Linneg Sca-1high CD49fhigh prostate cancer cells derived from the Hi-Myc mouse model are tumor-initiating cells with basal-epithelial characteristics and differentiation potential in vitro and in vivo.

A cell line was established from ventral prostate (VP) tumors of one-year-old Hi-Myc mice. These cells, called HMVP2 cells, are LinnegSca-1highCD49fhigh with high CD44 and CD29 expression and express CK14, Sca-1 and CD49f (but not CK8), suggesting basal-epithelial characteristics. Furthermore, HMVP2 cells form spheroids and both the cells and spheroids produce tumors in syngeneic mice. After four days of culture, HMVP2 spheroids underwent a gradual transition from LinnegSca-1highCD49fhigh expression to LinnegSca-1lowCD49flow while a subpopulation of the cells retained the original LinnegSca-1highCD49fhigh expression pattern. Additional cell subpopulations expressing Lin positive markers were also present suggesting further differentiation of HMVP2 spheroids. Two additional highly tumorigenic cell lines (HMVP2A1 and HMVP2A2) were isolated from HMVP2 cells after subsequent tumor formation in FVB/N mice. Concurrently, we also established cell lines from the VP of 6 months old Hi-Myc mice (named as HMVP1) and FVB/N mice (called NMVP) having less aggressive growth properties compared to the other three cell lines. AR expression was reduced in HMVP2 cells compared to NMVP and HMVP1 cells and almost absent in HMVP2A1 and HMVP2A2 cells. These cell lines will provide valuable tools for further mechanistic studies as well as preclinical studies to evaluate preventive and/or therapeutic agents for prostate cancer.

Constitutive Stat3 activation alters behavior of hair follicle stem and progenitor cell populations.

STATs play crucial roles in a wide variety of biological functions, including development, proliferation, differentiation and migration as well as in cancer development. In the present study, we examined the impact of constitutive activation of Stat3 on behavior of keratinocytes, including keratinocyte stem cells (KSC) in vivo. BK5.Stat3C transgenic (Tg) mice, which express a constitutively active form of Stat3 (Stat3C) in the basal layer of the epidermis and in the bulge region KSCs exhibited a significantly reduced number of CD34+/α6 integrin+ cells compared to non-transgenic (NTg) littermates. There was a concomitant increase in the Lgr-6, Lrig-1, and Sca-1 populations in the Tg mice in contrast to the CD34 and Keratin-15 positive population. In addition, increased expression of c-myc, ß-catenin, and epithelial-mesenchymal transition (EMT)-related genes as well as decreased expression of α6-integrin was observed in the hair follicles of Tg mice. Notably, Sca-1 was found to be a direct transcriptional target of Stat3 in keratinocytes. The current data suggest that elevated Stat3 activity leads to depletion of hair follicle KSCs along with a concomitant increase of stem/progenitor cells above the bulge region. Overall, the current data indicate that Stat3 plays an important role in keratinocyte stem/progenitor cell homeostasis.

Bile acid accelerates erbB2-induced pro-tumorigenic activities in biliary tract cancer.

Although very few studies have addressed the molecular and cellular mechanisms underlying the development of biliary tract cancer (BTC), several lines of evidence suggest a role for the erbB receptor family. Overexpression and activation of erbB2 has been reported in a significant percentage of human BTC. Further, we previously reported that overexpression of erbB2 basal epithelial cells of the biliary tract (BK5.erbB2 mouse) led to the development of BTC. However, the mechanisms by which erbB2 overexpression led to the spontaneous development of tumors specifically in the biliary tract are not completely understood. The goals of the current study were to (1) determine whether a cooperative relationship between bile acid exposure and erbB2 activation exists during biliary tract carcinogenesis and (2) to characterize the mechanism(s) underlying bile acid-mediated biliary tract carcinogenesis in cells with activated erbB2. In this study, we demonstrated that the secondary conjugated bile acid, taurochenodeoxycholic acid (TCDC), increased proliferation of primary cultured gallbladder epithelial cells from BK5.erbB2 mice and human BTC cells. TCDC treatment activated EGFR/erbB2 and downstream signaling molecules in both primary cultured cells and human BTC cells. TCDC also increased the expression of epidermal growth factor receptor (EGFR) ligands and TACE activity in human BTC cells. Inhibition of src activation led to attenuation of bile-induced upregulation of TACE activity as well as signaling through the EGFR/erbB2, suggesting that during the development of BTC erbB2 overexpression/activation accelerates the bile acid-induced signaling cascade: bile acid → src → TACE → EGFR/erbB2 → downstream signaling. We also provide direct evidence that bile acids possess tumor promoting capacity in epithelial cells overexpressing erbB2 using the two-stage skin carcinogenesis model. Collectively these findings suggest cooperative roles for bile acid and erbB2 activation in epithelial cell proliferation; bile acid appears to accelerate erbB2-induced pro-tumorigenic activities in the biliary tract and skin.

Stat3 binds to mtDNA and regulates mitochondrial gene expression in keratinocytes.

The nuclear transcription factor signal transducer and activator of transcription 3 (Stat3) has recently been reported to have a localized mitochondrial regulatory function. Current data suggest that mitochondrial Stat3 (mitoStat3) is necessary for maximal mitochondrial activity and for Ras-mediated transformation independent of Stat3 nuclear activity. We have previously shown that Stat3 has a pivotal role in epithelial carcinogenesis. Therefore, the aim of the current study was to determine the role of mitoStat3 in epidermal keratinocytes. Herein, we show that normal and neoplastic keratinocytes contain a pool of mitoStat3. EGF and 12-O-tetradecanoylphorbol-13-acetate induce Stat3 mitochondrial translocation mediated through the phosphorylation of Stat3 at Ser727. In addition, we report that mitoStat3 binds mtDNA and associates with the mitochondrial transcription factor A. Furthermore, Stat3 ablation resulted in an increase of mitochondrial-encoded gene transcripts. An increase in key nuclear-encoded metabolic genes, PGC-1α and NRF-1, was also observed in Stat3-null keratinocytes; however, no changes in nuclear-encoded electron transport chain gene transcripts or mtDNA copy number were observed. Collectively, our findings suggest a heretofore-unreported function for mitoStat3 as a potential mitochondrial transcription factor in keratinocytes. This mitoStat3-mtDNA interaction may represent an alternate signaling pathway that could alter mitochondrial function and biogenesis and have a role in tumorigenesis.

Molecular aspects of cholangiocarcinoma.

Novel targets for therapeutic or chemopreventive approaches against cholangiocarcinoma (CCA) are urgently needed. In this review article, we discuss the molecular aspects of CCA including the role of erbB receptor tyrosine kinases (RTKs), downstream signaling pathways of these erbB RTKs, inflammatory mediators during gallbladder carcinogenesis and bile acids based on our study using a mouse model for human CCA (BK5.erbB2 mice) as well as additional information in the literature.

Impact of mTORC1 inhibition on keratinocyte proliferation during skin tumor promotion in wild-type and BK5.AktWT mice.

In this study, we examined the impact of rapamycin on mTORC1 signaling during 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced keratinocyte proliferation and skin tumor promotion in both wild-type (FVB/N) and BK5.Akt(WT) mice. TPA activated mTORC1 signaling in a time-dependent manner in cultured primary mouse keratinocytes and a mouse keratinocyte cell line. Early activation (15-30 min) of mTORC1 signaling induced by TPA was mediated in part by PKC activation, whereas later activation (2-4 h) was mediated by activation of EGFR and Akt. BK5.Akt(WT) transgenic mice, where Akt1 is overexpressed in basal epidermis, are highly sensitive to TPA-induced epidermal proliferation and two-stage skin carcinogenesis. Targeting mTORC1 with rapamycin effectively inhibited TPA-induced epidermal hyperplasia and hyperproliferation as well as tumor promotion in a dose-dependent manner in both wild-type and BK5.Akt(WT) mice. A significant expansion (∼threefold) of the label retaining cell (LRC) population per hair follicle was observed in BK5.Akt(WT) mice compared to FVB/N mice. There was also a significant increase in K15 expressing cells in the hair follicle of transgenic mice that coincided with expression of phospho-Akt, phospho-S6K, and phospho-PRAS40, suggesting an important role of mTORC1 signaling in bulge-region keratinocyte stem cell (KSC) homeostasis. After 2 weeks of TPA treatment, LRCs had moved upward into the interfollicular epidermis from the bulge region of both wild-type and BK5.Akt(WT) mice. TPA-mediated LRC proliferation and migration was significantly inhibited by rapamycin. Collectively, the current data indicate that signaling through mTORC1 contributes significantly to the process of skin tumor promotion through effects on proliferation of the target cells for tumor development.

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.

Silencing of ribonucleotide reductase subunit M1 potentiates the antitumor activity of gemcitabine in resistant cancer cells.

Gemcitabine is a deoxycytidine analog used for the treatment of a wide range of solid tumors. Its efficacy is however often reduced due to the development of resistance. Ribonucleotide reductase M1 subunit (RRM1) is a key determinant of gemcitabine resistance, and tumor cells that overexpress RRM1 are resistant to the cytotoxicity of gemcitabine. In the present study, we showed that RRM1-specific small interfering RNA (siRNA), when complexed with polyethylenimine, effectively downregulated the expression of RRM1 protein in mouse tumor cells that overexpress RRM1, both in vitro and in vivo. More importantly, systemic administration of the RRM1-specific siRNA significantly inhibited the growth of RRM1-overexpressing tumors in mice and sensitized the tumors to gemcitabine treatment. These findings suggest that silencing RRM1 expression using siRNA could potentially be an effective strategy to overcome gemcitabine resistance.

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.

Control of solid tumor growth in mice using EGF receptor-targeted RNA replicase-based plasmid DNA.

AIM: Previously, it was shown that treatment of tumor-bearing mice with an RNA replicase-based plasmid that produces dsRNA when transfected into tumor cells significantly inhibited the tumor growth. In the present study, the feasibility of further improving the anti-tumor activity of the RNA replicase-based plasmid by targeting it into tumors cells was evaluated. MATERIAL & METHODS: An EGF-conjugated, polyethylene glycosylated cationic liposome was developed to deliver the RNA replicase-based plasmid, pSIN-ß, into EGF receptor-overexpressing human breast cancer cells (MDA-MB-468) in vitro and in vivo. RESULTS: Delivery of pSIN-ß using the EGF receptor-targeted liposome more effectively controlled the growth of MDA-MB-468 tumors (and human epidermoid carcinoma A431 tumors) in mice than using untargeted liposome. The pSIN-ß carried by the EGF receptor-targeted liposome caused the complete regression of MDA-MB-468 tumors in mice, probably due to the enhancement of its proapoptotic, antiproliferative and antiangiogenic activities. DISCUSSION: Tumor-targeted RNA replicase-based plasmids hold a strong potential in tumor therapy.

Transgenic insulin-like growth factor-1 stimulates activation of COX-2 signaling in mammary glands.

Studies show that elevated insulin-like growth factor-1 (IGF-1) levels are associated with an increased risk of breast cancer; however, mechanisms through which IGF-1 promotes mammary tumorigenesis in vivo have not been fully elucidated. To assess the possible involvement of COX-2 signaling in the pro-tumorigenic effects of IGF-1 in mammary glands, we used the unique BK5.IGF-1 mouse model in which transgenic (Tg) mice have significantly increased incidence of spontaneous and DMBA-induced mammary cancer compared to wild type (WT) littermates. Studies revealed that COX-2 expression was significantly increased in Tg mammary glands and tumors, compared to age-matched WTs. Consistent with this, PGE(2) levels were also increased in Tg mammary glands. Analysis of expression of the EP receptors that mediate the effects of PGE(2) showed that among the four G-protein-coupled receptors, EP3 expression was elevated in Tg glands. Up-regulation of the COX-2/PGE(2) /EP3 pathway was accompanied by increased expression of VEGF and a striking enhancement of angiogenesis in IGF-1 Tg mammary glands. Treatment with celecoxib, a selective COX-2 inhibitor, caused a 45% reduction in mammary PGE(2) levels, attenuated the influx of mast cells and reduced vascularization in Tg glands. These findings indicate that the COX-2/PGE(2) /EP3 signaling pathway is involved in IGF-1-stimulated mammary tumorigenesis and that COX-2-selective inhibitors may be useful in the prevention or treatment of breast cancer associated with elevated IGF-1 levels in humans. © 2011 Wiley Periodicals, Inc.

EGFR-targeted stearoyl gemcitabine nanoparticles show enhanced anti-tumor activity.

Previously, it was shown that a novel 4-(N)-stearoyl gemcitabine nanoparticle formulation was more effective than gemcitabine hydrochloride in controlling the growth of model mouse or human tumors pre-established in mice. In the present study, the feasibility of targeting the stearoyl gemcitabine nanoparticles (GemC18-NPs) into tumor cells that over-express epidermal growth factor receptor (EGFR) to more effectively control tumor growth was evaluated. EGFR is over-expressed in a variety of tumor cells, and EGF is a known natural ligand of EGFR. Recombinant murine EGF was conjugated onto the GemC18-NPs. The ability of the EGF to target the GemC18-NPs to human breast adenocarcinoma cells that expressed different levels of EGFR was evaluated in vitro and in vivo. In culture, the extent to which the EGF-conjugated GemC18-NPs were taken up by tumor cells was correlated to the EGFR density on the tumor cells, whereas the uptake of untargeted GemC18-NPs exhibited no difference among those same cell lines. The relative cytotoxicity of the EGF-conjugated GemC18-NPs to tumor cells in culture was correlated to EGFR expression as well. In vivo, EGFR-over-expressing MDA-MB-468 tumors in mice treated with the EGF-conjugated GemC18-NPs grew significantly slower than in mice treated with untargeted GemC18-NPs, likely due to that the EGF-GemC18-NPs were more anti-proliferative, anti-angiogenic, and pro-apoptotic. Fluorescence intensity data from ex vivo imaging showed that the EGF on the nanoparticles helped increase the accumulation of the GemC18-NPs into MDA-MB-468 tumors pre-established in mice by more than 2-fold as compared to the un-targeted GemC18-NPs. In conclusion, active targeting of the GemC18-NPs into EGFR-over-expressed tumors can further enhance their anti-tumor activity.

In vitro and in vivo anti-tumor activities of a gemcitabine derivative carried by nanoparticles.

Gemcitabine (Gemzar(®)) is the first line treatment for pancreatic cancer and often used in combination therapy for non-small cell lung, ovarian, and metastatic breast cancers. Although extremely toxic to a variety of tumor cells in culture, the clinical outcome of gemcitabine treatment still needs improvement. In the present study, a new gemcitabine nanoparticle formulation was developed by incorporating a previously reported stearic acid amide derivative of gemcitabine into nanoparticles prepared from lecithin/glyceryl monostearate-in-water emulsions. The stearoyl gemcitabine nanoparticles were cytotoxic to tumor cells in culture, although it took a longer time for the gemcitabine in the nanoparticles to kill tumor cells than for free gemcitabine. In mice with pre-established model mouse or human tumors, the stearoyl gemcitabine nanoparticles were significantly more effective than free gemcitabine in controlling the tumor growth. PEGylation of the gemcitabine nanoparticles with polyethylene glycol (2000) prolonged the circulation of the nanoparticles in blood and increased the accumulation of the nanoparticles in tumor tissues (>6-fold), but the PEGylated and un-PEGylated gemcitabine nanoparticles showed similar anti-tumor activity in mice. Nevertheless, the nanoparticle formulation was critical for the stearoyl gemcitabine to show a strong anti-tumor activity. It is concluded that for the gemcitabine derivate-containing nanoparticles, cytotoxicity data in culture may not be used to predict their in vivo anti-tumor activity, and this novel gemcitabine nanoparticle formulation has the potential to improve the clinical outcome of gemcitabine treatment.

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.

Targeted disruption of stat3 reveals a major role for follicular stem cells in skin tumor initiation.

The initiation stage of mouse skin carcinogenesis involves the induction of mutations in keratinocyte stem cells (KSC), which confers a selective growth advantage allowing clonal expansion during tumor promotion. Targeted disruption of signal transducer and activator of transcription 3 (Stat3) in bulge region KSCs was achieved by treating K15.CrePR1 x Stat3(fl/fl) mice with RU486. Deletion of Stat3 prior to skin tumor initiation with 7,12-dimethylbenz(a)anthracene significantly increased the number of apoptotic KSCs and decreased the frequency of Ha-ras codon 61 A(182)-->T transversion mutations in this cell population compared with wild-type littermates. Targeted disruption of Stat3 in bulge region KSCs at the time of initiation also dramatically reduced the number of skin tumors (by approximately 80%) produced following promotion with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate. These results show that Stat3 is required for the survival of bulge region KSCs during tumor initiation. Furthermore, these data provide direct evidence that bulge region KSCs are the primary targets for the initiation of skin tumors in this model system.

Multi-stage chemical carcinogenesis in mouse skin: fundamentals and applications.

For more than 60 years, the chemical induction of tumors in mouse skin has been used to study mechanisms of epithelial carcinogenesis and evaluate modifying factors. In the traditional two-stage skin carcinogenesis model, the initiation phase is accomplished by the application of a sub-carcinogenic dose of a carcinogen. Subsequently, tumor development is elicited by repeated treatment with a tumor-promoting agent. The initiation protocol can be completed within 1-3 h depending on the number of mice used; whereas the promotion phase requires twice weekly treatments (1-2 h) and once weekly tumor palpation (1-2 h) for the duration of the study. Using the protocol described here, a highly reproducible papilloma burden is expected within 10-20 weeks with progression of a portion of the tumors to squamous cell carcinomas within 20-50 weeks. In contrast to complete skin carcinogenesis, the two-stage model allows for greater yield of premalignant lesions, as well as separation of the initiation and promotion phases.

Targeted disruption of Bcl-xL in mouse keratinocytes inhibits both UVB- and chemically induced skin carcinogenesis.

Bcl-x(L) is one of several antiapoptotic proteins regulated by signal transducer and activator of transcription 3 (Stat3). We have recently shown that Stat3 is required for chemically induced and ultraviolet B (UVB)-induced skin carcinogenesis. In this study, the functional role of Bcl-x(L) in skin carcinogenesis was investigated using skin-specific Bcl-x(L)-deficient mice. In this model, Bcl-x(L) expression is disrupted in the basal compartment of mouse epidermis using the bovine keratin 5 (K5) promoter to drive expression of Cre recombinase (K5.Cre x Bcl-x(L) (fl/fl) mice). A significant increase in apoptosis induced by either UVB irradiation or 7,12-dimethylbenz[a]anthracene (DMBA) treatment was observed in the epidermis of Bcl-x(L)-deficient mice. Furthermore, an increase in apoptotic cells was noted in hair follicle keratinocytes, including those located in the bulge region. Cell proliferation was not affected by Bcl-x(L) deficiency following exposure to either UVB or 12-O-tetradecanoylphorbol-13-acetate (TPA). Bcl-x(L)-deficient mice were more resistant than wild-type controls to skin tumor development with delayed onset and reduced number of tumors using either UVB or the DMBA/TPA two-stage regimen. Moreover, Bcl-2, Mcl-1, and survivin protein levels were increased in the epidermis of Bcl-x(L)-deficient mice in the absence of stimuli. Furthermore, levels of these antiapoptotic proteins were also high in skin tumors from Bcl-x(L)-deficient mice that developed in response to either UVB or two-stage carcinogenesis protocols. Collectively, these studies demonstrate that Bcl-x(L) plays a role early in skin carcinogenesis through its anti-apoptotic functions to enhance survival of keratinocytes, including bulge region keratinocyte stem cells, following DNA damage.

Akt activation synergizes with Trp53 loss in oral epithelium to produce a novel mouse model for head and neck squamous cell carcinoma.

Head and neck squamous cell carcinoma (HNSCC) is a common human neoplasia with poor prognosis and survival that frequently displays Akt overactivation. Here we show that mice displaying constitutive Akt activity (myrAkt) in combination with Trp53 loss in stratified epithelia develop oral cavity tumors that phenocopy human HNSCC. The myrAkt mice develop oral lesions, making it a possible model of human oral dysplasia. The malignant conversion of these lesions, which is hampered due to the induction of premature senescence, is achieved by the subsequent ablation of Trp53 gene in the same cells in vivo. Importantly, mouse oral tumors can be followed by in vivo imaging, show metastatic spreading to regional lymph nodes, and display activation of nuclear factor-kappaB and signal transducer and activator of transcription-3 pathways and decreased transforming growth factor-beta type II receptor expression, thus resembling human counterparts. In addition, malignant conversion is associated with increased number of putative tumor stem cells. These data identify activation of Akt and p53 loss as a major mechanism of oral tumorigenesis in vivo and suggest that blocking these signaling pathways could have therapeutic implications for the management of HNSCC.

IKKalpha is required to maintain skin homeostasis and prevent skin cancer.

It has long been known that excessive mitotic activity due to H-Ras can block keratinocyte differentiation and cause skin cancer. It is not clear whether there are any innate surveillants that are able to ensure that keratinocytes undergo terminal differentiation, preventing the disease. IKKalpha induces keratinocyte terminal differentiation, and its downregulation promotes skin tumor development. However, its intrinsic function in skin cancer is unknown. Here, we found that mice with IKKalpha deletion in keratinocytes develop a thickened epidermis and spontaneous squamous cell-like carcinomas. Inactivation of epidermal growth factor receptor (EGFR) or reintroduction of IKKalpha inhibits excessive mitosis, induces terminal differentiation, and prevents skin cancer through repressing an EGFR-driven autocrine loop. Thus, IKKalpha serves as an innate surveillant.

The transcription factor ATF3 acts as an oncogene in mouse mammary tumorigenesis.

BACKGROUND: Overexpression of the bZip transcription factor, ATF3, in basal epithelial cells of transgenic mice under the control of the bovine cytokeratin-5 (CK5) promoter has previously been shown to induce epidermal hyperplasia, hair follicle anomalies and neoplastic lesions of the oral mucosa including squamous cell carcinomas. CK5 is known to be expressed in myoepithelial cells of the mammary gland, suggesting the possibility that transgenic BK5.ATF3 mice may exhibit mammary gland phenotypes. METHODS: Mammary glands from nulliparous mice in our BK5.ATF3 colony, both non-transgenic and transgenic, were examined for anomalies by histopathology and immunohistochemistry. Nulliparous and biparous female mice were observed for possible mammary tumor development, and suspicious masses were analyzed by histopathology and immunohistochemistry. Human breast tumor samples, as well as normal breast tissue, were similarly analyzed for ATF3 expression. RESULTS: Transgenic BK5.ATF3 mice expressed nuclear ATF3 in the basal layer of the mammary ductal epithelium, and often developed squamous metaplastic lesions in one or more mammary glands by 25 weeks of age. No progression to malignancy was seen in nulliparous BK5.ATF3 or non-transgenic mice held for 16 months. However, biparous BK5.ATF3 mice developed mammary carcinomas with squamous metaplasia between 6 months and one year of age, reaching an incidence of 67%. Cytokeratin expression in the tumors was profoundly disturbed, including expression of CK5 and CK8 (characteristic of basal and luminal cells, respectively) throughout the epithelial component of the tumors, CK6 (potentially a stem cell marker), CK10 (a marker of interfollicular epidermal differentiation), and mIRSa2 and mIRSa3.1 (markers of the inner root sheath of hair follicles). Immunohistochemical studies indicated that a subset of human breast tumors exhibit high levels of nuclear ATF3 expression. CONCLUSION: Overexpression of ATF3 in CK5-expressing cells of the murine mammary gland results in the development of squamous metaplastic lesions in nulliparous females, and in mammary tumors in biparous mice, suggesting that ATF3 acts as a mammary oncogene. A subset of human breast tumors expresses high levels of ATF3, suggesting that ATF3 may play an oncogenic role in human breast tumorigenesis, and therefore may be useful as either a biomarker or therapeutic target.