proteins via transglutaminase and forms a protective barrier as an insoluble envelope beneath the plasma membrane. Although the function and evolution of involucrin is known, the regulation of its gene expression is not well understood. An analysis of the hINV gene sequence, upstream of the transcription start site (-534 to +1 nt) revealed the presence of potential sites for binding of lens epithelium-derived growth factor (LEDGF); stress response element (STRE; A/TGGGGA/T) and heat shock element (HSE; nGAAn). We reported earlier that LEDGF activates stress-associated genes by binding to these elements and elevates cellular resistance to various stresses. Here, gel-shift and super-shift assays confirm the binding of LEDGF to the DNA fragments containing HSEs and STREs that are present in the involucrin gene promoter. Furthermore, hINV promoter linked to CAT reporter gene, cotransfected in human corneal simian virus 40-transformed keratinocytes (HCK), was transactivated by LEDGF significantly. In contrast, the activity of hINV promoter bearing mutations at the WT1 (containing HSE and STRE), WT2 (containing STRE) and WT3 (containing STRE) binding sites was diminished. In addition, in HCK cell over-expressing LEDGF, the levels of hINV mRNA and hINV protein are increased by four to five-fold. LEDGF is inducible to oxidants. Cells treated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA), known to stimulate production of H(2)O(2), showed higher levels of LEDGF mRNA. Furthermore, our immunohistochemical studies revealed that hINV protein is found in the cytoplasm of HCK cells over-expressing LEDGF, but not detectable in the normal HCK cells or HCK cells transfected with vector. This regulation appears to be physiologically important, as over-expression of HCK with LEDGF increases the expression of the endogenous hINV gene and may provide new insight to understand the molecular mechanism of transcriptional regulation of this gene. LEDGF may play an important role in establishing an important barrier in corneal keratinocytes by maintaining epidermal turn-over rate, and protecting HCKs against stress.

Protein kinase C-beta, fibronectin, alpha(5)beta(1)-integrin, and tumor necrosis factor-alpha are required for phorbol diester-induced apoptosis in human myeloid leukemia cells

The human myeloid HL-60 cell line and its cell variant HL-525 were used to study signaling events leading to apoptosis induction by phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC) enzymes. Unlike parental cells, HL-525 cells are PKC-beta deficient and resistant to PMA-induced apoptosis. These cells regain susceptibility to apoptosis induction after transfection with a PKC-beta expression vector. By using this vector and specific neutralizing monoclonal antibodies (mAbs), it was established that PMA-induced apoptosis also called for an interaction between cell-surface alpha(5)beta(1)-integrin and its deposited ligand fibronectin (FN), which is downstream of PKC-beta activation. Experiments with mAbs, the PKC-beta vector, and exogenous FN revealed that the next step entailed an interaction between secreted tumor necrosis factor-alpha and its type I receptor. By using a sphingomyelinase inhibitor, it was concluded that the subsequent step involved ceramide production. Moreover, a permeable ceramide was effective in inducing apoptosis in both HL-60 and HL-525 cells, and this induction was caspase-1 and/or -4 dependent because an inhibitor of these caspases abrogated the induced apoptosis. Based on these and related differentiation studies, we conclude that the above signaling events, the early ones in particular, are shared with PMA-induced macrophage differentiation in the HL-60 cells. It is likely that once these cells acquire their macrophage phenotype and perform their tasks, they become superfluous and are eliminated from the body by a self-triggered apoptotic process that involves our proposed signaling scheme.

Decreased growth inhibitory responses of squamous carcinoma cells to interferon-gamma involve failure to recruit cki proteins into cdk2 complexes

Interferon-gamma induces an irreversible growth arrest and squamous differentiation in normal human epidermal keratinocytes. We present for the first time a careful biochemical analysis of the cell-cycle-related events that occur during interferon-gamma treatment of normal human epidermal keratinocytes. The interferon-gamma-induced irreversible growth arrest state is characterized by inhibition of cyclin-dependent kinases, prevention of Rb and p130 (Rb2) phosphorylation, and increases in p27(Kip1), p16(Ink4a), and p130 proteins, together with a transient increase in p21(Waf1/Cip1). Cells derived from squamous cell carcinomas are less responsive to interferon-gamma and do not terminally differentiate. We exploited these differences in response to interferon-gamma in order to identify the particular molecular defects in cell cycle control that promote carcinogenesis in squamous epithelia. In several squamous cell carcinoma cell lines as well as in interferon-gamma-insensitive HaCaT cells, interferon gamma was unable to significantly induce levels of p130 and/or p16 protein. In addition, p21 association with cdk2 complexes was undetectable in either the absence or the presence of interferon-gamma and, unlike normal human epidermal keratinocytes, p27 association with cdk2 did not increase with interferon-gamma treatment. These multiple defects appear to be intrinsic to the mechanisms of cell cycle regulation rather than due to defects in the interferon-gamma signaling pathway, as induction of several interferon-gamma-responsive genes including Stat 1, IRF-1, and p21 itself was normal. Interestingly, exogenous expression of p21 protein in the squamous cell carcinoma cell lines by adenovirus carrying wildtype p53 or p21 cDNA cooperated with interferon-gamma to produce a greater inhibition of growth than either agent alone, even though p21 protein could barely be detected in cdk2 complexes. We conclude that squamous cell carcinoma cells have intrinsic defects in their ability to regulate cdk-cki complexes in response to differentiation signals.

Calcium- and vitamin D-regulated keratinocyte differentiation

Calcium and 1,25 dihydroxyvitamin D (1,25(OH)(2)D) regulate the differentiation of keratinocytes. We have examined the mechanisms by which such regulation takes place, focusing primarily on the events leading to cornified envelope (CE) formation, in particular the mechanisms by which calcium and 1,25(OH)(2)D regulate the induction of involucrin, a component of the CE, and transglutaminase, the enzyme cross-linking involucrin and other substrates to form the CE. Both extracellular calcium (Ca(o)) and 1,25(OH)(2)D raise intracellular free calcium (Ca(i)) as a necessary step toward stimulating differentiation. Cells lacking the calcium sensing receptor (CaR) or phospholipase C-gamma 1 (PLC-gamma 1) fail to respond to Ca(o) or 1,25(OH)(2)D with respect to differentiation. Residing in the promoter of involucrin is a region responsive to calcium and 1,25(OH)(2)D, the calcium response element (CaRE). The CaRE contains an AP-1 site, mutations of which result in loss of responsiveness to Ca(o) and 1,25(OH)(2)D, indicating a role for protein kinases C (PKC). PKC alpha is the major PKC isozyme involved at least for calcium-induced differentiation. Thus, the regulation of keratinocyte differentiation by calcium and 1,25(OH)(2)D involves a number of signaling pathways including PLC and PKC activation, leading to the induction of proteins required for the differentiation process.

Calprotectin expression by gingival epithelial cells

Calprotectin, a heterodimer of MRP8 and MRP14 with antimicrobial properties, is found in the cytosol of neutrophils, monocytes, and human gingival keratinocytes. During inflammation of the oral mucosa, the expression of immunoreactive calprotectin appears upregulated. Given the possible cell sources, we sought to learn if epithelial cells upregulate calprotectin in response to proinflammmatory agents. First, human gingival keratinocytes were maintained in primary culture until senescence. At each passage, cells were harvested and analyzed for quantitative expression of MRP8 and MRP14 subunit mRNA by RNase protection assays and calprotectin complex by enzyme-linked immunosorbent assay. Calprotectin expression was constitutive in the primary gingival keratinocytes, but calprotectin-specific mRNA and protein tended to increase as the cells neared senescence. To test whether calprotectin expression was inducible, immortalized gingival keratinocyte cultures were treated for 2 to 4 h with lipopolysaccharide (LPS) or interleukin-1 beta (IL-1 beta). As a positive control for inducible expression, immortalized keratinocytes were incubated with phorbol myristate acetate (PMA) (50 ng/ml) for 24 h. Incubation with PMA stimulated increased expression of MRP8 and MRP14 mRNA within 2 h, peaking within 5 h. MRP8- and MRP14-specific mRNA expression by immortalized keratinocytes appeared to be unaffected by LPS or IL-1 beta. In contrast, LPS, IL-1 beta, and PMA each upregulated IL-8. These data show that calprotectin mRNA is expressed constitutively in cultured keratinocytes, while expression by immortalized cells appears to be independent of the exogenous proinflammatory agents LPS and IL-1 beta.

Structure and transcriptional regulation of the human cystatin A gene. The 12-O-tetradecanoylphorbol-13-acetate (TPA) responsive element-2 site (-272 to -278) on cystatin A gene is critical for TPA-dependent regulation

Cystatin A, a cysteine proteinase inhibitor, is one of the precursor proteins of cornified cell envelope of keratinocytes and is expressed during the late stage of keratinocyte differentiation. We have isolated and characterized the human cystatin A gene. The cystatin A gene consists of three exons and two introns. The first, the second, and the third exons consist of coding sequences that are 66, 102, and 126 base pairs in length, respectively. The first and the second introns consist of 14 and 3.6 kilobase pairs, respectively. The transcription initiation site was located 55 base pairs upstream from the first translation site. The fragment, +77 to -2595 in the 5'-flanking region of the human cystatin A gene, was subcloned into a chloramphenicol acetyltransferase (CAT) reporter vector. The expression vector, p2672CAT, produced a significant CAT activity in transiently transfected SV40-transformed human keratinocytes (SVHK cells), that were further stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA), a potent protein kinase C activator. Sequence analysis of the gene detected three TPA responsive elements (TRE-1, TRE-2, and TRE-3) and one AP-2 site on the 5' upstream promoter region. Deletion analyses of the p2672CAT vector demonstrated that TRE-2, which was located between -272 and -278, was critical for the regulation by TPA. Gel shift analyses revealed that c-Jun, JunD, and c-Fos bound to the TRE-2 region and that the p2672CAT activity level was elevated by co-transfection with c-Jun and c-Fos or with JunD and c-Fos expression vectors. Furthermore, co-transfection of SVHK cells with the protein kinase C-alpha expression vector and the p2672CAT expression vector also resulted in an increased CAT activity. These results indicate that the 5'-flanking region of the human cystatin A gene confers promoter activity and contains a TRE (TRE-2) that mediates, at least in part, the enhanced expression of this gene by TPA.

Up-regulation of p21WAF1 by phorbol ester and calcium in human keratinocytes through a protein kinase C-dependent pathway

Terminal differentiation in a variety of cell types has been associated with p53-independent up-regulation of p21WAF1 p21WAF1 mRNA and protein are expressed at low levels in normal human skin, but overexpression of p21WAF1 has been observed in differentiating keratinocytes in involved psoriatic epidermis and in human squamous cell carcinoma. In this study we investigated by immunohistochemistry and Western blotting whether calcium and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate, well characterized differentiation signals, induce p21WAF1 in cultured normal human keratinocytes and whether induction of p21WAF1 in this system depends on protein kinase C activation or functional p53. Phorbol ester induced p21WAF1 expression, which was maximal at 4 to 8 h with reduction back to baseline by 24 to 48 h. In contrast, increasing the extracellular Ca2+ concentration from 70 micromol/L to 1.5 mmol/L resulted in upregulation of p21WAF1 expression with a slower time course, with peak induction at 18 to 24 h. No parallel increase in p53 expression was observed in normal human keratinocytes. Up-regulation of p21WAF1 was also observed in response to phorbol ester in HaCaT cells, which carry homozygous and inactivating mutations for p53. Induction of p21WAF1 by phorbol ester and Ca2+ was inhibited by the specific protein kinase C inhibitor Ro 31-8220. The results demonstrate a differential time course of p21WAF1 protein up-regulation in response to phorbol ester and Ca2+, signals that result in keratinocyte differentiation, and suggest that induction of p21WAF1 in differentiating human keratinocytes occurs through protein kinase C-dependent and p53-independent mechanisms.

Up-regulation of p27Kip1, p21WAF1/Cip1 and p16Ink4a is associated with, but not sufficient for, induction of squamous differentiation

Irreversible growth arrest is an early and integral part of squamous cell differentiation in normal human epidermal keratinocytes (NHEKs) and is assumed to be linked to the control of expression of differentiation-specific genes. In this study, we examine the link between the molecular events associated with growth arrest and the expression of differentiation genes. NHEKs that have been induced to undergo growth arrest and differentiation by suspension culture contain populations in both G1 and G2/M of the cell cycle. The irreversible growth arrest state in NHEKs is characterized by an accumulation of the hypophosphorylated forms of Rb and p130, with subsequent down-regulation of levels of Rb, up-regulation of p130 and associated down-regulation of E2F-regulated genes such as cyclin A. These events correlate with an inhibition of G1 cdk activity, mediated in part by an increase in the cdk inhibitors p21(WAF1/Cip1), p27(Kip1) and p16(Ink4a). Flow cytometric and immunoblot analysis demonstrated that the timing of the up-regulation of p27, p16 and p130 corresponds closely with the induction of the squamous-specific genes cornifin alpha (SPRR-1) and transglutaminase type I, suggesting a close link between control of growth arrest and differentiation. However, growth arrest induced by over-expression of p27, p21 or p16 by recombinant adenovirus is not sufficient to induce expression of the differentiation genes, or to invoke the pattern of cell cycle regulatory protein expression characteristic of the differentiation-specific irreversible growth arrest. We conclude that growth arrest mediated by activation of the Rb pathway is not sufficient to trigger terminal squamous differentiation and additional signals which can be generated during suspension culture are required to promote the complete differentiation program.

Modulation of intracellular calcium levels inhibits secretion of collagenase 1 by migrating keratinocytes

Calcium concentration influences keratinocyte differentiation, and, following injury, keratinocytes move through an environment of changing calcium levels. Because these migrating cells in wounds invariably express collagenase 1, we assessed if modulation of calcium levels regulates collagenase 1 production by primary human keratinocytes. Accurately reflecting the confined spatial pattern of enzyme production seen in vivo, collagenase 1 mRNA was expressed only by keratinocytes migrating from foci of differentiated cells. Treatment with calcium ionophores A23187 or thapsigargin markedly inhibited the basal and phorbol 12-myristate 13-acetate-(PMA) stimulated accumulation of keratinocyte collagenase 1 in the medium but did not affect collagenase 1 production by control or PMA-treated fibroblasts. A23187-mediated inhibition of collagenase 1 protein was not associated with a decrease in mRNA levels but rather was controlled by a selective and reversible block of enzyme secretion. This block in secretion was likely not due to altered protein folding as the proenzyme within A23187-treated cells remained capable of autolytic activation upon treatment with p-aminophenylmercuric acetate. In contrast, 92-kDa gelatinase mRNA and secreted protein levels were coordinately reduced by A23187. Keratin 14 expression, a basal keratinocyte marker, was reduced with PMA treatment, but A23187 did not affect keratin 14 expression. In human wounds, both basal and suprabasal keratinocytes at the migrating front of epidermis stained for keratin 14, but only the basal cells expressed collagenase 1. These data suggest that collagenase 1 production is not necessarily linked with expression of basal cell markers and that modulation of intracellular calcium levels can block secretion of collagenase 1 by keratinocytes which have moved away from the stratum basalis and from their natural substrate.

Transcriptional analysis of the 5'-noncoding region of the human involucrin gene

Human involucrin whose gene transcription is directed by a 2456-nucleotide (nt) 5'-noncoding region is a structural component of the epithelial cornified layer. Transient transfection assays demonstrated that this region is transcriptionally active in multiplying keratinocytes and is enhanced by 2 mM CaCl2 treatment. Calcium-independent transcriptional activity and the interaction with the AP-1 transcriptional factor was located on the proximal part (nt -159 to -1) of the 5'-noncoding region. However, CaCl2 responsiveness was mapped to a distal 1185-nt fragment (nt -2456 to -1272). Moreover, this fragment potentiated the Herpes simplex thymidine kinase promoter in normal keratinocytes and is responsive to calcium treatment in a cell type-specific manner. Interestingly, the absence of a 491-nt fragment located between the two enhancer domains (nt -651 to -160) resulted in transcriptional activation in multiplying keratinocytes. This fragment interacts with AP-1 and the YY1 transcriptional silencer. It is concluded that human involucrin 5'-noncoding region contains at least three regulatory domains, a distal CaCl2-responsive enhancer, a putative transcriptional silencer (that interacts with AP-1 and YY1), and a proximal enhancer/promoter (that interacts with AP-1). Thus, this study demonstrates the presence of particular transcriptional factors can potentially regulate the human involucrin expression.

Down-regulation of Langerhans cell protein kinase C-beta isoenzyme expression in inflammatory and hyperplastic dermatoses

The family of protein kinase C (PKC) isoenzymes plays a fundamental part in signal transduction, and thereby regulates important cellular functions, including growth, differentiation, cytokine production and adhesion molecule expression. In lesional psoriatic skin, Ca(2+)-dependent PKC activity, PKC-beta protein and epidermal Langerhans cell (LC) PKC-beta immunostaining are significantly decreased, indicating activation and subsequent down-regulation of PKC. Whether these changes occur in other inflammatory/hyperplastic dermatoses is, however, unknown. We examined PKC-alpha and PKC-beta expression in normal skin, psoriasis, cutaneous T-cell lymphoma (CTCL), lamellar ichthyosis, non-bullous ichthyosiform erythroderma, atopic dermatitis, urushiol-induced allergic contact dermatitis, and sodium lauryl sulphate (SLS)-induced irritant contact dermatitis. Cryostat sections were stained for PKC-alpha and PKC-beta, and the LC marker CD1a, using an immunoperoxidase technique and specific monoclonal antibodies. Double-labelling studies, in normal skin, revealed co-expression of PKC-beta and CD1a by epidermal LCs. Analysis of the number of PKC-beta+ and CD1a+ epidermal LCs, in diseased compared with normal skin, revealed three categories: (i) in psoriasis and CTCL, the PKC-beta+ epidermal LC number was significantly reduced, whereas the CD1a+ epidermal LC number was unchanged; (ii) in allergic and irritant contact dermatitis, both PKC-beta+ and CD1a+ epidermal LCs were significantly reduced in number; and (iii) in atopic dermatitis, the PKC-beta+ epidermal LC number was normal, and CD1a+ epidermal LCs were significantly increased in number. Moreover, the ratio of epidermal LC PKC+/CD1a+ was reduced in all the dermatoses studied, suggesting activation of PKC-beta, with subsequent down-regulation. Within the dermis, increased PKC-beta staining of infiltrating cells was observed in all the conditions studied except lamellar ichthyosis and non-bullous ichthyosiform erythroderma. These data indicate that: (i) down-regulation of LC PKC-beta occurs in a variety of inflammatory and hyperplastic skin disorders, and is not unique to psoriasis, and (ii) the pattern of epidermal LC PKC-beta and CD1a expression varies among the diseases studied. In mice, PKC activation induces LC migration. Thus, down-regulation of epidermal LC PKC-beta associated with reduced CD1a+ epidermal LCs in allergic and irritant contact dermatitis suggests that PKC-beta may transduce the signal for migration of LCs from human epidermis.

Proliferation and interferon-gamma receptor expression in psoriatic and healthy keratinocytes are influenced by interactions between keratinocytes and fibroblasts in a skin equivalent model

Epidermal-dermal interactions were studied in a skin equivalent model. Six combinations of keratinocytes and fibroblasts from healthy and psoriatic skin were used. TPA (12-O-tetradecanoylphorbol-13-acetate) was used to determine whether the expression of the IFN-gamma receptors in keratinocytes was related to epidermal differentiation and proliferation. These phenomena were assessed by immunohistochemistry. In all epidermal outgrowths, the epidermal growth factor receptor was expressed throughout the epidermis, cytokeratin 16 suprabasally, and filaggrin and involucrin in its superficial part. The IFN-gamma receptor was expressed throughout the epidermis, but was unevenly distributed. The expression of the IFN-gamma receptor was quantified by confocal laser scanning microscopy both in the whole of epidermis and in areas with the strongest intensity. The total amount varied to a minor degree in the epidermal outgrowths of different origins and was unaffected by TPA. In high-intensity areas interactions between keratinocytes and fibroblasts did influence the amount of IFN-gamma receptor expression and TPA decreased the expression by 13%. There was no correlation between the proliferation rate and the expression of the IFN-gamma receptor. Psoriatic and healthy keratinocytes were equally well differentiated in the skin equivalents. The interferon-gamma receptor was similarly expressed under these conditions. The growth rate, assessed by Ki-67-positive nuclei in the basal layer, was highest in healthy keratinocytes. Keratinocytes from psoriatic lesions increased their growth rate when cocultured with psoriatic fibroblasts compared with normal ones, indicating that fibroblasts may be of importance for epidermal hyperproliferation in psoriatic lesions.

Effects of 12-O-tetradecanoylphorbol-13-acetate on human papillomavirus type 16-positive keratinocytes at different stages of transformation

Normal human keratinocytes grown under serum-free conditions can be triggered to differentiate by exposure to serum or to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). We found that TPA treatment of human papillomavirus (HPV) type 16-immortalized cells in culture induced formation of cornified envelopes indicative of squamous differentiation. Concurrent with differentiation, TPA inhibited the expression of HPV 16 E6 and E7 mRNA transcripts. Adaptation of the immortalized cells to growth in serum-containing medium led to the selection of a subpopulation of HPV-transformed cells that was resistant to TPA-induced differentiation. In this cell line, a transient suppression of HPV transcripts was observed at 5 h, whereas in differentiation-resistant, carcinoma-derived lines, TPA had little effect on HPV oncogene expression. c-myc transcripts were suppressed for the duration of exposure to TPA in only the differentiation-competent cells; c-fos and c-jun were transiently induced in all cell lines. Transforming growth factor-alpha mRNAs were also increased approximately eightfold as HPV 16-immortalized cells were induced to differentiate. These results demonstrate that, in HPV 16-immortalized keratinocytes, acquisition of resistance to inducers of squamous differentiation is accompanied by altered regulation of cell growth and gene expression.

Concerted action of TGF-beta 1 and its type II receptor in control of epidermal homeostasis in transgenic mice

Transforming growth factor-beta 1 (TGF-beta 1) is a modulator of cellular proliferation, differentiation, and extracellular matrix deposition. It is a potent epithelial growth inhibitor and can alter the differentiative properties of keratinocytes, in vitro, but little is known about its normal physiological function in the epidermis in vivo. Transgenic mice were generated using a keratin 10 (K10) gene promoter to drive constitutive expression of TGF-beta 1 in the suprabasal keratinocyte compartment. Surprisingly, these mice showed a two- to threefold increase in epidermal DNA labeling index over control mice, in the absence of hyperplasia. The transgene, however, acted in the expected fashion, as a negative regulator of cell growth, when hyperplasia was induced by treatment by 12-tetradecanoyl-phorbol-13-acetate (TPA). Epidermal TGF-beta type I and II receptor (T beta RI and T beta RII) levels were examined in control and transgenic mice during induction of hyperplasia by TPA. Whereas T beta RI levels remained relatively constant, T beta RII expression was strongly induced in TPA-treated skins, prior to the induction of the growth inhibitory response to TGF-beta 1, and its level of expression correlated with growth sensitivity to TGF-beta 1 in vivo and in vitro. These results suggest that TGF-beta 1 and its type II receptor are part of the endogenous homeostatic regulatory machinery of the epidermis.

Chemical induction of interleukin-8, a proinflammatory chemokine, in human epidermal keratinocyte cultures and its relation to cytogenetic toxicity

Tumor promoters, proinflammatory cytokines, endotoxins, and protein synthesis inhibitors can modulate cell cycle kinetics of various cell types, stimulate production of reactive oxygen species, and induce keratinocytes to produce interleukin-8 (IL-8), a potent chemotactant for polymorphonuclear neutrophils and T lymphocytes. The aim of this study was to determine whether perturbations of cytogenetic responses correlated with the induction of IL-8 expression. Cultures of primary human keratinocytes were grown in serum-free medium with 5 mumol/L bromodeoxyuridine to label DNA and exposed either to phorbol-13-myristate-12-acetate (PMA) (0.0001-100 ng/ml), cycloheximide (CHX) (0.01-50 micrograms), lipopolysaccharide (0.1-100 micrograms/ml), tumor necrosis factor-alpha (TNF alpha) (3.13-50 ng/ml), or interleukin-1 alpha (IL-1 alpha) (1-182 pg/ml). Metaphase chromosome preparations were stained by a fluorescence-plus-Giemsa technique to differentiate sister chromatids. For IL-8 production, keratinocytes were grown to 70% confluency and then exposed to chemicals for 24 h. Immunoreactive IL-8 was quantitated from the supernatants by ELISA. With the exception of benzo(a)pyrene used as a positive control, none of the agents induced sister chromatid exchanges. However, PMA and TNF alpha induced IL-8 production that coincided with significant cell cycle inhibition. IL-1 alpha had no effect on cytogenetic endpoints, yet stimulated a 6.3-fold increase in IL-8. CHX inhibited cell cycle progression and mitotic activity at concentrations that were 200 times lower than required for IL-8 induction; however, puromycin (0.31-10 micrograms/ml), another protein synthesis inhibitor, did not induce IL-8. At all concentrations tested, TNF alpha reduced the mitotic index by approximately 45%, slowed cell cycle progression by approximately 3.5 h, and induced a flat, albeit large, IL-8 response at concentrations > or = 12.5 ng/ml. These agent-specific response patterns suggest that induction of IL-8 production is not always the inevitable result of cell cycle perturbations or genetic damage.

Application of cantharidin or 12-O-tetradecanoylphorbol-13-acetate on mouse epidermis induces a cell population shift that causes altered keratin distribution

The tumour promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) causes changes in epidermal protein expression, especially in the major differentiation products keratins K1 and K10. These keratins and filaggrin were studied in a pulse-labelled cell cohort in hairless mouse epidermis stimulated to proliferate by TPA or the hyperplasiogen cantharidin. Cells in DNA synthesis were pulse-labelled by 5-bromo-2-deoxyuridine (BrdU) 16 h after topical application of cantharidin or TPA. The BrdU-labelled cell cohort, the two keratins, and filaggrin were spatially mapped by paired immunofluorescence staining. Both cantharidin- and TPA-treated epidermis displayed altered distributions of K1 and K10 with expression only in the outermost cell layers, but the start of their postreplicative expression paralleled that in normal epidermis (18 h for K1 and 24 h for K10 after the last round of DNA synthesis). Cantharidin- and TPA-induced epidermal hyperplasia showed increased basal cell proliferation, accelerated suprabasal migration, and shortened transit time. Thus, the newly formed hyperplastic epidermis was composed of keratinocytes with a lower mean cellular age than that seen in unperturbed epidermis, which caused altered distribution of K1 and K10. Both hyperplastic and normal epidermis showed filaggrin expression in stratum granulosum; this started earlier in treated (30-36 h) than in untreated (96 h) skin. We concluded that the postmitotic onset of K1 and K10 expression was unaltered in regenerative epidermis, whereas filaggrin expression was considerably accelerated and thus influenced by the cell kinetic changes.

The involvement of protein kinase C in proliferation and differentiation of human keratinocytes--an investigation using inhibitors of protein kinase C

Protein kinase C, the major cellular receptor for tumour-promoting phorbol esters, has been suggested as playing a key role in the regulation of proliferation and differentiation of epidermal cells. In the present study, we investigated the effects of various well-characterized inhibitors of protein kinase C on proliferation and differentiation of SV 40-transformed and normal human keratinocytes. The drugs were found to inhibit cell proliferation in a dose-dependent manner, displaying similar effects in both cell types and reflecting their potencies in inhibiting purified protein kinase C. In contrast, keratinocyte differentiation induced by treatment with a calcium ionophore or spontaneously, i.e. by exposure of cells grown in the presence of low calcium concentration (0.06 mM) to normal calcium concentration (1.6 mM), was not inhibited by the compounds tested. The potent protein kinase C inhibitor, staurosporine, was found even to enhance cell differentiation. Therefore, the present study provides evidence that the classical protein kinase C pathway plays a critical role in the regulation of keratinocyte proliferation rather than in calcium-induced differentiation.

Staurosporine, a non-specific PKC inhibitor, induces keratinocyte differentiation and raises intracellular calcium, but Ro31-8220, a specific inhibitor, does not

The responsiveness of normal human keratinocytes to different modulators of protein kinase C (PKC) was investigated. The PKC agonist TPA, staurosporine (a non-specific inhibitor), and Ro31-8220 (a specific inhibitor) were studied for effect on cell morphology, growth rate, involucrin expression, and intracellular calcium levels. Surprisingly the response to nanomolar concentrations of staurosporine was similar to TPA and induced a fusiform morphology, inhibited growth, increased involucrin levels, and raised intracellular calcium. Staurosporine also increased the number of cornified envelopes, and its action therefore appeared identical to TPA. In contrast, Ro31-8220 had little effect on morphology or growth and blocked both the TPA-induced growth inhibition and calcium rise. Ro31-8220 had no effect on staurosporine-induced growth inhibition but partially reduced its associated calcium rise. These results suggest PKC activation is required for keratinocyte differentiation and that staurosporine acts like a PKC agonist to give a similar effect as TPA. Specific inhibition of PKC by Ro31-8220 inhibits TPA-induced differentiation.

Stem cells and corneal epithelial regeneration

Self-renewing tissues such as the corneal epithelium contain stem cells which represent the proliferative reserve. Studies of cellular differentiation and proliferation suggest that corneal epithelial stem cells are localised exclusively in the basal limbal epithelium. Although regulatory factors for the amplification of corneal stem cells are unknown, serum factors such as retinoic acid might induce differentiation of stem cells to transient amplifying cells which are responsible for cell amplification. These cells are regulated by various polypeptide growth factors and extracellular calcium. Loss or malfunction of stem cells does not permit maintenance or regeneration of the corneal epithelial mass but leads to conjunctivalisation of the corneal surface. Clinically, several ocular surface disorders such as chemical burns can cause limbal damage and consecutive limbal insufficiency. Treatment for these disorders is available only by transplantation of healthy stem cells, which can be performed as both autograft and allograft.

Differential induction of phosphatidylcholine hydrolysis, diacylglycerol formation and protein kinase C activation by epidermal growth factor and transforming growth factor-alpha in normal human skin fibroblasts and keratinocytes

We have investigated coupling between the epidermal growth factor (EGF) receptor and the phospholipase C (PLC)/protein kinase C (PKC) signal-transduction system in normal skin fibroblasts and keratinocytes, for which EGF and transforming growth factor alpha (TGF-alpha) are mitogenic. EGF and TGF-alpha induced a rapid increase in tyrosine phosphorylation of the EGF receptor, in both fibroblasts and keratinocytes, but failed to induce tyrosine phosphorylation of PLC-gamma 1 or detectable phosphoinositide hydrolysis, as measured by two sensitive assays. In fibroblasts, EGF induced phosphatidylcholine (PC) hydrolysis, resulting in increased diacylglycerol (DAG). In contrast, in keratinocytes, there was no detectable PC hydrolysis or elevation of DAG in response to EGF or TGF-alpha. EGF and TGF-alpha activated PKC in fibroblasts, as evidenced by increased phosphorylation of a specific cellular PKC substrate (myristoylated alanine-rich C-kinase substrate, 'MARCKS'). In keratinocytes, TGF-alpha and EGF induced only a modest increase in MARCKS protein phosphorylation. This apparent modest activation of PKC, in the absence of detectable DAG formation, may have been mediated by arachidonic acid, which was released from keratinocytes in response to TGF-alpha, and has been shown to stimulate PKC activity in vitro. These data demonstrate that (1) in dermal fibroblasts and keratinocytes, which express normal levels of EGF receptors, EGF receptor activation is not coupled to tyrosine phosphorylation of PLC-gamma 1 or PtdIns hydrolysis, suggesting that these events are not required for the mitogenic activity of EGF or TGF-alpha in these cells, (2) coupling of EGF receptor to PC hydrolysis is cell-type specific, and (3) in skin fibroblasts, DAG, formed through EGF-induced PC hydrolysis, is capable of activating PKC.

Analysis of the 5'-upstream promoter region of human involucrin gene: activation by 12-O-tetradecanoylphorbol-13-acetate

Involucrin is one of the precursor proteins of keratinocyte cornified envelope. Although the formation of the cornified envelope is induced by tumor-promoting phorbol esters, the effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the involucrin gene expression remains unknown. We have isolated a 5'-upstream region of human involucrin gene and examined its TPA-dependent promoter activity. The involucrin upstream region with the untranslated first exon was connected to chloramphenicol acetyltransferase (CAT)-involucrin promoter expression vector (INV-CAT) and was transfected into fetal rat keratinizing epidermal (FRSK) cells. The INV-CAT-transfected FRSK cells showed considerable CAT activity that was significantly augmented by the treatment of cells with TPA. FRSK cells that were transfected with a reversely oriented 5'-upstream sequence revealed little CAT activity and did not respond to TPA. The effect of TPA was significantly inhibited by the protein kinase C inhibitor 1-(5-isoquinoline-sulfonyl)-2-methyl piperazine dihydrochloride (H-7). Other protein kinase C activators (1-oleoyl-2-acetylglycerol and mezerein) also induced the INV-CAT promoter activity, whereas 4-O-methyl phorbol myristate acetate, a very weak protein kinase C activator, had only a slight effect. Analysis of the nucleotide sequence of the 5'-upstream region detected several 5'-TGANTCAA-3' sequences that are highly conserved TPA-response elements (TRE). Cotransfection of both c-jun and c-fos expression vectors with the INV-CAT vector into FRSK cells resulted in increased CAT activity. Cotransfection of either the c-jun or c-fos vector singly with the INV-CAT vector into FRSK cells had negligible effects. Dexamethasone significantly inhibited the TPA-induced promoter activity in the INV-CAT-transfected FRSK cells. These results indicate that involucrin gene expression is positively controlled by TPA through the activation of the protein kinase C/TRE system.

Phorbol ester- and calcium-induced reorganization of 180-kDa bullous pemphigoid antigen on the ventral surface of cultured human keratinocytes as studied by immunofluorescence and immunoelectron microscopy

The hemidesmosome is an adhesion structure of the epidermal-dermal junction in keratinocytes. When keratinocytes migrate laterally or upward to differentiate, they must control the formation and disintegration of the hemidesmosomes. When keratinocytes are cultured in low-calcium (below 0.1 mM) medium, all cells behave like basal cells, adhere to the culture dish, and proliferate without differentiation. The calcium addition induces the differentiation. A bullous pemphigoid antigen, 180-kDa BPA, has been shown to be a component of the hemidesmosome. Using a monoclonal antibody to the 180-kDa BPA and a human squamous cell carcinoma cell line (DJM-1 cells), the fate of hemidesmosomes was studied after the addition of calcium to low-calcium-grown cells and 12-tetradecanoylphorbol-13-acetate (TPA) to high-calcium (1.87 mM) grown cells by immunofluorescence and immunoelectron microscopy. The antigen was distributed evenly as fine dots on the entire ventral surface of low-calcium cells, whereas they formed a peculiar, concentric ring or arch arrangement on the ventral surface of high-calcium cells. Immunoelectron microscopy revealed the deposits of gold particles at sites on the membrane surface, where some filamentous or electron-dense materials were associated, although the complete structure of hemidesmosomes was not formed. They deposited directly onto the membrane surface in low-calcium cells and with a distance of 20-50 nm from the membrane surface in high-calcium cells. The calcium addition caused a profound reduction of the 180-kDa BPA-positive area for 30 to 120 min and then formed the high-calcium-ring pattern after 4 to 6 h. A similar calcium response was seen in normal human keratinocytes. TPA (16 nM) treatment caused disintegration of the ring pattern in high-calcium DJM-1 cells. This was inhibited with a protein kinase C (PKC) inhibitor. H7 (20 microM). These results suggest that the hemidesmosome is a dynamic structure and PKC can be one of the major factors in controlling the hemidesmosome, since it is known that the low-high calcium shift induces a calcium influx and a PKC activation, and TPA activates PKC in keratinocytes.

Regulation of transglutaminase 1 gene expression by 12-O-tetradecanoylphorbol-13-acetate, dexamethasone, and retinoic acid in cultured human keratinocytes

Transglutaminase 1 (TG1) is an enzyme that is expressed at the late stage of terminal differentiation of keratinocytes and catalyzes the epsilon-(gamma-glutamyl)lysine cross-linking reaction to form a highly insoluble cell envelope. To elucidate the mechanism of TG1 gene expression in keratinocytes, we examined the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA), dexamethasone, 1,25-dihydroxyvitamin D3, and retinoic acid on the levels of TG1 mRNA in cultured normal human epidermal keratinocytes (NHEK). Treatment of NHEK with TPA, up to 10 nM, markedly increased the levels of TG1 mRNA in a dose-dependent manner. The effect by treatment with 1 nM TPA reached a peak after 16 h of incubation (20-fold above the basal level). In contrast, phorbol had no effect on TG1 gene expression. The induction of TG1 mRNA expression by TPA was inhibited by 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H-7) and staurosporine. Dexamethasone at a concentration of 1 microM also increased the TG1 mRNA levels, but the maximum induction was observed (3-fold above the basal level) after 72 h of incubation. The effect of dexamethasone was not suppressed by H-7. Moreover, 1 microM of retinoic acid completely inhibited the induction of TG1 mRNA by both TPA and dexamethasone. 1,25-Dihydroxyvitamin D3 showed no effect on the TG1 mRNA levels. From these results, we suggest that the expression of TG1 gene may be upregulated by protein kinase C and glucocorticoid receptor systems and down-regulated by the retinoic acid receptor system.

Anti-proliferative effects of protein kinase C inhibitors in human keratinocytes

Various lines of evidence indicate that protein kinase C, a key enzyme in transmembraneous signal transduction, is involved in the regulation of keratinocyte proliferation. In the present study we have investigated the effects of various structurally unrelated protein kinase C inhibitors on the proliferation of HaCa T cells, a non-tumorigenic human keratinocyte cell line. All protein kinase C inhibitors dose-dependently inhibited cell proliferation as assessed by the incorporation of radioactively labelled thymidine and amino acids as well as the increase in total protein content in keratinocytes. The potencies of the drugs to inhibit cell proliferation were strongly correlated to their inhibitory potency on purified protein kinase C, displaying a correlation coefficient of 0.97. Methotrexate, an anti-proliferative drug, was found not to inhibit protein kinase C. Therefore, our data provide evidence that protein kinase C is crucially involved in the regulation of keratinocyte proliferation but is not the only target of anti-proliferative drug action.

The perinuclear factor, a rheumatoid arthritis-specific autoantigen, is not present in keratohyalin granules of cultured buccal mucosa cells

Rheumatoid arthritis patients have antibodies in their serum directed against the perinuclear factor, a protein component present in keratohyalin granules in the cytoplasm of human buccal mucosa cells. The anti-perinuclear factor (APF) can only be detected by an indirect immunofluorescence test performed on fresh buccal mucosa cells from 'selected donors'. To obtain a more reliable antigen source and to gain more insight into the origin and nature of the perinuclear factor we attempted to culture perinuclear factor-containing buccal mucosa cells. Here we describe the successful culturing of such cells, which, however, did not contain keratohyalin granules nor the perinuclear factor. By adding the phorbol ester 12-o-tetradecanoylphorbol-13-acetate (TPA) we were able to induce keratohyalin granules in both cultured primary buccal mucosa cells and a squamous carcinoma cell line of the cheek (SqCC/Y1). These induced keratohyalin granules do contain the protein profilaggrin, which in vivo, in fresh buccal mucosa cells, co-localizes with the perinuclear factor. However, we were not able to demonstrate the presence of the perinuclear factor, not even after induction of terminal differentiation of the cultured cells nor after Epstein-Barr virus infection. Our results suggest that the perinuclear factor, in contrast to profilaggrin, is not an integral component of buccal mucosa cells.

Induction of extracellular matrix gene expression in normal human keratinocytes by transforming growth factor beta is altered by cellular differentiation

Changes in epithelial substrate have been related to the cellular capacity for proliferation and to changes in cellular behavior. The effect of TGF beta 1 on the expression of the basement membrane genes, fibronectin, laminin B1, and collagen alpha 1 (IV), was examined. Northern analysis revealed that treatment of normal human epidermal keratinocytes with 100 pM TGF beta 1 increased the expression of each extracellular matrix (ECM) gene within 4 h of treatment. Maximal induction was reached within 24 h after treatment. The induction of ECM mRNA expression was dose dependent and was observed at doses as low as 1-3 pM TGF beta 1. Incremental doses of TGF beta 1 also increased cellular levels of fibronectin protein in undifferentiated keratinocytes and resulted in increased secretion of fibronectin. Squamous-differentiated cultures of keratinocytes expressed lower levels of the extracellular matrix RNAs than did undifferentiated cells. Treatment of these differentiated cells with TGF beta 1 induced the expression of fibronectin mRNA to levels seen in TGF beta-treated, undifferentiated keratinocytes but only marginally increased the expression of collagen alpha 1 (IV) and laminin B1 mRNA. The increased fibronectin mRNA expression in the differentiated keratinocytes was also reflected by increased accumulation of cellular and secreted fibronectin protein. The inclusion of cycloheximide in the protocol indicated that TGF beta induction of collagen alpha 1 (IV) mRNA was signaled by proteins already present in the cells but that TGF beta required the synthesis of a protein(s) to fully induce expression of fibronectin and laminin B1 mRNA. The differential regulation of these genes in differentiated cells may be important to TGF beta action in regulating reepithelialization.

Bradykinin induces phosphoinositide turnover, 1,2-diglyceride formation, and growth in cultured adult human keratinocytes

The effects of bradykinin on activation of phosphoinositide turnover, 1,2-diglyceride formation, and growth of cultured adult human keratinocytes were investigated. Keratinocytes specifically bound [3H]bradykinin with high affinity (kd = 3.4 nM) and displayed 1.5 X 10(5) binding sites/cell. Bradykinin caused a rapid dose-dependent increase in inositol trisphosphate (IP3) inositol bisphosphate, and inositol monophosphate. IP3 was maximally increased (fivefold) at 30 s and remained elevated for at least 10 min. Half maximal stimulation of IP3 formation was observed at 27 nM bradykinin. IP3 accumulation was equally elevated by bradykinin and lys-bradykinin but was not stimulated by des-Arg9-bradykinin, indicating that phospholipase C in cultured keratinocytes is coupled to B2 bradykinin receptors. Treatment of keratinocytes with active phorbol ester (TPA) caused a significant inhibition (50%) of bradykinin-induced IP3 accumulation, suggesting negative regulation of phospholipase C by protein kinase C. Bradykinin also caused a significant elevation in 1,2-diacylglycerol (DAG) content. DAG content was maximally elevated (twofold) at 1 min and remained elevated for at least 10 min. Bradykinin also caused a significant (twofold, p less than 0.02) increase in keratinocyte growth. These data demonstrate that bradykinin is a potent agonist of the phospholipase C/protein kinase C signal transduction system in cultured adult human keratinocytes and that activation of this pathway by bradykinin is associated with increased keratinocyte growth.

Different effects of TPA on two skin-derived cell lines: murine (HEL-30) and human (NCTC) epidermal cells

12-O-tetradecanoylphorbol-13-acetate (TPA) caused a rapid activation of protein kinase C in a murine (HEL-30) and in a human (NCTC) epidermal cell line. In HEL-30 cells, protein kinase C activation is followed by ornithine decarboxylase stimulation and cell proliferation, events inhibited by H-7, a specific inhibitor of protein kinase C. TPA in NCTC cells inhibited the basal ornithine decarboxylase activity and cell growth, whereas H-7 did not modify TPA effect. The response of NCTC cells was not due to direct toxicity of TPA. These data confirm that in murine epidermal cells, the proliferation induced by TPA is mediated by protein kinase C, whereas in a human skin-derived cell line these events are not or inversely associated.

Retinoic acid inhibits the production of collagenase by human epidermal keratinocytes

Lattices made of collagen and fibroblasts can be used as dermal equivalents to grow human keratinocytes in vitro. When these cultures are performed in a medium containing delipidized serum, the lattice is eventually degraded by the growing epithelium. The digestion of the dermal equivalent is due to the secretion of a collagenase by the keratinocytes. This degradation does not occur in cultures containing total serum or supplemented with retinoic acid. We show in this paper that retinoic acid inhibits the secretion of this keratinocyte collagenase in a dose-dependent manner. In the light of this result, the possible involvement of collagenase inhibition in the therapeutic effect of retinoic acid in skin disorders and skin aging must be considered.

Increased membrane-associated transglutaminase activity in psoriasis

Terminal differentiation of human skin involves the formation of an insoluble cross-linked protein envelope (CLE), which functions as an external barrier. To characterize terminal differentiation in the skin disease psoriasis, we have measured 1) membrane-associated transglutaminase (mTGase) activity, the rate limiting enzyme in the formation of CLE, and 2) the number of CLE in biopsies from normal and psoriatic skin. mTGase activity was increased 5-fold (p less than 0.0001) in psoriatic versus normal skin. Kinetic analysis revealed that the increased activity was due to an elevation in the Vmax of the enzyme. In addition, the number of CLE was 10-fold greater in psoriatic compared to normal skin. The increase in mTGase and CLE in psoriasis is in contrast to the decrease in other markers of terminal differentiation in skin, such as synthesis of specific intermediate filaments, observed in this disease.