Mechanism of action of bicyclic imidazoles defines a translational regulatory pathway for tumor necrosis factor alpha.
Expression of tumor necrosis factor alpha (TNF) by lipopolysaccharide-treated human monocytic cells is inhibited by bicyclic imidazoles. We studied the mechanism of action of a representative inhibitor, SK&F 86002, on synthesis of TNF by THP-1 cells. Levels of TNF protein were lowered by SK&F 86002 under conditions where TNF mRNA accumulation was unaffected, suggesting a post-transcriptional action. No effect of SK&F 86002 was detected on the rate of induction of TNF mRNA or steady state levels over a 5 hr period. The kinetics of SK&F 86002 inhibition of TNF protein synthesis coincided with those of anisomycin, not with actinomycin, suggesting an effect of SK&F 86002 on TNF mRNA translation. By using sucrose gradient sedimentation, we showed that quiescent THP-1 cells contained a substantial amount of TNF mRNA which was primarily associated with 43S pre-ribosomal complexes. Activation of the cells with lipopolysaccharide caused an elevation of the TNF mRNA level and increased the proportion associated with polyribosomes. Treatment with lipopolysaccharide plus SK&F 86002 led to a marked accumulation of TNF mRNA in the 43S complex-containing fractions and a concomitant reduction of polysome-associated TNF message. Neither lipopolysaccharide nor SK&F 86002 affected the amount or distribution of cyclophilin mRNA in the same fractions. The results suggest that lipopolysaccharide activates TNF translation at the initiation step and that SK&F 86002 inhibits this activation.
Prichett
W
W
Department of Cellular Biochemistry, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406, USA.
Hand
A
A
Sheilds
J
J
Dunnington
D
D
D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D001483:Base Sequence; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D017077:Culture Media, Conditioned; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D007700:Kinetics; D008969:Molecular Sequence Data; D009000:Monocytes / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects*; D012333:RNA, Messenger; D012270:Ribosomes; D013844:Thiazoles / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000235:genetics*
D000894:Anti-Inflammatory Agents, Non-Steroidal; D017077:Culture Media, Conditioned; D007093:Imidazoles; D012333:RNA, Messenger; D013844:Thiazoles; D014409:Tumor Necrosis Factor-alpha; C052026:6-(4-fluorophenyl)-2,3-dihydro-5-(4-pyridinyl)imidazo(2,1-b)thiazole