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Oncogenic Signaling Pathways Activated in DMBA-Induced Mouse Mammary Tumors
1 Boston University School of Medicine, Department of Medicine, Boston, Massachusetts, USA Correspondence: Address correspondence to: David C. Seldin, 650 Albany Street, Boston, Massachusetts 02118; e-mail:dseldin{at}bumc.bu.edu
Only about 5% of human breast cancers can be attributed to inheritance of breast cancer susceptibility genes, while the balance are considered to be sporadic in origin. Breast cancer incidence varies with diet and other environmental influences, including carcinogen exposure. However, the effects of environmental carcinogens on cell growth control pathways are poorly understood. Here we have examined oncogenic signaling pathways that are activated in mammary tumors in mice treated with the prototypical polycyclic aromatic hydrocarbon (PAH) 7,12-dimethylbenz[a]anthracene (DMBA). In female FVB mice given 6 doses of 1 mg of DMBA by weekly gavage beginning at 5 weeks of age, all of the mice developed tumors by 34 weeks of age (median 20 weeks after beginning DMBA); 75% of the mice had mammary tumors. DMBA-induced mammary tumors exhibited elevated expression of the aryl hydrocarbon receptor (AhR), c-myc, cyclin D1, and hyperphosphorylated retinoblastoma (Rb) protein. Because of this, the activation of upstream regulatory pathways was assessed, and elements of the Wnt signaling pathway, the NF-  B pathway, and the prolyl isomerase Pin-1 were found to be frequently up-regulated in the tumors when compared to normal mammary gland controls. These data suggest that environmental carcinogens can produce long-lasting alterations in growth and anti-apoptotic pathways, leading to mammary tumorigenesis.
Key Words: DMBA • Wnt • NF-
Although the second leading cause of cancer mortality in women is breast cancer, we still do not have a very complete understanding of the mechanisms of mammary tumorigenesis. Extensive investigation has identified breast cancer susceptibility genes that can be inherited, but these appear to play a minor role in most cases of breast cancer. The geographic variation in incidence of breast cancer suggests that environmental and dietary factors play a significant role. A major class of environmental carcinogens is a family of structurally related chemicals, the polycyclic aromatic hydrocarbons (PAH). These carcinogens and related halogenated compounds have been implicated in mammary tumorigenesis by epidemiological and laboratory studies. DMBA (7,12-dimethylbenz[a]anthracene) is a prototypical PAH that has been used to promote tumors in laboratory animals (Medina, 1974). Mammary tumors can be produced in rodents following administration of DMBA by oral gavage, leading to up-regulation of the cellular cytosolic receptor for DMBA, the aryl hydrocarbon receptor (AhR) (Trombino et al., 2000). Upon ligand activation, the AhR translocates into the nucleus and associates with the cofactor ARNT, the AhR nuclear translocation protein (Denison and Nagy, 2003; Swanson et al., 1995). This activated AhR/ARNT complex then binds to specific DNA recognition sites upstream of AhR responsive genes and induces gene transcription (Denison and Nagy, 2003). The early steps in tumorigenesis involve AhR-dependent up-regulation of cytochrome P450 enzymes, which metabolize DMBA into a mutagenic epoxide intermediate that readily forms DNA adducts. These adducts are associated with DNA mutations and the malignant transformation that is thought to be involved in PAH-mediated carcinogenesis (Nebert et al., 1990; Rundle et al., 2000). However, there is growing evidence that the AhR also regulates cell growth (Abdelrahim et al., 2003; Ge and Elferink, 1998; Holcomb and Safe, 1994; Ma and Whitlock, 1996; Puga et al., 2000) and survival (Caruso et al., 2004; Matikainen et al., 2001), suggesting that there are additional mechanisms through which the AhR may contribute to mammary tumorigenesis. Furthermore, while PAH-mediated DNA damage may be an important initiation factor, it has also been suggested that DNA damage may not be sufficient for the development of tumors (Miller and Miller, 1981).
We hypothesized that epigenetic changes in oncogene expression and intracellular signaling may play important roles. To test whether additional biochemical changes may occur that could lead to mammary tumor formation after PAH exposure, we established an oral dose regimen of DMBA that resulted in mammary tumors in 75% of FVB mice by 30 weeks of age, associated with tonic up-regulation of the AhR. RNA transcripts for cyclin D1 and c-myc, important oncogenes in human breast cancer (Bartkova et al., 1994; Jamerson et al., 2004), were increased in many of the DMBA-induced mammary tumors. These results led us to examine the effects of DMBA treatment on upstream regulators of c-myc and cyclin D1, including the NF-
NF- Another pathway that has been implicated in carcinogen-induced tumorigenesis, and may also lead to transactivation of the c-myc and cyclin D1 oncogenes is the Wnt pathway. The Wnt pathway was originally discovered in Drosophila as an important signaling pathway in development (Sharma and Chopra, 1976). Later it was appreciated to have a role in tumor development (Nusse and Varmus, 1982; Rijsewijk et al., 1987). The discovery of mutations in the adenomatous polyposis coli (APC) gene, an important tumor suppressor protein in the canonical Wnt pathway, as the underlying cause of the familial adenomatous polyposis colon cancer syndrome, provided molecular evidence for the role of Wnt signaling in human tumors (Nagase and Nakamura, 1993). Wnts are a family of secreted glycoproteins that bind to Frizzled (Fz) 7 transmembrane cell surface receptors. Activation of Fz leads to inhibition of glycogen synthase kinase 3β (GSK3β) via the Disheveled (Dvl) protein. Inhibition of GSK3β prevents N-terminal phosphorylation, and subsequent ubiquitination and degradation of β-catenin. The failure to degrade β-catenin then leads to cytoplasmic accumulation and nuclear translocation. Once in the nucleus, β-catenin binds transcription factors of the T cell (TCF) and lymphoid enhancing (LEF) families and stimulates transactivation of various genes such as cyclin D1 and c-myc, which are believed to be central to the tumorigenic potential of Wnt signaling (Polakis, 2000).
Cyclin D1 promotes cell growth by activating cyclin-dependent kinases (Cdks) 4 and 6, which phosphorylate the retinoblastoma protein (Rb), a critical step in regulation of the restriction point at the G1/S transition (Weinberg, 1995). Recent work from our lab has identified CK2, a ubiquitously expressed serine/threonine kinase consisting of 2 The prolyl isomerase Pin1, also shown to be up-regulated in human mammary tumors, has also been implicated in activation of Wnt signaling through various mechanisms. Pin1 is a prolyl isomerase that catalyzes the cis-trans isomerization of pSer/Thr-Pro motifs, and thereby facilitates conformational changes that affect a wide variety of protein functions including subcellular localization, catalytic activity, protein-protein interactions, and protein turnover. Up-regulation of Pin1 has been observed in a variety of human cancers (Bao et al., 2004), including breast cancer, where a strong correlation has been observed between Pin-1 and β-catenin up-regulation (Ryo et al., 2001). Pin1 directly potentiates Wnt signaling and expression of the target genes cyclin-D1 and c-myc by facilitating β-catenin release from APC, the adenomatous polyposis coli gene product (Ryo et al., 2001). Pin-1 also directly binds to and stabilizes cyclin D1, and Pin-1 knockout mice demonstrate many of the same phenotypes as cyclin D1 null mice, i.e., impairment of normal mammary gland development and retinal hypoplasia (Liou et al., 2002).
To begin to elucidate the mechanism leading to the DMBA-induced increase in cyclin D1 and c-myc, we assessed pathways implicated in the regulation of these genes by comparing tumor samples to normal mammary glands. Here, we demonstrate activation of signaling through the AhR, NF-
DMBA Treatment Virgin female FVB/N mice were treated according to a protocol approved by the Boston University Institutional Animal Care and Use Committee. Mice were housed in a 2-way barrier at the Boston University School of Medicine animal facility in accordance with the regulations of the American Association for the Accreditation of Laboratory Animal Care. Twenty mice were each given 6 weekly 1.0 mg doses of DMBA in 0.2 ml of sesame oil by oral gavage, beginning at 5 weeks of age. Mice were then mated continuously to provide an oscillating hormonal environment and followed until either tumors developed or the mice died. Mice bearing tumors >0.5 cm were euthanized by CO2 inhalation and necropsied. Mammary tumors and grossly normal mammary glands from parous age-matched control FVB mice were excised and portions of the tissues were prepared for histology. The remaining tissue was frozen on dry ice for molecular and biochemical studies. Frozen tissues were stored at –80°C.
Histology
Immunoblot Analysis
Electrophoresis was performed in a Bio-Rad Mini Protean II gel system at 110V for 2 hours. After electrophoresis, gels were transferred onto PVDF membranes (Millipore Inc.). Membranes were blocked in 5% milk in 1X TBS, 0.05% Tween, incubated with an appropriate primary antibody, washed, incubated with HRP-conjugated secondary antibody (Santa Cruz Biotechnology, Santa Cruz, CA), washed again and visualized by ECL (Pierce, Rockford, IL) according to the manufacturer’s instructions. Primary antibodies were the following antibodies: anti-β-catenin (BD, Upstate), anti-β-actin (SIGMA or C-11 Santa Cruz), anti-CK2
RNA Extraction and Reverse Transcription
Quantitative Real-Time PCR (QPCR)
Electromobility Shift Assay (EMSA) and Nuclear Extraction
Statistics
Tumor-Incidence and Histology in FVB/N Mice Treated with DMBA Female mice were treated with 6 weekly 1 mg doses of DMBA by oral gavage beginning at 5 weeks of age. Beginning 4 weeks after the final dose, at 15 weeks of age, mice began to develop evidence of tumors (Figure 1, Kaplan-Meier survival plot) and were then euthanized for analysis. By 34 weeks of age (29 weeks after beginning DMBA treatment), all mice had developed tumors. 75% of the mice had mammary tumors, 15% of the mice had lung tumors, 10% had lymphomas, and 5% had skin cancers; some mice had more than 1 malignancy. In addition, 30% of the mice had myeloid hyperplasia.
These findings can be compared with large reported series of female FVB mice, in which 15% of mice develop bronchoalveolar lung adenomas and carcinomas by 14 m of age; lymphomas (in 6%) and skin tumors (in 3%) have been reported at 24 m of age (Mahler et al., 1996). Mammary gland hyperplasia and carcinomas (both associated with and independent of pituitary hyperplasia) also can occur, but have not been reported in the first year of life (Nieto et al., 2003; Wakefield et al., 2003). The most common histologies of the DMBA-induced mammary tumors were squamous or adenosquamous carcinomas, accounting for 85% of the mammary tumors, with other tumors being of the Wnt type (Rosner et al., 2002), or scirrhous tubular, spindle cell, or papillary carcinomas (Table 1 and Figure 2).
DMBA-Induced Mammary Tumors Have Increased Expression of AhR mRNA, Protein If the AhR plays an ongoing role in mammary tumorigenesis, we predicted it would be up-regulated in carcinogen-induced tumors. To test this hypothesis, expression levels of the AhR protein and mRNA transcript were measured by immunoblot and quantitative PCR analysis, respectively. Proteins were extracted from tumors arising in DMBA-treated mice and the normal mammary glands from age-matched controls, and immunoblotting was performed for AhR. The blots were stripped and re-probed for β-actin to control for protein loading. AhR protein expression in 7 of 11 mammary tumors was considerably higher than in the controls (Figure 3a, 3b). The bands were quantitated by phosphoimager analysis, and the average level of AhR protein (expressed as a normalized ratio of Fluor-S units compared to actin) in tumors was 0.98 ± 0.09 (mean ± S.E.) as compared to 0.08 ± 0.03 in the controls (p = 0.011). Similar results were obtained in 4 separate experiments using 2 different AhR antibodies.
To measure the level of AhR mRNA, quantitative PCR (QPCR) was performed in tumor and normal samples, with GAPDH expression used for normalization. The ratio of AhR mRNA in each individual sample as compared to the mean of the normal tissues is presented as the fold-change. Similar to AhR protein results, AhR mRNA levels were higher in the majority of DMBA-induced tumors, as compared to normal mammary tissue (Figure 3c), although the magnitude of AhR mRNA and protein levels did not always directly correlate (e.g., Tumor T3). These results suggest that AhR up-regulation in mammary tumors may be regulated at multiple levels, but are consistent with a role for the AhR in mammary tumorigenesis.
Cyclin D1 and c-myc mRNA Levels in DMBA-Induced Mammary Tumors
Hyperphosphorylated Rb Protein Expression in DMBA-Induced Mammary Tumors G1 kinases, including cyclin D1-associated kinases, directly phosphorylate Rb, and the hyperphosphorylated Rb dissociates from E2F, which is critical in promoting cell cycle progression (Weinberg, 1995). Thus, Rb hyperphosphorylation is a measure of inactivation of Rb-mediated growth suppression and deregulated cell cycle control. Therefore, we examined the phosphorylation status of Rb protein in DMBA-induced mammary tumors. Increased amounts of phosphoRb and an increased proportion of Rb in the phosphorylated form was readily detected in DMBA tumors, in contrast to normal mammary gland (Figure 5a, 5b). Hyperphosphorylated Rb protein levels in tumors were 0.34 ± 0.03 compared with 0.03 ± 0.01 in normal controls (p = 0.013), indicating that Rb is inactivated in DMBA-induced mammary tumors.
DMBA-Induced Mammary Tumors Exhibit Increased Nuclear NF- B BindingThe NF- B pathway is capable of regulating transcription of the c-myc and cyclin D1 genes. To determine whether DMBA-induced mouse mammary tumors have constitutively active nuclear-NF-B, EMSAs were performed using the c-myc promoter URE as a probe (Duyao et al., 1990). Nuclear extracts from the DMBA-induced mouse mammary tumors were compared with those from mammary glands of age-matched female FVB/N mice or from a nulliparous animal (Figure 6). NF-B bands were identified using supershift analysis (data not shown). While NF-B binding in normal mammary gland fluctuates with the estrus cycle, the predominant complex seen was made up of p50 homodimers (Band 5) and a minor amount of p50/p65 heterodimers (Band 1), as seen previously (Clarkson et al., 2002). In addition, some clipping of p50 occurred (Band 6), as we have observed previously (Pianetti et al., 2001). In contrast, DMBA-induced tumors displayed increased levels of the potent transactivating complexes p50/p65, p50/c-Rel (Band 2), p52/RelB (Band 3), in addition to p50 or p52 (Band 2) homodimers. Equal loading and protein integrity of the nuclear extracts was confirmed by analysis of Oct-1 binding. Thus, DMBA-induced mammary tumors are characterized by elevated levels of NF-B binding complexes known to be able to activate transcription.
DMBA-Induced Mammary Tumors Have Elevated Expression of Canonical Wnt Signaling Components To evaluate the Wnt signaling pathway in DMBA-induced mammary tumors, we initially measured whole cell and nuclear levels of β-catenin protein, the essential transcriptional cofactor for canonical Wnt signaling. In the whole cell extracts, substantial up-regulation of β-catenin was found in 6 of 12 tumor samples tested, when compared to mammary glands from untreated, age-matched FVB mice (Figure 7a, 7b). The average level of β-catenin, expressed as a normalized ratio of Fluor-S units compared to β-actin, was significantly higher in the tumors, as compared to the normal controls [0.36 ± 0.35 vs. 0.03 ± 0.01 (p = 0.008)]. Similar results were obtained in 3 separate experiments using 2 different β-catenin antibodies (data not shown). We also examined β-catenin expression in the nuclear extracts prepared for EMSA, and found a similar pattern of increased nuclear β-catenin (data not shown).
One of the positive regulators of β-catenin protein stability is the serine-threonine kinase CK2, which phosphorylates β-catenin in the armadillo repeat region and stabilizes it. Interestingly, all but 1 tumor demonstrated a significant up-regulation of the major catalytic CK2  subunit (Figure 8a, 8b) as compared to the normal tissues. Mean tumor and normal values were [0.24 ± 0.014 vs. 0.003 ± 0.001 (p = 0.001)] respectively. The up-regulation of CK2 correlated well with the up-regulation of β-catenin (Figure 8c), consistent with the putative role of CK2 as a positive Wnt regulator. These results demonstrate activation of the Wnt signaling pathway in DMBA-induced mammary tumors.
Increased Pin1 Protein Expression in DMBA-Induced Mammary Tumors Expression of the prolyl-isomerase Pin1 is often increased in human cancers, including breast cancer (Bao et al., 2004). Therefore, we examined Pin1 expression in the DMBA-induced mammary tumors. As shown in Figure 9, Pin1 protein expression was significantly increased in many of the mammary tumors, compared to age-matched normal FVB mice mammary glands. The average level of Pin1, normalized ratio of Fluor-S units compared to β-actin, was 0.25 ± 0.02 in the tumors compared with 0.08 ± 0.06 in the controls (p = 0.032) (Figure 9a, 9b). Interestingly, QPCR analysis of Pin1 mRNA levels showed no significant differences between tumors and the age-matched normal controls (data not shown), suggesting that elevated Pin1 expression in DMBA-induced mammary tumors is likely due to a posttranscriptional mechanism. A correlation between the de-regulation of Pin1 protein and several important cell cycle regulators was observed (Table 2). In many of the tumor samples, increased Pin1 expression correlated well with an increase β-catenin (Figure 9c), and also with the level of hyperphosphorylated Rb and cyclin D1 mRNA (Table 2).
The present study describes an oral dose regimen of the environmental carcinogen DMBA capable of generating mammary tumors in FVB strain mice. We hypothesized that, in addition to its genotoxic properties, DMBA would also alter oncogenic signaling pathways in order to transform cells. Here we have shown evidence of up-regulation of cell cycle regulators that have well-established roles in mammary tumorigenesis and of the signaling pathways capable of up-regulating them. These data provide evidence of specific biochemical changes that accompany tumor formation in PAH-induced mammary tumors, and activation of critical regulatory pathways that can contribute to growth and oppose apoptosis in cancer in the process of carcinogen-induced mammary tumorigenesis in mice. These observations expand upon previous reports of DNA damaging events such as the induction of point mutations in genes such as c-H-ras by DMBA (Cardiff et al., 1988). As it is believed that both genotoxic and mitogenic activities of environmental carcinogens may be mediated through the aryl hydrocarbon receptor (AhR), our initial experiments involved measuring levels of the AhR protein and transcript. In tumors arising in the carcinogen-treated mice, as we have previously seen in rats treated with a single dose of DMBA (Trombino et al., 2000), there was evidence of constitutive up-regulation of the AhR itself. Preliminary data identified frequent up-regulation of an AhR target gene, CYP1B1, although CYP1B1 levels did not always correlate with AhR levels in any given tumor (data not shown). Since it has been well established that CYP1B1 is involved in activation of DMBA to its genotoxic metabolites and in metabolism of estradiol into mutagenic intermediates, our data suggest that AhR up-regulation in tumors may contribute to ongoing genetic changes through CYP1B1 induction.
As a means to evaluate fundamental cell cycle regulators known to be important in mammary tumorigenesis, initial studies measured mRNA levels of the cyclin D1 and c-myc oncogenes, and levels of hyperphosphorylated Rb. Quantitative PCR results suggested that cyclin D1 mRNA is frequently elevated, and c-myc is occasionally elevated. Western blot analysis demonstrated increased amounts of phosphoRb and an increased proportion of Rb in the phosphorylated form. When we examined upstream regulatory pathways, we found evidence of constitutive NF-
The NF- Our data also provide evidence of activation the Wnt pathway in the majority of PAH-induced mammary tumors. A second pathway capable of c-myc and cyclin D1 transactivation. Wnt signaling can be assessed by total levels of the co-transactivator β-catenin in cells and tissues, but particularly by measurement of nuclear levels. Both total and nuclear β-catenin levels were elevated in most of the tumors. Most tumors also had elevated protein levels of the positive kinase regulator, CK2. CK2 may be contributing to the increase in tumor β-catenin, as well as stabilizing other pro-oncogenic proteins. The majority of the tumors with significantly elevated levels of β-catenin (T1, T9, T11) also have histological characteristics associated with Wnt pathway mammary tumors (Rosner et al., 2002). Additionally, squamous cell carcinoma, seen histologically in the majority of the DMBA-induced mammary tumors, has been associated with Wnt-related tumors of the mammary gland (Rosner et al., 2002).
DMBA-induced mammary tumors also expressed elevated levels of Pin1, a prolyl isomerase that has been shown to be up-regulated in a variety of human cancers, and to function as a signaling integrator in the regulation of β-catenin (Pang et al., 2004; Ryo et al., 2001), cyclin D1 (Liou et al., 2002; Wulf et al., 2001), c-myc (Yeh et al., 2004), and NF-
Our observation of activation of these known oncogenic pathways not only correlates well with previous data from our lab using Sprague–Dawley rats (Landesman-Bollag et al., 2001; Sovak et al., 1997; Trombino et al., 2000), but with other studies of carcinogen-induced mammary tumors in which gene expression patterns were analyzed by microarray. In particular, various studies describe up-regulation of cyclin D1 transcripts in DMBA and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induced mammary tumors (Kuramoto et al., 2002; Shan et al., 2002). QPCR analysis of Pin1 mRNA levels showed no significant difference between tumors and the age-matched normal controls (data not shown), suggesting that Pin1 up-regulation in DMBA-induced mammary tumors is likely due to a posttranscriptional mechanism. This observation is consistent with the lack of Pin-1 mRNA up-regulation identified by microarray. Posttranscriptional mechanisms may also contribute to the activation of β-catenin and NF- While the current studies do not determine whether the signaling cascades are activated sequentially or in parallel in the course of transformation, this can be tested in the future using transgenic mouse models. For instance, by treating AhR-null mice with DMBA by this protocol, we can assess the role of this receptor in the activation of the downstream mediators. Understanding the interaction of these signaling pathways may provide targets for novel therapeutics in the future. Furthermore, since many transgenic models exist in the FVB background in which oncogenes produce mammary tumorigenesis in a multistep stochastic fashion, these studies provide us with the capability of examining the interaction of carcinogens and genetic predisposition to breast cancer.
We would like to thank Craig Lenz and Dr. Shi Yang for their assistance in dosing the FVB mice. We would like to thank Benjamin Schlechter and Dr. Mary Williams for their assistance with the quantitative PCR and Dr. Adrianne Rogers for many helpful discussions. This work was supported by P01 ES11624.
Abdelrahim, M, Smith, R, 3rd, and, & Safe, S. (2003). Aryl hydrocarbon receptor gene silencing with small inhibitory RNA differentially modulates Ah-responsiveness in MCF-7 and HepG2 cancer cells. Mol Pharmacol, 63, 1373-81 Bao, L, Kimzey, A, Sauter, G, Sowadski, JM, Lu, KP, & Wang, DG. (2004). Prevalent overexpression of prolyl isomerase Pin1 in human cancers. Am J Pathol, 164, 1727-37 Barnes-Ellerbe, S, Knudsen, KE, & Puga, A. (2004). 2,3,7,8-Tetrachlorodibenzo-p-dioxin blocks androgen-dependent cell proliferation of LNCaP cells through modulation of pRB phosphorylation. Mol Pharmacol, 66, 502-11 Bartkova, J, Lukas, J, Muller, H, Lutzhoft, D, Strauss, M, & Bartek, J. (1994). Cyclin D1 protein expression and function in human breast cancer. Int J Cancer, 57, 353-61[Web of Science][Medline] [Order article via Infotrieve] Brantley, DM, Chen, CL, Muraoka, RS, Bushdid, PB, Bradberry, JL, Kittrell, F, Medina, D, Matrisian, LM, Kerr, LD, & Yull, FE. (2001). Nuclear factor-kappaB (NF- Brooks, J, & Eltom, SE. (2005). Overexpression of the aryl hydrocarbon receptor in mammary epithelial cells increases proliferation by increasing G1/S phase transition. Era of Hope Department of Defense Breast Cancer Research Program Meeting: Philadelphia, 198, U.S. Army Medical Research and Material Command. Brown, AM. (2001). Wnt signaling in breast cancer: have we come full circle? Breast Cancer Res, 3, 351-5[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Cao, Y, Bonizzi, G, Seagroves, TN, Greten, FR, Johnson, R, Schmidt, EV, & Karin, M. (2001). IKK Cardiff, RD, Gumerlock, PH, Soong, MM, Dandekar, S, Barry, PA, Young, LJ, & Meyers, FJ. (1988). c-H-ras-1 expression in 7,12-dimethyl benzanthracene-induced Balb/c mouse mammary hyperplasias and their tumors. Oncogene, 3, 205-13[Web of Science][Medline] [Order article via Infotrieve] Caruso, JA, Mathieu, PA, Joiakim, A, Leeson, B, Kessel, D, Sloane, BF, & Reiners, JJ., Jr. (2004). Differential susceptibilities of murine hepatoma 1c1c7 and Tao cells to the lysosomal photosensitizer NPe6: influence of aryl hydrocarbon receptor on lysosomal fragility and protease contents. Mol Pharmacol, 65, 1016-28 Clarkson, RW, Heeley, JL, Chapman, R, Aillet, F, Hay, RT, Wyllie, A, & Watson, CJ. (2000). NF-kappaB inhibits apoptosis in murine mammary epithelia. J Biol Chem, 275, 12737-42 Denison, MS, & Nagy, SR. (2003). Activation of the aryl hydrocarbon receptor by structurally diverse exogenous and endogenous chemicals. Annu Rev Pharmacol Toxicol, 43, 309-34[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Dominguez, I, Mizuno, J, Wu, H, Song, DH, Symes, K, & Seldin, DC. (2004). Protein kinase CK2 is required for dorsal axis formation in Xenopus embryos. Dev Biol, 274, 110-24[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Duyao, MP, Buckler, AJ, & Sonenshein, GE. (1990). Interaction of an NF- Ge, NL, & Elferink, CJ. (1998). A direct interaction between the aryl hydrocarbon receptor and retinoblastoma protein. Linking dioxin signaling to the cell cycle. J Biol Chem, 273, 22708-13 Holcomb, M, & Safe, S. (1994). Inhibition of 7,12-dimethylbenzanthracene-induced rat mammary tumor growth by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Canc Lett, 82, 43-7[CrossRef] Jamerson, MH, Johnson, MD, & Dickson, RB. (2004). Of mice and Myc: c-Myc and mammary tumorigenesis. J Mammary Gland Biol Neoplasia, 9, 27-37[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Joyce, D, Albanese, C, Steer, J, Fu, M, Bouzahzah, B, & Pestell, RG. (2001). NF-kappaB and cell-cycle regulation: the cyclin connection. Cytokine Growth Factor Rev, 12, 73-90[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Kim, DW, Gazourian, L, Quadri, SA, Romieu-Mourez, R, Sherr, DH, & Sonenshein, GE. (2000). The RelA NF- Kim, DW, Sovak, MA, Zanieski, G, Nonet, G, Romieu-Mourez, R, Lau, AW, Hafer, LJ, Yaswen, P, Stampfer, M, Rogers, AE, Russo, J, & Sonenshein, GE. (2000). Activation of NF-kappaB/Rel occurs early during neoplastic transformation of mammary cells. Carcinogenesis, 21, 871-9 Koesters, R, Hans, MA, Benner, A, Prosst, R, Boehm, J, Gahlen, J, & Doeberitz, MK. (2001). Predominant mutation of codon 41 of the beta-catenin proto-oncogene in rat colon tumors induced by 1,2-dimethylhydrazine using a complete carcinogenic protocol. Carcinogenesis, 22, 1885-90 Kuramoto, T, Morimura, K, Yamashita, S, Okochi, E, Watanabe, N, Ohta, T, Ohki, M, Fukushima, S, Sugimura, T, & Ushijima, T. (2002). Etiology-specific gene expression profiles in rat mammary carcinomas. Cancer Res, 62, 3592-97 Landesman-Bollag, E, Romieu-Mourez, R, Song, DH, Sonenshein, GE, Cardiff, RD, & Seldin, DC. (2001). Protein kinase CK2 in mammary gland tumorigenesis. Oncogene, 20, 3247-57[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Li, Y, Hively, WP, & Varmus, HE. (2000). Use of MMTV-Wnt-1 transgenic mice for studying the genetic basis of breast cancer. Oncogene, 19, 1002-09[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Liou, YC, Ryo, A, Huang, HK, Lu, PJ, Bronson, R, Fujimori, F, Uchida, T, Hunter, T, & Lu, KP. (2002). Loss of Pin1 function in the mouse causes phenotypes resembling cyclin D1-null phenotypes. Proc Natl Acad Sci USA, 99, 1335-40 Ma, Q, & Whitlock, J. (1996). The aromatic hydrocarbon receptor modulates the Hepa 1c1c7 cell cycle and differentiated state independently of dioxin. Mol Cell Biol, 16, 2144-50 Mahler, JF, Stokes, W, Mann, PC, Takaoka, M, & Maronpot, RR. (1996). Spontaneous lesions in aging FVB/N mice. Toxicol Pathol, 24, 710-16 Matikainen, T, Perez, GI, Jurisicova, A, Mann, KK, Schlezinger, JJ, Ryu, H-T, Sakai, T, Korsmeyer, SJ, Casper, RF, Sherr, DH, & Tilly, JT. (2001). Aromatic hydrocarbon receptor-driven Bax gene expression is required for premature ovarian failure caused by biohazardous environmental chemicals. Nature Genetics, 28, 1-6[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Medina, D. (1974). Mammary tumorigenesis in chemical carcinogen-treated mice. I. Incidence in BALB-c and C57BL mice. J Natl Cancer Inst, 53, 213-21[Web of Science][Medline] [Order article via Infotrieve] Michaelson, JS, & Leder, P. (2001). beta-catenin is a downstream effector of Wnt-mediated tumorigenesis in the mammary gland. Oncogene, 20, 5093-99[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Miller, EC, & Miller, JA. (1981). Mechanisms of chemical carcinogenesis. Cancer, 47, 1055-64[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Miyoshi, K, Shillingford, JM, Le Provost, F, Gounari, F, Bronson, R, von Boehmer, H, Taketo, MM, Cardiff, RD, Hennighausen, L, & Khazaie, K. (2002). Activation of beta-catenin signaling in differentiated mammary secretory cells induces transdifferentiation into epidermis and squamous metaplasias. Proc Natl Acad Sci USA, 99, 219-24 Nagase, H, & Nakamura, Y. (1993). Mutations of the APC (adenomatous polyposis coli) gene. Hum Mutat, 2, 425-34[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Nebert, DW, Petersen, DD, & Fornace, AJ. (1990). Cellular responses to oxidative stress: the [Ah] gene battery as a paradigm. Env Health Persp, 88, 13[Web of Science][Medline] [Order article via Infotrieve] Nieto, AI, Shyamala, G, Galvez, JJ, Thordarson, G, Wakefield, LM, & Cardiff, RD. (2003). Persistent mammary hyperplasia in FVB/N mice. Comp Med, 53, 433-8[Web of Science][Medline] [Order article via Infotrieve] Nozaki, T, Fujihara, H, Watanabe, M, Tsutsumi, M, Nakamoto, K, Kusuoka, O, Kamada, N, Suzuki, H, Nakagama, H, Sugimura, T, & Masutani, M. (2003). Parp-1 deficiency implicated in colon and liver tumorigenesis induced by azoxymethane. Cancer Sci, 94, 497-500[CrossRef][Medline] [Order article via Infotrieve] Nusse, R, & Varmus, HE. (1982). Many tumors induced by the mouse mammary tumor virus contain a provirus integrated in the same region of the host genome. Cell, 31, 99-109[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Pang, R, Yuen, J, Yuen, MF, Lai, CL, Lee, TK, Man, K, Poon, RT, Fan, ST, Wong, CM, Ng, IO, Kwong, YL, & Tse, E. (2004). PIN1 overexpression and beta-catenin gene mutations are distinct oncogenic events in human hepatocellular carcinoma. Oncogene, 23, 4182-86[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Pianetti, S, Arsura, M, Romieu-Mourez, R, Coffey, RJ, & Sonenshein, GE. (2001). Her-2/neu overexpression induces NF-kappaB via a PI3-kinase/Akt pathway involving calpain-mediated degradation of IkappaB-alpha that can be inhibited by the tumor suppressor PTEN. Oncogene, 20, 1287-99[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Polakis, P. (2000). Wnt signaling and cancer. Genes Dev, 14, 1837-51 Puga, A, Barnes, SJ, Dalton, TP, Chang, C-Y, Knudsen, ES, & Maier, MA. (2000). Aromatic hydrocarbon receptor interaction with the retinoblastoma protein potentiates repression of E2F-dependent transcription and cell cycle arrest. J Biol Chem, 275, 2943-50 Rijsewijk, F, Schuermann, M, Wagenaar, E, Parren, P, Weigel, D, & Nusse, R. (1987). The Drosophila homolog of the mouse mammary oncogene int-1 is identical to the segment polarity gene wingless. Cell, 50, 649-57[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Romieu-Mourez, R, Kim, DW, Shin, SM, Demicco, EG, Landesman-Bollag, E, Seldin, DC, Cardiff, RD, & Sonenshein, GE. (2003). Mouse mammary tumor virus c-rel transgenic mice develop mammary tumors. Mol Cell Biol, 23, 5738-54 Rosner, A, Miyoshi, K, Landesman-Bollag, E, Xu, X, Seldin, DC, Moser, AR, MacLeod, CL, Shyamala, G, Gillgrass, AE, & Cardiff, RD. (2002). Pathway pathology: histological differences between ErbB/Ras and Wnt pathway transgenic mammary tumors. Am J Pathol, 161, 1087-97 Rundle, A, Tang, D, Hibshoosh, H, Estabrook, A, Schnabel, F, Cao, W, Grumet, S, & Perera, FP. (2000). The relationship between genetic damage from polycyclic aromatic hydrocarbons in breast tissue and breast cancer. Carcinogenesis, 21, 1281-9 Ryo, A, Nakamura, M, Wulf, G, Liou, YC, & Lu, KP. (2001). Pin1 regulates turnover and subcellular localization of beta-catenin by inhibiting its interaction with APC. Nat Cell Biol, 3, 793-801[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Ryo, A, Suizu, F, Yoshida, Y, Perrem, K, Liou, YC, Wulf, G, Rottapel, R, Yamaoka, S, & Lu, KP. (2003). Regulation of NF-kappaB signaling by Pin1-dependent prolyl isomerization and ubiquitin-mediated proteolysis of p65/RelA. Mol Cell, 12, 1413-26[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Shan, L, He, M, Yu, M, Qiu, C, Lee, NH, Liu, ET, & Snyderwine, EG. (2002). cDNA microarray profiling of rat mammary gland carcinomas induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 7,12-dimethylbenz[a]anthracene. Carcinogenesis, 23, 1561-8 Sharma, RP, & Chopra, VL. (1976). Effect of the Wingless (wg1) mutation on wing and haltere development in Drosophila melanogaster. Dev Biol, 48, 461-5[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Smalley, MJ, & Dale, TC. (2001). Wnt signaling and mammary tumorigenesis. J Mammary Gland Biol Neoplasia, 6, 37-52[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Song, DH, Dominguez, I, Mizuno, J, Kaut, M, Mohr, SC, & Seldin, DC. (2003). CK2 phosphorylation of the armadillo repeat region of beta-catenin potentiates Wnt signaling. J Biol Chem, 278, 24018-25 Sovak, MA, Bellas, RE, Kim, DW, Zanieski, GJ, Rogers, AE, Traish, AM, & Sonenshein, GE. (1997). Aberrant nuclear factor-kappaB/Rel expression and the pathogenesis of breast cancer. J Clin Invest, 100, 2952-60[Web of Science][Medline] [Order article via Infotrieve] Swanson, HI, Chan, WK, & Bradfield, CA. (1995). DNA binding specificities and pairing rules of the Ah receptor, ARNT, and SIM proteins. J Biol Chem, 270, 26292-302 Takahashi, M, Fukuda, K, Sugimura, T, & Wakabayashi, K. (1998). Beta-catenin is frequently mutated and demonstrates altered cellular location in azoxymethane-induced rat colon tumors. Cancer Res, 58, 42-6 Takahashi, M, & Wakabayashi, K. (2004). Gene mutations and altered gene expression in azoxymethane-induced colon carcinogenesis in rodents. Cancer Sci, 95, 475-80[CrossRef][Medline] [Order article via Infotrieve] Trombino, AF, Near, RI, Matulka, RA, Yang, S, Hafer, LJ, Toselli, PA, Kim, DW, Rogers, AE, Sonenshein, GE, & Sherr, DH. (2000). Expression of the aryl hydrocarbon receptor/transcription factor (AhR) and AhR-regulated CYP1 gene transcripts in a rat model of mammary tumorigenesis. Breast Cancer Res Treat, 63, 117-31[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Ubagai, T, Ochiai, M, Kawamori, T, Imai, H, Sugimura, T, Nagao, M, & Nakagama, H. (2002). Efficient induction of rat large intestinal tumors with a new spectrum of mutations by intermittent administration of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in combination with a high fat diet. Carcinogenesis, 23, 197-200 Wakefield, LM, Thordarson, G, Nieto, AI, Shyamala, G, Galvez, JJ, Anver, MR, & Cardiff, RD. (2003). Spontaneous pituitary abnormalities and mammary hyperplasia in FVB/NCr mice: implications for mouse modeling. Comp Med, 53, 424-32[Web of Science][Medline] [Order article via Infotrieve] Weinberg, RA. (1995). The retinoblastoma protein and cell cycle control. Cell, 81, 323-30[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Wulf, GM, Ryo, A, Wulf, GG, Lee, SW, Niu, T, Petkova, V, & Lu, KP. (2001). Pin1 is overexpressed in breast cancer and cooperates with Ras signaling in increasing the transcriptional activity of c-Jun towards cyclin D1. Embo J, 20, 3459-72[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Yeh, E, Cunningham, M, Arnold, H, Chasse, D, Monteith, T, Ivaldi, G, Hahn, WC, Stukenberg, PT, Shenolikar, S, Uchida, T, Counter, CM, Nevins, JR, Means, AR, & Sears, R. (2004). A signalling pathway controlling c-Myc degradation that impacts oncogenic transformation of human cells. Nat Cell Biol, 6, 308-18[CrossRef][Web of Science][Medline] [Order article via Infotrieve] Zhuang, SM, Wiseman, RW, & Soderkvist, P. (2002). Frequent mutations of the Trp53, Hras1 and beta-catenin (Catnb) genes in 1,3-butadiene-induced mammary adenocarcinomas in B6C3F1 mice. Oncogene, 21, 5643-8[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
Toxicologic Pathology, Vol. 33, No. 6,
726-737 (2005) This article has been cited by other articles:
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Abstract
Introduction
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