Localization and expression of cornifin-alpha/SPRR1 in mouse epidermis, anagen hair follicles, and skin neoplasms

Comparison of urine proteomes from tumor-bearing mice with those from tumor-resected mice

Objective

This study aimed to address on the most important concern of surgeons-whether to completely resect tumor. Urine can indicate early changes associated with physiological or pathophysiological processes. Based on these ideas, we conducted experiments to explore changes in the urine proteome between tumor-bearing mice and tumor-resected mice.

Method

The tumor-bearing mouse model was established with MC38 mouse colon cancer cells, and the mice were divided into the control group, tumor-resected group, and tumor-bearing group. Urine was collected 7 and 30 days after tumor resection. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was used to identify the urine proteome, which was analyzed for differentially expressed proteins and functional annotation.

Results

(1) Seven days after tumor resection, 20 differentially expressed proteins distinguished the tumor-resected group and the tumor-bearing group. The identified biological processes included circadian rhythm, Notch signaling pathway, leukocyte cell-cell adhesion, and heterophilic cell-cell adhesion via plasma membrane cell adhesion molecules. (2) Thirty days after tumor resection, 33 differentially expressed proteins distinguished the tumor-resected group and the tumor-bearing group. The identified biological processes included cell adhesion; complement activation, the alternative pathway; the immune system process; and angiogenesis. (3) The difference in the urine proteome between the tumor-resected group and the healthy control group was smaller 30 days after tumor resection.

Conclusion

Changes in the urinary proteome can reflect the complete resection of MC38 tumors.

Keratin 79 identifies a novel population of migratory epithelial cells that initiates hair canal morphogenesis and regeneration

The formation of epithelial tubes underlies the development of diverse organs. In the skin, hair follicles resemble tube-like structures with lumens that are generated through poorly understood cellular rearrangements. Here, we show that creation of the hair follicle lumen is mediated by early outward movement of keratinocytes from within the cores of developing hair buds. These migratory keratinocytes express keratin 79 (K79) and stream out of the hair germ and into the epidermis prior to lumen formation in the embryo. Remarkably, this process is recapitulated during hair regeneration in the adult mouse, when K79(+) cells migrate out of the reactivated secondary hair germ prior to formation of a new hair canal. During homeostasis, K79(+) cells line the hair follicle infundibulum, a domain we show to be multilayered, biochemically distinct and maintained by Lrig1(+) stem cell-derived progeny. Upward movement of these cells sustains the infundibulum, while perturbation of this domain during acne progression is often accompanied by loss of K79. Our findings uncover previously unappreciated long-distance cell movements throughout the life cycle of the hair follicle, and suggest a novel mechanism by which the follicle generates its hollow core through outward cell migration.

Regulatory role for Krüppel-like zinc-finger protein Gli-similar 1 (Glis1) in PMA-treated and psoriatic epidermis

In this study, we analyze the expression and potential function of the Krüppel-like zinc-finger protein Gli-similar protein 1 (Glis1) in normal and inflammatory skin and in the differentiation of epidermal keratinocytes. Glis1 mRNA is not expressed in normal human epidermis, but is significantly induced in psoriatic epidermis and in mouse skin upon treatment with the tumor promoter phorbol-12-myristate-13-acetate (PMA). The expression of Glis1 is restricted to the suprabasal layers. These observations suggest that Glis1 expression is associated with hyperplastic, inflammatory epidermis. Consistent with these findings, Glis1 mRNA is not expressed in undifferentiated or differentiated normal human epidermal keratinocytes (NHEK) in culture, but is dramatically induced after the addition of PMA or interferon gamma. A similar induction of Glis1 mRNA by PMA treatment was observed in the immortalized epidermal keratinocyte cell line NHEK-HPV, whereas PMA did not induce Glis1 in HaCaT cells or in several squamous cell carcinoma cell lines. To obtain insight into its function, Glis1 and a C-terminal deletion mutant Glis1DeltaC were expressed in NHEK-HPV cells and changes in epidermal differentiation and gene expression examined. Microarray analysis revealed that Glis1DeltaC promoted PMA-induced epidermal differentiation, as indicated by increased expression of many differentiation-specific genes. This, in association with its induction in psoriasis, suggests that transcriptional factor Glis1 is involved in the regulation of aberrant differentiation observed in psoriatic epidermis.

Small proline-rich protein 1 is the major component of the cell envelope of normal human oral keratinocytes

Oral keratinocytes of buccal and gingival tissues undergo a terminal differentiation program to form a protective epithelial barrier as non-keratinized or parakeratinized stratified cells. We have examined the protein composition of cell envelopes (CEs) from normal human buccal and gingival tissues as well as keratinocytes from normal human gingival cells grown in culture. Biochemical and sequencing analyses reveal that the CEs contain 60-70% small proline-rich protein 1a/b (SPR1a/b), together with smaller amounts of involucrin, annexin I and several other known CE proteins. The data imply a specialized role for SPR1 proteins in the unique barrier function requirements of oral epithelia.

Expression, regulation, and function of the SPR family of proteins. A review

The small, proline-rich (SPR) genes consist of three subclasses closely linked on human chromosome 1, a region referred to as the epidermal differentiation complex. SPR genes consist of two exons, with the second exon containing the entire open reading frame. SPRs are expressed in all squamous tissues of the skin, scalp, footpad, vaginal epithelia, and most of the epithelial lining of the digestive tract, including the lip, tongue, esophagus, and forestomach. Although SPR1 is absent in normal mucociliary epithelium of the respiratory tract, epithelia that undergo squamous differentiation in response to vitamin-A deficiency or to injury owing to exposure to environmental toxicants express SPR1. High levels of SPR1 are detected in various diseases and cancers of the skin or respiratory epithelia and in nonkeratinizing papillary adenocarcinomas. SPR expression can be regulated by transcriptional factors, by posttranscriptional factors, or by factors that affect SPR1 mRNA translation or protein turnover. Furthermore, regulation can be affected by the state of cell proliferation. The presence of SPR1 in most of these epithelia, and the absence of SPR3 in normal skin, suggest that these subclasses have distinct functions. Various approaches to the study of the cross-linked envelope (CE) components in identifying SPR1 and SPR2 and in suggesting that SPRs are one of the precursor proteins of the CE. However, expression of SPR1 in nonsquamous tissues and cell lines indicates a function not associated with squamous differentiation. Several studies have demonstrated that SPR1 antibodies react with nuclear proteins and that SPR1 is expressed in cells before entering the G0 phase of the cell cycle. Future studies should clarify the role of SPRs by modifying their contents in CE, and should identify SPR-associated proteins to clarify the cell growth-related role of SPR1.

Lysozyme expression during metaplastic squamous differentiation of retinoic acid-deficient human tracheobronchial epithelial cells

We previously reported (Gray, T. E., K. Guzman, C. W. Davis, L. H. Abdullah, and P. Nettesheim. 1996. Mucociliary differentiation of serially passaged normal human tracheobronchial epithelial cells. Am. J. Respir. Cell Mol. Biol. 14:104-112) that retinoic acid (RA)-deprived cultures of normal human tracheobronchial epithelial (NHTBE) cells became squamous, failed to produce mucin, and instead secreted or released large amounts of lysozyme (LZ). The purpose of the studies reported here was to elucidate the relationship between RA deficiency-induced squamous differentiation and increased LZ, and to determine what mechanisms were involved. We found that intracellular LZ began to accumulate in RA-deficient NHTBE cultures early during squamous differentiation. Between Days 10 and 18 of culture, cellular LZ levels were more than 10 times higher in RA-deficient than in RA-sufficient cultures. On Day 12, large numbers of cells began to exfoliate in RA-deficient cultures and extracellular LZ appeared at the apical surface, presumably released from the exfoliated cells. Metabolic labeling studies showed that the rate of LZ synthesis was not increased in RA-deficient cultures over that in RA-sufficient cultures; however, intracellular LZ half-life was much longer in RA-deficient cultures. We concluded that the increased accumulation of both intra- and extracellular LZ in RA-deficient cultures was due to increased LZ stability and was not the result of increased LZ synthesis. When RA-deficient cultures were treated on Day 7 with 10(-6) M RA, intracellular LZ levels did not substantially decrease until 3 d later, coinciding with a marked increase in mucin secretion. LZ messenger RNA levels were unchanged at 24 h, but were modestly increased (rather than decreased) at all subsequent time points. We concluded that RA does not directly regulate LZ, and that the excessive accumulation of LZ in RA-deprived NHTBE cells is a consequence of vitamin A deficiency-induced abnormal differentiation.

Transglutaminase cross-linking properties of the small proline-rich 1 family of cornified cell envelope proteins. Integration with loricrin

Small proline-rich 1 (SPR1) proteins are important for barrier function in stratified squamous epithelia. To explore their properties, we expressed in bacteria a recombinant human SPR1 protein and isolated native SPR1 proteins from cultured mouse keratinocytes. By circular dichroism, they possess no alpha or beta structure but have some organized structure associated with their central peptide repeat domain. The transglutaminase (TGase) 1 and 3 enzymes use the SPR1 proteins as complete substrates in vitro but in different ways: head domain A sequences at the amino terminus were used preferentially for cross-linking by TGase 3, whereas those in head domain B sequences were used for cross-linking by TGase 1. The TGase 2 enzyme cross-linked SPR1 proteins poorly. Together with our data base of 141 examples of in vivo cross-links between SPRs and loricrin, this means that both TGase 1 and 3 are required for cross-linking SPR1 proteins in epithelia in vivo. Double in vitro cross-linking experiments suggest that oligomerization of SPR1 into large polymers can occur only by further TGase 1 cross-linking of an initial TGase 3 reaction. Accordingly, we propose that TGase 3 first cross-links loricrin and SPRs together to form small interchain oligomers, which are then permanently affixed to the developing CE by further cross-linking by the TGase 1 enzyme. This is consistent with the known consequences of diminished barrier function in TGase 1 deficiency models.

Correlation between expression of peroxisome proliferator-activated receptor beta and squamous differentiation in epidermal and tracheobronchial epithelial cells

Previously, several members of the nuclear receptor superfamily have been implicated in the regulation of epidermal differentiation. In this study, we analyze the expression of members of the PPAR nuclear receptor subfamily in relation to the process of squamous differentiation in normal human epidermal keratinocytes (NHEK), human tracheobronchial epithelial (HBE) cells and the epidermis in vivo. Our results demonstrate that induction of differentiation in NHEK by either treatment with the phorbol ester phorbol 12-myristate-13-acetate (PMA), suspension culture or confluence greatly enhances the expression of PPARbeta mRNA. Likewise, topical treatment of mouse skin with PMA results in increased PPARbeta mRNA expression in the epidermis. In addition, the induction of squamous differentiation in HBE cells was also associated with an upregulation of PPARbeta mRNA expression. Finally, in situ hybridization analysis localized PPARbeta mRNA to the suprabasal layers of normal human skin. Our results demonstrate that the expression of PPARbeta is associated with squamous differentiation suggesting a regulatory role for this receptor in the control of specific genes during this differentiation process.

Mouse Sprr2 genes: a clustered family of genes showing differential expression in epithelial tissues

Small proline-rich (SPR) proteins are structural components of the cornified cell envelope of stratified squamous epithelia. They are subdivided into three families, i.e., SPR1, SPR2, and SPR3, of which the SPR2 family is the most complex. To understand the significance of this complexity, we have isolated 11 mouse Sprr2 genes, constructed a provisional physical map of the Sprr2 locus on mouse Chromosome 3, and examined the expression patterns of the Sprr2 genes in mouse epithelial tissues. The 11 Sprr2 sequences are highly conserved with a central domain containing a variable number of repeats. In situ hybridization showed the Sprr2 expression to be confined to epithelia. RT-PCR using primers specific for each of the 11 Sprr2 members demonstrated varying degrees of expression among the individual Sprr2 members in different tissues. The correlation between the physical location of the genes in the Sprr2 locus and their expression patterns suggests multiple levels of controlled expression.

Structural and transglutaminase substrate properties of the small proline-rich 2 family of cornified cell envelope proteins

The small proline-rich (SPR) proteins are components of the cornified cell envelope of stratified squamous epithelia and become cross-linked to other proteins by transglutaminases (TGases). The SPR2 family is the most complex, as it consists of several differentially expressed members of the same size. To explore their physical and cross-linking properties, we have expressed in bacteria a human SPR2 family member, and purified it to homogeneity. By circular dichroism, it possesses no alpha or beta structure but has some organized structure associated with the central peptide repeat domain. The TGase 1, 2, and 3 enzymes expressed in epithelia use the recombinant SPR2 protein as a complete substrate in vitro, but with widely differing kinetic efficiencies, and in different ways. With TGase 1, only one glutamine on the head domain and one lysine on the tail domain were used for limited interchain cross-linking. With TGase 3, multiple head and tail domain residues were used for extensive interchain cross-linking. The total usage of glutamine and lysine residues in vitro by TGase 3 was similar to that seen in earlier in vivo studies. We conclude that SPR2 proteins are cross-linked in epithelia primarily by the TGase 3 enzyme, a minor extent by TGase 1, and probably not by TGase 2.

Small proline-rich proteins are cross-bridging proteins in the cornified cell envelopes of stratified squamous epithelia

The cornified cell envelope (CE) is a specialized structure which contributes barrier function to stratified squamous epithelial cells. It is composed of an amalgam of several structural proteins that are rendered insoluble by isopeptide bond crosslinking by transglutaminases. One set of the structural proteins present in CEs of most such epithelia are the small proline rich (SPR) proteins, which are a family of about 12 related structural proteins. We have recovered a large number of peptides containing isopeptide crosslinks, including 236 involving SPR proteins, following proteolysis of CEs isolated from foreskin epidermal tissue and cultured epidermal keratinocytes. Analysis of this database has provided novel information on their function. First, we found that SPRs became crosslinked to many other structural proteins within the CE. Second, multiple glutamine and lysine residues located only on the amino- and carboxy-termini of the SPR proteins were involved in crosslinking, so that the two ends are functionally equivalent. Third, the SPRs functioned as cross-bridging proteins, by directly adjoining other CE structural proteins. In the specialized case of the epidermal CE, the SPRs cross-bridged between loricrin. In cultured keratinocytes which make little loricrin and serve as a model for internal stratified squamous epithelia, the SPRs formed extensive cross-bridges among themselves. Thus SPRs are ubiquitous cross-bridging proteins whose differential expression patterns apparently reflect specific barrier requirements of different epithelia.

Expression of CCAAT/enhancer binding proteins (C/EBP) is associated with squamous differentiation in epidermis and isolated primary keratinocytes and is altered in skin neoplasms

The epidermis is a stratified squamous epithelium composed primarily of keratinocytes that undergo sequential changes in gene expression during differentiation. CCAAT/enhancer binding proteins (C/EBP) are members of the bZIP family of DNA binding proteins/transcription factors. Northern analysis demonstrated that C/EBPalpha, C/EBPbeta, and C/EBPdelta mRNA are expressed in mouse epidermis and their mRNA levels were generally greater than those observed in other tissues known to express high levels of C/EBP. Western analysis of isolated epidermal cell nuclei demonstrated the presence of a 42 and 30 kDa C/EBPalpha protein and 35 kDa C/EBPbeta protein. Immunohistochemical localization of C/EBPalpha and C/EBPbeta in intact interfollicular epidermis revealed that C/EBPbeta expression is exclusive to the nuclei of a three-cell cluster of suprabasal keratinocytes that is morphologically consistent with the central column of the epidermal proliferative unit, and that C/EBPalpha is expressed in the nuclei and cytoplasm of suprabasal keratinocytes and weakly expressed in a perinuclear manner in some basal keratinocytes. In squamous cell carcinomas the expression of C/EBPalpha and C/EBPbeta was greatly diminished as both the intensity of nuclear staining and the number of cells expressing C/EBPalpha and C/EBPbeta were reduced. In isolated primary mouse keratinocytes, calcium-induced differentiation was accompanied by specific temporal changes in the expression of C/EBPalpha, C/EBPbeta, and C/EBPdelta mRNA and C/EBPalpha and C/EBPbeta protein. These results implicate a role for the C/EBP family in the regulation of genes involved in or specifically expressed during the process of squamous differentiation in epidermis.

Biochemical evidence that small proline-rich proteins and trichohyalin function in epithelia by modulation of the biomechanical properties of their cornified cell envelopes

The cornified cell envelope (CE) is a specialized structure involved in barrier function in stratified squamous epithelia, and is assembled by transglutaminase cross-linking of several proteins. Murine forestomach epithelium undergoes particularly rigorous mechanical trauma, and these CEs contain the highest known content of small proline-rich proteins (SPRs). Sequencing analyses of these CEs revealed that SPRs function as cross-bridgers by joining other proteins by use of multiple adjacent glutamines and lysines on only the amino and carboxyl termini and in functionally non-polar ways. Forestomach CEs also use trichohyalin as a novel cross-bridging protein. We performed mathematical modeling of amino acid compositions of the CEs of mouse and human epidermis of different body sites. Although the sum of loricrin + SPRs was conserved, the amount of SPRs varied in relation to the presumed physical requirements of the tissues. Our data suggest that SPRs could serve as modifiers of a composite CE material composed of mostly loricrin; we propose that increasing amounts of cross-bridging SPRs modify the structure of the CE, just as cross-linking proteins strengthen other types of tissues. In this way, different epithelia may use varying amounts of the cross-bridging SPRs to alter the biomechanical properties of the tissue in accordance with specific physical requirements and functions.

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

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

Epidermal differentiation and squamous metaplasia: from stem cell to cell death

Epidermal differentiation is a multi-step process defined by a cascade of interrelated changes in the expression of growth-regulatory and differentiation-specific genes (Fig. 1). Irreversible growth arrest is an early event in epidermal differentiation which occurs when cells transit from the basal to the innermost suprabasal layer of the skin and begin to express squamous-specific genes. In culture, interferon gamma, phorbol esters, confluence and growth in suspension are effective signals to induce irreversible growth arrest and differentiation. The induction of differentiation-specific genes occurs either concomitantly with or following growth arrest and is believed to be linked to the molecular events that control irreversible growth arrest. Such a link has been demonstrated in other cell systems undergoing terminal differentiation, such as myogenesis and adipogenesis. Genes encoding proteins involved in the formation of the cross-linked envelope are one set of squamous-specific genes which are induced in the suprabasal layers and include transglutaminase I and III, involucrin, loricrin and cornifins/small proline-rich proteins. Squamous-specific genes exhibit not only different patterns of tissue-specific expression but are also induced at different stages during differentiation, suggesting that transcription of individual genes is regulated by distinct mechanisms. The latter is supported by the identification of different sets of regulatory elements controlling the transcription of these genes. The importance of understanding both the mechanisms that regulate growth arrest and the differentiation program is emphasized by the association found between specific skin diseases and genetic alterations in growth-regulatory genes as well as differentiation markers. In addition, studies into those mechanisms will provide insight into the control of squamous metaplasia and the development of squamous cell carcinomas.

Differential expression of human cornifin alpha and beta in squamous differentiating epithelial tissues and several skin lesions

Cornifins/small proline-rich proteins (SPRRs) belong to a family of proline-rich proteins that function as cornified envelope precursors. We report here an immunohistochemical analysis of human cornifin-alpha and -beta expression in several stratified squamous epithelia. In normal human skin, cornifin-alpha was expressed in the granular layer of the epidermis of palmoplantar skin, in the inner lining cells of the follicular infundibulum, and in the inner root sheath of the hair follicle. It was also expressed in the upper squamous layers of the oral, esophageal, and vaginal epithelia. Cornifin-beta was detected in oral, esophageal, and vaginal epithelia, but not in normal skin. Immunoblot analysis revealed quantitative differences in cornifin-alpha expression in skin from different regions. Studies of specimens from various skin diseases showed that (i) cornifin-alpha was upregulated in inflammatory skin diseases, hyperplastic lesions, and in well-differentiated squamous cell carcinomas (SCCs), (ii) the expression of cornifin-beta was absent in inflammatory skin but was detected in highly differentiated keratinocytes in well-differentiated SCCs of the skin and some other hyperproliferative skin lesions, and in SCCs of the oral mucosa and esophagus. Northern blot analysis revealed that cornifin-alpha mRNA was present in all the squamous epithelial tissues studied, whereas cornifin-beta mRNA was expressed in oral mucosal epithelia and verrucous carcinoma of the skin but neither in normal nor in psoriatic skin. These results indicate that (i) the amount of cornifin alpha/SPRR1 expression in normal human skin depends on the body region, (ii) cornifin-alpha/SPRR1, but not cornifin-beta, contributes to the integrity of the hair follicle, and (iii) the expression of cornifin-beta is induced in some hyperplastic skin diseases only when the keratinocytes undergo extensive squamous differentiation.

Involucrin and SPRR are synthesized sequentially in differentiating cultured epidermal cells

Epidermal keratinocytes form cornified cell envelopes during terminal differentiation. These envelopes are composed of several cross-linked molecules, including involucrin, loricrin, and SPRR. We have previously reported that involucrin is synthesized earlier in terminal differentiation than loricrin. To further elucidate the mechanisms of terminal differentiation, we have now examined the expression of the two differentiation markers, involucrin and SPRR, in cultured human epidermal keratinocytes. In confluent nonstratified cultures, many involucrin-immunoreactive cells were detected, but few SPRR1/3-positive cells. Double staining demonstrated that cells containing SPRR1/3 almost always contained involucrin, but involucrin was present in many cells that did not contain SPRR. Light and electron microscopic immunohistochemistry of a stratified culture demonstrated that lower cells (close to the basal layer) were occasionally involucrin-positive, but lacked SPRR1/3, whereas more superficial cells contained both involucrin and SPRR. We conclude that involucrin and SPRR are sequentially induced in this order during keratinocyte differentiation.

Regulation of cornifin alpha expression in the vaginal and uterine epithelium by estrogen and retinoic acid

In this study, we analyze the regulation of the squamous-specific gene, cornifin alpha, by estrogen and retinoic acid in vaginal and uterine epithelial cells. In ovariectomized animals, the vaginal epithelium consists of a stratified, nonkeratinizing epithelium which changes into a highly-stratified, keratinizing epithelium upon treatment with estradiol. This transition is accompanied by a dramatic induction of the crosslinked envelope precursor, cornifin alpha. An increase in cornifin mRNA can be detected as early as 3 h after treatment. A similar effect is observed for the synthetic estrogenic agent diethylstilbestrol while other steroid hormones, including testosterone, progesterone or dexamethasone have little effect on cornifin expression. In contrast to the vagina, estradiol induces neither squamous differentiation nor expression of cornifin alpha in the uterine epithelium. Similar to the action of estradiol, vitamin A-deficiency greatly enhances squamous differentiation and keratinization in the vaginal epithelium. But unlike estradiol, it induces squamous metaplasia in the normally columnar, uterine epithelium, which eventually is replaced by a keratinizing epithelium in severe deficiency. This transition is associated with an induction of cornifin alpha expression. Immunohistochemical and in situ hybridization analysis localizes cornifin protein and mRNA in the suprabasal layers of the squamous epithelium. Our results demonstrate that estrogen and retinoids play key roles in the regulation of differentiation and cornifin alpha expression in the uterine and vaginal epithelium.

Epidermal protein kinase C-beta 2 is highly sensitive to downregulation and is exclusively expressed in Langerhans cells: downregulation is associated with attenuated contact hypersensitivity

Treatment of mice with multiple topical applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) or diacylglycerol resulted in a preferential decrease in epidermal protein kinase C-beta 2 (PKC-beta 2) compared with PKC-alpha as determined by western analysis. When PKC-alpha was decreased by 40%, PKC-beta 2 could no longer be detected, suggesting that PKC-beta 2 is more sensitive to downregulation, and/or specific epidermal cell types that contain PKC-beta 2 are more sensitive to TPA/diacylglycerol. To address this issue, we isolated Langerhans cells (LCs) from epidermal cell suspensions with immunomagnetic beads and an antibody to the class II major histocompatibility complex. Northern blot analysis revealed a PKC-beta 2 signal in isolated LCs that was 40-fold greater than that observed in unfractionated epidermal cells, and no PKC-beta 2 signal was detected in epidermal cells depleted of LCs, indicating that PKC-beta 2 is expressed exclusively in LCs within the epidermis. Western blot analysis confirmed the presence of PKC-beta 2 in LCs. PKC-beta 2 was highly sensitive to downregulation, because a single application of TPA resulted in a 90% loss of PKC-beta 2 within 6 h without a decrease in the number of LCs. To determine whether the decreased level of PKC-beta 2 within LCs was associated with an alteration in contact hypersensitivity, we treated mice with only a single application of TPA, and 6 hours later mice were sensitized with 2,4-dinitrofluorobenzene on the same dorsal area. Subsequent challenge revealed a 60% decrease in contact hypersensitivity in TPA-treated mice. These data indicate that (i) within the epidermis, PKC-beta 2 is highly sensitive to downregulation and is exclusively expressed in LCs, and (ii) the downregulation of PKC-beta 2 is associated with impaired LC function with respect to contact hypersensitivity.