A GC-RICH REGION CONTAINING SP1 AND SP1-LIKE BINDING-SITES IS A CRUCIAL REGULATORY MOTIF FOR FATTY-ACID SYNTHASE GENE PROMOTER ACTIVITY IN ADIPOCYTES - IMPLICATION IN THE OVERACTIVITY OF FAS PROMOTER IN OBESE ZUCKER RATS

We have previously shown that the proximal 2-kb sequence of the fatty acid synthase (FAS) promoter transfected into rat adipocytes was highl y sensitive to the cellular context, displaying an overactivity in obe se (fa/fa) versus lean Zucker rat adipocytes, Using deletional analysi s, we show here that FAS promoter activity mainly depends on a region from -200 to -126. This sequence exerts a strong negative effect on FA S promoter in adipocytes from lean rats but not in those from obese ra ts, resulting in a marked overtranscriptional activity in the latter c ells, This region, fused to a heterologous promoter, the E1b TATA box, induced differential levels of gene reporter activity in lean and obe se rat adipocytes, indicating it harbors fa-responsive element(s), Wha tever the rat genotype, adipocyte nuclear proteins were shown to footp rint the same protected sequence within the fa-responsive region, and supershift analysis demonstrated that Sp1 or Sp1-like proteins were bo und to this DNA subregion, Compelling evidence that the Sp1 binding si te contained in this sequence was implicated in the differential promo ter activity in lean versus obese rats, was provided by the observatio n that mutations at this Sp1 site induced a 2.5-fold increase in FAS p romoter activity in adipocytes from lean rats, whereas they had no eff ect in adipocytes from obese rats.