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Among the factors that regulate transcription of eukaryotic genes is a family of proteins known as nuclear factor 1 (NF1), CCAAT-box-binding transcription factor (CTF), or CCAATbox-binding protein (1)(2)(3)(4). These proteins are related in that they all bind to double-stranded sequences containing TGG and its complement, CCA making contact with the adjacent guanosines (4). NFl-like pNroteins bind to the promoters of many genes, including the gene for 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase), the rate-determining enzyme in cholesterol synthesis (5).NF1 binds to a TGG-containing sequence in adenovirus and thereby stimulates its replication (6, 7). The same protein (designated NF1/CTF) binds to the CCAAT box, making contact with TGG on the opposite strand and activating transcription of the human a-globin gene (1). NF1/CTF binds with highest affinity to sequences that contain the inverted repeat TGGN7CCA. It also binds to "half-sites" that contain only one copy of TGG. Purified NF1/CTF consists of a family of proteins in the molecular weight range of 55,000-62,000. Santoro et al. (3) isolated three cDNAs for NF1/CTF proteins from human HeLa cells. All of the mRNAs were derived from a single gene by alternative splicing and differed by the presence or absence of an insertion in the middle ofthe protein and the presence of various COOH termini. All three proteins, when produced in Escherichia coli, bound to the NF1/CTF recognition sequence, and at least two of them stimulated replication of adenovirus in vitro.Another member of the NF1/CTF family is the TGGCAbinding protein, which was described in chicken liver (8) and believed to have a molecular weight in the 30,000 range. The cDNA for this protein, designated pNF1/L, was isolated from rat liver (9). It encodes a protein of 505 amino acids, which was proteolyzed during its isolation. The first 175 amino acids of the rat TGGCA-binding protein show 98% identity with the NH2 terminus of human NF1/CTF, and the remaining portion shows an identity of "50% (3, 9).The 5' flanking region of the reductase gene contains the information necessary for transcription of the gene as well as for feedback repression by sterols. This region contains eight sequences that bind nuclear proteins as revealed by DNase I protection assays (10). We have purified (5) a protein doublet of 33 and 35 kDa, designated reductase promoter factor (RPF) that produces six of the eight footprints. The two proteins were active as monomers, and both recognized all six footprinted sequences. The only sequence shared by all six footprinted regions is the trinucleotide TGG. Methylation-interference analysis showed that both of the adjacent guanosines in this sequence made contact with RPF (5).The HMG-CoA reductase sequence that binds RPF with highest affinity (designated footprint 2B) contains the inverted repeat TGGN7CCA (5). The other five RPF-binding sites contain only half-sites. We speculated that RPF belonged to the NF1 family, and we demonstrated by gel retardation assays t...

Through the use of a quantitative solution hybridization assay with 32P-labeled cDNA probes, we found that mevinolin, an inhibitor of cholesterol synthesis, elevates the level of mRNA for the low density lipoprotein receptor in livers of hamsters and rabbits. In hamsters the maximal effect (3-fold increase) occurred at 0.1% mevinolin in the diet for 10 days. The same dose produced a maximal induction (10-fold) of mRNA levels for 3-hydroxy-3-methylglutaryl CoA reductase, the rate-limiting enzyme of cholesterol synthesis, and a maximal decrease (80%) in plasma cholesterol. The drug lowered the level of all cholesterol-carrying lipoproteins in plasma. In normal rabbits, mevinolin produced a 90% reduction in plasma low density lipoprotein-cholesterol levels, which was associated with a 2.5-fold increase in low density lipoprotein receptor mRNA levels. A similar induction of receptor mRNA occurred in livers of Watanabe-heritable hyperlipidemic rabbits, although the plasma cholesterol was not reduced to normal, presumably because the receptors produced by the mutant mRNA function poorly. These data are consistent with the hypothesis that mevinolin and other inhibitors of 3-hydroxy-3-methylglutaryl CoA reductase lower plasma cholesterol levels in part by stimulating production of mRNA for the low density lipoprotein receptor in liver.