Background: Plasma lipases and lipid transfer proteins are involved in the generation and speciation of high density lipoproteins. In this study we have examined the influence of plasma lipases and lipid transfer protein activities on the transfer of free cholesterol (FC) and phospholipids (PL) from lipid emulsion to human, rat and mouse lipoproteins. The effect of the lipases was verified by incubation of labeled (3 H-FC, 14 C-PL) triglyceride rich emulsion with human plasma (control, post-heparin and post-heparin plus lipase inhibitor), rat plasma (control and post-heparin) and by the injection of the labeled lipid emulsion into control and heparinized functionally hepatectomized rats.

The plasma cholesteryl ester transfer protein (CETP) facilitates the transfer of high density lipoprotein cholesteryl esters to other lipoproteins and appears to be a key regulated component of reverse cholesterol transport. Earlier studies showed that a CETP transgene containing natural flanking sequences (؊3.4 kilobase pairs (kbp) upstream, ؉2.2 kbp downstream) was expressed in an authentic tissue distribution and induced in liver and other tissues in response to dietary or endogenous hypercholesterolemia. In order to localize the DNA elements responsible for these effects, we prepared transgenic mice expressing six new DNA constructs containing different amounts of natural flanking sequence of the CETP gene. Tissue-specific expression and dietary cholesterol response of CETP mRNA were determined. The native pattern of predominant expression in liver and spleen with cholesterol induction was shown by a ؊3.4 (5), ؉0.2 (3) kbp transgene, indicating no major contribution of distal 3-sequences. Serial 5-deletions showed that a ؊570 base pairs (bp) transgene gave predominant expression in small intestine with cholesterol induction of CETP mRNA in that organ, and a ؊370 bp transgene gave highest expression in adrenal gland with partial dietary cholesterol induction of CETP mRNA and plasma activity. Further deletion to ؊138 bp 5-flanking sequence resulted in a transgene that was not expressed in vivo. Both the -3.4 kbp and ؊138 bp transgenes were expressed when transfected into a cultured murine hepatocyte cell line, but only the former was induced by treating the cells with LDL. When linked to a human apoA-I transgene, the ؊570 to ؊138 segment of the CETP gene promoter gave rise to a relative positive response of hepatic apoA-I mRNA to the high cholesterol diet in two out of three transgenic lines. Thus, 5-elements between ؊3,400 and ؊570 bp in the CETP promoter endow predominant expression in liver and spleen. Elements between ؊570 and ؊370 are required for expression in small intestine and some other tissues, and elements between ؊370 and ؊138 contribute to adrenal expression. The minimal CETP promoter element associated with a positive sterol response in vivo was found in the proximal CETP gene promoter between ؊370 and ؊138 bp. This region contains a tandem repeat of a sequence known to mediate sterol down-regulation of the HMG-CoA reductase gene, suggesting either the presence of separate positive and negative sterol response elements in this region or the use of a common DNA element for both positive and negative sterol responses. The cholesteryl ester transfer protein (CETP)1 is a hydrophobic M r 70,000 plasma glycoprotein that is synthesized by liver and small intestine as well as a variety of peripheral tissues (1). CETP mediates the net transfer of cholesteryl ester (CE) from HDL to triglyceride-rich lipoproteins (2) and appears to be a key component of reverse cholesterol transport, i.e. the transfer of cholesterol from the periphery back to the liver (3). By transferring CE to rapidly cleared triglycerid...

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The plasma cholesteryl ester transfer protein (CETP) plays a central role in high density lipoprotein metabolism and reverse cholesterol transport. Plasma CETP levels are increased in response to dietary or endogenous hypercholesterolemia as a result of increased gene transcription in liver and periphery. Deletional analysis in human CETP transgenic mice localized this response to a region of the proximal promoter which contains a tandem repeat of the sterol regulatory element (SRE) of the 3-hydroxy-3-methylglutaryl-CoA reductase gene. The purpose of the present study was to evaluate the role of the SRE-like element in CETP promoter activity. Gel shift assays using CETP promoter fragments containing these elements showed binding of the transcrip- The plasma cholesteryl ester transfer protein (CETP) 1 plays a central role in the catabolism of high density lipoprotein (HDL) cholesteryl esters and in reverse cholesterol transport i.e. the transfer of cholesterol from cells in peripheral tissues to the liver via the plasma compartment (1). In the initial steps of reverse cholesterol transport, cellular cholesterol is taken up by HDL and esterified by lecithin:cholesterol acyltransferase. CETP transfers cholesteryl esters from HDL to triglyceriderich lipoproteins with subsequent removal by the liver. The activity of CETP results in formation of smaller HDL species that may be efficient mediators of cellular cholesterol efflux and optimal substrates for the plasma lecithin:cholesterol acyltransferase reaction (2, 3). In human genetic CETP deficiency, HDL levels are increased but there appears to be an excess of coronary heart disease (4). Conversely, in hypertriglyceridemic CETP transgenic mice, where formation of small, pre-␤-HDL is increased, CETP expression decreases atherosclerosis even while lowering overall HDL levels (5). These findings could indicate that reverse cholesterol transport stimulated by CETP has an anti-atherogenic role.Plasma CETP levels and activity are increased in response to dietary or endogenous hypercholesterolemia, presumably reflecting the role of CETP in reverse cholesterol transport. This response has been observed in a variety of species including humans (6 -9). Mice do not normally have plasma CETP activity. However, natural flanking region CETP transgenic mice express the human gene in an authentic tissue pattern and show 2-3-fold induction of plasma CETP levels and hepatic CETP mRNA when placed on a high cholesterol diet (10). Moreover, after breeding onto LDL receptor and apoE gene knock-out backgrounds, a marked 4 -10-fold induction of plasma CETP levels and hepatic CETP mRNA is observed, and there is a close relationship between CETP and plasma cholesterol levels (11). These changes are due to increased CETP gene transcription in liver and peripheral tissues (10).In an attempt to define the regulatory elements responsible for increased CETP gene expression in response to hypercholesterolemia, we recently prepared CETP transgenic mice with different lengths of natural flanking sequ...