Functional analysis of peroxisome-proliferator-responsive element motifs in genes of fatty acid-binding proteins

Abstract

Retinoic acids and long-chain fatty acids are lipophilic agonists of nuclear receptors such as RXRs (retinoic X receptors) and PPARs (peroxisome-proliferator-activated receptors) respectively. These agonists are also ligands of intracellular lipid-binding proteins, which include FABPs (fatty acid-binding proteins). We reported previously that L (liver-type)-FABP targets fatty acids to the nucleus of hepatocytes and affects PPARα activation, which binds together with an RXR subtype to a PPRE (peroxisome-proliferator-responsive element). In the present study, we first determined the optimal combination of murine PPAR/RXR subtypes for binding to known murine FABP-PPREs and to those found by computer search and then tested their in vitro functionality. We show that all PPARs bind to L-FABP-PPRE, PPARα, PPARγ 1 and PPARγ 2 to A (adipocyte-type)-FABP-PPRE. All PPAR/RXR heterodimers transactivate L-FABP-PPRE, best are combinations of PPARα with RXRα or RXRγ . In contrast, PPARα heterodimers do not transactivate A-FABP-PPRE, best combinations are of PPARγ 1 with RXRα and RXRγ , and of PPARγ 2 with all RXR subtypes. We found that the predicted E (epidermal-type)-and H (heart-type)-FABP-PPREs are not activated by any PPAR/RXR combination without or with the PPAR pan-agonist bezafibrate. In the same way, C 2 C 12 myoblasts transfected with promoter fragments of E-FABP and H-FABP genes containing putative PPREs are also not activated through stimulation of PPARs with bezafibrate applied to the cells. These results demonstrate that only PPREs of L-and A-FABP promoters are functional, and that binding of PPAR/RXR heterodimers to a PPRE in vitro does not necessarily predict transactivation.

A‐FABP, a candidate progression marker of human transitional cell carcinoma of the bladder, is differentially regulated by PPAR in urothelial cancer cells

“…39 However, the molecular mechanism for the up-regulation of A-FABP by PPARg has not been addressed and functional PPRE has not been identified in the promoter of human A-FABP. Sequence analysis showed that there was no PPRE-like motif in human A-FABP promoter.…”

Maternal dietary omega-3 fatty acids and placental function

“…Once activated, PPARs form heterodimers with retinoic acid X receptor; this complex then binds to the PPAR-response element (PPRE) in the promoter region of target genes to drive their expression. PPREs have been identified in the promoter regions of genes encoding fatty acid transport proteins (Frohnert et al 1999, Schachtrup et al 2004. Accordingly, oral supplementation of a PPARg agonist, rosiglitazone, has been shown to increase placental mRNA expression of Fabppm, Fat (Cd36), Fatp1, and Fatp4 in mice, although Fatp2, Fatp3, and Fatp6 were reduced (Schaiff et al 2007).…”

Differentiation of Human Circulating Fibrocytes as Mediated by Transforming Growth Factor-β and Peroxisome Proliferator-activated Receptor γ

“…PPAR␥ is well documented as a critical transcription factor in the regulation of adipogenic differentiation. Upon activation, PPAR␥ binds to common consensus PPRE sites on promoters of specific adipocyte genes in the nucleus, including that of aP2 (15,18). aP2 is often used as a mature adipocyte marker because its expression parallels the degree of adipogenic differentiation.…”

“…troligtazone), PPAR␥ becomes activated and forms a heterodimer with RXR␣ (13,14). The complex then translocates to the nucleus and binds to specific PPAR response elements (PPREs) in the promoter region of its target genes, such as aP2, and contributes to differentiation (15).…”