Progressive alterations of cytokeratin expressions in the process of chronic arsenism

Proteomic profiling reveals candidate markers for arsenic-induced skin keratosis

Proteomics technology is an attractive biomarker candidate discovery tool that can be applied to study large sets of biological molecules. To identify novel biomarkers and molecular targets in arsenic-induced skin lesions, we have determined the protein profile of arsenic-affected human epidermal stratum corneum by shotgun proteomics. Samples of palm and foot sole from healthy subjects were analyzed, demonstrating similar protein patterns in palm and sole. Samples were collected from the palms of subjects with arsenic keratosis (lesional and adjacent non-lesional samples) and arsenic-exposed subjects without lesions (normal). Samples from non-exposed healthy individuals served as controls. We found that three proteins in arsenic-exposed lesional epidermis were consistently distinguishably expressed from the unaffected epidermis. One of these proteins, the cadherin-like transmembrane glycoprotein, desmoglein 1 (DSG1) was suppressed. Down-regulation of DSG1 may lead to reduced cell-cell adhesion, resulting in abnormal epidermal differentiation. The expression of keratin 6c (KRT6C) and fatty acid binding protein 5 (FABP5) were significantly increased. FABP5 is an intracellular lipid chaperone that plays an essential role in fatty acid metabolism in human skin. This raises a possibility that overexpression of FABP5 may affect the proliferation or differentiation of keratinocytes by altering lipid metabolism. KRT6C is a constituent of the cytoskeleton that maintains epidermal integrity and cohesion. Abnormal expression of KRT6C may affect its structural role in the epidermis. Our findings suggest an important approach for future studies of arsenic-mediated toxicity and skin cancer, where certain proteins may represent useful biomarkers of early diagnoses in high-risk populations and hopefully new treatment targets. Further studies are required to understand the biological role of these markers in skin pathogenesis from arsenic exposure.

Induction of human squamous cell-type carcinomas by arsenic

Arsenic is a potent human carcinogen. Around one hundred million people worldwide have potentially been exposed to this metalloid at concentrations considered unsafe. Exposure occurs generally through drinking water from natural geological sources, making it difficult to control this contamination. Arsenic biotransformation is suspected to have a role in arsenic-related health effects ranging from acute toxicities to development of malignancies associated with chronic exposure. It has been demonstrated that arsenic exhibits preference for induction of squamous cell carcinomas in the human, especially skin and lung cancer. Interestingly, keratins emerge as a relevant factor in this arsenic-related squamous cell-type preference. Additionally, both genomic and epigenomic alterations have been associated with arsenic-driven neoplastic process. Some of these aberrations, as well as changes in other factors such as keratins, could explain the association between arsenic and squamous cell carcinomas in humans.

Global Gene Expression Profiling of Hyperkeratotic Skin Lesions from Inner Mongolians Chronically Exposed to Arsenic

The skin is an organ that is highly sensitive to chronic arsenic (As) exposure. Skin lesions such as hyperkeratoses (HKs) are common early manifestations of arsenicosis in humans. HKs can be precursor lesions of nonmelanoma skin cancers (NMSCs), but the driving forces behind their formation and how they may ultimately progress to NMSCs are unknown. The goal of this study was to examine the global gene expression profiles of As-related HKs in an effort to better understand gene expression changes that are potentially associated with early stages of As carcinogenesis. HK biopsies were removed from individuals living in an arsenicosis-endemic region in Inner Mongolia who had been exposed to high As levels in their drinking water for >20 years. Gene expression profiling was performed on RNA isolated from 7 individuals in this group and from 4 lesion-free skin samples from healthy individuals. Consistent with the pathological characteristics of the HK lesions, major functional categories and known canonical pathways represented by altered transcripts include those involved in development, differentiation, apoptosis, proliferation, and stress response. The results of this study may help define a signature profile of gene expression changes associated with long-term As exposure in the skin.

Aberrant cytokeratin expression during arsenic-induced acquired malignant phenotype in human HaCaT keratinocytes consistent with epidermal carcinogenesis

Inorganic arsenic is a known human skin carcinogen. Chronic arsenic exposure results in various human skin lesions, including hyperkeratosis and squamous cell carcinoma (SCC), both characterized by distorted cytokeratin (CK) production. Prior work shows the human skin keratinocyte HaCaT cell line, when exposed chronically for >25 weeks to a low level of inorganic arsenite (100nM) results in cells able to produce aggressive SCC upon inoculation into nude mice. In the present study, CK expression analysis was performed in arsenic-exposed HaCaT cells during the progressive acquisition of this malignant phenotype (0-20 weeks) to further validate this model as relevant to epidermal carcinogenesis induced by arsenic in humans. Indeed, we observed clear evidence of acquired cancer phenotype by 20 weeks of arsenite exposure including the formation of giant cells, a >4-fold increase in colony formation in soft agar and a approximately 2.5-fold increase in matrix metalloproteinase-9 secretion, an enzyme often secreted by cancer cells to help invade through the local extra-cellular matrix. During this acquired malignant phenotype, various CK genes showed markedly altered expression at the transcript and protein levels in a time-dependent manner. For example, CK1, a marker of hyperkeratosis, increased up to 34-fold during arsenic-induced transformation, while CK13, a marker for dermal cancer progression, increased up to 45-fold. The stem cell marker, CK15, increased up to 7-fold, particularly during the later stages of arsenic exposure, indicating a potential emergence of cancer stem-like cells with arsenic-induced acquired malignant phenotype. The expression of involucrin and loricrin, markers for keratinocyte differentiation, increased up to 9-fold. Thus, during arsenic-induced acquired cancer phenotype in human keratinocytes, dramatic and dynamic alterations in CK expression occur which are consistent with the process of epidermal carcinogenesis helping validate this as an appropriate model for the study of arsenic-induced skin cancer.

A novel role of the NRF2 transcription factor in the regulation of arsenite-mediated keratin 16 gene expression in human keratinocytes

BACKGROUND

Inorganic sodium arsenite (iAs) is a ubiquitous environmental contaminant and is associated with an increased risk of skin hyperkeratosis and cancer.

OBJECTIVES

We investigated the molecular mechanisms underlying the regulation of the keratin 16 (K16) gene by iAs in the human keratinocyte cell line HaCaT.

METHODS

We performed reverse transcriptase polymerase chain reaction, luciferase assays, Western blots, and electrophoretic mobility shift assays to determine the transcriptional regulation of the K16 gene by iAs. We used gene overexpression approaches to elucidate the nuclear factor erythroid-derived 2 related factor 2 (NRF2) involved in the K16 induction.

RESULTS

iAs induced the mRNA and protein expression of K16. We also found that the expression of K16 was transcriptionally induced by iAs through activator protein-1-like sites and an antioxidant response element (ARE) in its gene promoter region. Treatment with iAs also enhanced the production and translocation of the NRF2 transcription factor, an ARE-binding protein, into the nucleus without modification of its mRNA expression. In addition, iAs elongated the half-life of the NRF2 protein. When overexpressed in HaCaT cells, NRF2 was also directly involved in not only the up-regulation of the detoxification gene thioredoxin but also K16 gene expression.

CONCLUSIONS

Our data clearly indicate that the K16 gene is a novel target of NRF2. Furthermore, our findings also suggest that NRF2 has opposing roles in the cell--in the activation of detoxification pathways and in promoting the development of skin disorders.

Defective beta1-integrins expression in arsenical keratosis and arsenic-treated cultured human keratinocytes

BACKGROUND

beta1-integrins, which localize to the basolateral surface of basal keratinocytes, are important in the differentiation control and proliferation of the epidermis. Many cutaneous diseases with perturbed differentiation, including arsenical keratosis, show altered patterns of integrin distribution and expression. Arsenic may induce arsenical keratosis through the differentiation and apoptosis aberration by integrins. The purpose of this study is to investigate the role of integrin and arsenic in the pathogenesis of arsenical keratosis.

METHODS

Twenty-five specimens obtained from 25 patients with arsenical keratosis disease were studied. Immunohistochemistry staining to beta1, alpha2beta1, or alpha3beta1 integrins was performed in arsenical keratosis and clinically normal perilesional skin. Western blotting was used to assess the expression of integrin beta1 and focal adhesion kinase (FAK) in arsenic-treated cultured keratinocytes.

RESULTS

A decreased expression of beta1, alpha2beta1, or alpha3beta1 integrins was demonstrated in arsenical keratosis and clinical normal perilesional skin in a large proportion of arsenical keratosis cases studied. The expressions of integrin beta1 and FAK were both decreased in arsenic-treated keratinocytes.

CONCLUSIONS

Our results suggest that arsenic induces abnormal differentiation in arsenical keratosis via the effects of integrin expression in keratinocytes.

Association of chromosomal alterations with arsenite-induced tumorigenicity of human HaCaT keratinocytes in nude mice

Inorganic arsenic is a well-documented human carcinogen. Chronic low-dose exposure to inorganic arsenic is associated with an increased incidence of a variety of cancers, including skin, lung, bladder, and liver cancer. Because genetic alterations often occur during cancer development, the objective of this study was to explore what types of genetic alterations were induced by chronic exposure of human HaCaT cells to arsenic. After 20 passages in the presence of inorganic trivalent arsenite at concentrations of 0.5 or 1 microM, HaCaT cells had higher intracellular levels of glutathione, became more resistance to arsenite, and showed an increased frequency of micronuclei. Furthermore, the previously nontumorigenic HaCaT cells became tumorigenic, as shown by subcutaneous injection into Balb/c nude mice. Cell lines derived from the tumors formed by injection of arsenite-exposed HaCaT cells into nude mice expressed higher levels of keratin 6, a proliferation marker of keratinocytes, than did parental HaCaT cells, whereas the expression of keratins 5, 8, and 10 was significantly decreased. Comparative genomic hybridization demonstrated chromosomal alterations in the 11 cell lines derived from these tumors; all 11 showed significant loss of chromosome 9q, and seven showed significant gain of chromosome 4q. The present results show that long-term exposure to low doses of arsenite transformed nontumorigenic human keratinocytes to cells that were tumorigenic in nude mice and that chromosomal alterations were observed in all cell lines established from the tumors.

Effects of arsenic on human keratinocytes: morphological, physiological, and precursor incorporation studies

Measurement of in vitro percutaneous absorption of As(III) and As(V) by artificial human skin shows a strong affinity of arsenic for the human keratinocytes, with 1-10% of the applied arsenic dose retained by the artificial skin per hour. The inordinate retention of arsenic by the skin is a risk factor for As toxicity. The calculated permeability constant (K(p)) averaged about 4.3 x 10(-5) cm/h for As(V) and 10.1 x 10(-5) cm/h for As(III). A facile calculation suggests that dermal absorption during showering and hand washing can be an important exposure route if the water contains more than 100 microg/L As(III) or As(V). The effects of the absorbed arsenic in artificial skin were evaluated in terms of morphological characteristics, integrity of the cell membrane (by means of lactate dehydrogenase and MTS assays), and rates of DNA, RNA, and protein synthesis estimated by incorporation of radioactive precursors. We found significant morphological changes, cytotoxicity associated with disruption of the cell membrane, and inhibition of DNA and protein syntheses at As(III) exposure doses as low as 10 microg/L.

Patterns of basal cell keratin 14 expression in Bowen's disease: a possible marker for tumour progression

BACKGROUND

Bowen's disease is a well-established in situ malignancy of the epidermis. The keratin expression in Bowen's disease has been studied in many reports. However, the patterns of keratin (K) 14 expression in each case have not been closely examined.

OBJECTIVES

To investigate if the pattern of expression of K14 has a relationship with tumour progression, we analysed the expression patterns of K14 in relation to the nature of tumour cells, comparing tumour cells in direct contact with the dermis, tumour cells separated from the dermis, and tumour cells invading into the dermis.

METHODS

Twenty-seven tissue sections from 22 patients were stained with anti-K14 antibody, as well as with antilaminin and periodic acid-Schiff (PAS) staining to evaluate the conditions of the basement membrane. Staining patterns of K10 and integrin beta1, and their relationships with proliferating cell nuclear antigen (PCNA) and Ki-67 staining patterns, were also examined.

RESULTS

Tumour cells with no, or with obscured, basement membranes always showed positive staining for K14, while those with continuous (intact) basement membranes usually did not. Of 10 sections showing dermal involvement of Bowen's disease, five were K14 positive and five were K14 negative. All of these K14-positive sections with dermal involvement showed negative or obscured laminin and PAS staining. Most of the sections having K14-negative tumour cells with dermal involvement showed K14-positive lining cells with continuous staining with laminin and PAS-positive basement membranes. K10 was reciprocally expressed with K14 in most of the sections. Integrin beta1 was expressed in the basal layers of non-tumour epidermal cells, but not in tumour cells. Ki-67 and PCNA were expressed at high frequencies in tumour cells, clearly demarcating tumour cells from non-tumour cells.

CONCLUSIONS

Tumour cells separated from the dermis by lining cells were K14 negative with PAS- and laminin-positive basement membranes around them; tumour cells without lining cells were K14 positive with or without continuous basement membranes. K14 expression may be a marker of tumour progression in Bowen's disease.

Merkel cell carcinoma, Bowen's disease and chronic occupational arsenic poisoning

We diagnosed a unique case of Merkel cell carcinoma (MCC) coexisting with Bowen's disease on the sole of the foot of a 72-year-old man who had worked for about 4 years in a factory handling inorganic arsenic. He had a past history of arsenical keratosis and multiple Bowen's disease. The tumour first appeared as a reddish macule and then showed marked growth over the next month. The tumour was excised and the specimen was examined histopathologically. The tumour consisted of two components: a group of atypical cells representing Bowen's disease in the epidermis and another group of atypical cells with a trabecular pattern characteristic of MCC in the dermis. Neither group of cells showed transitional findings, and the tumour elements were divided by a clear basement membrane. The tumour cells in the dermis were positive for neurone-specific enolase, and on electron microscopy had dense core granules in the cytoplasm. Inorganic arsenic can cause various cutaneous neoplasms, but to our knowledge, this is the first report of a case of MCC associated with Bowen's disease.

Arsenic alters cytosine methylation patterns of the promoter of the tumor suppressor gene p53 in human lung cells: a model for a mechanism of carcinogenesis

Arsenic is a potent human carcinogen to which there is significant worldwide exposure through natural contamination of food and drinking water sources. Because arsenic is detoxified via methylation using a methyltransferase (MTase) and S-adenosylmethionine (SAM) as the methyl donor, we hypothesized that a mechanism of carcinogenesis of arsenic could involve alterations of MTase/SAM-dependent DNA methylation of a tumor suppressor gene. We found that exposure of human lung adenocarcinoma A549 cells to sodium arsenite (0.08-2 microM) or sodium arsenate (30-300 microM), but not dimethylarsenic acid (2-2000 microM), produced significant dose-responsive hypermethylation within a 341-base pair fragment of the promoter of p53. This was determined by quantitative PCR/HpaII restriction site analysis to analyze methylation status of two CCGG sites. In experiments with arsenite, DNA sequencing using bisulfite to visualize 5-methylcytosine (5-MeC) over the entire promoter region confirmed data obtained by restriction analysis. Limited data using SssI methylase also suggested that over-methylation of CpG sequences may exist over the entire genome in response to arsenite exposure. We propose that alteration of DNA methylation by arsenic offers a plausible, unified hypothesis for the carcinogenic mechanism of action of arsenic, and we present a model for arsenic carcinogenesis that utilizes perturbations of DNA methylation as the basis for the carcinogenic effects of arsenic.