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Bystander macrophages silence transgene expression driven by the retroviral long terminal repeat.

The Moloney murine leukemia virus (MLV)-based retroviral vector has been widely used for transfer of exogenous genes to various organs and tissues. Although the long terminal repeat (LTR) of MLV allows for transgene expression in a wide range of cell type, its activity is often silenced in vivo. In reporter macrophages transduced with a MLV-based retroviral vector, activity of the LTR was transiently and reversibly suppressed following stimulation by lipopolysaccharide (LPS). When unstimulated reporter macrophages were co-cultured with LPS-stimulated, untransduced macrophages, the LTR activity was similarly depressed. Activity of the LTR in retrovirus-transduced, mesangial cells was also down-regulated when co-cultured with activated macrophages. This suppressive effect was reproduced by cross-feeding with culture media conditioned by activated macrophages. LPS-stimulated macrophages abundantly expressed cytokines including IL-1beta, tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1). When externally added, TNF-alpha and/or TGF-beta1, but not IL-1beta, depressed activity of the LTR in reporter macrophages and reporter mesangial cells. These results raise a possibility that expression of transgenes driven by the MLV-LTR may be silenced in vivo when the retrovirally-transduced cells are co-localized with activated macrophages.

Animals↗

Repression of the IL-6 gene is associated with hypermethylation.

The expression of the IL-6 gene is usually tightly controlled and may be induced in specific tissues after treatment with appropriate stimuli. Although much is known about the inducible expression of the IL-6 gene, the molecular mechanisms responsible for its repression in specific tissues or cell types remain poorly defined. To address this question we have studied two human breast carcinoma cell lines, MDA-MB-231, in which the IL-6 gene is expressed, and, MCF-7, in which the IL-6 message is undetectable by Northern blot assay even in the presence of inducers. The expression of the IL-6 message was estimated after treatment with 5-aza-2'deoxycytidine and the methylation state of the IL-6 gene was analyzed. We show herein that treatment of MCF-7 cells with an agent which reduces DNA methylation correlates with IL-6 gene hypomethylation and increases the level of its expression.

Azacitidine↗

Histone deacetylase and DNA methyltransferase in human prostate cancer.

CpG island hypermethylation and chromatin remodeling play important roles in repression of various genes during malignant transformation. We hypothesized that histone deacetylases (HDACs) and DNA methyltransferases (DNMTase) are associated with prostate cancer and we examined the enzyme activity, gene, and protein expression of HDAC1 and DNMT1 in cell lines and tissues. We found that DNMTase and HDACs activities were two- to threefold higher in cell lines compared to benign prostatic hyperplasia (BPH-1) cell line. Treatment of cells with 5-aza-2'-deoxycytidine decreased the activity of HDAC and DNMTase. The mRNA expression of these genes in BPH-1 cells and BPH tissues was lower than that in prostate cancer cells and tissues. HDAC1 and DNMT1 protein expression was higher in prostate cancer compared to BPH. This is the first report to demonstrate that DNMT1 and HDAC1 levels are up-regulated in prostate cancer compared to BPH, suggesting their roles in inactivation of various genes, by DNA-methylation-induced chromatin-remodeling, in prostate cancer.

Azacitidine↗

5-Aza-2'-deoxycytidine induces histone hyperacetylation of mouse centromeric heterochromatin by a mechanism independent of DNA demethylation.

5-Aza-2'-deoxycytidine (5-azadC) is widely used as a potent inhibitor of DNA methyltransferase. Cells treated with this drug show various phenomena such as the reactivation of repressed genes, change in replication timing, and decondensation of heterochromatin. A number of studies using this drug have been reported so far but it is still controversial whether such changes are due to 5-azadC-induced demethylation itself or the side effects of the drug. Here we report that 5-azadC treatment induces histone hyperacetylation in mouse centromeric heterochromatin which normally contains methylated DNA and hypoacetylated histones. Treatment also affects the intranuclear distribution of histone deacetylase 2 (HDAC2). However, histone hyperacetylation was not observed in DNA methyltransferase 1-deficient cells with a reduced level of genomic DNA methylation. Our results suggest that 5-azadC-induced histone hyperacetylation is independent of DNA demethylation and that DNA methylation is not essential for the maintenance of the histone hypoacetylated state in centromeric heterochromatin.

Acetylation↗

DNA methylation of the human oxytocin receptor gene promoter regulates tissue-specific gene suppression.

In the human oxytocin receptor (OTR) gene, there is a CpG island from 140 bp upstream to 2338 bp downstream of the transcription start site (TSS). We investigated whether the methylation state of this region affects the transcription of the OTR gene. HepG2 derived from human hepatoblastoma, in which OTR gene transcription was suppressed, was treated with a demethylating agent, 5-azacytidine (Aza-C) for 2 days. Semiquantitative RT-PCR indicated that OTR mRNA was significantly increased by Aza-C treatment in a dose-dependent manner. We estimated the level of methylation within the CpG islands of the OTR gene in peripheral blood leukocytes, nonpregnant uterine myometrium, term uterine myometrium and liver. A 1.5-kb region located 5' upstream of the translation start site was divided into four fragments. Each was amplified by PCR after complete digestion with methylation-sensitive restriction enzyme HpaII. The amount of PCR products was largest in the liver, suggesting that this CpG island in the OTR gene is most highly methylated in liver, where the gene is always inactivated. We compared the effect of in vivo methylation of the CpG island on transcriptional activity of an OTR-reporter plasmid. The reporter gene activity of expression plasmid -2860/+1342-GL3, containing the CpG island, in HepG2 cells was suppressed to 30.6% of the control level after methylation with SssI methylase, while that of -2840/+144-GL3, without the CpG island was suppressed only to 81.4%. The deletion of the segment (MT2) where the level of methylation was most different between liver and uterus (-2860/+1342(del)MT2-GL3) rescued the suppression rate to 68.0%. These results indicate that the methylation of the CpG island in the human OTR gene promoter suppressed its transcription at least in liver and may regulate tissue specific gene expression among organs.

Azacitidine↗

5-Azacytidine modulates the response of sensitive and multidrug-resistant K562 leukemic cells to cytostatic drugs.

In an endeavor to improve responsiveness of tumor cells to drug combination treatments, we analyzed the effect of 5-azacytidine (5AC) as a model compound for a new class of drugs, DNA-demethylating agents. We used parental K562/WT chronic myelogenous leukemia cells and a multidrug-resistant subline thereof, K562/ADM. Multidrug-resistant cells were more resistant to daunorubicin, but more sensitive to cisplatin than parental K562 cells as measured by growth inhibition and apoptosis assays. Resistance to daunorubicin can be explained by amplification of the MDR1 drug transporter gene. Cisplatin induced more DNA damage in specific genes and in the entire genome of K562/ADM cells compared to K562/WT cells using PCR stop assays and atomic absorption spectroscopy. Pretreatment with 5AC modulated the response of K562/ADM cells toward MDR-type drugs (daunorubicin, vincristine, etoposide) and reduced function and expression of MDR1 as analyzed by flow cytometry and RT-PCR. Analysis of CpG island methylation in the promotor region of the MDR1 gene by bisulfite sequencing and a methylation-sensitive HpaII-digestion/PCR approach revealed that methylation of the MDR1 promotor of K562/ADM cells was greater than in K562/WT cells. 5AC treatment completely abolished MDR1 promotor methylation. The unexpected observation that DNA demethylation by 5AC rather decreases than increases MDR1 expression in K5612/ADM cells points to still unexplored sequences in the MDR1 promotor whose transcriptional activity may be affected by the methylation status. 5AC pretreatment also modulated K562/WT and K562/ADM cells to non-MDR-type drugs such as cisplatin and increased cisplatin-induced DNA damage.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

Macronuclear DNA demethylation is involved in the encystment process of the ciliate Colpoda inflata.

Ciliate encystment is an eukaryotic cell differentiation process which involves a specific gene expression, to form the resting stage. In this study, we investigate, for first time, the DNA methylation pattern changes during encystment in the ciliate Colpoda inflata, and the 5-azacytidine effect on growing cells and encystment. Results indicate that 5-methylcytosine is present in macronuclear DNA of this ciliate and the 5-azacytidine treatment induces encystment in growth conditions. From restriction enzyme digestion and 5-azacytidine experiments, we conclude that a specific DNA demethylation is probably involved in the encystment gene expression of this ciliate.

Animals↗

Modulation of osteogenic differentiation in human skeletal cells in Vitro by 5-azacytidine.

Cellular differentiation is controlled by a variety of factors including gene methylation, which represses particular genes as cell fate is determined. The incorporation of 5-azacytidine (5azaC) into DNA in vitro prevents methylation and thus can alter cellular differentiation pathways. Human bone marrow fibroblasts and MG63 cells treated with 5azaC were used as models of osteogenic progenitors and of a more mature osteoblast phenotype, respectively. The capacity for differentiation of these cells following treatment with glucocorticoids was investigated. 5azaC treatment led to significant expression of the osteoblastic marker alkaline phosphatase in MG63 osteosarcoma cells, which was further augmented by glucocorticoids; however, in human marrow fibroblasts alkaline phosphatase activity was only observed in glucocorticoid-treated cultures. MG63 cells represent a phenotype late in the osteogenic lineage in which demethylation is sufficient to induce alkaline phosphatase activity. Marrow fibroblasts are at an earlier stage of differentiation and require stimulation with glucocorticoids. In contrast, the expression of osteocalcin, an osteoblastic marker, was unaffected by 5azaC treatment, suggesting that regulation of expression of the osteocalcin gene does not involve methylation. These models provide novel approaches to the study of the control of differentiation in the marrow fibroblastic system.

Alkaline Phosphatase↗

Novel regulation of an MHC class I gene response to interferon-gamma.

The ability of IFN-gamma to increase the expression of MHC class I gene products is likely to enhance cytolytic T lymphocyte recognition of viral pathogens and tumor cells. The murine lymphoma AKR SL3-cl.F AZR (SL3-cl.F) responds aberrantly to treatment with interferon-gamma such that H-2Dk surface expression is augmented, but H-2Kk expression remains at constitutive levels. Somatic cell fusions have been used to demonstrate that the lesion responsible for this phenotype is cis-dominant, implicating a primary lesion within the SL3-cl.F H-2Kk gene. In this communication, we have used PCR to analyze the nucleotide sequence in regions of the SL3-cl.F H-2Kk promoter known to contain interferon-responsive enhancer elements. Comparison of the SL3-cl.F H-2Kk sequences to known consensus elements revealed complete identity. In order to identify the lesion responsible for the SL3-cl.F phenotype, two H-2Kk genomic clones were independently isolated from SL3-cl.F. Each clone exists as a 10.5-kbp EcoRI fragment containing the entire structural gene. The site of transcription initiation is at the center of this fragment; therefore, all regulatory elements within 5 kbp of the transcript start site which could alter steady-state message levels are included. Interestingly, IFN-gamma-augmented expression of the H-2Kk gene was restored following DNA-mediated transfection of either of these clones into fibroblast cell lines and the parental cell line SL3-cl.F. Because isolation of these clones required passage of the DNA through a prokaryotic host, which alters the pattern of DNA methylation, there was the possibility that demethylation was responsible for the newly acquired IFN-gamma-responsive phenotype. Treatment of SL3-cl.F with 5-azacytidine, which inhibits de novo methylation, did not restore IFN-gamma-augmented expression, however, thus excluding H-2Kk specific methylation as a potential mechanism. Collectively, these data demonstrate that the alteration responsible for the phenotype observed in SL3-cl.F does not involve known transcriptional regulatory elements. Potential mechanisms which might account for the mutant phenotype are discussed.

3T3 Cells↗

Interleukin-3 increases the incidence of 5-azacytidine-induced thymic lymphomas in pBOR-Il-3 mice.

Interleukin-3 (Il-3) is a glycoprotein produced by a CD4+CD8- subpopulation of T-lymphocytes. Il-3 has been associated with the proliferation of bone marrow stem cells and their differentiation to granulocytes, macrophages, basophil/mast cells, megakaryocytes, erythroid cells, and neutrophils. The pBOR-Il-3 transgenic mice were developed by pronuclear microinjection to study how chemical insults modulate transcription of the Il-3 gene driven by a long-terminal repeat (LTR) of an endogenous retrovirus and to determine the biological consequences of interleukin-3 expression. We injected 5-azacytidine, a demethylating agent, to increase the LTR-driven expression of Il-3. Upon 5-azacytidine treatment, both the pBOR-Il-3 and the FVB/N nontransgenic controls developed thymic lymphomas. The pBOR-Il-3 mice developed thymic lymphomas at a higher frequency than the FVB/N mice. The thymic lymphoma cells were of a T-cell origin, as determined by T-cell receptor gene rearrangement analysis, and, in most cases, were of monoclonal origin. According to flow cytometric analysis of CD3, CD4, and CD8 cell surface markers, the thymic lymphoma cells did not lose their ability to differentiate, but the differentiation process was aberrant. Flow cytometric analyses also revealed that in pBOR-Il-3 mice the thymic lymphomas are mostly of a CD8+CD4- origin, whereas in the FVB/N group, the predominant type of thymic lymphoma is of a CD4+CD8- origin.

Animals↗

Mouse alloantigen Ly10 is identical to murine fusion regulatory protein-1 (mFRP-1)/4F2/CD98: aberrant expression of mFRP-1/Ly10 allotypes in cells derived from CDF1 mice due to the gene deletion.

Murine FRP-1 (mFRP-1) and Ly10 antigens are alloantigens. Anti-Ly10.1, monoclonal antibody (mAb) reacts to HeLa cells stably expressing mFRP-1.1 (HeLa cells/mFRP-1.1), but does not react to HeLa cells/ mFRP-1.2. On the other hand, anti-Ly10.2 mAb reacts to HeLa/mFRP-1.2 cells, but does not react to HeLa cells/mFRP-1.1. These findings indicate that Ly10.1 and Ly10.2 antigens are identical to the heavy chains of mFRP-1.1 and mFRP-1.2 molecules, respectively. Thymocytes and fibroblast cells obtained from CDF1 and BDF1 mice showed reactivity to both anti-Ly10.1 and anti-Ly10.2/FRP-2 antibodies, indicating that mFRP-1/Ly10 alloantigens are codominantly expressed in the F1 mice. Intriguingly, IMC carcinoma cells, derived from CDF1 mice, express mFRP-1.2, but do not express mFRP-1.1. Surprisingly, DBT cells, derived from CDF1 mice, consist of two different cell populations: one expresses both mFRP-1.1 and mFRP-1.2 antigens and the other expresses only mFRP-1.1 antigen. Consequently, we tried to isolate cloned DBT cell lines by limiting dilution. Finally, six cloned DBT cell lines were obtained, and three clones of these cloned DBT cells expressed both mFRP-1.1 and mFRP-1.2, and another three clones of these cloned DBT cells expressed both mFRP-1.1 and mFRP-1.2, and another three clones including clone 5 cells expressed only mFRP-1.1 antigen. No induction of mFRP-1.2/Ly10.2 by 5-azacytidine and sodium n-butyrate could be detected in DBT clone 5 cells. Neither mFRP-1.2 mRNA nor the genomic cDNA clone encoding mFRP-1.2 could be detected in DBT clone 5 cells, nor could the genomic cDNA encoding mFRP-1.1 be detected in IMC cells, indicating that aberrant expression of mFRP-1/Ly10 allotypes in CDF1 mice-derived cells is due to the gene deletion.

Animals↗

Loss of Fas (CD95/APO-1) expression by antigen-specific cytotoxic T cells is reversed by inhibiting DNA methylation.

Elimination of clonally expanded peripheral CD8 T cells was thought to involve apoptosis induction mediated principally by TNF, but recently Fas (CD95/APO-1) has been shown to play a role in certain responses. Here we study Fas expression and sensitivity to its ligation on murine CD8 cells specific for the CW3 antigen expressed by transfected P815 cells. Fas was progressively downregulated after successive in vitro restimulations of antigen-specific CD8 cells, until clones became Fas negative and totally resistant to the effects of recombinant Fas ligand. In contrast, Fas expression by in vivo restimulated antigen-specific cells did not diminish. Loss of Fas expression in vitro was not totally irreversible, since it could be reinduced by inhibition of DNA methylation. Understanding how Fas may be differentially regulated in vivo and in vitro is an important issue for the optimal manipulation of T cells for adoptive immunotherapy protocols.

Animals↗

5-azacytidine treatment induces autoimmune vitiligo in parental control strains of the Smyth line chicken model for autoimmune vitiligo.

The effect of 5-Azacytidine (5-AzaC) on melanization was examined in two sublines of the Smyth line (SL) chicken model for autoimmune vitiligo, in two MHC-matched vitiligo-susceptible but normally pigmented controls (BL), and in nonsusceptible controls (LBL). 5-AzaC was administered ip every 3 days from day of hatch to 18 weeks at levels of 1 or 3 mg/kg body wt. Both treatments increased (P < 0.01) the incidence of autoimmune vitiligo in BL controls. In contrast, treatment significantly depressed (P < 0.01) the expected high incidence of vitiligo in one SL subline, but not in the other. There were no apparent pigmentation changes in 5-AzaC-treated LBL controls. 5-AzaC had dose-dependent depressing effects (P < 0.01) on body and lymphoid organ weights. Histological and mitogen assay data suggest negative effects on lymphocyte number and function. The data show that 5-AzaC can initiate autoimmune disease in genetically susceptible but phenotypically normal individuals.

Animals↗

Effect of azacytidine in the release of leukemia inhibitory factor, oncostatin m, interleukin (IL)-6, and IL-11 by mononuclear cells of patients with refractory anemia.

5-azacytidine (AZA) yields hematologic improvement in patients with myelodysplastic syndromes (MDS). Ineffective hemopoiesis in MDS produce the paradox of high intramedullary cellularity with peripheral cytopenias. Leukemia inhibitory factor (LIF), oncostatin M (OSM), interleukin (IL)-6, and IL-11 regulate hemopoiesis and LIF, OSM, and IL-6 also inhibit the proliferation of myeloid leukemic cell lines through the signal-transducing subunit gp130. These IL-6-type cytokines were measured by enzyme-linked immunosorbent assay in cell culture supernatants (SN) obtained from peripheral blood mononuclear cells (MNC) and monocyte-depleted MNC of patients with refractory anemia (RA; n=12) and healthy individuals (n=10). AZA down-regulated OSM, IL-6, and IL-11 release by MNC of patients but not by MNC from healthy individuals. Patient's SN had significantly lower concentrations of LIF, OSM, and IL-11 than SN of normal subjects. When monocyte-depleted MNC of patients were stimulated with phytohemagglutinin a significant increment in OSM levels was observed. In contrast, monocyte depletion in healthy subjects did not cause any significant change in OSM values. We conclude that: (a) AZA inhibits the release of OSM, IL-6, and IL-11 exclusively in RA-diseased MNC, (b) Patient's MNC release subnormal amounts of LIF, OSM, and IL-11, and (c) RA-derived monocytes probably down-regulate OSM release by phytohemagglutinin-activated MNC.

Adult↗

A role for DNA methylation in gastrulation and somite patterning.

DNA methylation constitutes an important epigenetic factor in the control of genetic information. In this study, we analyzed expression of the DNA methyltransferase gene and examined DNA methylation patterns during early development of the zebrafish. Maternal transcripts of the zebrafish DNA methyltransferase gene (MTase) are ubiquitously present at high levels in early embryos with overall levels decreasing after the blastula stage. At 24 h, methyltransferase mRNA is predominantly found in the brain, neural tube, eyes, and differentiating somites. Expression of MTase in the somites is highest in the anterior cells of the somites. Despite the high levels of MTase mRNA in blastula-stage embryos, we observe DNA hypomethylation at the blastula and gastrula stages compared to sperm or older embryos. Zebrafish embryos treated with 5-azacytidine (5-azaC) and 5-aza-2-deoxycytidine (5-azadC), nucleotide analogs known to induce cellular differentiation and DNA hypomethylation in mammalian cells, exhibit DNA hypomethylation and developmental perturbations. These defects are specifically observed in embryos treated at the beginning of the blastula period, just prior to midblastula transition. The most common phenotype is the loss of tail and abnormal patterning of somites. Head development is also affected in some embryos. Histological and in situ hybridization analyses reveal whole or partial loss of a differentiated notochord and midline muscle in treated embryos. When examined during gastrulation, 5-azaC-treated embryos have a shortened and thickened axial mesoderm. We propose that DNA methylation is required for normal gastrulation and subsequent patterning of the dorsal mesoderm.

Abnormalities, Drug-Induced↗

DNA methylation is not involved in growth regulation of gene expression of proliferating cell nuclear antigen.

Expression of proliferating cell nuclear antigen (PCNA) gene is growth regulated. By Southern blot analysis with restriction enzymes such as HpaII and MspI, no change of DNA methylation state in this gene was detected during rat liver regeneration. There is only one HpaII site located in the promoter region of rat PCNA gene and this HpaII site was found to be demethylated in both normal and regenerating livers. Human hepatoma cell lines Hep G2 and Hep 3B were used to study the relation of PCNA gene expression and the DNA methylation. There are 16 HpaII sites in human PCNA gene, and according to the HpaII and MspI restriction patterns, many of the HpaII sites were methylated in vivo. Upon serum stimulation of quiescent cells, no change of DNA methylation state in the HpaII and HhaI sites was found. Demethylation by the methylation inhibitor, 5-azacytidine, did not affect the expression of PCNA gene in the hepatoma cells. With the human primary fibroblasts, Y2, the demethylation by 5-azacytidine did not seem to change the growth dependence of PCNA gene expression. This is consistent with the observation that the expression of PCNA gene of some cultured cell lines such as CHO.K1, in which the PCNA gene was unmethylated, showed growth dependence. Also, no variation in methylation pattern of PCNA gene was found among the different rat tissues in which the expression of PCNA varies. Therefore, we conclude that DNA methylation is not involved in growth regulation of the PCNA gene expression.

Animals↗

Exemption of satellite DNA from demethylation in immortalized differentiated derivatives of F9 mouse embryonal carcinoma cells.

DNA methylation in F9 embryonal carcinoma cells at various stages of retinoic acid-induced differentiation was compared to that in immortalized differentiated derivatives of this cell line. Different repetitive sequences, such as L1 LINE, GAPDH pseudogenes, and major and minor satellite DNA, lost their methylation to similar extents during F9 differentiation into parietal endoderm cells. In the immortalized derivatives 8a and P1, which phenotypically resemble F9 cells at intermediate stages of differentiation, methylation patterns diverged: Methylation of L1 and GAPDH sequences was strongly and moderately diminished, respectively, whereas methylation of satellite DNA was almost as high as that in stem cells. P19 embryonal carcinoma cells and D3 embryonic stem cells possessed methylation patterns similar to those of F9 stem cells. In immortalized cell lines with differentiated phenotypes derived from P19, methylation was diminished uniformly throughout the genome, but the overall level of methylation remained higher than that in terminally differentiated F9 cells. Treatment with the methylation inhibitor deoxyazacytidine halted the proliferation of 8a, P1, and F9 cells and elicited marked changes in morphology. However, markers of differentiation were not induced in F9 cells. The finding that all immortalized differentiated derivatives of embryonal carcinoma cells retained a higher level of DNA methylation--at least in parts of their genomes--than did terminally differentiated cells may indicate a function of demethylation of DNA and of satellite sequences in particular in terminal differentiation of extraembryonic tissues.

Animals↗

Exclusion of specific human chromosomes into micronuclei by 5-azacytidine treatment of lymphocyte cultures.

Lymphocyte cultures of a male proband were treated with 5-azacytidine. This cytidine analogue induces distinct undercondensation in the heterochromatic regions of chromosomes 1, 9, 15, 16, and Y and increases the frequency of micronuclei formation. In order to analyze the chromosomal content of these micronuclei, in situ hybridizations with biotinylated probes specific for chromosomes 1, 9, 15, 16, and Y were performed. Probes for chromosomes 11, 17, and X were used as controls. Each of 5000 hybridized cell nuclei was scored for associated micronuclei, and signal distribution was documented. In preparations hybridized with probes detecting the 5-azacytidine-sensitive chromosomes a significant fraction of micronuclei showed hybridizations. In contrast, micronuclei in preparations probed for chromosomes 11, 17, and X lacked hybridization signals. The results suggest that in 5-azacytidine-treated cultures the 5-azacytidine-sensitive chromosomes are preferentially excluded into the micronuclei.

Azacitidine↗