The roles of sterol regulatory element-binding proteins in the transactivation of the rat ATP citrate-lyase promoter

ATP citrate-lyase (ACL) is a key enzyme supplying acetyl-CoA for fatty acid and cholesterol synthesis. Its expression is drastically up-regulated when an animal is fed a low fat, high carbohydrate diet after prolonged fasting . In this report, we describe the role of sterol regulatory element-binding proteins (SREBPs) in the transactivation of the rat ACL promoter. ACL prom oter activity was markedly stimulated by the overexpression of SREBP-1a and , to a lesser extent, by SREBP-2 in Alexander human hepatoma cells. The pro moter elements responsive to SREBPs were located within the 55-base pair se quences from -114 to -60. The gel mobility shift assay revealed four SREBP- 1a binding sites in this region. Of these four elements, the -102/-94 regio n, immediately upstream of the inverted Y-box, and the -70/-61 region, just adjacent to Sp1 binding site, played critical roles in SREBPs-mediated sti mulation. The mutation in the inverted Y-box and the coexpression of domina nt negative nuclear factor-Y (NF-Y) significantly attenuated the transactiv ation by SREBP-1a, suggesting that NF-Y binding is a prerequisite for SREBP s to activate the ACL promoter. However, the multiple Sp1 binding sites did not affect the transactivation of the ACL promoter by SREBPs. The binding affinity of SREBP-1a to SREs of the ACL promoter also was much higher than that of SREBP-2. The transactivation potencies of the chimeric SREBPs, of w hich the activation domains (70 amino acids of the amino terminus) were der ived from the different species of their carboxyl-terminal region, were sim ilar to those of SREBPs corresponding to their carboxyl termini. Therefore, it is suggested that the carboxyl-terminal portions of SREBPs containing D NA binding domains are important in determining their transactivation poten cies to a certain promoter.