The expression and localization of bcl-2 protein in normal skin and in non-melanoma skin cancers

Dermal TRPV1 innervations engage a macrophage- and fibroblast-containing pathway to activate hair growth in mice

Pain, detected by nociceptors, is an integral part of injury, yet whether and how it can impact tissue physiology and recovery remain understudied. Here, we applied chemogenetics in mice to locally activate dermal TRPV1 innervations in naive skin and found that it triggered new regenerative cycling by dormant hair follicles (HFs). This was preceded by rapid apoptosis of dermal macrophages, mediated by the neuropeptide calcitonin gene-related peptide (CGRP). TRPV1 activation also triggered a macrophage-dependent induction of osteopontin (Spp1)-expressing dermal fibroblasts. The neuropeptide CGRP and the extracellular matrix protein Spp1 were required for the nociceptor-triggered hair growth. Finally, we showed that epidermal abrasion injury induced Spp1-expressing dermal fibroblasts and hair growth via a TRPV1 neuron and CGRP-dependent mechanism. Collectively, these data demonstrated a role for TRPV1 nociceptors in orchestrating a macrophage and fibroblast-supported mechanism to promote hair growth and enabling the efficient restoration of this mechano- and thermo-protective barrier after wounding.

A systematic review of case-control studies of cytokines in blister fluid and skin tissue of patients with Stevens Johnson syndrome and toxic epidermal necrolysis

Stevens Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are severe cutaneous adverse reactions characterised by keratinocyte apoptosis, necroptosis and epidermal detachment. Several cytokines and cytotoxic proteins have been shown to be elevated in the blood and skin of SJS/TEN sufferers and biologics such as intravenous immune globulin and tumour necrosis factor (TNF)-alpha inhibitors have demonstrated good therapeutic potential. The exact pathogenic model of SJS/TEN however remains elusive. This systematic review aimed to evaluate the case-control studies of cytokines and cytotoxic proteins in the blister fluid and skin of adults with Stevens Johnson syndrome and/or toxic epidermal necrolysis. This review was registered with INPLASY and conducted in accordance with the PRISMA reporting guidelines. Potential bias was assessed using the NIH criteria. Eleven articles describing results from 96 cases and 170 controls were included. Fas, Fas ligand, Interleukin (IL)-8 and B-cell lymphoma (Bcl)-2 were elevated in SJS/TEN blister fluid and skin tissue, compared with healthy controls. IL-2, IL-6, TNF-alpha, tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), interferon-gamma and matrix metalloproteinase-2 were elevated in SJS/TEN blister fluid compared with fluid sampled from lesional controls. Granulysin, IL-33, TGF-beta-1 and IL-13 were elevated in SJS/TEN skin tissue compared with lesional lichen planus tissue, as was IL-13, IFN-gamma, IL-2 and IL-5, when compared with erythema multiforme tissue. A wide array of cytokines and cytotoxic proteins are present at higher concentrations in the blister fluid and skin tissue of SJS/TEN patients compared with healthy and lesional controls. Our findings suggest that these proteins may be pathogenic, as well as possibly markers for diagnosis, disease severity and course. They may also prove to be useful therapeutic targets. More research is needed.

Dimethyl Itaconate Reduces α-MSH-Induced Pigmentation via Modulation of AKT and p38 MAPK Signaling Pathways in B16F10 Mouse Melanoma Cells

Dimethyl itaconate (DMI) exhibits an anti-inflammatory effect. Activation of nuclear factor erythroid 2-related factor 2 (NRF2) is implicated in the inhibition of melanogenesis. Therefore, DMI and itaconic acid (ITA), classified as NRF2 activators, have potential uses in hyperpigmentation reduction. The activity of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB), an important transcription factor for MITF gene promoter, is regulated by glycogen synthase kinase 3β (GSK3β) and protein kinase A (PKA). Here, we investigated the inhibitory effect of ITA and DMI on alpha-melanocyte-stimulating hormone (α-MSH)-induced MITF expression and the modulatory role of protein kinase B (AKT) and GSK3β in melanogenesis in B16F10 mouse melanoma cells. These cells were incubated with α-MSH alone or in combination with ITA or DMI. Proteins were visualized and quantified using immunoblotting and densitometry. Compared to ITA, DMI treatment exhibited a better inhibitory effect on the α-MSH-induced expression of melanogenic proteins such as MITF. Our data indicate that DMI exerts its anti-melanogenic effect via modulation of the p38 mitogen-activated protein kinase (MAPK) and AKT signaling pathways. In conclusion, DMI may be an effective therapeutic agent for both inflammation and hyperpigmentation.

Restrained Terminal Differentiation and Sustained Stemness in Neonatal Skin by Ha-Ras and Bcl-2

Nonmelanoma skin cancer is the most frequently diagnosed cancer in the United States. Deregulation of bcl-2 and ras family members is commonly observed in nonmelanoma skin cancer. It has been previously demonstrated that simultaneous bcl-2 and Ha-ras gene expression in keratinocytes results in resistance to cell death induced by ultraviolet radiation and enhanced multistep skin carcinogenesis. In this study, we aimed to elucidate the central roles of Ha-Ras and Bcl-2 in maintaining epidermal homeostasis. To assess the effect of deregulated Ha-Ras and Bcl-2 on skin differentiation, we have generated skin-specific transgenic mouse model constitutively expressing both oncogenic Ha-Ras and Bcl-2. Ectopic expression of Ha-Ras and Bcl-2 in newborn double transgenic epidermal keratinocytes induced abnormal epidermal differentiation accompanied by increased cell proliferation and suppressed apoptotic cell death, which resulted in thickened and wrinkled skin morphology in neonate skins. Expression of epidermal differentiation marker cytokeratin 1 was decreased. Expression of other differentiation markers loricrin and filaggrin was also decreased and delayed to be detected only in the upper stratum granulosum, whereas the proliferative markers cytokeratin 14 and cytokeratin 6, which are expressed in constitutively proliferative basal layer and stem cell niches such as hair follicles or neoplastic lesions, respectively, were highly expressed. The abnormal expression of epidermal cytokeratins suggests that Ha-Ras and Bcl-2 suppress the terminal differentiation and sustain the stem cell-like features in epidermal keratinocytes.

Emerging drugs and combination strategies for basal cell carcinoma

INTRODUCTION

Basal cell carcinoma (BCC) is a malignancy that is driven by an activated Hedgehog (Hh) pathway. Smoothened inhibitors are a new promising treatment option for patients with locally advanced or metastatic BCC or basal cell nevus syndrome. But long-term data are still limited, the optimal treatment duration is not yet defined and there are already documented cases with acquired resistance.

AREAS COVERED

Treatment modalities with Hh inhibitors, side effects and potential pharmacological combination options are discussed. The current literature, including PubMed, Cochrane database and registered trials on ClinicalTrials.gov, was searched.

EXPERT OPINION

BCCs typically regress during therapy with Hh inhibitors. Muscle toxicity, dysgeusia and hair loss can be considered as on target adverse reactions. Muscle toxicity is the dose-limiting toxicity of sonidegib. It was not seen with vismodegib because of its high binding to plasma protein α-1-acid glycoprotein. Sonidegib is different and shows a clear dose-toxicity relationship, which allows to address the question of whether there is a dose dependency of regression rate, cure rate and progression-free survival. In addition, basic research has offered strategies to enhance efficacy by the combination with other molecules, such as EGFR inhibitors, MEK inhibitors or immunotherapy.

The rate and pattern of bcl-2 and cytokeratin 15 expression in trichoepithelioma and nodular Basal cell carcinoma: a comparative study

Context:

Histopathological evaluations can differentiate between clinically resembling trichoepithelioma (TE) and basal cell carcinoma (BCC) unless the biopsy specimens are small or superficial. Previous studies used immunohistochemical evaluation for Bcl-2 and cytokeratin 15 (CK15), in attempts to differentiate between these two entities, with heterogeneous findings.

Aims:

This study intended to compare the rate and patterns of Bcl-2 and CK15 expressions between specimens of TE and nodular BCC.

Settings and Design:

Case-series including formalin-fixed, paraffin-embedded cutaneous biopsies.

Subjects and Methods:

Twenty-two BCC and 12 TE specimens were stained for Bcl-2 and CK15 and examined microscopically. The rate and patterns of expressions were compared between the two groups.

Statistical Analysis Used:

Statistical analysis was performed using the statistical software (SPSS version 16.0; SPSS Inc., Chicago, IL, USA), Pearson Chi-square, or Fisher's exact tests, wherever appropriate.

Results:

The two groups were comparable for the expression rate and patterns of Bcl-2 (86.4%: 5 central, 14 diffuse in BCC vs. 83.3%: 2 central, 8 diffuse in TE; P = 0.59 and 0.54 for rate and pattern, respectively). The rate of CK15 expression was significantly higher in TE specimens (66.7%: 4 central, 3 diffuse, 1 peripheral vs. 4.5%: 1 central; P < 0.001). The positive likelihood ratio in distinguishing the two neoplasms was 14.7 (95% confidence interval: 2.1-103.7).

Conclusions:

CK15 but not Bcl-2 staining may help in differentiating between BCC and TE even in BCCs with follicular differentiation.

A transgenic mouse for imaging caspase-dependent apoptosis within the skin

Apoptosis is an essential process for the maintenance of normal physiology. The ability to noninvasively image apoptosis in living animals would provide unique insights into its role in normal and disease processes. Herein, a recombinant reporter consisting of beta-galactosidase gene flanked by two estrogen receptor regulatory domains and intervening Asp-Glu-Val-Glu sequences was constructed to serve as a tool for in vivo assessment of apoptotic activity. The results demonstrate that when expressed in its intact form, the hybrid reporter had undetectable beta-galactosidase activity. Caspase 3 activation in response to an apoptotic stimulus resulted in cleavage of the reporter, and thereby reconstitution of beta-galactosidase activity. Enzymatic activation of the reporter during an apoptotic event enabled noninvasive measurement of beta-galactosidase activity in living cells, which correlated with traditional measures of apoptosis in a dose- and time-dependent manner. Using a near-infrared fluorescent substrate of beta-galactosidase (9H-{1,3-dichloro-9,9-dimethylacridin-2-one-7-yl} beta-D-galactopyranoside), noninvasive in vivo imaging of apoptosis was achieved in a xenograft tumor model in response to proapoptotic therapy. Finally, a transgenic mouse model was developed expressing the ER-LACZ-ER reporter within the skin. This reporter and transgenic mouse could serve as a unique tool for the study of apoptosis in living cells and animals, especially in the context of skin biology.

Hedgehog signaling regulates the survival of gastric cancer cells by regulating the expression of Bcl-2

Gastric cancer is the second most common cause of cancer deaths worldwide. The underlying molecular mechanisms of its carcinogenesis are relatively poorly characterized. Hedgehog (Hh) signaling, which is critical for development of various organs including the gastrointestinal tract, has been associated with gastric cancer. The present study was undertaken to reveal the underlying mechanism by which Hh signaling controls gastric cancer cell proliferation. Treatment of gastric cancer cells with cyclopamine, a specific inhibitor of Hh signaling pathway, reduced proliferation and induced apoptosis of gastric cancer cells. Cyclopamine treatment induced cytochrome c release from mitochondria and cleavage of caspase 9. Moreover, Bcl-2 expression was significantly reduced by cyclopamine treatment. These results suggest that Hh signaling regulates the survival of gastric cancer cells by regulating the expression of Bcl-2.

The p53 tumor suppressor network in cancer and the therapeutic modulation of cell death

The molecular subversion of cell death is acknowledged as a principal contributor to the development and progression of cancer. The p53 tumor suppressor protein is among the most commonly altered proteins in human cancer. The p53 protein mediates critical functions within cells including the response to genotoxic stress, differentiation, senescence, and cell death. Loss of p53 function can result in enhanced rates of cell proliferation, resistance to cell death stimuli, genomic instability, and metastasis. The community of cancer scientists is now in possession of a vast repository of information regarding the frequency, specific mechanisms, and clinical context of cell death deregulation in cancer. This information has enabled the design of therapeutic agents to target proteins, including p53. The feasibility and impact of targeting cell death signaling proteins has been established in preclinical models of human cancer. The appropriate application of these targeted agents is now being established in clinical trials.

Cooperation of Ha-ras and Bcl-2 during multistep skin carcinogenesis

Nonmelanoma skin cancer (NMSC) is the most frequently diagnosed cancer in the United States. Deregulation of bcl-2 and ras family members is commonly observed in NMSC. It has been previously demonstrated that simultaneous bcl-2 and Ha-ras gene expression in keratinocytes results in disordered differentiation and resistance to cell death induced by ultraviolet (UV) radiation. It was, therefore, interest to assess the extent of cooperation between bcl-2 and Ha-ras during multistep skin carcinogenesis. The keratin 1 promoter was used to generate HK1.ras and HK1.bcl-2 transgenic mice, which were subsequently crossed to generate HK1.ras/bcl-2 double transgenic mice. The apoptotic index (AI) following UV-irradiation was significantly lower in HK1.bcl-2 and HKI.ras/bcl-2 epidermis compared to control littermates. Interestingly, the AI of HK1.ras/bcl-2 mice was significantly lower than even HK1.bcl-2 mice following UV-irradiation. To investigate the interaction of these oncogenes in skin tumorigenesis, a two-stage chemical carcinogenesis protocol was used to induce tumors. The individual contributions of Ha-ras and bcl-2 to papilloma latency, incidence, and growth rate in HK1.ras/bcl-2 double transgenic mice was marginally additive. Papillomas arising in HK1.ras transgenic mice exhibited the highest rate of apoptosis whereas papillomas arising in the HK1.ras/bcl-2 double transgenic mice exhibited rates of apoptosis that were significantly lower than papillomas arising in either control littermate or HK1.ras mice. Constitutive expression of either Ha-ras or bcl-2 exhibited similar rates of malignant tumor progression and they were not significantly different than control littermates. Importantly, when these two oncoproteins were coexpressed, a significant, and synergistic, increase in malignant transformation was observed.

Evaluation of survivin and NF-kappaB in psoriasis, an immunohistochemical study

BACKGROUND

Suppression of apoptosis is generally one of the accepted pathogenetic mechanisms for psoriasis and any epidermal hyperproliferative states. Survivin is a member of the inhibitor of apoptosis protein family mediating its apoptosis suppressive function by the inhibition of caspase pathway. Nuclear factor kappa B (NF-kappaB) is a transcription factor that regulates hundreds of genes including many critically involved in apoptosis. The aim of this study was to explore the role could be played by survivin and NF-kappaB in psoriasis and the link between them.

METHODS

Thirty cases of lesional psoriasis, 10 perilesional and 10 control specimens from normal skin were studied by immunohistochemical method for expression of survivin and NF-kappaB.

RESULTS

Survivin was detected in 73% of psoriatic lesions distributed either in epidermis, in endothelial cells of proliferating capillaries or in both of them. In non-psoriatic lesions either perilesional or control specimens, survivin was confined to basal layer of epidermis, significantly up regulated in psoriasis in comparison with non-psoriatic lesions (p = 0.0001). Nuclear expression of NF-kappaB was detected in 66% of psoriatic lesions; this active phosphorylated form was significantly over expressed in psoriasis in comparison with normal skin (p = 0.0004). Diffuse nuclear expression of NF-kappaB was significantly associated with up-regulation of survivin in psoriatic plaque (p = 0.03).

CONCLUSIONS

Survivin and NF-kappaB appeared to be important factors in the pathogenesis of psoriasis. Survivin could be the target of NF-kappaB mediating its death signal inhibition pathway in psoriasis.

Molecular mediators of cell death in multistep carcinogenesis: a path to targeted therapy

A consistent, if not invariant, feature of cancer cells is the acquired ability to evade apoptosis. The pioneering work of Dr. Stan Korsmeyer was invaluable in characterizing the molecular foundations of cell death signaling mechanisms during normal development and during multistep carcinogenesis. This foundation now forms the basis for the rational design of therapeutic strategies to selectively activate cell death in cancer cell populations. These strategies are currently being evaluated in an increasing number of clinical trials targeting diverse tumor types.

Molecular aetiology and pathogenesis of basal cell carcinoma

Recent insights into the cell biology of the epidermis and its appendages are transforming our understanding of the pathogenesis of basal cell carcinoma (BCC). The significant progress that has been made warrants a comprehensive review of the molecular and cellular pathology of BCC. The items addressed include environmental and genetic risk factors, the biology of the putative precursor cell(s), and the contribution of aberrations in processes such as apoptosis, cell proliferation, differentiation and signalling to carcinogenesis. Furthermore, established and novel treatment modalities are discussed with particular attention to future biological approaches.

Activation of the BCL2 promoter in response to Hedgehog/GLI signal transduction is predominantly mediated by GLI2

Aberrant activation of the Hedgehog (HH)/GLI signaling pathway has been implicated in the development of basal cell carcinoma (BCC). The zinc finger transcription factors GLI1 and GLI2 are considered mediators of the HH signal in epidermal cells, although their tumorigenic nature and their relative contribution to tumorigenesis are only poorly understood. To shed light on the respective role of these transcription factors in epidermal neoplasia, we screened for genes preferentially regulated either by GLI1 or GLI2 in human epidermal cells. We show here that expression of the key antiapoptotic factor BCL2 is predominantly activated by GLI2 compared with GLI1. Detailed promoter analysis and gel shift assays identified three GLI binding sites in the human BCL2 cis-regulatory region. We found that one of these binding sites is critical for conferring GLI2-specific activation of the human BCL2 promoter and that the selective induction of BCL2 expression depends on the zinc finger DNA binding domain of GLI2. In vivo, GLI2 and BCL2 were coexpressed in the outer root sheath of hair follicles and BCC and in plasma cells that infiltrated BCC tumor islands. On the basis of the latter observation, we analyzed plasma cell-derived tumors and found strong expression of GLI2 and BCL2 in neoplastic cells of plasmacytoma patients, implicating HH/GLI signaling in the development of plasma cell-derived malignancies. The results reveal a central role for GLI2 in activating the prosurvival factor BCL2, which may represent an important mechanism in the development or maintenance of cancers associated with inappropriate HH signaling.

Human follicular stem cells: their presence in plucked hair and follicular cell culture

BACKGROUND AND OBJECTIVES

A considerable portion of the hair follicle remains attached to plucked hair and can be used for follicle cell culture. In this study we have phenotyped these cells in an attempt to identify the stem cell fraction. Reports in the literature have indicated that this cell population may be positive for cytokeratin (CK) 19. Because stem cells in general need to be protected from apoptosis, the presence of the apoptosis-suppressing Bcl-2 protein, together with the absence of the apoptosis-promoting Bax and the CK profile may be used as an indicator of the stem cell population in the hair follicle, and in cultures of hair follicle cells.

METHODS

Hair follicles from skin biopsies and plucked hair were derived from the scalps of healthy volunteers. Follicular cells were cultured from the plucked hairs. These hair follicles, plucked hairs and cultured cells were examined for their CK profiles, which are indicative of the type of cell (basal/stem cells) and for their status with respect to the proliferation marker Ki-67, Bax and Bcl-2.

RESULTS

We found coexpression for CK19 and Bcl-2, but not Bax in two distinct areas, localized in the upper and lower third of the follicle from both skin biopsies and plucked hairs, while proliferation markers were negative in these areas. CK19 and Bcl-2 were also coexpressed in combination in a fraction of the follicular cell culture. The skin basal cell marker CK14 could be found throughout the outer root sheath of the hair follicle from both skin biopsies and plucked hairs, as well as in the follicular cell culture.

CONCLUSIONS

Thus, CK19/Bcl-2-positive and Bax-negative cells can be obtained from cells derived from plucked hair and are retained in cultures made from these cells. If this phenotype represents follicular stem cells, our finding endorses the assumption that stem cells are located in the bulge area of the hair follicle, as we did not find them in or near the dermal papilla.

Transcriptional regulation of bcl-2 mediated by the sonic hedgehog signaling pathway through gli-1

Basal cell carcinomas (BCCs) express high levels of the antiapoptotic proto-oncogene, bcl-2, and we have shown that bcl-2 contributes to the malignant phenotype in a transgenic mouse model. The basis of bcl-2 transcriptional regulation in keratinocytes is unknown. The sonic hedgehog (SHH) signaling pathway is frequently altered in BCCs. Mediators of shh signaling include the downstream transactivator, gli-1, and transrepressor, gli-3. Seven candidate gli binding sites were identified in the bcl-2 promoter. Cotransfection of increasing amounts of gli-1 in keratinoycytes resulted in a corresponding dose-dependent increase in bcl-2 promoter luciferase activity. Gli-1 was also able to up-regulate endogenous bcl-2. Gli-3 cotransfection resulted in no significant changes in bcl-2 promoter activity compared with control. Gli-3 has been demonstrated to be proteolytically processed into an N-terminal repressive form that can inhibit downstream transactivation by gli-1. Gli-3 mutants possessing only the N-terminal region or the C-terminal region were made and used in luciferase assays. The N terminus of gli-3 inhibited gli-1 transactivation of the bcl-2 promoter. Gel shift analysis and luciferase assays demonstrated that gli binding site 4 (-428 to -420), is important for gli transcriptional regulation. Skin samples from transgenic mice expressing an RU486 gli-1 transgene exhibited significantly higher levels of endogenous bcl-2 protein in epidermal keratinocytes as assessed by immunoblotting and immunohistochemistry. Together, these findings provide consistent evidence that gli proteins can transcriptionally regulate the bcl-2 promoter and that gli-3 can inhibit transactivation by gli-1. These studies further suggest that one consequence of the deregulation of shh signaling in BCC is the up-regulation of bcl-2.

Ginsenoside F1 protects human HaCaT keratinocytes from ultraviolet-B-induced apoptosis by maintaining constant levels of Bcl-2

Ginsenosides, the major active ingredients of ginseng, show a variety of biomedical efficacies such as antiaging and antioxidation. Here, we investigate the protective activity of the ginsenoside F1, an enzymatically modified derivative of ginsenoside Rg1, against ultraviolet-B-induced damage in human HaCaT keratinocytes. Ginsenoside F1 significantly reduced ultraviolet-B-induced cell death and protected HaCaT cells from apoptosis caused by ultraviolet B irradiation. Furthermore, ginsenoside F1 prevented ultraviolet-B-induced cleavage of poly(ADP-ribose) polymerase in HaCaT cells. In search of the molecular mechanism responsible for the antiapoptotic effect of ginsenoside F1, we find that protection from ultraviolet-B-induced apoptosis is tightly correlated with ginsenoside-F1-mediated inhibition of ultraviolet-B-induced downregulation of Bcl-2 and Brn-3a expression.

Lamin expression in normal human skin, actinic keratosis, squamous cell carcinoma and basal cell carcinoma

BACKGROUND

Aberrant expression patterns of nuclear lamins have been described in various types of cancer depending on the subtype of cancer, its aggressiveness, proliferative capacity and degree of differentiation. In general, the expression of A-type lamins (lamins A and C) has been correlated with a non-proliferating, differentiated state of cells and tissues.

OBJECTIVES

To establish and compare the expression patterns of lamins in normal human skin, actinic keratosis (AK), squamous cell carcinoma (SCC) and basal cell carcinoma (BCC).

METHODS

Expression patterns of the individual lamin subtypes were studied immunohistochemically. The proliferation capacity of the tumour cells was detected using a specific antibody to Ki-67, and was related to the A-type lamin expression patterns.

RESULTS

In normal skin, lamin A was expressed in the suprabasal cell compartment of the epidermis, whereas the basal cells were mostly unstained. BCCs and SCCs stained positive in most cells, while the epidermis overlying BCC and SCC and the epidermis in AK stained homogeneously and strongly in the basal cells in addition to the suprabasal cells. Lamin C was expressed in some basal cells of normal epidermis while the suprabasal cells stained strongly positive. Both BCCs and SCCs stained strongly positive for lamin C, with the difference that in BCC the staining was predominantly present in nucleolar structures with occasional staining of the nuclear envelope. The epidermis overlying SCC showed strong positivity in the lamina of virtually all cells. The expression of lamin C in the basal cells of AK resembled the expression pattern seen in the epidermis overlying BCC, i.e. a nucleolar staining next to nuclear envelope staining. Lamin B1 and B2 were found in virtually all cells in normal epidermis, AK, BCC, SCC and the epidermis overlying cancer. The percentage of Ki-67-expressing cells was highest in BCC (45%), and gradually decreased via epidermis overlying BCC, AK, SCC, and epidermis overlying SCC, to normal skin (11%). Simultaneous expression of A-type lamins and Ki-67 occurred in approximately 50% of the proliferating (Ki-67 positive) cells in BCC and SCC.

CONCLUSIONS

Significant changes occur in the expression patterns of A-type lamins in both premalignant and malignant lesions of the skin. The profound overlap of lamin A and Ki-67 staining patterns indicates that the proliferating tumour cells may obtain a certain degree of differentiation. Finally, lamin A expression in the basal cell layer of the apparently normal epidermis overlying BCC may suggest its involvement in the primary process.

Life and death signaling pathways contributing to skin cancer

Apoptosis is generally regarded as a critical regulatory event in the development of malignancies in several different organ systems (Thompson, 1995). Initially, oncologists focused on alterations in rates of proliferation and cell cycle kinetics, but more recently an emphasis on apoptosis has dominated the fight against cancer (Evan and Vousden, 2001). As approximately 1,000,000 individuals in the U.S.A. develop skin cancer each year, it is important to elucidate the molecular mechanisms that govern cell survival and cell death in the epidermis (Miller and Weinstock, 1994). Moreover, given that most skin cancers occur on sun-exposed skin, the pro-apoptotic and antiapoptotic response of keratinocytes (KC) to UV light is of particular relevance to the development of skin cancer (Brash et al, 1996). Whereas both squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) arise from epidermal KC, it is becoming increasingly apparent that the natural history of their development, their underlying molecular pathogenesis, and potential involvement of antiapoptotic pathways are significantly different. Nonetheless, as pointed out later in the text, significant progress is being made in our understanding of the pathophysiology of these relatively common epithelial-cell-derived neoplasms. In this review we will explore four topics: first, a review of the life and death signaling pathways operative in normal human skin that prevents premature apoptosis of KC with an emphasis on nuclear factor kappaB (NFkappaB) survival signals; second, the molecular pathways that are engaged and regulate apoptosis after normal KC are exposed to ultraviolet (UV) light; third, the apoptotic resistant mechanisms that premalignant and malignant KC utilize to avoid cell death; fourth, therapeutic strategies that can render malignant cells more susceptible to apoptosis with an emphasis on a death pathway mediated by the death ligand TRAIL.

Molecular and cellular biology of basal cell carcinoma

The finding of mutations in the PTCH gene in both Gorlin's syndrome and sporadic basal cell carcinomas has significantly advanced our understanding of the molecular defects that lead to the formation of these tumours. Knowledge of the specific molecular and functional changes that have taken place in these tumours will help us devise more defined therapies, as well as give us a better understanding of normal molecular pathways involved in skin development and function. The following is a summary of our current understanding of the molecular and cellular biology of basal cell carcinoma.

Alteration of mast cell proliferation/apoptosis and expression of stem cell factor in the regression of mastocytoma--report of a case and a serial immunohistochemical study

BACKGROUND

Spontaneous regression of solitary mastocytoma is a well-described phenomenon, but its mechanism is unknown.

METHODS

Serial-section immunohistochemical analyses were performed on biopsies of a mastocytoma from a Japanese child during the proliferation stage (PS, 7 months of age) and the regression stage (RS, 5 years old).

RESULTS

Mast cell (MC) density in RS was markedly decreased (406 cells/mm2) compared to that in PS (3554 cells/mm2). MCs in RS were larger than those in PS. With proliferative cell nuclear antigen (PCNA) staining, 1.7% MCs were positive in PS, whereas no positive MCs were seen in RS. TUNEL-labeling index (LI) in RS (2.8%) increased 1.5-fold in PS (1.9%). With stem cell factor (SCF) staining, 57% of lesional MCs in RS revealed strong cytoplasmic immunoreactivity, whereas only 9% of MCs were positive in PS. Epidermal SCF reactivity was found as intracellular and intercellular patterns in both PS and RS.

CONCLUSIONS

Loss of MC proliferating activity, an increase in apoptotic MCs, and increased expression of SCF in remaining MCs in RS may play a role in the involution of mastocytomas.

Impact of Bcl-2 and Ha-ras on keratinocytes in organotypic culture

In this study, the role of specific molecular alterations associated with multistep skin carcinogenesis was assessed using in vitro organotypic cultures of the spontaneously immortalized, nontumorigenic HaCaT keratinocyte cell line. HaCaT vector control clones and clones expressing bcl-2, activated Ha-ras, or both genes were generated. Clones were induced to stratify and differentiate by culturing on dermal equivalents for 2 wk at the air-medium interface. In parental and vector control HaCaT rafts the expression and distribution of cytokeratin K1, K14, involucrin, proliferating cell nuclear antigen, and p21cip1/waf1 were assessed using immunohistochemistry and immunoblotting and were similar to normal epidermis. Apoptosis was also examined using the TUNEL technique. HaCaT-bcl-2 rafts were similar to control rafts but exhibited lower spontaneous rates of apoptosis and a moderate increase in the rate of proliferation. Differentiation was significantly inhibited in HaCaT-ras organotypic cultures and was associated with high rates of proliferation and lower rates of spontaneous apoptosis. Additionally, HaCaT-ras rafts exhibited significantly higher rates of apoptosis following ultraviolet irradiation compared with vector control or HaCaT-bcl-2 rafts. Bcl-2 was able to largely restore normal differentiation, proliferation, and apoptosis in HaCaT-ras/bcl-2 organotypic cultures. Bcl-2 also abrogated apoptosis induction following ultraviolet irradiation in HaCaT-ras/bcl-2 organotypic cultures. Organotypic keratinocyte culture represents a valuable in vitro system to evaluate the impact of individual molecular genetic alterations on the coordinate regulation of cell proliferation, differentiation, and cell death.

Distribution of Bcl-2 and Bax in embryonic and fetal human skin: antiapoptotic and proapoptotic proteins are differentially expressed in developing skin

The Bcl-2 protein is involved in the regulation of apoptosis. Bax has an antagonistic effect and enhances cell death. We report that in early gestation, Bcl-2 and Bax colocalize to the epidermal portion of the hair follicle. In the more advanced stages, Bax is located in the compartments where a hair canal is excavated and keratinization and holocrine secretion are initiated, in contrast to Bcl-2, which is expressed in the follicular papilla, preventing apoptosis and underscoring its role as a permanent and stable population of specialized fibroblasts. Scattered dendritic cells located in the basal and immediate suprabasal interfollicular epidermis as well as in the outer root sheath of the developing hair follicle, including the bulge, strongly express Bcl-2 and label for HMB-45, identifying them as melanocytes. The spatial and temporal expression pattern of Bcl-2 and Bax during human hair follicle development underscores their importance for hair biology and most likely is disturbed in the evolution of follicular tumors.

Carboxyfullerenes protect human keratinocytes from ultraviolet-B-induced apoptosis

Carboxyfullerene, a water-soluble carboxylic acid derivative of a fullerene, which acts as a free-radical scavenger, was investigated as a protective agent against ultraviolet-light-induced damage in human keratinocytes. First, we demonstrate that carboxyfullerene is not cytotoxic for these cells. In addition, this compound significantly reduces the ultraviolet-B-induced inhibition of keratinocyte proliferation and protects keratinocytes from apoptosis caused by ultraviolet B irradiation in a time- and dose-dependent fashion. Furthermore, the percentage of cells with depolarized mitochondria is significantly lower in ultraviolet-B-irradiated keratinocytes pretreated with carboxyfullerene than in cells provided with diluent alone. Carboxyfullerene also protects human keratinocytes from apoptosis induced by exposure to deoxy-D-ribose, a sugar that causes cell death through a pathway involving oxidative stress. On the other hand, ultraviolet B downregulates bcl-2 levels in human keratinocytes, and carboxyfullerene fails to prevent this effect. These results suggest that carboxy- fullerene protects human keratinocytes from ultraviolet B damage possibly via a mechanism interfering with the generation of reactive oxygen species from depolarized mitochondria without the involvement of bcl-2.

Nerve growth factor protects human keratinocytes from ultraviolet-B-induced apoptosis

Ultraviolet radiation is a potent inducer of apoptosis, whereas autocrine nerve growth factor protects human keratinocytes from programmed cell death. To evaluate the role of nerve growth factor in the mechanisms of ultraviolet B-induced apoptosis, cultured human keratinocytes were ultraviolet B irradiated following pretreatment with K252, a specific inhibitor of the tyrosine kinase high-affinity nerve growth factor receptor. Here we report that the addition of K252 significantly enhanced keratinocyte apoptosis. We then transfected normal human keratinocytes with pNUT-hNGF. Nerve growth factor overexpressing keratinocytes secreted the highest amounts of nerve growth factor in culture supernatants, were more viable, and had a higher rate of proliferation than mock-transfected cells. Whereas ultraviolet B radiation downregulated nerve growth factor mRNA and protein as well as the tyrosine kinase high-affinity nerve growth factor receptor in normal keratinocytes, it failed to do so in nerve growth factor-transfected cells. Moreover, nerve growth factor overexpressing keratinocytes were partially resistant to apoptosis induced by increasing doses of ultraviolet B at 24 and 48 h. These results indicate that downregulation of nerve growth factor function plays an important part in the mechanisms of ultraviolet B-induced apoptosis in human keratinocytes. In addition, ultraviolet B caused a decrease in BCL-2 and BCL-xL expression in mock-transfected keratinocytes, but not in nerve growth factor overexpressing cells. Finally, nerve growth factor prevented the cleavage of the enzyme poly(ADP-ribose) polymerase induced in human keratinocytes by ultraviolet B. These results are consistent with a model whereby the autocrine nerve growth factor protects human keratinocytes from ultraviolet B-induced apoptosis by maintaining constant levels of BCL-2 and BCL-xL, which in turn might block caspase activation.

Communication: expression of the novel inhibitor of apoptosis survivin in normal and neoplastic skin

Apoptosis plays a fundamental part in epidermal homeostasis, and apoptotic cells have been detected in normal and diseased skin. Little is known, however, on the inhibitory mechanisms of apoptosis at the skin level. In addition to bcl-2, a novel inhibitor of apoptosis designated survivin and structurally analogous to IAP apoptosis inhibitors has been recently identified. The expression of survivin in normal and pathologic skin was investigated. Immunohistochemical studies revealed that survivin is expressed in basal keratinocytes, but not in suprabasal epidermal layers, with a pattern similar to bcl-2. In western blots, the anti-survivin antibody recognized a single band of 16.5 kDa in protein extracts from normal human keratinocytes in culture, in agreement with the predicted size of survivin. In addition, survivin immunoreactivity was detected in benign and malignant melanocytic lesions, with strong expression in invasive lesions of melanomas. Whereas survivin staining was undetectable in benign epithelial tumors, such as seborrheic keratoses, it was observed in all epidermal layers in Bowen's disease. Interestingly, at variance with bcl-2, survivin was markedly expressed in squamous cell carcinoma, but virtually lacking in basal cell carcinoma, suggesting that these two apoptosis inhibitors may act through different anti-apoptotic pathways. Deregulation of survivin may influence both epidermal homeostasis and the development of melanoma and nonmelanoma skin cancer.

HPV16 E6 oncoprotein inhibits apoptosis induced during serum-calcium differentiation of foreskin human keratinocytes

Transfection of human papillomavirus (HPV) 16 E6 oncogene into foreskin primary human keratinocytes (PHKs) causes the formation of colonies of viable cells resistant to serum-calcium differentiation. To define the stage of keratinocyte differentiation inhibited by E6, we examined the response of PHKs to serum and calcium with respect to parameters of both growth and differentiation. The effect of HPV16 E6 was evaluated by infection with recombinant retroviruses encoding the E6 protein. Results of these studies indicated that terminal differentiation of cultured foreskin keratinocytes, triggered by serum and calcium, is a progressive process (2-3 weeks) that ends with cell death with characteristics of apoptosis. Human keratinocyte terminal differentiation was accompanied by time-related changes in the expression of cellular proteins involved in the control pathways of apoptosis, including downregulation of Bcl-2 and p53 and upregulation of Bax, which coincided with the appearance of morphological signs of apoptosis. E6 expression did not override the differentiation-associated G1 arrest or prevent the induction of squamous differentiation-specific markers, transglutaminase 1 and involucrin. E6 expression led, however, to a significant reduction in cell stratification and cell death by apoptosis, which correlated with prolonged expression of Bcl-2 and reduced elevation of Bax levels that occurred concomitant with a complete loss of p53. The data argue that E6 inhibits terminal differentiation of foreskin PHKs through inhibition of their differentiation-induced apoptotic program.

Differential expression of cell survival and cell cycle regulatory proteins in cutaneous squamoproliferative lesions

Previous models of cutaneous carcinogenesis have primarily focused on the regulation of keratinocyte (KC) proliferation and differentiation. However, it has become clear in many neoplastic systems that altered rates of cell death and/or inability to undergo growth arrest can also contribute to the development of cancer. Apoptosis-regulatory proteins include those that block apoptosis such as Bcl-2 and Bcl-x, whilst a related protein Bax promotes apoptosis. Cell cycle regulatory proteins include those associated with growth arrest, i.e. p21wafl, p53, and those associated with proliferation, i.e. Ki-67. Paraffin embedded samples from ten different lesions of squamous cell carcinoma (SCC), Bowen's disease (BD), keratoacanthomas (KA), and nine normal adult skin samples were stained by immunohistochemistry to detect expression of Bcl-2, Bcl-x, Bax, Ki-67, p21wafl, p53 and apoptosis (TUNEL assay). Compared to low levels of Bcl-x and Bcl-2 immunostaining in normal skin, all the squamoproliferative lesions had strong and diffuse KC expression of Bcl-x (>80%) but minimal to absent KC Bcl-2 expression (<15%). Bax immunopositivity was limited to the basal layer in normal skin and BD. In contrast, by examining serial sections both Bcl-x and Bax appeared to be coexpressed by the majority of malignant KCs in KA and SCC (>70%). These immunostaining profiles reveal that squamoproliferative lesions, including invasive transformed KCs, preferentially express Bcl-x over Bcl-2, in addition to upregulating their Bax levels. Even though there were numerous TUNEL positive cells in these squamoproliferative lesions, no other evidence of apoptosis was seen reinforcing the necessity to use caution when relying on TUNEL staining for identification of programmed cell death in skin biopsies. Normal sun-exposed skin had low but detectable p53 and rare p21wafl KC expression. Significantly higher numbers of p21wafl and p53 immunopositive KCs were noted throughout the lesions in BD and SCC in contrast to KA where p53 and rare p21wafl immunopositive KCs were primarily limited to the periphery of the tumor cell islands. In general, p53 KC expression was higher in all squamoproliferative lesions and sun-exposed normal skin compared to p21Wafl expression. Summary of the expression of cell cycle regulatory proteins for both p21wafl and p53 KC expression was: SCC > BD > KA, in marked contrast to Ki-67 KC expression which was: BD > KA > SCC. The relatively few malignant cells in SCC that were actively participating in the cell cycle (i.e. Ki-67 positive) suggests that these neoplasms may arise primarily by increased cell survival and resistance to apoptosis rather than by hyperproliferation. These studies emphasize the importance of examining multiple members of protein families that regulate apoptosis, proliferation, growth arrest, and differentiation. It is the overall balance between these cellular phenomena that determine whether a cell remains viable or undergoes programmed cell death and contributes to the appearance of a neoplasm. The overexpression of Bcl-x may confer a survival advantage to malignant KCs unable to growth arrest to repair damaged DNA (mutant p53) and/or undergo terminal differentiation (increased p21wafl). Thus, mutation or aberrant expression of such proteins may participate in the multistep process of carcinogenesis that gives rise to these squamoproliferative lesions.

Differentiation of odontogenic keratocysts from other odontogenic cysts by the expression of bcl-2 immunoreactivity

Odontogenic keratocysts (OKC) present an aggressive course with a marked tendency to recurrence. The epithelium of OKC is thought to have an intrinsic growth potential and has been shown to present a higher rate of proliferation as compared to other types of cyst. bcl-2 has a role in the extension of cell survival. The objective of the present study was to evaluate the bcl-2 protein expression in different odontogenic cysts. A total of 19 dentigerous cysts (DC), 20 radicular cysts (RC) and 14 OKC were used in the present study. DC and RC showed an almost complete negativity for bcl-2. OKC, on the other hand, presented in all cases a strong positivity in the cells of the basal layer, with, in most cases, more than 50% of the cells positive. This bcl-2 positivity of the basal layer of OKC could point to an abnormal control of the cell cycle. The bcl-2 protein overexpression could then produce an increase in the survival of the epithelial cells, and this increased lifespan could, in turn, lead to the peculiar aggressive growth pattern of OKC. Moreover the bcl-2 staining can be useful to differentiate OKC from other types of odontogenic cysts.

Bcl-2 expression in Langerhans' cell histiocytosis

Langerhans' cell histiocytosis (LCH) is an abnormal accumulation of dendritic histiocytes of unknown pathogenesis. It has recently been shown to be a clonal process. Bcl-2 is a proto-oncogene whose protein product is known to inhibit apoptosis. The overexpression of bcl-2 has been demonstrated in a number of neoplasms, presumably prolonging the survival of the neoplastic cells. We examined the expression of bcl-2 in normal Langerhans' cells in the skin and in LCH by immunohistochemistry for protein and in situ hybridization for mRNA to see if it could be implicated in the pathogenesis of this disorder. Additionally, we performed Southern analysis to determine if genomic rearrangement of the bcl-2 gene occurs in cases of LCH. Bcl-2 was not detected in normal skin Langerhans' cells. Eleven of thirteen cases of LCH demonstrated bcl-2 protein expression in the cytoplasm of the Langerhans' cells by immunohistochemistry, while 12 of 13 cases had evidence of bcl-2 mRNA by in situ hybridization. Southern analysis revealed a germline configuration of the bcl-2 gene in the five cases studied. These findings suggest that bcl-2 expression is present and up-regulated in pathologic Langerhans' cells, however, this overexpression does not appear to be due to genomic rearrangement.

Decreases in phorbol ester-induced papilloma development in v-Ha-ras transgenic TG.AC mice during reduced gene dosage of bcl-2

We have demonstrated that induction of transgene expression in the v-Ha-ras-transgenic TG.AC mouse is a critical event in skin tumorigenesis and that cutaneous papillomas arise from follicular epidermis after treatment with chemical carcinogens. The sensitivity of TG.AC mice to skin tumorigenesis, coupled with their low incidence of spontaneous skin tumors, makes this strain a good model for identifying carcinogens and for investigating the roles that other genes may play in the development of skin neoplasia. To investigate the possible involvement of the bcl-2 gene in skin tumorigenesis in the TG.AC mouse, we crossed heterozygous bcl-2-knockout mice (C57BI/6, 129 background) with TG.AC mice (FVB/N background). Female mice were genotyped by using a neo cassette to identify bcl-2-deficient mice. In addition, homozygous TG.AC mice were bred with FVB/N mice to generate hemizygous TG.AC mice on an FVB/N background to serve as a gene-dosage control. The F1 progeny consisted of FVB/N(v-Ha-ras+/-):C57BI/6,129(bcl-2+/+),FVB/N(v-Ha-ra s+/-):C57BI/6,129(bcl-2+/-), and FVB/N(v-Ha-ras+/-,bcl-2+/+). Ten-week-old mice were dosed twice weekly for 10 wk with acetone, 1.25 microg of 7,12-tetradecanoylphorbol-13-acetate (TPA), or 2.5 microg of TPA, and papillomas were counted weekly. Papillomas were analyzed for ras transgene and bcl-2 expression by reverse transcription-polymerase chain reaction, v-Ha-ras expression by in situ hybridization, and proliferating cell nuclear antigen expression by immunohistochemical analysis. Fewer papillomas (P < 0.05) were observed at the low dose of TPA (1.25 microg) in mice carrying the bcl-2 knockout allele than in the wild-type mice, suggesting that reduction of the bcl-2 gene product affects the susceptibility of TG.AC mice to TPA-induced papillomas. However, at the high dose of TPA (2.5 microg), there was no difference in papilloma response between knockout and wild-type mice, regardless of strain background. This suggests that at the higher dose of TPA, the effect of reduction in bcl-2 gene product was obscured. These results support the hypothesis that bcl-2 plays a limited role in skin tumorigenesis in the TG.AC mouse.

Apoptosis-associated markers in oral lichen planus

Hypothesizing that loss of basal cells in oral lichen planus is due to apoptosis, we evaluated LP specimens for apoptosis-regulating proteins [positive regulators Bcl-xS, Bax, Fas/Fas-ligand, p53, and negative regulators (anti-apoptotic) Bcl-2, Bcl-xL and compared results with reactions in normal mucosa and chronically inflamed gingiva. Also, sections were evaluated with an in situ TUNEL assay that identifies apoptotic DNA fragments. Basal keratinocytes in normal buccal mucosa, nonspecific gingivitis, and LP were negative for Bcl-2 protein, but melanocytes and lymphoid cells were positive. Keratinocyte staining for Bcl-x was negative to weak in normal buccal mucosa and gingivitis, and moderate in LP. Keratinocytes (especially upper prickle cells) in all tissues stained similarly for Bax at weak to moderate levels. Also, no differences in Fas and Fas-ligand staining were evident. Prominent p53-positive staining was seen in all LP biopsies (10-100% of basal keratinocytes) but not in normal buccal mucosa and gingivitis. Few basal keratinocytes in 5/10 LP cases exhibited a positive in situ signal for DNA fragment-associated apoptosis. That the Bcl-2 family of proteins and Fas/Fas-ligand were detected in normal and diseased tissues, and were occasionally expressed differently in oral LP, supports the notion that apoptosis is a potential mechanism of keratinocyte loss, especially in LP. The pattern of p53 staining in oral LP suggests over-expression of wild-type protein; a phenomenon that would arrest the cell cycle to allow repair of damaged DNA, or trigger apoptosis. While immunohistochemical evidence for apoptosis-associated basal keratinocyte death in LP was slight, it appeared that it may be p53 protein, and possibly Bcl-x associated.

Bcl-2 overexpression in basaloid proliferations overlying dermatofibromas and basal cell carcinomas

Basaloid proliferations overlying dermatofibromas resembling superficial basal cell carcinomas have been interpreted both as reactive/regressive and frankly malignant. Basal cell carcinoma is a slow-growing tumour, which so far has been regarded as an actively proliferating lesion with a high apoptotic activity. We examined immunohistochemically 6,dermatofibromas with overlying simple hyperplasia, 12 dermatofibromas with overlying basaloid proliferations, and 24 basal cell carcinomas for expression of Ki-67 protein, and bcl-2 protein. The Ki-67 labelling index represents an estimate of proliferative activity. Bcl-2 protein suppresses apoptosis. The Ki-67 labelling indexes of basaloid proliferations, basal cell carcinomas, and normal epidermis were similar (11-15%, p < 0.05, Mann-Whitney test). Bcl-2 protein was expressed in all cells of basaloid proliferations, similar to the expression pattern in basal cell carcinomas. We suggest that basaloid proliferations overlying dermatofibromas might have achieved a phenotype that equals an early stage of BCC carcinogenesis.

Merkel cells and Merkel cell carcinoma express the BCL-2 proto-oncogene

The bel-2 proto-oncogene, which is involved in the regulation of apoptosis, is expressed in a wide variety of fetal and adult tissues. We and others have demonstrated recently that in the human skin melanocytes, nevus cells and melanoma cells express bcl-2 constitutively. In the present study, we have analysed the expression of bcl-2 in Merkel cells and in Merkel cell carcinomas. In 2 colour immunofluorescence staining, normal human Merkel cells as identified by the expression of cytokeratins 8, 18 and 20, were also anti-bcl-2 positive. Staining of paraffin sections of Merkel cell carcinomas with an anti-bcl-2 monoclonal antibody revealed strong bcl-2 protein immunoreactivity in all 5 tumors tested. Serial sections of Merkel cell carcinomas stained with the monoclonal antibodies CK 20, CAM 5.2, anti-neuron-specific enolase and anti-bcl-2 showed that the anti-bcl-2 reactive cells were indeed tumor cells. Our data demonstrate for the first time, that normal human Merkel cells and Merkel cel carcinomas express bcl-2 constitutively. Considering the biological function of the bcl-2 proto-oncogene, i.e., its anti-apoptotic effect, it is conceivable that in the near future, modulations of the expression of this protein may offer a new strategy in the therapy of bcl-2 expressing tumors such as Merkel cell carcinoma.

Merkel cells and Merkel cell carcinoma express the BCL-2 proto-oncogene

The bcl-2 proto-oncogene, which is involved in the regulation of apoptosis, is expressed in a wide variety of fetal and adult tissues. We and others have demonstrated recently that in the human skin melanocytes, nervus cells and melanoma cells express bcl-2 constitutively. In the present study, we have analysed the expression of bcl-2 in Merkel cells and in Merkel cell carcinomas. In 2 colour immunofluorescence staining, normal human Merkel cells as identified by the expression of cytokeratins 8, 18 and 20, were also anti-bcl-2 positive. Staining of paraffin sections of Merkel cell carcinomas with an anti-bcl-2 monoclonal antibody revealed strong bcl-2 protein immunoreactivity in all 5 tumors tested. Serial sections of Merkel cell carcinomas stained with the monoclonal antibodies CK 20, CAM 5.2, anti-neuron-specific enolase and anti-bcl-2 showed that the anti-bcl-2 reactive cells were indeed tumor cells. Our data demonstrate for the first time, that normal human Merkel cells and Merkel cell carcinomas express bcl-2 constitutively. Considering the biological function of the bcl-2 proto-oncogene, i.e., its anti-apoptotic effect, it is conceivable that in the near future, modulations of the expression of this protein may offer a new strategy in the therapy of bcl-2 expressing tumors such as Merkel cell carcinoma.