Retinoic acid delays the terminal differentiation of keratinocytes in suspension culture

Main effects of retinol palmitate on skin structures and the technology of its use in dermatological practice

Vitamin A and its synthetic analogues are used in the treatment of numerous skin diseases. The main genomic effects of the natural form of vitamin A (retinol palmitate) are associated with its active metabolite all-trans-retinoic acid and are compensated by several restrictive mechanisms. Numerous studies have proved that retinol stimulates the proliferation of keratinocytes of the basal layer of the epidermis and endothelial cells, and also activates dermal fibroblasts to synthesize proteins of the extracellular matrix of the dermis. As a result, the thickening the epidermis, increases the mechanical strength of the skin and the hydrating ability of the dermis, angiogenesis increase. The ability of retinol to enhance the adhesion of endothelial cells and leukocytes, regulate the processes of keratinization and sebum secretion was found. Vitamin A is also a powerful antioxidant. Retinol palmitate is used as the main or auxiliary drug for the treatment of a wide range of dermatoses. The principle of application is based on clinical studies and confirmed by existing experimental data. In the treatment, the following algorithm is followed. If retinol palmitate is necessary to improve epithelialization and strengthen the epidermal barrier, medium therapeutic doses should be used. For the treatment of disorders of keratinization processes, depending on the severity of the pathological condition, medium and high therapeutic doses of the drug are used. Violation of the processes of sebum secretion and severe hyperkeratosis respond better to treatment at high therapeutic doses. It should be noted that many skins clinical manifestations mostly regress under the action of vitamin A in doses that do not lead to the appearance of signs of toxicity of the drug.

Accelerated human epidermal turnover driven by increased hyaluronan production

BACKGROUND

Hyaluronan (HA) is an essential component of extracellular matrix in the skin, but its functions in the epidermis remain elusive.

OBJECTIVE

We examined the interaction of increased HA production mediated by 1-ethyl-β-N-acetylglucosaminide (β-NAG2), a newly developed highly selective inducer of HA production which is intracellularly converted to UDP-N-acetylglucosamine, a substrate of HA, with epidermal proliferation and differentiation.

METHODS

The amount, molecular size and epidermal tissue distribution of HA and expression of CD44, a cell surface receptor for HA, were analyzed in β-NAG2-treated organ cultured human skin, reconstructed human skin equivalents or cultured human skin keratinocytes. The relationship between HA and epidermal proliferation or differentiation was examined.

RESULTS

β-NAG2 significantly increased HA production in the epidermis of skin explants or skin equivalents without affecting molecular size of HA (>2000 kDa) or CD44 mRNA expression. Histochemical experiments revealed that β-NAG2 enhances HA signals in the basal to granular layers of the epidermis of skin equivalents, accompanying increased epidermal stratification. Immunohistochemical experiments demonstrated that signals of Ki67, transglutaminase 1 and filaggrin are increased in β-NAG2-treated skin equivalents, and these observations were confirmed by the data showing that mRNA expression of PCNA, transglutaminase 1 (TGM1) and filaggrin (FLG) is significantly up-regulated by β-NAG2 in skin equivalents. Importantly, blockade of HA production by inhibiting conversion of β-NAG2 to UDP-NAG abolished β-NAG2-mediated up-regulation of PCNA, TGM1 and FLG mRNA expression in cultured keratinocytes.

CONCLUSION

These results suggest that increased epidermal HA production plays a key role in epidermal morphogenesis and homeostasis by accelerating keratinocyte proliferation and differentiation.

Hair follicle stem cells regulate retinoid metabolism to maintain the self-renewal niche for melanocyte stem cells

Metabolites are major biological parameters sensed by many cell types in vivo, whether they function as signaling mediators of SC and niche cross talk to regulate tissue regeneration is largely unknown. We show here that deletion of the Notch pathway co-factor RBP-J specifically in mouse HFSCs triggers adjacent McSCs to precociously differentiate in their shared niche. Transcriptome screen and in vivo functional studies revealed that the elevated level of retinoic acid (RA) caused by de-repression of RA metabolic process genes as a result of RBP-J deletion in HFSCs triggers ectopic McSCs differentiation in the niche. Mechanistically the increased level of RA sensitizes McSCs to differentiation signal KIT-ligand by increasing its c-Kit receptor protein level in vivo. Using genetic approach, we further pinpointed HFSCs as the source of KIT-ligand in the niche. We discover that HFSCs regulate the metabolite RA level in vivo to allow self-renewal of neighboring McSCs.

Inhibition of epidermal terminal differentiation and tumour promotion by retinoids

Retinoids are physiological regulators of growth and differentiation for a number of epithelial tissues. In several of these, retinoids also act as pharmacological anticarcinogens. Retinoids are most effective as anticarcinogens in the post-initiation portion of carcinogenesis. In mouse skin, retinoids are inhibitors of phorbol ester-mediated tumour promotion and can cause regression of pre-existing benign tumours. Studies in vivo and in vitro have indicated that phorbol ester-mediated skin tumour promotion results from selective clonal expansion of initiated cells. We have proposed that the biological basis for selection resides in the induction of terminal differentiation in subpopulations of keratinocytes while other keratinocytes, including initiated cells, are stimulated to proliferate. Terminal differentiation is accelerated by phorbol esters through the induction of epidermal transglutaminase and consequent cornification. Retinoids inhibit terminal differentiation of keratinocytes. Retinoids also induce transglutaminase in epidermis, but they inhibit cornification. Recent results suggest a biochemical basis for this paradox. The phorbol ester-induced transglutaminase is primarily particulate but the retinoid-induced enzyme is cytosolic. The induced enzymes differ in kinetic parameters, thermal stability and in elution from ion-exchange columns. Induction of the retinoid enzyme is associated with suppression of the induction of transglutaminase by phorbol esters. The retinoid-induced epidermal transglutaminase could interfere with normal or promoter-induced differentiation by inappropriately cross-linking precursor proteins before their assembly at the cell periphery. This could explain one aspect of the inhibitory action of retinoids on tumour promotion.

Mouse epidermal development: effects of retinoic acid exposure in utero

Epidermal morphogenesis was studied in vivo following prenatal exposure to retinoic acid (RA). In pregnant mice, a single oral dose of RA on day 11.5 of gestation failed to induce histological changes in fetal epidermal development except in epidermal thickness. Epidermal thickness increased from 16.5 days post-coitum (dpc) onwards, and temporal and spatial epidermal modifications in keratins K5 and K14 related to proliferative activity of keratinocytes were observed. An RA effect on cell proliferation was supported by a statistically significant increase in the number of epidermal S-phase cells, containing BrdU-incorporated DNA in RA-exposed mice compared with nonexposed animals. The prolonged in utero action of RA on epidermal proliferative activity in fetuses and newborns suggests a long-term RA effect that may play a role on the development and evolution of diseases in adult skin.

Effects of in utero retinoic acid exposure on mouse pelage hair follicle development

We investigated in vivo the histological and immunohistochemical responses of mouse hair pelage follicle morphogenesis to prenatal exposure to a potentially nonteratogenic dose of all-trans-retinoic acid (RA), as a basis studying the preventive effect of RA on adult mouse skin carcinogenesis. In pregnant mice, a single oral dose of RA at 30 mg kg-1 body weight given on day 11.5 of gestation caused no RA-induced changes in the morphology or temporal expression patterns of keratins during pelage hair follicle morphogenesis. The only differential effect of RA was a statistically significant increase in the number of BrdU-positive nuclei in hair bulbs from RA exposed fetuses compared with nonexposed mice. The absence of adverse RA effects suggests that this experimental design may represent a valuable protocol for use in studies on the in vivo effects of this retinoid on different skin diseases.

High-cell-density phorbol ester and retinoic acid upregulate involucrin and downregulate suprabasal keratin 10 in autocrine cultures of human epidermal keratinocytes

Autocrine growth of human epidermal keratinocytes is initiated in subconfluent cell cultures in the absence of exogenous growth factors, at low calcium concentration of the medium and with sufficient cell density. Culture confluence inhibits keratinocyte proliferation and upregulates expression of early, keratin 10 (K10), and late, involucrin, markers of differentiation. In this report, the phenotype of autocrine keratinocytes was studied at high cell density (postconfluence), specifically after treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA), or all-trans retinoic acid (RA). At postconfluence, K10 is decreased but not involucrin. TPA upregulates involucrin expression, but not K10 in subconfluent keratinocytes. Treatment of confluent keratinocytes with RA downregulates K10, but upregulates involucrin. This in vitro culture model, unlike others, simulates for the first time the in vivo effects of RA, a member of the retinoid family which potently modulates keratinocyte differentiation and the expression of selected gene products. It thus can be developed to further examine epidermal differentiation.

Anchorage-dependent expression of the vitamin D receptor in normal human keratinocytes

Although the nuclear vitamin D receptor (VDR) is involved in the control of keratinocyte proliferation and differentiation by its ligand 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], its role in epidermal physiology remains poorly understood. Because VDR abundance reflects cellular responsiveness to 1,25(OH)2D3, we investigated VDR expression in cultured human keratinocytes and identified cell anchorage and cytoskeletal integrity as essential requirements for the maintenance of VDR levels. Suspension culture rapidly suppressed VDR expression and 1,25(OH)2D3 responsiveness (as estimated by induction of 24-hydroxylase mRNA), due to decreased transcription of the VDR gene. Concomitantly, overt growth arrest with p21WAF1 induction and cyclin D1 and c-myc suppression occurred, together with induction of differentiation markers and retinoid X receptor alpha, the heterodimeric partner for VDR. Reattachment of suspended keratinocytes to fibronectin led to a rapid restoration of VDR expression, which could be blocked by RGD peptides or a blocking anti-beta1 integrin antibody. VDR expression was also reduced by disruption of the actin cytoskeleton with cytochalasin D. Malignant keratinocytes (SCC12B2 and A431), characterized by, anchorage-independent growth, displayed a profound resistance to suspension-induced suppression of VDR, cyclin D1, and c-myc. Taken together, our results associate VDR expression [and 1,25(OH)2D3 responsiveness] with cell adhesion and an organized cytoskeleton, which are also required for cell growth of primary cells.

Retinoic acid stimulates essential fatty acid-supplemented human keratinocytes in culture

The effect of all-trans retinoic acid on the proliferation of essential fatty acid (EFA)-deficient and of EFA-supplemented adult human keratinocytes was investigated. EFA-deficient cell strains were supplied with one of four different fatty acid-supplemented media at the P0 to P1 passage. All-trans retinoic acid at 0.5 or 1.0 microM was added to the cultures at the P1 to P2 passage. At passage P3, and 3 and 7 d thereafter, the cell growth rate was determined. The fatty acid content of cultures grown in each medium was measured using gas chromatography. All the EFA media "normalized" the cellular fatty acid composition and drastically decreased the cell number and total DNA and protein of the cultures. All-trans retinoic acid at 1 microM prevented the loss of cell viability and growth usually associated with EFA supplementation but did not affect the control (EFA deficient) or 18:1 fatty acid-supplemented cultures. All-trans retinoic acid at 1 microM altered the fatty acid content of the EFA-supplemented cultures. A statistically significant increase in 14:0, 14:1, 16:1, 18:1, and 20:4 fatty acids occurred, whereas the amounts of 18:0 and 18:2 fatty acids decreased. The largest changes were in 16:1 fatty acid (8-14%) and 18:2 fatty acid (12-5%). All-trans retinoic acid at 0.5 microM also affected both cell growth and fatty acid composition without induction of the CRABP II message. These studies demonstrate that all-trans retinoic acid stimulates the growth of EFA-supplemented keratinocyte cultures while also altering the fatty acid composition of the cells.

Expression of retinoid-X receptors (-alpha,-beta,-gamma) and retinoic acid receptors (-alpha,-beta,-gamma) in normal human skin: an immunohistological evaluation

Increasing evidence suggests that the retinoid-X receptors (RXR-alpha,-beta,-gamma) play a crucial role in regulating the transcriptional activity of several steroid hormone receptors, including the receptors for retinoic acid (RAR-alpha,-beta,-gamma), 1,25-dihydroxyvitamin D3 and thyroid hormone. We investigated the localization of the different types of RXR-alpha,-beta,-gamma and RAR-alpha,-beta,-gamma proteins in frozen sections of normal human skin (n = 12) in situ, applying recently raised corresponding specific monoclonal antibodies and an immunohistochemical technique that we established for the detection of these nuclear receptors. Our findings indicate that RXR-alpha,-beta,-gamma and RAR-alpha,-beta,-gamma proteins can be detected by immunohistochemistry in normal human skin. In contrast to RXR-alpha,-beta,-gamma as well as RAR-alpha and RAR-gamma proteins that were consistently detected in cell layers of the viable epidermis, RAR-beta was only focally demonstrated in single epidermal cells in three out of 12 biopsies analysed. Immunohistochemical labelling of RAR-alpha,-beta,-gamma and RXR-alpha,-beta,-gamma proteins in epidermal nuclei was also pronounced in the stratum granulosum, suggesting a function of RXR and RAR proteins in the transition from proliferation to differatiation in epidermal keratinocytes. Expression of RXRs and RARs in hair follicles, sebaceous glands and endothelial cell points to a biological function from these nuclear receptors to hair growth as well as to the physiology of sebaceous glands and endothelial cells.

In situ detection of retinoid-X receptor expression in normal and psoriatic human skin

Increasing evidence suggests that the retinoid-X receptors RXR(-alpha,-beta,-gamma) play a crucial part in regulating the transcriptional activity of several steroid hormone receptors, including 1,25-dihydroxyvitamin D3 receptors (VDR) and retinoic acid receptors (RAR-alpha,-beta,-gamma). We developed a new technique for immunohistochemical in situ detection of RXR receptors, and investigated the localization of RXR-alpha in normal and psoriatic human skin using a recently raised corresponding specific antibody. RXR-alpha positive cells related to the skin were phenotyped by sequential sections and a double-labelling procedure for the simultaneous demonstration of this nuclear receptor and cell membrane antigens, as well as cytokeratin 10, HLA-DR and vimentin. Our findings indicate that: (i) RXR-alpha is strongly expressed in normal and psoriatic human skin; (ii) most of the cell types in normal human skin, including keratinocytes, melanocytes, fibroblasts and skin immune cells such as Langerhans cells, reveal strong nuclear immunoreactivity for RXR-alpha, with less cytoplasmic staining; (iii) altered levels or distribution of RXR-alpha in the skin do not appear to be involved in the genesis of psoriasis vulgaris, but subepidermal and subcellular distribution suggest a function of RXR-alpha in the transition from proliferation to differentiation in epidermal keratinocytes; (iv) expression in the hair follicle points to a contribution from RXR-alpha to hair growth.

A two-colour flowcytometric study of cell kinetics and differentiation of human keratinocytes in culture

Double histochemical staining followed by flow cytometric analysis was performed to determine whether involucrin synthesis is associated with a particular phase of the cell cycle. In low-calcium medium (0.1 mM) monolayer cultures the expression of involucrin was confined to about 8% of the total cell populations. When the concentration of calcium was increased to 1.8 mM, the percentage increased and the distribution pattern of the cell cycle changed. The addition of retinoic acid at concentrations in the range 10(-8) M to 10(-6) M to a high-calcium medium induced a further increase. The greatest increase in involucrin expression (up to five-fold) occurred in both the G1/G0 and G2 + M phases, while S phase cells showed a two-fold increase. The results indicate that involucrin synthesis is induced by retinoic acid, which occurs at any stage of the cell cycle, even in the S phase.

Markers of keratinocyte differentiation in snuff-induced leukoplakia

Biopsy specimens from 12 patients who used snuff and had leukoplakia in the mucosa of the oral cavity were studied and compared with specimens from their own nonleukoplakic oral mucosa, as well as with biopsy specimens from corresponding areas of the oral cavity in 12 nonsmoking, nontobacco-using control subjects. The biopsy specimens were processed using standard immunohistochemical rabbit antibody to human involucrin and mouse antibody to human transglutaminase type I as the primary antibodies. A computer-driven light absorbance image analysis system was used to determine the optical density of each of the marker-stained specimens. Optical density measurements were compared using a one-way analysis of variance. The expression of involucrin was significantly higher in the epithelium of the nonsmoking, nontobacco-using control subjects (0.2937 +/- 0.0725 optical density) in comparison with the normal-appearing mucosa (0.2283 +/- 0.0488 optical density) and the leukoplakic mucosa of the snuff-using patients (0.2007 +/- 0.0669 optical density) (p < 0.05). The expression of transglutaminase type I was also significantly higher in the epithelium of the nonsmoking, nontobacco-using controls (0.2308 +/- 0.1381 optical density) than in the patients with leukoplakic mucosa (0.1310 +/- 0.0472 optical density) (p < 0.05). However, there was no difference when compared with the normal-appearing mucosa of the patients in the snuff-using group (0.1686 +/- 0.0323 optical density). This study has shown that involucrin and transglutaminase type I are expressed differently in leukoplakic oral mucosa of snuff users and in normal oral mucosa and that this difference can be measured objectively.

Simple assays of retinoid activity as potential screens for compounds that may be useful in treatment of psoriasis

Human epidermal cell cultures were used to study the effects of retinoids on keratinocyte differentiation. Keratin profiles were studied by quantitative gel electrophoresis of culture extracts, whereas the extent of envelope formation was assessed in an enzyme-linked immunosorbent assay (ELISA) using an antibody that specifically recognizes keratinocyte envelopes. Exposure of cultures to a variety of different retinoids produced both dose-dependent decreases in keratin 16 with consequent increases in the keratin 14: keratin 16 ratio, and a decrease in envelope formation. The order of activity in both assays was similar: arotinoid ethyl ester (Ro 13-6298) greater than or equal to arotinoid acid (Ro 13-7410) much greater than all trans retinoic acid (Ro 1-5488) greater than acitretin (Ro 10-1670) greater than or equal to etretinate (Ro 10-9359), the only difference being that acitretin was slightly more active than etretinate in the keratin assay whereas these retinoids were equi-active in the envelope assay. Analysis of the lesional keratins of psoriasis patients showed that etretinate caused a reduction in keratin 16 and an increase in the keratin 14:keratin 16 ratio, although the magnitude of these changes and their correlation with clinical improvement was variable. As the in vitro assays reported here are simple and quick, they allow rapid screening of compounds for retinoid-like activity.

Retinoic acid receptors and binding proteins in human skin

Nuclear retinoic acid receptors (RAR) are likely to mediate many of the pleiotypic cutaneous actions of retinoids by acting as ligand-dependent enhancer factors. The presence of nuclear RAR in skin was confirmed by identification of a 45-kDa nuclear RA binding activity by fast protein liquid chromatography (FPLC). Analysis of RNA extracted from skin specimens demonstrated expression of RAR-alpha and RAR-gamma transcripts, as well as expression of the homologous low-affinity receptor, RXR-alpha. Both isoforms of RAR-gamma RAR-gamma 1 and RAR-gamma 2 were detectable, with RAR-gamma 1 being the more strongly expressed. FPLC analysis also demonstrated a 15-kDa peak of specific RA binding activity, consistent with the presence of cellular retinoic acid binding protein (CRABP). Of the two known forms of CRABP, CRABP-II was much more strongly expressed than CRABP-I at the level of steady-state mRNA. CRABP-II was also expressed in keratinocytes and fibroblasts in vitro. CRABP-II was up-regulated by agents that induce keratinocyte differentiation, and inhibited by prolonged exposure to high concentrations of RA. In contrast, CRABP-II was consistently induced by RA in dermal, but not in lung fibroblasts. CRABP-I was expressed at low to undetectable levels under all these conditions. The presence of tissue-specific and differentiation-related regulation of CRABP-II suggests that it may be an important regulator of RA action in human skin.

Differential regulation of retinoic acid receptors and binding proteins in human skin

Many of the pleiotropic effects of retinoids are likely to be mediated by nuclear retinoic acid receptors (RAR) acting as ligand-dependent enhancer factors. However, in previous studies we have been unable to document altered RAR expression at the RNA level in response to retinoic acid (RA) treatment or in psoriatic lesions, conditions characterized by marked alterations in keratinocyte proliferation and differentiation, which are either caused by or responsive to RA. In an attempt to identify other potential regulators of RA responsiveness, we have used RNA blot hybridization to study the expression of the cellular retinoic acid binding proteins (CRABP) CRABP-I and CRABP-II, the RAR-gamma isoforms RAR-gamma 1 and RAR-gamma 2, and the low-affinity RAR homologue RXR in normal, RA-treated, and psoriatic human epidermis. CRABP-II is selectively and markedly induced by RA in adult human skin (J Biol Chem 266:17662-17666, 1991). However, in submerged, serum-free keratinocyte cultures, CRABP-II mRNA could not be induced by RA. Comparisons of intact human skin, submerged keratinocyte cultures, and human skin equivalent cultures indicated that induction of CRABP-II by RA requires epidermal stratification, dermal-epidermal interactions, or both. CRABP-II transcripts were also expressed in heat-separated human dermis at levels similar to those found in epidermal keratome biopsies, whereas CRABP-I transcripts were undetectable in dermal RNA. CRABP-II transcripts were markedly elevated in psoriatic lesions, as they were in RA-treated skin. In contrast, CRABP-I mRNA was undetectable and not increased in psoriatic lesions. Expression of RAR-gamma isoforms and RXR was not detectably altered in either psoriatic lesions or in RA-treated skin. Thus, altered expression of CRABP-II appears more likely to regulate the cutaneous actions of RA than does altered expression of CRABP-I, RXR, or RAR-gamma isoforms. From these and other results, a model for regulation of RA action involving sequestration of RA by CRABP-II is proposed.

Effects of Topical Retinoids on Cytoskeletal Proteins: Implications for Retinoid Effects on Epidermal Differentiation

In vivo effects of retinoids on epidermal differentiation were investigated by analyzing cytoskeletal proteins in rhino mice treated topically with all-trans-retinoic acid (RA) and other retinoids (13-cis-retinoic acid, etretinate, TTNPB). Non-disulfide-linked cytoskeletal proteins, including keratins from the epidermal "living layers," were first selectively extracted using 9.5 M urea; subsequently, keratins of the stratum corneum were isolated using 9.5 M urea plus a reducing agent. Gel electrophoresis and immunoblot analysis showed that urea extracts of epidermis from vehicle-treated skin were composed predominantly of four major keratins (analogous to human epidermal keratins K1, K5, K10, and K14), and the keratin filament-associated protein filaggrin. In contrast, extracts of epidermis from retinoid-treated skin contained additional keratins (K6, K16, and K17) and almost no detectable filaggrin. Furthermore, similar analysis of stratum corneum keratins demonstrated that extracts from RA-treated skin did not contain the partially proteolyzed keratins typically observed in stratum corneum extracts of control animals. Hyperplasia-inducing agents (salicylic acid, croton oil) caused an increase in keratins K6, K16, and K17, but they did not effect filaggrin or alter proteolysis of stratum corneum keratins. The result that RA induced expression of keratins K6, K16, and K17, as commonly expressed in hyperproliferative epidermis, is consistent with the notion that retinoids increase epidermal cell proliferation in the basal and/or lower spinous layers. The findings that topical RA decreased filaggrin expression and reduced proteolysis of stratum corneum keratins, despite increased size and number of granular cells and the presence of an anucleate stratum corneum, suggest that topical RA may also modulate a later stage of epidermal differentiation involved in stratum corneum formation.

Intracellular actions of vitamin A

Because the effects of vitamin A vary with tissue type and often with the form of vitamin A itself, a complete understanding of the mechanism(s) of action still has not been attained. The action of vitamin A may be at the level of genomic expression, at the membrane level, or both. Intercellular and intracellular transport of vitamin A are facilitated by specific binding proteins but probably not in the cellular uptake of vitamin A. Subcellularly, vitamin A may exert a direct effect on transit through the Golgi apparatus, as observed from both biochemical and morphological studies. In my laboratory, recent work using cell-free systems has shown that retinol stimulates transition vesicle formation from endoplasmic reticulum in a GTP-requiring step.

Effects of steroid, retinoid, and protease inhibitors on the formation of acantholysis induced in organ culture of skins from patients with benign familial chronic pemphigus

Skin explants from two lesional areas and four normal-appearing areas of four patients with benign familial chronic pemphigus (BFCP) were organ cultured with and without various reagents. After 24-h culturing of involved skin with medium only, dissociation of keratinocytes, which was also observed prior to culturing, was exacerbated, and the epidermis became edematous, with a large section detaching from the dermis. These phenomena were not suppressed even when betamethasone, retinol acetate, or camostat mesilate (serine protease inhibitor) was added to the medium. On the other hand, in the cultures of uninvolved skin explants with medium only, widened intercellular spaces were observed 24-48 h after initiation of culture, and dissociation of keratinocytes and acantholytic clefts became apparent after 72 h. Such culture-induced acantholysis was almost completely suppressed by the addition of betamethasone, but not suppressed by the addition of retinol acetate, EDTA, N-ethylmaleimaide, or pepstatin A. Camostat and SBTI incompletely suppressed the acantholysis. These findings suggest the possibility that steroid may reduce blistering and that an organ culture of non-lesional benign familial chronic pemphigus (BFCP) skin may be useful for clarifying the pathogenesis, as well as for discovering new drugs for the treatment of BFCP. Further experiments are required to clarify the role of serine proteases in the acantholysis in this disease.

Phorbol ester inhibits 13-cis-retinoic acid-induced hydrolysis of phosphatidylinositol 4,5-bisphosphate in cultured murine keratinocytes: a possible negative feedback via protein kinase C-activation

The incubation of double-labelled [( 14C]-glycerol and [3H]-myoinositol) keratinocytes with 13-cis retinoic acid induced the transient and simultaneous release of [3H]-inositol trisphosphate ([3H]-InsP3) and [14C]-diacylglycerol ([14C]-DAG) indicating that a possible mode of action of this retinoid on murine keratinocytes may be at least in part the early transient release of the two putative messengers (InsP3 and DAG) from phosphatidylinositol-4,5 bisphosphate (PtdIns4, 5P2). In contrast, the preincubation of the keratinocytes with 12-O-tetradecanoylphorbol-13-acetate (TPA) prior to incubation with 13-cis-RA suppressed the 13-cis-RA-induced release of [3H]-InsP3 and [14C]-DAG. The specificity of the TPA effect was established by the lack of effect of the biologically inactive 4 alpha-phorbol 12, 13-didecanoate. Furthermore, the incubation of the TPA-primed keratinocytes with 13-cis-RA caused a delayed and sustained accumulation of [14C]-DAG. An exploration of the source of this late release of [14C]-DAG revealed that this [14C]-DAG was released from non-inositol containing phospholipids, particularly, phosphatidylcholine. This latter DAG released in the TPA-primed cells correlated with the translocation of the cytoplasmic protein kinase C (PKC) activity to the membrane associated PKC activity. Taken together, these results suggest that alteration of PKC activity, presumably induced by DAG released from non-inositol phospholipids, may play a major role in the TPA-induced negative feedback inhibition of 13-cis RA-induced hydrolysis of keratinocyte PtdIns4, 5P2.

Formation and removal of 8-MOP-DNA photoadducts in keratinocytes: effects of calcium concentration and retinoids

8-methoxypsoralen (8-MOP)-DNA photoadducts were quantified in freshly isolated human and murine keratinocytes and cultured keratinocyte cell lines after in vitro treatment with 8-MOP (1-200 ng/ml) and ultraviolet A (UVA; 0.2-24.0 J/cm2). Greater doses of 8-MOP and UVA led to proportionately greater numbers of photoadducts, with a dose reciprocity relationship between the amounts of 8-MOP and UVA. No significant difference in photoadduct formation was observed between basal and differentiated cells. However, the transformed keratinocyte cell lines showed fewer photoadducts than did normal keratinocytes, which appeared to be correlated with the finding that the adduct formation was inhibited in normal keratinocytes cultured with phorbol 12-myristate 13-acetate, because this agent leads to epidermal hyperproliferation. In viable keratinocytes that were treated with a sublethal dose of 8-MOP and UVA (15 ng/ml and 1 J/cm2, respectively), 54% of photoadducts formed were removed over a 20-h period. Adduct removal depended on the calcium concentration in the media; cells cultured in standard high calcium levels showed a higher removal rate than those cultured in low-calcium media. The addition of retinoids (etretinate, acitretin, and 13-cis retinoic acid) to the culture induced 55 to 80% of suppression of the adduct removal. The calcium ionophore A23187 partially restored the suppression of photoadduct removal induced by retinoids. The present studies suggest that calcium performs an important role in the photoadduct removal and raise the possibility that the synergism of systemic retinoids and psoralen plus UVA photochemotherapy relates to the former's inhibition of repair of 8-MOP photoadducts in DNA.

Inhibited morphological terminal differentiation and enhanced proliferation of cultured mouse epidermal cells at different concentrations of dimethyl sulphoxide

Dimethyl sulphoxide (DMSO), at concentrations of 1-2%, induces terminal differentiation in several different cell types in vitro and enhances the growth of newborn mouse epidermal cells in primary culture under conditions that also permit terminal differentiation. We have found that DMSO concentrations approaching 4% reversibly inhibited (with little overt toxicity) terminal differentiation of normal epidermal cells from newborn SENCAR mice. Cells cultured in medium containing 4% DMSO and calcium in excess of 1 mM did not stratify extensively or slough large amounts of keratinized debris into the medium as occurred in control cultures, nor did they form large numbers of squamous cells or keratin bundles, as revealed by light and electron microscopy. The number of detergent-insoluble cornified envelopes was similarly reduced. Long-term growth of epidermal colonies in secondary culture was optimum in 1% DMSO, this concentration also permitting normal terminal differentiation of these cells. Since DMSO had these effects on epidermal cells in vitro, it may also affect epidermal cell proliferation and terminal differentiation in vivo, an important consideration should DMSO ever be approved for topical use in the US.

Inhibition of growth and squamous-cell differentiation markers in cultured human head and neck squamous carcinoma cells by beta-all-trans retinoic acid

Vitamin A and some of its metabolites such as beta-all-trans retinoic acid (RA) have been implicated in the regulation of differentiation of normal and malignant epithelial cells in vivo and in vitro. In the present study the effects of RA on the growth and differentiation of 7 cell lines derived from human head and neck squamous-cell carcinomas (HNSCCs) were examined. RA (greater than 0.01 microM) inhibited the proliferation in monolayer culture of 6 of 7 HNSCC cell lines. One cell line (UMSCC-35) was very sensitive, 5 (UMSCC-10A, -19, -30, -22B and HNSCC 1483) were moderately sensitive, and 1 (HNSCC 183) was insensitive. Three of the cell lines (UMSCC-22B, -30, and HNSCC 1483) were capable of forming colonies in semisolid medium--a capability that was suppressed by RA. The HNSCC cell lines expressed various levels of the squamous-cell differentiation markers type I (particulate, epidermal) transglutaminase (TGase) and cholesterol sulfate (CS). RA treatment (I microM, 6 days) decreased TGase activity by more than 50% in 3 (UMSCC-10A, -22B and 1483) of the 7 cell lines, and the effect on UMSCC-22B was dose-dependent. Type II TGase (soluble, tissue type) activity was detected in 3 cell lines, and after RA treatment its activity increased in HNSCC 1483 and 183 cells and decreased in UMSCC-19. Following RA treatment, CS levels decreased by 20, 25, 70, 76, 89 and 91% in cell lines UMSCC-30, -10A, 183, UMSCC-35, -22B, and HNSCC 1483, respectively. The suppression by RA of CS accumulation in the 1483 cells was dose-dependent. Cholesterol sulfotransferase activity, which is responsible for CS synthesis, was suppressed by 40-97% after RA treatment of UMSCC-19, -22B, and HNSCC 1483. Our results demonstrate that RA inhibits the growth and decreases the level of 2 squamous differentiation markers in HNSCC cells.

Effect of donor age and prior sun exposure on growth inhibition of cultured human dermal fibroblasts by all trans-retinoic acid

The effect of retinoic acid on human fibroblasts was studied in a cell culture model of chronologic aging and photoaging. During early exponential phase, all trans-retinoic acid significantly stimulated growth rate of adult arm-derived dermal fibroblasts but not of newborn or adult foreskin-derived fibroblasts. Retinoic acid also significantly reduced saturation density in most young adult arm-derived lines and all 24 lines derived from old adult arm and foreskin. However, four of ten young adult outer arm (relatively sun-exposed) and one of ten young adult inner arm (relatively sun-protected) fibroblasts lines increased their saturation density in response to retinoic acid. These data suggest that prior sun exposure and/or donor age may influence cellular responsiveness to retinoic acid. Neither the stimulatory nor the inhibitory effect of retinoic acid could be attributed to cell density, to breakdown of retinoic acid in culture, to nutrient depletion or to serum dependency. However, stationary phase fibroblasts from all sites (foreskin, inner and outer arm) showed an increase in filopodia and in intracellular actin after treatment with retinoic acid that was roughly proportional to the degree of growth inhibition, irrespective of donor age. We suggest that retinoic acid induces premature density dependent growth inhibition at least in part by increasing filopodia-mediated cell contact that is in turn directly related to an increase in fibrillar actin.

Comparison of the uptake and metabolism of retinol delivered to primary mouse keratinocytes either free or bound to rat serum retinol-binding protein

Serum retinol-binding protein (RBP) is believed to be responsible for the transport of retinol from its storage site in the liver to vitamin A requiring target cells such as keratinocytes. We have used primary mouse keratinocytes as a model system to compare the uptake and metabolism of [3H] retinol delivered to them either free in solution or bound to RBP. RBP was purified from rat serum, loaded with [3H]retinol, and the [3H]retinol-RBP complex purified by affinity chromatography on human transthyretin-Sepharose. Keratinocytes incubated with either free [3H]retinol or [3H]retinol-RBP complex accumulated [3H]retinol in a time and temperature dependent manner. However, cells incubated with free [3H]retinol acquired 15- to 20-fold more ligand than if the retinol was delivered via RBP. The uptake of free [3H]retinol or [3H]retinol from RBP was not inhibited by excess unlabeled free retinol. The uptake of [3H]retinol from RBP was inhibited by high concentrations of holo-RBP, with half maximal inhibition occurring at 3 microM holo-RBP. However, no specific binding of 125I-labeled RBP to monolayers of keratinocytes or membranes prepared from them was found indicating the absence of a high affinity RBP receptor on keratinocytes. Surprisingly, 50% of the [3H]retinol delivered to the keratinocytes during a 30-min uptake period was released from them within 30-min irrespective of whether or not it was initially delivered to them as free [3H]retinol or bound to RBP. The remaining 50% was lost at a much slower rate, but only 20% remained 24-h after delivery. Studies on retinol metabolism demonstrated that 7%-12% of the total cell-associated [3H]retinol delivered during a 90-min uptake period was esterified (mostly as retinyl palmitate) whether or not it was given free in solution or bound to RBP. Additionally, [3H]retinol taken up by the keratinocytes during the initial 90-min incubation was not chased into a stable retinyl ester pool in a subsequent 9.5-h incubation, but instead, retinyl ester was lost from the cells with kinetics similar to those of total cell-associated radioactivity. These results suggest that a function of RBP is to protect cells from a rapid accumulation of the vitamin which occurs when it is delivered free in solution. However, the cellular fate and metabolism of retinol appears to be the same whether the vitamin is delivered free in solution or bound to RBP.

Regulatory role of retinoic acid on cultured mouse keratinocyte inositol phospholipid metabolism: dose-dependent release of inositol triphosphate

The incorporation of precursor 14C-myoinositol into the three cellular inositol phospholipids (PtdIns, PtdInsP, and PtdInsP2) of cultured, rapidly proliferating keratinocytes is significantly enhanced by the exogenous addition of a high concentration (1 X 10(-7) M) of all-trans retinoic acid or its analog 13-Cis analog, whereas a similar incubation with a low concentration (1 X 10(-10) M) of the same retinoid resulted in an insignificant incorporation of the radio-precursor into the three inositol phospholipids. Incorporation was most marked into the more phosphorylated PtdIns4P and PtdIns4,5P2. These results indicate that retinoic acid affects the biosynthesis of the inositol phospholipids at high concentrations. In contrast, the hydrolysis of 14C-PtdIns4,5P2 and release of 14C-InsP3 from the prelabeled keratinocytes is markedly enhanced by a low physiologic concentration (1 X 10(-10) M) of retinoic acid or its 13-Cis analog. The hydrolysis is rapid, with an accompanying elevated transient release of 14C-InsP3. High concentration (1 X 10(-5) M), on the other hand, supresses 14C-InsP3 release. These results taken together underscore a bifunctional, dose-dependent effect of both the all-trans-RA and its 13-Cis analog on the synthesis and hydrolysis of keratinocyte PtdIns4,5P2. Furthermore, the results suggest that at low physiologic concentrations, these retinoids may function as agonists to perturb the membrane resulting in induced rapid hydrolysis of cellular PtdIns4,5P2, which is coupled to a "transient" generation of InsP3 (an intracellular second messenger). The rapid formation of this putative "second messenger" may in turn play a role in the cellular proliferative or differentiating biochemical events in the murine keratinocytes.

Effects of retinoids on differentiation, lipid metabolism, epidermal growth factor, and low-density lipoprotein binding in squamous carcinoma cells

The relationship among keratinocyte differentiation capacity, lipid synthesis, low-density lipoprotein (LDL) metabolism, plasma membrane composition, and epidermal growth factor (EGF) binding has been studied in SCC-12F2 cells. The differentiation capacity of the cells, i.e., ionophore-induced cornified envelope formation, was inhibited by various retinoids and stimulated by hydrocortisone. Retinoids that caused a significant reduction of cornified envelope formation, i.e., retinoic acid and 13-cis-retinoic acid, caused only minor changes in lipid synthesis and plasma membrane composition. Arotinoid ethylsulfone, having a minor effect on cornified envelope formation, caused a drastic inhibition of cholesterol synthesis, resulting in changes in the plasma membrane composition. Hydrocortisone stimulated cornified envelope formation but had only minor effects on lipid synthesis and plasma membrane composition. Of all retinoids tested, only arotinoid ethylsulfone caused a drastic increase in EGF binding, while hydrocortisone had no effect. Retinoic acid, arotinoid ethylsulfone, and hydrocortisone had no effects on LDL binding and only minor effects on LDL degradation. These results clearly demonstrate that the plasma membrane composition is not related to keratinocyte differentiation capacity, but most likely does determine EGF binding. Furthermore, EGF binding does not determine keratinocyte differentiation capacity.

Selective suppression of two postnatally acquired 70 kD and 65 kD keratin proteins during continuous treatment of adult mouse tail epidermis with vitamin A

Using mouse tail epidermis as a model system we have studied the morphologic and biochemical effects of continuous topical treatment with vitamin A acid. Normal tail epidermis shows a regular pattern of parakeratotic scale regions and orthokeratotic interscale regions which arise postnatally from a uniformly orthokeratinizing neonatal epidermis. Daily treatment of tail epidermis with vitamin A acid for 14 days results in the induction of hyperplasia and the orthokeratotic conversion of the scale regions. The degree of these alterations is dose-dependent and maximally brought about by repetitive 30-microgram doses of the vitamin. To correlate morphologic with biochemical alterations, we have analyzed the keratin patterns of normal and vitamin A acid-treated epidermis by one- and two-dimensional gel electrophoresis. The results indicate that repetitive vitamin A treatment leads to the selective suppression of two postnatally acquired 70 kD and 65 kD type II keratin proteins. Again the minimum repetitive dose required for their complete suppression is 30 micrograms vitamin A acid. Kinetic studies reveal an initial lag phase of 6 days of apparent nonresponsiveness, followed by a 5-day period during which the adult pattern is gradually replaced by the neonatal pattern. Repetitive treatment of tail epidermis with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate leads to a strong hyperplasia; however, it strictly maintains the scale parakeratosis. Under these conditions only the 70 kD keratin subunit is suppressed. This indicates that the suppression of the 70 kD keratin is generally linked to the induction of hyperproliferation, whereas the suppression of the scale-associated 65 kD subunit is due to the metaplastic potency of vitamin A. We provide evidence that this vitamin A-specific in vivo effect can be used to determine the biologic activity of synthetic retinoids relative to vitamin A acid.

Epidermal effects of retinoids: in vitro studies

Cell culture provides controlled conditions in which to investigate the effects of retinoids on the molecular and cell biology of epidermal differentiation. In general, retinoids enhance proliferation and desquamation of cultured epidermal cells and suppress differentiation. In the presence of 10(-6) mol/L retinoic acid, cultured human epidermal cells stratify, but they do not form the granular layer and anucleate, stratum corneum-like superficial layer typical of normal epidermis. Retinoic acid in the growth medium alters keratin synthesis and inhibits the formation of cross-linked envelopes. Expression of other keratinocyte proteins, including filaggrin and components of desmosomes, may also be affected by retinoids. The molecular mechanisms of retinoid action on epidermal cells are still unclear. Cells cultured from normal and pathologic epidermis appear to differ significantly in their responsiveness to retinoids. Recent data suggest that retinoids may modulate gene transcription, stabilize cell membranes, and alter posttranslational processing of several keratinocyte proteins.

Responsiveness and ultrastructure of slowly adapting type I cutaneous mechanoreceptors in vitamin A deficient rats

Single-unit recordings were made from afferent nerve fibres supplying slowly adapting type I (s.a. I) cutaneous mechanoreceptors in anaesthetized vitamin A deficient and control rats. Trains of thirty repetitive mechanical stimuli with 0.1 s rise time, 1.9 s plateau phase, and 0.7 s interstimulus interval were applied. A feed-back mechanism maintained the force of stimulation at 20 mN during the plateau phases and the contact force between stimuli at 0.5 mN. All displacement values in the group of vitamin A deficient rats were significantly larger than the corresponding control values. Residual indentations were increased by 70-100% while maximal indentations were only about 40% higher. These results indicate a non-linear increase in compliance of the skin and underlying tissues. S.a. I receptors were found to be significantly less responsive in vitamin A deficient animals. Mean numbers of impulses were about 25% lower in the vitamin A deficient group than in controls throughout the entire train of thirty stimuli. In vitamin A deficient rats, Merkel cells and adjoining nerve terminals showed signs of degeneration of a variety of cell organelles, particularly the mitochondria. Degenerative changes induced by vitamin A deficiency especially in the Merkel cells appeared to be a major cause of the reduction of responsiveness in s.a. I receptors.

Retinoids alter the direction of differentiation in primary cultures of cutaneous keratinocytes

The effects of vitamin A on the morphological expression of differentiation were studied in cell cultures of cutaneous keratinocytes from the newborn rat. The cells were first cultivated in a medium containing 0.11 mM calcium until a confluent monolayer had been formed. Stratification and terminal differentiation were then triggered by raising the calcium concentration of the medium to 1.96 mM ('normal' culture). The rise in the concentration of calcium was coupled with the addition of retinol (RL) of retinoic acid (RAC) to the medium to produce an excess of vitamin A (high-retinoid culture). Delipidized serum was used to produce a deficiency of vitamin A (low-retinoid culture). The tissue organization and the ultrastructure of the keratinocytes in the stratified culture were the same as those seen in conventional cultures and skin explants. These stratified cultures expressed the morphological features of the epidermis of intact skin. The addition of RL or RAC to the medium enhanced features characteristic of the secretory epithelium, such as the formation of an extensive endoplasmic reticulum, an enlargement of the Golgi zone, and an increase in the number of vacuoles. At the same time, the addition of retinoids diminished features characteristic of the terminal differentiation of the stratified squamous epithelium, such as stratification and keratinization. Deficiency of vitamin A in the medium resulted in a culture with many differentiated layers. The differentiated cells of the low-retinoid cultures contained densely packed tonofilaments and synthesized products that reacted with the monoclonal antibody AE2 that is specific for keratin peptides which are markers of epidermal differentiation. In the cell culture system that is presented here, an excess of retinoids redirected epithelial differentiation from a stratifying and keratinizing epithelium towards a secretory epithelium. This system is a useful tool for elucidating the mechanisms responsible for the effect of vitamin A on the differentiation of epithelial cells.

Effects of retinoic acid on adult human epidermis in whole skin organ culture

Adult human skin was cultured in whole-skin organ culture under chemically defined conditions. Retinoic acid was added to the culture at final concentrations of 5 X 10(-7) and 5 X 10(-6) M. Both concentrations elicited cell death in the upper epidermal layers and prevented the terminal differentiation of the cells to mature corneocytes. The inhibition of terminal differentiation was not permanent, as the corneocytes produced later during the culture showed no signs of inhibition. The upper vital cells in epidermis cultured with retinoic acid were very flattened and contained reduced amounts of cytoskeleton components. Fine, granular material not present in normal epidermis was observed in both the intercellular spaces and the intracytoplasmic vesicles of retinoid-treated epidermis. The present results indicate that the response of normal human skin to retinoic-acid treatment involves the same kind of modulation of the epidermal structure previously described in embryonic avian and diseased human skin.

Regulation of the expression of epidermal keratinocyte proliferation and differentiation by vitamin A analogs

A number of vitamin A analogs (retinoids) were used to manipulate the growth of epidermal keratinocytes in culture. The retinoids used were the TMMP analog of ethyl retinoate (Ro 10-9359), 13-cis retinoic acid, all trans retinoic acid and retinol (trans). These were added to primarily neonatal mouse epidermal keratinocyte cultures that proliferate, stratify, and differentiate over 2-3 weeks. [3H]Tdr labeling technics were used to quantitate proliferation. A histologic stain, and a four buffer protein extraction protocol, used in conjunction with polyacrylamide gel electrophoresis and fluorographic technics, were used to assess the differentiation of the cultures. Our results showed that all of the vitamin A analogs we tested inhibited keratinocyte proliferation. Quantitation of specific differentiation proteins showed that Ro 10-9359 and 13-cis retinoic acid partially inhibited the differentiation of the cultures. The Ro 10-9359 retinoid was unusual in that it increased the synthesis of keratohyalin granule-related proteins. These studies showed that inhibition of basal cell proliferation did not result in the obligatory expression of cell differentiation and that at least one of the events that is a part of epidermal keratinocyte differentiation can be separately controlled.

Topical and systemic effects of retinoids on horn-filled utriculus size in the rhino mouse. A model to quantify "antikeratinizing" effects of retinoids

A method was developed to quantify the "antikeratinizing" effects of various retinoids (all-trans-retinoic acid, 13-cis-retinoic acid, motretinide, etretinate) in rhino mouse skin, which contains many keratinized pilosebaceous structures or horn-filled utriculi. Mean utriculus diameters in whole mount epidermis were determined and dose-response relationships were constructed after topical or oral administration of test retinoids. All-trans-retinoic acid was 3.7x, 12.5x, and 50x more potent than 13-cis-retinoic acid, etretinate, and motretinide, respectively, after topical administration. Administered orally, all-trans-retinoic acid was 2.3x more potent than 13-cis-retinoic acid. At 5 mg/kg, each retinoid produced a significant reduction in utriculus size. The rhino mouse model represents a novel and useful assay to quantify antikeratinizing activity and potency differences of biologically active retinoids.

Cloning of cDNAs specifying vitamin A-responsive human keratins

In human cultured epidermal and conjunctival keratinocytes, vitamin A promotes the synthesis of keratins 13 and 19 of the catalog of Moll et al. [Moll, R., Franke, W.W., Schiller, D.L., Geiger, B. & Krepler, R. (1982) Cell 31, 11-24] but does not alter the synthesis of keratins 5 and 6. To study this effect of the vitamin, cDNAs specifying each of these keratins were cloned in pBR322. Characterization of the clones by hybrid selection of mRNA and by hybridization of size-fractionated mRNA indicated that each was specific for a single mRNA. Treatment of epidermal cells with arotinoid Ro 13-6298, a potent synthetic analog of retinoic acid, increased the abundance of mRNA for keratin 13 by 25-fold and for keratin 19 by greater than 40-fold but had no effect on the abundance of mRNA for keratins 5 and 6.

Bioassay of retinoids using cultured human conjunctival keratinocytes

The biological action of retinoids has been assayed using the differentiated properties of cultured human conjunctival keratinocytes. The effects measured were the suppression of envelope cross-linking and the promotion of synthesis of a keratin of molecular weight 40,000. Among the retinoids tested, the most powerful was the arotinoid Ro 13-6298, which reduced envelope formation detectably at 10(-11) M and by 90% at a concentration of 2 X 10(-10) M. The arotinoid was about 15 times more potent than trans-retinoic acid. The order of effectiveness of the retinoids in suppressing envelope cross-linking was the same as the order of effectiveness in promoting the synthesis of the 40-kd keratin.

The effect of retinoic acid on the expression of pemphigus and pemphigoid antigens in cultured human keratinocytes

Vitamin A and its derivatives (retinoids) have both profound effects on epidermal differentiation and beneficial therapeutic effects in various dermatologic diseases. In order to understand these effects, much work has been done with cultured keratinocytes, which show specific morphologic, cellular, and biochemical changes modulated by retinoids. In an attempt to further define specific molecular effects of retinoids in cultured human keratinocytes, we studied the expression of pemphigus (P) and pemphigoid (BP) antigens by human keratinocytes cultured with retinoic acid (RA) in concentrations which modulated differentiation. Cultures of human keratinocytes in medium with 10% delipidized fetal bovine serum (vitamin A-depleted medium) demonstrated areas of extensive differentiation with flattened stratifying cells, keratohyaline granules, and an anucleate stratum corneum-like superficial layer. These cells also synthesized a 67 kd keratin, characteristic of well-differentiated epidermis. In contrast, cultures of human keratinocytes in the same medium supplemented with (10(-7) M, 3 X 10(-7) M, or 10(-6) M) RA demonstrated less differentiated small cuboidal cells that were stratified but did not form an anucleate layer or keratohyaline granules, and did not synthesize the 67 kd keratin. In order to detect P and BP antigens in these cultures, we used indirect immunofluorescence. In vitamin A-depleted cultures, P antigen either was not detected or was seen focally on the cell surface of basal cells. BP antigen was seen on the basal pole of the basal cells, approximating its in vivo location. In RA-treated cells, P antigen was seen on the cell surface of most of the cells, and BP antigen was seen throughout the cytoplasm of the basal cells. In order to study the expression of newly synthesized antigens, we radiolabeled cultures with 14C-amino acids and quantitatively immunoprecipitated the antigens, which were then identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis. We detected a major decrease in newly synthesized P antigen precipitated from extracts of vitamin A-depleted cells compared to RA-supplemented cells, whereas amounts of newly synthesized BP antigen were about the same. Taken together these data demonstrate that RA, at concentrations that decrease differentiation of cultured human keratinocytes, increases the expression of P antigen and changes the subcellular location of BP antigen.

Transglutaminase activity in human and rabbit ear comedogenesis: a histochemical study

Using monodansylcadaverine as a fluorescent, lysine-substrate analogue, alterations in the histochemical profile of transglutaminase activity during human and coal tar-induced rabbit ear comedogenesis were examined. When compared to the normal pilosebaceous follicles of both species, a marked increase in enzyme-specific fluorescence in the hyperplastic epidermal lining and in the epithelium of the sebaceous duct was observed in human and rabbit early lesions. In mature human open and closed comedones, an intact band of transglutaminase activity corresponding to the differentiating epidermal cell layers was seen to surround the lesion. In mature rabbit comedones this band of activity was most striking. In most lesions, transglutaminase activity was closely apposed to the plasma membrane of the differentiating keratinocytes, the site of cornified envelope formation. In normal human and rabbit interfollicular epidermis the cornified layer immediately above the fluorescent granular layer was histochemically inactive, while the surface stratum corneum showed an increase in activity. A similar phenomenon was observed in many comedones. This pattern of activity may relate to the process of desquamation. Finally, the changes in transglutaminase activity observed during comedogenesis suggest the possibility that inhibitors of transglutaminase could be useful in acne therapy.

Rat esophageal and epidermal keratinocytes: intrinsic differences in culture and derivation of continuous lines

Serially cultivated with 3T3 feeder layer support as colonies of stratified squamous epithelium, rat epidermal and esophageal epithelial cells were readily distinguishable by three criteria. First, the epidermal colonies, exhibiting extensive piling up of squames in the centers, were more stratified than esophageal colonies. Second, in sparse culture 70 to 90% of the esophageal cells but as few as 1 to 5% of the epidermal cells were competent in cross-linked envelope formation upon treatment with the ionophore X537A. After reaching confluence, up to 90% of the cells of both types formed envelopes upon ionophore treatment. Third, epidermal cells in suspension culture reached maximal levels of spontaneously cross-linked envelopes in 1 day or less, while esophageal cells required about 4 days in suspension to reach maximal levels. A reproducible finding with both cell types was that initial colony-forming efficiencies of less than 1% increased to about 40% upon serial passage with consequent derivation of continuous lines. Sparse cultures of esophageal cells with high colony-forming ability retained a high degree of envelope competence (70 to 90%), indicating these two properties are not mutually exclusive. The derived lines exhibited reduced dependence upon feeder layer support at clonal density, but in suspension culture the cells did not grow and lost colony-forming ability with a half-time of several hours. We conclude that cells from these keratinized rat epithelia exhibit intrinsic differences in culture and become continuous lines expressing characteristic regulation of envelope competence and loss of germinative capability in suspension.

Convergent differentiation in cultured rat cells from nonkeratinized epithelia: keratinocyte character and intrinsic differences

Epithelial cells derived from a variety of glandular and other nonkeratinized rat tissues (pituitary, thyroid, bladder, endometrium, trachea, seminal vesicle, prostate, and mammary epithelium) were serially cultivated using a feeder layer of lethally irradiated 3T3 cells. The epithelial cells grew as progressively expanding colonies, in some cases stratified, and were shown to form cornified envelopes upon ionophore-induced activation of cross-linking. Cultures derived from each tissue were distinguishable from the others by characteristic cellular appearance and colony morphology. Those examined in greater detail could be distinguished biochemically in three ways. (a) A majority of cells in sparse cultures of bladder, tracheal, endometrial, and vaginal epithelial cells were capable of envelope formation, whereas those from pituitary, thyroid, seminal vesicle, and mammary epithelia did not attain maximal envelope forming ability until after confluence. (b) Bladder, thyroid, and pituitary cells exhibited different electrophoretic profiles of keratins, which accounted for 20-50% of the cellular protein. (c) Bladder cells were distinguished from thyroid and pituitary cells by a greater suppression of envelope-forming ability by vitamin A. These observations showed that cells from many epithelia have the potential to express properties of keratinocytes in culture while maintaining morphological and physiological differences. Serial passage of these cells generated continuous lines.

Phenotypic expression of epidermal cells in vitro: a review

Disaggregated epidermal cells, sheets of epidermis, and explants of partial and full-thickness skin have been grown in cell, organ, and explant cultures. Each type of epidermal sample has also been "cultured" as a graft on a living animal host. The extent of tissue-specific phenotypic expression by the epidermal cell varies with the type of culture and the culture conditions: medium, biologic and pharmacologic additives, substrate, cell density, pH, and temperature. Specific culture conditions can be chosen to select for certain phenotypic traits. In spite of the diversity of conditions that may be used for culture, keratinocytes in cell, explant, and organ cultures undergo a similar pattern of differentiation. They stratify and keratinize, but rarely express a complete program of keratinization. Many of the characteristics associated with this pattern of differentiation are also observed in fetal epidermis during development. In culture, normal tissue architecture is usually absent; cells organize in flattened, loosely associated layers, synthesize a different pattern of keratin polypeptides, form keratohyalin granules only sporadically, and rarely contain lamellar granules. Epidermal differentiation in explant and organ cultures can be evaluated in regions of the explant, epibolic zone, and outgrowth apron. The epidermis of the original explant undergoes hyperproliferation, degeneration, sloughing, and then regeneration of a thin tissue. The cells in the epithelial outgrowth zone stratify and differentiate almost identically with those in cell culture. Neogenesis of structures in the basement-membrane zone can be followed in all three regions of the explant culture. Sheets of epidermis or epidermal cells transplanted onto or into a host animal show the most complete expression of the epidermal phenotype. After a period of hyperplastic growth, the cell layers become established in a pattern nearly identical to that in vivo. A complete granular layer is formed and stratum corneum cells, which are structurally and biochemically equivalent to those in tissue, differentiate. In some instances, the epidermis reconstructed from cells or tissue is indistinguishable from adjacent host epidermis. Experiments that include serial transfer from one culture system to another demonstrate the plasticity of the epidermal cell and its ability to respond variously to its environment.