Control of growth regulatory and differentiation-specific genes in human epidermal keratinocytes by interferon gamma. Antagonism by retinoic acid and transforming growth factor beta 1

Interferon-gamma-dependent stimulation of Fas antigen in SV40-transformed human keratinocytes: modulation of the apoptotic process by protein kinase C

Fas antigen is a cell membrane protein that has been suggested to mediate apoptosis. Using SV40-transformed human keratinocytes, we investigated the Fas-antigen-dependent apoptotic process. The expression of Fas antigen mRNA was markedly induced by interferon-gamma (IFN-gamma) treatment (500 U/ml). After IFN-gamma treatment in the presence of anti-Fas monoclonal antibody, apoptosis was induced, as detected by the formation of nucleosome-sized fragments of DNA and morphologically by apoptotic cells with round homogeneous nuclear beads detected by acridine orange staining. The apoptotic SV40-transformed keratinocytes were analyzed quantitatively by enzyme-linked immunosorbent assay using antihistone and peroxidase-conjugated anti-DNA antibodies to detect cell death. The IFN-gamma- and anti-Fas antibody-dependent apoptotis was observed by 3 h, and the maximal response was observed by 12 h. The induction of apoptosis was significantly augmented by treatment with 10 ng/ml 12-o-tetradecanoyl-phorbol-13-acetate (TPA). TPA alone had no effect on either Fas antigen expression or on the apoptotic process. Other protein kinase C activators (1-oleoyl-2-acetylglycerol and mezerein) also stimulated IFN-gamma-dependent apoptosis, whereas 4-o-methyl phorbol myristate acetate, a very weak protein kinase C activator, had only a slight effect. The TPA-induced augmentation of apoptosis was inhibited by the protein kinase C inhibitor, 1-(5-isoquinoline-sulfonyl)-2-methyl piperazine dihydrochloride (H-7). However, H-7 inhibited only the TPA-induced augmentation of apoptosis; the basal IFN-gamma- and anti-Fas-dependent apoptosis remained in the presence of H-7. Northern blot analysis revealed that c-jun mRNA was induced by IFN-gamma plus anti-Fas antibody treatment as well as by TPA treatment; the addition of IFN-gamma alone to the incubation medium had no effect on the expression of c-jun mRNA. These results indicate that IFN-gamma induces a Fas-antigen-dependent apoptotic process in SV40-transformed keratinocytes and that TPA augments the process through the activation of protein kinase C.

Identification and characterization of a novel squamous cell-associated gene related to PMP22

In this study, we identify and characterize a novel gene, CL-20, that encodes a 17.8-kDa protein with sequence and structural similarity to the growth arrest-specific gene gas3/peripheral myelin protein gene PMP22. The CL-20 protein exhibits a 43% identity with PMP22. The positions of the four lipophilic domains and the N-glycosylation site of PMP22 are conserved in CL-20, suggesting that it also is an integral membrane glycoprotein. The CL-20 gene is located on human chromosome 12 rather than 17 and encodes a 2.8-kilobase mRNA instead of 1.7-kilobase mRNA. These observations indicate that the CL-20 gene is related to but distinct from PMP22. In contrast to PMP22, CL-20 mRNA and protein are induced during squamous differentiation of rabbit tracheal epithelial cells in vitro, and Northern blot analysis and in situ hybridization demonstrated that CL-20 mRNA is most abundant in squamous epithelia. These results indicate that the high expression of CL-20 is closely correlated with squamous differentiation. The differences in tissue-specific expression and regulation between CL-20 and PMP22 suggest different roles for these two proteins. Retinoids, which inhibit squamous differentiation, repress the induction of CL-20. The retinoic acid receptor-selective retinoid SRI-6751-84 is the most effective in suppressing CL-20, suggesting that the activation of the retinoic acid receptor signaling pathway is important in this suppression.

Expressions of c-jun and p53 proteins in human middle ear cholesteatoma: relationship to keratinocyte proliferation, differentiation, and programmed cell death

The c-jun protein functions as a transcription factor for many genes, and the p53 protein functions as a negative regulator of cellular proliferation, which is related to the apoptosis pathway that induces DNA damage. It has recently been shown that c-jun promotes keratinocyte proliferation and p53 induces apoptosis of various cells. In this study, the presence of c-jun and p53 in cholesteatoma was demonstrated by immunoblotting assays using polyclonal rabbit anti-c-jun antibody and monoclonal anti-p53 protein antibody, respectively. The cholesteatoma tissue incubated with anti-c-jun antibody showed the staining of keratinocytes on the basal and spinous layers of epithelium. The c-jun protein was localized in the basal layer of normal skin, and the p53 protein was present in the nucleus of keratinocytes in the granular layer of cholesteatoma epithelium. The keratinocytes of normal external ear canal skins and normal human skins were slightly stained in the granular layer of the epidermis. The present findings suggest that c-jun and p53 proteins have a role in keratinocyte differentiation, proliferation, and apoptosis in the cholesteatoma.

Phosphorylation of eukaryotic elongation factor 2 in differentiating and proliferating HL-60 cells

Ca(2+)-and calmodulin-dependent protein kinase III (CaM PKIII) phosphorylates eukaryotic elongation factor 2 (eEF-2) in HL-60 cells. Dephosphorylation of the factor in these cells is catalyzed by phosphoprotein phosphatase 2A alone. Differentiation of the HL-60 cells by all-trans retinoic acid resulted in a reduced growth rate and a marked decrease in the intracellular concentration of eEF-2. During differentiation the activity of the eEF-2 kinase is gradually reduced and reaches 10% of that found in undifferentiated cells 5 days after the onset of differentiation. The capacity to dephosphorylate phospho-eEF-2 remained unaltered in the growth-arrested cells. Differentiation without reduced proliferation was induced in the HL-60 cells by interferon-gamma. Under these conditions, differentiation had no effect on the cellular content of eEF-2 or the ability to dephosphorylate phospho-eEF-2. However, the differentiated cells showed a dramatic decrease in the specific activity of the eEF-2 kinase. The results show that the cellular content of eEF-2 varies with the rate of proliferation and that the activity of the eEF-2 kinase is high in undifferentiated proliferating cells and decreases upon differentiation even under conditions of an unaltered growth rate.

Interferon-gamma-mediated inactivation of transcription of the 230-kDa bullous pemphigoid antigen gene (BPAG1) provides novel insight into keratinocyte differentiation

Interferon-gamma (IFN-gamma) has been shown to regulate epidermal keratinocyte growth and differentiation. In this study, we examined the effects of recombinant human IFN-gamma on the expression of the gene encoding the 230-kDa bullous pemphigoid antigen (BPAG1), a marker of the mitotic basal cell phenotype in the epidermis. Northern analysis revealed a dose- and time-dependent suppression of BPAG1 expression by IFN-gamma in cultured human keratinocytes from several different donors, and incubation of the cells with IFN-gamma in the presence of cycloheximide demonstrated that this effect required ongoing protein synthesis. The inhibition of BPAG1 gene expression was also demonstrated at the protein level by indirect immunofluorescence using a monoclonal antibody recognizing the human 230-kDa bullous pemphigoid antigen. Transient transfections of cultured keratinocytes with BPAG1 promoter-chloramphenicol acetyltransferase reporter gene plasmids indicated marked suppression of the promoter activity by IFN-gamma, and deletion constructs were able to identify a defined region containing the responsive element (IFN-gamma inhibitory element). Reduced transcription of the BPAG1 gene by IFN-gamma was also demonstrated by in vitro nuclear run-on assays. These data, which indicate inactivation of transcription of a basal keratinocyte-specific gene of transcription of a basal keratinocyte-specific gene (BPAG1) by IFN-gamma, provide novel insight into the mechanisms of IFN-gamma-mediated keratinocyte gene regulation and epidermal differentiation in inflammatory diseases.