Characterization of two monoclonal antibodies to human epidermal keratohyalin: reactivity with filaggrin and related proteins

Filaggrin gene mutations and the distribution of filaggrin in oral mucosa of patients with oral lichen planus and healthy controls

BACKGROUND

Lichen planus (LP) is a chronic inflammatory disease of unknown aetiology affecting the skin and oral mucosa. Oral lichenoid lesions (OLLs), like oral contact reactions, may resemble oral lichen planus (OLP) both clinically and histopathologically. As OLP and OLL are hyperkeratotic diseases and filaggrin is essential to keratinization, the distribution of filaggrin may be altered in these lesions.

OBJECTIVES

To investigate whether patients with OLP/OLL have (i) altered distribution of filaggrin in the oral mucosa; (ii) a higher incidence of mutations in the filaggrin gene (FLG); (iii) active dermatoses, apart from cutaneous LP, than healthy controls; and (iv) patients with OLP/OLL and a defect in the FLG have more widespread oral lesions and report more symptoms than OLP/OLL patients without a concomitant defect in the FLG.

METHODS

Forty-nine Caucasian patients (42 women and 7 men, mean age 61.0 ± 10.3 years), with symptomatic OLP, OLL or stomatitis, and 29 matched healthy controls underwent a clinical oral and dermatological examination, oral mucosal biopsy and filaggrin genotyping (testing for R2447X, R501X, 2282del4). Smear tests for Candida spp. were performed in all patients to exclude oral candidiasis. Immunohistochemistry were performed using poly- and monoclonal filaggrin antibodies.

RESULTS

The immunoreactivity for filaggrin was significantly more intense in the oral mucosa in the patients with OLP/OLL compared with healthy controls (P = 0.000025). No difference was noted in the incidence of defects in the FLG and active dermatoses between patients and healthy controls. No difference was noted in extension and number of symptoms reported by patients with OLP/OLL with or without a concomitant defect in the FLG.

CONCLUSION

OLP/OLL is associated with an altered distribution of filaggrin in the oral mucosa independently of defects in the FLG. Patients with OLP/OLL did not display more active dermatoses other than cutaneous LP when compared to healthy controls.

IL-17 downregulates filaggrin and affects keratinocyte expression of genes associated with cellular adhesion

Atopic eczema and psoriasis are common skin diseases. While it is well established that the pathogenesis of these diseases varies, both are characterized by impairment in epidermal barrier function and abnormal IL-17 expression in the skin and peripheral blood. Recent findings indicated that filaggrin is essential during barrier formation and its insufficiency underlies the pathogenesis of atopic eczema. Filaggrin downregulation has also been reported in psoriasis. It is clear that Th1/Th2 bias influences expression of the protein, but an analysis of the effects of interleukin-17 (IL-17) on the expression of the protein and profilaggrin-processing enzymes has not yet been reported. In addition, the effect of the cytokine on components of functional epidermal barrier, tight junctions and adhesion/desmosomal proteins, has not been elucidated. Keratinocytes were exposed to interleukin-17A, and microarray analysis was performed. Filaggrin protein level was assessed by western blot. We have observed a significant decrease in profilaggrin mRNA level in interleukin-17A-exposed cultures (P = 0.008). Expression of processing enzymes was also altered, indicating an indirect effect of the cytokine on filaggrin production/degradation. Moreover, expression of many genes involved in cellular adhesion was also decreased. A significant downregulation of filaggrin at the protein level was detected by western blot in immortal and primary keratinocytes. Gene ontology analysis indicated changes in keratinization, epidermal differentiation and formation of the cornified envelope. We conclude that IL-17A downregulates the expression of filaggrin and genes important for cellular adhesion which could affect epidermal barrier formation. This effect potentially contributes to barrier dysfunction and could become a possible therapeutic target.

Alterations in PNA binding of keratinocytes in oral keratosis

Changes in the expression of peanut lectin (PNA) were examined in keratinocytes of oral keratosis showing a mixture of hyperortho- and hyperparakeratinized epithelium. In the hyperorthokeratinized epithelium, which was reacted with anti-filaggrin antibody in both granular and cornified cells, PNA bound to the surface of keratinocytes from the spinous layer to the granular layer. Neither anti-filaggrin nor PNA reactions were detected in keratinocytes of the hyperparakeratinized epithelium. After neuraminidase pretreatment, however, PNA staining appeared in all cells, except cornified cells, of both hyperortho- and hyperparakeratinized epithelia. These findings suggest that PNA-binding epitopes in keratinocytes were modified by sialic acid during the hyperparakeratotic process of oral keratosis.

Large haematoxylin-stainable keratohyaline granules in solar keratoses: immunohistochemical comparison using anti-Ted-H-1 antibody and antiloricrin antibody

BACKGROUND

Our previous study showed that large keratohyaline granules (KHG) in molluscum contagiosum that stained with haematoxylin also reacted with anti-Ted-H-1 monoclonal antibody (mAb), but not with antifilaggrin mAb or antiloricrin polyclonal antibody (pAb). This finding indicated that the Ted-H-1 antigenic protein is a haematoxylin-stainable protein in KHG.

OBJECTIVES

To clarify the identity of the major component protein of the large KHG in solar keratosis, another disorder in which large KHG are observed.

METHODS

An enzyme immunohistochemical study was performed using antifilaggrin mAb, anti-Ted-H-1 mAb and antiloricrin pAb. Immunofluorescent double staining and immunoelectron microscopic analyses were performed using anti-Ted-H-1 mAb and antiloricrin pAb.

RESULTS

Antifilaggrin mAb, anti-Ted-H-1 mAb and antiloricrin pAb reacted with normal KHG in nonlesional skin of solar keratosis, while only anti-Ted-H-1 mAb reacted with the large KHG in the lesions of solar keratosis. Antifilaggrin mAb did not react with large KHG. Antiloricrin pAb reacted with the cell membrane of the stratum granulosum, but not with large KHG.

CONCLUSIONS

These findings suggest that the haematoxylin-stainable protein in the large KHG would be a Ted-H-1 antigen protein which was neither filaggrin nor loricrin.

Putative histidin-rich proteins in the epidermis of lizards

In the stratum granulosum of mammalian epidermis, histidin-rich proteins (filaggrins) determine keratin clumping and matrix formation into terminal keratinocytes of the stratum corneum. The nature of matrix, interkeratin proteins in the epidermis of nonmammalian vertebrates, and in particular in that of reptilian, mammalian progenitors are unknown. The present biochemical study is the first to address this problem. During a specific period of the renewal phase of the epidermis of lizards and during epidermal regeneration, keratohyalin-like granules are formed, at which time they take up tritiated histidine. The latter also accumulate in cells of the alpha-keratin layer (soft keratin). This pattern of histidine incorporation resembles that seen in keratohyalin granules of the stratum granulosum of mammalian epidermis. After injection of tritiated histidine, we have analysed the distribution of the radioactivity by histoautoradiography and electrophoretic gel autoradiography of epidermal proteins. Extraction and electrophoretic separation of interfilamentous matrix proteins from regenerating epidermis 3-48 hours post-injection reveals the appearance of protein bands at 65-70, 55-58, 40-43, 30-33, 25-27, and 20-22 kDa. Much weaker bands were seen at 100, 140-160, and 200 kDa. A weak band at 20-22 kDa or no bands at all are seen in the normal epidermis in resting phase and in the dermis. In regenerating epidermis at 22 and 48 hours post-injection, little variation in bands is detectable, but low molecular weight bands tend to increase slightly, suggesting metabolic turnover. Using anti-filaggrin antibodies against rat, human, or mouse filaggrins, some cross-reactivity was seen with more reactive bands at 40-42 and 33 kDa, but it was reduced or absent at 140, 95-100, 65-70, 50-55, and 25 kDa. This suggests that different intermediate degradative proteins of lizard epidermis may share some epitopes with mammalian filaggrins and are different from keratins with molecular weight ranging from 40 to 65-68 kDa. The immunocytochemical observation confirms that a weak filaggrin-like immunoreactivity characterizes differentiating alpha-keratogenic layers in normal and regenerating tail. A weak filaggrin labeling is discernable in small keratohyalin-like granules but is absent from the larger granules and from mature keratinocytes. The present results indicate, for the first time, that histidine-rich proteins are involved in the process of alpha-keratinization in reptilian epidermis. The cationic, interkeratin matrix proteins implicated may be fundamentally similar in both theropsid-derived and sauropsid amniotes.

Epidermal Ras blockade demonstrates spatially localized Ras promotion of proliferation and inhibition of differentiation

While important in carcinogenesis, the role of Ras in normal self-renewing tissues such as epidermis is unclear. To address this, we altered Ras function in undifferentiated and differentiating epidermal layers. Ras blockade within undifferentiated basal epidermal cells leads to decreased integrin expression, diminished growth capacity and induction of differentiation. Ras blockade in post-mitotic suprabasal epidermis exerts no effect. In contrast, regulated Ras and Raf activation inhibits differentiation. These findings indicate that spatially restricted Ras/Raf signaling divides epidermis into an undifferentiated proliferative compartment and a differentiating post-mitotic compartment and suggest a new role for Ras in tissue homeostasis.

Human peptidylarginine deiminase type III: molecular cloning and nucleotide sequence of the cDNA, properties of the recombinant enzyme, and immunohistochemical localization in human skin

Peptidylarginine deiminase catalyzes the post-translational modification of proteins through the conversion of arginine to citrulline in the presence of calcium ions. In rodents, peptidylarginine deiminase has been classified into four isoforms, types I, II, III, and IV, which are distinct in their molecular weights, substrate specificities, and tissue localization. Of these isoforms, only type III was detected in epidermis and hair follicles. Although the role of this enzyme in these tissues is not yet clear, indirect data have shown that several structural proteins such as filaggrin, trichohyalin, and keratin are substrates for peptidylarginine deiminase. In this study, we cloned the full-length cDNA of human peptidylarginine deiminase type III (3142 bp) from cultured human keratinocytes by reverse transcription-polymerase chain reaction and by rapid amplification of cDNA ends methods. This cDNA contained a 1995 bp open reading frame encoding 664 amino acids (Mr = 74 770). To explore the physicochemical and enzymatic properties of human peptidylarginine deiminase type III, we constructed a plasmid for producing a recombinant human peptidylarginine deiminase type III in bacteria. The enzymatic characteristics of the recombinant enzyme were very similar to those of the rodent peptidylarginine deiminase type III. The recombinant enzyme showed the catalytic activities toward structural proteins of epidermis and hair follicle, filaggrin and trichohyalin, in which the deiminations maxima of about 60% and 13% arginine residues were observed in filaggrin and trichohyalin, respectively. An immunohistochemical study of human scalp skin with a monospecific anti-peptidyl-arginine deiminase type III antibody revealed that the type III enzyme was localized to the inner root sheath and outer root sheath of hair follicles. Peptidylarginine deiminase type III in the inner root sheath was notable between supramatrix and keratogenous zone and was scarcely detected in cornified hair zone. The enzyme was also expressed in the cuticle layer of hair. On the other hand, expression of the enzyme in the epidermis was very low. These data imply that human peptidylarginine deiminase type III is the predominant isoform in hair follicles and may function as a modulator of hair structural proteins, including trichohyalin during hair and hair follicle formation.

Expression of epidermal growth factor and platelet-derived growth factor receptors during cervical carcinogenesis

Altered expression of epidermal growth factor receptor (EGFR) is common in a variety of epithelial malignancies, including cervical cancer. However, the prognostic significance of EGFR expression is controversial for cervical cancer. Platelet-derived growth factor receptor (PDGFR) expression status is unknown in cervical cancer. Our results demonstrated that expression of EGFR and PDGFR was greatly enhanced in vivo and in organotypic cultures of low-grade cervical dysplastic tissues, but levels were decreased in high-grade lesions. To our knowledge, this is the first report identifying the expression of PDGFR in human epithelium. When low-grade dysplastic organotypic culture tissues were induced to differentiate more completely, EGFR expression, but not PDGFR expression, was relocalized to the basal layer as seen in normal tissues. Differentiation also induced phosphorylation of EGFR but not PDGFR. Our results suggest a role for EGFR and PDGFR during the early stages of cervical carcinogenesis, and demonstrate the facility of organotypic cultures to study the role of these growth factors in the development of cervical cancer.

Inhibition of cadherin function differentially affects markers of terminal differentiation in cultured human keratinocytes

Cadherin function is required for normal keratinocyte intercellular adhesion and stratification. In the present study, we have investigated whether cadherin-cadherin interactions may also modulate keratinocyte differentiation, as evidenced by alterations in the levels of several differentiation markers. Confluent keratinocyte cultures, propagated in low Ca(2+) medium in which cadherins are not active, were pre-incubated with antibodies that block the function of E-cadherin and/or P-cadherin; Ca(2+)was then elevated to 1 mM to activate the cadherins and induce differentiation. In control cultures (incubated with no antibody or with antibodies to other cell surface molecules), Ca(2+) elevation induced an increase in type 1 transglutaminase, profilaggrin, and loricrin, as measured by western blotting and in agreement with previous results. However, the concurrent addition of antibodies against both E- and P-cadherin prevented this increase in transglutaminase 1 protein. Incubation with either antibody alone had no consistent effect. Profilaggrin and loricrin, which are later markers of keratinocyte differentiation, responded differently from transglutaminase 1 to addition of antibodies. In the presence of anti-E-cadherin antibody, both loricrin and profilaggrin levels were dramatically enhanced compared to the high Ca(2+) control cells, while addition of antibody to P-cadherin slightly attenuated the Ca(2+)-induced increase. In the presence of both antibodies, loricrin and profilaggrin protein levels were intermediate between those observed in the presence of either antibody alone. The expression of involucrin, however, was unaffected by addition of antibodies. In addition, effects of the anti-cadherin antibodies were not secondary to alterations in proliferation or programmed cell death, as determined by several independent assays of these processes. Thus, the consequences of cadherin inhibition depend upon both the particular cadherin and the differentiation marker under study. Taken together, these data suggest that E-cadherin and P-cadherin contribute to the orderly progression of terminal differentiation in the epidermis in multiple ways.

Profilaggrin requires both linker and filaggrin peptide sequences to form granules: implications for profilaggrin processing in vivo

Filaggrin is an intermediate filament associated protein that aids the packing of keratin filaments during terminal differentiation of keratinocytes. Premature aggregation of keratin filaments is prevented by filaggrin expression as the inactive precursor, profilaggrin, which is localized in keratohyalin granules in vivo. Profilaggrin is phosphorylated and contains multiple filaggrin repeats separated by a hydrophobic linker peptide. We have previously shown that filaggrin constructs containing the linker, when transiently transfected into epithelial cells, lead to expression of a protein that resembles keratohyalin (Dale et al. J Invest Dermatol 108:179-187 1997). To characterize further the region(s) of the linker and/or filaggrin that are necessary for granule formation, we generated several mutant constructs from Flag-FG-1, and generated fusions of filaggrin with green fluorescent protein. We also subjected profilaggrin to protein phosphatase 2A treatment and measured its subsequent solubility. We found that granular morphology is not dependent on the linker or conserved phosphorylation sites, nor is solubility affected by protein phosphatase 2A treatment. Granule morphology was abrogated only in a truncated construct, which still contains the linker. A construct consisting of 16 amino acids of filaggrin fused to green fluorescent protein led to rounded and bizarrely shaped transfected cells with compact keratin filaments, suggesting that very little filaggrin sequence is required for keratin filament interaction. Radiolabeled filaggrin-green fluorescent protein constructs specifically bound keratin in overlay assays confirming that the observed cytoskeletal collapse is due to filaggrin-keratin interaction. Our findings indicate that profilaggrin must be extensively processed before it loses both its granule forming ability as well as its insolubility, suggesting that granule formation in vivo correlates with insolubility in vitro. Further, filaggrin retains its ability to bind keratin as it is degraded to smaller peptides.

Long-term culture of murine epidermal keratinocytes

The production of transgenic and null mice with skin abnormalities makes it increasingly important to establish cultures of mouse epidermal keratinocytes for in vitro studies. This requires that each cell line be derived from a single mouse and that the cells be carried for multiple passages. Freezing the cells would also be advantageous by allowing comparison of keratinocytes from several mouse lines at the same time. Mouse keratinocytes, however, have been exceedingly difficult to grow as primary cultures, and subculturing these cells has been virtually impossible until now. We describe a gentle dissociation method and a highly supplemented fibroblast conditioned medium that allows us to grow and subculture total mouse keratinocytes for up to 19 subcultures, allowing an increase in cell number of greater than 10 logs. Epidermal keratinocytes from newborn mice were grown on collagen IV coated dishes in murine fibroblast conditioned medium with 0.06 mM calcium and added growth factors. The cells could be passaged, frozen as viable stocks, and induced to differentiate. Morphologically the cultured keratinocytes demonstrated a pattern characteristic of basal cells. Stratified cultures which made mouse keratin 1 and profilaggrin through passage 10 were induced by purging the monolayer cultures of growth factors, then adding medium with 0.15 mM calcium; expression of mouse keratin 1 and profilaggrin was lost by passage 15. The methods explained in detail here should be of great interest to investigators who are now trying to analyze skin phenotypes and expression of markers of epidermal differentiation of their transgenic or knockout mice.

Temporal and spatial expression of the E5a protein during the differentiation-dependent life cycle of human papillomavirus type 31b

Human papillomaviruses (HPVs) are epitheliotropic viruses, and their life cycle is intimately linked to the stratification and differentiation state of the host epithelial tissues. Defining a role for the E5 gene product in the differentiation-dependent viral life cycle has been difficult due to the lack of a suitable culture system. We used the organotypic (raft) culture system to investigate the spatial and temporal expression pattern of the E5 protein during the differentiation-dependent life cycle of HPV-31b. We report the generation of antisera specific to the HPV-31b E5a protein. The HPV-31b E5a protein was detected throughout the viral life cycle in raft cultures as determined by immunostaining analyses, and the protein was localized predominantly to the basal and granular layers. Expression of epidermal growth factor receptor or platelet-derived growth factor receptors, two proteins with which E5 has been shown to interact in cell culture, did not specifically colocalize with E5a expression. However, HPV-31b E5a expression did colocalize with the epithelial differentiation-specific marker filaggrin. The kinetics of E5a protein expression during the complete viral life cycle was analyzed by immunoblotting, and the highest level was found to be coincidental with the onset of virion morphogenesis.

Transglutaminase 1 expression in a patient with features of harlequin ichthyosis: case report

Harlequin ichthyosis (HI) is a life-threatening disorder characterized clinically by massive generalized hyperkeratosis and ultrastructurally by an absence of lamellar bodies. However, infants who survive the perinatal period develop a phenotype resembling the nonbullous ichthyosiform erythrodermic (CIE) form of autosomal recessive ichthyosis. We studied a child with a severe hyperkeratotic skin disorder present at birth that developed into a CIE-like phenotype. Electron microscopy demonstrated an absence of lamellar bodies consistent with HI. Abnormalities of filaggrin and involucrin expression by immunostaining were evident. However, transglutaminase 1 (TGase1) was expressed in the epidermis in a pattern consistent with other diseases that involve epidermal acanthosis. Analysis of patient keratinocytes grown in vitro demonstrated expression of normal amounts of TGase1 mRNA and full length TGase1 protein, as well as normal levels of transglutaminase enzymatic activity.

Induction of basal cell carcinoma features in transgenic human skin expressing Sonic Hedgehog

Hedgehog (HH) signaling proteins mediate inductive events during animal development. Mutation of the only known HH receptor gene, Patched (PTC), has recently been implicated in inherited and sporadic forms of the most common human cancer, basal cell carcinoma (BCC). In Drosophila, HH acts by inactivating PTC function, raising the possibility that overexpression of Sonic Hedgehog (SHH) in human epidermis might have a tumorigenic effect equivalent to loss of PTC function. We used retroviral transduction of normal human keratinocytes to constitutively express SHH. SHH-expressing cells demonstrated increased expression of both the known HH target, BMP-2B, as well as bcl-2, a protein prominently expressed by keratinocytes in BCCs. These keratinocytes were then used to regenerate human skin transgenic for long terminal repeat-driven SHH (LTR-SHH) on immune-deficient mice. LTR-SHH human skin consistently displays the abnormal specific histologic features seen in BCCs, including downgrowth of epithelial buds into the dermis, basal cell palisading and separation of epidermis from the underlying dermis. In addition, LTR-SHH skin displays the gene expression abnormalities previously described for human BCCs, including decreased BP180/BPAG2 and laminin 5 adhesion proteins and expression of basal epidermal keratins. These data indicate that expression of SHH in human skin recapitulates features of human BCC in vivo, suggest that activation of this conserved signaling pathway contributes to the development of epithelial neoplasia and describe a new transgenic human tissue model of neoplasia.

Sustainability of keratinocyte gene transfer and cell survival in vivo

The epidermis is an attractive site for therapeutic gene delivery because it is accessible and capable of delivering polypeptides to the systemic circulation. A number of difficulties, however, have emerged in attempts at cutaneous gene delivery, and central among these is an inability to sustain therapeutic gene production. We have examined two major potential contributing factors, viral vector stamina and involvement of long-lived epidermal progenitor cells. Human keratinocytes were either untreated or transduced with a retroviral vector for beta-galactosidase (beta-Gal) at > 99% efficiency and then grafted onto immunodeficient mice to regenerate human epidermis. Human epidermis was monitored in vivo after grafting for clinical and histologic appearance as well as for gene expression. Although integrated vector sequences persisted unchanged in engineered epidermis at 10 weeks post-grafting, retroviral long terminal repeat (LTR)-driven beta-Gal expression ceased in vivo after approximately 4 weeks. Endogenous cellular promoters, however, maintained consistently normal gene expression levels without evidence of time-dependent decline, as determined by immunostaining with species-specific antibodies for human involucrin, filaggrin, keratinocyte transglutaminase, keratin 10, type VII collagen, and Laminin 5 proteins out to week 14 post-grafting. Transduced human keratinocytes generated multilayer epidermis sustained through multiple epidermal turnover cycles; this epidermis demonstrated retention of a spatially appropriate pattern of basal and suprabasal epidermal marker gene expression. These results confirm previous findings suggesting that viral promoter-driven gene expression is not durable and demonstrate that keratinocytes passaged in vitro can regenerate and sustain normal epidermis for prolonged periods.

Transient expression of epidermal filaggrin in cultured cells causes collapse of intermediate filament networks with alteration of cell shape and nuclear integrity

Filaggrin is an intermediate filament-associated protein (IFAP) that aggregates epidermal keratin filaments in vitro and is thought to perform a similar function during terminal differentiation in vivo. To test this function in living cells, we transiently expressed constructs encoding human filaggrin in both simple epithelial cells (COS-7) and rat keratinocytes. Scanning laser confocal microscopy showed that filaggrin-positive cells had collapsed keratin and vimentin intermediate filament (IF) networks, and that filaggrin partially co-localized with the IF networks. Filaggrin was also detected diffusely in the cytoplasm and nucleus. In contrast, when profilaggrin-like constructs, containing five filaggrin domains separated by the linker sequences, were expressed in cultured cells, immunoreactive granules formed. This finding is reminiscent of the insoluble nature of native profilaggrin that accumulates in keratohyalin granules in vivo, suggesting that the linker peptides (present in profilaggrin but not filaggrin) are important for granule formation. Cells expressing filaggrin also displayed disruption of the nucleus and the nuclear envelope; they rounded up and lost attachment to the substratum, in contrast to control cells over-expressing beta-galactosidase. This functional test of filaggrin in living cells supports its role in the reorganization and packing of keratin IF in epidermal differentiation. Moreover, the observed effects on cell morphology and nuclear integrity suggest that filaggrin may contribute to the form of apoptosis associated with terminal differentiation in epidermis.

Evidence for specific proteolytic cleavage of the N-terminal domain of human profilaggrin during epidermal differentiation

Profilaggrin is a large phosphoprotein that is expressed in the granular cells of epidermis where it is localized in keratohyalin. It consists of multiple copies of single filaggrin units plus N- and C-terminal sequences that differ from filaggrin. Profilaggrin is dephosphorylated and proteolytically processed during terminal differentiation to yield filaggrin, which associates with keratin intermediate filaments to form macrofibrils in the lower layers of the stratum corneum. The N-terminal sequence of human profilaggrin comprises two distinct domains; an acidic A domain of 81 amino acids that binds Ca2+, and a cationic B domain of 212 residues. In this report, we further characterize the N-terminal domain by immunohistochemistry and immunoblot analysis using anti-peptide antibodies raised to the A and B regions. All of these antibodies (n = 4) immunostained keratohyalin in the granular layer of human epidermis and also showed some reaction with the lower stratum corneum. In immunoblot studies, the high molecular weight human profilaggrin reacted with both B domain antibodies whereas it showed a weak and variable reaction with A domain antibodies. In addition to profilaggrin, a cationic 32-kDa protein was detected with all N-terminal antibodies. A similar-sized N-terminal peptide was also produced by in vitro proteolysis of human profilaggrin with endoproteinase 1 (PEP1), a protease involved in processing of mouse profilaggrin, and in cultured rat epidermal keratinocytes transfected with a human profilaggrin cDNA construct. Evidence for at least one additional cleavage within the N-terminal domain is shown by immunoreactivity of smaller (16-20 kDa) acidic and basic proteins with A and B domain antibodies, respectively. These results demonstrate that the N-terminal domain is an integral part of profilaggrin in keratohyalin but is proteolytically cleaved from profilaggrin during the terminal differentiation of keratinocytes to yield a 32-kDa peptide.

Corrective gene transfer in the human skin disorder lamellar ichthyosis

Lamellar ichthyosis (LI) is a disfiguring skin disease characterized by abnormal epidermal differentiation and defective cutaneous barrier function. LI has been associated with loss of keratinocyte transglutaminase 1 (TGase1), an enzyme believed necessary for normal formation of the cornified epidermal barrier. Using LI as a prototype for therapeutic cutaneous gene delivery, we have used the human skin/immunodeficient mouse xenograft model to correct the molecular, histologic and functional abnormalities of LI patient skin in vivo. We have used TGase1-deficient primary keratinocytes from LI patients combined with high-efficiency transfer of functional TGase1 to regenerate engineered human LI epidermis on immunodeficient mice. Engineered LI epidermis displayed normal TGase1 expression in vivo, unlike unengineered LI epidermis where TGase1 was absent. Epidermal architecture was also normalized by TGase1 restoration, as was expression of the epidermal differentiation marker filaggrin. Engineered LI skin demonstrated restoration of cutaneous barrier function measures to levels seen in epidermis regenerated by keratinocytes from patients with normal skin, indicating functional correction in vivo of the proposed primary pathophysiologic defect in LI. These results confirm a major role for TGase1 in epidermal differentiation and demonstrate a potential future approach to therapeutic gene delivery in human skin.

A limited role for retinoic acid and retinoic acid receptors RAR alpha and RAR beta in regulating keratin 19 expression and keratinization in oral and epidermal keratinocytes

Different types of stratified squamous epithelia-for example, the "orthokeratinized" epidermis, the "parakeratinized" gingiva, and the "nonkeratinized" oral lining mucosal epithelia-are formed by intrinsically distinct keratinocyte subtypes. These subtypes exhibit characteristic patterns of keratin protein expression in vivo and in culture. Keratin 19 is an informative subtype-specific marker because the basal cells of only nonkeratinizing epithelia express K19 in vivo and in culture. Epidermal keratinocytes normally do not express K19, but can be induced to do so in culture by retinoic acid (RA). Keratinocyte subtypes express the retinoic acid receptor (RAR) beta at levels roughly correlated with their level of K19 expression in culture and their potential for forming a nonkeratinized epithelium in vivo. We tested the hypothesis that the level of RAR beta expressed by a keratinocyte determines its K19 expression and its form of suprabasal differentiation. Normal human epidermal and gingival keratinocytes stably overexpressing either RAR beta or RAR alpha were generated by defective retroviral transduction. Overexpression of either receptor enhanced the RA inducibility of K19 in conventional culture, in that the proportion of the transductants becoming K19+ in response to RA was markedly increased compared with controls. The pattern of differentiation of the epithelium formed in organotypic culture, assessed by basal K19 and suprabasal K1, K4, and filaggrin expression, however, was unaltered by RAR overexpression. Thus, the susceptibility of keratinocytes to regulation of K19 expression by retinoids is conditional, and levels of neither RAR beta nor RAR alpha are limiting to the intrinsic mechanism that specifies alternate differentiation pathways for stratified squamous epithelia.

Decreased expression of filaggrin in atopic skin

The amounts of the epidermal proteins filaggrin, involucrin, cystatin A and Ted-H-1 antigen produced during the terminal differentiation of keratinocytes were immunohistochemically measured in lesional and nonlesional skin of atopic dermatitis (AD) patients. In addition, the amount of filaggrin in the skin of the inner surface of the upper arm of AD patients (nonlesional skin) and normal controls, obtained by punch biopsy, was measured by an enzyme-linked immunosorbent assay (ELISA) technique. The immunohistochemical study showed that all four proteins were decreased in lesional skin. By contrast, only filaggrin was decreased in nonlesional skin of AD patients. The ELISA showed that the amount of filaggrin in the skin of the inner surface of the upper arm was 2.48 +/- 0.45 microgram/7 mm2 (n = 8) in AD patients, which was 32% of that in the normal controls (7.7 +/- 0.55 microgram/7 mm2; n = 4). This decrease in filaggrin production in atopic skin may be one of the reasons why atopic skin can easily become dry, because filaggrin is thought to be the precursor protein of the emollient factors in the stratum corneum. The evidence that only the expression of filaggrin was suppressed in AD patients, though the genes of filaggrin and involucrin are localized to a very restricted portion of the same gene 1q21, indicates that the filaggrin gene does not share regulatory elements with the involucrin gene.

Differences of reactivity to interferon gamma in HeLa and CaSki cells: a combined immunocytochemical and flow-cytometric study

We characterized the changes induced by treatment for 48 h with 100 U/ ml interferon gamma (IFN-gamma) on HeLa and CaSki cells, derived from human uterine carcinomas and containing human papillomavirus (HPV) type 16 and HPV type 18 respectively, by studying cell growth, cell morphology, the cell cycle and expression of epidermal growth factor (EGF) receptor, filaggrin-profilaggrin and MHC class II antigen, HLA-DR. The response of the two cell lines to IFN gamma differed in some cases. In both cell lines, the cells remained viable; cell growth was similarly inhibited as shown by cell counts. Signs of morphological changes were essentially observed in HeLa cells. The cell cycle phases, analyzed by flow cytometry were more disturbed in CaSki than in HeLa cells; the proportion of CaSki cells in S phase increased and those in G2 + M decreased. Expression of EGF receptors related to proliferation increased only in CaSki cells while expression of filaggrin-profilaggrin, a marker of differentiation, and HLA-DR, a marker of epithelial cell immune response, was enhanced in both cell lines. The presence of filaggrin-profilaggrin being unexpected in these cells, the specificity of the reaction with the monoclonal antibody AKH1 was confirmed by immunoblotting. In conclusion, our results show that the two cell lines reacted differently to IFN gamma although they are of similar origin and the different antigens studied may be useful to predict the progression of lesions infected with HPV towards malignancy or the reactivity to IFN gamma of such lesions. However, enhanced synthesis of EGF receptors is probably independent of the antiproliferative effect of IFN gamma but an increase in HLA-DR antigen expression by epithelial cells, which corresponds to an immune response favored by IFN gamma, could act synergistically with cell growth inhibition and differentiation to exclude tumoral and/or HPV-infected cells.

Monoclonal antibodies to human epidermal filaggrin, some not recognizing profilaggrin

To improve understanding of human profilaggrin processing to filaggrin, we produced seven monoclonal antibodies against epidermal filaggrin (AHF1-7). They were characterized on human epidermis by indirect immunofluorescence, immunogold labeling, and immunoblotting and found to be directed against seven different epitopes of (pro)filaggrin. AHF1-5 labeled the keratohyalin granules and the fibrous matrix of the lower corneocytes, and recognized filaggrin and profilaggrin. AHF6 also labeled the keratohyalin granules and the corneocyte matrix, but only recognized filaggrin. In addition to this reactivity within the upper epidermis, AHF4-6 stained the cytoplasm of the basal cells, and cross-reactivity of AHF5 and AHF6 with cytokeratin K14 was revealed on immunoblots. It is interesting that AHF7 recognized filaggrin, but not profilaggrin, and labeled only the corneocyte matrix and not the keratohyalin granules. This indicates that filaggrin and cytokeratins share several antigenic determinants and that filaggrin bears at least one epitope absent from its precursor. The original series of monoclonal antibodies described here appears to be a powerful tool for studying human profilaggrin processing in normal conditions and in the keratinization disorders in which processing is altered.

The antiperinuclear factor and the so-called antikeratin antibodies are the same rheumatoid arthritis-specific autoantibodies

The so-called antikeratin antibodies (AKA) and the antiperinuclear factor (APF) are the most specific serological markers of RA. Using indirect immunofluorescence, AKA label the stratum corneum of various cornified epithelia and APF the keratohyalin granules of human buccal mucosa epithelium. We recently demonstrated that AKA recognize human epidermal filaggrin. Here, we report the identification of the major APF antigen as a diffuse protein band of 200-400 kD. This protein is seen to be closely related to human epidermal (pro) filaggrin since it was recognized by four antifilaggrin mAbs specific for different epitopes, and since the APF titers of RA sera were found to be correlated to their AKA titers and to their immunoblotting reactivities to filaggrin. Immunoabsorption of RA sera on purified epidermal filaggrin abolished their reactivities to the granules of buccal epithelial cells and to the 200-400-kD antigen. Moreover, antifilaggrin autoantibodies, i.e., AKA, affinity purified from RA sera, were shown to immunodetect the 200-400-kD antigen and to stain these granules. These results indicate that AKA and APF are largely the same autoantibodies. They recognize human epidermal filaggrin and (pro) filaggrin-related proteins of buccal epithelial cells. Identification of the epitopes recognized by these autoantibodies, which we propose to name antifilaggrin autoantibodies, will certainly open new paths of research into the pathophysiology of RA.

CHILD syndrome: analysis of abnormal keratinization and ultrastructure

A new patient with CHILD syndrome (congenital hemidysplasia, ichthyosiform erythroderma, and limb defects), the thirtieth in the literature, was observed for over three years. Initially, the right-sided lesion spared the breast area. At 10 months of age the trunk lesion extended to cover the entire area of the right chest. At age 20 months the patient developed linear, bandlike, keratotic, brown-black lesions on her left thigh that subsided within six weeks, leaving a slight hyperpigmentation. This patient was studied by routine histologic methods as well as with markers of keratinization and electron microscopy. In hematoxylin and eosinstained sections, parakeratosis and orthokeratosis alternated. In some parakeratotic areas, large granular cells, and in others, ghost granular cells, were present. The latter showed basophilic cytoplasm, and palestaining or vacuolated nucleus and were seen either above the normal granular layer or without it. Although regional variations existed, basal cell-type keratins as recognized by AE1 continued to be expressed in suprabasal layers. Filaggrin- and involucrin-positive layers were expanded, particularly the latter, down to the lower prickle cell layer. Ultrastructurally, numerous lamellar or membranous structures were found in upper layers of the epidermis, both intracellulary and intercellularly. Normal cementsomes coexisted with these abnormal lamellar structures, and it was thought that the latter represent modified cementsomes because the discharge of those from the cell periphery was often detected.

Retinoic acid provokes metaplasia of epithelium formed in vitro by adult human epidermal keratinocytes

A striking effect of retinoids is their ability to alter cell fate during development. The mucous metaplasia produced by treating chick embryo skin in organ culture with retinoic acid is a classical example of this property. It has been impossible so far to demonstrate that retinoids are able to provoke metaplasia of adult keratinocytes grown in vitro, although these agents have been shown to block terminal epidermal differentiation, to induce increased synthesis of mucopolysaccharides, and to induce the ectopic expression of K19 and K13 keratins. Our previous work showed that adult human epidermal keratinocytes grown on dermal equivalents at the surface of a culture medium containing physiological amounts of retinoids form a normal keratinized epidermis, while when excess retinoic acid is added to the culture medium, keratinization is prevented but stratification is not. Here we show that the distribution of tissue- and differentiation-stage-specific markers in retinoic acid-treated epithelium is similar to that of the oral mucosa. Moreover, when the excess retinoic acid is removed, a new epithelium is formed beneath the "old" one and this epithelium displays an epidermal orthokeratinized phenotype, whereas the "old" epithelium remains unchanged. This phenomenon of "partial reversibility", as well as the mutually exclusive distribution of the markers of the two alternative routes of differentiation, demonstrate that retinoic acid is indeed able to provoke metaplasia of adult epidermal keratinocytes.

Retinoic acid regulates oral epithelial differentiation by two mechanisms

The effect of retinoic acid (RA) concentration on differentiation of oral keratinocytes and the influence of fibroblasts on RA-dependent regulation were investigated in a lifted culture system. Keratinocyte differentiation was assessed by morphology, immunohistochemistry and immunoblotting. Filaggrin/profilaggrin and keratin 1 were used as biochemical markers for cornified epithelium and keratins 13 and 19 as markers for noncornified epithelium. Cultured oral keratinocytes in RA-free conditions differentiated in a manner that closely resembled the differentiation pattern of gingival epithelia in vivo. Increasing RA concentrations altered the in vivo-like terminal differentiation of oral keratinocytes by disruption of organized stratification, inhibition of filaggrin/profilaggrin and K1 expression, and stimulation of K13 and K19 expression. Differentiation of keratinocytes from both cornified and noncornified regions of the oral cavity varied in a similar manner in response to added RA, with the exception of K19 expression. K19 was consistently expressed at higher levels in keratinocytes originating from noncornified epithelial as compared to those from cornified epithelia. The level of RA regulation was ultimately dependent on the type of fibroblasts underlying the epithelial cells. Homologous fibroblasts rendered the oral keratinocytes less sensitive to the effects of RA than skin fibroblasts. In addition, at a given RA concentration, fibroblasts from cornified oral mucosa potentiated keratinocyte expression of RA sensitive markers of keratinization as compared to the influence exerted by fibroblasts originating from noncornified oral mucosa. These results indicate that the RA regulation of oral epithelial differentiation is mediated by two separate mechanisms: a direct, RA concentration-dependent effect, and an indirect, fibroblast-mediated effect.

Retinoic acid regulates oral epithelial differentiation by two mechanisms

The effect of retinoic acid (RA) concentration on differentiation of oral keratinocytes and the influence of fibroblasts on RA-dependent regulation were investigated in a lifted culture system. Keratinocyte differentiation was assessed by morphology, immunohistochemistry and immunoblotting. Filaggrin/profilaggrin and keratin 1 were used as biochemical markers for cornified epithelium and keratins 13 and 19 as markers for noncornified epithelium. Cultured oral keratinocytes in RA-free conditions differentiated in a manner that closely resembled the differentiation pattern of gingival epithelia in vivo. Increasing RA concentrations altered the in vivo-like terminal differentiation of oral keratinocytes by disruption of organized stratification, inhibition of filaggrin/profilaggrin and K1 expression, and stimulation of K13 and K19 expression. Differentiation of keratinocytes from both cornified and noncornified regions of the oral cavity varied in a similar manner in response to added RA, with the exception of K19 expression. K19 was consistently expressed at higher levels in keratinocytes originating from noncornified epithelia as compared to those from cornified epithelia. The level of RA regulation was ultimately dependent on the type of fibroblasts underlying the epithelial cells. Homologous fibroblasts rendered the oral keratinocytes less sensitive to the effects of RA than skin fibroblasts. In addition, at a given RA concentration, fibroblasts from cornified oral mucosa potentiated keratinocyte expression of RA sensitive markers of keratinization as compared to the influence exerted by fibroblasts originating from noncornified oral mucosa. These results indicate that the RA regulation of oral epithelial differentiation is mediated by two separate mechanisms: a direct, RA concentration-dependent effect, and an indirect, fibroblast-mediated effect.

Decreased profilaggrin expression in ichthyosis vulgaris is a result of selectively impaired posttranscriptional control

Ichthyosis vulgaris is an autosomal dominant disorder of keratinization characterized by mild hyperkeratosis and reduced or absent keratohyalin granules in the epidermis. Profilaggrin, a major component of keratohyalin granules, is reduced or absent from the skin of individuals with ichthyosis vulgaris. In this report, we have further characterized the molecular basis of low profilaggrin expression, which occurs in this disease. In situ hybridization revealed little profilaggrin mRNA in ichthyosis vulgaris-affected epidermis. In keratinocytes cultured from the epidermis of affected individuals, the abundance of profilaggrin was reduced to less than 10% of normal controls, while the mRNA level was decreased to 30-60% of controls. Expression of K1 and loricrin, other markers of epidermal differentiation, were not affected. Nuclear run-on assays indicated that the decrease in mRNA levels was not caused by aberrant transcription. Nucleotide sequencing of 5'-upstream, 3'-non-coding, and flanking regions of the profilaggrin gene from ichthyosis vulgaris-affected individuals revealed only minor changes, probably due to genetic polymorphisms. Our results indicate that defective profilaggrin expression in ichthyosis vulgaris is a result of selectively impaired posttranscriptional control.

Filaggrin expression in epidermolytic ichthyosis (epidermolytic hyperkeratosis)

To evaluate the role of filaggrin in keratin filament aggregation in epidermolytic ichthyosis (epidermolytic hyperkeratosis, EH), we studied EH skin by light and electron microscopic immunohistochemistry, and biochemical analysis using sodium dodecylsulphate-polyacrylamide gel electrophoresis and immunoblotting. Immunohistochemical staining showed an increased number of filaggrin-immunoreactive cell layers, but the reaction was still confined to the mid- and upper epidermal layers, whereas an abnormal granular pattern of staining for K10 began in the lower suprabasal cell layers. This suggests that the aggregation of keratin filaments precedes, and occurs independently of, profilaggrin synthesis during epidermal differentiation. Although keratohyalin granules were frequently associated with clumped filaments, immunoelectron microscopy showed that K10 labelling was confined to keratin filaments (including clumped filaments), and that antifilaggrin antibodies stained only keratohyalin granules, at least in the living cells. Certain keratin aggregates in the cornified cells were still devoid of filaggrin staining. However, in some cells which appeared partially cornified, filaggrin immunoreactivity occurred over the aggregated keratin filaments. Immunoblotting showed a clear increase of filaggrin/profilaggrin expression, without evidence for a qualitative abnormality. It seems unlikely, therefore, that filaggrin is primarily involved in the keratin filament clumping in EH, but that in some EH cases it interacts with keratins in a defective manner, possibly due to premature cell death and profilaggrin processing and/or altered keratin filament structure involving the interaction points of keratin with filaggrin.

Immunohistochemical localization of filaggrin in benign, premalignant and malignant cervical tissue

Epithelial distribution of filaggrin, a histidine-rich protein related to squamous terminal differentiation, was investigated in 87 cervical biopsies using an avidin-biotin-peroxidase technique with a monoclonal anti-human filaggrin antibody (AKH1). Normal squamous cervical epithelium exhibited a positive homogeneous immunoperoxidase stain in the upper parabasal, intermediate and superficial cell layers. Similar findings were obtained in cervical condylomas, although full-thickness staining was observed in 35.7% of the cases (P < 0.001). Filaggrin expression in CIN was inversely related to the severity of the lesion (P < 0.001). An irregular staining pattern was present in most high-grade CIN. Filaggrin expression was closely connected to the degree of tumour differentiation (P < 0.05) in squamous cell carcinomas of the cervix. Abnormal filaggrin stainings identified a premalignant/malignant cervical squamous lesion with a positive predictive value of 92.3%. Non-squamous epithelia showed lack of filaggrin expression. Filaggrin may therefore be considered a marker of squamous differentiation in both the normal and pathological human uterine cervix.

The cytokeratin filament-aggregating protein filaggrin is the target of the so-called "antikeratin antibodies," autoantibodies specific for rheumatoid arthritis

In rheumatoid arthritis (RA), the high diagnostic value of serum antibodies to the stratum corneum of rat esophagus epithelium has been widely reported. These so-called "antikeratin antibodies," detected by indirect immunofluorescence, were found to be autoantibodies since they also labeled human epidermis. Despite their name, the actual target of these autoantibodies was not known. In this study, a 40-kD protein (designated as 40K), extracted from human epidermis and specifically immunodetected by 75% of RA sera, was purified and identified as a neutral/acidic isoform of basic filaggrin, a cytokeratin filament-aggregating protein, by peptide mapping studies and by the following evidences: (a) mAbs specific for filaggrin reacted with the 40K protein; (b) the autoantibodies, affinity-purified from RA sera on the 40K protein, immunodetected purified filaggrin; (c) the reactivity of RA sera to the 40K protein was abolished after immunoadsorption with purified filaggrin; (d) the 40K protein and filaggrin had similar amino acid compositions. Furthermore, autoantibodies against the 40K protein and the so-called "antikeratin antibodies" were shown, by immunoadsorption experiments, to be largely the same. The identification of filaggrin as a RA-specific autoantigen could contribute to the understanding of the pathogenesis of this disease and, ultimately, to the development of methods for preventing the autoimmune response.

Profilaggrin is a major epidermal calcium-binding protein

Profilaggrin is a major highly phosphorylated protein component of the keratohyalin granules of mammalian epidermis. It contains 10 to 12 tandemly repeated filaggrin units and is processed into the intermediate filament-associated protein filaggrin by specific dephosphorylation and proteolysis during terminal differentiation of the epidermal cells. Later, filaggrin itself is degraded to free amino acids that participate in maintenance of epidermal flexibility. The present paper describes the structural organization of the 5' region of the human profilaggrin gene as well as the amino terminus of the profilaggrin protein. The primary profilaggrin transcript consists of three exons and two introns. The first exon (exon I) is only 54 bp and is untranslated. The coding sequences are distributed between exon II (159 bp) and exon III, which contains the information for 10 to 12 filaggrin repeats (972 bp each) and the 3' noncoding sequences. A very large intron separates exons I and II. The combination of a very short exon I with an unusually long intron 1 makes the structure of the profilaggrin gene unique among the epidermally expressed genes investigated so far. Comparison of the expression patterns revealed by primer extension and RNase protection analysis of foreskin epidermal and cultured keratinocyte RNAs suggests that alternately spliced messages, which are different from profilaggrin mRNA, are transcribed from the profilaggrin gene system at earlier stages of epidermal differentiation. The amino terminus of profilaggrin exhibits a significant homology to the small calcium-binding S100-like proteins. It contains two alpha-helical regions, termed EF-hands, that bind calcium in vitro. This is the first example of functional calcium-binding domains fused to a structural protein. We suggest that in addition to its role in filament aggregation and the maintenance of epidermal flexibility, profilaggrin may play an important role in the differentiation of the epidermis by autoregulating its own processing in a calcium-dependent manner or by participating in the transduction of calcium signal in epidermal cells.

Special program of differentiation expressed in keratinocytes of human haarscheiben: an analysis of individual cytokeratin polypeptides

Human haarscheiben, epidermal Merkel cell-rich sensory organs of hairy skin, were studied for the expression of various cytokeratin (CK) polypeptides and other epithelial and neuronal differentiation markers by applying immunoperoxidase and immunofluorescence microscopy to frozen sections and by two-dimensional gel electrophoresis. The basal clusters of Merkel cells were specifically detected by antibodies against CK 20. Haarscheiben keratinocytes were unique mainly by the prominent expression of CK 17 in the lower and middle layers. Further differences as compared to keratinocytes of usual epidermis included the enlargement of the basal compartment, characterized by the expression of CK 5 and the absence of the maturation-associated CKs 1/10/11, and the reduction of CK 15, which is a constituent of normal basal cells. Using CK 17 as a highly sensitive Haarscheibe marker in skin tissue sections, variabilities in the spatial relationship of the haarscheibe and the corresponding hair follicle were recorded. The results show that haarscheibe keratinocytes express a special program of differentiation that may be important for optimal stimulus perception. Immunohistochemical stainings for CK 17 will facilitate further studies on the distribution and biology of haarscheibe.

Profilaggrin is a major epidermal calcium-binding protein

Profilaggrin is a major highly phosphorylated protein component of the keratohyalin granules of mammalian epidermis. It contains 10 to 12 tandemly repeated filaggrin units and is processed into the intermediate filament-associated protein filaggrin by specific dephosphorylation and proteolysis during terminal differentiation of the epidermal cells. Later, filaggrin itself is degraded to free amino acids that participate in maintenance of epidermal flexibility. The present paper describes the structural organization of the 5' region of the human profilaggrin gene as well as the amino terminus of the profilaggrin protein. The primary profilaggrin transcript consists of three exons and two introns. The first exon (exon I) is only 54 bp and is untranslated. The coding sequences are distributed between exon II (159 bp) and exon III, which contains the information for 10 to 12 filaggrin repeats (972 bp each) and the 3' noncoding sequences. A very large intron separates exons I and II. The combination of a very short exon I with an unusually long intron 1 makes the structure of the profilaggrin gene unique among the epidermally expressed genes investigated so far. Comparison of the expression patterns revealed by primer extension and RNase protection analysis of foreskin epidermal and cultured keratinocyte RNAs suggests that alternately spliced messages, which are different from profilaggrin mRNA, are transcribed from the profilaggrin gene system at earlier stages of epidermal differentiation. The amino terminus of profilaggrin exhibits a significant homology to the small calcium-binding S100-like proteins. It contains two alpha-helical regions, termed EF-hands, that bind calcium in vitro. This is the first example of functional calcium-binding domains fused to a structural protein. We suggest that in addition to its role in filament aggregation and the maintenance of epidermal flexibility, profilaggrin may play an important role in the differentiation of the epidermis by autoregulating its own processing in a calcium-dependent manner or by participating in the transduction of calcium signal in epidermal cells.

Abnormal lamellar granules in harlequin ichthyosis

Lamellar granules are specialized lipid-rich organelles present in epidermal granular cells. They fuse with the apical cell surface and discharge their contents into the intercellular space forming lamellar sheets. It was previously shown by electron microscopy that lamellar granules in biopsies of infants affected with harlequin ichthyosis are either absent or abnormal and no intercellular lamellae could be detected. A monoclonal antibody (AE17) directed against a protein component of lamellar granules was used for immunoblotting and immunohistochemical studies as an indication of both the presence and function of lamellar granules. Epidermal extracts from all harlequin and normal specimens tested showed an immunoreactive protein of 25-28 kD. Immunohistochemical staining of normal skin using AE17 showed apical cytoplasmic staining in the granular layer and intercellular staining between the granular and stratum corneum cells. Harlequin samples showed variable degrees of staining ranging from little to heavy apical cytoplasmic staining of granular cells. No intercellular staining was detected. The immunohistochemical staining pattern correlated with the electron microscopic localization of abnormal vesicles and the absence of intercellular lamellae in the affected samples. We conclude that the vesicles represent lamellar granules that contain the AE17 antigen but are structurally abnormal and defective in their ability to discharge both their lipid and protein contents into the intercellular space. We suggest that this defect in the lamellar granules represents the underlying basis for stratum corneum cell retention and subsequent accumulation of scale in harlequin ichthyosis.

[Differentiation of the ruminal epithelium of cattle during intrauterine development]

The prenatal development of the bovine ruminal epithelium was studied with light- and electronmicroscopical techniques. During the period of the nonstratified epithelium a pseudostratified epithelium is found in the dorso-cranial part, whereas the other areas possess a one-layered epithelium, which is, like the pseudostratified epithelium, transformed to a multilayered epithelium from the 7th week onwards. From the 9th week the period of the stratified epithelium starts with the formation of the stratum profundum and stratum superficiale. First signs of keratinization are seen in the superficial cells from 2.3 months onwards. With 4 months fetal cornified cells can be identified, with 5.5 months a single-layered stratum basale is seen on the differentiating papillar connective tissue, and the superficial cells are transformed to balloon-cells. In suprapapillar areas, a stratum spinosum is formed at the prenatal age of 7.5 months. During epitheliogenesis a horizontal and vertical differentiation of the cells can be observed. The first one includes the differentiation of undifferentiated, embryonal cells to the basal cells of the stratum profundum, the latter the development of the basal cells to spinous cells and then to fetal cornified and balloon-cells. The ultrastructural changes during the process of keratinization were especially considered.

Biosynthesis of human papillomavirus from a continuous cell line upon epithelial differentiation

The study of the human pathogen papillomaviruses (HPVs) has been hampered by the inability to propagate the virus in tissue culture. The addition of 12-O-tetradecanoyl phorbol-13-acetate to the media of organotypic (raft) cultures increased expression of physiological markers of keratinocyte differentiation and concomitantly induced production of virions. Capsid production was detected in differentiated suprabasal cells. Virions approximately 54 nanometers in size were observed by electron microscopy in raft tissue cross sections in the suprabasal layers. Virions purified through isopycnic gradients were found to contain type 31b DNA and exhibited an icosahedral shape similar to that of papillomaviruses found in clinical samples.

CHILD Syndrome: Lack of Expression of Epidermal Differentiation Markers in Lesional Ichthyotic Skin

Congenital hemidysplasia with ichthyosiform erythroderma and limb defects (CHILD) syndrome is a rare genetic disorder. The epidermal abnormalities associated with the unilateral ichthyosis have previously been examined only by morphology. In order to describe these abnormalities more completely we analyzed the expression of markers of epidermal differentiation (keratins and filaggrin), grew keratinocytes in culture, and correlated the results with ultrastructural features. Expression of all differentiation markers was significantly reduced or absent, whereas keratins K5 and K14 and keratins K6 and K16 were strongly expressed in lesional epidermis, suggesting that basal cell keratin expression was not down-regulated as in normal epidermis and that lesional keratinocytes mature via an abnormal pathway. When removed from the tissue and grown in culture, keratinocytes from lesional and non-lesional biopsies had similar phase microscopic morphology as well as keratin and profilaggrin expression, in contrast to the extreme differences in vivo. Lesional keratinocytes also had similar contents of keratin filaments and keratohyalin, but showed abnormal accumulation of intercellular vesicles and debris and altered cell-cell and cell-substratum interaction. Comparison of the results in tissue and in culture suggests that systemic or dermal factors influence the abnormal structural protein expression and ichthyosiform epidermal differentiation seen in CHILD syndrome, but that lesional keratinocytes maintain abnormalities in the secretion and accumulation of extracellular material in vitro similar to the lesional tissue in vivo.

Control of Epidermal Differentiation by a Retinoid Analogue Unable to Bind to Cytosolic Retinoic Acid-Binding Proteins (CRABP)

The role played by cytosolic retinoic acid-binding proteins (CRABP) in the control of differentiation and morphogenesis by retinoids remains unclear, which contrasts with the presence of these binding proteins in tissues known to be targets for retinoic acid effects. Human epidermis represents a good system to address this question because 1) the effect of retinoids on keratinocyte differentiation is well documented; 2) epidermis contains CRABP, and the amount of these proteins is modulated both by keratinization and retinoids; 3) the architecture of epidermis obtained in vitro by growing adult human keratinocytes on a dermal substrate can be modulated by retinoids added to the culture medium in a dose-dependent manner; and 4) most markers of epidermal differentiation are also modulated by retinoids in a dose-dependent manner. In this study, we compared, in dose-response experiments, the biologic activities of retinoic acid and CD271, a substance unable to bind to CRABP, but able to bind to nuclear retinoic acid receptors (RAR). Our results show that retinoic acid and CD271 exert similar controls on epidermal morphogenesis and keratinocyte differentiation, as shown by the inhibition of the synthesis of suprabasal keratins, filaggrin, and transglutaminase. Therefore, we exclude a qualitative role for CRABP in the control exerted by retinoids on the differentiation and morphogenesis of cultured human keratinocytes. Instead of being involved in the pathway via which retinoids control epidermal gene expression, CRABP might regulate the amount of intracellular-active retinoic acid and thus control quantitatively the intensity of biologic effects.

Methotrexate induces differentiation of human keratinocytes

Terminal differentiation is a key element in the maintenance of tissue homeostasis in the epidermis. We show here that methotrexate (MTX) induces differentiation of human epidermal keratinocytes in vitro. MTX inhibits proliferation of keratinocytes and also induces several markers of differentiation: a change in cell morphology, a marked increase in cell size, an increase in the proportion of cells that express involucrin, and an increase in the amount of cornified envelope protein. These effects of MTX are dose- and exposure-time-dependent and become irreversible after 24 hr, approximately one population doubling time. These effects of MTX cannot be attributed to cytotoxicity since keratinocytes not only remain viable but also actively synthesize proteins. MTX causes reproducible changes in the SDS/PAGE profiles of newly synthesized proteins and, in particular, increases the amount of involucrin synthesis. Thymidine completely prevents these effects of MTX, suggesting that they are caused by a depletion of thymine deoxyribonucleotides. The effect of MTX on keratinocytes may provide a model for studying the relationship between deoxyribonucleotide metabolism and differentiation in normal cells. In addition, the ability of MTX to induce differentiation in keratinocytes suggests a mechanism to explain its therapeutic action in psoriasis.

Keratohyalin granules are heterogeneous in ridged and non-ridged human skin: evidence from anti-filaggrin immunogold labelling of normal skin and skin of autosomal dominant ichthyosis vulgaris patients

Recent biochemical and morphological investigations have provided evidence for a heterogeneous composition of keratohyalin in human skin. A major component is filaggrin. In interfollicular epidermis the heterogeneity of keratohyalin is not directly visible, whereas in normal ridged skin bicomponent keratohyalin is revealed by electron microscopy. Skin biopsies of ridged and non-ridged skin of normal individuals and patients with autosomal dominant ichthyosis vulgaris (ADI)--characterized by defective keratohyalin synthesis and lack of filaggrin--were investigated by routine transmission electron microscopy and immunogold postembedding techniques using a commercial monoclonal anti-filaggrin antibody. In normal interfollicular epidermis filaggrin labelling was demonstrated on keratohyalin granules and in the lowermost cornified cells, whereas in ADI patients crumbly keratohyalin granules were present that did not show specific labelling for filaggrin. In normal ridged skin only the major (more electron-dense) component reacted with anti-filaggrin, whereas the attached (less electron-dense) component did not react. Ridged skin of ADI patients contained globular keratohyalin that did not react with anti-filaggrin, thus corresponding to the attached keratohyalin component in normal ridged skin. Our results provide a visible counterpart to the recent biochemical investigations of keratohyalin protein heterogeneity and contribute to the understanding of terminal differentiation in human skin and of the defective keratohyalin synthesis in ADI.

Antiperinuclear factor, a marker autoantibody for rheumatoid arthritis: colocalisation of the perinuclear factor and profilaggrin

The antiperinuclear factor, an autoantibody specific for rheumatoid arthritis, was found in 51/63 (81%) patients with rheumatoid arthritis by indirect immunofluorescence on human buccal mucosa cells. The sensitivity of the antiperinuclear factor test was increased by pretreating the buccal mucosa cells with 0.5% Triton-X100. The specificity of the test for rheumatoid arthritis as compared with control serum samples was maintained. The localisation of the perinuclear factor in the keratohyalin granules of the buccal mucosa cells was verified by immunoelectron microscopy. The perinuclear factor was found to be an insoluble protein whose antigenicity was sensitive to various fixation procedures. In serum samples from patients with rheumatoid arthritis there was a positive correlation between the presence of antiperinuclear factor and the presence of the so called antikeratin antibodies as detected by immunofluorescence on unfixed rat oesophagus cryostat sections. No relation was found between the presence of the perinuclear factor and either the rheumatoid factor, Epstein-Barr virus components, or any cytokeratin. By double immunofluorescence an exact colocalisation of the perinuclear factor and profilaggrin was found. Although the precise biochemical identity of the perinuclear factor remains unclear, our results suggest that it is a protein only present in the fully differentiated squamous epithelial cell layer.

Trichohyalin: presence in the granular layer and stratum corneum of normal human epidermis

Trichohyalin, a protein contained in granules in the cells of the hair-follicle inner root sheath and in the medulla of the hair shaft, has been purified previously from sheep hair bulbs and is also a major protein of filiform papillae of tongue epithelium. Polyclonal affinity-purified antibodies and a monoclonal antibody raised to purified pig tongue trichohyalin both stained the inner root sheath of hair follicles and the medulla of hair fibers and identified human trichohyalin as a single 220-kDa band on immunoblots of human hair bulb proteins. These antibodies were used to examine human epidermis by immunofluorescence and immunoblotting. The antibodies decorate granules in cells in the granular layer and stratum corneum of non-hair-bearing human skin, and immunoblots identify a protein in epidermis comigrating with trichohyalin from human hair and human tongue epithelium. Absorption of antibody to trichohyalin on a trichohyalin affinity column abrogated staining of the epidermis and the bands on the immunoblots. Trypsin-separated epidermis contained 220 and 160 kDa bands identified as trichohyalin, but epidermis shaved from skin and quickly frozen showed only a single 220-kDa band, indicating that the 160-kDa protein was generated by proteolysis. Double immunofluorescence for trichohyalin and filaggrin showed that some cells containing filaggrin also contain trichohyalin. These studies show that trichohyalin is not limited to hair and tongue but is present in isolated cells in the granular layer and stratum corneum of normal epidermis.

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.

Hereditary palmoplantar keratosis of the Gamborg Nielsen type. Clinical and ultrastructural characteristics of a new type of autosomal recessive palmoplantar keratosis

A new kind of diffuse palmoplantar keratoderma with autosomal recessive inheritance and without associated symptoms was described in Norrbotten, Sweden by Gamborg Nielsen in 1985. Clinically, it ranges between the less severe dominant Unna-Thost type and the more severe recessive Meleda type, as it is milder than the latter. Skin biopsies of five patients from three different families with this new palmoplantar keratoderma, as well as five obligatory heterozygotes from one family, were investigated ultrastructurally in order to characterize this new entity and to differentiate it from the Meleda type. Several features are common to both autosomal recessive palmoplantar keratoses. They show a broadened granular layer, a transit region consisting of cells with a marginal envelope, and considerable hyperkeratosis. Morphologically, this transformation delay is less pronounced in the Gamborg Nielsen type than in the classical Meleda type. As is typical for ridged skin, both types of palmoplantar keratoses possess composite keratohyaline granules. In contrast to the normal appearance of keratohyaline granules in the Meleda type, the Gamborg Nielsen type also shows qualitative deviations of keratohyaline granules with different degrees of spongiosity and electron density and sometimes with a granular border. It seems that abnormal keratohyaline proteins are synthesized that behave differently. The sudden transformation of a granular into a horny cell is physiologically regulated by different enzymes. A delay in this process may be caused by a mutation that reduces or alters the enzymes concerned. We assume the palmoplantar keratoderma of the Gamborg Nielsen type to be a variant of the heterogeneous group of the Meleda type of palmoplantar keratoderma with autosomal recessive inheritance.