Abstract
Global DNA hypomethylation in CD4+ cells in systemic lupus erythematosus (SLE) was suggested to play a key role in the pathogenesis. To identify new methylation-sensitive genes, we integrated genome-wide DNA methylation and mRNA profiling data in CD4+ cells of MRL/lpr (MRL) and C57BL6/J (B6) mice. We identified Cathepsin E (Ctse), in which 13 methyl-CpGs within 583 bp region of intron 1 were hypomethylated, and Ctse mRNA upregulated in MRL compared with B6 mice. One of methyl-CpGs, mCGCG was 93.3 ± 2.05% methylated in B6 mice, while 80.0 ± 6.2% methylated and mutated to CGGG in MRL mice. Kaiso is known to bind to mCGCG and we hypothesized that it represses expression of Ctse in B6 mice. The binding of Kaiso to mCGCG site in B6 mice was reduced in MRL mice revealed by ChIP-PCR. EL4 cells treated with 5-azaC and/or Trichostatin A showed the suppression of binding of Kaiso to mCGCG motif by ChIP-PCR and the overexpression of Ctse was demonstrated by qPCR. Ctse gene silencing by siRNA in EL4 cells resulted in reduction of IL-10 secretion. The hypomethylation of mCGCG motif, reduced recruitment of Kaiso, and increased expression of Ctse and Il-10 in CD4+ cells may be involved in the pathogenesis of SLE.
Highlights
We previously demonstrated that hypomethylation of a CpG within cAMP response element (CRE) motif links to increased expression of PP2Acα in T cells derived from the patients with SLE9
We found that knockdown of cathepsin E (Ctse) gene in cultured EL4 cells resulted in decreased production of IL-10 and that up-regulated expression of IL-10 was observed in CD4+ T cells isolated from MRL mice compared with B6 mice
Since RNA sequence data demonstrated most abundant and highly up-regulated expression and of Ctse in splenic CD4+ T cells from MRL mice, we investigated the expression of Ctse in immune-mediated cells
Summary
We previously demonstrated that hypomethylation of a CpG within cAMP response element (CRE) motif links to increased expression of PP2Acα in T cells derived from the patients with SLE9. To identify the putative methylation-sensitive genes involved in the pathogenesis of SLE, we performed the integration analysis of genome-wide DNA methylation and global mRNA profiling in CD4+ T cells purified from spleen of MRL and compared with B6 mice. We demonstrate that Kaiso directly binds to mCGCG site in intron 1 of Ctse gene in methyl-CpG-dependent manner and represses the transcriptional activity of Ctse in B6 mice, while the demethylation and mutation of mCGCG to CGGG caused the reduced binding of Kaiso and up-regulated expression of Ctse. Because of its B cell-promoting effects, T cell-derived IL-10 may contribute to autoantibody production and tissue damage in SLE In this communication, we postulate that Ctse represents a new methylation-sensitive gene, like previously recognized CD70, CD40L and CD11a15, contributes to the pathogenesis of SLE
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