Retinoid suppression of transglutaminase activity and envelope competence in cultured human epidermal carcinoma cells. Hydrocortisone is a potent antagonist or retinyl acetate but not retinoic acid

Glyphosate, pathways to modern diseases II: Celiac sprue and gluten intolerance

Celiac disease, and, more generally, gluten intolerance, is a growing problem worldwide, but especially in North America and Europe, where an estimated 5% of the population now suffers from it. Symptoms include nausea, diarrhea, skin rashes, macrocytic anemia and depression. It is a multifactorial disease associated with numerous nutritional deficiencies as well as reproductive issues and increased risk to thyroid disease, kidney failure and cancer. Here, we propose that glyphosate, the active ingredient in the herbicide, Roundup(®), is the most important causal factor in this epidemic. Fish exposed to glyphosate develop digestive problems that are reminiscent of celiac disease. Celiac disease is associated with imbalances in gut bacteria that can be fully explained by the known effects of glyphosate on gut bacteria. Characteristics of celiac disease point to impairment in many cytochrome P450 enzymes, which are involved with detoxifying environmental toxins, activating vitamin D3, catabolizing vitamin A, and maintaining bile acid production and sulfate supplies to the gut. Glyphosate is known to inhibit cytochrome P450 enzymes. Deficiencies in iron, cobalt, molybdenum, copper and other rare metals associated with celiac disease can be attributed to glyphosate's strong ability to chelate these elements. Deficiencies in tryptophan, tyrosine, methionine and selenomethionine associated with celiac disease match glyphosate's known depletion of these amino acids. Celiac disease patients have an increased risk to non-Hodgkin's lymphoma, which has also been implicated in glyphosate exposure. Reproductive issues associated with celiac disease, such as infertility, miscarriages, and birth defects, can also be explained by glyphosate. Glyphosate residues in wheat and other crops are likely increasing recently due to the growing practice of crop desiccation just prior to the harvest. We argue that the practice of "ripening" sugar cane with glyphosate may explain the recent surge in kidney failure among agricultural workers in Central America. We conclude with a plea to governments to reconsider policies regarding the safety of glyphosate residues in foods.

Retinoic acid receptors and cancer

Retinoids have been shown to inhibit the growth of many human tumor cells. Although the exact molecular mechanism of retinoid-mediated growth suppression remains known, the importance of the retinoic acid receptors (RARs) and retinoid X receptors (RXRs) has been in established a number of tumor cell models. We wanted to determine if modulation of RAR/RXR function would alter the retinoid sensitivity of oral squamous carcinoma cells (SCCs). Growth of SCCs was significantly suppressed by treatment with either all-trans retinoic acid (RA) or the synthetic, conformationally restricted RAR-gamma-selective retinoids SR 11254 and SR 11389. In contrast, stable oral SCC clones that constitutively overexpressed the mouse dominant negative mutant, RAR-beta (R269Q), were shown to exhibit reduced RAR/RXR transcriptional transactivation function and reduced sensitivity to growth inhibition by RA, SR 11254 and SR 11389. Likewise, the RAR-gamma antagonist SR 11253 was found to block the ability of SR 11254 and SR 11389 to inhibit SCC growth. These results indicate that modulation of RAR function through the use of either an RAR-gamma-selective antagonist or a pan-RAR dominant negative mutant significantly alters the growth inhibitory response of oral SCCs to retinoids.

Epidermal growth factor signaling pathway influences retinoid metabolism by reduction of retinyl ester hydrolase activities in normal and malignant keratinocytes

The effects of EGFR signaling on retinol metabolism were evaluated in the squamous cell carcinoma cell lines defective in LRAT. In a 24-h incubation, the presence of EGF resulted in a 20-25% increase in retinyl ester accumulation. Assessment of retinol esterification and retinyl ester utilization (hydrolysis), in cell cultures and in cell homogenates, revealed that the increase in retinyl ester mass was the result of a reduction in retinyl ester hydrolysis. When grown in the absence of EGF, the cultures used about 40% of their retinyl esters, compared to about 21% in cultures grown with EGF. This effect of EGF was blocked by an EGF receptor-neutralizing antibody, an EGF receptor tyrosine-kinase inhibitor (PD153035), and a specific inhibitor of MEK kinase influencing the mitogen-activated protein kinase (MAPK) cascade (PD98059). Both transcription and translation were required, suggesting that signaling from the EGF receptor through the MAPK cascade controls the expression of modulators or inhibitors of the retinyl ester hydrolase(s). Thus EGFR signaling can alter the intracellular concentration of retinol by suppressing the access to the retinyl ester pool. Similar EGF effects were seen in cultures of normal keratinocytes.

Modulation of retinoic acid receptor function alters the growth inhibitory response of oral SCC cells to retinoids

Retinoids have been shown to inhibit the growth of many human tumor cells including breast, ovarian and squamous cell carcinoma (SCC). While the exact mechanism of retinoid mediated growth suppression is not known, a role for the retinoic acid receptors (RARs) and retinoid X receptors (RXRs) has been established in both the breast and ovarian tumor cell models. We set out to determine if modulation of RAR/RXR function would alter the retinoid sensitivity of oral SCC cells. We found that the growth of SCC cells was significantly inhibited by treatment with either all-trans-retinoic acid (trans-RA) or the synthetic, conformationally restricted RARgamma selective retinoids MM11254 and MM11389. In order to demonstrate a role for RAR/RXR function in this process, stable oral SCC cell clones constitutively overexpressing the dominant negative mutant RARbeta2 (R269Q) were prepared and shown to exhibit reduced RAR/RXR transcriptional transactivation activity. We found that oral SCC cells exhibiting reduced RAR/RXR function became resistant to growth inhibition by all-trans-RA, MM11254 and MM11389. Likewise, treatment of oral SCC cells with the RARgamma antagonist MM11253 was found to block the ability of MM11254 and MM11389 to inhibit SCC cell growth. Thus, modulation of RAR function through the use of RAR-gamma selective agonists, an RAR-gamma selective antagonist or a pan-RAR dominant negative mutant significantly alters the growth inhibitory response of oral SCC cells to retinoids.

Reduced lecithin:retinol acyl transferase activity in cultured squamous cell carcinoma lines results in increased substrate-driven retinoic acid synthesis

The uptake and metabolism of retinol was compared in squamous cell carcinoma lines, SCC12b and SCC13, and in normal human keratinocytes (NHK). Long chain fatty acid esters of retinol and 3,4-didehydroretinol were the predominant metabolites formed in both cell types. Lesser amounts of unesterified retinol, 3,4-didehydroretinol, and their respective active acid forms were also observed. Despite a qualitatively similar retinoid composition, there were significant quantitative differences between cell types. Most notable was that SCC formed only about one-fourth the retinoid ester as did normal cells. In parallel with this, unesterified retinol and retinoic acid concentrations in SCC were significantly elevated over those in normal cells. This altered pattern of retinoid metabolites in SCC was found to be due to very low lecithin:retinol acyltransferase (LRAT) activity. SCC exhibited less than one-tenth the LRAT activity of normal cells. Acyl-coenzyme A:retinol acyltransferase (ARAT) and retinyl ester hydrolase activities were not different between cell types. Challenging cells with increasing medium retinol concentrations resulted in dose-dependent increases in retinol and retinoic acid within SCC. In contrast, retinol and retinoic acid concentrations in similarly challenged normal cells remained relatively low across a wide retinol concentration range. This was accomplished by the storage of retinol, via LRAT activity, as retinyl ester. Consistent with increased substrate-driven retinoic acid synthesis in SCC, the expression of transglutaminase 1 was suppressed to a greater extent in the SCCs than in NHK, when cells were exposed to equivalent medium concentrations of retinol. The data demonstrate a central role of LRAT in regulating retinoic acid synthesis via its capacity to modulate cellular levels of substrate retinol.

An Eastern Cooperative Oncology Group phase I trial of all-trans-retinoic acid and interferon-alpha: E2Y92

The Eastern Cooperative Oncology Group conducted a Phase I trial to determine the maximally tolerated doses of combination therapy with alpha interferon (IFN-alpha) and all-trans-retinoic acid (tRA). Fifty patients with incurable malignancies received IFN-alpha administered subcutaneously three times weekly, and tRA administered by mouth at bedtime. Doses were escalated between patient groups, starting at tRA dose level of 45 mg/m2 and 3 million units of IFN-alpha. Major, dose-limiting toxicities were attributable to either the tRA (rash, chelitis) or IFN (constitutional symptoms), and were observed only at tRA dose levels of 224 mg/m2 and 291 mg/m2, or 6 million units of IFN-alpha. The maximally tolerated dose level of 172.5 mg/m2 of tRA and 3 million units of IFN-alpha was well-tolerated, with no grade 3 or 4 toxicities attributable to therapy. One patient at the third dose level (75 mg/m2 of tRA and 3 million units of IFN-alpha) developed acute hepatic and renal failure and a metabolic encephalopathy of unclear etiology. We conclude that tRA and IFN-alpha may be safely administered together at the maximally tolerated dose of tRA as a single agent without unexpected side effects. The recommended doses of IFN-alpha and tRA for Phase II trials are 3 million units of IFN-alpha and 172.5 mg/m2 of tRA.

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.

Keratinocyte transglutaminase expression varies in squamous cell carcinomas

Type I transglutaminase (TGase I, keratinocyte or particulate transglutaminase) is a 92-kilodalton (kDa) protein expressed in abundance in cultured keratinocytes and in the hyperproliferative skin disorder psoriasis. To determine the expression of TGase I protein and mRNA, we studied tissue and established squamous carcinoma lines derived from different sources. Immunohistochemistry and Western blotting were used to detect TGase I protein with the B.C1 mouse monoclonal antibody. Only well-differentiated, skin-derived squamous carcinomas stained for TGase I. However, a precocious pattern of expression was seen overlying less-differentiated tumors. Compared to cultured human keratinocytes, squamous cell carcinoma (SCC) had many times less to 7.8 times more TGase I protein, greatest in the two most differentiated tumor lines 14-83 and ME-180. TGase I mRNA levels ranged from 0.010 to 0.00004 pg/microgram total RNA by reverse transcriptase-polymerase chain reaction using an internal standard. Protein expression correlated with mRNA levels in most SCC lines. When a human TGase I promoter was isolated and used to study genomic DNA, SCC1-83 was shown to have unique restriction enzyme fragments, including one indicative of methylation differences, also present within DNA from the KB line. These studies suggest that transcriptional control of TGase I gene expression in squamous carcinomas may be influenced both by cis elements in the promoter and by the degree of tumor squamous differentiation.

Keratin and keratinization

A flood of new knowledge and discoveries in the basic science of keratins and keratinization has appeared in the past several years. This review summarizes this recent information with a focus on the epithelial keratin polypeptides, keratin intermediate filaments, keratohyaline granule proteins, cell envelope formation and cell envelope proteins, "soft" keratinization, true disorders of keratinization (i.e., epidermolysis bullosa simplex and epidermolytic hyperkeratosis), and disease and drug effects on keratinization.

Differential regulation of tissue transglutaminase in rat hepatoma cell lines McA-RH7777 and McA-RH8994: relation to growth rate and cell death

Close correlation between tissue transglutaminase (tTG) induction and growth regulation and/or cell death processes has been suggested in many cell lineages. In this study, the regulation of the tTG levels by various growth and differentiation factors and its relation to growth rate and cell death processes were investigated in two rat hepatoma cell lines, McA-RH7777 and McA-RH8994, using a monoclonal antibody against liver tTG. Transforming growth factor-beta 1 (TGF-beta 1) and retinoic acid (RA) each increased tTG to the level of 8- to 32-fold above that of control cultures in both cell lines after 72-h treatment. Dexamethasone (DEX) induced a 16- to 32-fold of tTG in McA-RH8994 cells while it did not change the enzyme level in McA-RH7777 cells. Simultaneous addition of DEX and RA increased the tTG level to more than 50-fold in McA-RH7777 cells as well as McA-RH8994 cells. Other factors, such as TGF-alpha, hepatocyte growth factor, dimethyl sulfoxide, and protein kinase C activator, did not show significant increases of the tTG levels. Although tTG induction by TGF-beta 1 or DEX appeared to be correlated with their growth suppressive effects, RA increased the tTG level without suppressing the growth rate of hepatoma cells. TGF-beta 1 was also shown to induce cell death in both cell lines. Our results demonstrate that RA and DEX are capable of modulating the TGF-beta 1-induced cell death processes independent of the tTG levels. We present evidence here that tTG induction by itself is not the direct cause of growth suppression and cell death in these hepatoma cells.

Keratinocyte transglutaminase membrane anchorage: analysis of site-directed mutants

Keratinocyte transglutaminase is anchored on the cytosolic side of the plasma membrane by fatty acid thioesterification near the amino terminus, a process which is seen to occur within 30 min of synthesis. The importance of a cluster of five cysteines (residues 47, 48, 50, 51, and 53) where acylation was presumed to occur is now demonstrated by site-directed mutagenesis. Transglutaminase mutants in which the cluster is deleted or the cysteines are all converted to alanine or serine are cytosolic. Partial replacement of the cluster, leaving two contiguous cysteines, is sufficient to confer membrane anchorage, while a single cysteine is only partially effective. As demonstrated with a soluble transglutaminase mutant, membrane anchorage confers susceptibility of the amino-terminal region to phorbol ester-stimulated phosphorylation. Attachment of 105 residues from the transglutaminase amino terminus to involucrin, a highly soluble protein, results in membrane anchorage of the hybrid protein. Attachment of the cysteine cluster alone does not result in membrane attachment of involucrin, but a 32-residue segment containing this cluster is sufficient. Stable transfectants of the human transglutaminase in mouse 3T3 cells are membrane-bound, indicating the fatty acid transacylation is not keratinocyte-specific.

Retinoid regulation of human ectocervical epithelial cell transglutaminase activity and keratin gene expression

Cornified envelope formation, the level of transglutaminase activity and the pattern of cytokeratin gene expression are important biochemical markers of cervical epithelial cell differentiation in vivo. In the present study we examine the effects of retinoid treatment on transglutaminase (TG) activity and keratin gene expression in cultured human ectocervical epithelial cells (ECE cells). All-trans-retinoic acid (RA) and a synthetic retinoid, Ro 13-6298, suppress TG activity by 85-90% with half-maximal inhibition at 0.1 nM Ro 13-6298 or 1 nM RA. In contrast, the predominant circulating retinoid, retinol, does not inhibit TG activity. The level of type I transglutaminase protein, measured using a type I TG-specific antibody, decreases in parallel with the decrease in activity as does the level of the TG RNA transcript. Cytokeratin K16 decreases more than 20-fold while the level of K7, K8 and K19 increase 5 to 10-fold in the presence of 10 nM RA. Studies using cDNAs encoding K5, K13, K16 and K19 indicate that the RNA transcript levels change in parallel with the change in keratin protein production. Thus, all-trans-retinoic acid suppresses ectocervical epithelial cell differentiation in vitro, a result that suggests an in vivo role for retinoids in regulating cervical cell differentiation.

Differential modulation of epidermal keratinization in immortalized (HaCaT) and tumorigenic human skin keratinocytes (HaCaT-ras) by retinoic acid and extracellular Ca2+

The growth and differentiation response to retinoic acid (RA) was studied in the human keratinocyte line HaCaT and tumorigenic clones transfected with c-Ha-ras oncogene (HaCaT-ras). Differentiation (mainly keratin synthesis) was evaluated and correlated to cell proliferation in vitro but also growth behaviour in vivo (tumorigenicity). Comparable to normal keratinocytes, HaCaT cells and ras clones showed increased expression of the epidermal suprabasal keratins K1 and K10 upon RA depletion of the media (delipidized serum), while simple epithelial type keratins K7, K8 and K18 as well as K19 and K13 (typical of internal stratified epithelia) were almost completely suppressed. The cell density-dependent increase of K1 and K10 at intermediate RA levels (as in regular media with untreated serum) was also observed at Ca2+ levels below 0.1 mM, thus being clearly unrelated to stratification, whereas K13 synthesis was Ca(2+)-dependent and initiated with stratification. The effects on keratins were fully reversed by increasing RA concentrations. There was only mild stimulation of proliferation at RA doses (10(-10) to 10(-8) M) not directly corresponding to suppression of keratinization. Thus, the negative RA influence on K1 and K10, opposed to the effect on simple keratins, substantiates the preserved regulatory capacity rendering these cells appropriate models for biological testing. Among the various tumorigenic HaCaT-ras clones highly and moderately differentiating ones could be distinguished, accordingly induction in vitro led to a comparable spectrum of differentiation markers (K1 and K10 appearing early, and filaggrin late) as growth in vivo. These in vitro results demonstrate that, in spite of some differences in RA sensitivity, virtually all clones possess the epidermal differentiation repertoir which is regulated according to the same principles. Finally, this confirms our in vivo data that differentiation potential is not inversely related to the state of transformation or tumorigenicity.

Epidermal growth factor induces terminal differentiation in human epidermoid carcinoma cells

Previous studies have reported that the proliferation of A431 cells, a human squamous cell carcinoma cell line, was stimulated by picomolar epidermal growth factor (EGF) but inhibited by nanomolar EGF. This biphasic dose-response phenomenon is not observed in normal human epithelial cells where nanomolar EGF is usually mitogenic. We have examined the effects of inhibitory and stimulatory concentrations of EGF on the growth and differentiation of A431 cells. In the presence of 100 pM EGF, A431 cells showed a mild increase in growth rate (129% of control) compared to cells grown in the absence of EGF. At 10 nM EGF, growth inhibition to 63% of control was observed. EGF at 10 nM stimulates a twofold increase both in cornified envelope formation and in epidermal transglutaminase activity, suggesting that high concentrations of EGF induce terminal differentiation in A431 cells. Mitogenic concentrations of EGF (100 pM) had no significant effect on these differentiation markers. Chronic exposure of A431 cells to 20 or 50 nM EGF resulted in EGF-resistant A431 variants that are neither growth arrested nor induced to terminally differentiate by 10 nM EGF. Removal of EGF from the growth medium of the EGF-resistant cells resulted in the reversion of these cells back to the wild-type A431 biphasic response pattern within 2 weeks. Our results suggest that A431 cells have the capacity to non-mutatively alter their response pattern to EGF in vitro to maintain themselves in a state of optimum proliferation and away from terminal differentiation.

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.

Antiproliferative effects of free and liposome-encapsulated retinoic acid in a squamous carcinoma model: monolayer cells and multicellular tumor spheroids

Antiproliferative effects of free retinoic acid (RA) and liposome-encapsulated RA (RAlp) were compared in a squamous carcinoma system using both monolayer cells and multicellular tumor spheroids (MTS), an in-vivo-like model with three-dimensional histological structure. Initial studies examined the effect of lipid composition on the efficiency of RA encapsulation and on the subsequent toxicity of RAlp to red blood cells. In 5-day growth assays for monolayer cells, RA and RAlp (1 microM-0.1 nM) produced similar growth inhibition. In 6-day growth assays for MTS, RAlp was shown to have increased effectiveness. Liposomal uptake by the squamous carcinoma cells was examined by culturing monolayers and MTS with fluorescence-tagged liposomes and examining them under fluorescence microscopy between days 1 and 6. Phagocytosed liposomes were present, but their low levels suggested that other mechanisms of drug delivery such as adsorption, fusion or direct lipid transfer probably occurred for RAlp. Histological examination of MTS showed that RA and RAlp produced similar alterations. In this squamous carcinoma system, liposomes are effective in delivering retinoic acid and in producing biological effects in monolayer cells and within the three-dimensional structure of MTS.

Identification of a new squamous cell differentiation marker and its suppression by retinoids

Rabbit tracheobronchial epithelial cells (RbTE) can undergo squamous cell differentiation under defined culture conditions and, therefore, have been used as a model to study the regulation of squamous cell differentiation markers. In the present study, we identified a 20-kDa protein, designated rSQ20, in the serum-free growth medium conditioned by RbTE cells undergoing squamous cell differentiation. The protein was also found in extracts of squamous differentiated cells. rSQ20 was labeled by cells incubated with [35S]methionine but not with [3H]glucosamine, suggesting that it is not a glycoprotein. Undifferentiated cells did not produce this protein. rSQ20 was detected in the conditioned medium of RbTE cells after they reached a confluent and growth-arrested state, and thereafter its level increased markedly and concurrently with an increase in type I (epidermal) transglutaminase, an established marker of squamous cell differentiation. rSQ20 found in concentrated conditioned medium of squamous differentiated RbTE cells was eluted from a gel filtration column as a protein of 20 kDa, similar to that found by gel electrophoresis under denaturing conditions, suggesting that it is not a multimeric protein. A protein with an apparent molecular weight of 16 kDa (rSQ16), probably the product of partial proteolysis of rSQ20, was often found in various amounts in the conditioned medium of differentiated RbTE cells. beta-All-trans retinoic acid and other vitamin A analogues (retinoids), which suppress squamous cell differentiation, inhibited the expression of rSQ20 in RbTE cells. RbTE cells immortalized by transfection with SV40 large T antigen as well as malignantly transformed derivatives obtained from the immortalized cells by further transfection with v-Ha-ras secreted SQ20 and SQ16 when grown to high cell densities although their squamous differentiation was impaired. An analogous protein with an apparent molecular weight of 16 kDa, designated hSQ16, was detected in the medium of differentiated normal human bronchial epithelial (NHBE) cells and normal human epidermal keratinocytes (NHEK). No such protein could be detected in the medium in which undifferentiated NHBE or NHEK cells were grown. These results suggest that rSQ20 and hSQ16 are new markers of squamous cell differentiation.

Expression of loricrin is negatively controlled by retinoic acid in human epidermis reconstructed in vitro

In epidermis, the last steps of keratinocyte differentiation are characterized by the covalent cross-linking of cornified envelope precursors such as involucrin and loricrin, a hydrophobic protein recently described in mouse and human epidermis. In situ hybridization of normal human skin sections with a human loricrin cRNA probe and immunolabeling with an antiserum directed against a synthetic peptide corresponding to the carboxyterminus of human loricrin revealed the presence of loricrin transcripts and protein in the granular layers of epidermis. In human epidermis reconstructed in vitro by growing keratinocytes on dermal equivalents, loricrin and loricrin mRNAs were also restricted to granular cells, but their amounts seemed higher than in epidermis from skin biopsies. The reactivities for both loricrin and loricrin mRNAs were abolished by a treatment of the cultures with a retinoic acid concentration (10(-6) M) provoking a complete inhibition of terminal epidermal differentiation (parakeratosis). Thus, the regulation of loricrin synthesis is different from that of another envelope precursor, involucrin, which does not seem to be significantly modulated by retinoic acid. Together with the well-documented inhibition of epidermal transglutaminase by retinoic acid, our results provide a molecular basis for the inhibition of cornified envelope formation by retinoic acid.

Biology of cutaneous squamous cell carcinoma

Nonmelanoma skin cancer is the leading cause of cancer in the United States. Cutaneous squamous cell carcinoma is second only to basal cell carcinoma in prevalence and its incidence is increasing. The biology of squamous cell carcinoma is reviewed under the broad areas of etiology, immunobiology, biochemistry, metastatic potential, and therapy, with emphasis on prevention, diagnosis, and management.

Short term retinol treatment in vitro induces stable transdifferentiation of chick epidermal cells into mucus-secreting cells

Epidermal mucous metaplasia of cultured skin can be induced by treatment with excess retinol for several days (Fell 1957). In the induction of mucous metaplasia, retinol primarily affects the dermal cells and retinol-pretreated dermis can alter epidermal differentiation towards secretory epithelium (Obinata et al. 1987). In this work, we found that mucous metaplasia could be induced by culturing 13-day-old chick embryonic tarsometatarsal skin in medium containing retinol (20 μM) for only 8-24 h, followed by culture in a chemically defined medium (BGJb) without retinol or serum for 6 days. The application of cycloheximide together with retinol during the first 8 h of culture inhibited epidermal mucous metaplasia during subsequent culture for 6 days in BGJb, indicating that induction of a signal(s) in the dermis by excess retinol requires protein synthesis. However, the presence of 20 nM hydrocortisone (Takata et al. 1981) throughout the culture period did not inhibit retinol-induced epidermal mucous metaplasia of the epidermis. This indicates that a brief treatment of the skin with excess retinol determines the direction of epithelial differentiation toward secretory epithelium; this is a simpler in vitro system for the induction of epidermal mucous metaplasia than those established before.

Comparison of the rate of uptake and biologic effects of retinol added to human keratinocytes either directly to the culture medium or bound to serum retinol-binding protein

Retinol circulates in the plasma bound to retinol-binding protein (RBP), but the mechanism by which retinol is transferred from RBP to target cells is not known. To study retinol delivery, human keratinocytes (HKc) were incubated with [3H]retinol added directly to the culture medium or bound to RBP and the uptake of [3H]retinol was determined at various times. During the first hour of incubation, the rate of [3H]retinol accumulation by HKc was about 40 times greater when the vitamin was added directly to the media rather than bound to RBP. Although maximal uptake of [3H]retinol added directly to the culture medium occurred at 3 h, the uptake of [3H]retinol from RBP was linear with time for at least 72 h. By 57 h, cell-associated [3H]retinol was the same whether it was added directly to the culture medium or bound to RBP. Excess unlabeled retinol or pretreatment of HKc with retinol had no effect on the uptake of [3H]retinol added directly to the culture medium or bound to RBP. Apo- but not holo-RBP was capable of competing with HKc for the uptake of [3H]retinol from RBP. No specific or saturable binding of 125I-labeled RBP to HKc cultured in the absence or the presence of retinol was found. The dose response of retinol inhibition of cholesterol sulfate synthesis and phorbol ester-induced ornithine decarboxylase activity or retinol modulation of keratin expression was the same whether the retinol was delivered to HKc bound to RBP or added directly to the medium. Our data support a mechanism for retinol delivery from RBP to HKc that does not involve cell-surface RBP receptors but instead suggest that the vitamin is first slowly released from RBP and then becomes cell-associated from the aqueous phase. This mechanism is consistent with the finding that HKc respond identically to retinol whether or not it is delivered to them bound to RBP.

Retinoic acid suppression of squamous differentiation in human head-and-neck squamous carcinoma cells

Retinoids (vitamin A analogues) inhibit the squamous differentiation of normal and malignant epithelial cells. This study investigated the ability of the head-and-neck squamous-cell carcinoma (HNSCC) cell line 1483 to undergo squamous differentiation in the absence and presence of beta-all-trans retinoic acid (RA). The growth of these cells in culture is accompanied by an increase in keratinocyte transglutaminase, involucrin and keratin KI, 3 established markers of squamous cell differentiation. Higher levels of these differentiation markers were detected in cells cultured in delipidized serum (DLS), from which endogenous retinoids have been extracted, than in cells cultured in fetal bovine serum (FBS), which contains retinoids. Treatment with I microM RA decreased the levels of the various differentiation markers in cells cultured in either FBS or DLS as revealed by immunofluorescent labelling of permeabilized cells and by immunoblotting of cell extracts using specific monoclonal or polyclonal antibodies. The cells' ability to cross-link proteins to form envelopes under the plasma membrane was stimulated in the presence of calcium ionophore but inhibited by RA. These results indicate that the malignant 1,483 HNSCC cells recapitulate the main characteristics of normal squamous-cell differentiation in culture and that RA suppresses this differentiation as it does in normal keratinizing epithelial cells.

Transcription of the human loricrin gene in vitro is induced by calcium and cell density and suppressed by retinoic acid

We have previously shown that loricrin is a major component of the cornified cell envelope (CE) expressed late in epidermal differentiation in the granular layers of normal skin. Normal human keratinocytes were cultured under various conditions and loricrin mRNA levels were assessed at various time points. Only Ca++ concentrations above 0.1 mM Ca++ were permissive for the expression of lori-crin mRNA. Maximal mRNA levels were found at 0.35 mM Ca++ and a critical cell density appeared to be required for optimal accumulation of loricrin transcripts. Retinoic acid (RA) at 10(-7) to 10(-9) M completely blocked Ca+(+)-induced loricrin mRNA synthesis when applied simultaneously. Furthermore, addition of RA to cultures already exposed to higher Ca++ levels resulted in the complete loss of loricrin mRNA within 48-72 h. So far, no other components of the CE have been shown to be suppressed by RA. However, similar patterns of expression were reported for filaggrin, a matrix protein also expressed late in epidermal differentiation. Therefore, we compared the mRNA levels of loricrin and filaggrin and found them to change in parallel in response to the various culture conditions. These results suggest that Ca++, cell density, and RA are crucial regulators of loricrin expression in vitro and that the transcriptional control of loricrin and filaggrin expression in the epidermis are closely coordinated.

Phorbol ester-stimulated phosphorylation of keratinocyte transglutaminase in the membrane anchorage region

The membrane-bound transglutaminase of cultured keratinocytes became radioactively labelled upon addition of [32P]Pi to the medium. Transglutaminase phosphorylation was also demonstrable using particulate material isolated from cell homogenates. Compatible with mediation of the labelling by protein kinase C, the degree of phosphorylation in intact cells was stimulated approx. 5-fold in 4 h on treatment with the tumour-promoting phorbol ester phorbol 12-myristate 13-acetate, but not by phorbol. The extent of labelling was virtually unaffected by cycloheximide inhibition of protein synthesis, indicating that it arose primarily through turnover of phosphate in the membrane-bound enzyme. Phosphoamino acid analysis detected labelling only of serine residues. Most of the label was removed by trypsin release of the enzyme from the particulate fraction of cell homogenates, which deletes a membrane anchorage region of approximately 10 kDa. Upon trypsin treatment of the enzyme after immunoprecipitation, the phosphate label was recovered in soluble peptide material with a size of several thousand Da or less. Indicative of fragmentation of the membrane anchorage region, this material was separable by h.p.l.c. into two equally labelled peptides. Moreover, when the enzyme was labelled with [3H]palmitate or [3H]myristate, the fatty-acid-labelled peptide material required non-ionic detergent for solubilization and was separable from the phosphate-labelled material by gel filtration. Phorbol ester treatment of cultured keratinocytes in high- or low- Ca2(+)-containing medium was not accompanied by an appreciable protein-synthesis-independent change in transglutaminase activity. Independent of possible alteration of the intrinsic catalytic activity of the enzyme, phosphorylation may well modulate its interaction with substrate proteins, a potential site for physiological regulation.

Effects of beta-all-trans retinoic acid on growth, proliferation, and cell death in a multicellular tumor spheroid model for squamous carcinomas

The growth of multicellular tumor spheroids, MTSs, from squamous carcinoma line MDA 886Ln was inhibited by beta-all-trans retinoic acid (RA). Inhibition occurred within 3 to 5 days of treatment, and MTS size then remained static for up to 2 weeks. Although their growth stopped, 10-day-treated MTSs incorporated [3H]thymidine into trichloroacetic acid-precipitable material, and the [3H]thymidine labeling index, determined by autoradiography, was equivalent between control and RA-treated MTSs. Bivariate flow cytometric analysis of bromodeoxyuridine-labeled MTSs showed equivalent S phase progression of labeled cells over an 8-hour chase. MTS growth stasis was not related to RA-induced cell cycle effects. Monitoring of MTSs for cell sloughing showed no significant cell shedding that could account for stasis. Quantitation of cell number and DNA content per MTS showed an RA-induced decrease. This was confirmed by histological analysis, which demonstrated the temporal appearance of acellular areas. MTS growth statis is thus related to an RA-induced cell loss in this MTS model for squamous carcinomas.

Epidermal G1-chalone and transforming growth factor-beta are two different endogenous inhibitors of epidermal cell proliferation

Epidermal G1-chalone and transforming growth factor-beta (TGF beta), two endogenous inhibitors of epidermal cell proliferation, were compared with regard to several effects on epidermis in vivo and in vitro. Both factors inhibited DNA labeling in a rat tongue epithelial cell line, with similar kinetics and half-maximal effects at approximately 1 pg/ml (enriched chalone) and 1 ng/ml (TGF beta). For primary neonatal mouse keratinocytes, TGF beta was found to be a rather strong inhibitor of cell proliferation, whereas chalone showed only a weak effect on cells grown in medium containing 1.2 mM Ca2+ and no effect at all in the presence of 0.06 mM Ca2+. Vice versa, upon i.p. injection, only chalone was able to inhibit mouse epidermal DNA synthesis in vivo, whereas TGF beta had no effect at all. A moderate increase of transglutaminase activity in neonatal primary mouse keratinocytes was induced by both factors at concentrations of about 300 pg TGF beta/ml and 10 pg chalone fraction/ml. Chalone did not compete with [125I]TGF beta for specific binding sites on primary murine keratinocytes. A polyclonal "chalone antiserum" did not interact with TGF beta, and a neutralizing TGF beta antibody that inhibited the effect of TGF beta on cell proliferation could not block the inhibitory effect of chalone on RTE2 cells. In contrast to TGF beta, epidermal G1-chalone did not induce proliferation of NIH-3T3 cells. These results indicate that epidermal G1-chalone and TGF beta are two different inhibitors of epidermal cell proliferation.

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.

Chemoprevention of upper aerodigestive tract cancers: a report of the third Upper Aerodigestive Cancer Task Force workshop

The National Cancer Institute Organ Systems Program-sponsored Upper Aerodigestive Cancer Task Force workshops are specifically designed to enhance interactions between basic science and clinical investigators and between academic institutions and the community, and ultimately will contribute to more expeditious clinical advances. The third workshop in this series focused on the rapidly expanding area of chemoprevention of upper aerodigestive epithelial cancers. The first two sessions were devoted to discussion of in vitro and animal-model data documenting the multistep process of squamous differentiation and carcinogenesis, associated molecular and biochemical alterations, and modulation by chemopreventive agents. Animal-model studies have identified several promising chemopreventive agents and synergistic combinations for clinical trial. The last two sessions reviewed nutritional epidemiology, major methodologic issues of large intervention studies, and the novel concept of biologic markers as intermediate endpoints for chemoprevention trials.

Retinoic acid controls expression of epidermal transglutaminase at the pre-translational level

Human epidermal keratinocytes were cultured until sub-confluence in low Ca2+ (0.15 mM) serum-free synthetic MCDB 153 medium. Raising the Ca2+ concentration to 1.15 mM caused an increase in envelope competence as well as plasma membrane associated transglutaminase (TGm) activity. This increase was not observed when the high Ca2+ medium contained retinoic acid. Immunofluorescence studies as well as immunoblotting with the TGm-specific monoclonal antibody B.C1 revealed that retinoic acid inhibits expression of TGm. Isolation and in vitro translation of mRNA with subsequent immunoprecipitation showed that retinoic acid inhibits TGm expression at the pretranslational level.

Modulation of growth, differentiation and glycoprotein synthesis by beta-all-trans retinoic acid in a multicellular tumor spheroid model for squamous carcinoma of the head and neck

Cell line MDA 886Ln was established from a laryngeal lymph node metastasis. When grown as a multicellular tumor spheroid (MTS), it exhibits squamous differentiation. We studied the effects of beta-all-trans retinoic acid (RA) on the growth, differentiation and glycoprotein content of this MTS model for squamous carcinomas of the head and neck. The growth of MTSs was inhibited in a dose-dependent manner by 10(-6) to 10(-10) M RA. Growth inhibition occurred between 3 and 5 days of RA treatment (10(-6)M). Immunohistochemical and electrophoretic analyses revealed that RA suppressed the morphological markers of squamous differentiation (squames), involucrin expression, and keratin expression. Gly-coprotein expression was examined by metabolic labelling using 3H-glucosamine, in situ labelling of polyacrylamide gels with 125I-labelled wheat-germ agglutinin (WGA), localization of fluorescein isothionate-WGA in frozen sections, and determination of sialyltransferase activity. Treatment using 10(-6) M RA altered glycoprotein expression both biochemically and morphologically, and WGA was shown to bind preferentially to sialic acid residues. The sensitivity of this MTS model to RA treatment and its ability to be analyzed through morphological, immunohistochemical and biochemical techniques suggest that it will prove useful in studying the relationships between growth, differentiation and RA-induced alterations in squamous carcinomas.

Uncoupling of the calcium-induced terminal differentiation and the activation of membrane-associated transglutaminase in murine keratinocytes by type-beta transforming growth factor

Calcium is an important regulator of terminal differentiation of cultured epidermal cells. In order to investigate the relationship between the termination of proliferative activity and the process of keratinization, we studied the time course of events induced by a sudden increase of extracellular calcium (calcium-switch) in cultures of established murine skin keratinocytes (BALB/c MK-1). These cells displayed density-dependent growth arrest without undergoing terminal differentiation in the presence of serum- and mitogen-free medium with a calcium concentration less than 0.10 mM. The calcium-switch alone was sufficient to induce a dose-dependent burst of DNA synthesis, which was followed by a state in which the cells became progressively refractory to mitogenic stimulation with epidermal growth factor. Treatment of cultures with type beta transforming growth factor during the first 6- to 10 h following the calcium-switch completely eliminated the initial burst of DNA synthesis as well as the terminal differentiation in response to calcium. On the other hand, the calcium-switch also caused the induction of a four- to fivefold increase of the activity of the membrane-associated form of transglutaminase that is required for keratinization, which was not affected by the presence of type beta transforming growth factor. These observations suggest that type beta transforming growth factor regulates the calcium-induced terminal cell division independently of the induction of phenotypic markers of keratinization, such as transglutaminase.

Retinoic acid improves epidermal morphogenesis

Hyper- and hypovitaminosis A both provoke epithelial pathologies in animals and humans. This suggests that a critical level of retinoic acid (RA) is required in vivo for the maintenance of normal architecture and function of these tissues. However, no beneficial, but only adverse effects of RA on epithelia have been so far observed in vitro. For instance, addition of RA to keratinocyte cultures has been shown to inhibit epidermal differentiation while this process is stimulated by serum delipidization, which reduces RA concentration in the medium. Assuming that the previous failure to demonstrate beneficial effects of RA on the epidermal phenotype in vitro was due to culture conditions too far from the in vivo conditions we decided to reevaluate the effect of RA in a culture system optimized for epidermal morphogenesis: the "emerged dermal equivalent." When human keratinocytes were grown in such a system with total fetal calf serum, the resulting epithelium was very similar to normal epidermis. But when delipidized serum was used, the epithelium was abnormal in the direction of excessive maturation (hyperkeratosis). When physiological concentrations of RA (10(-9) and 10(-8) M) were added to the delipidized serum supplement, a normal architecture (orthokeratosis) was restored. However, as classically described in the literature, higher RA concentrations (greater than 10(-7) M) reduced epidermal maturation and produced parakeratosis. Thus, although it is unquestionable that RA reduces the synthesis of epidermal-specific differentiation markers, an optimal epidermal morphogenesis seems to be achieved only in the presence of a critical RA concentration.

Modulation of 3-methylcholanthrene toxicity in cultured neoplastic keratinocytes by glucocorticoids and retinoids is not accounted for by macromolecular adduct formation

3-Methylcholanthrene (3-MC) greatly inhibits the growth of two lines of human squamous carcinoma cells, SCC-9 and SCC-12B2. Exposure of the cells to 2,3,7,8-tetrachlorodibenzo-p-dioxin alone was much less effective and, in the presence of 3-MC, did not alter the sensitivity (EC50 = 0.3 microM) or extent of growth inhibition by the latter. The degree of 3-MC-mediated inhibition, however, was markedly alleviated by inclusion of retinoic acid (EC50 greater than or equal to 0.7 microM) and hydrocortisone (EC50 = 40 nM) or dexamethasone (EC50 = 3 nM) in the culture medium. These physiological effectors, which are known to have opposing actions on keratinocyte character in SCC cells, did not significantly alter either aryl hydrocarbon hydroxylase activity or macromolecular adduct formation. Further analysis of the cellular responses indicated that hydrocortisone and, in some experiments, retinoids increased the growth rate in 3-MC-exposed cultures, while 3-MC increased the saturation density in retinoic acid-exposed cultures, an example of interference with a physiological response of the cells. These results indicate that alteration of the differentiated state, regardless of the direction of the change, can alter the sensitivity of the cells to toxic stimuli. Further investigation of the bases of such toxic responses and their modulation by the microenvironment may enhance our understanding of the target cell specificity of polycyclic aromatic hydrocarbons.

Coordination of keratinocyte programming in human SCC-13 squamous carcinoma and normal epidermal cells

Exploiting the sensitivity of neoplastic keratinocytes to physiological effectors, this work analyzes the degree of coordination among differentiation markers in the established human epidermal squamous carcinoma cell line SCC-13 in comparison to normal human epidermal cells. This analysis showed that overall keratin content was modulated substantially and in parallel with particulate transglutaminase activity in response to variation of calcium, retinoic acid, and hydrocortisone concentrations in the medium. The changes in keratin expression were evident primarily in the striking stimulation by hydrocortisone or calcium and the virtual suppression by retinoic acid of species in the 56-58 kd region, which have not previously been reported subject to such physiological modulation. In contrast, involucrin levels were coordinated only to a limited degree with particulate transglutaminase activity and keratin content. The very low involucrin levels observed in low calcium medium were increased 5- to 10-fold in high calcium medium. However, they were also increased 5- to 30-fold in low calcium medium by retinoic acid, a clear example of uncoupling. Activities of the tissue transglutaminase were altered considerably by the various culture conditions but were not obviously coordinated to keratinocyte markers. In normal epidermal cells, the suppressive effect of retinoic acid was much more evident with particulate transglutaminase than involucrin levels. While calcium had a large stimulatory effect on both markers, hydrocortisone had little or no influence. These results emphasize the potential importance of quantitative analysis of differentiation markers for resolving the contribution of physiological elements in coordination of cellular programming.

Opposite effects of EGF on involucrin accumulation of A431 keratinocytes and a variant which is not growth-arrested by EGF

The A431 cell line is composed of malignant keratinocytes derived from a vulval epidermoïd carcinoma. These cells have the peculiarity to stop their proliferation when they are treated with physiological concentrations of EGF, which is a mitogen for normal keratinocytes. We reported earlier that EGF induces involucrin accumulation in A431 cells and proposed that the arrest of proliferation triggers differentiation as shown by the induction of this cornified envelope precursor protein. To test this hypothesis, we compared the A431 subclone 15, which is not growth arrested by EGF-treatment, to the parental A431 cells. We found indeed that EGF reduces the involucrin content of clone 15 cells in a dose dependent manner. These opposite effects of EGF on the expression of terminal differentiation marker involucrin in A431 and A431 clone 15 keratinocytes were observed in defined medium as well as in presence of fetal calf serum. Nevertheless, when growth of parental A431 cells was inhibited by treatment with TGF-beta or simply when cultures reached confluency, no involucrin accumulation was observed. Therefore growth arrest per se is not directly correlated with the induction of differentiation.

Characterization of the calcium sensitivity of differentiation in SCC-13 human squamous carcinoma cells

The sensitivity to calcium of the human squamous carcinoma cell line, SCC-13, was demonstrated and characterized. Cultures grown to confluence in the presence of 0.2 to 2 mM calcium had approximately 10-fold higher levels of particulate transglutaminase activity and envelope competence than those grown in low calcium (0.025 to 0.05 mM) medium. Raising the calcium from 0.025 to 1.8 mM induced expression of this enzyme and of competence over the course of a week. Conversely, for cultures grown to confluence in 1.8 mM calcium, subsequent reduction of calcium to 0.025 mM resulted in a substantial decline in transglutaminase over a similar time period. Immunoprecipitable transglutaminase was clearly identifiable in cultures grown in 1.8 mM calcium-containing medium but not in those grown in low calcium medium or in the presence of retinoic acid, suggestive of regulation at the level of mRNA accumulation or translation rather than posttranslational modification.

The new basement membrane antigen recognized by the monoclonal antibody GB3 is a large size glycoprotein: modulation of its expression by retinoic acid

Further biochemical investigations on the hemidesmosome-associated epidermal basement membrane component recognized by the monoclonal antibody GB3 are presented in this study. We previously found that the expression of this constituent is impaired in a severe genodermatosis termed lethal junctional epidermolysis bullosa. We demonstrate now that this factor is a very large glycoprotein (apparent molecular weight, 600 kDa) made up of polypeptides in the range of 93.5 to 150 kDa, and containing N-linked oligosaccharide chains. Both endo-beta-N-acetylglucosaminidases and neuraminidase hydrolysis, as well as concanavalin A binding experiments were performed on the GB3 radioimmunoprecipitated polypeptides from cultured human keratinocytes. They showed that the antigen subunits probably bear both 'high-mannose' and 'complex' type glycosidic chains. The chronic exposure of cultured human keratinocytes to retinoic acid (10(-8) to 10(-6) M) resulted in no apparent changes in the overall bulk of these glycosidic chains, but a dose-dependent increase of synthesis and secretion of the antigen was observed. A relative induction factor of 4 was obtained in cultures treated with 10(-6) M retinoic acid. This induction was also observed morphologically by indirect immunofluorescence at the basement membrane zone from cultured human keratinocytes grown on dead de-epidermized dermis. These results further emphasize the influence of glycoproteins in cell-cell and cell-substratum attachment. Furthermore, the ability to modulate this antigen may be relevant for the understanding of the molecular defect involved in lethal junctional epidermolysis bullosa.

Differentiation of normal and tumoral human keratinocytes cultured on dermis: reconstruction of either normal or tumoral architecture

Normal human keratinocytes isolated from skin and squamous carcinoma cells established from a human tumor (TR146 cell line) both exhibit limited morphologic differentiation when they are grown on conventional plastic dishes. However, when they are seeded on human de-epidermized dermis and cultured at the air-liquid interface, they are able to reform an epithelium having the morphology of the tissue of origin (i.e. skin or squamous carcinoma). The distribution in such reconstructed tissues of differentiation markers such as bullous pemphigoid antigen, 67K keratin, involucrin, membrane-bound transglutaminase, and filaggrin was very similar to their distribution in normal skin and squamous carcinoma specimens, respectively. The degree of differentiation is for both cell types extremely sensitive to culture conditions such as retinoic acid concentration, emersion of the cultures, etc. These results show that subcultured normal or tumoral keratinocytes are able to recover their specific morphogenetic potential when cultured in an environment close to their in vivo situation.

Retinoic acid-induced modulation of rat liver transglutaminase and total polyamines in vivo

The effect of a single intraperitoneal injection of retinoic acid on liver transglutaminase (EC 2.3.2.13) activity and total putrescine, spermidine and spermine was studied. The results demonstrate that: (1) transglutaminase activity is increased over control values as early as 4-6 h after treatment, reaching a maximum (2-fold increase) at 12 h and returning to control values at 36 h; (2) the retinoic acid-induced form of enzyme is the soluble tissue transglutaminase; (3) actinomycin D treatment does not completely inhibit the early (6 h) increase of activity, while suppressing that at 12 h; (4) the immunoassay of the soluble transglutaminase shows that, 6 h after treatment, there is no increase in the protein, whereas at 12 and 24 h a significant increase is observed; (5) putrescine, but not spermidine and spermine, increases (5-7-fold) 6 and 18 h after the retinoic acid treatment. The possibility also that the expression of soluble transglutaminase is modulated in vivo by retinoic acid and the relationship to polyamine levels are discussed.

Reinitiation of DNA synthesis in quiescent mouse keratinocytes; regulation by polypeptide hormones, cholera toxin, dexamethasone, and retinoic acid

Cloned mouse keratinocytes (MK-1 cells) display density-dependent growth arrest when reaching confluency in a serum-free medium with a calcium concentration less than 0.1 mM, supplemented only with insulin and transferrin. In this quiescent state, greater than 95% of the cell population is in the Go/1 phase of the cell cycle. Treatment of quiescent MK-1 cells with 1 to 10 ng/ml epidermal growth factor (EGF) resulted in a sharp burst of DNA synthetic activity. Both insulin and cholera toxin potentiated the mitogenic effect of EGF, but neither agent was necessary or sufficient to induce thymidine incorporation into DNA. Dexamethasone abolished the effect of insulin, but not the mitogenic effect of EGF alone. In contrast, retinoic acid (RA) did not possess any mitogenic effect for quiescent MK-1 cells, nor did it modulate the actions of EGF or dexamethasone. A number of commercially available crude extracts of bovine brain and pituitary were also capable of initiating DNA synthesis in resting MK-1 cells. Finally, transforming growth factor type beta (TGF beta) proved to be a potent inhibitor of the mitogen-induced DNA synthesis in MK-1 cells (IC50:10 pM). This defined culture system is eminently suited to study the regulation of DNA synthesis of epidermal cells. In addition, it can be used as a sensitive bioassay for the detection of epidermal mitogens, as well as inhibitors of DNA synthesis such as TGF beta.

Plasma membrane transglutaminase and cytosolic transglutaminase form distinct envelope-like structures in transformed human keratinocytes

Cross-linked envelope formation in the transformed human keratinocyte line SV-K14 requires treatment of the cells with a Ca2+ ionophore. Depending on the culture conditions, different extracellular Ca2+ concentrations are necessary to trigger the process which is catalyzed by the enzyme transglutaminase. Confluent cells grown in the presence of serum express only the cytosoluble form of the enzyme and need 5 mM Ca2+ for optimum protein cross-linking, whereas serum-starved cells which additionally contain the plasma membrane associated form of the enzyme require only 1 mM Ca2+. The envelope-like structures thus synthesized are morphologically and biochemically distinct.

Differential effects of retinoic acid on the in vitro growth and cell-surface glycoconjugates of 2 human head and neck squamous-cell carcinomas

As a part of an assessment of the potential use of retinoids in preventive and adjuvant treatment of HNSCC, we examined the effects of beta-all-trans retinoic acid (RA) on the growth and cell-surface glycoconjugates of 2 HNSCC cell lines. These lines, designated 1483 and 183A, were established from an untreated patient with a well-differentiated SCC of the retromolar trigone and one with a poorly differentiated SCC of the tonsil. Whereas the 1483 cells were sensitive to RA in that their anchorage-dependent growth, their colony growth on solid substratum, and their anchorage-independent growth in semi-solid agarose gel were all inhibited in a dose-dependent fashion by RA concentrations in the range between 1 nM and 10 microM, the 183A cells were not inhibited by RA. Their anchorage-dependent growth and colony formation were stimulated by RA, whereas their anchorage-dependent colony formation was not altered. Cell-surface glycoconjugates were modulated by RA in the sensitive 1483 cells but not in the 183A cells. Treatment of the 1483 cells resulted in a large increase in the cell-surface labelling of high-molecular-weight (Mr greater than 400,000) galactoglycoconjugates and sialoglycoconjugates, as well as an Mr 280,000 sialoglycoconjugate. Glycoconjugates with similar electrophoretic mobilities in polyacrylamide gels were labelled intensely on the surface of the 183A cells even before RA treatment and only minor changes were noticed in their labelling after treatment. These results demonstrate that RA can exert different effects on different HNSCC lines, and suggest that correlations might exist between responsiveness to RA and the stage of differentiation of the HNSCC, and between modulation of cell growth and enhancement of cell-surface glycoconjugate glycosylation by RA.

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.

Effect of retinoic acid on cornified envelope formation: difference between spontaneous envelope formation in vivo or in vitro and expression of envelope competence

A large number of cross-linked envelopes form spontaneously when cell lines derived from chemically induced mouse skin papillomas are cultured in medium containing 1.2 mM calcium. This phenomenon is associated with high activity of the cross-linking enzyme, epidermal transglutaminase (TGase). The influence of retinoic acid (RA) on envelope formation was studied in detail in a papilloma cell line, PE. Retinoic acid (3 microM) completely blocked cornified envelope (CE) production but reduced TGase activity only 50%. A rabbit antiserum was produced against sonicated CEs isolated from newborn mouse skin. On Western blots of epidermal extracts, diffuse staining was observed for particulate proteins of suprabasal, but not basal, cells and similar immunoreactive material was absent from the cytosolic fraction of both cell layers. The antibody also recognized particulate proteins from PE cells induced to differentiate by calcium, but not from cells grown in the presence of high calcium and RA. The antiserum appears to recognize partially cross-linked CE precursor proteins judging by the diffuse staining, the molecular weight range of the proteins stained, and their origin in the particulate cellular fraction. Cross-linked envelopes could be induced in RA-treated PE cells by permeabilization with 0.75 M NaCl or 50 micrograms/ml A23187. However, this treatment failed to cause the appearance of proteins recognized by the antiserum. Preincubation of the antiserum with purified fragments of CEs from newborn mouse epidermis, but not with cross-linked envelopes from permeabilized, RA-treated PE cells, removed immunoreactivity. These results indicate that the cross-linked envelopes formed in RA-treated cells after permeabilization lack a set of proteins contained in CEs from stratum corneum and may even be composed of different proteins. Retinoic acid appears to prevent CE formation in part by inhibiting activation of epidermal TGase but in addition by influencing the synthesis of precursor proteins.