[Effects of dnmt1 gene silencing on cell cycle, proliferation, and apoptosis of gastric cancer cell line AGS]

BACKGROUND & OBJECTIVE

Dnmt1, a major DNA methyltransferase gene, is highly expressed in many cancers and lowly expressed in normal adult cells, therefore, its overexpression is closely related to tumorigenesis. This study was to assess effects of dnmt1 gene silencing on cell cycle, proliferation, and apoptosis of gastric cancer cell line AGS.

METHODS

The eukaryotic expression plasmid pshRNA-dnmt1, containing the sequence of short hairpin RNA (shRNA) targeting dnmt1, was constructed and transfected into AGS cells. PBS-treated cells and pTZU6+1-transfected cells were set as control. The expression levels of dnmt1 were detected by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. Cell cycle was analyzed by flow cytometry; cell survival was analyzed by MTT assay; cell apoptosis was evaluated by AO/EB double staining, electron microscopy, and TUNEL.

RESULTS

pshRNA-dnmt1 targeting dnmt1 was successfully constructed, and confirmed by sequencing. Relative to control, 24, 48, and 72 h after transfection of pshRNA-dnmt1, the inhibitory rates of dnmt1 protein levels in AGS cells were 28.24%, 68.54%, and 81.47%, respectively, and those of dnmt1 mRNA levels were 21.63%, 52.97%, and 72.06%, respectively. The growth of AGS cells was suppressed 72 h after transfection: S phase cells were reduced from (36.58+/-1.76)% to (18.54+/-6.59)% (P<0.05), and G(2)/M phase cells were increased from (6.18+/-0.32)% to (18.53+/-1.42)% (P<0.05). Cell survival rates were 79.49%, 51.63%, and 39.16%, respectively, 24, 48, and 72 h after transfection of pshRNA-dnmt1. A lot of apoptotic and necrosis cells were observed after transfection.

CONCLUSIONS

The recombinant plasmid pshRNA-dnmt1 can efficiently and specifically inhibit the expression of dnmt1 gene and the proliferation of AGS cells, and induce cell apoptosis. It provides evidence for gene therapy of human cancers.

Inhibition of DNA methyltransferase activity prevents tumorigenesis in a mouse model of prostate cancer

Transcriptional silencing of tumor suppressor genes by DNA methylation plays an important role in tumorigenesis. These aberrant epigenetic modifications may be mediated in part by elevated DNA methyltransferase levels. DNA methyltransferase 1 (DNMT1), in particular, is overexpressed in many tumor types. Recently, we showed that Dnmt1 is transcriptionally regulated by E2F transcription factors and that retinoblastoma protein (pRb) inactivation induces Dnmt1. Based on these observations, we investigated regulation of Dnmt1 by polyomavirus oncogenes, which potently inhibit the pRb pocket protein family. Infection of primary human prostate epithelial cells with BK polyomavirus dramatically induced Dnmt1 transcription following large T antigen (TAg) translation and E2F activation. For in vivo study of Dnmt1 regulation, we used the transgenic adenocarcinoma of the mouse prostate (TRAMP) model, which expresses the SV40 polyomavirus early region, including TAg, under control of a prostate-specific promoter. Analysis of TRAMP prostate lesions revealed greatly elevated Dnmt1 mRNA and protein levels beginning in prostatic intraepithelial neoplasia and continuing through advanced prostate cancer and metastasis. Interestingly, when TRAMP mice were treated in a chemopreventive manner with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-aza), 0 of 14 mice developed prostate cancer at 24 weeks of age, whereas 7 of 13 (54%) control-treated mice developed poorly differentiated prostate cancer. Treatment with 5-aza also prevented the development of lymph node metastases and dramatically extended survival compared with control-treated mice. Taken together, these data suggest that Dnmt1 is rapidly activated by pRb pathway inactivation, and that DNA methyltransferase activity is required for malignant transformation and tumorigenesis.

Effect of antisense DNMT3b gene eukaryotic expression plasmid on expression of the DNMT3b gene in human biliary tract carcinoma cells

BACKGROUND

Hypermethylation of the promoter region is one of the major mechanisms of tumor suppressor gene inactivation. DNA methyltransferase 3b (DNMT3b), an enzyme that participates in the establishment of de novo methylation patterns, is highly expressed in many tumor cells and tissues, and it is closely associated with hypermethylation of the promoter of tumor suppressor genes. The aim of this study was to explore the effect of transfection with antisense DNMT3b gene eukaryotic expression plasmid on the expression of the DNMT3b gene in human biliary tract carcinoma cell.

METHODS

The constructed antisense DNMT3b gene eukaryotic expression plasmid was transfected into the human biliary tract carcinoma cell line QBC-939 with lipofectamine transfection reagent, and positive cell clones were formed using G418 selection after transfection. The constructed recombinant plasmid was transfected into QBC-939 cells successfully and was confirmed by amplification of the exogenous neoR gene with the polymerase chain reaction method. The expression of DNMT3b gene mRNA and protein was detected by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and flow cytometry respectively.

RESULTS

Following transfection, the mRNA level of the DNMT3b gene decreased from 0.956+/-0.053 to 0.209+/-0.023, and the protein level of the DNMT3b gene also decreased from (75.38+/-3.22)% to (29.87+/-3.46)%. Very significant differences were observed both at the transcription and post-transcription levels in the expression of the DNMT3b gene between the non-transfection group and the antisense DNMT3b gene eukaryotic expression plasmid transfection group (P<0.01).

CONCLUSIONS

Transfection with the antisense DNMT3b gene eukaryotic expression plasmid can significantly reduce the expression level of the DNMT3b gene in the human biliary tract carcinoma cell line QBC-939. This study may provide a valid method to investigate the function of the DNMT3b gene and its role in biliary tract carcinoma.

Expression ofDNMT3A transcripts and nucleolar localization of DNMT3A protein in human testicular and fibroblast cells suggest a role for de novo DNA methylation in nucleolar inactivation

Transcriptional silencing during differentiation of human male germ cells and serum starvation of human fibroblasts is controlled by epigenetic mechanisms that involve de novo DNA methylation. It is associated with high expression of different transcripts of the DNA methyltransferase 3A (DNMT3A) gene that encode two isoforms with de novo methyltransferase activity and one without catalytic activity. Western blots revealed that DNMT3A protein (with catalytic domain) is present at low levels in several tissues and at increased levels in testicular cells and growth-arrested fibroblasts. Immunofluorescence experiments localized DNMT3A to discrete nucleolar foci in B spermatogonia and resting fibroblasts. The data here suggest a role for de novo DNA methylation in nucleolar inactivation.

Tissue-specific and de novo promoter methylation of the mouse glucose transporter 2

Glucose transporter 2 (GLUT2) is tissue-specifically expressed in liver and kidney, and reduced in neoplastic hepatic lesions and in most hepatoma cell lines. Here we examined the involvement of epigenetic modifications in the regulation of GLUT2. Four CpGs in the GLUT2 promoter were undermethylated in GLUT2-expressing tissues. In isolated hepatocytes, GLUT2 expression declined and the promoter was methylated de novo. This de novo methylation occurred with a similar time-course in hepatocytes cultured in a high-glucose medium that induced GLUT2 expression, suggesting that de novo methylation can be induced independently of GLUT2 expression. GLUT2 was reactivated in hepatocytes following exposure to the methylation inhibitor 5-aza-2'-deoxycytidine (AzaC) but only after the methylation had occurred. In p53-deficient mouse liver, the CpGs were methylated de novo; the GLUT2 expression declined. The GLUT2 promoter was hypermethylated in Hepa1c1c7 cells, but expression could be rescued by AzaC. Thus, it is proposed that DNA methylation has an important role in the regulation of GLUT2 in mouse tissues and liver-derived cells.

DNA methyltransferase expression in the mouse germ line during periods of de novo methylation

DNA methyltransferase (DNMT) 3A and DNMT3B are both active de novo DNA methyltransferases required for development, whereas DNMT3L, which has no demonstrable methyltransferase activity, is required for methylation of imprinted genes in the oocyte. We show here that different mechanisms are used to restrict access by these proteins to their targets during germ cell development. Transcriptional control of the Dnmt3l promoter guarantees that message is low or absent except during periods of de novo activity. Use of an alternative promoter at the Dnmt3a locus produces the shorter Dnmt3a2 transcript in the germ line and postimplantation embryo only, whereas alternative splicing of the Dnmt3b transcript ensures that Dnmt3b1 is absent in the male prospermatogonia. Control of subcellular protein localization is a common theme for DNMT3A and DNMT3B, as proteins were seen in the nucleus only when methylation was occurring. These mechanisms converge to ensure that the only time that functional products from each locus are present in the germ cell nuclei is around embryonic day 17.5 in males and after birth in the growing oocytes in females.

An association of DNMT3b protein expression with P16INK4a promoter hypermethylation in non-smoking female lung cancer with human papillomavirus infection

Our recent report indicated that HPV infection may be associated with an increased frequency of p16INK4a promoter hypermethylation to cause p16 inactivation. In this study, we further speculated that the HPV infection may be linked with the expression of DNA methyltransferase (DNMT) protein in lung cancer patients and it was observed that an association of p16INK4a promoter hypermethylation with HPV infection existed, but only in female cases (P<0.0001). Interestingly, DNMT3b protein expression was significantly correlated with p16INK4a promoter hypermethylation (P=0.023) and HPV 16/18 infections (P<0.001), respectively. Moreover, the correlation between p16INK4a promoter hypermethylation and DNMT3b protein expression was exclusively seen in female cases (P=0.035). These results strongly suggested that the involvement of HPV infection in nonsmoking female lung tumorigenesis may be mediated, at least to a certain extent, through the increase of DNMT3b protein expression to cause p16INK4a promoter hypermethylation.

Isolation and expression analysis of genes encoding DNA methyltransferase in wheat (Triticum aestivum L.)

DNA methylation of cytosine residues, catalyzed by DNA methyltransferases, is suggested to play important roles in regulating gene expression and plant development. In this study, we isolated four wheat cDNA fragments and one cDNA with open reading frame encoding putative DNA methyltransferase and designated TaMET1, TaMET2a, TaMET2b, TaCMT, TaMET3, respectively. BLASTX searches and phylogenetic analysis suggested that five cDNAs belonged to four classes (Dnmt1, Dnmt2, CMT and Dnmt3) of DNA methyltransferase genes. TaMET2a encoded a protein of 376 aa and contained eight of ten conserved motifs characteristic of DNA methyltransferase. Genomic sequence of TaMET2a was obtained and found to contain ten introns and eleven exons. The expression analysis of the five genes revealed that they were expressed in developing seed, during germination and various vegetative tissues, but in quite different abundance. It was interesting to note that TaMET1 and TaMET3 mRNAs were clearly detected in dry seeds. Moreover, the differential expression patterns of five genes were observed between wheat hybrid and its parents in leaf, stem and root of jointing stage, some were up-regulated while some others were down-regulated in the hybrid. We concluded that multiple wheat DNA methyltransferase genes were present and might play important roles in wheat growth and development.

Interleukin 6 supports the maintenance of p53 tumor suppressor gene promoter methylation

A strong association exists between states of chronic inflammation and cancer, and it is believed that mediators of inflammation may be responsible for this phenomenon. Interleukin 6 (IL-6) is an inflammatory cytokine known to play a role in the growth and survival of many types of tumors, yet the mechanisms employed by this pleomorphic cytokine to accomplish this feat are still poorly understood. Another important factor in tumor development seems to be the hypermethylation of CpG islands located within the promoter regions of tumor suppressor genes. This common epigenetic alteration enables tumor cells to reduce or inactivate the expression of important tumor suppressor and cell cycle regulatory genes. Here we show that in the IL-6-responsive human multiple myeloma cell line KAS 6/1, the promoter region of p53 is epigenetically modified by methyltransferases, resulting in decreased levels of expression. Furthermore, cells treated with IL-6 exhibit an increase in the expression of the DNA maintenance methylation enzyme, DNMT-1. The DNA methyltransferase inhibitor zebularine reverses the methylation of the p53 promoter, allowing the resumption of its expression. However, when zebularine is withdrawn from the cells, the reestablishment of the original CpG island methylation within the p53 promoter does not occur in the absence of IL-6, and cells which do not receive IL-6 eventually die, as p53 expression continues unchecked by remethylation. Interestingly, this loss of viability seems to involve not the withdrawal of cytokine, but the inability of the cell to resilence the promoter. Consistent with this model, when cells that express IL-6 in an autocrine fashion are subjected to identical treatment, p53 expression is reduced shortly after withdrawal of zebularine. Therefore, it seems IL-6 is capable of maintaining promoter methylation thus representing one of the possible mechanisms used by inflammatory mediators in the growth and survival of tumors.

Genome-wide gene expression profiling of testicular carcinoma in situ progression into overt tumours

The carcinoma in situ (CIS) cell is the common precursor of nearly all testicular germ cell tumours (TGCT). In a previous study, we examined the gene expression profile of CIS cells and found many features common to embryonic stem cells indicating that initiation of neoplastic transformation into CIS occurs early during foetal life. Progression into an overt tumour, however, typically first happens after puberty, where CIS cells transform into either a seminoma (SEM) or a nonseminoma (N-SEM). Here, we have compared the genome-wide gene expression of CIS cells to that of testicular SEM and a sample containing a mixture of N-SEM components, and analyse the data together with the previously published data on CIS. Genes showing expression in the SEM or N-SEM were selected, in order to identify gene expression markers associated with the progression of CIS cells. The identified markers were verified by reverse transcriptase–polymerase chain reaction and in situ hybridisation in a range of different TGCT samples. Verification showed some interpatient variation, but combined analysis of a range of the identified markers may discriminate TGCT samples as SEMs or N-SEMs. Of particular interest, we found that both DNMT3B (DNA (cytosine-5-)-methyltransferase 3 beta) and DNMT3L (DNA (cytosine-5-)-methyltransferase 3 like) were overexpressed in the N-SEMs, indicating the epigenetic differences between N-SEMs and classical SEM.

Histone deacetylase inhibitors decrease DNA methyltransferase-3B messenger RNA stability and down-regulate de novo DNA methyltransferase activity in human endometrial cells

It is well known that the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) acts synergistically with the DNA methyltransferase (DNMT) inhibitor 5-aza-2'-deoxycytidine (ADC) to reactivate DNA methylation-silenced genes. Moreover, in several studies, TSA was capable of inducing DNA demethylation even in the absence of ADC. Here we describe a mechanism by which HDAC inhibitors affect DNA methylation through their regulation on DNMT3B, a methyltransferase responsible for de novo DNA methylation. Using quantitative real-time PCR and Western blot analysis, we show that TSA down-regulates DNMT3B mRNA and protein expression in human endometrial cancer cells. This decrease in DNMT3B mRNA results in a significant reduction in de novo methylation activities. Further experiments indicated that TSA decreases DNMT3B mRNA stability and reduces its half-life from approximately 4 to 2.5 hours. We established that protein synthesis is required for posttranscriptional regulation, suggesting the involvement of an RNase and/or key mRNA stabilization factor(s) controlling the DNMT3B mRNA stability. Therefore, TSA may not only modify histone acetylation, but also potentially alter DNA methylation. Since the HDAC inhibitors are frequently used in epigenetic studies and are considered to be promising anticancer drugs, these new findings will have implications in both laboratory and clinical settings.

Expression of Dnmt3b in mouse hematopoietic progenitor cells and spermatogonia at specific stages

Two de novo-type DNA methyltransferases, Dnmt3a and Dnmt3b, are responsible for the creation of DNA methylation patterns during development. Dnmt3b is specifically expressed in the totipotent cells of mouse early embryos and Dnmt3a, a longer form of the two isoforms, is ubiquitously expressed in mesenchyme cells after the 10 day embryo stage [Mech. Dev. 118 (2002) 187]. In the present study, we demonstrated that Dnmt3b was expressed in the nuclei of specific cells in certain tissues after the 10 day embryo stage. In fetal liver, dorsal aorta and portal vein, Dnmt3b was expressed in cells expressing CD34, indicating that the cells were hematopoietic progenitor cells. However, Dnmt3b was not expressed in the hematopoietic progenitor cells in yolk sac blood islands at 8 day embryo stage and in adult bone marrow cells. Dnmt3b was also expressed in type-A spermatogonia after birth. Dnmt3b was expressed not only in the totipotent stem cells but also in the progenitor cells the direction of differentiation of which had been already determined. On the other hand, the long form of Dnmt3a was not expressed in these hematopoietic progenitor cells in fetal liver or type-A spermatogonia, but was expressed in hepatocytes in fetal liver and type-B spermatogonia. While Dnmt3b was distributed in both the heterochromatin and euchromatin regions, Dnmt3a was specifically localized to the euchromatin region.

Opposite alterations of DNA methyltransferase gene expression in endometrioid and serous endometrial cancers

OBJECTIVE

To examine the DNA methyltransferase (DNMT) mRNA and protein levels in endometrioid and serous cancers and to study the relationship between DNA methyltransferase expression and endometrial cancer development.

METHODS

Normal endometrium, Grade I and Grade III endometrioid carcinoma tissues and cell lines, as well as serous cancer tissues, were analyzed for DNMT expression. Real-time PCR and Western blot techniques were employed to measure the mRNA and protein levels of the four DNA methyltransferases, DNMT1, DNMT2, DNMT3A, and DNMT3B. Immunohistochemistry was performed to detect alterations in DNMT nuclear localization and spatial organization patterns.

RESULTS

While DNMT2 and DNMT3A expression appear to be normal, two- to fourfold increase in DNMT1 and DNMT3B were found in both Grade I and Grade III endometrioid cancers. In addition, the poorly differentiated cell lines expressed relatively higher DNMT levels than well-differentiated cells. In contrast to endometrioid carcinomas, serous cancers expressed substantially lower levels of DNMT1 and DNMT3B than normal controls, with four- and twofold reduction observed in DNMT1 and DNMT3B mRNA levels, respectively. Western blot analysis confirmed opposite expression patterns of DNMT1 and DNMT3B protein in endometrioid and serous cancers. Immunohistochemistry showed normal nuclear localization of DNMT1 and DNMT3B in Type I and Type II cancer specimens as well as cell cultures.

CONCLUSION

Two opposite DNMT expression patterns were identified in endometrioid and serous cancers. The concerted upregulation in maintenance and de novo DNA methyltransferases in endometrioid carcinomas is consistent with a tendency for gene-specific hypermethylation observed in this histologic subtype, and may be implicated in tumor suppressor silencing. In contrast, the downregulation of maintenance and de novo DNA methyltransferases in serous cancers suggests that these tumors may contain hypomethylated genomic DNA, which has been associated with a higher mutation rate and is consistent with the known pathogenesis of serous-specific phenotypes. Taken together, the data suggest that divergent DNA methylation pathways may be implicated in the development of Type I and Type II endometrial cancers.

DNA HYPERMETHYLATION ON MULTIPLE CpG ISLANDS ASSOCIATED WITH INCREASED DNA METHYLTRANSFERASE DNMT1 PROTEIN EXPRESSION DURING MULTISTAGE UROTHELIAL CARCINOGENESIS

PURPOSE

We elucidated the significance of aberrant DNA methylation on multiple CpG islands and its correlation with DNA methyltransferase DNMT1 protein expression during urothelial carcinogenesis.

MATERIALS AND METHODS

We examined the DNA methylation status on multiple CpG islands by methylation specific polymerase chain reaction and combined bisulfite restriction enzyme analysis in 12 specimens of normal urothelium, 23 of noncancerous urothelium showing no remarkable histological changes obtained from patients with bladder cancer (NBC) and 70 of transitional cell carcinoma (TCC).

RESULTS

DNA methylation on CpG islands of the p16 (0%, 17% and 21%) and death-associated protein kinase (13%, 33% and 29%) genes, and methylated in tumor-2 (56%, 60% and 76%), 12 (0%, 6% and 30%), 25 (25%, 27% and 35%) and 31 (45%, 56% and 79%) clones was detected in normal urothelium, NBCs and TCCs, respectively. The incidence of concurrent DNA hypermethylation on 3 or more CpG islands in NBCs (38%) was significantly higher than that in normal urothelium (0%, p = 0.0455) and even higher in TCCs (59%, p = 0.0043). The incidence of the CpG island methylator phenotype in nonpapillary carcinomas (nodular invasive carcinomas and their precursors, ie flat carcinoma in situ, 71%) was significantly higher than in papillary carcinomas (40%, p = 0.0143). In all specimens examined concurrent DNA hypermethylation on 3 or more CpG islands significantly correlated with immunohistochemically evaluated DNMT1 protein over expression (p = 0.0167).

CONCLUSIONS

DNA hypermethylation on multiple CpG islands in association with DNMT1 protein over expression may participate in multistage urothelial carcinogenesis even at the precancerous stage and particularly in the development of nodular invasive carcinomas of the bladder.

Increased Protein Stability Causes DNA Methyltransferase 1 Dysregulation in Breast Cancer

We report that DNA methyltransferase 1 (DNMT1) expression is dysregulated in breast cancer. The elevated protein levels are not a result of increased mRNA levels, but rather an increase in protein half-life. We found that DNMT1 protein levels were elevated in breast cancer tissues and in MCF-7 breast cancer cells relative to normal human mammary epithelial cells (HMECs) without a concomitant increase in DNMT1 mRNA or proliferative fraction. Although DNMT1 mRNA levels were properly S-phase-regulated in both cell types, DNMT1 protein levels did not follow S-phase fraction in MCF-7 cells. Rather, an increase in DNMT1 protein stability was found for MCF-7 cells relative to HMECs, and a destruction domain was mapped to the N-terminal 120 amino acids of DNMT1, which was required for its proper ubiquitination and degradation in HMECs. Furthermore, overexpression of DNMT1 with this deleted destruction domain in HMECs resulted in significantly increased genomic 5-methylcytosine levels relative to overexpression of the full-length protein. The regulation of DNMT1 destruction via this domain may be dysfunctional in cancer cells leading to subsequent cytosine hypermethylation in the genome.

Regulation of DNA methyltransferase 1 by the pRb/E2F1 pathway

Tumor suppressor gene silencing by DNA hypermethylation contributes to tumorigenesis in many tumor types. This aberrant methylation may be due to increased expression and activity of DNA methyltransferases, which catalyze the transfer of methyl groups from S-adenosylmethionine to cytosines in CpG dinucleotides. Elevated expression of the maintenance DNA methyltransferase, DNA methyltransferase 1 (DNMT-1), has been shown in carcinomas of the colon, lung, liver, and prostate. Based on the nearly ubiquitous alterations of both DNA methylation and the retinoblastoma protein (pRb) pathway found in human cancer, we investigated a potential regulatory pathway linking the two alterations in murine and human prostate epithelial cells. Analysis of DNA methyltransferase levels in Rb-/- murine prostate epithelial cell lines revealed elevated Dnmt-1 levels. Genomic DNA sequence analysis identified conserved E2F consensus binding sites in proximity to the transcription initiation points of murine and human Dnmt-1. Furthermore, the Dnmt-1 promoter was shown to be regulated by the pRb/E2F pathway in murine and human cell lines of epithelial and fibroblast origin. In the absence of pRb, Dnmt-1 transcripts exhibited aberrant cell cycle regulation and Rb-/- cells showed aberrant methylation of the paternally expressed gene 3 (Peg3) tumor suppressor gene. These findings show a link between inactivation of the pRb pathway and induction of DNA hypermethylation of CpG island-containing genes in tumorigenesis.

[Clinical significance of the expression of DNA methyltransferase genes (DNMT) in acute leukemia patients]

To investigate the relationship between the expression of DNMT and clinical prognosis in adult patients with acute leukemia (AL), the mRNA expressions of DNMT, p15(INK4B), mdr1 were measured in 72 AL patients and 20 normal controls by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR); the ratio of p15 CpG land methylation was measured in 56 AL patients and 14 normal controls by methylation-specific PCR (MSP-PCR). The results showed that all three DNMT mRNA expressions in AL patients were significantly higher than that in normal controls (P < 0.01). When the internal control was changed into PCNA, a kind of cell proliferation marker gene, the difference still showed a statistic significance. All three DNMT genes were significantly expressed and positively correlated with AL patients, showing high synergistic expression, and there was a negative correlation between the levels of p15, mdr1 gene expression and DNMT. The complete remission (CR) rate in AL patients with the positive expression of all DNMT genes was significantly higher than that of AL patients with partially positive or negative expression (P < 0.01) of DNMT genes. In 56 AL patients, the P15I(NK4B) was completely methylated in 55.4% (31 of 56), partly methylated in 21.4% (12 of 56) and all 14 cases of normal controls were not methylated. It is concluded that DNMT genes are abnormally high expressed in adult AL patients, which lead to methylation-silence of tumor suppressor genes by CpG land hypermethylation, the AL patients with high expression of DNMT are more sensitive to chemotherapy, which may be a good prognostic factor for AL patients.

Suppression of DNA methyltransferase 1 levels in head and neck squamous carcinoma cells using small interfering RNA results in growth inhibition and increase in Cdk inhibitor p21

The ectopic expression of DNA methyltransferase 1 (DNMT 1) can transforms mammalian cells, and the inhibition of DNMT1 activity reverses that phenotypic transformation. Therefore, DNMT1 is considered to be an excellent target for therapeutic intervention. Previously, inhibition of DNMT1 was accomplished by using an antagonist or by antisense oligonucleotides. In this study, we examined the ability of the novel approach using small interfering RNA (siRNA) to disrupt the expression of DNMT1 in human non-small cell lung carcinoma A549 cells and the consequences of such an intervention. Transfection of DNMT1 siRNA decreased DNMT1 protein levels specifically and effectively. This decrease was accompanied by suppression of cell proliferation and colony-forming ability. The mechanism of this inhibition may be related to the increased levels of the cyclin dependent kinase inhibitor p21. These results suggest that the siRNA approach can be used to disrupt effectively DNMT1 activity and cancer cell growth.

Up-regulation of DNA methyltransferase 3B expression in endometrial cancers

OBJECTIVE

To understand the role of epigenetic regulation in the pathogenesis of endometrial cancer, we have characterized DNA methyltransferase 3B (DNMT3B) gene expression in normal, Grade I and Grade III endometrioid cancers, and examined DNMT3B promoter activities in endometrial cancer cell lines.

METHODS

DNMT3B expression was measured in normal, Grade I, and Grade III endometrioid cancer samples. Real-time PCR and Western blot analysis were performed to compare DNMT3B mRNA and protein levels. DNMT3B levels were also compared among endometrial cell lines including those for Ishikawa, KLE, AN3, RL-95, HEC-1A, and HEC-1B. DNMT3B promoter reporter plasmids were constructed. Promoter activities in well and poorly differentiated cell lines were compared by in vitro reporter gene transfection.

RESULTS

DNMT3B was significantly up-regulated in both Grade I and Grade III cancers as compared to normal controls. Western blot analysis confirmed the increased DNMT3B protein expression in cancer tissues. It was also found that the well-differentiated endometrial cell line, Ishikawa, expressed lower levels of DNMT3B than the poorly differentiated KLE cells, the expression patterns similar to those observed in tumor specimens.

CONCLUSION

The results suggest that DNMT3B overexpression may play a significant role in endometrial cancer development. In addition, the transfection experiments indicated that DNMT3B promoters are more active in the poorly differentiated endometrial cancer cell lines, suggesting that the in vitro assay provides a useful model for studying the DNMT3B transactivation mechanism related to tumor transformation.

Identification of a three-gene expression signature of poor-prognosis breast carcinoma

BACKGROUND

The clinical course of breast cancer is difficult to predict on the basis of established clinical and pathological prognostic criteria. Given the genetic complexity of breast carcinomas, it is not surprising that correlations with individual genetic abnormalities have also been disappointing. The use of gene expression profiles could result in more accurate and objective prognostication.

RESULTS

To this end, we used real-time quantitative RT-PCR assays to quantify the mRNA expression of a large panel (n = 47) of genes previously identified as candidate prognostic molecular markers in a series of 100 ERalpha-positive breast tumor samples from patients with known long-term follow-up. We identified a three-gene expression signature (BRCA2, DNMT3B and CCNE1) as an independent prognostic marker (P = 0.007 by univariate analysis; P = 0.006 by multivariate analysis). This "poor prognosis" signature was then tested on an independent panel of ERalpha-positive breast tumors from a well-defined cohort of 104 postmenopausal breast cancer patients treated with primary surgery followed by adjuvant tamoxifen alone: although this "poor prognosis" signature was associated with shorter relapse-free survival in univariate analysis (P = 0.029), it did not persist as an independent prognostic factor in multivariate analysis (P = 0.27).

CONCLUSION

Our results confirm the value of gene expression signatures in predicting the outcome of breast cancer.

Co-expression of de novo DNA methyltransferases Dnmt3a2 and Dnmt3L in gonocytes of mouse embryos

In mouse male germ cells, global DNA methylation occurs in gonocytes at 16-18 days postcoitum. In the present study, we examined which de novo-type DNA methyltransferase, Dnmt3a, Dnmt3a2 or Dnmt3b is expressed in gonocytes at these stages. Immuno-histochemical and Western blot analyses revealed that Dnmt3a2 was the major DNA methyltransferase expressed in gonocytes at 14-18 day postcoitum. Dnmt3L, which is necessary for spermatogenesis, was co-expressed in gonocytes at identical stages to Dnmt3a2. On the other hand, Dnmt3a was expressed not in germ cells but in the Sertoli cells and connective tissue cells that surround gonocytes and spermatogonia. Dnmt3b2, an isoform of Dnmt3b, was expressed faintly but significantly in gonocytes at 16 days postcoitum, and increased in spermatogonia at 4 and 6 days postpartum. The expression of Dnmt3a2, Dnmt3L, and Dnmt3b2 at 14-18 dpc was confirmed by reverse transcriptase-coupled polymerase chain reaction amplification and nucleotide sequencing of the amplified fragments. The results strongly suggest that Dnmt3a2 and Dnmt3L are responsible for the global DNA methylation in mouse male germ cells.

Effects of trichostatin a, a histone deacetylase inhibitor, on mouse gonadal development in vitro

Sry, Sox9 and M33 are thought to act as architectural transcription factors or as a chromatin regulator in gonadal development. However, the direct relationship between chromatin structure and sex determination has not yet been revealed. To clarify the effect of chromatin structural change on gonadal development, we examined the effects of trichostatin A, a histone deacetylase inhibitor, on mouse gonadal development in vitro. In the 0.1 microM treated testicular explants, the size of the gonad was significantly decreased, although the testicular cord formation occurred normally. In the 1.0 microM treated explants, the gonads revealed one or two large testicular cords. Sox9 and MIS expressions suggest that Sertoli cell differentiation is induced normally within the testicular cord, while Dnmt3b expression suggests that several immature Sertoli cells are located on the outside of the testicular cord. The 3beta-hsd expression indicates that Leydig cell differentiation occurs normally. On the other hand, germ cell loss was observed in the treated testicular explants. In the treated ovarian explants, the number of premeiotic germ cells was reduced without gonadal size change. Thus, trichostatin A affects the development of germ cells, but does not affect sex determination.

Hypermethylation of the inducible nitric-oxide synthase gene promoter inhibits its transcription

Exuberant generation of nitric oxide (NO) by inducible nitric-oxide synthase (iNOS) can cause unintended injury to host cells during glomerulonephritis and other inflammatory diseases. Although much is known about the mechanisms of iNOS induction, few transcriptional repression mechanisms have been found. We explored the role of cytosine methylation in the regulation of iNOS transcription. Treatment of mesangial cells with DNA methylation inhibitors augmented cytokine induction of endogenous NO production and iNOS protein levels, as well as iNOS promoter activity. In a corresponding manner, in vitro methylation of the murine iNOS promoter was sufficient to silence its activity in mesangial cells. In contrast, antisense knockdown of DNA methyltransferase-3b expression and activity increased iNOS promoter activity and nitrite production. Bisulfite treatment and sequencing analysis of the iNOS promoter identified methylation of cytosines framing an enhancer element at -879/-871. In vitro methylation inhibited binding of NFkappaB p50 to this element, and deletion of the element resulted in relief of transcriptional repression. These results provide evidence for a unique molecular mechanism involved in transcriptional regulation of iNOS gene expression.

Alterations in gene expression associated with the overexpression of a splice variant of DNA methyltransferase 3b, DNMT3b4, during human hepatocarcinogenesis

PURPOSE

Overexpression of a splice variant of DNA methyltransferase 3b, DNMT3b4, correlates significantly with DNA hypomethylation in pericentromeric satellite regions, which is known to result in centromeric decondensation and enhanced chromosomal recombination in precancerous conditions and hepatocellular carcinomas (HCCs). We aimed to elucidate further the significance of DNMT3b4 during human hepatocarcinogenesis.

METHODS

DNMT3b4-transfected human epithelial 293 cells were characterized using growth rate measurements, gene expression microarray, and quantitative reverse transcription-polymerase chain reaction (RT-PCR) analyses. RT-PCR was also performed on eight normal liver specimens, 45 noncancerous liver specimens showing chronic hepatitis or cirrhosis, which are considered to be precancerous conditions, and 56 HCCs.

RESULTS

The growth rate of the DNMT3b4 transfectants was about double that of mock-transfectants. Induction of signal transducer and activator of transcription 1 (STAT1), an effector of interferon signaling, and of a set of downstream genes implicated in such signaling, was observed in the DNMT3b4 transfectants. There was significant correlation between the mRNA expression levels of DNMT3b4 and STAT1 in HCCs. mRNA expression levels of STAT1 and the three downstream genes examined were all significantly elevated in the chronic hepatitis and cirrhosis specimens compared with the normal liver specimens. Among the HCCs, the mRNA expression levels of STAT1 and the downstream genes were higher in tumors without portal vein involvement than in more malignant HCCs with portal vein involvement. Significant correlations between the mRNA expression levels of STAT1 and each of the downstream genes were observed in the tissue samples.

CONCLUSIONS

Overexpression of DNMT3b4 is involved in human hepatocarcinogenesis, even at the precancerous stages, not only by inducing chromosomal instability but also by affecting the expression of specific genes.

Psychostimulant Alters Expression of DNA Methyltransferase mRNA in the Rat Brain

Methamphetamine (MAP), the most frequently abused substance in Japan, causes severe drug dependence and psychosis, similar to schizophrenia. It is suggested that long-term alterations in gene expression is related to MAP-induced brain dysfunction, including dependence and psychosis. DNA (cytosine-5) methyltransferase (Dnmt), a methylating enzyme of cytosine residues on CpG-dinucleotides, plays an important role in X chromosome inactivation, genomic imprinting, and gene expression. Reelin is an extracellular matrix protein secreted by GABAergic interneurons. Heterozygous reeler mice that exhibit a 50% downregulation of reelin expression replicate the dendritic spine and GABAergic defects described in schizophrenia. DNA methylation plays an important role in the epigenetic modification of reelin expression. We previously found that MAP could alter expression of Dnmt1 mRNA in the rat brain. In this study, we examined the brain mRNA for Dnmt2 and reelin in MAP-treated Wistar rats. Acute MAP (4 mg/kg) treatment significantly decreased Dnmt2 mRNA by 27% to 39% in hippocampus dentate gyrus, CA1, and CA3 24 h after treatment, and significantly decreased reelin mRNA by 28% in frontal cortex 3 h after treatment. These results suggest that (1) MAP can alter DNA methylation as well as expression of genes in these brain regions, and (2) decrease in reelin mRNA in the frontal cortex is similar to heterozygous reeler mice, which might be related to schizophrenia-like psychotic symptoms of MAP psychosis.