Functional analysis of peroxisome-proliferator-responsive element motifs in genes of fatty acid-binding proteins.
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 PPARalpha 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, PPARalpha, PPARgamma1 and PPARgamma2 to A (adipocyte-type)-FABP-PPRE. All PPAR/RXR heterodimers transactivate L-FABP-PPRE, best are combinations of PPARalpha with RXRalpha or RXRgamma. In contrast, PPARalpha heterodimers do not transactivate A-FABP-PPRE, best combinations are of PPARgamma1 with RXRalpha and RXRgamma, and of PPARgamma2 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, C2C12 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.
Schachtrup
Christian
C
Department of Biochemistry, University of Münster, Wilhelm-Klemm-Str. 2, 48149 Münster, Germany.
Emmler
Tanja
T
Bleck
Bertram
B
Sandqvist
Anton
A
Spener
Friedrich
F
D000818:Animals; D001482:Base Composition / Q000502:physiology; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D004247:DNA / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D050556:Fatty Acid-Binding Proteins; D005786:Gene Expression Regulation / Q000502:physiology; D005796:Genes / Q000502:physiology*; D017930:Genes, Reporter / Q000235:genetics; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000473:pathology; D051379:Mice; D032446:Myoblasts / Q000737:chemistry / Q000378:metabolism; D047492:Peroxisome Proliferator-Activated Receptors / Q000378:metabolism / Q000502:physiology; D020025:Peroxisome Proliferators / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000502:physiology; D020218:Response Elements / Q000502:physiology*; D047488:Retinoid X Receptors / Q000378:metabolism / Q000502:physiology; D015533:Transcriptional Activation / Q000235:genetics / Q000502:physiology
D002352:Carrier Proteins; C493319:FABP1 protein, human; C493412:FABP5 protein, human; C493320:Fabp1 protein, mouse; D050556:Fatty Acid-Binding Proteins; D047492:Peroxisome Proliferator-Activated Receptors; D020025:Peroxisome Proliferators; D047488:Retinoid X Receptors; D004247:DNA