Identification of a functional peroxisome proliferator-responsive element in the murine fatty acid transport protein gene

Fatty acid transport protein (FATP), a plasma membrane protein implicated i n controlling adipocyte transmembrane fatty acid flux, is up-regulated as a consequence of adipocyte differentiation and down-regulated by insulin, Ba sed upon the sequence of the FATP gene upstream region (Hui, T. Y,, Frohner t, B. I., Smith, A. J., Schaffer, J. A, and Bernlohr, D, A, (1998) J. Biol, Chem. 273, 27420-27429) a putative peroxisome proliferator-activated recep tor response element (PPRE) is present from -458 to -474. To determine whet her the FATP PPRE was functional, and responded to lipid activators, transi ent transfection of FATP-luciferase reporter constructs into CV-1 and 3T3-L 1 cells was carried out. In CV-1 cells, FATP-luciferase activity was up-reg ulated 4- and 5.5-fold, respectively, by PPAR alpha and PPAR gamma in the p resence of their respective activators in a PPRE-dependent mechanism. PPAR delta, however, was unable to mediate transcriptional activation under any condition. In 3T3-L1 cells, the PPRE conferred a small but significant incr ease in expression in preadipocytes, as well as a more robust up-regulation of FATP expression in adipocytes. Furthermore, the PPRE conferred the abil ity for luciferase expression to be up-regulated by activators of both PPAR gamma and retinoid X receptor alpha (RXR alpha) in a synergistic manner. P PAR alpha and PPAR delta activators did not up-regulate FATP expression in 3T3-L1 adipocytes, however, suggesting that these two subtypes do not play a significant role in differentiation-dependent activation in fat cells. El ectromobility shift assays showed that all three PPAR subtypes were able to bind specifically to the PPRE as heterodimers with RXR alpha. Nuclear extr acts from 3T3-L1 adipocytes also showed a specific gel-shift complex with t he FATP PPRE. To correlate the expression of FATP to its physiological func tion, treatment of 3T3-L1 adipocytes with PPAR gamma and RXR alpha activato rs resulted in an increased uptake of oleate. Moreover, linoleic acid, a ph ysiological ligand, up-regulated FATP expression 2-fold in a PPRE-dependent manner. These results demonstrate that the FATP gene possesses a functiona l PPRE and is up-regulated by activators of PPAR alpha and PPAR gamma, ther eby linking the activity of the protein to the expression of its gene. More over, these results have implications for the mechanism by which certain PP AR gamma activators such as the antidiabetic thiazolidinedione drugs affect adipose lipid metabolism.