Pubertal exposure to dietary advanced glycation end products disrupts ductal morphogenesis and induces atypical hyperplasia in the mammary gland.

BACKGROUND: Advanced glycation end products (AGEs) are reactive metabolites intrinsically linked with modern dietary patterns. Processed foods, and those high in sugar, protein and fat, often contain high levels of AGEs. Increased AGE levels are associated with increased breast cancer risk, however their significance has been largely overlooked due to a lack of direct cause-and-effect relationship. METHODS: To address this knowledge gap, FVB/n mice were fed regular, low AGE, and high AGE diets from 3 weeks of age and mammary glands harvested during puberty (7 weeks) or adulthood (12 weeks and 7 months) to determine the effects upon mammary gland development. At endpoint mammary glands were harvested and assessed histologically (n ≥ 4). Immunohistochemistry and immunofluorescence were used to assess cellular proliferation and stromal fibroblast and macrophage recruitment. The Kruskal-Wallis test were used to compare continuous outcomes among groups. Mammary epithelial cell migration and invasion in response to AGE-mediated fibroblast activation was determined in two-compartment co-culture models. In vitro experiments were performed in triplicate. The nonparametric Wilcoxon rank sum test was used to compare differences between groups. RESULTS: Histological analysis revealed the high AGE diet delayed ductal elongation, increased primary branching, as well as increased terminal end bud number and size. The high AGE diet also led to increased recruitment and proliferation of stromal cells to abnormal structures that persisted into adulthood. Atypical hyperplasia was observed in the high AGE fed mice. Ex vivo fibroblasts from mice fed dietary-AGEs retain an activated phenotype and promoted epithelial migration and invasion of non-transformed immortalized and tumor-derived mammary epithelial cells. Mechanistically, we found that the receptor for AGE (RAGE) is required for AGE-mediated increases in epithelial cell migration and invasion. CONCLUSIONS: We observed a disruption in mammary gland development when mice were fed a diet high in AGEs. Further, both epithelial and stromal cell populations were impacted by the high AGE diet in the mammary gland. Educational, interventional, and pharmacological strategies to reduce AGEs associated with diet may be viewed as novel disease preventive and/or therapeutic initiatives during puberty.

STAT3 in tumor fibroblasts promotes an immunosuppressive microenvironment in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is associated with an incredibly dense stroma, which contributes to its recalcitrance to therapy. Cancer-associated fibroblasts (CAFs) are one of the most abundant cell types within the PDAC stroma and have context-dependent regulation of tumor progression in the tumor microenvironment (TME). Therefore, understanding tumor-promoting pathways in CAFs is essential for developing better stromal targeting therapies. Here, we show that disruption of the STAT3 signaling axis via genetic ablation of Stat3 in stromal fibroblasts in a Kras G12D PDAC mouse model not only slows tumor progression and increases survival, but re-shapes the characteristic immune-suppressive TME by decreasing M2 macrophages (F480+CD206+) and increasing CD8+ T cells. Mechanistically, we show that loss of the tumor suppressor PTEN in pancreatic CAFs leads to an increase in STAT3 phosphorylation. In addition, increased STAT3 phosphorylation in pancreatic CAFs promotes secretion of CXCL1. Inhibition of CXCL1 signaling inhibits M2 polarization in vitro. The results provide a potential mechanism by which CAFs promote an immune-suppressive TME and promote tumor progression in a spontaneous model of PDAC.

Imaging Mass Spectrometry Reveals Alterations in N-Linked Glycosylation That Are Associated With Histopathological Changes in Nonalcoholic Steatohepatitis in Mouse and Human.

Nonalcoholic steatohepatitis (NASH) is the progressive form of nonalcoholic fatty liver disease (NAFLD) and is characterized by inflammation, hepatocyte injury, and fibrosis. Further, NASH is a risk factor for cirrhosis and hepatocellular carcinoma. Previous research demonstrated that serum N-glycan profiles can be altered in NASH patients. Here, we hypothesized that these N-glycan modifications may be associated with specific liver damage in NAFLD and NASH. To investigate the N-glycome profile in tissue, imaging mass spectrometry was used for a qualitative and quantitative in situ N-linked glycan analysis of mouse and human NAFLD/NASH tissue. A murine model was used to induce NAFLD and NASH through ad libitum feeding with either a high-fat diet or a Western diet, respectively. Mice fed a high-fat diet or Western diet developed inflammation, steatosis, and fibrosis, consistent with NAFLD/NASH phenotypes. Induction of NAFLD/NASH for 18 months using high caloric diets resulted in increased expression of mannose, complex/fucosylated, and hybrid N-glycan structures compared to control mouse livers. To validate the animal results, liver biopsy specimens from 51 human NAFLD/NASH patients representing the full range of NASH Clinical Research Network fibrosis stages were analyzed. Importantly, the same glycan alterations observed in mouse models were observed in human NASH biopsies and correlated with the degree of fibrosis. In addition, spatial glycan alterations were localized specifically to histopathological changes in tissue like fibrotic and fatty areas. We demonstrate that the use of standard staining's combined with imaging mass spectrometry provide a full profile of the origin of N-glycan modifications within the tissue. These results indicate that the spatial distribution of abundances of released N-glycans correlate with regions of tissue steatosis associated with NAFLD/NASH.

Non-phosphorylatable cyclin D1 mutant potentiates endometrial hyperplasia and drives carcinoma with Pten loss.

Cyclin D1 is a regulatory subunit of -Cyclin Dependent Kinases 4 and 6 (CDK4/6) and regulates progression from G1 to S phase of the cell cycle. Dysregulated cyclin D1-CDK4/6 contributes to abnormal cell proliferation and tumor development. Phosphorylation of threonine 286 of cyclin D1 is necessary for ubiquitin-dependent degradation. Non-phosphorylatable cyclin D1 mutants are stabilized and concentrated in the nucleus, contributing to genomic instability and tumor development. Studies investigating the tumor-promoting functions of cyclin D1 mutants have focused on the use of artificial promoters to drive the expression which unfortunately may not accurately reflect tumorigenic functions of mutant cyclin D1 in cancer development. We have generated a conditional knock-in mouse model where cyclin D1T286A is expressed under the control of its endogenous promoter following Cre-dependent excision of a lox-stop-lox sequence. Acute expression of cyclin D1T286A following tamoxifen-inducible Cre recombinase triggers inflammation, lymphocyte abnormality and ultimately mesenteric tumors in the intestine. Tissue-specific expression of cyclin D1T286A in the uterus and endometrium cooperates with Pten loss to drive endometrial hyperplasia and cancer. Mechanistically, cyclin D1T286A mutant activates NF-κB signaling, augments inflammation, and contributes to tumor development. These results indicate that mutation of cyclin D1 at threonine 286 has a critical role in regulating inflammation and tumor development.

Type 2 dendritic cells mediate control of cytotoxic T cell resistant tumors.

Type 2 DCs (DC2s) comprise the majority of conventional DCs within most tumors; however, little is known about their ability to initiate and sustain antitumor immunity, as most studies have focused on antigen cross-presenting DC1s. Here, we report that DC2 infiltration identified by analysis of multiple human cancer data sets showed a significant correlation with survival across multiple human cancers, with the benefit being seen in tumors resistant to cytotoxic T cell control. Characterization of DC subtype infiltration into an immunotherapy-resistant model of breast cancer revealed that impairment of DC1s through 2 unique models resulted in enhanced DC2 functionality and improved tumor control. BATF3 deficiency depleted intratumoral DC1s, which led to increased DC2 lymph node migration and CD4+ T cell activation. Enhancing DC2 stimulatory potential by genetic deletion of Hsp90b1 (encoding molecular chaperon GP96) led to a similar enhancement of T cell immunity and improved survival in a spontaneous breast cancer model. These data highlight the therapeutic and prognostic potential of DC2s within checkpoint blockade-resistant tumors.

Stromal Platelet-Derived Growth Factor Receptor-ß Signaling Promotes Breast Cancer Metastasis in the Brain.

Platelet-derived growth factor receptor-beta (PDGFRß) is a receptor tyrosine kinase found in cells of mesenchymal origin such as fibroblasts and pericytes. Activation of this receptor is dependent on paracrine ligand induction, and its preferred ligand PDGFB is released by neighboring epithelial and endothelial cells. While expression of both PDGFRß and PDGFB has been noted in patient breast tumors for decades, how PDGFB-to-PDGFRß tumor-stroma signaling mediates breast cancer initiation, progression, and metastasis remains unclear. Here we demonstrate this paracrine signaling pathway that mediates both primary tumor growth and metastasis, specifically, metastasis to the brain. Elevated levels of PDGFB accelerated orthotopic tumor growth and intracranial growth of mammary tumor cells, while mesenchymal-specific expression of an activating mutant PDGFRß (PDGFRßD849V) exerted proproliferative signals on adjacent mammary tumor cells. Stromal expression of PDGFRßD849V also promoted brain metastases of mammary tumor cells expressing high PDGFB when injected intravenously. In the brain, expression of PDGFRßD849V was observed within a subset of astrocytes, and aged mice expressing PDGFRßD849V exhibited reactive gliosis. Importantly, the PDGFR-specific inhibitor crenolanib significantly reduced intracranial growth of mammary tumor cells. In a tissue microarray comprised of 363 primary human breast tumors, high PDGFB protein expression was prognostic for brain metastases, but not metastases to other sites. Our results advocate the use of mice expressing PDGFRßD849V in their stromal cells as a preclinical model of breast cancer-associated brain metastases and support continued investigation into the clinical prognostic and therapeutic use of PDGFB-to-PDGFRß signaling in women with breast cancer. SIGNIFICANCE: These studies reveal a previously unknown role for PDGFB-to-PDGFRß paracrine signaling in the promotion of breast cancer brain metastases and support the prognostic and therapeutic clinical utility of this pathway for patients.See related article by Wyss and colleagues, p. 594.

Evaluating the efficacy of enzalutamide and the development of resistance in a preclinical mouse model of type-I endometrial carcinoma.

Androgen Receptor (AR) signaling is a critical driver of hormone-dependent prostate cancer and has also been proposed to have biological activity in female hormone-dependent cancers, including type I endometrial carcinoma (EMC). In this study, we evaluated the preclinical efficacy of a third-generation AR antagonist, enzalutamide, in a genetic mouse model of EMC, Sprr2f-Cre;Ptenfl/fl. In this model, ablation of Pten in the uterine epithelium leads to localized and distant malignant disease as observed in human EMC. We hypothesized that administering enzalutamide through the diet would temporarily decrease the incidence of invasive and metastatic carcinoma, while prolonged administration would result in development of resistance and loss of efficacy. Short-term treatment with enzalutamide reduced overall tumor burden through increased apoptosis but failed to prevent progression of invasive and metastatic disease. These results suggest that AR signaling may have biphasic, oncogenic and tumor suppressive roles in EMC that are dependent on disease stage. Enzalutamide treatment increased Progesterone Receptor (PR) expression within both stromal and tumor cell compartments. Prolonged administration of enzalutamide decreased apoptosis, increased tumor burden and resulted in the clonal expansion of tumor cells expressing high levels of p53 protein, suggestive of acquired Trp53 mutations. In conclusion, we show that enzalutamide induces apoptosis in EMC but has limited efficacy overall as a single agent. Induction of PR, a negative regulator of endometrial proliferation, suggests that adding progestin therapy to enzalutamide administration may further decrease tumor burden and result in a prolonged response.

Ablation of the Brca1-Palb2 Interaction Phenocopies Fanconi Anemia in Mice.

Heterozygous mutations in the BRCA1 gene predispose women to breast and ovarian cancer, while biallelic BRCA1 mutations are a cause of Fanconi anemia (FA), a rare genetic disorder characterized by developmental abnormalities, early-onset bone marrow failure, increased risk of cancers, and hypersensitivity to DNA-crosslinking agents. BRCA1 is critical for homologous recombination of DNA double-strand breaks (DSB). Through its coiled-coil domain, BRCA1 interacts with an essential partner, PALB2, recruiting BRCA2 and RAD51 to sites of DNA damage. Missense mutations within the coiled-coil domain of BRCA1 (e.g., L1407P) that affect the interaction with PALB2 have been reported in familial breast cancer. We hypothesized that if PALB2 regulates or mediates BRCA1 tumor suppressor function, ablation of the BRCA1-PALB2 interaction may also elicit genomic instability and tumor susceptibility. We generated mice defective for the Brca1-Palb2 interaction (Brca1 L1363P in mice) and established MEF cells from these mice. Brca1 L1363P/L1363P MEF exhibited hypersensitivity to DNA-damaging agents and failed to recruit Rad51 to DSB. Brca1 L1363P/L1363P mice were viable but exhibited various FA symptoms including growth retardation, hyperpigmentation, skeletal abnormalities, and male/female infertility. Furthermore, all Brca1 L1363P/L1363P mice exhibited macrocytosis and died due to bone marrow failure or lymphoblastic lymphoma/leukemia with activating Notch1 mutations. These phenotypes closely recapitulate clinical features observed in patients with FA. Collectively, this model effectively demonstrates the significance of the BRCA1-PALB2 interaction in genome integrity and provides an FA model to investigate hematopoietic stem cells for mechanisms underlying progressive failure of hematopoiesis and associated development of leukemia/lymphoma, and other FA phenotypes. SIGNIFICANCE: A new Brca1 mouse model for Fanconi anemia (FA) complementation group S provides a system in which to study phenotypes observed in human FA patients including bone marrow failure.See related commentary by Her and Bunting, p. 4044.

Murine models for familial pancreatic cancer: Histopathology, latency and drug sensitivity among cancers of Palb2, Brca1 and Brca2 mutant mouse strains.

Alterations of the PALB2 tumor suppressor gene have been identified in familial breast, ovarian and pancreatic cancer cases. PALB2 cooperates with BRCA1/2 proteins through physical interaction in initiation of homologous recombination, in maintenance of genome integrity following DNA double-strand breaks. To determine if the role of PALB2 as a linker between BRCA1 and BRCA2 is critical for BRCA1/2-mediated tumor suppression, we generated Palb2 mouse pancreatic cancer models and compared tumor latencies, phenotypes and drug responses with previously generated Brca1/2 pancreatic cancer models. For development of Palb2 pancreatic cancer, we crossed conditional Palb2 null mouse with mice carrying the KrasG12D; p53R270H; Pdx1-Cre (KPC) constructs, and these animals were observed for pancreatic tumor development. Individual deletion of Palb2, Brca1 or Brca2 genes in pancreas per se using Pdx1-Cre was insufficient to cause tumors, but it reduced pancreata size. Concurrent expression of mutant KrasG12D and p53R270H, with tumor suppressor inactivated strains in Palb2-KPC, Brca1-KPC or Brca2-KPC, accelerated pancreatic ductal adenocarcinoma (PDAC) development. Moreover, most Brca1-KPC and some Palb2-KPC animals developed mucinous cystic neoplasms with PDAC, while Brca2-KPC and KPC animals did not. 26% of Palb2-KPC mice developed MCNs in pancreata, which resemble closely the Brca1 deficient tumors. However, the remaining 74% of Palb2-KPC animals developed PDACs without any cysts like Brca2 deficient tumors. In addition, the number of ADM lesions and immune cells infiltrations (CD3+ and F/480+) were significantly increased in Brca1-KPC tumors, but not in Brca2-KPC tumors. Interestingly, the level of ADM lesions and infiltration of CD3+ or F/480+ cells in Palb2-KPC tumors were intermediate between Brca1-KPC and Brca2-KPC tumors. As expected, disruption of Palb2 and Brca1/2 sensitized tumor cells to DNA damaging agents in vitro and in vivo. Altogether, Palb2-KPC PDAC exhibited features observed in both Brca1-KPC and Brca2-KPC tumors, which could be due to its role, as a linker between Brca1 and Brca2.

Abrupt involution induces inflammation, estrogenic signaling, and hyperplasia linking lack of breastfeeding with increased risk of breast cancer.

BACKGROUND: A large collaborative analysis of data from 47 epidemiological studies concluded that longer duration of breastfeeding reduces the risk of developing breast cancer. Despite the strong epidemiological evidence, the molecular mechanisms linking prolonged breastfeeding to decreased risk of breast cancer remain poorly understood. METHODS: We modeled two types of breastfeeding behaviors in wild type FVB/N mice: (1) normal or gradual involution of breast tissue following prolonged breastfeeding and (2) forced or abrupt involution following short-term breastfeeding. To accomplish this, pups were gradually weaned between 28 and 31 days (gradual involution) or abruptly at 7 days postpartum (abrupt involution). Mammary glands were examined for histological changes, proliferation, and inflammatory markers by immunohistochemistry. Fluorescence-activated cell sorting was used to quantify mammary epithelial subpopulations. Gene set enrichment analysis was used to analyze gene expression data from mouse mammary luminal progenitor cells. Similar analysis was done using gene expression data generated from human breast samples obtained from parous women enrolled on a tissue collection study, OSU-2011C0094, and were undergoing reduction mammoplasty without history of breast cancer. RESULTS: Mammary glands from mice that underwent abrupt involution exhibited denser stroma, altered collagen composition, higher inflammation and proliferation, increased estrogen receptor α and progesterone receptor expression compared to those that underwent gradual involution. Importantly, when aged to 4 months postpartum, mice that were in the abrupt involution cohort developed ductal hyperplasia and squamous metaplasia. Abrupt involution also resulted in a significant expansion of the luminal progenitor cell compartment associated with enrichment of Notch and estrogen signaling pathway genes. Breast tissues obtained from healthy women who breastfed for < 6 months vs ≥ 6 months showed significant enrichment of Notch signaling pathway genes, along with a trend for enrichment for luminal progenitor gene signature similar to what is observed in BRCA1 mutation carriers and basal-like breast tumors. CONCLUSIONS: We report here for the first time that forced or abrupt involution of the mammary glands following pregnancy and lack of breastfeeding results in expansion of luminal progenitor cells, higher inflammation, proliferation, and ductal hyperplasia, a known risk factor for developing breast cancer.

MRI Findings of Suprasellar Germ Cell Tumors in Two Dogs.

A 4 yr old border collie presenting for mydriasis and decreased mentation and a 7 yr old Boston terrier presenting for obtundation, head tilt, and paraparesis were both evaluated using MRI. Findings in both included mass lesions of the thalamus and brainstem that were hypo- to isointense on T1-weighted images and hyperintense on T2-weighted images with regions of hypointensity, and robust contrast enhancement and displacement of adjacent structures. Postmortem histopathology findings, tumor location, and a mixed pattern of epithelial cell differentiation were consistent with germ cell tumor in both cases. Germ cell tumor of the suprasellar region is an infrequently reported neoplasm of dogs and imaging findings in this species have not been well described in the prior literature.

Dosage-dependent copy number gains in E2f1 and E2f3 drive hepatocellular carcinoma.

Disruption of the retinoblastoma (RB) tumor suppressor pathway, either through genetic mutation of upstream regulatory components or mutation of RB1 itself, is believed to be a required event in cancer. However, genetic alterations in the RB-regulated E2F family of transcription factors are infrequent, casting doubt on a direct role for E2Fs in driving cancer. In this work, a mutation analysis of human cancer revealed subtle but impactful copy number gains in E2F1 and E2F3 in hepatocellular carcinoma (HCC). Using a series of loss- and gain-of-function alleles to dial E2F transcriptional output, we have shown that copy number gains in E2f1 or E2f3b resulted in dosage-dependent spontaneous HCC in mice without the involvement of additional organs. Conversely, germ-line loss of E2f1 or E2f3b, but not E2f3a, protected mice against HCC. Combinatorial mapping of chromatin occupancy and transcriptome profiling identified an E2F1- and E2F3B-driven transcriptional program that was associated with development and progression of HCC. These findings demonstrate a direct and cell-autonomous role for E2F activators in human cancer.

E2f8 mediates tumor suppression in postnatal liver development.

E2F-mediated transcriptional repression of cell cycle-dependent gene expression is critical for the control of cellular proliferation, survival, and development. E2F signaling also interacts with transcriptional programs that are downstream of genetic predictors for cancer development, including hepatocellular carcinoma (HCC). Here, we evaluated the function of the atypical repressor genes E2f7 and E2f8 in adult liver physiology. Using several loss-of-function alleles in mice, we determined that combined deletion of E2f7 and E2f8 in hepatocytes leads to HCC. Temporal-specific ablation strategies revealed that E2f8's tumor suppressor role is critical during the first 2 weeks of life, which correspond to a highly proliferative stage of postnatal liver development. Disruption of E2F8's DNA binding activity phenocopied the effects of an E2f8 null allele and led to HCC. Finally, a profile of chromatin occupancy and gene expression in young and tumor-bearing mice identified a set of shared targets for E2F7 and E2F8 whose increased expression during early postnatal liver development is associated with HCC progression in mice. Increased expression of E2F8-specific target genes was also observed in human liver biopsies from HCC patients compared to healthy patients. In summary, these studies suggest that E2F8-mediated transcriptional repression is a critical tumor suppressor mechanism during postnatal liver development.

WWP2 and its association with PTEN in endometrial cancer.

We wished to determine if WWP2 gene expression and PTEN protein levels inversely correlate in human endometrial cancer tissues. Fifty-one endometrioid endometrial tumors and five normal endometrial controls were available for analysis. PTEN protein levels were assessed by immunohistochemistry (IHC). WWP2 and PTEN gene expression were quantitated by RT PCR. Clinical and pathologic information was collected by chart review. We found that in tumors with low PTEN protein but normal mRNA expression there were significantly higher levels of WWP2 expression (p = 0.0017). Increased WWP2 expression was not associated with clinical prognostic factors including lymphovascular space invasion, ≥ 50% myometrial invasion, grade, stage or recurrence. WWP2 expression was not different statistically between tumors and normal controls (p = NS). Therefore, in this cohort, tumors with low PTEN protein but normal mRNA expression had elevated levels of WWP2 expression. This suggests that WWP2 may be playing a role in PTEN degradation in endometrial cancer.

Noncatalytic PTEN missense mutation predisposes to organ-selective cancer development in vivo.

Inactivation of phosphatase and tensin homology deleted on chromosome 10 (PTEN) is linked to increased PI3K-AKT signaling, enhanced organismal growth, and cancer development. Here we generated and analyzed Pten knock-in mice harboring a C2 domain missense mutation at phenylalanine 341 (Pten(FV)), found in human cancer. Despite having reduced levels of PTEN protein, homozygous Pten(FV/FV) embryos have intact AKT signaling, develop normally, and are carried to term. Heterozygous Pten(FV/+) mice develop carcinoma in the thymus, stomach, adrenal medulla, and mammary gland but not in other organs typically sensitive to Pten deficiency, including the thyroid, prostate, and uterus. Progression to carcinoma in sensitive organs ensues in the absence of overt AKT activation. Carcinoma in the uterus, a cancer-resistant organ, requires a second clonal event associated with the spontaneous activation of AKT and downstream signaling. In summary, this PTEN noncatalytic missense mutation exposes a core tumor suppressor function distinct from inhibition of canonical AKT signaling that predisposes to organ-selective cancer development in vivo.

Redeployment of Myc and E2f1-3 drives Rb-deficient cell cycles.

Robust mechanisms to control cell proliferation have evolved to maintain the integrity of organ architecture. Here, we investigated how two critical proliferative pathways, Myc and E2f, are integrated to control cell cycles in normal and Rb-deficient cells using a murine intestinal model. We show that Myc and E2f1-3 have little impact on normal G1-S transitions. Instead, they synergistically control an S-G2 transcriptional program required for normal cell divisions and maintaining crypt-villus integrity. Surprisingly, Rb deficiency results in the Myc-dependent accumulation of E2f3 protein and chromatin repositioning of both Myc and E2f3, leading to the 'super activation' of a G1-S transcriptional program, ectopic S phase entry and rampant cell proliferation. These findings reveal that Rb-deficient cells hijack and redeploy Myc and E2f3 from an S-G2 program essential for normal cell cycles to a G1-S program that re-engages ectopic cell cycles, exposing an unanticipated addiction of Rb-null cells on Myc.

Viral oncogene expression in the stem/progenitor cell compartment of the mouse intestine induces adenomatous polyps.

UNLABELLED: Genetic and epigenetic events that alter gene expression and/or protein function or localization are thought to be the primary mechanism that drives tumorigenesis and governs the clinical behavior of cancers. Yet, a number of studies have shown that the effects of oncogene expression or tumor suppressor ablation are highly dependent on cell type. The molecular basis for this cell-type specificity and how it contributes to tumorigenesis are unknown. Here, expression of a truncated SV40 large T antigen in murine intestinal crypts promoted the formation of numerous adenomatous polyps in the colon and small intestine. In contrast, when the same T-antigen construct is expressed in villous enterocytes, the consequences are limited to hyperplasia and dysplasia. The T-antigen-induced polyps show high levels of the proto-oncogene c-Myc protein even though there is no transport of ß-catenin to the nucleus. Targeting the expression of viral oncogenes to intestinal crypts or villi provides a murine model system for studying cell-type specific effects in tumorigenesis, and is particularly relevant to the study of APC/ß-catenin-independent pathways contributing to the generation of intestinal polyps. IMPLICATIONS: This mouse model system describes the formation of colon polyps in the absence of Wnt/ß-catenin signaling.

Immunohistochemical investigation of F344/N rat islet cell tumors from national toxicology program studies.

In this study, we have investigated the immunoexpression of peptide hormones and mediators associated with human islet cell tumors in a group of proliferative islet cell lesions in F344 rats including islet cell hyperplasias, adenomas, and carcinomas, as defined by conventional histopathologic criteria. All proliferative islets expressed synaptophysin, although decreased expression intensity was observed in hyperplasias and adenomas. Most of the proliferative lesions expressed insulin, which generally decreased as lesions progressed toward malignancy. The distribution of glucagon, somatostatin, and gastrin-expressing cells was altered in proliferative islet lesions but did not comprise a large proportion of cells. Islet cell tumors were associated with increased nuclear expression of cyclin-dependent kinase 4 as well as increased proliferating cell nuclear antigen and decreased ß-catenin expression. c-Myelocytomatosis oncogene expression was variable. This is the first study to describe the immunophenotype of islet cell tumors in the F344 rat and to show that islet cell tumors in the F344 rat exhibit similarities in protein expression to the human counterpart.