Blue light inhibits the growth of skin tumors in the v-Ha-ras transgenic mouse

12-O-Tetradecanoylphorbol-13-acetate (TPA) was applied to the back skin of v-Ha-ras (TG-AC) female transgenic mice at a dose of 2.5 microg/200 microl twice a week for 9 weeks. The back skin was then exposed to blue light (wavelength, 470 nm; irradiance, 5.7 mW/cm2) for 1 h daily for 9 weeks. The mice to which TPA was applied developed skin tumors at 6 weeks after the start of application. The tumor incidence rates at 6, 7, 8 and 9 weeks after the start of application were 70%, 80%, 100% and 100%, respectively, and the numbers of tumors 1 mm or more in diameter were 1, 5, 10 and 19, respectively. In the mice that were exposed to blue light after TPA application, the tumor incidence rates were 10%, 40%, 60% and 80%, respectively, and the numbers of tumors 1 mm or more in diameter were 0, 2, 5 and 9, respectively. Histopathological examination of the skin revealed that TPA application induced diffuse hyperplasia, exaggerated keratinization, and papillomas in all 10 mice. A localized form of epidermal hyperplasia was also observed in 4 mice. The incidence rate of papillomas in the mice that were exposed to blue light after TPA application was lower and the degree of exaggerated keratinization was greater. Exaggerated keratinization was considered to represent a regressive change following exposure. These findings suggest that exposure to blue light may be a promising new approach in the treatment of skin tumors.

HLA class II polymorphisms and susceptibility to recurrent respiratory papillomatosis

Recurrent respiratory papillomatosis (RRP) is characterised by multiple laryngeal papillomas. Left untreated, the lesions enlarge, spread, and endanger the airway. Medical treatments are unsatisfactory, and repeated surgery remains the mainstay of therapy. RRP is caused by human papillomavirus (HPV) infection. However, since oral HPV infection is common and RRP is rare, other host and/or viral factors may contribute to pathogenesis. In an attempt to identify such factors, we have investigated 60 patients. The patients were HLA class I, II, and tumor necrosis factor TNF typed by sequence-specific primer PCR, and the results compared to those for 554 healthy controls by using Fisher's exact test. Peripheral blood mononuclear cell proliferative responses of 25 controls and 10 patients to HPV-11 L1 virus-like particles (VLP) were compared. Short-term VLP-specific T-cell lines were established, and recognition of L1 was analyzed. Finally, the L1 open reading frames of HPV isolates from four patients were sequenced. Susceptibility to RRP was associated with HLA DRB1*0301 (33 of 60 patients versus 136 of 554 controls, P < 0.0001). The three most severely affected patients were homozygous for this allele. A range of T-cell proliferative responses to HPV-11 VLP were observed in DRB1*0301-positive healthy donors which were comparable to those in DRB1*0301-negative controls. Individuals with juvenile-onset RRP also mounted a range of VLP responses, and their magnitude was negatively correlated with the clinical staging score (P = 0.012 by the Spearman rank correlation). DRB1*0301-positive patients who responded to L1 recognized the same epitope as did matched controls and produced similar cytokines. Sequencing of clinical isolates excluded the possibility that nonresponsiveness was the result of mutation(s) in L1.

Expression of the the cyclin-kinase inhibitors p21(WAF1) and p27(Kip1) and the p53 tumor suppressor genes in adult-onset laryngeal papillomas

Different types of human papilloma virus are known to be closely associated with laryngeal papillomas. On the other hand, the proliferation of epithelial cells is associated with various abnormalities in the mechanisms of cellular regulation. In this study, we detected the expressions of p53, p21 and p27 proteins in adult-onset laryngeal papillomas by immunohistochemical techniques. The objective of this study is to evaluate the expression of these factors in adult-onset laryngeal papillomas and to determine whether such expression is correlated with the existence of dysplastic epithelium covering the papillomas. Eighteen patients with adult-onset papillomas who were surgically treated at the Department of Otolaryngology at the University of Istanbul between January 1994 and December 1999 were included in this study. Anti-p21, -p27 and -p53 antibodies were used to perform immunostaining. Positive nuclear staining for p21 was detected in 14 of the 18 (78%) cases, especially in the parabasal layer. Also, in 78% of the cases, weak to strong immunoreactivity was observed for p27. In all cases, negative immunoreactivity was observed for p53 throughout the epithelium except for the basal and parabasal cells. A negative correlation was observed between the existence of dysplastic epithelium and p21 expression (P=0.02). In conclusion, variable p21 and p27 expression was detected by immunohistochemistry in our series of 18 cases of adult-onset laryngeal papillomatosis, and a statistically significant inverse correlation was detected between p21 expression and the existence of dysplastic epithelium covering the papillomas. Further prospective studies are warranted to determine the prognostic values of these variables and to evaluate their role in the pathogenesis of adult-onset laryngeal papillomas.

Survivin expression in juvenile-onset recurrent respiratory papillomatosis

Recurrent respiratory papillomatosis (RRP), caused by the human papillomavirus, is characterized by unregulated growth of wartlike neoplasms on laryngeal mucosa. Apoptosis is important in normal cellular homeostasis, and dysregulation of this process is thought to govern the behavior of certain neoplasms. This study evaluates the expression of several pro-apoptotic and anti-apoptotic factors in papillomas of patients with RRP, with a specific interest in survivin, a cell cycle-regulated anti-apoptotic factor. Three anti-apoptotic and 6 pro-apoptotic messenger RNA (mRNA) species were quantified by ribonuclease protection assay in 11 RRP papilloma specimens and 5 normal laryngeal specimens. Anti-apoptotic and pro-apoptotic mRNA ratios were quantified by normalizing to the ribosomal protein L32 and compared between specimens. Protein expression of survivin in tissue samples was also evaluated. The mean (+/- SD) expression of survivin was almost fivefold greater in the RRP papillomas than in normal tissue (14.2% +/- 2.5% versus 3.0% +/- 0.8% of L32, p = .003). The RRP specimens also had greater expression of XIAP, Fas, and p53 than did the normal tissue. Survivin protein was differentially expressed in the papilloma specimens, and was greatest in a papilloma that underwent malignant transformation. Survivin was absent in all normal laryngeal tissue tested. Apoptotic factors in general appear to be upregulated in papillomatous tissue as compared to normal laryngeal tissue and may suggest a higher proliferation rate and cell turnover. Survivin is abundant in papillomas and absent in normal laryngeal tissue. Dysregulation of apoptosis as determined by abnormal expression of anti-apoptotic factors like survivin and XIAP probably favors papilloma growth and survival. Such factors may represent potential targets in the treatment of this disease.

Genetic interaction between the unstable v-Ha-RAS transgene (Tg.AC) and the murine Werner syndrome gene: transgene instability and tumorigenesis

Tg.AC transgenic mice provide a sensitive assay for oncogenic agents and a convenient alternative to the two-stage initiation/promoter model of skin tumorigenesis. Although extensively used, this model has remained in part an enigma since mice that carry the Tg.AC transgene (consisting of v-Ha-Ras driven by an embryonic zeta-globin promoter) would not ordinarily be expected to develop skin and other adult tumors. Cloning and characterizing the inserted transgene has provided an insight into the Tg.AC phenotype. We find that the transgene is inserted into a Line-1 element in such a way as to create extended inverted repeats consisting of both transgene and Line-1 sequences. Such structures would be expected to contribute to the instability of the Tg.AC locus and we suggest that this instability is critical to the Tg.AC phenotype. Further, we strengthen this notion by introducing an inactivating mutation in the murine Wrn gene (a gene important in maintenance of genome stability) and showing that bigenic Tg.AC/Wrn(Deltahel/Deltahel) mice experience an eightfold increase in inactivating germline mutations at the Tg.AC locus. Similarly, Tg.AC/Wrn(Deltahel/Deltahel) mice that retain an intact and thus active Tg.AC locus experience a sharp increase in papillomas as compared to Tg.AC/Wrn(+/+) mice. This work demonstrates a genetic interaction between the instability of the multicopy transgene and the Werner Syndrome gene. From this, we conclude that genetic instability remains a key element in this tumor promoter model.

Genetic analyses of mouse skin tumor progression susceptibility using SENCAR inbred derived strains

Susceptibility to tumor development varies among individuals in the human population. This variability can also be found among different strains of mice, particularly in the mouse skin chemical carcinogenesis model. The genetic mechanisms underlying mouse skin tumor susceptibility are not fully understood. The SENCAR stock has been found to be the most sensitive mice for skin carcinogenesis studies; however, little is known about the genes underlying tumor susceptibility, particularly, those involved in tumor progression. Experiments with the SSIN/Sprd mice, an inbred strain derived from the outbred SENCAR stock, suggested that papilloma development, tumor promotion, and their conversion into squamous cell carcinomas (SCCs), progression, are regulated by different genes. In the highly sensitive SSIN/Sprd mice, papillomas rarely progress to SCC. Using crosses between the outbred SENCAR and the SSIN/Sprd mice, we previously determined that papilloma progression in the SENCAR stock could be controlled by at least one autosomal dominant gene. However, the outbred nature of the SENCAR stock precluded us from extending those findings. More recently, another inbred strain was developed from the outbred SENCAR stock, the SENCARB/Pt. These mice have similar tumor promotion sensitivity to the SSIN/Sprd but in contrast, have high papilloma progression susceptibility, similar to the outbred original stock. In the present study, we generated F(1), F(2), and backcross hybrids between the SSIN/Sprd and SENCARB/Pt mice to determine a possible model for tumor progression susceptibility and to map the putative tumor susceptibility genes. Our tumor data suggests that papilloma progression susceptibility in the SENCAR mouse skin model could be genetically determined by one susceptibility gene. Our preliminary linkage analysis failed to identify one strong susceptibility locus to confirm this but provided some evidence for at least one possible susceptibility locus in mouse chromosome 14.

Modulation of epidermal tumor development caused by targeted overexpression of epidermis-type 12S-lipoxygenase

In contrast to other 12S-lipoxygenase (LOX) isoforms expressed in the skin of mice, epidermis-type (e) 12S-LOX was found to be transcriptionally down-regulated in the course of epidermal tumor development in NMRI mice. This may indicate that this enzyme is related to antitumorigenic rather than protumorigenic effects. To test this hypothesis, two transgenic mouse lines were generated that differentially expressed e12S-LOX under the control of the bovine keratin 6 promoter known to be constitutively up-regulated in mouse skin tumors. As compared with the wild-type, low transgene expression correlated with a decreased skin tumor response paralleled by an up-regulation of leukocyte-type 12S-LOX and an accumulation of the linoleic acid derivative 13S-hydroxyoctadecadienoic acid. In contrast, high transgene expression coincided with an increased tumor response paralleled by a strong keratin 6 promoter-driven up-regulation of the transgenic e12S-LOX and an accumulation of the arachidonic acid derivative 12S-hydroxyeicosatetraenoic acid as the predominant LOX product. These results indicate a complex interaction between different LOX isoforms and an opposite role of arachidonic acid and linoleic acid products in the modulation of skin carcinogenesis.

Comparative genomic hybridization detects specific cytogenetic abnormalities in pediatric ependymomas and choroid plexus papillomas

Pathogenesis and genetic abnormalities of ependymomas are not well known and differential diagnosis with choroid plexus tumors may be difficult when these tumors are located in the ventricles. We analyzed 16 samples of primary pediatric ependymomas and seven choroid plexus tumors for significant gains or losses of genomic DNA, using comparative genomic hybridization (CGH). Four ependymoma samples were obtained after surgery for relapse, including one patient whose tumor was analyzed at diagnosis and at first and second relapses. Three out of 16 ependymomas and none of the choroid plexus tumors appeared normal by CGH. In the remaining ependymomas, the number of regions with genomic imbalance was limited. The most frequent copy number abnormality in ependymomas was 22q loss. In one patient from whom multiple samples could be analyzed during tumor progression, no abnormality was present at diagnosis; gain of chromosome 9 and loss of 6q were observed at first relapse and, at second relapse, additional genomic imbalances were loss of 3p, 10q, and chromosome 15. In choroid plexus tumors, recurrent abnormalities were gains of chromosome 7 and region 12q. The recurrent chromosomal abnormalities were clearly different between ependymomas and choroid plexus papillomas (CPP). Recurrent loss of 22q suggests that this region harbors tumor suppressor genes important in the pathogenesis of ependymomas; however, other pathogenic pathways may exist involving 6q and chromosome 10 losses or gain of 1q and chromosome 9. CPP can be distinguished from ependymoma on the basis of CGH abnormalities.

Calgranulins S100A8 and S100A9 are negatively regulated by glucocorticoids in a c-Fos-dependent manner and overexpressed throughout skin carcinogenesis

The two calgranulins S100A8 and S100A9 were found to be differentially expressed at sites of acute and chronic inflammation. Here we have employed the phorbol ester-induced multistage skin carcinogenesis protocol in mice to determine the expression of both genes in inflamed skin and in skin tumors. We show that expression is coordinately induced by the phorbol ester TPA in epithelial cells as well as infiltrating leukocytes. By comparing S100A8 and S100A9 mRNA levels in wild type and c-Fos deficient mice (c-fos(-/-)) we found that expression is negatively regulated by c-Fos/AP-1. Glucocorticoids, which exhibit potent anti-inflammatory and anti-tumor promoting activities repressed TPA-mediated S100A8 and S100A9 induction in wild type, but not in c-fos(-/-) mice, thus identifying both genes as the first examples of AP-1 target genes whose repression of TPA-induced transcription by glucocorticoids depends on c-Fos. Finally, we show that enhanced expression is not restricted to the initial TPA-induced inflammatory response but is observed at all stages of skin carcinogenesis. These data identify S100A8 and S100A9 as novel, tumor-associated genes and may point to an as yet unrecognized function of both genes in the development of epithelial skin tumors.

Deficiency of either cyclooxygenase (COX)-1 or COX-2 alters epidermal differentiation and reduces mouse skin tumorigenesis

Nonsteroidal anti-inflammatory drugs are widely reported to inhibit carcinogenesis in humans and in rodents. These drugs are believed to act by inhibiting one or both of the known isoforms of cyclooxygenase (COX). However, COX-2, and not COX-1, is the isoform most frequently reported to have a key role in tumor development. Here we report that homozygous deficiency of either COX-1 or COX-2 reduces skin tumorigenesis by 75% in a multistage mouse skin model. Reduced tumorigenesis was observed even though the levels of stable 7,12-dimethylbenz(a)anthracene-DNA adducts were increased about 2-fold in the COX-deficient mice compared with wild-type mice. The premature onset of keratinocyte terminal differentiation appeared to be the cellular event leading to the reduced tumorigenesis because keratin 1 and keratin 10, two keratins that indicate the commitment of keratinocytes to differentiate, were expressed 8-13-fold and 10-20-fold more frequently in epidermal basal cells of the COX-1-deficient and COX-2-deficient mice, respectively, than in wild-type mice. Papillomas on the COX-deficient mice also displayed the premature onset of keratinocyte terminal differentiation. However, loricrin, a late marker of epidermal differentiation, was not significantly altered, suggesting that it was the early stages of keratinocyte differentiation that were primarily affected by COX deficiency. Because keratin 5, a keratin associated with basal cells, was detected differently in papillomas of COX-1-deficient as compared with COX-2-deficient mice, it appears that the isoforms do not have identical roles in papilloma development. Interestingly, apoptosis, a cellular process associated with nonsteroidal anti-inflammatory drug-induced inhibition of tumorigenesis, was not significantly altered in the epidermis or in papillomas of the COX-deficient mice. Thus, both COX-1 and COX-2 have roles in keratinocyte differentiation, and we propose that the absence of either isoform causes premature terminal differentiation of initiated keratinocytes and reduced tumor formation.

Investigations on a clinically and functionally unusual and novel germline p53 mutation

This report describes an individual with a rare choroid plexus papilloma in adulthood (age 29) after earlier having an osteosarcoma (age 22). The results from this study, and others, suggest that it may be advisable to consider the possibility of a germline p53 mutation in adults presenting with choroid plexus tumours. In the current study automated DNA sequencing of genomic DNA detected a novel germline 7 base pair insertion in exon 5 of the p53 gene in this patient. The alteration in frame would produce amino acid substitutions beginning with alanine to glycine at position 161 and a stop codon at position 182 in the mutated protein. Surprisingly two assays of p53 function gave apparently wild-type results on peripheral blood lymphocytes from this individual. These results led us to carry out more detailed functional tests on the mutant protein. The mutant allele was expressed either at very low levels or not at all in phytohaemagglutinin stimulated lymphocytes. Further, the mutant protein was completely non-functional in terms of its ability to transactivate a series of p53-responsive genes (p21(WAF1), bax, PIG3), to transrepress a target gene and to inhibit colony growth in transfected Saos-2 cells. However, surprisingly, data from irradiated peripheral blood lymphocytes and transfected Saos-2 cells, suggested that this truncated, mutant protein retains significant ability to induce apoptosis.

Overexpression of a dominant-negative ornithine decarboxylase in mouse skin: effect on enzyme activity and papilloma formation

A transgenic mouse line expressing a truncated form of the ornithine decarboxylase (ODC) dominant-negative mutant K69A/C360A under the control of the keratin 6 promoter has been established (K6/ODCdn mice). These mice were backcrossed onto both the DBA/2J and C57BL/6J backgrounds for subsequent tumorigenesis experiments utilizing an initiation/promotion protocol. In short-term experiments, expression of the ODCdn protein product was induced in the epidermis within 24 h after application of the tumor promoter tetradecanoyl phorbol acetate (TPA) to the skin, and ODC activity in the epidermis of K6/ODCdn mice was reduced by at least 75% compared with littermate controls. However, in tumorigenesis experiments utilizing a variety of initiator (7,12-dimethylbenz[a]anthracene; DMBA) and promoter (TPA) concentrations, K6/ODCdn mice formed at least as many tumors as their littermate controls regardless of background strain. In experiments utilizing chrysarobin, a tumor promoter with a different mechanism of action than TPA, again there was no significant difference in tumor formation between K6/ODCdn mice and littermate controls. Similarly, when K6/ODCdn mice were crossed with K5/ODC mice, a transgenic line described previously which forms tumors without application of a promoting agent, double transgenic mice formed as many tumors as mice expressing the K5/ODC transgene alone. Analysis of epidermis following multiple TPA applications revealed a dramatic spike in ODC activity in both K6/ODCdn mice and non-transgenic mice after six applications, and western blot analysis suggested a stabilization of endogenous wild-type ODC in K6/ODCdn transgenic mice. ODC activity, endogenous protein and polyamines were also elevated in tumors from K6/ODCdn mice. The accumulation of endogenous ODC protein is most probably the result of competition from the transgene-derived ODCdn protein for binding of antizyme, which is known to regulate ODC activity by stimulating degradation of the ODC protein.

The Tg.AC (v-Ha-ras) transgenic mouse: nature of the model

The Tg.AC (v-Ha-ras) transgenic mouse model provides a reporter phenotype of skin papillomas in response to either genotoxic or nongenotoxic carcinogens. In common with the conventional bioassay, the Tg.AC model responds to known human carcinogens and does not respond to noncarcinogens. It also does not respond to most chemicals that are positive in conventional bioassays principally at sites of high spontaneous tumor incidence. The mechanism of response of the Tg.AC model is related to the structure and genomic position of the transgene and the induction of transgene expression through specific mediated interactions between the chemicals and target cells in the skin.

Tg.AC genetically altered mouse: assay working group overview of available data

In a Government/Industry/Academic partnership to evaluate alternative approaches to carcinogenicity testing, 21 pharmaceutical agents representing a variety of chemical and pharmacological classes and possessing known human and or rodent carcinogenic potential were selected for study in several rodent models. The studies from this partnership project, coordinated by the International Life Sciences Institute, provide additional data to better understand the models' limitations and sensitivity in identifying carcinogens. The results of these alternative model studies were reviewed by members of Assay Working Groups (AWG) composed of scientists from government and industry with expertise in toxicology, genetics, statistics, and pathology. The Tg.AC genetically manipulated mouse was one of the models selected for this project based on previous studies indicating that Tg.AC mice seem to respond to topical application of either mutagenic or nonmutagenic carcinogens with papilloma formation at the site of application. This communication describes the results and AWG interpretations of studies conducted on 14 chemicals administered by the topical and oral (gavage and/or diet) routes to Tg.AC genetically manipulated mice. Cyclosporin A, an immunosuppresant human carcinogen, ethinyl estradiol and diethylstilbestrol (human hormone carcinogens) and clofibrate, an hepatocarcinogenic peroxisome proliferator in rodents, were considered clearly positive in the topical studies. In the oral studies, ethinyl estradiol and diethylstilbestrol were negative, cyclosporin was considered equivocal, and results were not available for the clofibrate study. Of the 3 genotoxic human carcinogens (phenacetin, melphalan, and cyclophosphamide), phenacetin was negative by both the topical and oral routes. Melphalan and cyclophosphamide are, respectively, direct and indirect DNA alkylating agents and topical administration of both caused equivocal responses. With the exception of clofibrate, Tg.AC mice did not exhibit tumor responses to the rodent carcinogens that were putative human noncarcinogens, (di(2-ethylhexyl) phthalate, methapyraline HCl, phenobarbital Na, reserpine, sulfamethoxazole or WY-14643, or the nongenotoxic, noncarcinogen, sulfisoxazole) regardless of route of administration. Based on the observed responses in these studies, it was concluded by the AWG that the Tg.AC model was not overly sensitive and possesses utility as an adjunct to the battery of toxicity studies used to establish human carcinogenic risk.

Clinical implications of human papillomavirus infection

Human papillomaviruses (HPV) are small DNA viruses associated with specific mucosal and epithelial lesions ranging from benign proliferative lesions to invasive carcinomas. Over 100 types of HPV have been identified, some of which are associated with benign lesions (low risk types) and others are associated with malignancies (high risk types). While the genome consists of 6 early genes and 2 late genes, the E6 and E7 genes have been most studied because they interact with p53 and Rb, respectively, thus contributing to the ability of HPV to mediate oncogenesis. Cervical carcinoma is the most common and most studied HPV-related malignancy. These lesions are thought to be originated from persistent high-risk type HPV infections which progress to well characterized precursor lesions and finally to carcinoma. This same HPV related progression has also been observed in other anogenital malignancies including anal, penile and vulvar carcinomas. Although the evidence is not as conclusive, HPV also likely plays a role in the development of a subset of squamous cell carcinomas of the head and neck as well as other cutaneous malignancies. While HPV infection is common, the progression to malignancy is relatively rare indicating a potential role for immune protection against persistent infection. This is supported by the fact that HPV infection and related malignancies are common in the immunosuppressed population. Thus, efforts have been placed on development of HPV vaccines to prevent and treat these common and diverse groups of HPV related malignancies.

Mouse homologue of HOS (mHOS) is overexpressed in skin tumors and implicated in constitutive activation of NF-kappaB

NF-kappaB transcription factor is activated upon ubiquitination and subsequent proteolysis of its inhibitor IkappaB. The phosphorylation-dependent ubiquitination is mediated by SCF E3 ubiquitin ligase. In this study, we identified a novel murine F-box/WD40 repeat-containing protein, mHOS (a homologue of HOS/betaTrCP2). mHOS efficiently binds Skp1 protein (a 'core' component of SCF ubiquitin ligase), and phosphorylated IkappaB(alpha). We found that mHOS associates with SCF-ROC1 E3 ubiquitin ligase activity. We have also observed that mHOS is overexpressed in chemically-induced mouse skin tumors, and its overexpression (but not accelerated IkappaB phosphorylation) coincides with the accelerated degradation of IkappaB in vivo. The role of mHOS in the constitutive activation of NF-kappaB in skin carcinogenesis is discussed.

Inhibition of both skin and lung tumorigenesis by Car-R mouse-derived cancer modifier loci

The Car-R outbred mouse line was phenotypically selected for high resistance to two-stage skin tumorigenesis. In the present study we tested the hypothesis that a subset of genetic loci responsible for resistance to skin tumorigenesis of Car-R mice might also inhibit lung tumorigenesis. Skin and lung tumorigenesis were induced in groups of Car-R, SWR/J, (SWR/JxCar-R)F1 and SWR/Jx(SWR/JxCar-R) backcross mice by i.p. urethane initiation and skin TPA promotion. Car-R mice showed a much lower susceptibility to both skin and lung tumorigenesis as compared to SWR/J mice, which are susceptible to both lung and skin tumorigenesis. The Car-R-inherited genome significantly inhibited both skin and lung cancer development in the F1 progeny of Car-R with SWR/J mice. In the backcross population, skin and lung tumor phenotypes showed a statistically significant correlation, indicating that a subset of the cancer resistance alleles, which segregated in the Car-R line during selection for resistance to skin carcinogenesis, provides resistance to both skin and lung tumorigenesis.

Functional roles of Akt signaling in mouse skin tumorigenesis

The mouse skin carcinogenesis protocol is a unique model for understanding the molecular events leading to oncogenic transformation. Mutations in the Ha-ras gene, and the presence of functional cyclin D1 and the EGF receptor, have proven to be important in this system. However, the signal transduction pathways connecting these elements during mouse skin carcinogenesis are poorly understood. This paper studies the relevance of the Akt and ERK pathways in the different stages of chemically induced mouse skin tumors. Akt activity increases throughout the entire process, and its early activation is detected prior to increased cyclin D1 expression. ERK activity rises only during the later stages of malignant conversion. The observed early increase in Akt activity appears to be due to raised PI-3K activity. Other factors acting on Akt such as ILK activation and decreased PTEN phosphatase activity appear to be involved at the conversion stage. To further confirm the involvement of Akt in this process, PB keratinocytes were transfected with Akt and subsequently injected into nude mice. The expression of Akt accelerates tumorigenesis and contributes to increased malignancy of these keratinocytes as demonstrated by the rate of appearance, the growth and the histological characteristics of the tumors. Collectively, these data provide evidence that Akt activation is one of the key elements during the different steps of mouse skin tumorigenesis.

Evaluation of the Tg.AC transgenic mouse assay for testing the human carcinogenic potential of pharmaceuticals--practical pointers, mechanistic clues, and new questions

Transgenic mouse strains with genetic alterations known to play a role in the multistage process of carcinogenesis are being used increasingly as models for evaluating the human carcinogenic potential of chemicals and pharmaceuticals. The Tg.AC transgenic mouse is one of the strains currently being used in such alternative short-term carcinogenicity testing protocols. This review is focused on recent data from studies designed to evaluate this model's ability to discriminate carcinogens from noncarcinogens. Details relating to protocol design that can significantly impact study outcome are described. Data relating to mechanisms of chemical tumor induction in the Tg.AC model are reviewed, and questions have been formulated to encourage research to further guide appropriate future applications of this model.

Loss of critical palindromic transgene promoter sequence in chemically induced Tg.AC mouse skin papillomas expressing transgene-derived mRNA

The Tg.AC transgenic mouse carries a v-Ha-ras transgene. Skin papillomas develop in Tg.AC mice upon repeated dermal application of tumor promoters and carcinogens. The transgene is inserted at a single site on chromosome 11 in a multiple-copy array. Although most of the >or= 40 copies are arranged in a direct-repeat orientation, two copies of the transgene are inserted in a palindromic, inverted-repeat orientation. Deletion of the palindromic transgene promoter sequence is associated strongly with and diagnostic of loss of phenotypic responsiveness to Tg.AC papillomagens, such as 12-O-tetradecanoylphorbol-13-acetate (TPA). Unexpectedly, a loss of palindromic transgene sequence, in the absence of an observable reduction in copy number of the direct-repeat-oriented transgene sequence, is seen in DNA from papillomas when compared to genomic DNA from tail clips or skin samples away from the application site. Transgene-derived transcripts were detectable in all Tg.AC papillomas sampled. The transgene locus was hypomethylated in papillomas but not in samples from tail clips from the same animal or from skin samples away from the application site in responder Tg.AC mice, as shown by loss of resistance to digestion by HpaII. A cell line derived from a Tg.AC squamous cell carcinoma showed complete loss of the palindromic transgene sequence, hypomethylation of the transgene locus, and strong expression of v-Ha-ras mRNA. These data indicate that the palindromic transgene sequence, which appears to be necessary for initial responsiveness to tumorigens, may be susceptible to deletion during rapid cellular proliferation and is not required for transgene expression in later phases of papilloma growth.

Decreased focal adhesion kinase suppresses papilloma formation during experimental mouse skin carcinogenesis

Although focal adhesion kinase (FAK) is elevated in epithelial cancers, it is not known whether FAK expression influences tumor development in vivo. We found that fak +/- heterozygous mice display reduced 7,12-dimethylbenz[a]anthracene-induced papilloma formation that correlates with reduced FAK protein expression in the skin. However, the frequency of malignant conversion of papillomas into carcinomas is indistinguishable in fak +/- mice and their wild-type fak +/+ littermates, most likely because papilloma FAK protein expression is elevated to wild-type levels. We also found that keratinocyte FAK protein expression is important for cellular responses downstream of ras in vitro (monitored by extracellular signal-regulated kinase activation after integrin engagement). Because 7,12-dimethylbenz[a]anthracene induces an activating mutation of H-ras, this provides one possible explanation for suppression of papilloma formation when FAK protein is limiting.

Confirmation of the mapping of a 12-O-tetradecanoylphorbol-13-acetate promotion susceptibility locus, Psl1, to distal mouse chromosome 9

Susceptibility to two-stage skin carcinogenesis in the mouse is affected by several genes. In addition, studies suggest that genes that modify the response of mice to skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) also may influence histologic changes in the skin as the result of TPA treatment. One TPA susceptibility locus, Psl1, previously was mapped to distal chromosome 9. The mapping of this locus was confirmed by marker-based genotypic selection. Furthermore, Psl1 or a gene closely linked to Psl1 influenced epidermal hyperplasia and epidermal labeling index of mice treated with TPA.

Induction of melanoma in murine macrophage inflammatory protein 2 transgenic mice heterozygous for inhibitor of kinase/alternate reading frame

The molecular and genetic events that contribute to the genesis and progression of cutaneous malignant melanoma are poorly understood, attributable in large part to the different genetic alterations accompanying tumorigenesis. Inhibitor of kinase 4a (INK4a) is often inactivated in families with hereditary melanoma. Loss of INK4a/alternate reading frame (ARF) in mice is associated with increased incidence of other tumors such as lymphoma and fibrosarcoma. However, the incidence of melanoma in INK4a/ARF-deficient mice is very low. Our previous studies have revealed that the CXC chemokine, CXCL1, is overexpressed in human malignant melanoma cells and is linked to transformation of immortalized murine melanocytes. To study the direct role of CXCL1 on the genesis of primary melanoma lesions, transgenic mouse lines were established that express the murine homologue of CXCL1, murine macrophage inflammatory protein 2 (MIP-2), under the transcriptional control of the tyrosinase promoter/enhancer (Tyr-MIP-2) in the mice that were deficient or not deficient for INK4a/ARF. Strong MIP-2 immunoreactivity was associated with pigmented melanocytes in the hyperproliferative hair follicles in the Tyr-MIP-2 transgenic mice, and the level of MIP-2 expression was similar in both INK4a/ARF heterozygous or wild-type mice. After treatment of mice with 7,12-dimethylbenz(a)anthracene, cutaneous melanomas formed in 12% (17/145) of the Tyr-MIP-2 transgene-positive mice, whereas only 2% (3/146) of the Tyr-MIP-2 transgene-negative mice developed melanoma. When melanocytes cultured from MIP-2 transgenic mice null for INK4a/ARF were transplanted into nude mice, melanoma formation occurred in 83% (10/12) of the cases with a latency period of 3 months. However, no melanoma lesions arose in nude mice injected with INK4a/ARF -/- melanocytes, which did not express the MIP-2 transgene. Our results demonstrate that constitutive expression of MIP-2 in INK4a/ARF-deficient melanocytes facilitates formation of malignant melanoma.

Inducible expression of transforming growth factor beta1 in papillomas causes rapid metastasis

Transforming growth factor beta1 (TGF-beta1) acts as a tumor suppressor at early stages of carcinogenesis, however, it has also been suggested to promote tumor progression at late stages. To determine at which stage and by what mechanisms this functional switch occurs, we have generated gene-switch-TGF-beta1 mice in which TGF-beta1 transgene expression can be induced in skin tumors at specific stages. These mice were exposed to a chemical carcinogenesis protocol, which allows tumorigenesis to develop in progressive stages from benign papillomas to malignant carcinomas. Remarkably, TGF-beta1 transgene induction in papillomas rapidly induced metastasis. This function is in sharp contrast to its tumor suppressive effect when TGF-beta1 transgene expression was induced early in the protocol. Transgenic papillomas exhibited down-regulation of TGF-beta receptors and their signal transducer, the Smads, and loss of the invasion suppressor E-cadherin/catenin complex in the cell membrane. These molecules were lost only in malignant carcinomas in control mice at a much later stage. Furthermore, transgenic papillomas exhibited elevated expression of matrix metalloproteinases and increased angiogenesis. Our study suggests that TGF-beta1 overexpression may directly induce tumor metastasis by initiating events necessary for invasion. Down-regulation of TGF-beta signaling components in tumor epithelia selectively abolishes growth inhibition, thus, switching the role of TGF-beta1 to a metastasis promoter.