Abstract
The adipose differentiation-related protein (ADFP)/adipophilin belongs to a family of PAT (for perilipin, ADFP, and TIP47) proteins that associate on the surface of lipid droplets (LDs). Except for LD association, a clear role for ADFP has not been found. We demonstrate that ADFP is transcriptionally regulated by peroxisome proliferator-activated receptor alpha (PPARalpha) in mouse liver and rat and human hepatoma cells through a highly conserved direct repeat-1(DR-1) element. Although the ADFP mRNA is highly increased by a synthetic PPARalpha agonist, the ADFP protein is only substantially increased in cells containing LDs, such as hepatocytes incubated with fatty acids, and in livers of fasted mice. ADFP is induced by fasting even in the absence of a functional PPARalpha, in marked contrast to the PPARalpha target gene acyl-coenzyme A oxidase-1. Activation of LXRs, which stimulates LD formation through the activation of lipogenesis, does not affect ADFP mRNA levels. TIP47, another PAT member known to be expressed in liver, was unaffected by all treatments. This constitutively expressed PAT member seems to be less transcriptionally regulated than ADFP. These observations suggest that ADFP is primarily a fasting-induced protein in liver that coats the newly synthesized triacylglycerol-containing LDs formed during fasting.
Highlights
The adipose differentiation-related protein (ADFP)/adipophilin belongs to a family of PAT proteins that associate on the surface of lipid droplets (LDs)
Expression of ADFP mRNA is induced by a synthetic peroxisome proliferator-activated receptor a (PPARa) agonist in rat hepatoma 7800-C1 cells
The same was observed for the two characterized PPARa target genes acyl-coenzyme A oxidase-1 (ACO-1) [45] and cytosolic malic enzyme-1 (ME-1) [46, 47]
Summary
The adipose differentiation-related protein (ADFP)/adipophilin belongs to a family of PAT (for perilipin, ADFP, and TIP47) proteins that associate on the surface of lipid droplets (LDs). Vimentin [4], perilipin [5, 6], and mouse adipose differentiation-related protein (ADFP; adipophilin in humans) [7] were the first proteins experimentally demonstrated to associate with the LD surface. This cellular location was more recently experimentally confirmed for tailinteracting protein of 47 kDa (TIP47) [8, 9] and S3-12 [10]. When cloned, ADFP was thought to be preferentially expressed in adipocytes, with increasing mRNA expression during adipocyte differentiation [20]
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