Inhibition of lipopolysaccharide-stimulated TNF-alpha promoter activity by S-adenosylmethionine and 5'-methylthioadenosine.
S-adenosylmethionine (SAM) is the principal biological methyl donor and precursor for polyamines. SAM is known to be hepatoprotective in many liver disease models in which TNF-alpha is implicated. The present study investigated whether and how SAM inhibited LPS-stimulated TNF-alpha expression in Kupffer cells (hepatic macrophages). SAM downregulated TNF-alpha expression in LPS-stimulated Kupffer cells at the transcriptional level as suggested by a transfection experiment with a TNF-alpha promoter-reporter gene. This inhibition was not mediated through decreased NF-kappaB binding to four putative kappaB binding elements located within the promoter. The inhibited promoter activity was neither prevented by overexpression of p65 and/or its coactivator p300 nor enhanced by overexpression of coactivator-associated arginine methyltransferase-1, an enzyme that methylates p300 and inhibits a p65-p300 interaction. SAM did not lead to DNA methylation at the most common CpG target sites in the TNF-alpha promoter. Moreover, 5'-methylthioadenosine (MTA), which is derived from SAM but does not serve as a methyl donor, recapitulated SAM's effect with more potency. These data demonstrate that SAM inhibits TNF-alpha expression at the level downstream of NF-kappaB binding and at the level of the promoter activity via mechanisms that do not appear to involve the limited availability of p65 or p300. Furthermore, our study is the first to demonstrate a potent inhibitory effect on NF-kappaB promoter activity and TNF-alpha expression by a SAM's metabolite, MTA.
Veal
Nary
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Keck School of Medicine of the Univ. of Southern California, 1333 San Pablo St., MMR-402, Los Angeles, CA 90033, USA.
Hsieh
Chih-Lin
CL
Xiong
Shigang
S
Mato
Jose M
JM
Lu
Shelly
S
Tsukamoto
Hidekazu
H
D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D019175:DNA Methylation / Q000187:drug effects; D003839:Deoxyadenosines / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D050881:E1A-Associated p300 Protein; D007728:Kupffer Cells / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008715:Methionine / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects*; D011484:Protein-Arginine N-Methyltransferases / Q000378:metabolism; D012333:RNA, Messenger / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D012436:S-Adenosylmethionine / Q000008:administration & dosage / Q000494:pharmacology*; D013872:Thionucleosides / Q000494:pharmacology*; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000235:genetics*
D003839:Deoxyadenosines; D008070:Lipopolysaccharides; D016328:NF-kappa B; D009687:Nuclear Proteins; D012333:RNA, Messenger; D013872:Thionucleosides; D015534:Trans-Activators; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; C008500:5'-methylthioadenosine; D012436:S-Adenosylmethionine; D008715:Methionine; D011484:Protein-Arginine N-Methyltransferases; C119966:coactivator-associated arginine methyltransferase 1; D050881:E1A-Associated p300 Protein; C494362:Ep300 protein, rat