Cyclin A and beta-catenin expression in actinic keratosis, Bowen's disease and invasive squamous cell carcinoma of the skin

Overlapping tumor-specific expression of p53, p16INK4a, and sirtuin 1 in Bowen's disease: A case report

Understanding the impact of inactivating mutations in SIRT1 on the p53 and p16 tumor suppressor genes may yield new insight into the oncogenic mechanisms underlying Bowen's disease.

Aberrant Expression of E-cadherin/β-catenin During Epidermal Tumourigenesis in Dogs

Clinically relevant epidermal tumours in dogs include cutaneous papillomas (CPs) and cutaneous squamous cell carcinomas (CSCCs). The development of CPs and CSCCs involves dysregulation in expression of E-cadherin/β-catenin; however, knowledge about the contribution of these molecules to epidermal tumourigenesis in dogs is limited. This study examined the immunohistochemical expression pattern of E-cadherin/β-catenin in samples of normal canine epidermis, CPs, preneoplastic epidermis and CSCCs, using tissue microarrays, in order to elucidate whether the dysregulated expression of these molecules may contribute to the pathogenesis of clinically relevant epidermal tumours in dogs. We also investigated the correlation between the immunohistochemical expression pattern of E-cadherin/β-catenin in these tissue microarrays to further evaluate whether the disruption of the adherens junction interactions plays a relevant role in canine epidermal tumourigenesis. In samples of CP and preneoplastic epidermis, the membrane immunoreactivity of E-cadherin/β-catenin was conserved, while in CSCC, the immunoreactivity of these molecules was significantly reduced, independently of the tumour location. There was significant correlation between the membrane expression of E-cadherin/β-catenin in CSCC. β-catenin also showed cytoplasmic and nuclear expression in samples of CP, preneoplastic epidermis and CSCC. These results support the hypothesis that dysregulated expression of E-cadherin/β-catenin may play a critical role in the pathogenesis of relevant canine epidermal tumours, not only due to the disruption of the intercellular adherens junctions, but also due to the dysregulated activity of the signalling pathways in which these molecules are involved.

Tumor Suppressive Function of NQO1 in Cutaneous Squamous Cell Carcinoma (SCC) Cells

Cutaneous squamous cell carcinoma (SCC) is a common cancer that significantly decreases the quality of life. It is known that external stimulus such as ultraviolet (UV) radiation induces cutaneous SCC via provoking oxidative stress. NAD(P)H dehydrogenase 1 (NQO1) is a ubiquitous flavoenzyme that functions as a guardian against oxidative stress. However, the effect of NQO1 on cutaneous SCC is not clearly elucidated. In this study, we investigated the effect of NQO1 on cutaneous SCC cells using the recombinant adenoviruses that can upregulate and/or downregulate NQO1 expression. Overexpression of NQO1 resulted in significant decrease of cell proliferation and colony forming activity of SCC lines (SCC12 and SCC13 cells). By contrast, knockdown of NQO1 increased the cell proliferation and colony forming activity. Accordingly, the levels of proliferation-related regulators, such as Cyclin D1, Cyclin E, PCNA, SOX2, and p63, were decreased by the overexpression of NQO1, while those were increased by knockdown of NQO1. In addition, NQO1 affected the invasion and migration of SCC cells in a very similar way, with the regulation of epithelial-mesenchymal transition- (EMT-) related molecules, including E-cadherin, N-cadherin, Vimentin, Snail, and Slug. Finally, the overexpression of NQO1 decreased the level of phosphorylated AKT, JNK, and p38 MAPK, while the knockdown of NQO1 increased the level of phosphorylated signaling molecules. Based on these data, NQO1 has tumor suppressive function in cutaneous SCC cells.

WNT Signaling in Cutaneous Squamous Cell Carcinoma: A Future Treatment Strategy?

The molecular mechanisms underlying cutaneous squamous cell carcinoma are less well established than those for other common skin cancers, but recent evidence has highlighted a potentially critical role for WNT signaling in both the development and progression of cutaneous squamous cell carcinoma. WNT pathways are aberrantly regulated in multiple tumor types (albeit in a context-dependent manner), and this has stimulated the development of WNT inhibitory compounds for cancer treatment. In this review, we examine existing evidence for a role of WNT signaling in cutaneous squamous cell carcinoma and discuss if WNT inhibition represents a realistic therapeutic strategy for the future.

Sox9 is a β-catenin-regulated transcription factor that enhances the colony-forming activity of squamous cell carcinoma cells

Squamous cell carcinoma (SCC) is a common skin cancer, of which the incidence is relatively high, ranking second among the non‑melanoma skin cancers. It is known that numerous intracellular signal regulators are involved in the pathogenesis of SCC. The Wnt/β-catenin signaling pathway serves an important role in cancer development. However, the downstream effectors of β‑catenin remain to be clearly elucidated yet. The present study investigated the functional importance of Wnt/β‑catenin signaling in cutaneous SCC. β‑catenin expression was reduced using recombinant adenovirus expressing specific microRNA (miR). Knockdown of β‑catenin resulted in a marked reduction of the colony-forming activity of the SCC cells, SCC12. In an attempt to identify the β‑catenin downstream genes, it was found that Sox9 was regulated by β‑catenin in SCC12 cells. Overexpression of a constitutively active form of β‑catenin led to the induction of Sox9, while knockdown of β‑catenin resulted in downregulation of Sox9. When the expression of Sox9 was reduced using specific miR, colony-forming activity of the SCC12 cells was significantly reduced. When Sox9 was overexpressed in cells where β‑catenin was knocked down, it partially restored the colony‑forming potential. Taken together, the present results suggested that Sox9 is a β-catenin downstream transcription factor and is positively involved in SCC development.

Wnt-3a-activated human fibroblasts promote human keratinocyte proliferation and matrix destruction

Aberrant Wnt regulation, detectable by nuclear translocation of beta-catenin, is a hallmark of many cancers including skin squamous cell carcinomas (SCCs). By analyzing primary human skin SCCs, we demonstrate that nuclear beta-catenin is not restricted to SCC cells but also detected in stromal fibroblasts, suggesting an important role for aberrant Wnt regulation also in the tumor microenvironment. When human keratinocytes and fibroblasts were treated with Wnt-3a, fibroblasts proved to be more responsive. Accordingly, Wnt-3a did not alter HaCaT cell functions in a cell-autonomous manner. However, when organotypic cultures (OTCs) were treated with Wnt-3a, HaCaT keratinocytes responded with increased proliferation. As nuclear beta-catenin was induced only in the fibroblasts, this argued for a Wnt-dependent, paracrine keratinocyte stimulation. Global gene expression analysis of Wnt-3a-stimulated fibroblasts identified genes encoding interleukin-8 (IL-8) and C-C motif chemokine 2 (CCL-2) as well as matrix metalloproteinase-1 (MMP-1) as Wnt-3a targets. In agreement, we show that IL-8 and CCL-2 were secreted in high amounts by Wnt-3a-stimulated fibroblasts also in OTCs. The functional role of IL-8 and CCL-2 as keratinocyte growth regulators was confirmed by directly stimulating HaCaT cell proliferation in conventional cultures. Most important, neutralizing antibodies against IL-8 and CCL-2 abolished the Wnt-dependent HaCaT cell hyperproliferation in OTCs. Additionally, MMP-1 was expressed in high amounts in Wnt-3a-stimulated OTCs and degraded the stromal matrix. Thus, our data show that Wnt-3a stimulates fibroblasts to secrete both keratinocyte proliferation-inducing cytokines and stroma-degrading metalloproteinases, thereby providing evidence for a novel Wnt deregulation in the tumor-stroma directly contributing to skin cancer progression.

Epithelial to mesenchymal transition in cutaneous squamous cell carcinoma is correlated with COX-2 expression but not with the presence of stromal macrophages or CD10-expressing cells

Epithelial to mesenchymal transition (EMT) is an intricate process by which epithelial cells loose epithelial characteristics and acquire a mesenchymal-like phenotype. EMT and cyclooxygenase 2 (COX-2) expression are related to tumor invasion and metastasis. The tumor microenvironment plays a major role in tumor progression and the induction of EMT. Here, we investigated the relationship between EMT and COX-2 expression as well as tumor-associated macrophages (TAM) and CD10-positive stromal cells during the development of cutaneous squamous neoplastic lesion. We performed immunohistochemical staining for vimentin, E-cadherin, β-catenin, COX-2, CD68, and CD10 in 41 cases of squamous cell cancers (SCC), 20 of Bowen's disease, 30 of actinic keratosis, and 30 samples of normal skin. SCC cells showed significantly increased vimentin expression and reduced expression of membranous E-cadherin and β-catenin compared with cells in precursor lesions and in normal skin. COX-2 expression was also markedly increased in SCC cells. E-cadherin expression was positively correlated with β-catenin expression and inversely correlated with COX-2 expression in SCC cells. The number of TAM and CD10-positive stromal cells increased from the normal skin to precursor lesions and SCC cells. The number of TAM and of CD10-positive stromal cells did not correlate with the expression of E-cadherin, β-catenin, COX-2, and vimentin in SCC cells. We suggest that cutaneous SCC cells show EMT, which appears to be correlated with COX-2 expression but not with stromal CD10 expression and TAM.

Stem cells of the human epidermis and their niche: composition and function in epidermal regeneration and carcinogenesis

Skin, as the largest organ, has long been subject of excellent and pioneering studies on stem cells and their role in tissue regulation and tumor formation. In particular, intensive research on mouse skin, and here especially the hair follicle, has largely extended our knowledge. Surprisingly, human skin, although the most easily accessible tissue in man, is far less conceived with regard to its stem cells and their specific environment (the niche). In consequence, these features are as yet only insufficiently defined and it still has to be elucidated how insights in cutaneous stem cell biology gained in mice can be extrapolated to humans. In the last few years, human model systems such as humanized mice or in vitro organotypic cultures that support maintenance or reconstruction of human skin and long-term epidermal regeneration have been developed. These models allow lineage tracing experiments and can be modified by adopting genetically manipulated cell types. Accordingly, they represent proper tools for human stem cell research and will clearly help to improve our still incomplete understanding. Like normal skin, the non-melanoma skin cancers and their respective tumors have gained considerable interest in basic as well as in clinical research. Being the most frequent human tumors globally, basal cell carcinomas and cutaneous squamous cell carcinomas (SCCs) continue to increase in incidence and specifically SCCs predominate in immunosuppressed transplant recipients. This review intends to compile the present knowledge on keratinocyte stem cells and their niches in normal skin and skin carcinomas with a special focus on the human situation. In particular, the role of the microenvironment, the niche, is emphasized, promoting our view of the decisive importance of the niche as a key regulatory element for controlling position, fate and regenerative potential of the stem cell population both in healthy skin and in carcinomas.

UVB radiation-induced β-catenin signaling is enhanced by COX-2 expression in keratinocytes

UVB radiation is the major carcinogen responsible for skin carcinogenesis, thus elucidation of the molecular pathways altered in skin in response to UVB would reveal novel targets for therapeutic intervention. It is well established that UVB leads to upregulation of cyclooxygenase 2 (COX-2) in the skin which contributes to skin carcinogenesis. Overexpression of COX-2 has been shown to promote colon cancer cell growth through β-catenin signaling, however, little is known about the connection between UVB, COX-2, and β-catenin in the skin. In the present study, we have identified a novel pathway in which UVB induces β-catenin signaling in keratinocytes, which is modulated by COX-2 expression. Exposure of the mouse 308 keratinocyte cell line (308 cells) and primary normal human epidermal keratinocytes (NHEKs) to UVB resulted in increased protein levels of both N-terminally unphosphorylated and total β-catenin. In addition, we found that UVB-enhanced β-catenin-dependent TOPflash reporter activity and expression of a downstream β-catenin target gene. We demonstrated that UVB-induced β-catenin signaling is modulated by COX-2, as treatment of keratinocytes with the specific COX-2 inhibitor NS398 blocked UVB induction of β-catenin. Additionally, β-catenin target gene expression was reduced in UVB-treated COX-2 knockout (KO) MEFs compared to wild-type (WT) MEFs. Furthermore, epidermis from UVB-exposed SKH-1 mice exhibited increased N-terminally unphosphorylated and total β-catenin protein levels and increased staining for total β-catenin, and both responses were reduced in COX-2 heterozygous mice. Taken together, these results suggest a novel pathway in which UVB induces β-catenin signaling in keratinocytes which is enhanced by COX-2 expression.

β-catenin in canine skin: immunohistochemical pattern of expression in normal skin and cutaneous epithelial tumours

In normal adult skin, β-catenin is a structural component of the intercellular junction and the Wnt/β-catenin pathway plays a key role in the regulation of cutaneous homeostasis, particularly in the maintenance of hair follicle stem cells. No data are available on the expression pattern of β-catenin in normal canine skin and in canine cutaneous epidermal and follicular tumours. The present study used immunohistochemistry to determine β-catenin expression in four samples of normal canine skin and 62 cutaneous epithelial tumours (14 epidermal, 30 follicular and 18 glandular). β-catenin expression was localized to the nucleus of matrical and dermal papilla cells in anagen hair follicles and was also found in scattered cells of the outer root sheath, suggesting that these follicular epithelial cells may have a high proliferative potential. Nuclear labelling, considered a hallmark of activation of the Wnt/β-catenin signalling pathway, was observed in canine follicular tumours with matrical differentiation (100% of cases of trichoepithelioma and pilomatricoma), suggesting that a possible mutation of the canine CTNBB1 gene may underlie these tumours. In contrast, malignant tumours (squamous cell carcinoma, basal cell carcinoma, sebaceous and apocrine gland carcinoma and epithelioma) were characterized by reduction/loss of β-catenin membrane labelling compared with normal cutaneous epithelial cells and benign tumours, suggesting that reduction/loss of β-catenin expression is important in the acquisition of the malignant phenotype and may have a role in the infiltration and metastasis of these tumours.

Altered β-catenin expression related to cancer progression on actinic cheilitis and squamous cell carcinoma of the lip

β-Catenin is a bifunctional protein related to cell adhesion and gene transcription when activated by Wnt pathway. Altered expression of β-catenin was related to loss of differentiation, more aggressive phenotype, increase of tumor invasion, and poor prognosis in a number of different cancers. Actinic cheilitis is caused by excessive exposure to ultraviolet radiation and has a high potential to suffer malignant transformation into squamous cell carcinoma (SCC) of the lip, the most frequent oral malignancy. Studies of oral cancer have shown the correlation of β-catenin expression and oral SCC prognosis, and loss of membrane expression may be considered as a potential marker for early tumor recurrence. Thirty-five cases of actinic cheilitis and 12 cases of SCC of the lip were select and submitted to immunohistochemical staining using β-catenin antibody. β-Catenin was positive on the membrane for all cases. Eighty-five percent of actinic cheilitis cases showed cytoplasmatic staining, and 22% nuclear staining. Eighty-three percent of SCC was positive for β-catenin, and none of them had nuclear staining. Cytoplasmatic and nuclear staining of β-catenin on studied cases point to pathway alterations. Results demonstrated that β-catenin expression is altered on epithelial dysplasia, and it is related to degree of alterations.

Phenol peels as a novel therapeutic approach for actinic keratosis and Bowen disease: prospective pilot trial with assessment of clinical, histologic, and immunohistochemical correlations

BACKGROUND

Although chemical peels may be used for precancerous lesions, no histologic or immunohistochemical studies have been performed to validate clinical impressions and/or outcome.

OBJECTIVE

Our purpose was to investigate the efficacy and prognostic relevance of phenol peels in Japanese patients with actinic keratosis and Bowen disease using clinical and histologic criteria.

METHODS

A total of 46 patients were treated with phenol peels, and followed up for at least 1 year after treatment. Biopsy specimens were taken before and after treatment. Cases of complete response were classified by the number of treatment sessions. We evaluated parameters for epidermal thickness, proliferation, dysplasia, and apoptosis, and clinical characteristics to correlate phenol peels with assessments of efficacy, patient-selection criteria, and risk for transformation to cutaneous squamous cell carcinoma.

RESULTS

There were 39 (84.8%) patients with a complete response after one to 8 treatment sessions. Statistically, differences in clinical improvement with peels and the number of treatment sessions correlated with histology, personal history of skin cancer, tumor thickness, and cyclin A expression.

LIMITATIONS

This study was a prospective pilot trial. Blinded, placebo-controlled, randomized studies would be ideal.

CONCLUSION

We conclude that phenol peels are very effective for treating precancerous lesions of actinic keratosis and Bowen disease. In addition, our study clearly demonstrates that tumor thickness and cyclin A could be specific and useful markers as adjunctive diagnostic tools to predict the efficacy of phenol treatment of these lesions.

WNT-5A, but not matrix metalloproteinase 3 or beta-catenin protein, expression is related to early stages of lip carcinogenesis

BACKGROUND

Oncogenic Wnt/beta-catenin signaling occurs in numerous types of cancers, but little is known about the role of the Wnt protein family member, WNT-5A, in lip carcinogenesis. The aim of this study was to investigate WNT-5A, beta-catenin, and matrix metalloproteinase (MMP)-3 protein expression in actinic cheilitis (AC), and lip squamous cell carcinoma (LSCC).

METHODS

Twenty-one cases of AC, and fifty-one cases of LSCC were analyzed, with normal lip mucosa used as a control. Qualitative and semi-quantitative analyses of WNT-5A, beta-catenin, and MMP-3 immunostaining pattern and cellular distribution were performed.

RESULTS

WNT-5A was observed in more than 50% of the cells, scattered in all layers of AC, in contrast to the absence of immunostaining in normal lip mucosa. AC presented a higher level of WNT-5A expression than LSCC (P = 0.0289, Fisher test), while MMP-3 immunoexpression was statistically more significant in LSCC than in AC (P = 0.0285, Fisher test). Immunolabeling of beta-catenin protein was differentially distributed between samples; the majority of AC cases (61.90%) demonstrated a membranous-cytoplasmic pattern, while a considerable number of LSCC cases (29.41%) revealed a cytoplasmic pattern, instead of the usual membranous pattern.

CONCLUSIONS

The present results suggest that WNT-5A may be an important marker during initial events of AC malignant transformation, in which non-canonical and canonical Wnt/beta-catenin signaling pathways could be involved. Additionally, WNT-5A might recruit other events in LSCC, such as MMP-3 protein synthesis, as its presence is increased in established malignant processes without beta-catenin dependency.

The novel protein PTPIP51 is expressed in human keratinocyte carcinomas and their surrounding stroma

Background: The novel protein PTPIP51 (SwissProt accession code Q96SD6) is known to interact with two non-transmembrane protein-tyrosine phosphatases, PTP1B and TCPTP in vitro. Overexpression of the full-length protein induces apoptosis in HeLa and HEK293T cells (Lv et al. 2006). PTPIP51 shows a tissue-specific expression pattern and is associated with cellular differentiation and apoptosis in some mammalian tissues, especially in human follicular and interfollicular epidermis. PTPIP51 protein is expressed in all suprabasal layers of normal epidermis, whereas the basal layer contains PTPIP51 mRNA only but lacks the protein. Objectives: The expression of PTPIP51 was investigated in keratinocyte carcinomas, that is human basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) as well as Bowen's disease (BD) and keratoacanthomas (KAs) on a transcriptional (mRNA) and translational (immunohistochemical) level. Methods: Formalin-fixed, paraffin-embedded sections of BCCs, SCCs, KAs and BD, respectively, were analysed by RT-PCR, as well as immunohistochemistry and subsequent fluorescence microscopy. PTPIP51-positive cells of the tumour and the surrounding stroma were identified on the basis of specific morphological features by means of H & E staining. To obtain further information about a putative function of PTPIP51, a possible association of PTPIP51 with apoptotic cells, as well as an assumed negative correlation with proliferating cells was investigated by means of an in-situ TUNEL assay and Ki67/MIB-1 antigen staining, respectively. Co-immunostainings with PTPIP51 were performed for the following antigens: TCPTP, PTP1B and β-catenin. Results: PTPIP51-expression was detected in BCCs and SCCs of the skin, as well as in KAs and BD. Both types of keratinocyte carcinoma revealed a specific localization pattern of PTPIP51 in malignant keratinocytes. Whereas PTPIP51 -positive cells of BCC were found to form two cluster types with a different subcellular localization of the protein, i.e. cytoplasmic and nuclear or predominantly membranous, investigation of SCC revealed a meshwork-like appearance of PTPIP51-positive malignant keratinocytes, created by a mainly membranous localization. BD and KA resembled the findings of PTPIP51-expression in SCC. Furthermore, we observed a partial co-localization of PTP1B and PTPIP51 in BCC. SCC and BCC showed a co-expression and partial co-localization of PTPIP51 with β-catenin. Some PTPIP51-positive cells were found to undergo apoptosis. PTPIP51 was also expressed in cells comprising the surrounding stromal microenvironment. This was particularly noticed for endothelial cells lining peritumoural vessels as well as for infiltrating cells of both, the innate and the adaptive immune system. Conclusions: The results showed a distinct mainly membranous expression pattern of PTPIP51 in BCCs and SCCs. Since PTPIP51 was also detected in the peritumoural tissue, the protein may play a crucial role in keratinocyte tumour development.

Cutaneous cancer stem cell maintenance is dependent on beta-catenin signalling

Continuous turnover of epithelia is ensured by the extensive self-renewal capacity of tissue-specific stem cells. Similarly, epithelial tumour maintenance relies on cancer stem cells (CSCs), which co-opt stem cell properties. For most tumours, the cellular origin of these CSCs and regulatory pathways essential for sustaining stemness have not been identified. In murine skin, follicular morphogenesis is driven by bulge stem cells that specifically express CD34. Here we identify a population of cells in early epidermal tumours characterized by phenotypic and functional similarities to normal bulge skin stem cells. This population contains CSCs, which are the only cells with tumour initiation properties. Transplants derived from these CSCs preserve the hierarchical organization of the primary tumour. We describe beta-catenin signalling as being essential in sustaining the CSC phenotype. Ablation of the beta-catenin gene results in the loss of CSCs and complete tumour regression. In addition, we provide evidence for the involvement of increased beta-catenin signalling in malignant human squamous cell carcinomas. Because Wnt/beta-catenin signalling is not essential for normal epidermal homeostasis, such a mechanistic difference may thus be targeted to eliminate CSCs and consequently eradicate squamous cell carcinomas.

Altered expression of desmocollin 3, desmoglein 3, and beta-catenin in oral squamous cell carcinoma: correlation with lymph node metastasis and cell proliferation

Desmocollin 3 (Dsc3) and desmoglein 3 (Dsg3) are both transmembrane glycoproteins that belong to the cadherin family of calcium-dependent cell adhesion molecules. beta-Catenin is a member of the cadherin-catenin complex that mediates homotypic cell-cell adhesion and is also an important molecule in the wnt signaling pathway. In this study, we examined the simultaneous expression level of Dsc3, Dsg3, and beta-catenin in oral squamous cell carcinomas (OSCCs) and normal oral epithelia using immunohistochemistry. There was a significant correlation (p < 0.05) among the following variables in OSCCs: reduced or loss of expression of Dsc3, Dsg3, and beta-catenin compared to normal oral epithelium, reduced or loss of expression of Dsc3 and histological grade (moderately or poorly differentiated), and reduced or loss of expression of beta-catenin and lymph node metastasis. Furthermore, a positive correlation was found between reduced or loss of beta-catenin staining and reduced or loss of Dsc3 staining in lymph node metastatic cancer tissue (r = 0.734, p < 0.05). These results suggest an abnormal expression of Dsc3, Dsg3, and beta-catenin induced in the progression of oral carcinomas and that the Dsc3 expression level might be related to the regulation of beta-catenin in lymph node metastasis and cell proliferation in OSCCs.

Epigenetic abnormalities in cutaneous squamous cell carcinomas: frequent inactivation of the RB1/p16 and p53 pathways

BACKGROUND

Aberrant methylation of CpG islands in the promoter regions of cancer-related genes has been demonstrated in many human tumours. However, the methylation profile of these regions in cutaneous squamous cell carcinomas (SCCs) has not been well studied.

OBJECTIVES

To examine epigenetic abnormalities of a wide range of cancer-related genes in SCCs.

METHODS

We investigated the methylation status of 11 candidate cancer-related genes (CDH1, p16(INK4a), p14(ARF), DAPK1, MGMT, RB1, RASSF1, p15(INK4b), PTEN, PRDM2 and p53) in 20 cases of SCC by methylation-specific polymerase chain reaction, and comparatively examined the protein production of E-cadherin (CDH1), p16, RB1, p14, BMI1 and cyclin A by immunohistochemical analysis.

RESULTS

The frequency of cancer-related gene methylation in SCCs was: CDH1 (95%), p16 (20%), p14 (15%), DAPK1 (15%), MGMT (15%), RB1 (5%), RASSF1 (5%), p15 (0%), PTEN (0%), PRDM2 (0%) and p53 (0%). Almost all cases with hypermethylation of CDH1, p16, RB1 and p14 showed no obvious production of each protein, suggesting that promoter hypermethylation of these genes contributes to the loss of protein production. The results of methylation analysis, in combination with the results of our previous mutation analysis of CDKN2A locus and p53, revealed that 70% of SCCs have alterations in the RB1/p16 or p53 pathway.

CONCLUSIONS

Our findings indicate that the promoter hypermethylation of cancer-related genes, especially CDH1, is frequently shown in SCCs, and dysregulation of the RB1/p16 and/or p53 pathway through either genetic or epigenetic mechanisms, except for epigenetic abnormalities of p53 itself, should contribute to the carcinogenesis of SCCs.

Strong expression of a longevity-related protein, SIRT1, in Bowen's disease

The class III histone deacetylase (HDAC), SIRT1, is a mammalian homologue of the Saccharomyces cerevisiae chromatin-silencing factor Sir2 that regulates longevity. SIRT1 regulates cell survival via deacetylation of p53 and forkhead transcription factors, and overexpression of SIRT1 is reported to be essential for cell growth and survival in some kinds of cancer. To elucidate the role of SIRT1 in human skin carcinogenesis, we have examined SIRT1 protein expression in 20 cases each of squamous cell carcinoma (SCC), basal cell carcinoma (BCC), Bowen's disease (BD), and actinic keratosis (AK) by immunohistochemical analysis. Overexpression of SIRT1 is frequently observed in all kinds of non-melanoma skin cancers included in this study. In particular, strong expression was observed in all cases of BD. In addition, no obvious difference between AK and SCC was observed in the expression of SIRT1, suggesting that overexpression of SIRT1 may have some relevance to the early stage of skin carcinogenesis. We suppose that SIRT1 could be one of the critical targets for future therapy with the aim of inhibiting cell proliferation and promoting apoptosis in non-melanoma skin cancers.