Altered gene expression profile in chemically induced rat mammary adenocarcinomas and its modulation by an aromatase inhibitor

Retinol Saturase: More than the Name Suggests

Retinol saturase (RetSat) is an oxidoreductase that is expressed in metabolically active tissues and is highly regulated in conditions related to insulin resistance and type 2 diabetes. Thus far, RetSat has been implicated in adipocyte differentiation, hepatic glucose and lipid metabolism, macrophage function, vision, and the generation of reactive oxygen species (ROS). Although initially described to transform retinol to 13,14-dihydroretinol, a function it was named after, alternative enzymatic reactions may underlie some of these biological effects. We summarize recent findings and identify major obstacles standing in the way of its pharmacological exploitation, how we might overcome these, and discuss the therapeutic potential of modulating the activity of RetSat in alleviating human pathologies.

Global Gene Expression Profiling of Chemically Induced Rat Mammary Gland Carcinomas and Adenomas

Chemical carcinogens induce both benign and malignant mammary gland tumors in female Sprague-Dawley rats. To identify gene expression profiles associated with malignancy, cDNA microarray analysis was used to compare gene expression profiles in rat mammary gland carcinomas, adenomas, and normal mammary gland. Tumors were induced with various chemical carcinogens including 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline (MeIQx), 7-12-dimethylbenz[ a]anthracene (DMBA), N-nitrosomethylurea (NMU), and 4-aminobiphenyl. The global gene expression profiles in carcinomas and adenomas were distinguishable by hierarchical clustering and multi-dimensional scaling analyses. Permutation analysis revealed 110 clones statistically differentially expressed between benign and malignant tumors ( p < 0.0005). Carcinomas showed relatively high expression of several genes associated with mammary epithelial cell growth and proliferation (e.g., cyclin D1, PDGFα) and relatively low expression of differentiation marker genes (e.g., β-casein, whey acidic protein, transferrin). Other categories of genes showing differential expression between carcinomas and adenomas were associated with protein homeostasis, cytoskeleton, extracellular matrix, and cell metabolism (fatty acid metabolism, oxidative phosphorylation, and glycolysis). Major gene families implicated in malignancy by over-expression in carcinomas included the annexins (annexin A1 and A4) and Stat family of transcription factors (Stat3 and Stat5a). The elevated expression of the prolactin receptor in carcinomas concomitant with several components of the mitogenic prolactin signaling pathway implicated prolactin/prolactin receptor/Stat5a/cyclin D1 in rat mammary gland malignancy.

Decidua mesenchymal stem cells migrated toward mammary tumors in vitro and in vivo affecting tumor growth and tumor development

Mesenchymal stem cells (MSCs) have affinity to tumor sites where they home, affecting their biology and growth. Previously, we have isolated mesenchymal cells from the decidua of the human placenta named as decidua-derived MSCs (DMSCs). The aims of the present study were to investigate the migration capacity of DMSCs in vitro, and in vivo in a preclinical model of mammary tumors induced by N-nitroso-N-methylurea (NMU). Additionally, we assessed the safety of DMSC administration in vivo and their effect on tumor growth. In vitro studies showed that DMSCs significantly migrate toward both, healthy human breast tissue and breast adenocarcinoma. Nevertheless, the effect on DMSC migration was significantly higher in the presence of tumor tissue. DMSCs also significantly migrated in vitro in the presence of NMU-mammary tumor homogenate when compared with control media alone. In vivo studies showed both migration and engraftment of DMSCs into NMU-induced tumors. Interestingly, DMSCs showed an inhibitory effect on the growth of primary tumors and in the development of new tumors. DMSCs did not affect the growth of secondary tumors, although secondary tumors appeared 2 weeks later, and the number of secondary tumors was lower in the DMSC-treated rats as compared with vehicle-treated rats. To our knowledge, this is the first report showing placental MSCs effect on tumor growth. In conclusion, DMSCs could serve as a therapeutic agent themselves and as a cellular vehicle of anticancer drugs.

Serial transplantation of NMU-induced rat mammary tumors: A model of human breast cancer progression

Human breast cancer is a heterogeneous disease that appears to progress from an in situ tumor to invasive cancer. Little is known about the molecular events driving this progression. Although microarray technology has helped us understand the genetic heterogeneity of breast cancer, its application to studying the transition from in situ to invasive disease is limited by the inability to follow the progression of a single patient's tumor. We previously used rat specific microarrays to show that N-methyl-N-nitrosourea induced tumors are similar to low-grade estrogen-receptor positive human breast cancer. Here, we transplanted these tumors through 5 generations of syngeneic hosts, and studied 65 resulting tumors. Most transplanted tumors gradually progressed from a noninvasive, low-grade cancer to a higher-grade invasive disease, losing p63 localization and basement membrane integrity. Invasive cancers frequently demonstrated a more mesenchymal phenotype with increased vimentin expression. Additionally, a unique transplant series is described with a phenotype similar to human basal-like breast cancer. Rat-specific Affymetrix gene arrays containing 15,866 gene probes identified genes that differentiated highly invasive tumors from those of low invasive potential. A linear regression analysis was used to find genes whose change in expression paralleled increasing invasive features independent of the transplant lineage of origin. Genes identified were assigned membership in cell adhesion, signal transduction, cell cycle and extracellular matrix groups, among others. This animal model overcomes the difficulty in studying human breast cancer progression. Our data support a gradual and continuous alteration in programs of gene expression during breast cancer invasion.

Organ-specific expression profiles of rat mammary gland, liver, and lung tissues treated with targretin, 9-cis retinoic acid, and 4-hydroxyphenylretinamide

A rexinoid, targretin, and two retinoids, 9-cis retinoic acid (9cRA) and 4-hydroxyphenylretinamide (4HPR), were examined for their effects on gene expression in rat mammary gland, liver, and lung tissues. The chemopreventive effects of these agents have largely been attributed to their ability to interact with retinoic acid receptors (RAR) and/or retinoid X receptors (RXR). Targretin interacts with the RXR receptors. 9cRA interacts with both the RAR and RXR receptors, whereas 4HPR has a moderate affinity primarily for RAR gamma. Based on previous studies on mammary chemoprevention, targretin (150 mg/kg diet), 9cRA (100 mg/kg diet), and 4HPR (782 mg/kg diet), were administered to rats continually in their diet for 7 days. Tissue- and agent-specific expression differences were determined by comparing tissues from treated rats with those from rats given a control diet. There were significantly more changes associated with targretin than 9cRA or 4HPR. Only a limited number of expression changes were found with 4HPR treatment. For each organ, targretin- and 9cRA-treated tissues clustered closely together, whereas 4HPR-treated tissues clustered with the tissues from the control diet group. In contrast to 9cRA treatment, targretin treatment altered genes that involved fatty acid metabolism and modulation of various cytochromes P450 in the liver, clearly demonstrating the very disparate nature of these two retinoids. These expression signatures could provide useful pharmacodynamic biomarkers for retinoid treatment and chemoprevention.

High-fat feeding period affects gene expression in rat white adipose tissue

The expression of 76 sequences, previously isolated as differentially expressed in visceral white adipose tissue (WAT) of female rats, fed with a high-fat diet for 11 days (Lopez et al., Biochem Biophys Res Comm 318: 234-239, 2004), was analyzed in epidydimal WAT of male rats after a feeding period of 65 days with the same diet, using microarray technology. After Northern blot validation of the results, only three genes appeared upregulated (caveolin-2, the alpha-1 chain of haemoglobin and rat mammary tumor-7) and two downregulated (adiponectin and dystroglycan). We have also analyzed caveolin-1 gene expression and found that follows the opposite pattern of caveolin-2, indicating that they are inversely regulated. Our results suggest that if feeding with a high-fat diet is prolonged, many of the initial changes in gene expression, probably aimed to consume the energy surplus and prevent excessive fat deposition, are not maintained, and adaptation to an increased lipid storage is developed.

AT1 receptor and ACE mRNA are increased in chemically induced carcinoma of rat mammary gland

Angiotesin II has except of strong vasoconstrict effect also ability to potentiate protein synthesis and cellular growth. The aim of this study was to investigate the gene expression of components of the renin-angiotensin system, angiotensinogen, renin, angiotensin-converting enzyme and AT(1) receptor, in rat mammary gland and in chemically induced carcinoma of this gland. Retinoids are known to inhibit cell proliferation and induce cell differentiation so they are considered as a promising chemopreventive agents. We studied the effect of 13-cis-retinoic acid on the gene expression of mentioned elements of the renin-angiotensin system in tumour tissue. The expressions in control and carcinoma tissue were investigated using RT-PCR and activity of angiotensin-converting enzyme was measured. The amount of angiotensin-converting enzyme and AT(1) receptor mRNA and angiotensin-converting enzyme activity always showed a significant increase in the carcinoma tissue in comparison with the control. Administration of 13-cis-retinoic acid to rats with induced mammary gland carcinoma was without significant effect on either tumour numbers or tumour burden and volume. Similarly, 13-cis-retinoic acid did not change the angiotensin-converting enzyme expression and activity. The AT(1) receptor gene expression displayed a clear tendency to decrease in tumour tissue after retinoic acid treatment. Our results demonstrate the presence of angiotensin-converting enzyme and AT(1) receptor in control and carcinoma tissue of mammary gland. We assume that both proteins might play a role in development of tumour cells and vasculature.

Characterization of medroxyprogesterone and DMBA-induced multilineage mammary tumors by gene expression profiling

Mouse mammary tumors arising during medroxyprogesterone-DMBA-mediated mammary carcinogenesis comprised three distinct phenotypes: adenocarcinoma, squamous cell carcinoma, and myoepithelial carcinoma. The molecular signature for each of the three tumor subsets was characterized by gene microarray analysis, and three distinct sets of gene expression profiles were obtained that were corroborated in part by quantitative RT-PCR and immunohistochemistry. These results suggest that this carcinogenesis and gene expression model will be useful for rapidly assessing the histopathological differences arising in mammary carcinogenesis and the effects of tumor promoting or chemoprevention agents.

Gene expression profiling of NMU-induced rat mammary tumors: cross species comparison with human breast cancer

Breast cancer is a complex genetic disease characterized by the accumulation of multiple molecular alterations. The NMU breast cancer model induced in the rat is used for the study of mammary carcinogenesis because it closely mimics human breast disease. To assess the validity of this model from a more global molecular perspective, and also to devise a general technique to compare animal profiles with human microarray studies, we have characterized 25 NMU-induced mammary tumors and 11 normal glands using a combination of immunohistochemical and microarray analyses. The rat mammary carcinomas were classified as non-invasive, ER-positive ductal carcinomas with a composition of differentiated epithelial and myoepithelial cell lineages. Gene expression profiles generated using rat Affymetrix arrays containing 15,866 genes demonstrated that the rat mammary tumors are homogeneous and that H-ras mutations did not confer a unique molecular signature. We compared the resulting rat profiles with those obtained from a human dataset by merging the raw microarray data, using an approach that involves a combination of cross-species and cross-platform analysis. Using this novel strategy, we demonstrate the ability of 2305 rat orthologs to recapitulate the classification of human tumors derived from human Affymetrix arrays. The gene expression profiles of the NMU-induced primary tumors were most similar to ER-positive, low to intermediate grade breast cancer. Our technique provides a means to correlate gene expression data from animal models of cancer to human cancer and disease states.

Global Analysis of Altered Gene Expressions during the Process of Esophageal Squamous Cell Carcinogenesis in the Rat: A Study Combined with a Laser Microdissection and a cDNA Microarray

The genetic alterations that occur during esophageal tumorigenesis have yet to be determined. We previously established a Wister rat carcinogenesis model of esophageal squamous cell carcinoma. To understand more about the molecular mechanisms during carcinogenesis, we produced esophageal neoplastic lesions by administering N-amyl-N-methylnitrosamine and 12-O-tetradecanoylphorbol-13-acetate to rats. We used laser microdissection to specifically isolate the cells from the normal epithelium, papilloma, dysplasia, and invasive carcinoma. Using a cDNA microarray representing 14,815 clones, we then analyzed the gene expression profiles for each esophageal lesion. The number of differentially expressed genes compared with the normal control dramatically increased in a step-by-step fashion from normal epithelium (1,151 ± 119 genes) to papilloma (1,899 ± 543 genes), dysplasia (1,991 ± 193 genes), and invasive carcinoma (2,756 ± 87 genes). A hierarchical clustering analysis showed that the three stages of normal epithelium, dysplasia (papilloma), and invasive carcinoma could be clearly classified, whereas the gene expression patterns of papilloma and dysplasia were indistinguishable. Using the Fisher criterion, we also identified 50 genes whose expression level had either significantly increased or decreased in a step-by-step manner from the normal epithelium to dysplasia and then finally to invasive carcinoma. Many of these genes were not previously known to be associated with esophageal carcinogenesis. The present findings in our rat model thus seem to provide us with a better understanding of the molecular alterations that occur during esophageal carcinogenesis and hopefully will also help lead to the development of novel diagnostic and therapeutic targets.

Identification of all-trans-retinol:all-trans-13,14-dihydroretinol saturase

Retinoids carry out essential functions in vertebrate development and vision. Many of the retinoid processing enzymes remain to be identified at the molecular level. To expand the knowledge of retinoid biochemistry in vertebrates, we studied the enzymes involved in plant metabolism of carotenoids, a related group of compounds. We identified a family of vertebrate enzymes that share significant similarity and a putative phytoene desaturase domain with a recently described plant carotenoid isomerase (CRTISO), which isomerizes prolycopene to all-trans-lycopene. Comparison of heterologously expressed mouse and plant enzymes indicates that unlike plant CRTISO, the CRTISO-related mouse enzyme is inactive toward prolycopene. Instead, the CRTISO-related mouse enzyme is a retinol saturase carrying out the saturation of the 13-14 double bond of all-trans-retinol to produce all-trans-13,14-dihydroretinol. The product of mouse retinol saturase (RetSat) has a shifted UV absorbance maximum, lambda(max) = 290 nm, compared with the parent compound, all-trans-retinol (lambda(max) = 325 nm), and its MS analysis (m/z = 288) indicates saturation of a double bond. The product was further identified as all-trans-13,14-dihydroretinol, since its characteristics were identical to those of a synthetic standard. Mouse RetSat is membrane-associated and expressed in many tissues, with the highest levels in liver, kidney, and intestine. All-trans-13,14-dihydroretinol was also detected in several tissues of animals maintained on a normal diet. Thus, saturation of all-trans-retinol to all-trans-13,14-dihydroretinol by RetSat produces a new metabolite of yet unknown biological function.

Gene expression changes in rat white adipose tissue after a high-fat diet determined by differential display

The differences in gene expression pattern of visceral white adipose tissue between control and high-fat-fed rats were compared using the mRNA differential display methodology. The results, confirmed by Northern blot, showed eight genes upregulated: adiponectin, fibrillin-1, transferrin, Y-box binding protein-1, IgE receptor beta chain (FcRIbeta), alpha-1 haemoglobin, and ribosomal proteins S10 and L7 and four genes downregulated: caveolin-2, lactate dehydrogenase-A, mitochondrial 16S rRNA, and mitochondrial cytochrome oxidase subunit I/serine tRNA. Two of these genes have been already related to obesity (adiponectin and caveolin-2) while the others are known to participate in metabolic, signalling or transcription regulation pathways that can be relevant in energy (lipid and/or carbohydrate) metabolism.

Sex hormone-induced mammary carcinogenesis in female Noble rats: detection of differentially expressed genes

Breast cancer is the most common cancer and the second most frequent cause of cancer death in women. Epidemiological data has recognized that an increased cumulative exposure to estrogen is the common tie linking most of the established risk factors for breast cancer. Sex hormone-induced mammary gland carcinogenesis of the Noble rat (using testosterone and 17beta-estradiol) resembles that of the human counterpart in its growth pattern as well as the histopathology of the tumors induced. This model may provide a paradigm for examination of genetic alterations and changes in gene expression between different histological groups and to make inferences about the role of known and putative oncogenes and tumor suppressor genes. We studied the gene expression profile during sex hormone-induced mammary carcinogenesis using a cDNA array technique; the results were further confirmed by RT-PCR, western blotting and immunohistochemical analyses. From the 10 differentially expressed genes identified, we have studied four highly overexpressed genes, two cell cycle/growth control regulators, the cyclins D1 and D2, a growth factor, IGF-2 and a cytokine TNF-alpha. Cyclins D1 and D2 were highly expressed in the nuclei of carcinoma cells but at low levels in the nuclei of the hyperplastic and normal mammary tissue. IGF-2 was found to expressed in the cytoplasm of the carcinoma cells but not in the stromal cells. Western blot showed expression of big IGF-2 consistent with the tumor derived truncated forms of pro-IGF-2. The matured circulating IGF-2 at 7.5 kDa identified in the serum was not expressed in any of the breast tissue samples. TNF-alpha expression was found not only in the macrophages but also in the mammary carcinoma cells. The result of the present study provides some information on the molecular basis of this sex hormone-induced mammary carcinogenesis and the role of these proteins in tumor progression.

Differential gene expression in chemically induced mouse lung adenomas

Because of similarities in histopathology and tumor progression stages between mouse and human lung adenocarcinomas, the mouse lung tumor model with lung adenomas as the endpoint has been used extensively to evaluate the efficacy of putative lung cancer chemopreventive agents. In this study, a competitive cDNA library screening (CCLS) was employed to determine changes in the expression of mRNA in chemically induced lung adenomas compared with paired normal lung tissues. A total of 2555 clones having altered expression in tumors were observed following competitive hybridization between normal lung and lung adenomas after primary screening of over 160,000 clones from a mouse lung cDNA library. Among the 755 clones confirmed by dot blot hybridization, 240 clones were underexpressed, whereas 515 clones were overexpressed in tumors. Sixty-five clones with the most frequently altered expression in six individual tumors were confirmed by semiquantitative RT-PCR. When examining the 58 known genes, 39 clones had increased expression and 19 had decreased expression, whereas the 7 novel genes showed overexpression. A high percentage (>60%) of overexpressed or underexpressed genes was observed in at least two or three of the lesions. Reproducibly overexpressed genes included ERK-1, JAK-1, surfactant proteins A, B, and C, NFAT1, alpha-1 protease inhibitor, helix-loop-helix ubiquitous kinase (CHUK), alpha-adaptin, alpha-1 PI2, thioether S-methyltransferase, and CYP2C40. Reproducibly underexpressed genes included paroxanase, ALDH II, CC10, von Ebner salivary gland protein, and alpha- and beta-globin. In addition, CCLS identified several novel genes or genes not previously associated with lung carcinogenesis, including a hypothetical protein (FLJ11240) and a guanine nucleotide exchange factor homologue. This study shows the efficacy of this methodology for identifying genes with altered expression. These genes may prove to be helpful in our understanding of the genetic basis of lung carcinogenesis and in developing biomarkers for lung cancer chemoprevention studies in mice.