[Show abstract][Hide abstract] ABSTRACT: Inhibiting DNA methylation in CD4+ T cells causes aberrant gene expression and autoreactive monocyte/macrophage killing in vitro, and the hypomethylated cells cause a lupus-like disease in animal models. Similar decreases in T cell DNA methylation occur in idiopathic lupus, potentially contributing to disease pathogenesis. The genes affected by DNA hypomethylation are largely unknown. Using DNA methylation inhibitors and oligonucleotide arrays we have identified perforin as a methylation-sensitive gene. Our group has also reported that DNA methylation inhibitors increase CD4+ T cell perforin by demethylating a conserved methylation-sensitive region that is hypomethylated in primary CD8+ cells, which express perforin, but is largely methylated in primary CD4+ cells, which do not. As lupus T cells also have hypomethylated DNA and promiscuously kill autologous monocytes/macrophages, we hypothesized that perforin may be similarly overexpressed in lupus T cells and contribute to the monocyte killing. We report that CD4+ T cells from patients with active, but not inactive, lupus overexpress perforin, and that overexpression is related to demethylation of the same sequences suppressing perforin transcription in primary CD4+ T cells and demethylated by DNA methylation inhibitors. Further, the perforin inhibitor concanamycin A blocks autologous monocyte killing by CD4+ lupus T cells, suggesting that the perforin is functional. We conclude that demethylation of specific regulatory elements contributes to perforin overexpression in CD4+ lupus T cells. Our results also suggest that aberrant perforin expression in CD4+ lupus T cells may contribute to monocyte killing.
The Journal of Immunology 04/2004; 172(6):3652-61. DOI:10.4049/jimmunol.172.6.3652 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: DNA methylation is one mechanism of epigenetic gene regulation and influences gene expression by recruiting methylcytosine-binding proteins and/or inducing changes in chromatin structure. In mammals, DNA methylation is mediated by at least four DNA methyltransferase (Dnmt) enzymes, including Dnmt1, Dnmt2, Dnmt3a, and Dnmt3b. To understand fully how DNA methylation is involved in gene regulation, knowledge of Dnmt mRNA transcript levels is required, both as a surrogate measure of Dnmt protein levels and also to facilitate an understanding of the regulation of expression of the corresponding genes. Measurement of transcript levels has traditionally been achieved by Northern blot analysis and more recently either by the ribonuclease protection assay or by reverse-transcription polymerase chain reaction (RT-PCR), followed by agarose gel electrophoresis. In the past few years, a form of PCR has been developed that measures the accumulation of PCR product in real time. In conjunction with RT, real-time RT-PCR has become a widely accepted tool for measuring mRNA transcript levels and is now probably the method of choice. This technique is both sensitive and specific and allows for the rapid assessment of Dnmt mRNA transcript levels as well transcripts for other genes that may be involved in DNA methylation.
[Show abstract][Hide abstract] ABSTRACT: Perforin is a cytotoxic effector molecule expressed in NK cells and a subset of T cells. The mechanisms regulating its expression are incompletely understood. We observed that DNA methylation inhibition could increase perforin expression in T cells, so we examined the methylation pattern and chromatin structure of the human perforin promoter and upstream enhancer in primary CD4(+) and CD8(+) T cells as well as in an NK cell line that expresses perforin, compared with fibroblasts, which do not express perforin. The entire region was nearly completely unmethylated in the NK cell line and largely methylated in fibroblasts. In contrast, only the core promoter was constitutively unmethylated in primary CD4(+) and CD8(+) cells, and expression was associated with hypomethylation of an area residing between the upstream enhancer at -1 kb and the distal promoter at -0.3 kb. Treating T cells with the DNA methyltransferase inhibitor 5-azacytidine selectively demethylated this area and increased perforin expression. Selective methylation of this region suppressed promoter function in transfection assays. Finally, perforin expression and hypomethylation were associated with localized sensitivity of the 5' flank to DNase I digestion, indicating an accessible configuration. These results indicate that DNA methylation and chromatin structure participate in the regulation of perforin expression in T cells.
The Journal of Immunology 06/2003; 170(10):5124-32. DOI:10.4049/jimmunol.170.10.5124 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine whether hydralazine might decrease DNA methyltransferase (DNMT) expression and induce autoimmunity by inhibiting extracellular signal-regulated kinase (ERK) pathway signaling.
The effect of hydralazine on DNMT was tested in vitro using enzyme inhibition studies, and in vivo by measuring messenger RNA (mRNA) levels and enzyme activity. Effects on ERK, c-Jun N-terminal kinase, and p38 pathway signaling were tested using immunoblotting. Murine T cells treated with hydralazine or an ERK pathway inhibitor were injected into mice and anti-DNA antibodies were measured by enzyme-linked immunosorbent assay.
In vitro, hydralazine did not inhibit DNMT activity. Instead, hydralazine inhibited ERK pathway signaling, thereby decreasing DNMT1 and DNMT3a mRNA expression and DNMT enzyme activity similar to mitogen-activated protein kinase kinase (MEK) inhibitors. Inhibiting T cell ERK pathway signaling with an MEK inhibitor was sufficient to induce anti-double-stranded DNA antibodies in a murine model of drug-induced lupus, similar to the effect of hydralazine.
Hydralazine reproduces the lupus ERK pathway signaling abnormality and its effects on DNMT expression, and inhibiting this pathway induces autoimmunity. Hydralazine-induced lupus could be caused in part by inducing the same ERK pathway signaling defect that occurs in idiopathic lupus.