Abstract
Lymphocytes depend on transmethylation reactions for efficient activation and function. These reactions are primarily catalyzed by S-adenosylmethionine-dependent methyltransferases, which convert S-adenosylmethionine to S-adenosyl-l-homocysteine. S-adenosyl-l-homocysteine is then hydrolyzed by S-adenosyl-l-homocysteine hydrolase to prevent feedback inhibition of transmethylation reactions. By impeding S-adenosyl-l-homocysteine hydrolase, a build-up of S-adenosyl-l-homocysteine occurs, and most intracellular transmethylation reactions cease. Thus, a nontoxic inhibitor of this enzyme might be a useful immunosuppressive therapeutic agent. We identified a potent reversible type III inhibitor of S-adenosyl-l-homocysteine hydrolase, DZ2002 [methyl 4-(adenin-9-yl)-2-hydroxybutanoate], and determined its cytotoxic and immunologic effects. We demonstrated that DZ2002 blocked S-adenosyl-l-homocysteine hydrolase more effectively than a type I inhibitor, but cytotoxicity from DZ2002 was greatly reduced. Although DZ2002 did not prevent concanavalin A-induced T cell proliferation or interleukin (IL)-2 production, it significantly reduced both a mixed lymphocyte reaction and IL-12 production from in vitro-stimulated splenocytes. In addition, levels of CD80 and CD86 on human monocytic THP-1 cells were decreased in a dose-dependent manner in the presence of 0.1 to 10 μM DZ2002, and decreases were also seen in IL-12 and tumor necrosis factor-α production from both mouse thioglycollate-stimulated peritoneal macrophages and THP-1 cells. In vivo, DZ2002 significantly suppressed a delayed-type hypersensitivity reaction as well as antibody secretion. We conclude that DZ2002's immunosuppressive effects are likely not solely attributed to T cell inhibition but also to the obstruction of macrophage activation and function through reductions in cytokine output and/or T cell costimulation. These data suggest an important dual role for the S-adenosyl-l-homocysteine hydrolase in both macrophage and T cell function.
Footnotes
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This work was supported by Chinese National Natural Science Foundation Grant A30171086 and the Knowledge Innovation Program of Chinese Academy of Sciences Grant KSCX2-SW-202.
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doi:10.1124/jpet.104.080416.
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ABBREVIATIONS: AdoMet, S-adenosylmethionine; AdoHcy, S-adenosyl-l-homocysteine; DTH, delayed-type hypersensitivity; MDL-28,842, (Z)-5′-fluoro-4′,5′-didehydro-5′-deoxyadenosine; DHCaA, 9-[(1′R,2′S,3′R)-2′,3′-dihydroxycyclopent-4′-en-1-yl]adenine; IL, interleukin; LPS, lipopolysaccharide; TNF, tumor necrosis factor; DZ2002, methyl 4-(adenin-9-yl)-2-hydroxybutanoate; Con A, concanavalin A; SAC, Staphylococcus aureus Cowan strain I; MTT, 3-[4,5-dimethylthylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide; DNFB, 2,4-dinitrofluorobenzene; IFN, interferon; FBS, fetal bovine serum; TG, thioglycollate; DMSO, dimethyl sulfoxide; ELISA, enzyme-linked immunosorbent assay; QHS, quantitative hemolysis of sheep red blood cells; SRBC, sheep red blood cell; MLR, mixed lymphocyte reaction; APC, antigen-presenting cell.
- Received November 8, 2004.
- Accepted January 5, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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