DNA methylation contributes to the tissue-specific expression of the rPL-Iv gene

Altered DNA methylation and Dnmt expression in obese uterus may cause implantation failure

Obesity is defined by increased adipose tissue volume and has become a major risk factor for reproduction. Recent studies have revealed a substantial link between obesity and epigenetics. The epigenome is dynamically regulated mainly by DNA methylation. DNA methylation, which is controlled by DNA methyltransferases (Dnmts), has been widely studied because it is essential for imprinting and regulation of gene expression. In our previous study, we showed that the levels of Dnmt1, Dnmt3a and global DNA methylation was dramatically altered in the testis and ovary of high-fat diet (HFD)-induced obese mice. However, the effect of HFD on Dnmts and global DNA methylation in mouse uterus has not yet been demonstrated. Therefore, in the present study, we aimed to evaluate the effect of HFD on the level of Dnmt1, Dnmt3a, Dnmt3b, Dnmt3l and global DNA methylation in uterus. Our results showed that HFD significantly altered the levels of Dnmts and global DNA methylation in the uterus. The total expression of Dnmt1, Dnmt3a and Dnmt3b was significantly upregulated, while level of Dnmt3l and global DNA methylation were dramatically decreased (p < 0.05). Furthermore, we observed that the expression of Dnmt3b and Dnmt3l was significantly increased in endometrium including gland and epithelium (p < 0.05). Although Dnmt3b was the only protein whose expression significantly increased, the level of global DNA methylation and Dnmt3l significantly decreased in stroma and myometrium (p < 0.05). In conclusion, our results show for the first time that obesity dramatically alters global DNA methylation and expression of Dnmts, and decreased DNA methylation and Dnmt expression may cause abnormal gene expression, especially in the endometrium.

Epigenetic changes through DNA methylation contribute to uterine stromal cell decidualization

Embryo-uterine interaction during early pregnancy critically depends on the coordinated expression of numerous genes at the site of implantation. The epigenetic mechanism through DNA methylation (DNM) plays a major role in the control of gene expression, although this regulatory event remains unknown in uterine implantation sites. Our analysis revealed the presence of DNA methyltransferase 1 (Dnmt1) in mouse endometrial cells on the receptive d 4 of pregnancy and early postattachment (d 5) phase, whereas Dnmt3a had lower abundant expression. Both Dnmt1 and Dnmt3a were coordinately expressed in decidual cells on d 6-8. 5-Methycytosine showed a similar expression pattern to that of Dnmt1. The preimplantation inhibition of DNM by 5-aza-2'-deoxycytodine was not antagonistic for embryonic attachment, although endometrial stromal cell proliferation at the site of implantation was down-regulated, indicating a disturbance with the postattachment decidualization event. Indeed, the peri- or postimplantation inhibition of DNM caused significant abrogation of decidualization, with concomitant loss of embryos. We next identified decidual genes undergoing alteration of DNM using methylation-sensitive restriction fingerprinting. One such gene, Chromobox homolog 4, an epigenetic regulator in the polycomb group protein family, exhibited hypomethylation in promoter DNA and increased expression with the onset of decidualization. Furthermore, inhibition of DNM resulted in enhanced expression of hypermethylated genes (Bcl3 and Slc16a3) in the decidual bed as compared with control, indicating aberration of gene expression may be associated with DNM-inhibition-induced decidual perturbation. Overall, these results suggest that uterine DNM plays a major role for successful decidualization and embryo development during early pregnancy.

Transcriptional and epigenetic regulation of KIAA1199 gene expression in human breast cancer

Emerging evidence has demonstrated that upregulated expression of KIAA1199 in human cancer bodes for poor survival. The regulatory mechanism controlling KIAA1199 expression in cancer remains to be characterized. In the present study, we have isolated and characterized the human KIAA1199 promoter in terms of regulation of KIAA1199 gene expression. A 3.3 kb fragment of human genomic DNA containing the 5′-flanking sequence of the KIAA1199 gene possesses both suppressive and activating elements. Employing a deletion mutagenesis approach, a 1.4 kb proximal region was defined as the basic KIAA1199 promoter containing a TATA-box close to the transcription start site. A combination of 5′-primer extension study with 5′RACE DNA sequencing analysis revealed one major transcription start site that is utilized in the human KIAA1199 gene. Bioinformatics analysis suggested that the 1.4 kb KIAA1199 promoter contains putative activating regulatory elements, including activator protein-1(AP-1), Twist-1, and NF-κB sites. Sequential deletion and site-direct mutagenesis analysis demonstrated that the AP-1 and distal NF-κB sites are required for KIAA1199 gene expression. Further analyses using an electrophoretic mobility-shift assay and chromatin immunoprecipitation confirmed the requirement of these cis- and trans-acting elements in controlling KIAA1199 gene expression. Finally, we found that upregulated KIAA1199 expression in human breast cancer specimens correlated with hypomethylation of the regulatory region. Involvement of DNA methylation in regulation of KIAA1199 expression was recapitulated in human breast cancer cell lines. Taken together, our study unraveled the regulatory mechanisms controlling KIAA1199 gene expression in human cancer.

DNA methylation of intronic enhancers directs tissue-specific expression of steroidogenic factor 1/adrenal 4 binding protein (SF-1/Ad4BP)

The nuclear receptor steroidogenic factor 1/adrenal 4 binding protein (SF-1/Ad4BP) is an essential regulator of endocrine development and function, and the expression of the corresponding gene (sf-1/ad4bp) is precisely regulated in a time- and tissue-dependent manner. We previously demonstrated that the basal promoter of sf-1/ad4bp is controlled by DNA methylation and that its methylation status reflects the expression pattern of SF-1/Ad4BP. Recently, three intronic enhancers were identified in the sf-1/ad4bp gene that target SF-1/Ad4BP expression to the fetal adrenal (FAdE; fetal adrenal-specific enhancer), to pituitary gonadotropes (PGE; pituitary gonadotrope-specific enhancer), and to the ventromedial hypothalamic nucleus (VMHE; ventromedial hypothalamic nucleus-specific enhancer). Here, we demonstrate that the activity of these enhancers is correlated with their DNA methylation status. We show that they are hypomethylated in tissues where they are active and generally hypermethylated in tissues where they are not active. Furthermore, we demonstrate in transient transfection experiments that forced DNA methylation represses reporter gene activity driven by these enhancers. These data directly demonstrate a functional significance for the enhancers' methylation status. Intriguingly, further analyses of the basal promoter in gonadotropes revealed that it is methylated in these cells, in contrast to other SF-1/Ad4BP-expressing tissues. Consistent with this, sf-1/ad4bp is transcribed from an alternative promoter in gonadotropes. Taken together, our experiments show that the tissue-specific expression of SF-1/Ad4BP is epigenetically regulated and identify tissue-specific differentially methylated regions within the sf-1/ad4bp locus that are essential for its transcriptional control.