Differential gene expression in epidermis of mice sensitive and resistant to phorbol ester skin tumor promotion

Role of hair follicles in the pathogenesis of arsenical-induced cutaneous damage

Arsenical vesicants cause skin inflammation, blistering, and pain. The lack of appropriate animal models causes difficulty in defining their molecular pathogenesis. Here, Ptch1+/- /C57BL/6 mice were employed to investigate the pathobiology of the arsenicals lewisite and phenylarsine oxide (PAO). Following lewisite or PAO challenge (24 h), the skin of animals becomes grayish-white, thick, leathery, and wrinkled with increased bi-fold thickness, Draize score, and necrotic patches. In histopathology, infiltrating leukocytes (macrophages and neutrophils), epidermal-dermal separation, edema, apoptotic cells, and disruption of tight and adherens junction proteins can be visualized. PCR arrays and nanoString analyses showed significant increases in cytokines/chemokines and other proinflammatory mediators. As hair follicles (HFs), which provide an immune-privileged environment, may affect immune cell trafficking and consequent inflammatory responses, we compared the pathogenesis of these chemicals in this model to that in Ptch1+/- /SKH-1 hairless mice. Ptch1+/- /SKH-1 mice have rudimentary, whereas Ptch1+/- /C57BL/6 mice have well-developed HFs. Although no significant differences were observed in qualitative inflammatory responses between the two strains, levels of cytokines/chemokines differed. Importantly, the mechanism of inflammation was identical; both reactive oxygen species induction and consequent activation of unfolded protein response signaling were similar. These data reveal that the acute molecular pathogenesis of arsenicals in these two murine models is similar.

Coxfa4l3, a novel mitochondrial electron transport chain Complex 4 subunit protein, switches from Coxfa4 during spermatogenesis

We identified Coxfa4l3, previously called C15orf48 or Nmes1, as a novel accessory protein of Complex IV of the mitochondrial electron transport chain (ETC). Amino acid sequence comparison, the intracellular localization and the protein expression data showed that the protein is the third isoform of Coxfa4 and the expression of Coxfa4 and Coxfa4l3 proteins during spermatogenesis showed a mutually exclusive pattern, implying that Coxfa4 replaces Coxfa4l3 in Complex IV after meiosis. These results may provide some insight into the unique mechanism of ATP production in late spermatogenesis.

Hypermethylation of normal mucosa of esophagus-specific 1 is associated with an unfavorable prognosis in patients with non-small cell lung cancer

Lung cancer is the leading cause of cancer-associated mortality due to high incidence and poor survival rates, irrespective of global variations in its biology and treatment. Changes in DNA methylation are frequent in cancer and constitute an important mechanism in tumorigenesis. Normal mucosa of esophagus-specific 1 (NMES1) is expressed in epithelial tissue and is believed to be a tumor suppressor gene. The present study investigated the methylation status of the NMES1 promoter in 178 cases of primary non-small cell lung cancer (NSCLC) by pyrosequencing and evaluated the prognostic value of this methylation. NMES1 methylation-positive tumors above the background threshold for non-malignant tissue were found in 15 cases (8.4%) and were detected exclusively in malignant tissues. In addition, univariate and multivariate analyses showed that methylation-positive patients experienced worse overall survival rate (OSR) compared with methylation-negative patients (adjusted hazard ratio, 2.62; 95% confidence interval, 1.20-5.69; P=0.02). Notably, within the methylation-positive group, patients with strong methylation tended to experience worse OSR compared with those with weak methylation (adjusted hazard ratio, 2.45 vs. 3.05; P_trend=0.02). These findings suggest that NMES1 may serve an important role in lung cancer pathogenesis, and its methylation could be considered a prognostic marker for NSCLC. Further studies with large numbers of samples are required to confirm this conclusion.

Rapamycin Modulates Glucocorticoid Receptor Function, Blocks Atrophogene REDD1, and Protects Skin from Steroid Atrophy

Glucocorticoids have excellent therapeutic properties; however, they cause significant adverse atrophogenic effects. The mTORC1 inhibitor REDD1 has been recently identified as a key mediator of glucocorticoid-induced atrophy. We performed computational screening of a connectivity map database to identify putative REDD1 inhibitors. The top selected candidates included rapamycin, which was unexpected because it inhibits pro-proliferative mTOR signaling. Indeed, rapamycin inhibited REDD1 induction by glucocorticoids dexamethasone, clobetasol propionate, and fluocinolone acetonide in keratinocytes, lymphoid cells, and mouse skin. We also showed blunting of glucocorticoid-induced REDD1 induction by either catalytic inhibitor of mTORC1/2 (OSI-027) or genetic inhibition of mTORC1, highlighting role of mTOR in glucocorticoid receptor signaling. Moreover, rapamycin inhibited glucocorticoid receptor phosphorylation, nuclear translocation, and loading on glucocorticoid-responsive elements in REDD1 promoter. Using microarrays, we quantified a global effect of rapamycin on gene expression regulation by fluocinolone acetonide in human keratinocytes. Rapamycin inhibited activation of glucocorticoid receptor target genes yet enhanced the repression of pro-proliferative and proinflammatory genes. Remarkably, rapamycin protected skin against glucocorticoid-induced atrophy but had no effect on the glucocorticoid anti-inflammatory activity in different in vivo models, suggesting the clinical potential of combining rapamycin with glucocorticoids for the treatment of inflammatory diseases.

Evaluation of pentacyclic triterpenes found in Perilla frutescens for inhibition of skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate

A series of pentacyclic tritperpenes found in Perilla frutescens (P. frutescens), including ursolic acid (UA), oleanolic acid (OA), corosolic acid (CA), 3-epi-corosolic acid (3-epiCA), maslinic acid (MA), and 3-epi-maslinic acid (3-epiMA) were evaluated for their effects on epidermal cell signaling, proliferation, and skin inflammation in relation to their ability to inhibit skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) and compared to UA as the prototype compound. All compounds were given topically 30 min prior to each TPA application and significantly inhibited skin tumor promotion. 3-epiCA and MA were significantly more effective than UA at inhibiting tumor development. All of these compounds significantly inhibited epidermal proliferation induced by TPA, however, CA, 3-epiCA and MA were more effective than UA. All compounds also reduced skin inflammation (assessed by infiltration of mast cells and T-cells) and inflammatory gene expression induced by TPA, however, 3-epiCA and MA were again more effective than UA. The greater ability of 3-epiCA and MA to inhibit skin tumor promotion was associated with greater reduction of Cox-2 and Twist1 proteins and inhibition of activation (i.e., phosphorylation) of IGF-1R, STAT3 and Src. Further study of these compounds, especially 3-epiCA and MA, for chemopreventive activity in other cancer model systems is warranted.

SerpinB2 Deficiency Results in a Stratum Corneum Defect and Increased Sensitivity to Topically Applied Inflammatory Agents

SerpinB2 (plasminogen activator inhibitor type 2) is constitutively expressed at high levels by differentiating keratinocytes in mice and humans; however, the physiological function of keratinocyte SerpinB2 remains unclear. Herein, we show that SerpinB2(-/-) mice are more susceptible to contact dermatitis after topical application of dinitrofluorobenzene, and show enhanced inflammatory lesions after topical applications of phorbol ester. Untreated SerpinB2(-/-) mice showed no overt changes in epithelial structure, and we were unable to find evidence for a role for keratinocyte SerpinB2 in regulating immunity, apoptosis, IL-1β production, proteasomal activity, or wound healing. Instead, the phenotype was associated with impaired skin barrier function and a defective stratum corneum, with SerpinB2(-/-) mice showing increased transepidermal water loss, increased overt loss of stratum corneum in inflammatory lesions, and impaired stratum corneum thickening after phorbol ester treatment. Immunoblotting suggested that SerpinB2 (cross-linked into the cornified envelope) is present in the stratum corneum and retains the ability to form covalent inhibitory complexes with urokinase. Data suggest that the function of keratinocyte SerpinB2 is protection of the stratum corneum from proteolysis via inhibition of urokinase, thereby maintaining the integrity and barrier function of the stratum corneum, particularly during times of skin inflammation. Implications for studies involving genetically modified mice treated with topical agents and human dermatological conditions, such as contact dermatitis, are discussed.

Fine mapping reveals that promotion susceptibility locus 1 (Psl1) is a compound locus with multiple genes that modify susceptibility to skin tumor development

Although it is well known that the majority of human cancers occur as the result of exposure to environmental carcinogens, it is clear that not all individuals exposed to a specific environmental carcinogen have the same risk of developing cancer. Considerable evidence indicates that common allelic variants of low-penetrance, tumor susceptibility genes are responsible for this interindividual variation in risk. We previously reported a skin tumor promotion susceptibility locus, Psl1, which maps to the distal portion of chromosome 9, that modified skin tumor promotion susceptibility in the mouse. Furthermore, Psl1 was shown to consist of at least two subloci (i.e., Psl1.1 and Psl1.2) and that glutathione S-transferase alpha 4 (Gsta4), which maps to Psl1.2, is a skin tumor promotion susceptibility gene. Finally, variants of human GSTA4 were found to be associated with risk of nonmelanoma skin cancer. In the current study, a combination of nested and contiguous C57BL/6 congenic mouse strains, each inheriting a different portion of the Psl1 locus from DBA/2, were tested for susceptibility to skin tumor promotion with 12-O-tetradecanoylphorbol-13-acetate. These analyses indicate that Psl1 is a compound locus with at least six genes, including Gsta4, that modify skin tumor promotion susceptibility. More than 550 protein-coding genes map within the Psl1 locus. Fine mapping of the Psl1 locus, along with two-strain haplotype analysis, gene expression analysis, and the identification of genes with amino acid variants, has produced a list of fewer than 25 candidate skin tumor promotion susceptibility genes.

Evaluation of methods for the isolation of high quality RNA from bovine and cervine hide biopsies

Molecular investigations of the ruminant response to ectoparasites at the parasite-host interface are critically dependent upon the quality of RNA. The complexity of ruminant skin decreases the capacity to obtain high quality RNA from biopsy samples, which directly affects the reliability of data produced by gene expression experiments. Two methods for isolating total RNA from skin were compared and the use of 4M guanidinium isothiocyanate (GITC) during frozen storage of the specimens was evaluated. In addition, the best procedure for RNA isolation from bovine skin punch biopsies was also tested on white-tailed deer skin biopsies. Skin biopsy punches were collected and frozen prior to pulverization for RNA isolation. Total RNA quantity and integrity were determined by spectrophotometry and capillary electrophoresis technology, respectively. Significantly increased total RNA yield (P < 0.05) and higher integrity (P < 0.05) were obtained with a TRI Reagent® isolation method. Freezing and subsequent storage of bovine skin punch biopsies in 4 M GITC did not affect the amount or integrity of total RNA recovered by either RNA isolation method. However, quantity and integrity of total RNA extracted with the TRI Reagent method were again significantly higher than with the alternate technique, confirming it as the superior method. The TRI Reagent isolation method also yielded high quality total RNA from white-tailed deer skin punch biopsies, suggesting the usefulness of this method for obtaining RNA of a quality suitable for gene expression studies in other ruminant species.

Proteomic and pathway analyses reveal a network of inflammatory genes associated with differences in skin tumor promotion susceptibility in DBA/2 and C57BL/6 mice

Genetic susceptibility to two-stage skin carcinogenesis is known to vary significantly among different stocks and strains of mice. In an effort to identify specific protein changes or altered signaling pathways associated with skin tumor promotion susceptibility, a proteomic approach was used to examine and identify proteins that were differentially expressed in epidermis between promotion-sensitive DBA/2 and promotion-resistant C57BL/6 mice following treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA). We identified 19 differentially expressed proteins of which 5 were the calcium-binding proteins annexin A1, parvalbumin α, S100A8, S100A9, and S100A11. Further analyses revealed that S100A8 and S100A9 protein levels were also similarly differentially upregulated in epidermis of DBA/2 versus C57BL/6 mice following topical treatment with two other skin tumor promoters, okadaic acid and chrysarobin. Pathway analysis of all 19 identified proteins from the present study suggested that these proteins were components of several networks that included inflammation-associated proteins known to be involved in skin tumor promotion (e.g. TNF-α, NFκB). Follow-up studies revealed that Tnf, Nfkb1, Il22, Il1b, Cxcl1, Cxcl2 and Cxcl5 mRNAs were highly expressed in epidermis of DBA/2 compared with C57BL/6 mice at 24h following treatment with TPA. Furthermore, NFκB (p65) was also highly activated at the same time point (as measured by phosphorylation at ser276) in epidermis of DBA/2 mice compared with C57BL/6 mice. Taken together, the present data suggest that differential expression of genes involved in inflammatory pathways in epidermis may play a key role in genetic differences in susceptibility to skin tumor promotion in DBA/2 and C57BL/6 mice.

The therapeutic effect of histone deacetylase inhibitor PCI-24781 on gallbladder carcinoma in BK5.erbB2 mice

BACKGROUND & AIMS

Gallbladder carcinoma (GBCa), a type of biliary tract cancer (BTC), has proven challenging to treat, demonstrating the need for more effective therapeutic strategies. In our current study, we examined the therapeutic effects of the histone deacetylase (HDAC) inhibitor PCI-24781 against GBCa that developed in BK5.erbB2 mice.

METHODS

PCI-24781 [50 mg/kg/day] and control solutions were administered to BK5.erbB2 mice for 4 weeks. The therapeutic effect of PCI-24781 was evaluated by ultrasound biomicroscopy (USBM) throughout the experiment and histological analyses at the end of the experiment. To investigate potential mechanisms underlining the therapeutic effects of PCI-24781 on GBCa in BK5.erbB2 mice, PCI-24781-treated gallbladders were subjected to Western blot and RT-PCR analysis. The inhibitory effect of PCI-24781 on the growth of BTC cells was compared to the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) and gemcitabine. To study the role of miRNAs in GBCa tumorigenesis, the expression profile of 368 miRNAs in GBCas from BK5.erbB2 (both treated and untreated) and wild type mice was analyzed.

RESULTS

Treatment of BK5.erbB2 mice with PCI-24781 for 1 month prevented 79% of GBCa cases from progression and showed a clinical effect in 47% of cases. We also confirmed a potent inhibitory effect on tumor cell growth in human BTC cell lines treated with PCI-24781. This effect was associated with downregulation of ErbB2 mRNA and ErbB2 protein/activity and upregulation of acetylated histone and acetylated tubulin. Treatment with PCI-24781 resulted in decreased expression of Muc4, an intramembrane ligand for ErbB2, in BTC cells. PCI-24781 had more effects on growth inhibition of BTC cells than SAHA. In addition, PCI-24781 effectively inhibited the growth of gemcitabine-resistant cells. miRNA profiling revealed that the expression of several miRNAs was significantly altered in GBCa in the BK5.erbB2 mouse compared to normal gallbladder, including upregulated miR21, which was downregulated by PCI-24781.

CONCLUSIONS

These results indicate that PCI-24781 potently inhibits the growth of BTC cells by decreasing ErbB2 expression and activity as well as regulating altered miRNA expression. PCI-24781 may have a potential value as a novel chemotherapeutic agent against human BTC in which ErbB2 is overexpressed.

Spermine synthase overexpression in vivo does not increase susceptibility to DMBA/TPA skin carcinogenesis or Min-Apc intestinal tumorigenesis

Numerous studies have demonstrated a link between elevated polyamine biosynthesis and neoplastic growth, but the specific contribution of spermine synthase to epithelial tumor development has never been explored in vivo. Mice with widespread overexpression of spermine synthase (CAG-SpmS) exhibit decreased spermidine levels, increased spermine and a significant rise in tissue spermine:spermidine ratio. We characterized the response of CAG-SpmS mice to two-stage skin chemical carcinogenesis as well as spontaneous intestinal carcinogenesis induced by loss of the Apc tumor suppressor in Apc (Min) (/+) (Min) mice. CAG-SpmS mice maintained the canonical increases in ornithine decarboxylase (ODC) activity, polyamine content and epidermal thickness in response to tumor promoter treatment of the skin. The induction of S-adenosylmethionine decarboxylase (AdoMetDC) activity and its product decarboxylated AdoMet were impaired in CAG-SpmS mice, and the spermine:spermidine ratio was increased 3-fold in both untreated and 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated skin. The susceptibility to 7,12-dimethylbenz[a]anthracene (DMBA)/TPA skin carcinogenesis was not altered in CAG-SpmS mice, and SpmS overexpression did not modify the previously described tumor resistance of mice with targeted antizyme expression or the enhanced tumor response in mice with targeted spermidine/spermine-N ( 1) -acetyltransferase expression. CAG-SpmS/Min mice also exhibited elevated spermine:spermidine ratios in the small intestine and colon, yet their tumor multiplicity and size was similar to Min mice. Therefore, studies in two of the most widely used tumorigenesis models demonstrate that increased spermine synthase activity and the resulting elevation of the spermine:spermidine ratio does not alter susceptibility to tumor development initiated by c-Ha-Ras mutation or Apc loss.

Evidence that Gsta4 modifies susceptibility to skin tumor development in mice and humans

BACKGROUND

The incidence of nonmelanoma skin cancer (NMSC) is equivalent to that of all other cancers combined. Previously, we mapped the 12-O-tetradecanoylphorbol-13-acetate (TPA) skin tumor promotion susceptibility locus, Psl1, to distal chromosome 9 in crosses of sensitive DBA/2 mice with relatively resistant C57BL/6 mice. Here, we used the mouse two-stage skin carcinogenesis model to identify the gene(s) responsible for the effects of Psl1.

METHODS

Interval-specific congenic mouse strains (n ≥ 59 mice per strain) were used to more precisely map the Psl1 locus. Having identified glutathione S-transferase α4 (Gsta4) as a candidate tumor promotion susceptibility gene that mapped within the delimited region, we analyzed Gsta4-deficient mice (n = 62) for susceptibility to skin tumor promotion by TPA. We used quantitative polymerase chain reaction, western blotting, and immunohistochemistry to verify induction of Gsta4 in mouse epidermis following TPA treatment and biochemical assays to associate Gsta4 activity with tumor promotion susceptibility. In addition, single-nucleotide polymorphisms (SNPs) in GSTA4 were analyzed in a case-control study of 414 NMSC patients and 450 control subjects to examine their association with human NMSC. Statistical analyses of tumor studies in mice were one-sided, whereas all other statistical analyses were two-sided.

RESULTS

Analyses of congenic mice indicated that at least two loci, Psl1.1 and Psl1.2, map to distal chromosome 9 and confer susceptibility to skin tumor promotion by TPA. Gsta4 maps to Psl1.2 and was highly induced (mRNA and protein) in the epidermis of resistant C57BL/6 mice compared with that of sensitive DBA/2 mice following treatment with TPA. Gsta4 activity levels were also higher in the epidermis of C57BL/6 mice following treatment with TPA. Gsta4-deficient mice (C57BL/6.Gsta4(-/-) mice) were more sensitive to TPA skin tumor promotion (0.8 tumors per mouse vs 0.4 tumors per mouse in wild-type controls; difference = 0.4 tumors per mouse; 95% confidence interval = 0.1 to 0.7, P = .007). Furthermore, inheritance of polymorphisms in GSTA4 was associated with risk of human NMSC. Three SNPs were found to be independent predictors of NMSC risk. Two of these were associated with increased risk of NMSC (odds ratios [ORs] = 1.60 to 3.42), while the third was associated with decreased risk of NMSC (OR = 0.63). In addition, a fourth SNP was associated with decreased risk of basal cell carcinoma only (OR = 0.44).

CONCLUSIONS

Gsta4/GSTA4 is a novel susceptibility gene for NMSC that affects risk in both mice and humans.

Dual inhibition of both the epidermal growth factor receptor and erbB2 effectively inhibits the promotion of skin tumors during two-stage carcinogenesis

The erbB family of receptor tyrosine kinases are known to play important roles in normal epithelial development and epithelial neoplasia. Considerable evidence also suggests that signaling through the epidermal growth factor receptor (EGFR) plays an important role in multistage skin carcinogenesis in mice; however, less is known about the role of erbB2. In this study, to further examine the role of both erbB2 and EGFR in epithelial carcinogenesis, we examined the effect of a dual erbB2/EGFR tyrosine kinase inhibitor, GW2974, given in the diet on skin tumor promotion during two-stage carcinogenesis in wild-type and BK5.erbB2 mice. In BK5.erbB2 mice, erbB2 is overexpressed in the basal layer of epidermis and leads to heightened sensitivity to skin tumor development. GW2974 effectively inhibited skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate in wild-type and BK5.erbB2 mice, although a more marked effect was seen in BK5.erbB2 mice. In addition, this inhibitory effect was reversible when GW2974 treatment was withdrawn. GW2974 inhibited 12-O-tetradecanoylphorbol-13-acetate-induced epidermal hyperproliferation, which correlated with reduced activation of both the EGFR and erbB2. These results support the hypothesis that both the EGFR and erbB2 play an important role in the development of skin tumors during two-stage skin carcinogenesis, especially during the tumor promotion stage. Furthermore, the marked sensitivity of BK5.erbB2 mice to the inhibitory effects of GW2974 during tumor promotion suggest greater efficacy for this compound when erbB2 is overexpressed or amplified as an early event in the carcinogenic process.

A high-throughput 1,536-well luminescence assay for glutathione S-transferase activity

Glutathione S-transferases (GSTs) constitute a family of detoxification enzymes that catalyze the conjugation of glutathione with a variety of hydrophobic compounds, including drugs and their metabolites, to yield water-soluble derivatives that are excreted in urine or bile. Profiling the effect of small molecules on GST activity is an important component in the characterization of drug candidates and compound libraries. Additionally, specific GST isozymes have been implicated in drug resistance, especially in cancer, and thus represent potential targets for intervention. To date, there are no sensitive miniaturized high-throughput assays available for GST activity detection. A series of GST substrates containing a masked luciferin moiety have been described recently, offering the potential for configuring a sensitive screening assay via coupled luciferase reaction and standard luminescence detection. We report on the optimization and miniaturization of this homogeneous method to 1,536-well format using GSTs from 3 different species: mouse isozyme A4-4, human isozymes A1-1, M1-1, and P1-1, and the major GST from the parasitic worm Schistosoma japonicum.

Transcriptome of normal lung distinguishes mouse lines with different susceptibility to inflammation and to lung tumorigenesis

AIRmax and AIRmin mouse lines show a differential lung inflammatory response and differential lung tumor susceptibility after urethane treatment. The transcript profile of approximately 24,000 known genes was analyzed in normal lung tissue of untreated and urethane-treated AIRmax and AIRmin mice. In lungs of untreated mice, inflammation-associated genes involved in pathways such as "leukocyte transendothelial migration", "cell adhesion" and "tight junctions" were differentially expressed. Moreover, gene expression levels differed significantly in urethane-treated mice; in AIRmin mice, modulation of expression of genes involved in pathways associated with inflammatory response paralleled the previously observed persistent infiltration of inflammatory cells in the lung of these mice.

Defective TPA signalling compromises HaCat cells as a human in vitro skin carcinogenesis model

HaCat cells, a human keratinocyte line, are commonly utilised as an in vitro cell model for toxicity testing and the discernment of processes of chemically induced skin carcinogenesis. Here, as part of an ongoing program of carcinogenesis research, we tested the genomic transcriptional response of two keratinocyte cell lines HaCat (human) and Pam212 (mouse) to 12-O-tetradecanoylphorbol 13-acetate (TPA), one of the most studied skin carcinoma promoting agents, and compared this with the response in primary keratinocytes. Differences in the genomic response profile indicated an insufficiency in the MEK/ERK pathway signalling in HaCat but not Pam212 cells compared to primary keratinocytes. TPA can also activate NFkappaB and so we tested whether this was also deficient in the HaCat cells using TNFalpha which signals directly to NFkappaB. By this method NFkappaB was found to be equally active in both HaCat and Pam212 cells. Analysis of ERK phosphorylation showed that while TPA mediated ERK phosphorylation occurred in both cell lines it was more robust and difficult to inhibit in Pam212 cells suggesting that there may be an insufficiency in this step in HaCat cells leading to a reduced response. Overall these data indicate that caution should be employed when using HaCat cells as an in vitro skin model for biochemical research or toxicological evaluation.

p38delta Mitogen-activated protein kinase is essential for skin tumor development in mice

Activating Ras mutations occur in a large portion of human tumors. Yet, the signaling pathways involved in Ras-induced tumor formation remain incompletely understood. The mitogen-activated protein kinase pathways are among the best studied Ras effector pathways. The p38 mitogen-activated protein kinase isoforms are important regulators of key biological processes including cell proliferation, differentiation, survival, inflammation, senescence, and tumorigenesis. However, the specific in vivo contribution of individual p38 isoforms to skin tumor development has not been elucidated. Recent studies have shown that p38delta, a p38 family member, functions as an important regulator of epidermal keratinocyte differentiation and survival. In the present study, we have assessed the effect of p38delta deficiency on skin tumor development in vivo by subjecting p38delta knockout mice to a two-stage 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate chemical skin carcinogenesis protocol. We report that mice lacking p38delta gene exhibited a marked resistance to development of 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate-induced skin papillomas, with increased latency and greatly reduced incidence, multiplicity, and size of tumors compared with wild-type mice. Our data suggest that the underlying mechanism for reduced susceptibility to skin carcinogenesis in p38delta-null mice involves a defect in proliferative response associated with aberrant signaling through the two major transformation-promoting pathways: extracellular signal-regulated kinase 1/2-activator protein 1 and signal transducer and activator of transcription 3. These findings strongly suggest an in vivo role for p38delta in promoting cell proliferation and tumor development in epidermis and may have therapeutic implication for skin cancer.

Identification of tumor promotion marker genes for predicting tumor promoting potential of chemicals in BALB/c 3T3 cells

Tumor promoters can cause development of tumors in initiated cells and the majority of them are non-genotoxic carcinogens. The detection of tumor promoters is important for the prevention of cancer. The in vitro two-stage transformation assay, using BALB/c 3T3 cells, is a useful system, and benefits from a convenient protocol and high predictability of mammalian carcinogenicity. But these assays are time-consuming and often require expertise for microscopic observation. To construct an in vitro tumor promoting activity test system, we performed large-scale gene expression analyses, using DNA microarrays, of BALB/c 3T3 cells following treatment with nine chemicals that are known to induce tumor promotion: TPA, zinc chloride, sodium orthovanadate, okadaic acid, insulin, lithocolic acid, phenobarbital sodium, sodium saccharide, sodium arsenite. As a result of DNA microarray and real time PCR analyses, 22 marker genes were identified. These consisted of genes related to cell cycle, regulation of transcription, anti-apoptosis, and positive regulation of cell proliferation. There was a correlation between these 22 marker genes and the cell transformation assay results in BALB/c 3T3 cells. These results suggest that this tumor promoting activity test system, based on 22 marker genes, can become a valuable tool for screening potential tumor promoters.

RasGRP1 overexpression in the epidermis of transgenic mice contributes to tumor progression during multistage skin carcinogenesis

RasGRP1 is a guanine nucleotide exchange factor for Ras, activated in response to the second messenger diacylglycerol and its ultrapotent analogues, the phorbol esters. We have previously shown that RasGRP1 is expressed in mouse epidermal keratinocytes and that transgenic mice overexpressing RasGRP1 in the epidermis under the keratin 5 promoter (K5.RasGRP1) are prone to developing spontaneous papillomas and squamous cell carcinomas, suggesting a role for RasGRP1 in skin tumorigenesis. Here, we examined the response of the K5.RasGRP1 mice to multistage skin carcinogenesis, using 7,12-dimethylbenz(a)anthracene as carcinogen and 12-O-tetradecanoylphorbol-13-acetate (TPA) as tumor promoter. We found that whereas tumor multiplicity did not differ between transgenic and wild-type groups, the transgenic tumors were significantly larger than those observed in the wild-type mice (wild-type, 4.58 +/- 0.25 mm; transgenic, 9.83 +/- 1.05 mm). Histologic analysis further revealed that squamous cell carcinomas generated in the transgenic mice were less differentiated and more invasive than the wild-type tumors. Additionally, 30% of the transgenic mice developed tumors in the absence of initiation, suggesting that RasGRP1 overexpression could partially substitute for the initiation step induced by dimethylbenz(a)anthracene. In primary keratinocytes isolated from K5.RasGRP1 mice, TPA stimulation induced higher levels of Ras activation compared with the levels measured in the wild-type cells, indicating that constitutive overexpression of RasGRP1 in epidermal cells leads to elevated biochemical activation of endogenous Ras in response to TPA. The present data suggests that RasGRP1 participates in skin carcinogenesis via biochemical activation of endogenous wild-type Ras and predisposes to malignant progression in cooperation with Ras oncogenic signals.

AZGP1 mRNA levels in normal human lung tissue correlate with lung cancer disease status

Evidence in animal models has suggested an association between susceptibility to lung tumorigenesis and gene-expression profiles in normal lung. Here, we compared RNA pools from normal lung tissue of lung adenocarcinoma patients (cases) or non-lung cancer patients (controls) by hybridization of whole-human genome expression arrays. Principal component analysis identified a gene-expression signature of 85 genes that distinguishes cases from controls as well as smokers from nonsmokers. Elevated mRNA levels of one of these genes, AZGP1, were significantly associated with disease status. These results support the hypothesis that differences in the gene-expression levels of the normal tissue may be predictive of genetic predisposition to lung cancer in humans.

Mouse skin chemical carcinogenesis is inhibited by antizyme in promotion-sensitive and promotion-resistant genetic backgrounds

Elevated polyamine content and increased ornithine decarboxylase (ODC) activity have been associated with neoplastic growth in numerous animal models and human tissues. Antizyme (AZ) is a negative regulator of polyamine metabolism that inhibits ODC activity, stimulates ODC degradation, and suppresses polyamine uptake. Preliminary evidence, obtained from transgenic mice with tissue specific overexpression of AZ indicates that tumor development can be suppressed by AZ. To extend these studies, we have examined the effect of keratin 5 (K5)- or K6-driven AZ transgenes on 7,12-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) chemical carcinogenesis of the skin, in promotion-resistant C57BL/6 and promotion-sensitive DBA/2 mice. On both genetic backgrounds, K6-AZ mice showed a reduction in tumor multiplicity, with 85% fewer tumors than wild-type controls on the C57BL/6 background and 50% fewer tumors on the DBA/2 background. K5-AZ mice developed 50% fewer tumors than controls on both backgrounds. The percent of mice with tumors and tumor size were also reduced in the K5-AZ and K6-AZ groups. Tumor and TPA-treated skin sections from K6-AZ mice exhibited the strongest AZ expression, with localization mainly in suprabasal keratinocytes. K6-AZ mice also had slightly reduced cell proliferation rates in tumors and TPA-treated skin. The lack of a more pronounced effect on cell proliferation is probably explained by the observation that AZ staining did not colocalize with proliferating cell nuclear antigen (PCNA), a marker for the proliferative compartment. These studies demonstrate a tumor-suppressive effect of AZ in C57BL/6 and DBA/2 mice, and confirm the importance of ODC and polyamines in tumor development.

S100A8 and S100A9 in inflammation and cancer

Calprotectin (S100A8/A9), a heterodimer of the two calcium-binding proteins S100A8 and S100A9, was originally discovered as immunogenic protein expressed and secreted by neutrophils. Subsequently, it has emerged as important pro-inflammatory mediator in acute and chronic inflammation. More recently, increased S100A8 and S100A9 levels were also detected in various human cancers, presenting abundant expression in neoplastic tumor cells as well as infiltrating immune cells. Although, many possible functions have been proposed for S100A8/A9, its biological role still remains to be defined. Altogether, its expression and potential cytokine-like function in inflammation and in cancer suggests that S100A8/A9 may play a key role in inflammation-associated cancer.