title: Adenosine and homocysteine together enhance TNF-mediated cytotoxicity but do not alter activation of nuclear factor-kappa B in L929 cells.
abstract: This paper shows that a combination of adenosine and homocysteine potentiates TNF-alpha-mediated cytotoxicity, but does not modulate activation of NF-kappa B transcription factor controlling the expression of various TNF-alpha-inducible genes. Adenosine and homocysteine at concentrations (1 mM each) that enhance TNF-alpha-induced cytotoxicity accumulate S-adenosyl-L-homocysteine (AdoHcy), a potent inhibitor of S-adenosyl-L-methionine-dependent methylation reactions. In addition, preloading L929 cells with AdoHcy resulted in enhanced responses to TNF-alpha, suggesting that AdoHcy potentiates TNF-alpha-induced cytotoxicity. Moreover, the combination of adenosine and homocysteine changed the dependency of the TNF-alpha-mediated cytolysis on reactive oxygen intermediates. In the absence of adenosine and homocysteine TNF-alpha-mediated cytotoxicity was inhibited by antioxidants such as butylated hydroxyanisole and pyrrolidine dithiocarbamate. In the presence of adenosine and homocysteine, however, TNF-alpha-mediated cytotoxicity is not inhibited by these antioxidants. A L929 subclone, defective in the respiratory chain, resisted the cytotoxic action of TNF-alpha, but was rendered TNF-alpha sensitive in the presence of adenosine and homocysteine. Unlike TNF-alpha-mediated cytotoxicity, the TNF-alpha-induced activation of NF-kappa B was inhibited by antioxidants regardless whether adenosine and homocysteine were present or absent in the culture medium. In conclusion, a combination of adenosine and homocysteine selectively modulates TNF-alpha-mediated cytotoxicity without changing the TNF-alpha-induced activation of NF-kappa B. Our results could facilitate the development of strategies that permit dissection of cytotoxic and gene-activating pathways.
authors.affiliation: German Cancer Research Center, Division of Immunochemistry, Heidelberg.
authors.forename: S
authors.initials: S
authors.lastname: Bergmann
authors.forename: V
authors.initials: V
authors.lastname: Shatrov
authors.forename: F
authors.initials: F
authors.lastname: Ratter
authors.forename: S
authors.initials: S
authors.lastname: Schiemann
authors.forename: K
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: V
authors.initials: V
authors.lastname: Lehmann
mesh_terms: D000241:Adenosine / Q000008:administration & dosage*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004357:Drug Synergism; D006710:Homocysteine / Q000008:administration & dosage*; D066298:In Vitro Techniques; D008745:Methylation; D016328:NF-kappa B / Q000378:metabolism*; D017382:Reactive Oxygen Species; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage*
chemical_list: D016328:NF-kappa B; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha; D006710:Homocysteine; D012435:S-Adenosylhomocysteine; D000241:Adenosine