CHARACTERIZATION OF THE MURINE FATTY-ACID TRANSPORT PROTEIN GENE AND ITS INSULIN-RESPONSE SEQUENCE

Fatty acid transport protein (FATP) was identified by expression cloni ng strategies (Schaffer, J. E., and Lodish, H. F. (1994) Cell 79, 427- 436) and shown by transfection analysis to catalyze the transfer of lo ng-chain fatty acids across the plasma membrane of cells. It is expres sed highly in tissues exhibiting rapid fatty acid metabolism such as s keletal muscle, heart, and adipose. FATP mRNA levels are down-regulate d by insulin in cultured 3T3-L1 adipocytes and up-regulated by nutrien t depletion in murine adipose tissue (Man, M. Z., Hui, T. Y., Schaffer , J. E., Lodish, H. F., and Bernlohr, D. A. (1996) Mol.. Endocrinol. 1 0, 1021-1028). To determine the molecular mechanism of insulin regulat ion of FATP transcription, we have isolated the murine FATP gene and i ts 5'-flanking sequences. The FATP gene spans similar to 16 kilobases and contains 13 exons, of which exon 2 is alternatively spliced. S1 nu clease and RNase protection assays revealed the presence of multiple t ranscription start sites; the DNA sequence upstream of the predominant transcription start sites lacks a typical TATA box. By transient tran sfection assays in 3T3-L1 adipocytes, the inhibitory action of insulin on FATP transcription was localized to a cis-acting element with the sequence 5'-TGTTTTC-3' from -1347 to -1353, This sequence is very simi lar to the insulin response sequence found in the regulatory region of other genes negatively regulated by insulin such as those encoding ph osphoenolpyruvate carboxykinase, tyrosine aminotransferase, and insuli n-like growth factor-binding protein 1. Fluorescence in situ hybridiza tion analysis revealed that the murine FATP gene is localized to chrom osome 8, band 8B3.3. Interestingly, this region of chromosome 8 contai ns a cluster of three other genes important for fatty acid homeostasis , lipoprotein lipase, the mitochondrial uncoupling protein 1 (UCP1) an d sterol regulatory element-binding protein 1. These results character ize the murine FATP gene and its insulin responsiveness as well as pre sent a framework for future studies of its role in lipid metabolism, o besity, and type II diabetes mellitus.