Studies on intracellular lipid droplet-associated proteins : Its regulatory mechanism and clinical application

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Adipose differentiation-related protein (ADRP) is an intracellular, lipid droplet-associated protein, being expressed ubiquitously including hepatocytes and macrophages, and is involved in intracellular lipid accumulation. Phorbol ester (PMA) stimulated ADRP expression in mouse macrophage RAW264.7 cells. PMA also stimulated ADRP promoter activity in this cell line, and the responsible promoter region was identified between -2090 and -2005bp. When mutations were introduced into the PU.1/AP-1 composite element in this region, the promoter activity decreased. Using gel mobility shift analyses (EMSA), PU.1 as well as AP-1 were shown to bind conjointly bind to this element. On the other hand, PPARγ ligands such as troglitazone stimulated ADRP expression in mouse hepatocyte NMuLi cells. The effect of PPARγ ligands was also mediated by the PU.1/AP-1 element, since mutations in this element decreased the effect. In EMSA complex formation by AR-1 with this element increased when nuclear extracts from troglitazone-treated NMuLi cells were used. A P13 kinase inhibitor, but not inhibitors of MEK and PKC, inhibited troglitazone-induced expression of the ADRP mRNA., thus indicating that PPARγ ligands stimulated AR-1 transcriptional activity through P13 kinase. All these results indicated that the ADRP gene is regulated differently through the same enhancer in the promoter.