A Crucial Role of Sterol Regulatory Element-binding Protein-1 in the Regulation of Lipogenic Gene Expression by Polyunsaturated Fatty Acids

Dietary polyunsaturated fatty acids (PUFA) are negative regulators of hepatic lipogenesis that exert their effects primarily at the level of transcription. Sterol regulatory element-binding proteins (SREBPs) are transcription factors responsible for the regulation of cholesterol, fatty acid, and triglyceride synthesis. In particular, SREBP-1 is known to play a crucial role in the regulation of lipogenic gene expression in the liver. To explore the possible involvement of SREBP-1 in the suppression of hepatic lipogenesis by PUFA, we challenged wild-type mice and transgenic mice overexpressing a mature form of SREBP-1 in the liver with dietary PUFA. In the liver of wild-type mice, dietary PUFA drastically decreased the mature, cleaved form of SREBP-1 protein in the nucleus, whereas the precursor, uncleaved form in the membranes was not suppressed. The decreases in mature SREBP-1 paralleled those in mRNAs for lipogenic enzymes such as fatty acid synthase and acetyl-CoA carboxylase. In the transgenic mice, dietary PUFA did not reduce the amount of transgenic SREBP-1 protein, excluding the possibility that PUFA accelerated the degradation of mature SREBP-1. The resulting sustained expression of mature SREBP-1 almost completely canceled the suppression of lipogenic gene expression by PUFA in the SREBP-1 transgenic mice. These results demonstrate that the suppressive effect of PUFA on lipogenic enzyme genes in the liver is caused by a decrease in the mature form of SREBP-1 protein, which is presumably due to the reduced cleavage of SREBP-1 precursor protein. Dietary polyunsaturated fatty acids (PUFA) are negative regulators of hepatic lipogenesis that exert their effects primarily at the level of transcription. Sterol regulatory element-binding proteins (SREBPs) are transcription factors responsible for the regulation of cholesterol, fatty acid, and triglyceride synthesis. In particular, SREBP-1 is known to play a crucial role in the regulation of lipogenic gene expression in the liver. To explore the possible involvement of SREBP-1 in the suppression of hepatic lipogenesis by PUFA, we challenged wild-type mice and transgenic mice overexpressing a mature form of SREBP-1 in the liver with dietary PUFA. In the liver of wild-type mice, dietary PUFA drastically decreased the mature, cleaved form of SREBP-1 protein in the nucleus, whereas the precursor, uncleaved form in the membranes was not suppressed. The decreases in mature SREBP-1 paralleled those in mRNAs for lipogenic enzymes such as fatty acid synthase and acetyl-CoA carboxylase. In the transgenic mice, dietary PUFA did not reduce the amount of transgenic SREBP-1 protein, excluding the possibility that PUFA accelerated the degradation of mature SREBP-1. The resulting sustained expression of mature SREBP-1 almost completely canceled the suppression of lipogenic gene expression by PUFA in the SREBP-1 transgenic mice. These results demonstrate that the suppressive effect of PUFA on lipogenic enzyme genes in the liver is caused by a decrease in the mature form of SREBP-1 protein, which is presumably due to the reduced cleavage of SREBP-1 precursor protein. acetyl-CoA carboxylase fatty acid synthase pyruvate kinase polyunsaturated fatty acids sterol regulatory element-binding protein eicosapentaenoic acid peroxisome proliferator-activated receptor phosphoenolpyruvate carboxykinase The liver, the principal lipogenic organ, is responsible for the conversion of excess dietary carbohydrates to triglycerides. A high carbohydrate diet induces the synthesis of several lipogenic and glycolytic enzymes including acetyl-CoA carboxylase (ACC),1 fatty acid synthase (FAS), stearoyl-CoA desaturase, ATP citrate lyase, malic enzyme, glucose-6-phosphate dehydrogenase, and pyruvate kinase (PK) (1Goodridge A.G. Annu. Rev. Nutr. 1987; 7: 157-185Crossref PubMed Scopus (160) Google Scholar, 2Granner D. Pilkis S. J. Biol. Chem. 1990; 265: 10173-10176Abstract Full Text PDF PubMed Google Scholar, 3Ntambi J.M. J. Biol. Chem. 1992; 267: 10925-10930Abstract Full Text PDF PubMed Google Scholar). This coordinate induction of enzymes is due to increased mRNA levels, resulting primarily from the accelerated transcription. Dietary polyunsaturated fatty acids (PUFA) have been well established as negative regulators of hepatic lipogenesis. Allmann and Gibson (4Allmann D.W. Gibson D.M. J. Lipid Res. 1965; 6: 51-62Abstract Full Text PDF PubMed Google Scholar) discovered that adding 2% linoleate to a high carbohydrate fat-free diet suppressed the rate of hepatic fatty acid biosynthesis and the activities of FAS and glucose-6-phosphate dehydrogenase by nearly 70% in mice. In contrast, supplementing the high carbohydrate diet with palmitate, oleate, or cholesterol had no effect on hepatic lipogenesis or the activity of lipogenic enzymes. Since then, several investigators have demonstrated that dietary PUFA of the n-6 and n-3 families suppress hepatic lipogenesis. This anti-lipogenic action of PUFA reflects decreases in mRNA levels of hepatic enzymes including ACC, FAS, stearoyl-CoA desaturase, ATP citrate lyase, malic enzyme, glucose-6-phosphate dehydrogenase, and PK. The regulation by PUFA has been shown to be primarily at the transcriptional level; however, the precise mechanism for this action remains unknown (5Jump D.B. Clarke S.D. Thelen A. Liimatta M. Ren B. Badin M. Prog. Lipid Res. 1996; 35: 227-241Crossref PubMed Scopus (95) Google Scholar, 6Fukuda H. Katsurada A. Iritani N. Eur. J. Biochem. 1992; 209: 217-222Crossref PubMed Scopus (44) Google Scholar, 7Iritani N. Eur. J. Biochem. 1992; 205: 433-442Crossref PubMed Scopus (120) Google Scholar). Sterol regulatory element-binding proteins (SREBPs) are transcription factors that belong to the basic helix-loop-helix-leucine zipper family and regulate enzymes responsible for the synthesis of cholesterol, fatty acids, and triglycerides (8Brown M.S. Goldstein J.L. Cell. 1997; 89: 331-340Abstract Full Text Full Text PDF PubMed Scopus (3028) Google Scholar). Unlike other members of the basic helix-loop-helix-leucine zipper family, SREBPs are synthesized as precursors bound to the endoplasmic reticulum and nuclear envelope. Upon activation, SREBPs are released from the membrane into the nucleus as a mature protein by a sequential two-step cleavage process. To date, three SREBP isoforms, SREBP-1a, -1c and -2, have been identified and characterized. The predominant SREBP-1 isoform in the liver is SREBP-1c. Whereas SREBP-2 is relatively selective in transcriptionally activating cholesterol biosynthetic genes, SREBP-1c has a greater role in regulating fatty acid synthesis than cholesterol synthesis in the liver (9Shimano H. Horton J.D. Shimomura I. Hammer R.E. Brown M.S. Goldstein J.L. J. Clin. Invest. 1997; 99: 846-854Crossref PubMed Scopus (688) Google Scholar, 10Horton J.D. Shimomura I. Brown M.S. Hammer R.E. Goldstein J.L. Shimano H. J. Clin. Invest. 1998; 101: 2331-2339Crossref PubMed Google Scholar, 11Shimomura I. Shimano H. Korn B.S. Bashmakov Y. Horton J.D. J. Biol. Chem. 1998; 273: 35299-35306Abstract Full Text Full Text PDF PubMed Scopus (322) Google Scholar, 30Shimano H. Yahagi N. Amemiya-Kudo M. Hasty A.H. Osuga J. Tamura Y. Shionoiri F. Iizuka Y. Ohashi K. Harada K. Gotoda T. Ishibashi S. Yamada N. J. Biol. Chem. 1999; 274: 35832-35839Abstract Full Text Full Text PDF PubMed Scopus (583) Google Scholar). The role of SREBP-1 for the regulation of hepatic lipogenesis has been recently established. Changes in hepatic mature SREBP-1c protein levels were shown to parallel those of mRNAs for lipogenic genes in the liver using a dietary manipulation and a transgenic technology (12Horton J.D. Bashmakov Y. Shimomura I. Shimano H. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 5987-5992Crossref PubMed Scopus (540) Google Scholar). Moreover, SREBP-1 has been demonstrated to be crucial for the carbohydrate stimulation of lipogenic genes in mice with a targeted disruption of SREBP-1 (30Shimano H. Yahagi N. Amemiya-Kudo M. Hasty A.H. Osuga J. Tamura Y. Shionoiri F. Iizuka Y. Ohashi K. Harada K. Gotoda T. Ishibashi S. Yamada N. J. Biol. Chem. 1999; 274: 35832-35839Abstract Full Text Full Text PDF PubMed Scopus (583) Google Scholar). These findings led us to hypothesize that the suppressive effect of PUFA on lipogenic gene transcription in liver is mediated through a decrease in mature SREBP-1 levels. To verify this hypothesis, the current studies were designed using wild-type mice and transgenic mice overexpressing mature SREBP-1c in the liver (TgSREBP-1c). First, we show that the amount of mature SREBP-1 in the liver is decreased by dietary PUFA. Next, we demonstrate that the expression of lipogenic genes in the liver of TgSREBP-1c mice is maintained at a relatively high level and that this expression follows the pattern of SREBP-1 levels that remain elevated even in the presence of dietary PUFA. These results indicate that the suppression of hepatic gene expression of lipogenic enzymes by PUFA is most likely due to the decrease in the mature SREBP-1 protein. Triolein (95% grade) and ethyl linoleate were purchased from Sigma, and tristearin and casein were purchased from Wako Pure Chemical Industries (Osaka, Japan). Eicosapentaenoic acid (EPA) ethyl ester (95% grade) was provided by Mochida Pharmaceutical (Tokyo, Japan), fenofibrate by Laboratoires Fournier (Paris, France), and troglitazone by Sankyo pharmaceutical (Tokyo, Japan). Fish oils (sardine and tuna) were provided by NOF (Tokyo, Japan). Standard laboratory chow, high carbohydrate fat-free diet (70% sucrose and 20% casein supplemented with methionine, vitamins and minerals), and high protein fat-free diet (90% casein and no carbohydrate with methionine, vitamins, and minerals) were obtained from Oriental Yeast (Tokyo, Japan). 7-week-old male C57BL/6J mice (21–23 g) were purchased from CLEA (Tokyo, Japan) and adapted to the environment for 1 week prior to study. SREBP-1c transgenic mice overexpressing amino acids 1–436 of human SREBP-1c under control of the rat PEPCK promoter (TgSREBP-1c) were made as described previously (9Shimano H. Horton J.D. Shimomura I. Hammer R.E. Brown M.S. Goldstein J.L. J. Clin. Invest. 1997; 99: 846-854Crossref PubMed Scopus (688) Google Scholar). A line homozygous for the transgene was established. All mice were housed in a controlled environment with a 12-h light/dark cycle and free access to water and diet. Prior to sacrifice, each group of three animals was fed a diet containing the indicated fatty acids, prepared fresh daily, for 7 days. The diet for wild-type mice consisted of a high carbohydrate fat-free chow supplemented with 20% (w/w) tristearin, 20% triolein, 20% fish oil (sardine or tuna), 5% linoleic acid, or 5% EPA ethyl ester. The diet for TgSREBP-1c mice was a high protein diet mixed with 20% triolein, 20% triolein plus 5% EPA ethyl ester, or 20% fish oil (sardine). For the comparison of high protein and high carbohydrate diets, wild-type mice were examined on diets composed of high protein or high carbohydrate chow mixed with 20% triolein or 20% fish oil (sardine). All mice were sacrificed during the early phase of the light cycle in a nonfasted state. Nuclear extracts and membrane fractions from mice livers were prepared as described previously (13Sheng Z. Otani H. Brown M.S. Goldstein J.L. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 935-938Crossref PubMed Scopus (279) Google Scholar). Aliquots of nuclear (20 μg) and membrane (30 μg) proteins were subjected to SDS-polyacrylamide gel electrophoresis. Immunoblot analysis was performed using the ECL Western Blotting Detection System kit (Amersham Pharmacia Biotech) and exposed to Eastman Kodak Co. XAR-5 film. The primary antibodies (polyclonal) were as described previously (14Shimano H. Shimomura I. Hammer R.E. Herz J. Goldstein J.L. Brown M.S. Horton J.D. J. Clin. Invest. 1997; 100: 2115-2124Crossref PubMed Scopus (356) Google Scholar, 15Shimano H. Horton J.D. Hammer R.E. Shimomura I. Brown M.S. Goldstein J.L. J. Clin. Invest. 1996; 98: 1575-1584Crossref PubMed Scopus (699) Google Scholar). Total hepatic RNA was isolated with Trizol reagent (Life Technologies), and 10-μg RNA samples (equally pooled from three mice) were run on a 1% agarose gel containing formaldehyde and transferred to a nylon membrane. The cDNA probes used were cloned as described previously (15Shimano H. Horton J.D. Hammer R.E. Shimomura I. Brown M.S. Goldstein J.L. J. Clin. Invest. 1996; 98: 1575-1584Crossref PubMed Scopus (699) Google Scholar, 30Shimano H. Yahagi N. Amemiya-Kudo M. Hasty A.H. Osuga J. Tamura Y. Shionoiri F. Iizuka Y. Ohashi K. Harada K. Gotoda T. Ishibashi S. Yamada N. J. Biol. Chem. 1999; 274: 35832-35839Abstract Full Text Full Text PDF PubMed Scopus (583) Google Scholar). The probes were labeled with α-32PdCTP using the Megaprime DNA Labeling System kit (Amersham Pharmacia Biotech). The membranes were hybridized with the radiolabeled probe in Rapid-hyb Buffer (Amersham Pharmacia Biotech) at 65 °C and washed in 0.1× SSC, 0.1% SDS at 65 °C. Blots were exposed to Kodak XAR-5 film. To examine the effect of PUFA on SREBP-1 in mice livers, wild-type mice were fed a high carbohydrate diet supplemented with PUFA (linoleate, EPA, or two kinds of fish oil rich in EPA or docosahexaenoic acid) for 7 days. Immunoblot analysis of liver nuclear extracts from these mice showed that feeding wild-type mice a diet with EPA for 7 days resulted in a ∼3-fold decrease in the amount of hepatic mature SREBP-1 protein, compared with feeding with the control diet (high carbohydrate without fat). This suppressive effect of EPA on the mature SREBP-1 was consistently observed in six independent experiments including Figs. 1, a b, andc, 2, and 7. Fish oil (sardine, rich in EPA, or tuna, rich in docosahexaenoic acid) decreased mature SREBP-1 protein more profoundly, as shown in Figs. 1, b and c, 2, and7. Dietary linoleate also suppressed mature SREBP-1 to a lesser extent (Fig. 2). In contrast, neither saturated (tristearin) nor monounsaturated fatty acids reduced mature SREBP-1 (Fig. 2). The amount of mature SREBP-2 protein did not with of the dietary and b, 2, and analysis of SREBP-1 and in nuclear extracts from livers of mice fed a high carbohydrate diet containing fatty male were fed a high carbohydrate fat-free diet or a high carbohydrate diet supplemented with 20% tristearin 20% triolein 5% linoleate ethyl ester 5% EPA ethyl ester 20% fish oil or 20% fish oil for 7 days and sacrificed in a nonfasted state. Aliquots of nuclear extracts (20 of from pooled livers of each group were subjected to with SREBP-1 or analysis of SREBP-1 and in nuclear extracts from livers of mice fenofibrate or were as 1, a high carbohydrate 2, a high carbohydrate diet with 5% EPA ethyl 20% fish 0.1% male were fed the diet for 7 days and sacrificed in a nonfasted state. Aliquots of nuclear extracts (20 from pooled livers of each group were subjected to with SREBP-1 or analysis of SREBP-1 and in nuclear extracts and analysis of lipogenic enzymes from livers of wild-type mice fed a high protein or high carbohydrate diet with or without PUFA male were fed a high protein diet mixed with 20% triolein a high protein diet with 20% fish oil a high carbohydrate diet with 20% triolein or a high carbohydrate diet with 20% fish oil for 7 days and sacrificed in a nonfasted state. For of nuclear extracts (20 of from pooled livers of each group were For of RNA was pooled from livers of each group and to a nylon by with the indicated cDNA stearoyl-CoA The of mature SREBP-1 protein several including and a cleavage from To the mechanism by which PUFA mature SREBP-1 protein, the of SREBP-1 precursor and mature in the membrane and nuclear 1 as well as SREBP-1 mRNA levels (Fig. were compared control and PUFA or fish mice. In to the mature protein, which was decreased by PUFA no was observed in mRNA or precursor protein levels. This that PUFA the of mature SREBP-1 protein at a presumably through cleavage compared mRNA levels of genes lipogenic enzymes in the liver of mice fed diets with or without PUFA (linoleate, EPA, or fish for 7 days as by with dietary PUFA suppressed hepatic expression of lipogenic genes such as ACC, FAS, stearoyl-CoA 1, ATP citrate lyase, malic enzyme, glucose-6-phosphate dehydrogenase, and (Fig. This of lipogenic genes was to PUFA (linoleate, EPA, fish of mice and was not observed in mice fed saturated or monounsaturated fatty This to PUFA to the pattern of suppression observed with mature SREBP-1 protein (Fig. 2). These findings are in of the that PUFA decreases mRNA levels of lipogenic genes through the suppression of mature SREBP-1. To examine the PUFA suppression of lipogenic genes was to the decrease in mature a transgenic that a mature form of SREBP-1 protein in the liver (TgSREBP-1c) was In these transgenic mice, the expression of a nuclear form of SREBP-1c that is without cleavage is under control of the rat PEPCK promoter and is animals are fed a high protein, carbohydrate diet (9Shimano H. Horton J.D. Shimomura I. Hammer R.E. Brown M.S. Goldstein J.L. J. Clin. Invest. 1997; 99: 846-854Crossref PubMed Scopus (688) Google Scholar). shown in the mature SREBP-1 in the liver of TgSREBP-1c mice fed a high protein diet is by the transgene the amount of which was with that of SREBP-1 mature form in wild-type mice on a high carbohydrate diet (Fig. 1 The hepatic mRNA levels of lipogenic genes in these TgSREBP-1c mice were also to those in wild-type mice on a high carbohydrate diet (Fig. 1 and analysis of lipogenic and glycolytic enzymes from livers of wild-type or TgSREBP-1c mice on PUFA mice were fed a high carbohydrate fat-free diet and homozygous TgSREBP-1c mice were fed a high protein diet with 20% triolein 5% EPA ethyl ester plus 20% triolein or 20% fish oil for 7 days and sacrificed in a nonfasted state. Total RNA μg) pooled from livers of each group was subjected to by with the indicated cDNA A cDNA probe for was used to stearoyl-CoA ATP citrate malic glucose-6-phosphate The effects of PUFA on the amount of mature SREBP-1 and the mRNA levels of lipogenic genes were examined in these transgenic mice. was that the amount of the transgene was not by dietary PUFA or fish (Fig. dietary PUFA did not the mRNA levels of lipogenic genes such as ACC, FAS, stearoyl-CoA 1, ATP citrate lyase, malic enzyme, glucose-6-phosphate dehydrogenase, or in the liver of TgSREBP-1c mice (Fig. These results demonstrate that the suppressive effect of PUFA on lipogenic genes is primarily mediated through the decrease in the amount of mature SREBP-1. To that dietary PUFA mature SREBP-1 and lipogenic genes in mice fed diets in the as in mice on diets, wild-type mice were fed a high protein diet supplemented with triolein or fish oil for 7 and the amount of mature SREBP-1 (Fig. and the mRNA levels of lipogenic genes (Fig. in the liver were by and dietary PUFA the suppressive effect on the of high protein diets as was observed on high carbohydrate was also that a high carbohydrate diet elevated mature SREBP-1 as well as mRNAs for lipogenic genes more than a high protein diet. These results for the of lipogenic gene transcription on mature SREBP-1. is well known that PUFA are for Brown J.M. J.M. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google Scholar, J. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google and effects of PUFA such as induction of and fatty acid are mediated by B. Thelen J.M. D.B. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). To is in the suppression of mature SREBP-1 by PUFA, the amount of mature SREBP-1 in wild-type mice fed a diet containing a for for 7 days was Immunoblot analysis of liver nuclear extracts showed that neither fenofibrate nor a for the amount of mature SREBP-1 in the liver (Fig. These that the suppressive effect of PUFA on mature SREBP-1 is not mediated by or The effects of were by the of increased mRNAs of and not In the we showed that the suppression of lipogenic gene expression by PUFA in the liver was primarily due to decreases in the mature form of SREBP-1. demonstrated that the of mature SREBP-1 in the liver was decreased by dietary PUFA. A has been in a in T. J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus Google Scholar). was that mature SREBP-1 was also decreased by oleate, a monounsaturated fatty acid, which no effect on hepatic SREBP-1 in in study. studies using or rat liver have demonstrated that effect is to PUFA and that this to be to liver S.D. D.B. Prog. Lipid Res. PubMed Scopus Google Scholar). results the effects of fatty acids on SREBP-1 nuclear protein in the liver are with these The for the in the effect of liver and is shown in we demonstrate that PUFA the of mature SREBP-1 protein primarily at the Moreover, we show that PUFA did not decrease the amount of mature SREBP-1 from the that PUFA not the degradation of SREBP-1 mature protein. These that the regulation of SREBP-1 by PUFA at the of cleavage of the precursor protein from the suppression of lipogenic gene expression by PUFA is caused by the decrease in mature SREBP-1 protein, sustained SREBP-1 expression the effect of PUFA. To verify this hypothesis, homozygous TgSREBP-1c mice fed a high protein diet were described the rat PEPCK promoter used for the transgene is by feeding a high protein, carbohydrate diet Hammer R.E. Cell. Biol. 1992; PubMed Scopus Google Scholar). the hepatic expression of mature SREBP-1 in these mice was to that of wild-type mice and was not by PUFA. In the presence of sustained SREBP-1 mature protein levels, the expression of lipogenic genes in the liver of TgSREBP-1c mice was maintained as high as that of wild-type mice on a high carbohydrate diet of PUFA This that the mature form of SREBP-1 is a in the suppressive effect of dietary PUFA on lipogenic gene be that the mRNA of was more in wild-type mice fed a high carbohydrate diet than in TgSREBP-1c mice fed a high protein of mature SREBP-1 were This the possibility that the transcriptional regulation of the gene is more controlled by transcription other than SREBP-1. This the effect of PUFA on the mRNA level of PK. is also with the that SREBP-1 disruption had a on mRNA expression of in comparison with those of other lipogenic enzymes induction by a high carbohydrate diet was completely in the SREBP-1 mice. The in the promoter for carbohydrate stimulation and PUFA suppression of lipogenic genes have been by In the of enzymes such as FAS H. Iritani N. T. 1997; PubMed Scopus Google ATP citrate H. Iritani N. Katsurada A. T. 1996; PubMed Scopus Google and M. Clarke S. D.B. Google with PUFA the and PUFA in the FAS promoter has been shown to J.M. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). The PUFA in the stearoyl-CoA 1 promoter is also to have J.M. 1997; PubMed Scopus Google Scholar, J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus Google Scholar). These are of that carbohydrate stimulation and PUFA suppression are mediated by a SREBP-1. In contrast, promoter of the gene previously that the was from the for dietary carbohydrate and (5Jump D.B. Clarke S.D. Thelen A. Liimatta M. Ren B. Badin M. Prog. Lipid Res. 1996; 35: 227-241Crossref PubMed Scopus (95) Google Scholar). Since are known as of Brown J.M. J.M. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google Scholar, J. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google the effects of PUFA through were also The that fenofibrate did not the amount of mature SREBP-1 in the liver that the suppressive effect of PUFA on mature SREBP-1 is not mediated by This is with the using mice, which showed that was not for the of FAS or gene expression B. Thelen J.M. D.B. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). has been established that SREBP-1 and SREBP-2 to regulate fatty acid synthesis and cholesterol with in (9Shimano H. Horton J.D. Shimomura I. Hammer R.E. Brown M.S. Goldstein J.L. J. Clin. Invest. 1997; 99: 846-854Crossref PubMed Scopus (688) Google Scholar, 10Horton J.D. Shimomura I. Brown M.S. Hammer R.E. Goldstein J.L. Shimano H. J. Clin. Invest. 1998; 101: 2331-2339Crossref PubMed Google Scholar). Since SREBP-2 is a of the cholesterol biosynthetic is controlled by sterol levels. This including the of SREBP protein and the 1 and has been (8Brown M.S. Goldstein J.L. Cell. 1997; 89: 331-340Abstract Full Text Full Text PDF PubMed Scopus (3028) Google Scholar, J. D. Goldstein J.L. Brown M.S. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, D. J. J. Brown M.S. Goldstein J.L. Cell. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). the more regulation of SREBP-1 has to be The indicate for the that the cleavage of SREBP-1 in the liver be by a mechanism other than sterol and presumably in a to fatty acid studies are to the mechanism by which PUFA the cleavage of SREBP-1 precursor protein in of the regulation of hepatic lipogenesis. In we have demonstrated that dietary PUFA decreased the amount of hepatic SREBP-1 mature protein by a in the cleavage of SREBP-1 precursor protein, the suppression of lipogenic gene expression in the liver.