Estrogen inducibility of c-Ha-ras transcription in breast cancer cells. Identification of functional estrogen-responsive transcriptional regulatory elements in exon 1/intron 1 of the c-Ha-ras gene

Novel Clofarabine-Based Combinations with Polyphenols Epigenetically Reactivate Retinoic Acid Receptor Beta, Inhibit Cell Growth, and Induce Apoptosis of Breast Cancer Cells

An epigenetic component, especially aberrant DNA methylation pattern, has been shown to be frequently involved in sporadic breast cancer development. A growing body of literature demonstrates that combination of agents, i.e. nucleoside analogues with dietary phytochemicals, may provide enhanced therapeutic effects in epigenetic reprogramming of cancer cells. Clofarabine (2-chloro-2′-fluoro-2′-deoxyarabinosyladenine, ClF), a second-generation 2′-deoxyadenosine analogue, has numerous anti-cancer effects, including potential capacity to regulate epigenetic processes. Our present study is the first to investigate the combinatorial effects of ClF (used at IC₅₀ concentration) with epigallocatechin-3-gallate (EGCG, tea catechin) or genistein (soy phytoestrogen), at physiological concentrations, on breast cancer cell growth, apoptosis, and epigenetic regulation of retinoic acid receptor beta (RARB) transcriptional activity. In MCF7 and MDA-MB-231 cells, RARB promoter methylation and expression of RARB, modifiers of DNA methylation reaction (DNMT1, CDKN1A, TP53), and potential regulator of RARB transcription, PTEN, were estimated using methylation-sensitive restriction analysis (MSRA) and quantitative real-time polymerase chain reaction (qPCR), respectively. The combinatorial exposures synergistically or additively inhibited the growth and induced apoptosis of breast cancer cells, followed by RARB hypomethylation with concomitant multiple increase in RARB, PTEN, and CDKN1A transcript levels. Taken together, our results demonstrate the ability of ClF-based combinations with polyphenols to promote cancer cell death and reactivate DNA methylation-silenced tumor suppressor genes in breast cancer cells with different invasive potential.

Polymorphism T81C in H-RAS Oncogene Is Associated With Disease Progression in Imatinib (TKI) Treated Chronic Myeloid Leukemia Patients

Background

Mammalian cells contain three functional RAS proto-oncogenes, known as H-RAS, K-RAS, and N-RAS, which encode small GTP-binding proteins in terms of p21^rass. RAS genes have been elucidated as major participants in the development and progression of cancer. A single nucleotide polymorphism (SNP) at H-RAS cDNA position 81 T→C (rs12628) has been found to be associated with the risk of many human cancers like gastrointestinal, oral, colon, bladder and thyroid carcinomas. Therefore, we hypothesized that this polymorphisms in H-RAS could influence susceptibility to chronic myeloid leukemia as well, and we conducted this study to test the hypothesis in Indian population.

Method

H-RAS polymorphism was studied in 100 chronic myeloid leukemia (CML) patients and 100 healthy controls by restriction fragmentation length polymorphism (RFLP-PCR). Associations between polymorphism and clinicopathological features of CML patients were investigated.

Results

In CML patients, the TT, TC and CC genotype frequency was 38%, 61% and 1% respectively, compared to 92%, 8% and 0% in healthy controls respectively. Compared to TT genotype, CT was significantly associated with increased risk of CML (odds ratio (OR): 8.4, P < 0.00001). There was a statistically significant correlation of H-RAS polymorphism with phases (P < 0.0003), molecular response (P < 0.0001), hematological response (P < 0.04) and thrombocytopenia (P < 0.003). However, there was no correlation of this polymorphism found with other clinical parameters.

Conclusion

H-RAS T81C polymorphism was found to be associated with CML risk and prognosis of CML. These results suggest that C heterozygosis may be considered a potential risk factor for CML development in the North Indian population.

Identification of estrogen-responsive genes based on the DNA binding properties of estrogen receptors using high-throughput sequencing technology

Estrogens are important endocrine hormones that control physiological functions in reproductive organs, and play a pivotal role in the generation and progression of breast cancer. Therapeutic drugs including anti-estrogen and aromatase inhibitors are used to treat patients with breast cancer. The estrogen receptors, ERα and ERβ, function as hormone-dependent transcription factors that directly regulate the expression of their target genes. Therefore, a better understanding of the function and regulation of estrogen-responsive genes provides insight into the gene regulation network associated with breast cancer. Recent technological developments in high-throughput sequencing have enabled the genome-wide identification of estrogen-responsive genes. Further elucidating the estrogen gene cascade is critical for advancements in the diagnosis and treatment of breast cancer.

Eicosapentaenoic acid activates RAS/ERK/C/EBPβ pathway through H-Ras intron 1 CpG island demethylation in U937 leukemia cells

Epigenetic alterations, including aberrant DNA methylation, contribute to tumor development and progression. Silencing of tumor suppressor genes may be ascribed to promoter DNA hypermethylation, a reversible phenomenon intensely investigated as potential therapeutic target. Previously, we demonstrated that eicosapentaenoic acid (EPA) exhibits a DNA demethylating action that promotes the re-expression of the tumor suppressor gene CCAAT/enhancer-binding protein δ (C/EBPδ). The C/EBPβ/C/EBPδ heterodimer formed appears essential for the monocyte differentiation commitment. The present study aims to evaluate the effect of EPA on RAS/extracellular signal regulated kinases (ERK1/2)/C/EBPβ pathway, known to be induced during the monocyte differentiation program. We found that EPA conditioning of U937 leukemia cells activated RAS/ERK/C/EBPβ pathway, increasing the C/EBPβ and ERK1/2 active phosphorylated forms. Transcriptional induction of the upstream activator H-Ras gene resulted in increased expression of H-Ras protein in the active pool of non raft membrane fraction. H-Ras gene analysis identified an hypermethylated CpG island in intron 1 that can affect the DNA-protein interaction modifying RNA polymerase II (RNAPII) activity. EPA treatment demethylated almost completely this CpG island, which was associated with an enrichment of active RNAPII. The increased binding of the H-Ras transcriptional regulator p53 to its consensus sequence within the intronic CpG island further confirmed the effect of EPA as demethylating agent. Our results provide the first evidence that an endogenous polyunsaturated fatty acid (PUFA) promotes a DNA demethylation process responsible for the activation of RAS/ERK/C/EBPβ pathway during the monocyte differentiation commitment. The new role of EPA as demethylating agent paves the way for studying PUFA action when aberrant DNA methylation is involved.

Regulated proteolysis of Candida albicans Ras1 is involved in morphogenesis and quorum sensing regulation

In Candida albicans, a fungal pathogen, the small G-protein Ras1 regulates many important behaviors including white-opaque switching, biofilm formation, and the induction and maintenance of hyphal growth. Like other Ras proteins, Ras1 is activated upon guanine triphosphate binding, and its activity is further modulated by post-translational lipid modifications. Here, we report that the levels of membrane-associated, full-length Ras1 were higher in hyphae than in yeast, and that yeast contained a shorter, soluble Ras1 species that resulted from cleavage. Deletion of the putative cleavage site led to more rapid induction of hyphal growth and delayed hypha-to-yeast transitions. The cleaved Ras1 species was less able to activate its effector, adenylate cyclase (Cyr1), unless tethered to the membrane by a heterologous membrane-targeting domain. Ras1 cleavage was repressed by cAMP-signalling, indicating the presence of a positive feedback loop in which Cyr1 and cAMP influence Ras1. The C. albicans quorum sensing molecule farnesol, which inhibits Cyr1 and represses filamentation, caused an increase in the fraction of Ras1 in the cleaved form, particularly in nascent yeast formed from hyphae. This newly recognized mode of Ras regulation may control C. albicans Ras1 activity in important ways.

Epigenetic mechanisms in anti-cancer actions of bioactive food components--the implications in cancer prevention

The hallmarks of carcinogenesis are aberrations in gene expression and protein function caused by both genetic and epigenetic modifications. Epigenetics refers to the changes in gene expression programming that alter the phenotype in the absence of a change in DNA sequence. Epigenetic modifications, which include amongst others DNA methylation, covalent modifications of histone tails and regulation by non-coding RNAs, play a significant role in normal development and genome stability. The changes are dynamic and serve as an adaptation mechanism to a wide variety of environmental and social factors including diet. A number of studies have provided evidence that some natural bioactive compounds found in food and herbs can modulate gene expression by targeting different elements of the epigenetic machinery. Nutrients that are components of one-carbon metabolism, such as folate, riboflavin, pyridoxine, cobalamin, choline, betaine and methionine, affect DNA methylation by regulating the levels of S-adenosyl-L-methionine, a methyl group donor, and S-adenosyl-L-homocysteine, which is an inhibitor of enzymes catalyzing the DNA methylation reaction. Other natural compounds target histone modifications and levels of non-coding RNAs such as vitamin D, which recruits histone acetylases, or resveratrol, which activates the deacetylase sirtuin and regulates oncogenic and tumour suppressor micro-RNAs. As epigenetic abnormalities have been shown to be both causative and contributing factors in different health conditions including cancer, natural compounds that are direct or indirect regulators of the epigenome constitute an excellent approach in cancer prevention and potentially in anti-cancer therapy.

Association between HRAS rs12628 and rs112587690 polymorphisms with the risk of melanoma in the North American population

HRAS belongs to the RAS genes superfamily. RAS genes are important players in several human tumors and the single-nucleotide polymorphism rs12628 has been shown to contribute to the risk of bladder, colon, gastrointestinal, oral, and thyroid carcinoma. We hypothesized that this SNP may affect the risk of cutaneous melanoma as well. HRAS gene contains a polymorphic region (rs112587690), a repeated hexanucleotide -GGGCCT- located in intron 1. Three alleles of this region, P1, P2, and P3, have been identified that contain two, three, and four repeats of the hexanucleotide, respectively. We investigated the clinical impact of these polymorphisms in a case-control study. A total of 141 melanoma patients and 118 healthy donors from the North America Caucasian population were screened for rs12628 and rs112587690 polymorphisms. Genotypes were assessed by capillary sequencing or fragment analysis, respectively, and rs12628 CC and rs112587690 P1P1 genotypes significantly associated with increased melanoma risk (OR = 3.83, p = 0.003; OR = 11.3, p = 0.033, respectively), while rs112587690 P1P3 frequency resulted significantly higher in the control group (OR = 0.5, p = 0.017). These results suggest that rs12628 C homozygosis may be considered a potential risk factor for melanoma development in the North American population possibly through the linkage to rs112587690.

TEX11 modulates germ cell proliferation by competing with estrogen receptor β for the binding to HPIP

Klinefelter syndrome (KS), characterized by the presence of more than one X-chromosome in men, is a major genetic cause of male infertility. Germ cell degeneration in KS patients is thought to be the consequences of overexpression of some genes on the X-chromosome. However, the identity of these genes and the underlying mechanisms remain unclear. Testis-expressed 11 (TEX11) is an X-chromosome-encoded germ-cell-specific protein that is expressed most abundantly in spermatogonia and early spermatocytes in the testes. In our search for TEX11-interacting partners using the yeast two-hybrid system, we identified hematopoietic pre-B cell leukemia transcription factor-interacting protein (HPIP), which anchors estrogen receptors (ER) to the cytoskeleton and modulates their functions. We found that mouse spermatogonial stem cells expressed Tex11, Hpip, and Esr2 but not Esr1. In cultured cells, TEX11 competed with ERβ for binding to HPIP. Upon treatment with 17β-estradiol or an ERβ agonist diarylpropionitrile, TEX11 promoted the nuclear translocation of ERβ and enhanced its transcriptional activities. On the other hand, TEX11 suppressed the nongenomic activities of ERβ in the cytoplasm, as indicated by reduced phosphorylation of AKT and ERK signaling molecules. Overexpression of TEX11 in mouse germ-cell-derived GC-1 and GC-2 cells suppressed the cell proliferation and the expression of cFos, Ccnd1, and Ccnb1 that were stimulated by 17β-estradiol or diarylpropionitrile and elevated the expression level of the proapoptotic Bax gene. The negative effect of TEX11 on cell proliferation suggests that increased expression of TEX11 in the germ cells may partially contribute to the spermatogenic defect observed in KS patients.

Intervention of human breast cell carcinogenesis chronically induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

More than 85% of breast cancers are sporadic and attributable to long-term exposure to environmental carcinogens, such as those in the diet, through a multistep disease process progressing from non-cancerous to premalignant and malignant stages. The chemical carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is one of the most abundant heterocyclic amines found in high-temperature cooked meats and is recognized as a mammary carcinogen. However, the PhIP's mechanism of action in breast cell carcinogenesis is not clear. Here, we demonstrated, for the first time, that cumulative exposures to PhIP at physiologically achievable, pico to nanomolar concentrations effectively induced progressive carcinogenesis of human breast epithelial MCF10A cells from a non-cancerous stage to premalignant and malignant stages in a dose- and exposure-dependent manner. Progressive carcinogenesis was measured by increasingly- acquired cancer-associated properties of reduced dependence on growth factors, anchorage-independent growth, acinar-conformational disruption, proliferation, migration, invasion, tumorigenicity with metastasis and increased stem-like cell populations. These biological changes were accompanied by biochemical and molecular changes, including upregulated H-Ras gene expression, extracellular signal-regulated kinase (ERK) pathway activation, Nox-1 expression, reactive oxygen species (ROS) elevation, increased HIF-1α, Sp1, tumor necrosis factor-α, matrix metalloproteinase (MMP)-2, MMP-9, aldehyde dehydrogenase activity and reduced E-cadherin. The Ras-ERK-Nox-ROS pathway played an important role in not only initiation but also maintenance of cellular carcinogenesis induced by PhIP. Using biological, biochemical and molecular changes as targeted endpoints, we identified that the green tea catechin components epicatechin-3-gallate and epigallocatechin-3-gallate, at non-cytotoxic doses, were capable of suppressing PhIP-induced cellular carcinogenesis and tumorigenicity.

Comparative effects of retinoic acid, vitamin D and resveratrol alone and in combination with adenosine analogues on methylation and expression of phosphatase and tensin homologue tumour suppressor gene in breast cancer cells

Aberrations in DNA methylation patterns have been reported to be involved in driving changes in the expression of numerous genes during carcinogenesis and have become promising targets for chemopreventive action of natural compounds. In the present study, we investigated the effects of all-trans retinoic acid (ATRA), vitamin D₃ and resveratrol alone and in combination with adenosine analogues, 2-chloro-2'-deoxyadenosine (2CdA) and 9-β-d-arabinosyl-2-fluoroadenine (F-ara-A), on the methylation and expression of phosphatase and tensin homologue (PTEN) tumour suppressor gene in MCF-7 and MDA-MB-231 breast cancer cells. The present results showed that in non-invasive MCF-7 cells, ATRA, vitamin D₃ and resveratrol possess high efficacy in the reduction of PTEN promoter methylation. It was associated with PTEN induction as well as DNA methyltransferase down-regulation and p21 up-regulation after treatments with vitamin D₃ and resveratrol, suggesting a complex regulation of the DNA methylation machinery. Vitamin D₃ and resveratrol improved the inhibitory effects of 2CdA and F-ara-A on PTEN methylation in MCF-7 cells; however, only the combined action of vitamin D₃ and 2CdA boosted the induction of PTEN expression, suggesting a cooperation of these compounds in additional processes driving changes in PTEN expression. In contrast, in highly invasive MDA-MB-231 cells, only vitamin D₃ reduced PTEN methylation and induced its expression without notable effects in combined treatments. The present results suggest that natural compounds can find application in epigenetic anticancer therapy aimed at inhibition of promoter methylation of tumour suppressor genes and induction of their expression at early stages of carcinogenesis.

Pre- and postpubertal irradiation induces mammary cancers with distinct expression of hormone receptors, ErbB ligands, and developmental genes in rats

Childhood exposure to carcinogens renders a higher risk of breast cancer. The molecular mechanisms underlying cancer development after such exposure are not, however, well understood. Here we examined how the mechanism of cancer development relates to the age at exposure to ionizing radiation (IR) or the carcinogen 1-methyl-1-nitrosourea (MNU). Pre- and postpubertal (3- and 7-wk-old, respectively) female Sprague-Dawley rats were whole-body γ-irradiated (2 Gy), injected intraperitoneally with MNU (20 mg/kg) or left untreated and were autopsied at 50 wk of age. Mammary carcinomas were examined for estrogen receptor (ER) α, progesterone receptor (PR) and ErbB ligand expression and for expression microarrays. Early histological changes of the ovaries were also evaluated. The incidence of mammary cancer was higher after postpubertal, rather than prepubertal, IR exposure; the inverse was true for MNU. Most cancers were positive for both ERα and PR except for the prepubertal IR group. Cancers of the prepubertal IR group expressed a different set of ErbB ligands from those of the other groups and did not overexpress Areg, which encodes an estrogen-regulated ErbB ligand, or other developmentally related genes including those for hormonally regulated mammary gland development. Prepubertal IR exposure resulted in ovarian dysfunction as revealed by a reduced follicular pool. Evidence thus suggests that mammary carcinogenesis induced by prepubertal IR exposure is independent of ovarian hormones but requires certain ErbB ligands; induction by postpubertal exposure depends on ovarian hormones and different ErbB ligands. In contrast, the mechanism of MNU-induced carcinogenesis was less influenced by the age at exposure.

Location analysis for the estrogen receptor-alpha reveals binding to diverse ERE sequences and widespread binding within repetitive DNA elements

Location analysis for estrogen receptor-α (ERα)-bound cis-regulatory elements was determined in MCF7 cells using chromatin immunoprecipitation (ChIP)-on-chip. Here, we present the estrogen response element (ERE) sequences that were identified at ERα-bound loci and quantify the incidence of ERE sequences under two stringencies of detection: <10% and 10–20% nucleotide deviation from the canonical ERE sequence. We demonstrate that ∼50% of all ERα-bound loci do not have a discernable ERE and show that most ERα-bound EREs are not perfect consensus EREs. Approximately one-third of all ERα-bound ERE sequences reside within repetitive DNA sequences, most commonly of the AluS family. In addition, the 3-bp spacer between the inverted ERE half-sites, rather than being random nucleotides, is C(A/T)G-enriched at bona fide receptor targets. Diverse ERα-bound loci were validated using electrophoretic mobility shift assay and ChIP-polymerase chain reaction (PCR). The functional significance of receptor-bound loci was demonstrated using luciferase reporter assays which proved that repetitive element ERE sequences contribute to enhancer function. ChIP-PCR demonstrated estrogen-dependent recruitment of the coactivator SRC3 to these loci in vivo. Our data demonstrate that ERα binds to widely variant EREs with less sequence specificity than had previously been suspected and that binding at repetitive and nonrepetitive genomic targets is favored by specific trinucleotide spacers.

Grape and wine polyphenols down-regulate the expression of signal transduction genes and inhibit the growth of estrogen receptor-negative MDA-MB231 tumors in nu/nu mouse xenografts

The antitumor properties of the Merlot grape (and Merlot wine) polyphenols were evaluated in relation to their ability to modulate gene expression in developing tumors using an athymic nude mouse model transplanted with the estrogen receptor-negative MDA-MB231 cells. Groups of mice were fed a modified AIN 93G diet (Research Diets Inc, New Brunswick, NJ) with the experimental groups receiving 100 mg/kg body weight equivalent of polyphenols by gavage 3 times per week. After 1 week of acclimation and another week of polyphenol supplementation, MDA-MB231 cells were transplanted and the growth patterns of the tumors monitored. After 33 days of tumor growth, the animals were euthanized, the tumors isolated, and gene expression profiles analyzed using signal transduction and cell cycle arrays. The development of tumors was almost totally arrested in grape polyphenol-treated mice. Total polyphenols isolated from the wine were more effective in reducing tumor growth as compared with a hydrophobic polyphenol fraction isolated from the wine, showing a 50% and 60% reduction in tumor growth on day 33, respectively. Analysis of gene expression showed that genes such as CDK2, FAS, LEF1, PRKCE, and PTGS2, belonging to the NFkappaB, phospholipase C, and calcium signaling pathways, were down-regulated in tumors that developed in grape polyphenol-treated mice. Several genes related to cell cycle regulation, such as CDK5RAP1, RBBP8, and SERTAD1, were up-regulated in these tumors. Changes in the expression of these genes were less pronounced in tumors of wine polyphenol-treated mice. The study highlights the potential influences of dietary polyphenolic components on gene expression in estrogen receptor-negative tumors and its relation to inhibition of tumor growth.

A novel sampling design to explore gene-longevity associations: the ECHA study

To investigate the genetic contribution to familial similarity in longevity, we set up a novel experimental design where cousin-pairs born from siblings who were concordant or discordant for the longevity trait were analyzed. To check this design, two chromosomal regions already known to encompass longevity-related genes were examined: 6p21.3 (genes TNFalpha, TNFbeta, HSP70.1) and 11p15.5 (genes SIRT3, HRAS1, IGF2, INS, TH). Population pools of 1.6, 2.3 and 2.0 million inhabitants were screened, respectively, in Denmark, France and Italy to identify families matching the design requirements. A total of 234 trios composed by one centenarian, his/her child and a child of his/her concordant or discordant sib were collected. By using population-specific allele frequencies, we reconstructed haplotype phase and estimated the likelihood of Identical By Descent (IBD) haplotype sharing in cousin-pairs born from concordant and discordant siblings. In addition, we analyzed haplotype transmission from centenarians to offspring, and a statistically significant Transmission Ratio Distortion (TRD) was observed for both chromosomal regions in the discordant families (P=0.007 for 6p21.3 and P=0.015 for 11p15.5). In concordant families, a marginally significant TRD was observed at 6p21.3 only (P=0.06). Although no significant difference emerged between the two groups of cousin-pairs, our study gave new insights on the hindrances to recruiting a suitable sample to obtain significant IBD data on longevity-related chromosomal regions. This will allow to dimension future sampling campaigns to study-genetic basis of human longevity.

Resequencing PNMT in European hypertensive and normotensive individuals: no common susceptibilily variants for hypertension and purifying selection on intron 1

BACKGROUND

Human linkage and animal QTL studies have indicated the contribution of genes on Chr17 into blood pressure regulation. One candidate gene is PNMT, coding for phenylethanolamine-N-methyltransferase, catalyzing the synthesis of epinephrine from norepinephrine.

METHODS

Fine-scale variation of PNMT was screened by resequencing hypertensive (n = 50) and normotensive (n = 50) individuals from two European populations (Estonians and Czechs). The resulting polymorphism data were analyzed by statistical genetics methods using Genepop 3.4, PHASE 2.1 and DnaSP 4.0 software programs. In silico prediction of transcription factor binding sites for intron 1 was performed with MatInspector 2.2 software.

RESULTS

PNMT was characterized by minimum variation and excess of rare SNPs in both normo- and hypertensive individuals. None of the SNPs showed significant differences in allelic frequencies among population samples, as well as between screened hypertensives and normotensives. In the joint case-control analysis of the Estonian and the Czech samples, hypertension patients had a significant excess of heterozygotes for two promoter region polymorphisms (SNP-184; SNP-390). The identified variation pattern of PNMT reflects the effect of purifying selection consistent with an important role of PNMT-synthesized epinephrine in the regulation of cardiovascular and metabolic functions, and as a CNS neurotransmitter. A striking feature is the lack of intronic variation. In silico analysis of PNMT intron 1 confirmed the presence of a human-specific putative Glucocorticoid Responsive Element (GRE), inserted by Alu-mediated transfer. Further analysis of intron 1 supported the possible existence of a full Glucocorticoid Responsive Unit (GRU) predicted to consist of multiple gene regulatory elements known to cooperate with GRE in driving transcription. The role of these elements in regulating PNMT expression patterns and thus determining the dynamics of the synthesis of epinephrine is still to be studied.

CONCLUSION

We suggest that the differences in PNMT expression between normotensives and hypertensives are not determined by the polymorphisms in this gene, but rather by the interplay of gene expression regulators, which may vary among individuals. Understanding the determinants of PNMT expression may assist in developing PNMT inhibitors as potential novel therapeutics.

Investigation of the estrogen receptor-alpha gene with type 2 diabetes and/or nephropathy in African-American and European-American populations

The estrogen receptor-alpha gene (ESR1) was selected as a positional candidate under a type 2 diabetes linkage peak at 6q24-27. A total of 42 ESR1 single nucleotide polymorphisms (SNPs) were genotyped in 380 African-American type 2 diabetic case subjects with end-stage renal disease (ESRD) and 276 African-American control subjects. A total of 22 ancestry informative markers were also genotyped, and the program Admixmap was used to adjust allelic and haplotypic association tests for individual estimates of admixture. The most significant association with type 2 diabetes-ESRD was with rs1033182 in intron 2 (P = 0.013, admixture-adjusted P(a) = 0.021). Genotyping 17 SNPs across a region of ESR1 intron 1-intron 2 in an expanded population of 851 case and 635 control subjects supported association with rs1033182 (P = 0.004, P(a) = 0.027) and with an independent six-SNP haplotype of high linkage disequilibrium spanning 6.4 kb (P < 0.0001, P(a) < 0.0001). The same 17 ESR1 SNPs were genotyped in 300 European-American type 2 diabetes-ESRD case subjects and 310 European-American control subjects. Two intron 2 SNPs, rs2431260 (P = 0.015) and rs1709183 (P = 0.019), and a four-SNP haplotype containing these SNPs (P = 0.033) were associated with type 2 diabetes and/or ESRD. Results suggest that intron 1 and intron 2 of the ESR1 gene may contain functionally important regions related to type 2 diabetes or ESRD risk.

Orchiectomy reduces hepatotumorigenesis of H-ras12V transgenic mice via the MAPK pathway

A common characteristic of hepatocellular carcinoma in humans and animals is a striking male prevalence. However, the underlying mechanisms remain largely unknown. We have reported that hepatotumorigenesis is prevalent in male H-ras12V transgenic mice (Wang et al., 2005). Orchiectomy and ovariectomy were performed to determine if the presence of sex organ-related factors contributes to hepatotumorigenesis. After orchiectomy and ovariectomy, the mice were sampled at 6 months of age. The pathological diagnosis, sex hormone levels, expression of the H-ras12V transgene, and ras related signal pathways were determined. Orchiectomy significantly reduced the incidence of hepatotumorigenesis in males. However, no significant difference was detected in the incidence of tumorigenesis between ovariectomized and non-ovariectomized females. Molecular biochemical experiments showed that the sex organ-related factors significantly influenced transgene expression, which contributed to activation of the MAPK signaling pathway. The present study demonstrates that testis-related factors play important roles in hepatotumorigenesis in H-ras12V transgenic mice.

Gender-dependent hepatic alterations in H-ras12V transgenic mice

BACKGROUND/AIMS

Although it has been proposed that Ras and related signal pathways play important roles in hepatocarcinogenesis, appropriate in vivo models are lacking.

METHODS

Two hepatocellular carcinoma lines were established using pronuclear microinjection techniques to create an insertion of the H-ras12V transgene under the control of the albumin enhancer/promoter. The resulting phenotypes and related molecular events were then examined.

RESULTS

Male (but not female) transgenic mice older than 2 months showed hepatic alterations with a high degree of reproducibility, as compared to the wild-type mice. The liver/body-weight ratios were lower for the females than for the males. The transgene-carrying line 28 was investigated extensively with respect to molecular differences between the genders. Male hepatocytes showed higher Ras activity and higher reactive oxygen species (ROS) levels than female hepatocytes. The female hepatocytes showed higher expression levels of p53 and p21Waf1/Cip1, enhanced cytochrome c release, which correlated with cell cycle arrest, and higher levels of hypodiploid cell formation, as compared to the male hepatocytes.

CONCLUSIONS

The gender-related differences in molecular responses to activated Ras may have implications for the prevalence of hepatic alterations in males. Our transgenic mice represent a potentially valuable animal model for future investigations.

Inhibition of estradiol-induced mammary proliferation by dibenzoylmethane through the E 2 –ER–ERE-dependent pathway

The phytochemical dibenzoylmethane (DBM) has been shown to inhibit 7,12-dimethylbenz[a]anthracene induced mammary tumorigenesis in Sencar mice. However, the molecular basis of this activity is still elusive. In the present study, we demonstrated that DBM inhibits estradiol (E2)-induced incorporation of bromodeoxyuridine into mammary DNA in immature female Sencar mice by 52%, when 10 micromol of DBM was intraperitoneally injected into mice prior to the injection of E2. Examination of the influence of DBM on the expressions of E2-ERE-dependent oncogenes in MCF-7 cells indicated that DBM inhibits the E2-induced cell growth as well as the expressions of four oncogenes, telomerase, c-myc, Ha-ras and bcl-2. Further mechanistic study using chromatin immunoprecipitation assay demonstrated that DBM acts as a pure antagonist by attenuating the binding of estrogen receptor to the estrogen response elements in the regulatory regions of c-myc, hTERT and bcl-2 genes in vivo. Taken together, our results strongly suggest that DBM plays an inhibitory role in E2-induced proliferations, which establishes DBM as a model molecule for studying the antiestrogenic drugs.

Aldosterone Stimulates Proliferation of Mesangial Cells by Activating Mitogen-Activated Protein Kinase 1/2, Cyclin D1, and Cyclin A

Recently, attention has been focused on the role of aldosterone in the pathophysiology of hypertension and cardiovascular disease. Several clinical and experimental data support the hypothesis that aldosterone contributes to the progression of renal injury. However, the molecular mechanisms of the effects of aldosterone in signal transduction and the cell-cycle progression of mesangial cells are not well known. For determining the signaling pathway of aldosterone in cultured mesangial cells, the effects of aldosterone on the mitogen-activated protein kinase 1/2 (MAPK1/2) pathway and the promoter activities of cyclin D1, cyclin A, and cyclin E were investigated. First, it was shown that the mineralocorticoid receptor (MR) was expressed in rat mesangial cells and glomeruli and that aldosterone stimulated the proliferation of mesangial cells via the MR and MAPK1/2 pathway. Next, it was demonstrated that aldosterone stimulated Ki-RasA, c-Raf kinase, MEK1/2, and MAPK1/2 in rat mesangial cells. Aldosterone induced cyclin D1 and cyclin A promoter activities and protein expressions, as well as the increments of CDK2 and CDK4 kinase activities. The presence of CYP11B2 and 11beta-HSD2 mRNA in rat mesangial cells also was shown. In conclusion, aldosterone seems to exert mainly MR-induced effects that stimulate c-Raf, MEK1/2, MAPK1/2, the activities of CDK2 and CDK4, and the cell-cycle progression in mesangial cells. MR antagonists may serve as a potential therapeutic approach to mesangial proliferative disease.

Intronic hormone response elements mediate regulation of FKBP5 by progestins and glucocorticoids

Expression of FKBP51, a large molecular weight immunophilin, is strongly enhanced by glucocorticoids, progestins, and androgens. However, the activity of a 3.4-kb fragment of the FKBP51 gene (FKBP5) promoter was only weakly increased by progestin and we show here that it is unresponsive to glucocorticoids and androgens. The entire FKBP5 was scanned for consensus hormone response elements (HREs) using MatInspector. We found that 2 regions of intron E, which are conserved in rat and mouse FKBP5, contain HRE-like sequences with high match scores. Deoxyribonucleic acid fragments (approximately 1 kb in length) containing these regions were amplified and tested in reporter gene assays for steroid responsiveness. One region of intron E of FKBP5 (pIE2) conferred both glucocorticoid and progestin responsiveness to 2 heterologous reporter genes, whereas the other, less-conserved region of intron E (pIE1) was responsive only to progestins. The inclusion of pIE1 upstream of pIE2 (pIE1IE2) enhanced progestin but not glucocorticoid responsiveness. None of the constructs containing intronic sequences was responsive to androgens. Mutation of the putative HREs within pIE1 and pIE2 eliminated hormone responsiveness. Electrophoretic mobility shift assays demonstrated that progesterone receptors (PR) bound to the HRE in pIE1, whereas both PR and glucocorticoid receptors interacted with the HRE in pIE2. These data suggest that distal intronic elements significantly contribute to transcriptional regulation of FKBP5 by glucocorticoids and progestins.

Allelic imbalance at 11p15.5-15.4 correlated with c-Ha-ras mutation during radiation-induced neoplastic transformation of human breast epithelial cells

Breast cancer is the most frequent malignancy in women throughout much of the developed world and is associated with a multistage process involving a number of genetic mutations and their corresponding cellular phenotypic alterations. It has already been shown that neoplastic transformation of a spontaneously immortalized human breast epithelial (MCF-10F) cell line by radiation, in combination with estrogen, represents a successful model in studying the molecular and biological alterations that may contribute to the tumorigenic process. In the present study, the incidence of allelic alterations (microsatellite instability/loss of heterozygosity) on chromosome 11 in different radiation-induced primary and secondary tumorigenic cell lines, relative to the control MCF-10F cells was investigated. We identified 3 regions of the chromosome 11 (11p15-p15.5, 11q13 and 11q23) that showed high incidence of LOH among these tumor cell lines and suggested a potential role for these chromosomal regions in breast carcinogenesis. Among them, locus 11p15.5, where c-Ha-ras oncogene is located, had incidence of allelic imbalance between 25-40%. Furthermore, direct sequencing analysis of codons 12 and 61 of the c-Ha-ras oncogene identified various point mutations. These data highlight the importance of chromosome 11 in radiation induced malignant transformation of human breast epithelial cells and suggest the usefulness of the model in uncovering specific derangements during breast cancer progression.

Aldosterone stimulates proliferation of cardiac fibroblasts by activating Ki-RasA and MAPK1/2 signaling

Aldosterone plays a pathological role in cardiac fibrosis by directly affecting cardiac fibroblasts. Understanding of the cellular mechanisms of aldosterone action in cardiac fibroblasts, however, is rudimentary. One possibility is that aldosterone promotes proliferation of cardiac fibroblasts by activating specific cellular signaling cascades. The current study tests whether aldosterone stimulates proliferation of isolated adult rat cardiac myofibroblasts (RCF) by activating Kirsten Ras (Ki-RasA) and its effector, the MAPK1/2 cascade. Aldosterone (10 nM) significantly increased RCF proliferation. This action was sensitive to the mineralocorticoid receptor (MR) antagonist spironolactone. Expression of MR in RCF and the whole rat heart was confirmed by immunoblotting. Aldosterone significantly increased absolute and active (GTP bound) Ki-RasA levels in RCF. Aldosterone, in addition, significantly increased phospho-c-Raf and phospho-MAPK1/2. The effects of aldosterone on Ki-RasA and phospho-c-Raf proteins were inhibited by spironolactone but not RU-486, suggesting that aldosterone acts via MR. Inhibitors of MEK1/2 and c-Raf prevented aldosterone-induced activation of MAPK1/2 and proliferation. These results show that aldosterone directly increases RCF proliferation through MR-dependent activation of Ki-RasA and its effector, the MAPK1/2 cascade. Activation of cardiac fibroblasts through such a cascade may play a role in the pathological actions exerted by aldosterone on the heart.

Activation of mitogen-activated protein kinase (mitogen-activated protein kinase/extracellular signal-regulated kinase) cascade by aldosterone

Aldosterone in some tissues increases expression of the mRNA encoding the small monomeric G protein Ki-RasA. Renal A6 epithelial cells were used to determine whether induction of Ki-ras leads to concomitant increases in the total as well as active levels of Ki-RasA and whether this then leads to subsequent activation of its effector mitogen-activated protein kinase (MAPK/extracellular signal-regulated kinase) cascade. The molecular basis and cellular consequences of this action were specifically investigated. We identified the intron 1-exon 1 region (rasI/E1) of the mouse Ki-ras gene as sufficient to reconstitute aldosterone responsiveness to a heterologous promotor. Aldosterone increased reporter gene activity containing rasI/E1 threefold. Aldosterone increased the absolute and GTP-bound levels of Ki-RasA by a similar extent, suggesting that activation resulted from mass action and not effects on GTP binding/hydrolysis rates. Aldosterone significantly increased Ki-RasA and MAPK activity as early as 15 min with activation peaking by 2 h and waning after 4 h. Inhibitors of transcription, translation, and a glucocorticoid receptor antagonist attenuated MAPK signaling. Similarly, rasI/E1-driven luciferase expression was sensitive to glucocorticoid receptor blockade. Overexpression of dominant-negative RasN17, addition of antisense Ki-rasA and inhibition of mitogen-activated protein kinase kinase also attenuated steroid-dependent increases in MAPK signaling. Thus, activation of MAPK by aldosterone is dependent, in part, on a genomic mechanism involving induction of Ki-ras transcription and subsequent activation of its downstream effectors. This genomic mechanism has a distinct time course from activation by traditional mitogens, such as serum, which affect the GTP-binding state and not absolute levels of Ras. The result of such a genomic mechanism is that peak activation of the MAPK cascade by adrenal corticosteroids is delayed but prolonged.

New ideas about aldosterone signaling in epithelia

The systemic actions of aldosterone are well documented; however, in comparison, our understanding of the cellular and molecular mechanisms by which aldosterone orchestrates these actions is rudimentary. Aldosterone exerts most of its physiological actions by modifying gene expression. It is now apparent that aldosterone represses almost as many genes as it induces. Several aldosterone-sensitive genes, including serum and glucocorticoid-inducible kinase (sgk) and small, monomeric Kirsten Ras GTP-binding protein (Ki-ras) have recently been identified. The molecular mechanisms and elements bestowing corticosteroid sensitivity on these and many other genes are becoming clear. Induction of Ki-Ras and Sgk is necessary and sufficient for some portion of aldosterone action in epithelia. These two signaling factors are components of a converging pathway with phosphatidylinositol 3-kinase positioned between them that enables both stabilizing the epithelial Na(+) channel (ENaC) in the open state as well as increasing the number of ENaC in the apical membrane. This aldosterone-induced signaling pathway contains many potential sites for feedback regulation and cross talk from other cascades and potentially impinges directly on the activity of transport proteins and/or cellular differentiation to modify electrolyte transport.

Mammary carcinomas induced in human c-Ha-ras proto-oncogene transgenic rats are estrogen-independent, but responsive to d-limonene treatment

We have previously shown that transgenic rats carrying three copies of the human c-Ha-ras proto-oncogene (Hras128) are highly susceptible to N-methyl-N-nitrosourea (MNU) mammary carcinogenesis. All transgenic rats treated with 50 mg / kg MNU, i.v. at 50 days of age, were found to rapidly develop multiple, large mammary carcinomas within as short a period as 8 weeks. In the present study, the effects of ovariectomy and treatment with d-limonene, known to inhibit mammary carcinogenesis in non-transgenic female rats, were investigated in Hras128 animals treated with MNU to clarify the role of the human c-Ha-ras proto-oncogene and to characterize the induced mammary carcinomas. Although ovariectomy completely inhibited development of mammary carcinomas in their wild-type counterparts, it did not affect either the incidence or the multiplicity of the mammary carcinomas in the Hras128 rats. On the other hand, treatment with d-limonene, an inhibitor of ras protein isoprenylation, inhibited the breast tumor development. These results indicate that aberrant c-Ha-ras gene expression is involved in ovarian hormone-independent growth and c-Ha-ras protein isoprenylation plays an important role in mammary carcinogenesis.

Regulation of Dexras1 expression by endogenous steroids

Dexras1, a newly identified member of the Ras superfamily of proteins, was discovered in AtT-20 corticotrope cells because its expression was induced in response to glucocorticoids (dexamethasone; Dex). As yet, the function of Dexras1 is unknown, but its rapid induction in response to glucocorticoids suggests the possibility that it may be involved in negative feedback regulation of corticotropin secretion. To better understand the control of Dexras1 expression, possible effects of other steroid hormones on its expression were studied in both AtT-20 cells and in mouse pituitaries. AtT-20 cells were treated with each of 6 steroids [aldosterone, corticosterone (Cort), Dex, beta-estradiol (E(2)), progesterone and testosterone] for 2 h. Dexras1 expression was assessed using both reverse transcription polymerase chain reaction (RT-PCR) and Northern analysis. Expression of the gene was only induced in response to glucocorticoid treatment (Dex or Cort). The 6 steroids were also injected into mice, pituitaries were harvested and total RNA was obtained for RT-PCR analysis. Surprisingly, treatment with E(2), not only injection of glucocorticoids, induced Dexras1 expression in mouse pituitary. Other steroids were without effect. The results suggest that in AtT-20 corticotropes, Dexras1 expression is only induced by glucocorticoid-type steroids. In pituitary glands of mice, the gene's expression is also responsive to E(2). We conclude that either Dexras1 expression in corticotropes from normal mice is regulated differently from that in AtT-20 cells, or that Dexras1 is also expressed in other pituitary cells than corticotropes.

Estrogen receptor interaction with estrogen response elements

The estrogen receptor (ER) is a ligand-activated enhancer protein that is a member of the steroid/nuclear receptor superfamily. Two genes encode mammalian ER: ERalpha and ERbeta. ER binds to specific DNA sequences called estrogen response elements (EREs) with high affinity and transactivates gene expression in response to estradiol (E(2)). The purpose of this review is to summarize how natural and synthetic variations in the ERE sequence impact the affinity of ER-ERE binding and E(2)-induced transcriptional activity. Surprisingly, although the consensus ERE sequence was delineated in 1989, there are only seven natural EREs for which both ERalpha binding affinity and transcriptional activation have been examined. Even less information is available regarding how variations in ERE sequence impact ERbeta binding and transcriptional activity. Review of data from our own laboratory and those in the literature indicate that ERalpha binding affinity does not relate linearly with E(2)-induced transcriptional activation. We suggest that the reasons for this discord include cellular amounts of coactivators and adaptor proteins that play roles both in ER binding and transcriptional activation; phosphorylation of ER and other proteins involved in transcriptional activation; and sequence-specific and protein-induced alterations in chromatin architecture.

Additional characterization of a hexanucleotide polymorphic site in the first intron of human H-ras gene: comparative study of its alterations in non-small cell lung carcinomas and sporadic invasive breast carcinomas

Intron 1 of the human H-ras gene possesses a polymorphism consisting of repetitions of the GGGCCT consensus. Three alleles have been reported at this locus. We confirmed that two, P1 and P2, display four and two repeats, respectively, with their internal sequence structure similar to that previously described. The third, P3, previously assigned as a three-unit repetition allele according to its electrophoretic mobility and with no other information regarding its internal structure, was also found. Sequence analysis of the P3 allele revealed that it consists of three perfect repeats of the GGGCCT consensus. This polymorphism is present only in human c-H-ras gene, although single hexanucleotide repeats are found scattered within intron 1 of this gene in rodents. Analysis of this locus in matched tumor/distant normal samples from: (i) 38 patients with non-small-cell lung carcinoma (NSCLC), and (ii) 35 patients with sporadic invasive breast carcinoma, revealed: (1) 6.6% and 19% loss of heterozygosity (LOH) respectively, and (2) 10.5% and 2.9% hexanucleotide instability (HI) respectively, detected by the presence of shifted in length alleles. Shifted alleles exhibited altered internal sequence structure in comparison to normal ones, suggesting complex mutational events. The same pattern of alterations was also detected in tissues adjacent to lung adenocarcinomas and dysplasias adjacent to squamous cell carcinomas (7.7% LOH, 5.9% HI), implying that abnormalities at this locus may be early events in lung carcinogenesis. The frequency of alterations (LOH vs. HI) was significantly different among NSCLC and breast cancer (P=.005), probably due to the different tumor biology of each system. Finally, altered mRNA expression of H-ras gene was detected in all cases with HI, but this finding was also observed in samples without HI. In view of reports showing that elements in intron 1 of H-ras gene potentially influence its transcriptional regulation, from our results we cannot exclude that the hexanucleotide locus could be an element with possible involvement in expressional regulation of this gene.

WISP-2 as a novel estrogen-responsive gene in human breast cancer cells

In order to search for novel estrogen-responsive genes, we performed serial analysis of gene expression (SAGE) for estrogen-treated MCF-7 human breast cancer cells. SAGE analysis of 31,000 and 30,856 tags from non-treated and 17 beta-estradiol (E2)-treated cells for 24 h, respectively, facilitated the identification of 15,037 different transcripts. Comparison of these two SAGE libraries indicated a remarkable similarity in expression profiles. Among the identified transcripts, four genes were found to be markedly increased for E2-treated cells compared with control cells. Three of the transcripts were cathepsin D, pS2 and high mobility group 1 protein, which have been described as estrogen-inducible genes. The fourth gene was WISP-2 (Wnt-1 inducible signaling pathway protein 2) which has recently been reported as an up-regulated gene in the mammary epithelial cell line C57 MG transformed by the Wnt-1 oncogene. The increase in WISP-2 mRNA was completely prevented by co-incubation with a pure anti-estrogen ICI 182,780, but not by coincubation with cycloheximide, indicating that WISP-2 is directly regulated by the estrogen receptor. The WISP-2 gene was also induced by treating with environmental estrogens, such as bisphenol-A or nonylphenol. This study represents the first comprehensive gene expression analysis of estrogen-treated human breast cancer cells.

The importance of being K-Ras

The ras genes give rise to a family of related proteins that have strong transforming potential. Typical in vitro studies fail to discriminate between the transforming activity of the Ras proteins. Although activating mutations in ras genes are commonly found in human disease, they are not evenly distributed between the different ras members. Instead, they are concentrated in k-ras. With the absence of evidence to suggest that k-ras DNA is more prone to mutation than h-ras DNA, this imbalance in mutational frequency suggests a special biological role for the K-Ras protein in vivo.