The proximal promoter of the mouse loricrin gene contains a functional AP-1 element and directs keratinocyte-specific but not differentiation-specific expression

Regulation of the Dlx3 homeobox gene upon differentiation of mouse keratinocytes

The Distal-less Dlx3 homeodomain gene is expressed in terminally differentiated murine epidermal cells, and there is evidence to support an essential role as a transcriptional regulator of the terminal differentiation process in these cells. In an attempt to determine the factors that induce Dlx3 gene expression, we have cloned the 1.2-kilobase pair proximal region of murine gene and analyzed its cis-regulatory elements and potential trans-acting factors. The proximal region of the Dlx3 gene has a canonical TATA box and CCAAT box, and the transcription start site was located 205 base pairs upstream from the initiation of translation site. Serial deletion analysis showed that the region between -84 and -34 confers the maximal promoter activity both in undifferentiated and differentiated primary mouse keratinocytes. Gel retardation assays and mutational analysis demonstrated that the transcriptional regulator NF-Y (also referred to as CBF) binds to a CCAAT box motif within this region and is responsible for the majority of the Dlx3 promoter activity. In addition, an Sp1-binding site was located immediately upstream of transcription start site that acts as a positive regulatory element of the Dlx3 promoter, independent of the CCAAT box motif. Importantly, elements residing between +30 to +60 of the Dlx3 gene are responsible for the Ca(2+)-dependent induction of Dlx3 during keratinocyte differentiation.

Opposite effects of Ras or PKC activation on the expression of the SPRR2A keratinocyte terminal differentiation marker

Epidermal growth factor (EGF) enhances the expression of the keratinocyte terminal differentiation marker SPRR2A, when added to monolayers of basal keratinocytes, induced to stratify by increasing the extracellular calcium concentration. A similar stimulation is found during suspension-induced differentiation in methylcellulose. This effect, which is observed after several hours of EGF addition, is restricted to terminally differentiating keratinocytes and is dependent on PKC signaling. EGF also transiently activates the Ras signaling pathway, with a maximum induction after 10 min (Medema et al., 1994, Mol. Cell. Biol. 14, 7078-7085). The cellular effects of activated Ras were determined by transient transfection of Ha-ras(Leu-61) into normal human keratinocytes. Activated Ras completely inhibited PKC-mediated expression of SPRR2A. This inhibition is mediated via c-Jun as it is reversed by a dominant-negative c-Jun mutant (cJunDelta6/194) and c-Jun can substitute for activated Ras. The inhibitory effect is targeted to a 150-bp minimal promoter region, which is essential and sufficient for SPRR2A expression during keratinocyte terminal differentiation. This indicates that the Ras and PKC pathways, which both can be triggered by EGF, although at different time points, have opposite effects on SPRR2A gene expression.

Development of gene-switch transgenic mice that inducibly express transforming growth factor beta1 in the epidermis

Previous attempts to establish transgenic mouse models to study the functions of transforming growth factor beta1 (TGFbeta1) in the skin revealed controversial roles for TGFbeta1 in epidermal growth (inhibition vs. stimulation) and resulted in neonatal lethality in one instance. To establish a viable transgenic model for studying functions of TGFbeta1 in the skin, we have now developed transgenic mice, which allow focal induction of the TGFbeta1 transgene in the epidermis at different expression levels and at different developmental stages. This system, termed "gene-switch," consists of two transgenic lines. The mouse loricrin vector targets the GLVPc transactivator (a fusion molecule of the truncated progesterone receptor and the GAL4 DNA binding domain), and a thymidine kinase promoter drives the TGFbeta1 target gene with GAL4 binding sites upstream of the promoter. These two transgenic lines were mated to generate bigenic mice, and TGFbeta1 transgene expression was controlled by topical application of an antiprogestin. On epidermal-specific induction of the TGFbeta1 transgene, the BrdUrd labeling index in the transgenic epidermis decreased 6-fold compared with controls. Induction of the TGFbeta1 transgene expression also caused epidermal resistance to phorbol 12-myristate 13-acetate-induced hyperplasia, with a reduction in both epidermal thickness and BrdUrd labeling compared with those in controls. In addition, TGFbeta1 transgene expression induced an increase in angiogenesis in the dermis. Given that the TGFbeta1 transgene can affect both the epidermis and dermis, this transgenic model will provide a useful tool for studying roles of TGFbeta1 in wound-healing and skin carcinogenesis in the future.

Carotenoids and gene regulation

Consumption of dietary carotenoids, plant pigments found in green, yellow, and orange fruits and vegetables, has been linked to decreased risk of cancer. Several intervention trials with beta-carotene, however, have failed to confirm this association. Indeed, in current smokers, beta-carotene appeared to increase risk. These disturbing results have not been explained. Laboratory studies with experimental animals and cells in culture have shown cancer preventive activity for a diverse range of carotenoids. Studies using human and animal cells have identified a gene, connexin 43, whose expression is upregulated by chemopreventive carotenoids and which allows direct intercellular gap junctional communication (GJC). GJC is deficient in many human tumors and its restoration or upregulation is associated with decreased proliferation. This review will focus on the growing body of evidence that carotenoids have unexpected biologic effects in experimental systems, some of which may contribute to their observed cancer preventive properties in models of carcinogenesis.

Characterization of loricrin regulation in vitro and in transgenic mice

We have previously shown that the promoter of a 6.5 kb mouse loricrin clone contains a functional AP-1 element and directs tissue-specific, but not differentiation-specific, expression. We now report the isolation of a 14-kb genomic clone containing an additional 7 kb of genomic sequence. The additional sequences limit expression of a reporter construct to differentiated keratinocytes in culture. The expression of the 6.5-kb and 14-kb loricrin constructs were also analyzed in transgenic mice. Significantly, loricrin was found in all layers of the epidermis of the 6.5-kb transgenics, including basal and spinous cells. The expression of the 14-kb clone was indistinguishable from that of the endogenous gene, confirming that the additional sequences contain negative regulatory elements that restrict loricrin expression to the granular layer in vivo. In addition, we show the AP-1 element localized in the loricrin proximal promoter is necessary but not sufficient for expression of the loricrin gene in vivo in transgenic mice. Finally, to gain further insight into how AP-1 family members regulate expression of the loricrin gene, we co-transfected the loricrin reporter constructs with expression plasmids for various fos and jun family members and demonstrated that c-Fos/Jun-B heterodimers could mimic the differentiation-specific induction of loricrin.

Regulation of forestomach-specific expression of the murine adenosine deaminase gene

The maturation of stratified squamous epithelium of the upper gastrointestinal tract is a highly ordered process of development and differentiation. Information on the molecular basis of this process is, however, limited. Here we report the identification of the first murine forestomach regulatory element using the murine adenosine deaminase (Ada) gene as a model. In the adult mouse, Ada is highly expressed in the terminally differentiated epithelial layer of upper gastrointestinal tract tissues. The data reported here represent the identification and detailed analysis of a 1. 1-kilobase (kb) sequence located 3.4-kb upstream of the transcription initiation site of the murine Ada gene, which is sufficient to target cat reporter gene expression to the forestomach in transgenic mice. This 1.1-kb fragment is capable of directing cat reporter gene expression mainly to the forestomach of transgenic mice, with a level comparable to the endogenous Ada gene. This expression is localized to the appropriate cell types, confers copy number dependence, and shows the same developmental regulation. Mutational analysis revealed the functional importance of multiple transcription factor-binding sites.

CRE DNA binding proteins bind to the AP-1 target sequence and suppress AP-1 transcriptional activity in mouse keratinocytes

Previously, we have shown that nuclear extracts from cultured mouse keratinocytes induced to differentiate by increasing the levels of extra-cellular calcium contain Fra-1, Fra-2, Jun B, Jun D and c-Jun proteins that bind to the AP-1 DNA binding sequence. Despite this DNA binding activity, AP-1 reporter activity was suppressed in these cells. Here, we have detected the CREB family proteins CREB and CREMalpha as additional participants in the AP-1 DNA binding complex in differentiating keratinocytes. AP-1 and CRE DNA binding activity correlated with the induction of CREB, CREMalpha and ATF-1 and CREB phosphorylation at ser133 (ser133 phospho-CREB) in the transition from basal to differentiating keratinocytes, but the activity of a CRE reporter remained unchanged. In contrast, the CRE reporter was activated in the presence of the dominant-negative (DN) CREB mutants, KCREB and A-CREB, proteins that dimerize with CREB family members and block their ability to bind to DNA. The increase in CRE reporter activity in the presence of these mutants suggests that CRE-mediated transcriptional activity is suppressed in keratinocytes through protein-protein interactions involving a factor that dimerizes with the CREB leucine zipper. In experiments where the A-CREB mutant was co-transfected with an AP-1 reporter construct, transcriptional activity was also increased indicating that a CREB family member binds AP-1 sites and represses AP-1 transcriptional activity as well. Exogenous expression of the transcriptional repressor CREMalpha down-regulated both CRE and AP-1 reporters in keratinocytes suggesting that this factor may contribute to the suppression of AP-1 transcriptional activity observed in differentiating keratinocytes.

Involvement of a nuclear matrix association region in the regulation of the SPRR2A keratinocyte terminal differentiation marker

The small proline-rich protein genes ( SPRRs ) code for precursors of the cornified cell envelope, and are specifically expressed during keratinocyte terminal differentiation. The single intron of SPRR2A enhanced the activity of the SPRR2A promoter in transient transfection assays. This enhancement was position dependent, and did not function in combination with a heterologous promoter, indicating that the intron does not contain a classical enhancer, and that the enhancement was not due to the splicing reaction per se. Mild DNAse-I digestion of nuclei showed the SPRR2 genes to be tightly associated with the nuclear matrix, in contrast to the other cornified envelope precursor genes mapping to the same chromosomal location (epidermal differentiation complex). In vitro binding studies indicated that both the proximal promoter and the intron of SPRR2A are required for optimal association of this gene with nuclear matrices. Neither nuclear matrix association nor the relative transcriptional enhancement by the intron changed during keratinocyte differentiation. Apparently, the association of the SPRR2A gene with the nuclear matrix results in a general, differentiation-independent enhancement of gene expression.

The distal regulatory region of the human involucrin promoter is required for expression in epidermis

Human involucrin (hINV) is a precursor of the keratinocyte cornified envelope that is specifically expressed in the suprabasal layers of stratifying squamous epithelia. The promoter distal (DRR) and proximal regulatory regions (PRR) are required for optimal in vitro expression (Welter, J. F., Crish, J. F., Agarwal, C., and Eckert, R. L. (1995) J. Biol. Chem. 270, 12614-12622; and Banks, E. B., Crish, J. F., Welter, J. F., and Eckert, R. L. (1998) Biochem. J. 331, 61-68). We now present the complete sequence of these regions and evaluate their ability to drive in vivo transcription. Transgenes containing 5000 or 2473 base pairs of upstream regulatory region drive tissue- and differentiation-appropriate expression in stratifying surface epithelia. In contrast, transgenes containing 1953, 1333, 986, or 41 base pairs of upstream regulatory region are not expressed in surface epithelia, indicating that loss of the DRR (nucleotides -2474/-1953) results in loss of expression. Fusing the isolated DRR region directly to the hINV minimal promoter restores surface epithelial expression. Sequences downstream of the transcribed gene are not required for appropriate expression. The -1953/-41 segment influences the pattern of differentiation-dependent expression. The -986/-41 region, which includes the PRR, drives expression in internal epithelia.

AP-1 and ets transcription factors regulate the expression of the human SPRR1A keratinocyte terminal differentiation marker

The 173-base pair proximal promoter of SPRR1A is necessary and sufficient for regulated expression in primary keratinocytes induced to differentiate either by increasing extracellular calcium or by 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment. Whereas calcium-induced expression depends both on an AP-1 and an Ets binding site in this region, responsiveness to TPA resides mainly (but not exclusively) on the Ets element, indicating that Ets factors are important targets for protein kinase C signaling during keratinocyte terminal differentiation. This conclusion is further substantiated by the finding that expression of ESE-1, an Ets transcription factor involved in SPRR regulation, is also induced by TPA, with kinetics similar to SPRR1A. The strict AP-1 requirement in SPRR1A for calcium-induced differentiation is not found for SPRR2A, despite the presence of an identical AP-1 consensus binding site in this gene. Binding site swapping indicates that both the nucleotides flanking the TGAGTCA core sequence and the global promoter context are essential in determining the contribution of AP-1 factors in gene expression during keratinocyte terminal differentiation. In the distal SPRR1A promoter region, a complex arrangement of positive and negative regulatory elements, which are only conditionally needed for promoter activity, are likely involved in gene-specific fine-tuning of the expression of this member of the SPRR gene family.

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.

The alpha and eta isoforms of protein kinase C stimulate transcription of human involucrin gene

Involucrin is one of the precursor proteins of the cornified cell envelope that is formed beneath the cell membrane during terminal differentiation of keratinocytes. 12-O-tetradecanoylphorbol-13-acetate (TPA), which is a potent protein kinase C (PKC) activator, induces terminal differentiation of keratinocytes. We previously demonstrated that involucrin promoter activity is stimulated by TPA in cultured fetal rat skin keratinocytes. PKC is a large family of proteins and keratinocytes containing five PKC isozymes: alpha, delta, epsilon, eta, and zeta. In order to determine the role of the PKC isozyme(s) on involucrin gene expression, we constructed the chloramphenicol acetyl transferase (CAT)-involucrin promoter expression vector by connecting the 5'-upstream region of the human involucrin gene containing the untranslated first exon to the CAT reporter gene. The CAT-involucrin promoter expression vector was transfected with various PKC isozyme expression vectors into SV40-transformed human keratinocytes (SVHK cells). Transfection of the CAT-involucrin promoter expression vector with PKC-alpha or PKC-eta expression vectors resulted in a significant increase in the TPA-dependent involucrin promoter activity. The PKC inhibitor, 1-(5-isoquinoline-sulfonyl)-2-methyl piperazine dihydrochloride, inhibited the promoter activity stimulated by TPA. Transfection of PKC-delta, -epsilon, and -zeta had no effect on the involucrin-promoter activity. Although the promoter activity was stimulated by transfection of PKC-gamma, TPA did not enhance the promoter activity in the PKC-gamma-transfected SVHK cells. Previously we showed three AP-1 binding sites (AP1-1, -2, and -3) on the involucrin promoter region. Both the basal and the TPA-stimulated involucrin promoter activities were suppressed by deleting the AP1-1 site (-119 to -113) that is the most proximal to the transcription start site. The deletion of AP1-2 (-297 to -303) or AP1-3 (-447 to -453) did not affect the involucrin promoter activity. Gel retardation analyses disclosed that TPA stimulated the specific DNA binding of the nuclear protein(s) of control, PKC-alpha, or PKC-eta-transfected SVHK cells, but not of PKC-gamma-transfected cells. Addition of anti-c-Jun and anti-c-Fos antibodies decreased the specific protein-DNA complex band with a concomitant appearance of supershifted bands. These results indicate that PKC, specifically PKC-alpha and PKC-eta, mediates the TPA-dependent activation of involucrin gene expression of SVHK cells. PKC-gamma, which is not present in keratinocytes, also induces involucrin gene expression in a TPA-independent manner, when introduced into SVHK cells.

Structural organization of cornified cell envelopes and alterations in inherited skin disorders

The cornified cell envelope is a highly insoluble and extremely tough structure formed beneath the cell membrane during terminal differentiation of keratinocytes. Its main function is to provide human skin with a protective barrier against the environment. Sequential cross-linking of several integral components catalyzed by transglutaminases leads to a gradual increase in the thickness of the envelope and underscores its rigidity. Key structural players in this cross-linking process include involucrin, loricrin, SPRRs, elafin, cystatin A, S100 family proteins, and some desmosomal proteins. The recent identification of genetic skin diseases with mutations in the genes encoding some of these proteins, including transglutaminase 1 and loricrin, has disclosed that abnormal cornified cell envelope synthesis is significantly involved in the pathophysiology of certain inherited keratodermas and reflects perturbations in the complex, yet highly orderly process of cornified cell envelope formation in normal skin biology.

Effect of AP1 transcription factors on the regulation of transcription in normal human epidermal keratinocytes

The conversion of basal keratinocytes to spinous and granular cells is accompanied by the synthesis of a series of epidermal proteins in a differentiation-specific pattern. The transcription of several of these epidermal marker genes is regulated by activator protein 1 (AP1) interactions at their promoter regions. In the epidermis the various AP1 transcription factors are not present uniformly but appear to have a differentiation-specific distribution. We have explored whether the AP1 regulated expression of the keratin 5, transglutaminase 1, involucrin, and loricrin genes reflects the distribution of the AP1 factors in the epidermis. We have found that c-jun and junD activate and junB downregulates the transcription of both basal and suprabasal genes. The effect of c-jun is exerted through interactions with c-fos at the AP1 motifs in the target promoters, whereas both junB and junD act independently of the binding at the AP1 sites. Thus c-jun and junD act as general positive regulators whereas junB acts as a general suppressor of epidermal-specific genes. Therefore, the differentiation specificity of the AP1 regulation must be determined not only by the formation of distinct DNA/AP1 complexes but also by interactions involving other transcriptional regulators and/or distal regulatory elements.

Characterization of the regulatory regions in the human desmoglein genes encoding the pemphigus foliaceous and pemphigus vulgaris antigens

The adhesive proteins in the desmosome type of cell junction consist of two members of the cadherin superfamily, the desmogleins and desmocollins. Both desmogleins and desmocollins occur as at least three different isoforms with various patterns of expression. The molecular mechanisms controlling the differential expression of the desmosomal cadherin isoforms are not yet known. We have begun an investigation of desmoglein gene expression by cloning and analysing the promoters of the human genes coding for the type 1 and type 3 desmogleins (DSG1 and DSG3). The type 1 isoform is restricted to the suprabasal layers of the epidermis and is the autoantigen in the autoimmune blistering skin disease pemphigus foliaceous. The type 3 desmoglein isoform is also expressed in the epidermis, but in lower layers than the type 1 isoform, and is the autoantigen in pemphigus vulgaris. Phage lambda genomic clones were obtained containing 4.2 kb upstream of the translation start site of DSG1 and 517 bp upstream of the DSG3 start site. Sequencing of 660 bp upstream of DSG1 and 517 bp upstream of DSG3 revealed that there was no obvious TATA box, but a possible CAAT box was present at -238 in DSG1 and at -193 in DSG3 relative to the translation start site. Primer extension analysis and RNase protection experiments revealed four putative transcription initiation sites for DSG1 at positions -163, -151, -148 and -141, and seven closely linked sites for DSG3, the longest being at -140 relative to the translation start site. The sequences at these possible sites at -166 to -159 in DSG1 (TTCAGTCC) and at -124 to -117 in DSG3 (CTTAGACT) have some similarity to the initiator sequence (CTCANTCT) described for a TATA-less promoter often from -3 to +5, and the true transcription initiator site might therefore be the A residue in these sequences. There were two regions of similarity between the DSG1 and DSG3 promoters just upstream of the transcription initiation sites, of 20 and 13 bp, separated by 41 bp in DSG1 and 36 bp in DSG3. The significance of these regions of similarity remains to be elucidated, but the results suggest that they represent a point at which these two desmoglein genes are co-ordinately regulated. Analysis of the upstream sequences revealed GC-rich regions and consensus binding sites for transcription factors including AP-1 and AP-2. Exon boundaries were conserved compared with the classical cadherin E-cadherin, but the equivalent of the second cadherin intron was lacking. A 4.2 kb region of the human DSG1 promoter sequence was linked to the lacZ gene reporter gene in such a way that there was only one translation start site, and this construct was used to generate transgenic mice. We present the first transgenic analysis of a promoter region taken from a desmosomal cadherin gene. Our results suggest that the 4.2 kb upstream region of DSG1 does not contain all the regulatory elements necessary for correct expression of this gene but might have elements that regulate activity during hair growth.

The epidermis: genes on - genes off

The epidermal keratinocyte stem cell is distinguished by a relatively undifferentiated phenotype and an ability to proliferate. As part of a carefully orchestrated process, the offspring of these stem cells lose the ability to proliferate and begin a process of morphologic and biochemical transformation that results in their conversion into corneocytes. This process requires the coordinated expression of a host of cellular genes. The mechanisms responsible for regulation of these genes is an area of intense interest. In keratinocytes, as in other cell types, the expression of most genes is regulated at the transcriptional level by a class of proteins called transcription factors. Transcription factors are nuclear proteins that regulate transcription by mediating the final steps in the relay of information from the cell surface to the nucleus and the gene. These factors bind to specific DNA sequence elements located within the target gene. In this brief review we summarize evidence implicating activator protein 1 (AP1), AP2, Sp1, POU domain, CCAAT enhancer binding protein, and several other transcription factors as regulators of expression of keratinocyte genes.

Regulation of gene expression in developing epidermal epithelia

Skin is one of the most thoroughly studied epithelia and can be used as a model for transcriptional control of epithelial differentiation. In particular, the stages of epidermal development and differentiation from a simple epithelium are well characterized. Temporal gene expression during development can be used to assign roles for transcription factors in epidermal differentiation. Approaches to understanding transcriptional regulation in epidermis include extensive promoter analysis and expression studies, in some cases coupled to functional studies. This work has not produced any consensus about the importance of any particular factor or class of factors in epidermal specification. There is, as yet, nothing similar to the myo D family of tissue-specific and cell-type determining factors in epidermis. These studies, however, have revealed much about control of the differentiation process in epidermis. Most recently, there has been a suggestion that epithelial transcription can be influenced directly by the status of the adhesion complexes at the cell surface, providing a direct link between one of the distinguishing features of the epithelial state and gene transcription.

Immune responses to reporter proteins and high viral dose limit duration of expression with adenoviral vectors: comparison of E2a wild type and E2a deleted vectors

Experiments designed to evaluate the effect of deletion of E2a on duration of expression using adenoviral vectors led to a series of observations regarding host responses to adenoviral vectors and reporter proteins. In studies using human alpha1-antitrypsin (hAAT) as a reporter gene, we found that the duration of expression is very brief for C3H/J and CBA/J mice but is prolonged for C57BL/6J mice, that disappearance of hAAT from the blood is correlated with the appearance of antibodies, and that immunization against hAAT can prevent appearance of the protein in the blood after administration of an adenoviral vector. Deletion of E2a in hAAT vectors did not prolong expession in C3H/J or CBA/J mice and did not shorten duration of expression in C57BL/6J mice. Using similar vectors expressing Escherichia coli beta-galactosidase (beta-Gal) in immunocompetent mice, short duration of expression with a beta-Gal reporter was remarkably different from the long expression with an identical vector expressing hAAT in C57BL/6J. In the case of vectors expressing hAAT, adenoviral sequences persisted in the liver, and inflammatory responses were minimal compared to vectors expressing beta-Gal, where adenoviral sequences disappeared from the liver concomitant with a prominent inflammatory response. The duration of expression of beta-Gal in hepatocytes was increased in transgenic mice expressing the reporter in keratinocytes, indicating that host immune responses to the reporter can limit duration of expression. Dosage studies indicated that persistence of expression of hAAT can be markedly decreased by administration of high doses of vector in a manner consistent with a nonimmune-mediated toxicity following injection. These experiments indicate that host responses to reporter genes rather than host responses to adenoviral proteins can be the primary determinant of duration of expression under many experimental conditions.

Cloning of human keratolinin cDNA: keratolinin is identical with a cysteine proteinase inhibitor, cystatin A, and is regulated by Ca2+, TPA, and cAMP

Keratolinin has been described as one of the precursor proteins of cornified cell envelope of keratinocytes. Using rabbit polyclonal anti-human keratolinin antibody, we isolated a cDNA clone of human keratolinin gene from a human Agt11 cDNA expression library that was constructed by random priming from poly(A)+RNA extracted from cultured normal human keratinocytes. Screening by rabbit anti-human keratolinin antibody detected one positive clone (HKL-1). The recombinant 12.5-kDa protein constructed from the clone reacted specifically with the anti-human keratolinin antibody. DNA sequence analysis revealed that HKL-1 clone was 448 bp long, and its putative amino acid sequence was identical with that of a human cysteine proteinase inhibitor, cystatin A. Western blot analysis showed that the commercially available recombinant cystatin A also reacted specifically with the anti-human keratolinin antibody. Northern blot analysis indicated that HKL-1 clone hybridizes with mRNA of about 0.5 kb, consistent with the size of the HKL-1 clone. The keratolinin mRNA was highly expressed in cultured human keratinocytes in high Ca2+ (1 mM); in low Ca2+ (0.05 mM), the keratolinin mRNA expression was significantly lower. Using SV40-transformed human keratinocytes (SVHK cells), we further analyzed the regulation of keratolinin mRNA. In low Ca2+ (0.05 mM), keratolinin mRNA in SVHK cells was marginally detectable. Upon shift to 1 mM calcium, keratolinin mRNA was markedly increased. The upregulation of keratolinin mRNA was also observed by the treatment of SVHK cells with 10 ng TPA per ml or 100 microM forskolin under low calcium conditions (0.05 mM). Our results indicate that keratolinin is identical with cystatin A, a cysteine proteinase inhibitor, and its expression is positively regulated by Ca2+, TPA, and forskolin.

Arsenate suppression of human keratinocyte programming

The human keratinocyte line SCC-9 has been used as a model for arsenate-induced perturbations of differentiation. Growth of these cells in 10 microM arsenate permitted the cultures to reach confluence, but prevented expression of 6 markers of suprabasal differentiation (involucrin, loricrin, filaggrin, spr 1, keratin 1 and keratin 10) as assayed by Northern blotting. By contrast, only slight alterations in mRNA levels were observed for one differentiation marker (keratinocyte transglutaminase) and for keratin 5, keratin 14, AP2 or glyceraldehyde phosphate dehydrogenase. The transition metal oxyanions vanadate and chromate had essentially the same suppressive effect on these markers as arsenate, while chronic treatment with tetradecanoylphorbol acetate was generally less effective in suppressing differentiation. To determine whether the previously observed arsenate-mediated alteration in AP1 and AP2 activities could account for the suppression of involucrin, a promoter analysis was conducted. Putative AP1 and AP2 response elements were identified in regions important for transcriptional activity of the 5'-flanking DNA. Mutations in two AP1 sites and one AP2 site were observed to decrease promoter activity significantly, and in combination, to reduce it to approximately 10% of that conferred by the native sequence. These results lend support to the working hypothesis that arsenate suppresses involucrin expression, and, more generally, keratinocyte programming, by altering the transcription factors AP1 and AP2.

Expression of a dominant-negative type II transforming growth factor beta (TGF-beta) receptor in the epidermis of transgenic mice blocks TGF-beta-mediated growth inhibition

To determine whether a functional type II receptor of transforming growth factor beta (TGF-beta) is required to mediate the growth inhibitory effect of TGF-beta on the skin in vivo, we have generated transgenic mice that overexpress a dominant negative-type II TGF-beta receptor (delta beta RII) in the epidermis. The delta beta RII mice exhibited a thickened and wrinkled skin, and histologically the epidermis was markedly hyperplastic and hyperkeratotic. In vivo labeling with BrdUrd showed a 2.5-fold increase in the labeling index over controls, with labeled nuclei occurring in both basal and suprabasal cells of transgenic epidermis. In heterozygotes, this skin phenotype gradually diminished, and by 10-14 days after birth the transgenic mice were indistinguishable from their normal siblings. However, when F1 mice were mated to homozygosity, perinatal lethality occurred due to the severe hyperkeratotic phenotype, which restricted movement. Cultured primary keratinocytes from delta beta RII mice also exhibited an increased rate of growth in comparison with nontransgenic controls, and were resistant to TGF-beta-induced growth inhibition. These data document the role of the type II TGF-beta receptor in mediating TGF-beta-induced growth inhibition of the epidermis in vivo and in maintenance of epidermal homeostasis.

Cloning and transcriptional analysis of the promoter of the human type 2 desmocollin gene (DSC2)

The desmocollins, together with the desmogleins, are members of the cadherin family and constitute the adhesive proteins of the desmosome type of cell-cell junction. Here we describe a study of the promoter of the human form of the DSC2 gene which is the equivalent of the first isoform expressed in the developing mouse embryo and that has the most widespread tissue distribution in epithelia and also in desmosome-bearing non-epithelial tissues. Analysis of the 5' upstream region by DNA sequencing and Southern blotting suggested that it contained a CpG island, and a major site of transcription initiation 201 bp upstream of the translation start site was found by RNase protection and primer extension. There were no obvious CCAAT or TATA boxes present. Analysis of 1.9 kb upstream of the translation start site revealed consensus binding sites for transcription factors including Ap-2 and Sp-1, and motifs common to the promoters of other epithelially expressed genes such as keratin 14 and the desmoglein genes DSG1 and DSG3. Deletion derivatives defined a promoter of 525 bp which was active in epithelial cells and in mouse blastocysts with an intact epithelium. This promoter showed reduced expression in non-epithelial cells.

Activator protein 1 activity is involved in the regulation of the cell type-specific expression from the proximal promoter of the human profilaggrin gene

The human profilaggrin gene is expressed in the granular layer during the late stages of terminal differentiation of the epidermis. In in vitro transcription experiments we show that the abundance of the mRNA and the specificity of the expression are regulated primarily at the level of transcription. We found that the 5'-flanking sequences control the transcription in a keratinocyte-specific mode and that as little as 116 base pairs preceding the mRNA initiation site is sufficient to restrict the transcription to epidermal cells in vitro. This specificity depends critically on the presence of an activator protein 1 (AP1) motif at position -77. Binding of c-jun/c-fos heterodimers to this sequence confers high levels of expression to the reporter constructs in cultured epidermal keratinocytes, while having little effect in HeLa cells. The transactivating properties of c-jun are essential in this process. On the other hand, junB and junD, which are involved in transactivating the transcription of earlier epidermal differentiation markers, control profilaggrin expression through a pathway which does not depend on a direct binding at the AP1 site and is not cell-type specific. These data indicate that AP1 factors are involved in a complex, multipathway regulation of the profilaggrin gene expression.

Identification of a functional determinant of differentiation-dependent expression in the involucrin gene

Involucrin is an integral component of the cornified envelope which is a characteristic feature of the differentiated keratinocyte. Involucrin expression is tightly linked to the onset of differentiation and first expressed in the immediate suprabasal layers of the epidermis. We have identified a transcriptional response element within the distal 5'-flanking region of the involucrin gene which contributes to differentiation-dependent expression. Deletion of this site impairs differentiation-dependent promoter activity in transient transfection analysis, and conversely, this region imparts differentiation-dependent expression to a heterologous promoter. The identified site bears sequence similarity to several AP2-like response elements identified in keratinocyte-specific genes and binds a protein complex (keratinocyte differentiation factor, KDF-1) which is distinct from AP2 by several criteria. The migration of KDF-1 is distinct from AP2 in electrophoretic mobility shift assays, KDF-1 is antigenically unrelated to AP2 since AP2 specific antibodies do not supershift the KDF-1-DNA complex and KDF-1 is poorly competed by oligonucleotides representing consensus AP2 recognition sequences. In addition, the KDF-1 complex is not detected in nuclear extracts derived from human dermal fibroblasts or an enriched population of basal keratinocytes. These findings provide insights to the underlying basis of differentiation-dependent expression of a keratinocyte specific gene.

Staurosporine induces a sequential program of mouse keratinocyte terminal differentiation through activation of PKC isozymes

Staurosporine (stsp) induces assembly of cornified envelopes in mouse keratinocyte cultures. To clarify whether this effect is the consequence of a coordinated differentiation program similar to that observed in epidermis, we assessed the expression of multiple differentiation-specific markers in stsp-treated keratinocytes. In medium containing 0.05 mM Ca2+, in which the basal cell phenotype is normally maintained, stsp induced dose-dependent increases in keratin 1, epidermal and keratinocyte transglutaminases, SPR-1, loricrin, and profilaggrin mRNA. Based on nuclear run-on analysis, stsp-mediated marker expression was found to be due at least in part to increased transcription. Since protein kinase C (PKC) activation is required for keratinocyte differentiation, we tested whether stsp influenced this signaling pathway. Stsp induced the translocation of multiple PKC isoforms from the cytosol to membrane and/or cytoskeletal fractions, inducing isozyme downregulation within 24 h. Moreover, AP-1 DNA binding activity was elevated in stsp-treated keratinocytes, consistent with the notion that this agent influences keratinocyte-specific gene expression via the PKC pathway. Stsp-mediated marker expression was inhibited by the PKC inhibitor GF 109203X. In cells pre-treated with bryostatin 1 to selectively down-modulate specific PKC isoforms, stsp-induced loricrin, filaggrin, and SPR-1 expression was suppressed when PKC alpha, epsilon, and/or delta were downregulated, suggesting that these isozymes may be necessary for marker expression in response to this agent. Thus, in addition to its effects on cornified envelope assembly, stsp induces a coordinate program of differentiation-specific keratinocyte gene expression that is mediated at least in part by the PKC signaling pathway.

Transcription factor regulation of epidermal keratinocyte gene expression

The epidermis is a tissue that undergoes a very complex and tightly controlled differentiation program. The elaboration of this program is generally flawless, resulting in the production of an effective protective barrier for the organism. Many of the genes expressed during keratinocyte differentiation are expressed in a coordinate manner; this suggests that common regulatory models may emerge. The simplest model envisions a 'common regulatory element' that is possessed by all genes that are regulated together (e.g., involucrin and transglutaminase type 1). Studies to date, however, have not identified any such elements and, if anything, the available studies suggest that appropriate expression of each gene is achieved using sometime subtly and sometime grossly different mechanisms. Recent studies indicate that a variety of transcription factors (AP1, AP2, POU domain. Sp1, STAT factors) are expressed in the epidermis and, in many cases, multiple members of several families are present (e.g., AP1 and POU domain factors). The simultaneous expression of multiple members of a single transcription factor family provides numerous opportunities for complex regulation. Some studies suggest that specific members of these families interact with specific keratinocyte genes. The best studied of these families in epidermis is the AP1 family of factors. All of the known AP1 factors are expressed in epidermis [52] and each is expressed in a specific spatial pattern that suggests the potential to regulate multiple genes. It will be important to determine the role of each of these members in regulating keratinocyte gene expression. Finally, information is beginning to emerge regarding signal transduction in keratinocytes. Some of the early events in signal transduction have been identified (e.g., PLC and PKC activation, etc.) and some of the molecular targets of these pathways (e.g., AP1 transcription factors) are beginning to be identified. Eventually we can expect to elucidation of all of the steps between the interaction of the stimulating agent with its receptor and the activation of target gene expression.