Idiopathic pulmonary fibrosis (IPF) is a devastating lung disease that is characterized by excessive proliferation of fibroblasts. The lipid mediator prostaglandin E 2 (PGE 2 ) has the capacity to limit fibrosis through its inhibition of numerous functions of these fibroblasts; however, in the setting of fibrosis, fibroblasts have been shown to be resistant to PGE 2 . We have linked such resistance to decreased expression levels of the E prostanoid 2 (EP2) receptor. In this study, in fibroblasts from both mice and humans with pulmonary fibrosis, we show that DNA hypermethylation is responsible for diminished EP2 expression levels and PGE 2 resistance. Bisulfite sequencing of the prostaglandin E receptor 2 gene (PTGER2) promoter revealed that fibrotic fibroblasts exhibit greater PTGER2 methylation than nonfibrotic control cells. Treatment with the DNA methylation inhibitors 5-aza-2-deoxycytidine and zebularine as well as DNA methyltransferase-specific siRNA decreased PTGER2 methylation, increased EP2 mRNA and protein expression levels, and restored PGE 2 responsiveness in fibrotic fibroblasts but not in nonfibrotic controls. PTGER2 promoter hypermethylation was driven by an increase in Akt signal transduction. In addition to results described for the PTGER2 promoter, fibrotic fibroblasts also exhibited increased global DNA methylation. These findings demonstrate that the down-regulation of PTGER2 and consequent PGE 2 resistance are both mediated by DNA hypermethylation; we identified increased Akt signal transduction as a novel mechanism that promotes DNA hypermethylation during fibrogenesis. (Am J
Although alterations in DNA methylation patterns have been associated with specific diseases and environmental exposures, the mediators and signaling pathways that direct these changes remain understudied. The bioactive lipid mediator prostaglandin E(2) (PGE(2)) has been shown to exert a myriad of effects on cell survival, proliferation, and differentiation. Here, we report that PGE(2) also signals to increase global DNA methylation and DNA methylation machinery in fibroblasts. HumanMethylation27 BeadChip array analysis of primary fetal (IMR-90) and adult lung fibroblasts identified multiple genes that were hypermethylated in response to PGE(2). PGE(2), compared with nontreated controls, increased expression and activity (EC(50)∼10(7) M) of one specific isoform of DNA methyltransferase, DNMT3a. Silencing of DNMT3a negated the ability of PGE(2) to increase DNMT activity. The increase in DNMT3a expression was mediated by PGE(2) signaling via its E prostanoid 2 receptor and the second messenger cAMP. PGE(2), compared with the untreated control, increased the expression and activity of Sp1 and Sp3 (EC(50)∼3×10(7) M), transcription factors known to increase DNMT3a expression, and inhibition of these transcription factors abrogated the PGE(2) increase of DNMT3a expression. These findings were specific to fibroblasts, as PGE(2) decreased DNMT1 and DNMT3a expression in RAW macrophages. Taken together, these findings establish that DNA methylation is regulated by a ubiquitous bioactive endogenous mediator. Given that PGE(2) biosynthesis is modulated by environmental toxins, various disease states, and commonly used pharmacological agents, these findings uncover a novel mechanism by which alterations in DNA methylation patterns may arise in association with disease and certain environmental exposures.
A gold(I) N-heterocyclic carbene complex catalyzes the intermolecular hydration of allenes to form allylic alcohols in modest yield with selective delivery of water to the terminal carbon atoms of the allenyl moiety.
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