Activation of gene expression by hypolipidemic peroxisome proliferators (e.g. native and substituted long chain fatty acids, aryloxyalkanoic fibrate drugs) is accompanied by transcriptional suppression of liver transferrin gene in treated animals or human hepatoma cell line. Transcriptional suppression of liver transferrin by hypolipidemic peroxisome proliferators results from (a) displacement of hepatic nuclear factor (HNF)-4 from the transferrin promoter by nonproductive binding of the

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... ome proliferator-activated receptor-retinoic acid X receptor heterodimer to the (؊76/ ؊52) PRI promoter element of the human transferrin gene and (b) suppression of liver HNF-4 gene expression by hypolipidemic peroxisome proliferators with a concomitant decrease in its availability for binding to the transferrin PRI promoter element. HNF-4 gene suppression and its displacement from the transferrin promoter result in eliminating HNF-4-enhanced transcription of transferrin. Liver transferrin suppression by hypolipidemic peroxisome proliferators may result in reduced iron availability as well as modulation of transferrininduced differentiation processes. Transcriptional suppression of HNF-4-enhanced liver genes (e.g. apolipoprotein C-III, transferrin) may complement the pleiotropic biological effect exerted by hypolipidemic peroxisome proliferators.