Cholesterol and fatty acid (FA) biosynthetic gene expression is regulated by the sterol regulatory element-binding protein (SREBP) family of transcription factors (Horton et al., 2002). The three family members—SREBP-1a, SREBP-1c, and SREBP-2—are basic-helix-loop helix transcription factors that bind to sterol response elements of promoters to activate transcription. SREBP-1a and SREBP-1c are encoded by the same gene but have independent promoters that utilize a unique first exon. SREBP-2 is encoded by a separate gene.

The membrane-bound, inactive forms of SREBPs are located in the endoplasmic reticulum bound to Scap, an escort protein that serves as a sensor of cellular sterol levels (Brown and Goldstein, 2009). When cellular sterol levels are high, Scap binds an ER retention protein, Insig, which retains the SREBP/Scap complex in the ER. To generate the active nuclear form of SREBPs, SREBP/Scap dissociates from Insig, and the complex moves from the ER to the Golgi where two proteases, designated S1P and S2P, sequentially cleave SREBPs releasing the amino-terminal fragment, which travels to the nucleus to activate regulated genes.

The in vivo transcriptional-activating properties of each SREBP isoform have been investigated through the generation and characterization of transgenic and knockout mice (Horton et al., 2002). In most tissues, the predominant SREBP-1 isoform expressed is SREBP-1c (Shimomura et al., 1997). Overexpression of nuclear SREBP-1c (nSREBP-1c) in livers of mice resulted in the transcriptional activation of genes involved in FA and triglyceride (TG) synthesis (Horton et al., 2002). As a consequence of increased de novo lipogenesis, mice expressing nSREBP-1c developed fatty livers. Consistent with the role of SREBP-1c in activating lipogenesis, SREBP-1c is activated in the liver by insulin through a partially defined pathway that involves the insulin receptor, Akt, and mTORC1 (Owen et al., 2012). Conversely, genetic deletion of Srebf-1c led to a selective reduction in the expression of genes involved in FA and TG synthesis (Liang et al., 2002).

The SREBP-1a isoform is a more potent transcription activator than SREBP-1c, owing to its longer transactivation domain (Horton et al., 2002). Overexpression of the minor nSREBP-1a isoform in mouse liver led to the activation of genes involved in both FA and cholesterol biosynthesis; resulting in the accumulation of both cholesterol and TGs in liver (Horton et al., 2002). In stark contrast, the selective deletion of Srebf-1a reduced the expression of only acetyl-CoA carboxylase (ACC) 2 in the liver, one of the two ACC isoforms that carry out the first committed enzymatic step in FA synthesis (Im et al., 2009).

The genetic ablation of both Srebf-1a and Srebf-1c resulted in significant, but incomplete, embryonic lethality (Horton et al., 2002). In those few Srebf-1a/Srebf-1c knockout mice that survived to adulthood, the gene expression profile in the liver was similar to that observed in livers from mice that had the genetic ablation of only the Srebf-1c isoform.

Transgenic overexpression of nSREBP-2 in liver led to the preferential activation of genes involved in cholesterol biosynthesis, the LDL receptor (LDLR), and PCSK9 (Horton et al., 2003). However, nSREBP-2 overexpression also increased the mRNA levels of FA biosynthetic genes, albeit to a lesser extent than those involved in cholesterol synthesis.

To further delineate genes specifically regulated by SREBP-2, we initially attempted to obtain mice with homozygous germ-line deletions of Srebf-2 using a traditional gene-replacement approach. Crosses of Srebf-2^+/-mice did not produce viable offspring homozygous for the disrupted Srebf-2 allele. Most embryos homozygous for the disrupted Srebf-2 allele appeared to die between day 7–8 post-coitum, but the cause of this embryonic lethality was not investigated (Horton et al., 2002). Mice that were heterozygous for the germ-line deletion of Srebf-2 had no discernable phenotype.

To bypass the embryonic lethality, here we used albumin-driven, Cre-mediated recombination to delete Srebf-2 in hepatocytes of mice. The results confirm that SREBP2 is required for normal levels of cholesterol biosynthetic gene expression, but unexpectedly, we found the expression of Srebf-1c and its target genes for FA and TG synthesis was also dependent on SREBP-2 expression. The absence of SREBP-2 lead to reduced LXR activity, which explained the loss of SREBP-1c expression, possibly owing to the loss of an endogenous sterol ligand that is dependent on flux through the cholesterol biosynthesis pathway.

The vector and targeting strategy used to conditionally disrupt Srebf-2 is shown in Figure 1A and B. Mice homozygous for the floxed Srebf-2 allele, were bred to transgenic mice that express Cre recombinase driven by the albumin promoter to obtain hepatocyte-specific gene deletion (hepatocyte-Srebf-2^-/-). Littermates bearing two floxed Srebf-2 alleles with no albumin-cre were designated as wild type controls. Hepatocyte -Srebf-2^-/- mice weighed slightly less than littermate controls but liver weights were unchanged (Table 1). In the absence of SREBP-2, plasma and liver cholesterol concentrations were reduced by 68% and 20%, respectively. Unexpectedly, plasma and liver TGs were also reduced by 50% and 76%, in hepatocyte -Srebf-2^-/- mice (Table 1).

Figure 1

Download asset Open asset

Immunoblot analyses of SREBPs from livers of mice described in Table 1 are shown in Figure 1C. As expected, the precursor (P) and nSREBP-2 (N) protein were undetectable in hepatocyte-Srebf-2^-/- livers. However, the SREBP-1 precursor and nuclear protein levels were also reduced by ~90% in hepatocyte-Srebf-2^-/- livers. Calnexin and CREB were used as controls for membrane and nuclear proteins, respectively.

Figure 2 shows the results of quantitative PCR assays that measured mRNA levels of lipid metabolism related genes in livers of mice described in Table 1. The mRNA levels of SREBP-2-regulated genes involved in cholesterol biosynthesis and uptake (HMG-CoA synthase, HMG-CoA reductase, farnesyl diphosphate synthase, squalene synthase, and PCSK9) were reduced by 60–80% in hepatocyte-Srebf-2^-/- livers compared to controls. The mRNA for the LDLR was only reduced by 20%. SREBP-1c mRNA levels also were 90% lower than that measured in livers of wild type (WT) mice, while SREBP-1a mRNA levels remained unchanged. SREBP-1c-regulated genes in the FA biosynthetic pathway (ACC1), fatty acid synthase (FAS), ELOVL6, and stearoyl-CoA desaturase-1 (SCD1)) were reduced ~50 to>95% in hepatocyte-Srebf-2^-/- livers; however, ACC2 expression, which is primarily regulated by SREBP-1a (Im et al., 2009), was only slightly lower. Srebf-1c transcription is regulated by LXR and by nSREBP-1c itself through a feed-forward loop (Repa et al., 2000). SREBP-1c mRNA levels were reduced by 90%, which explains the loss of SREBP-1 protein in hepatocyte-Srebf-2^-/- livers. The mRNA levels of LXRα and β were unchanged but the mRNA levels of additional LXR-regulated genes, ABCG5 and ABCG8, were reduced by 60–70% (Supplementary file 2), suggesting that LXR activity was lower in the absence of SREBP-2.

Figure 2

Download asset Open asset

To confirm that the reduced expression of cholesterol and FA synthesis genes in hepatocyte-Srebf-2^-/- livers translated into lower rates of lipid synthesis, we measured the incorporation of tritiated water into newly synthesized sterols and FAs. In hepatocyte-Srebf-2^-/- livers, rates of sterol and FA synthesis were decreased by 59% and 68%, respectively (Figure 3).

Figure 3

Download asset Open asset

Inasmuch as the expression of LXRα and β were unaffected by deleting Srebf-2, we hypothesized that the loss of SREBP-1c expression and reduced FA synthesis in hepatocyte-Srebf-2^-/- livers was due to the absence of a ligand for LXR that is either generated within or derived from the cholesterol biosynthetic pathway. To test this hypothesis, we first fed mice a synthetic ligand for LXR, T0901317. Administration of T0901317 to hepatocyte-Srebf-2^-/- mice induced SREBP-1c mRNA and protein expression to levels similar to that measured in WT livers (Figure 4A,B). Increased SREBP-1c expression was associated with higher mRNA levels of ACC1 and FAS (Figure 4B). Inasmuch as LXR can independently transcriptionally activate the same FA synthesis genes, we verified that the induction of ACC1 and FAS was specifically due to SREBP-1c by feeding mice that lack all SREBPs as a result of the deletion of Scap the LXR agonist (Moon et al., 2012). Administration of T0901317 to mice with hepatocyte-specific deletion of Scap did not significantly change the mRNA levels of ACC1 or FAS (Figure 4—figure supplement 1). This suggests that LXR administration to the hepatocyte-Srebf-2^-/- mice induced the mRNA levels of FA synthesis genes through the restoration of SREBP-1c expression and not through direct transcriptional activation by LXR.

Figure 4 with 1 supplement see all

Download asset Open asset

Cholesterol feeding leads to the production of oxysterols in the liver that can also activate LXR; therefore, we next fed mice diets supplemented with cholesterol to determine whether dietary cholesterol could restore SREBP-1c expression in hepatocyte-Srebf-2^-/- livers. Dietary supplementation of 0.2% cholesterol increased liver cholesterol concentrations and SREBP-1c mRNA levels to that measured in WT mice fed chow (Figure 5A,C). As shown in Figure 5B, nSREBP-1c protein levels in hepatocyte-Srebf-2^-/- livers were slightly lower than that in WT mice fed chow, but this was sufficient to restore the expression of mRNAs for FA biosynthetic genes to levels found in WT livers (Figure 5C). SREBP-2 regulated genes remained low and unaffected by cholesterol feeding (Figure 5C).

Figure 5

Download asset Open asset

To identify the potential missing LXR ligand in hepatocyte-Srebf-2^-/- mice, we performed LC-MS/MS to quantify the cholesterol biosynthetic intermediates and oxysterol concentrations in the liver. As shown in Supplementary file 1, the concentrations of intermediates in the cholesterol biosynthetic pathway were not consistently changed or slightly higher in livers of hepatocyte-Srebf-2^-/- mice compared to controls. The cholesterol biosynthetic intermediate, desmosterol, has been previously identified as an LXR ligand (Yang et al., 2006); however, the concentration of this intermediate was actually higher in hepatocyte-Srebf-2^-/- livers. Other reported ligands of LXR include: 20(S)-hydroxycholesterol, 22(R)-hydroxycholesterol, 24(S)-hydroxycholesterol, 24(S),25-epoxycholesterol, 25-hydroxycholesterol, and 27-hydroxycholesterol (Huang, 2014; Yang et al., 2006). Of these ligands, 20(S)-hydroxycholesterol and 22(R)-hydroxycholesterol were not detected and concentrations of 24(S)-hydroxycholesterol, 24(S),25-epoxycholesterol, 25-hydroxycholesterol, and 27-hydroxycholesterol. 20(S)-hydroxycholesterol and 22(R)-hydroxycholesterol were either not consistently changed or slightly higher in hepatocyte-Srebf-2^-/- livers compared to controls, suggesting that the missing SREBP-2-dependent endogenous LXR ligand is not one previously identified (Supplementary file 1).

In addition to LXR, Srebf-1c is transcriptionally activated by insulin, which is stimulated by feeding mice a high carbohydrate diet (Horton et al., 1998; Shimomura et al., 1999). To determine whether insulin-mediated activation of SREBP-1c was intact in hepatocyte-Srebf-2^-/- livers, we subjected mice to a fasting/refeeding protocol using a high carbohydrate/low fat diet previously shown to induce SREBP-1c expression (Horton et al., 1998) (Table 2). In the fasted state, SREBP-1c levels are extremely low. As shown in Table 3, refeeding the high carbohydrate diet to fasted WT mice increased the expression of SREBP-1c mRNA in WT mice by 41-fold. In contrast, the SREBP-1c mRNA levels in livers from refed hepatocyte-Srebf-2^-/- mice only increased to a level that was slightly higher than fasted WT mice. There were also blunted increases in the expression of FA synthesis genes in hepatocyte-Srebf-2^-/- livers. The increase in FA synthesis mRNA expression that remained was likely mediated by ChREBP, a glucose-responsive transcription factor that can independently activate these genes (Ishii et al., 2004). These studies confirm that insulin-mediated induction of SREBP-1c requires intact LXR activity.

Deletion of SREBP-2 in the liver reduced the amount of LDLR mRNA by ~20% but there was an accompanying ~80% reduction in the mRNA level of PCSK9 (Figure 2A). PCSK9 is a secreted protein that degrades LDLRs in liver (Lagace et al., 2006). In livers of hepatocyte-Srebf-2^-/- mice, the reduction in LDLR production was balanced by the reduction in PCSK9-mediated LDLR destruction, which ultimately led to no measurable change in steady-state LDLR protein levels (data not shown). Nevertheless, plasma cholesterol levels in hepatocyte-Srebf-2^-/- mice were still 50% lower than those measured in WT mice (Table 1). To determine whether lower plasma cholesterol levels were a result of increased clearance of apoB-containing lipoproteins, we measured the ¹²⁵I-labeled LDL clearance. LDL was isolated from LDL receptor knockout mice and labeled the apoB with ¹²⁵I (Horton et al., 1999). As shown in Figure 6A, the clearance of LDL was identical in WT and hepatocyte-Srebf-2^-/- mice. Therefore, the lower plasma and TG concentrations were likely a result of reduced VLDL production; therefore we measured rates of TG secretion in mice following the administration of Triton. As shown in Figure 6B and C, TG secretion rates from livers of hepatocyte-Srebf-2^-/- mice reduced by 29%.

Figure 6

Download asset Open asset

The current data confirm that SREBP-2 is the primary transcriptional regulator of cholesterol biosynthesis in vivo. Deletion of Srebf-2 in hepatocytes reduced the expression of all cholesterol biosynthetic genes and rates of hepatic cholesterol synthesis. Despite the deficiency in liver cholesterol content, no apparent additional mechanisms are present in the livers capable of restoring cholesterol levels to normal in the absence of SREBP-2. The unexpected finding in Srebf-2 knockout livers was the marked reduction of SREBP-1c expression and genes involved in FA synthesis. While this manuscript was in preparation, Vergnes et al. (Vergnes et al., 2016) also reported that SREBP-1c expression and its regulated genes were reduced in livers of SREBP-2 hypomorphic mice. Here, dietary supplementation of cholesterol or an LXR agonist restored SREBP-1c expression and the mRNAs encoding the FA biosynthetic enzymes, which suggests that the loss of flux through the cholesterol biosynthetic pathway results in the loss of an endogenous LXR ligand required for normal LXR activity.

The current studies also have identified the first molecular mechanism linking cholesterol and FA synthesis in liver. This link requires SREBP-2 expression and is apparently supplied by an intermediate or product of cholesterol biosynthesis that serves as a ligand for LXR, which is required for SREBP-1c expression. Coupling cholesterol and FA synthesis may be important for the efficient esterification of cholesterol since oleic acid is the preferred substrate for the cholesterol esterifying enzyme ACAT (Yang et al., 1997). Cholesterol may also be required for the normal formation of the VLDL particle lipid core and thus linking cholesterol and FA synthesis might be necessary for efficient VLDL production by the liver.

LXR can be activated by 20(S)-hydroxycholesterol, 22(R)-hydroxycholesterol, 24(S)-hydroxycholesterol, 24(S),25-epoxycholesterol, 25-hydroxycholesterol, and 27-hydroxycholesterol as well as the cholesterol biosynthetic intermediate desmosterol (Huang, 2014; Yang et al., 2006). Supplementation of a synthetic LXR ligand or feeding cholesterol were both capable of restoring the SREBP-1c expression indicating that LXR was present and that if a ligand was provided it was capable of normally activating Srebf-1c transcription in the SREBP-2 deficient mice. However, we were unable to identify any changes in concentrations of known LXR ligands hepatocyte-Srebf-2^-/- liver, indicating that the missing ligand is unique and not previously identified. Further studies will be required to identify this endogenous ligand.

The phenotype that resulted from the deletion of Srebf-2 in hepatocytes was nearly indistinguishable from mice that lack Scap in hepatocytes (Matsuda et al., 2001; Moon et al., 2012). The only molecular signature we found that differed between hepatocyte-Srebf-2^-/- and hepatocyte-Scap^-/- livers was the retained expression of SREBP-1a and ACC2 in the livers of hepatocyte-Srebf-2^-/- mice. These studies confirm that SREBP-1a has only a minor role in regulating basal and stimulated cholesterol and fatty acid synthesis in the liver. The phenotypic similarities between hepatocyte-Srebf-2^-/- and hepatocyte-Scap^-/- mice also suggest that blocking SREBP-2 action would be effective in preventing the development of hepatic steatosis in mice with insulin resistance and/or diabetes. The markedly reduced expression of lipogenic genes in hepatocyte-Srebf-2^-/- livers and the blunted response of these genes to refeeding a high carbohydrate diet suggest that blocking SREBP-2 action would also be effective in preventing the development of hepatic steatosis induced by hyperinsulinemia, similar to the results obtained in Scap deficient mice that also lack leptin (Moon et al., 2012).

Plasma cholesterol and TG concentrations were also significantly lower in hepatocyte-Srebf-2^-/- mice. The LDLR protein level was not reduced in hepatocyte-Srebf-2^-/- livers despite a 20% reduction in LDLR mRNA levels; however, the mRNA levels of PCSK9 were reduced by 80% in hepatocyte-Srebf-2^-/- livers. Inasmuch as LDL clearance was not altered in hepatocyte-Srebf-2^-/- mice, the reduced LDLR protein destruction by PCSK9 likely offset the reduced LDLR production since LDL clearance from the plasma of hepatocyte-Srebf-2^-/- mice was not lower. Thus, the lower plasma lipid levels were a reflection of reduced VLDL secretion from the liver.

A potential additional benefit of inhibiting SREBP expression in the liver, independent of the reduction in hepatic TGs, is the reduced expression of PNPLA3. Polymorphisms in PNPLA3 are associated with hepatic steatosis, nonalcoholic steatohepatitis, cirrhosis, and hepatocellular carcinoma in humans (Romeo et al., 2008; Speliotes et al., 2010). SREBP-1c is the only known transcriptional activator of PNPLA3 expression (Huang et al., 2010). In WT mice refed a high carbohydrate diet, PNPLA3 mRNA levels increased >200–fold above the fasted state, whereas in livers of hepatocyte-Srebf-2^-/- mice PNPLA3 only increased 15–fold (Table 3). The blunted PNPLA3 expression in livers of hepatocyte-Srebf-2^-/- mice was likely due to the accompanying loss of SREBP-1c since feeding the hepatocyte-Srebf-2^-/- mice diets supplemented with an LXR agonist or cholesterol (data not shown) restored SREBP-1c and PNPLA3 expression. Studies by Hobbs and colleagues (Li et al., 2012; Smagris et al., 2015) previously demonstrated that high expression levels of the mutant PNPLA3 protein are required for the development of hepatic steatosis in mice. Thus, a reduction in mutant PNPLA3 expression as a result of inhibiting SREBP-2 or Scap may be of therapeutic benefit in individuals who carry the PNPLA3 polymorphism.

The current report represents the last in a series of studies that we have carried out using genetically manipulated mice to elucidate the in vivo function of the SREBP family members (Horton et al., 2002). They confirm that SREBP-2 mediates the regulated expression of cholesterol biosynthetic genes and also controls steady-state tissue cholesterol concentrations by simultaneously regulating cholesterol synthesis and uptake from plasma and by modulating the expression of the LDLR and PCSK9. The physiological changes that result from deleting Srebf-2 mirror that of mice that lack Scap in hepatocytes since we show that SREBP-2 expression is required to produce an LXR ligand required for normal SREBP-1c expression. The resulting phenotypes suggest that the inhibition of SREBP-2 or Scap in the liver, which reduces cholesterol and FA synthesis, may be therapeutically advantageous for the treatment of hypertriglyceridemia and nonalcoholic fatty liver disease.

1. 1. Brown MS
   2. Goldstein JL

   (2009) Cholesterol feedback: from Schoenheimer's bottle to Scap's MELADL

   Journal of Lipid Research 50 Suppl:S15–27.

   https://doi.org/10.1194/jlr.R800054-JLR200

   • PubMed
   • Google Scholar
2. 1. Engelking LJ
   2. Kuriyama H
   3. Hammer RE
   4. Horton JD
   5. Brown MS
   6. Goldstein JL
   7. Liang G

   (2004) Overexpression of Insig-1 in the livers of transgenic mice inhibits SREBP processing and reduces insulin-stimulated lipogenesis

   Journal of Clinical Investigation 113:1168–1175.

   https://doi.org/10.1172/JCI20978

   • PubMed
   • Google Scholar
3. 1. Horton JD
   2. Bashmakov Y
   3. Shimomura I
   4. Shimano H

   (1998) Regulation of sterol regulatory element binding proteins in livers of fasted and refed mice

   PNAS 95:5987–5992.

   https://doi.org/10.1073/pnas.95.11.5987

   • PubMed
   • Google Scholar
4. 1. Horton JD
   2. Shimano H
   3. Hamilton RL
   4. Brown MS
   5. Goldstein JL

   (1999) Disruption of LDL receptor gene in transgenic SREBP-1a mice unmasks hyperlipidemia resulting from production of lipid-rich VLDL

   Journal of Clinical Investigation 103:1067–1076.

   https://doi.org/10.1172/JCI6246

   • PubMed
   • Google Scholar
5. 1. Horton JD
   2. Goldstein JL
   3. Brown MS

   (2002) SREBPs: activators of the complete program of cholesterol and fatty acid synthesis in the liver

   Journal of Clinical Investigation 109:1125–1131.

   https://doi.org/10.1172/JCI0215593

   • PubMed
   • Google Scholar
6. 1. Horton JD
   2. Shah NA
   3. Warrington JA
   4. Anderson NN
   5. Park SW
   6. Brown MS
   7. Goldstein JL

   (2003) Combined analysis of oligonucleotide microarray data from transgenic and knockout mice identifies direct SREBP target genes

   PNAS 100:12027–12032.

   https://doi.org/10.1073/pnas.1534923100

   • PubMed
   • Google Scholar
7. 1. Huang Y
   2. He S
   3. Li JZ
   4. Seo YK
   5. Osborne TF
   6. Cohen JC
   7. Hobbs HH

   (2010) A feed-forward loop amplifies nutritional regulation of PNPLA3

   PNAS 107:7892–7897.

   https://doi.org/10.1073/pnas.1003585107

   • PubMed
   • Google Scholar
8. 1. Huang C

   (2014) Natural modulators of liver X receptors

   Journal of Integrative Medicine 12:76–85.

   https://doi.org/10.1016/S2095-4964(14)60013-3

   • PubMed
   • Google Scholar
9. 1. Im SS
   2. Hammond LE
   3. Yousef L
   4. Nugas-Selby C
   5. Shin DJ
   6. Seo YK
   7. Fong LG
   8. Young SG
   9. Osborne TF

   (2009) Sterol regulatory element binding protein 1a regulates hepatic fatty acid partitioning by activating acetyl coenzyme A carboxylase 2

   Molecular and Cellular Biology 29:4864–4872.

   https://doi.org/10.1128/MCB.00553-09

   • PubMed
   • Google Scholar
10. 1. Ishibashi S
    2. Brown MS
    3. Goldstein JL
    4. Gerard RD
    5. Hammer RE
    6. Herz J

    (1993) Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediated gene delivery

    Journal of Clinical Investigation 92:883–893.

    https://doi.org/10.1172/JCI116663

    • PubMed
    • Google Scholar
11. 1. Ishii S
    2. Iizuka K
    3. Miller BC
    4. Uyeda K

    (2004) Carbohydrate response element binding protein directly promotes lipogenic enzyme gene transcription

    PNAS 101:15597–15602.

    https://doi.org/10.1073/pnas.0405238101

    • PubMed
    • Google Scholar
12. 1. Lagace TA
    2. Curtis DE
    3. Garuti R
    4. McNutt MC
    5. Park SW
    6. Prather HB
    7. Anderson NN
    8. Ho YK
    9. Hammer RE
    10. Horton JD

    (2006) Secreted PCSK9 decreases the number of LDL receptors in hepatocytes and in livers of parabiotic mice

    Journal of Clinical Investigation 116:2995–3005.

    https://doi.org/10.1172/JCI29383

    • PubMed
    • Google Scholar
13. 1. Li JZ
    2. Huang Y
    3. Karaman R
    4. Ivanova PT
    5. Brown HA
    6. Roddy T
    7. Castro-Perez J
    8. Cohen JC
    9. Hobbs HH

    (2012) Chronic overexpression of PNPLA3I148M in mouse liver causes hepatic steatosis

    Journal of Clinical Investigation 122:4130–4144.

    https://doi.org/10.1172/JCI65179

    • PubMed
    • Google Scholar
14. 1. Liang G
    2. Yang J
    3. Horton JD
    4. Hammer RE
    5. Goldstein JL
    6. Brown MS

    (2002) Diminished hepatic response to fasting/refeeding and liver X receptor agonists in mice with selective deficiency of sterol regulatory element-binding protein-1c

    Journal of Biological Chemistry 277:9520–9528.

    https://doi.org/10.1074/jbc.M111421200

    • PubMed
    • Google Scholar
15. 1. Matsuda M
    2. Korn BS
    3. Hammer RE
    4. Moon YA
    5. Komuro R
    6. Horton JD
    7. Goldstein JL
    8. Brown MS
    9. Shimomura I

    (2001) SREBP cleavage-activating protein (SCAP) is required for increased lipid synthesis in liver induced by cholesterol deprivation and insulin elevation

    Genes & Development 15:1206–1216.

    https://doi.org/10.1101/gad.891301

    • PubMed
    • Google Scholar
16. 1. McDonald JG
    2. Thompson BM
    3. McCrum EC
    4. Russell DW

    (2007) Extraction and analysis of sterols in biological matrices by high performance liquid chromatography electrospray ionization mass spectrometry

    Methods in Enzymology 432:145–170.

    https://doi.org/10.1016/S0076-6879(07)32006-5

    • PubMed
    • Google Scholar
17. 1. McFarlane MR
    2. Cantoria MJ
    3. Linden AG
    4. January BA
    5. Liang G
    6. Engelking LJ

    (2015) Scap is required for sterol synthesis and crypt growth in intestinal mucosa

    Journal of Lipid Research 56:1560–1571.

    https://doi.org/10.1194/jlr.M059709

    • PubMed
    • Google Scholar
18. 1. Moon YA
    2. Liang G
    3. Xie X
    4. Frank-Kamenetsky M
    5. Fitzgerald K
    6. Koteliansky V
    7. Brown MS
    8. Goldstein JL
    9. Horton JD

    (2012) The scap/SREBP pathway is essential for developing diabetic fatty liver and carbohydrate-induced hypertriglyceridemia in animals

    Cell Metabolism 15:240–246.

    https://doi.org/10.1016/j.cmet.2011.12.017

    • PubMed
    • Google Scholar
19. 1. Owen JL
    2. Zhang Y
    3. Bae SH
    4. Farooqi MS
    5. Liang G
    6. Hammer RE
    7. Goldstein JL
    8. Brown MS

    (2012) Insulin stimulation of SREBP-1c processing in transgenic rat hepatocytes requires p70 S6-kinase

    PNAS 109:16184–16189.

    https://doi.org/10.1073/pnas.1213343109

    • PubMed
    • Google Scholar
20. 1. Park SW
    2. Moon YA
    3. Horton JD

    (2004) Post-transcriptional regulation of low density lipoprotein receptor protein by proprotein convertase subtilisin/kexin type 9a in mouse liver

    Journal of Biological Chemistry 279:50630–50638.

    https://doi.org/10.1074/jbc.M410077200

    • PubMed
    • Google Scholar
21. 1. Rashid S
    2. Curtis DE
    3. Garuti R
    4. Anderson NN
    5. Bashmakov Y
    6. Ho YK
    7. Hammer RE
    8. Moon YA
    9. Horton JD

    (2005) Decreased plasma cholesterol and hypersensitivity to statins in mice lacking Pcsk9

    PNAS 102:5374–5379.

    https://doi.org/10.1073/pnas.0501652102

    • PubMed
    • Google Scholar
22. 1. Repa JJ
    2. Liang G
    3. Ou J
    4. Bashmakov Y
    5. Lobaccaro JM
    6. Shimomura I
    7. Shan B
    8. Brown MS
    9. Goldstein JL
    10. Mangelsdorf DJ

    (2000) Regulation of mouse sterol regulatory element-binding protein-1c gene (SREBP-1c) by oxysterol receptors, LXRalpha and LXRbeta

    Genes & Development 14:2819–2830.

    https://doi.org/10.1101/gad.844900

    • PubMed
    • Google Scholar
23. 1. Romeo S
    2. Kozlitina J
    3. Xing C
    4. Pertsemlidis A
    5. Cox D
    6. Pennacchio LA
    7. Boerwinkle E
    8. Cohen JC
    9. Hobbs HH

    (2008) Genetic variation in PNPLA3 confers susceptibility to nonalcoholic fatty liver disease

    Nature Genetics 40:1461–1465.

    https://doi.org/10.1038/ng.257

    • PubMed
    • Google Scholar
24. 1. Shimano H
    2. Horton JD
    3. Hammer RE
    4. Shimomura I
    5. Brown MS
    6. Goldstein JL

    (1996) Overproduction of cholesterol and fatty acids causes massive liver enlargement in transgenic mice expressing truncated SREBP-1a

    Journal of Clinical Investigation 98:1575–1584.

    https://doi.org/10.1172/JCI118951

    • PubMed
    • Google Scholar
25. 1. Shimano H
    2. Shimomura I
    3. Hammer RE
    4. Herz J
    5. Goldstein JL
    6. Brown MS
    7. Horton JD

    (1997) Elevated levels of SREBP-2 and cholesterol synthesis in livers of mice homozygous for a targeted disruption of the SREBP-1 gene

    Journal of Clinical Investigation 100:2115–2124.

    https://doi.org/10.1172/JCI119746

    • PubMed
    • Google Scholar
26. 1. Shimomura I
    2. Shimano H
    3. Horton JD
    4. Goldstein JL
    5. Brown MS

    (1997) Differential expression of exons 1a and 1c in mRNAs for sterol regulatory element binding protein-1 in human and mouse organs and cultured cells

    Journal of Clinical Investigation 99:838–845.

    https://doi.org/10.1172/JCI119247

    • PubMed
    • Google Scholar
27. 1. Shimomura I
    2. Bashmakov Y
    3. Ikemoto S
    4. Horton JD
    5. Brown MS
    6. Goldstein JL

    (1999) Insulin selectively increases SREBP-1c mRNA in the livers of rats with streptozotocin-induced diabetes

    PNAS 96:13656–13661.

    https://doi.org/10.1073/pnas.96.24.13656

    • PubMed
    • Google Scholar
28. 1. Smagris E
    2. BasuRay S
    3. Li J
    4. Huang Y
    5. Lai KM
    6. Gromada J
    7. Cohen JC
    8. Hobbs HH

    (2015) Pnpla3I148M knockin mice accumulate PNPLA3 on lipid droplets and develop hepatic steatosis

    Hepatology 61:108–118.

    https://doi.org/10.1002/hep.27242

    • PubMed
    • Google Scholar
29. 1. Speliotes EK
    2. Butler JL
    3. Palmer CD
    4. Voight BF
    5. Hirschhorn JN
    6. GIANT Consortium
    7. MIGen Consortium
    8. NASH CRN

    (2010) PNPLA3 variants specifically confer increased risk for histologic nonalcoholic fatty liver disease but not metabolic disease

    Hepatology 52:904–912.

    https://doi.org/10.1002/hep.23768

    • PubMed
    • Google Scholar
30. 1. Vergnes L
    2. Chin RG
    3. de Aguiar Vallim T
    4. Fong LG
    5. Osborne TF
    6. Young SG
    7. Reue K

    (2016) SREBP-2-deficient and hypomorphic mice reveal roles for SREBP-2 in embryonic development and SREBP-1c expression

    Journal of Lipid Research 57:410–421.

    https://doi.org/10.1194/jlr.M064022

    • PubMed
    • Google Scholar
31. 1. Yang H
    2. Cromley D
    3. Wang H
    4. Billheimer JT
    5. Sturley SL

    (1997) Functional expression of a cDNA to human acyl-coenzyme A:cholesterol acyltransferase in yeast. Species-dependent substrate specificity and inhibitor sensitivity

    Journal of Biological Chemistry 272:3980–3985.

    https://doi.org/10.1074/jbc.272.7.3980

    • PubMed
    • Google Scholar
32. 1. Yang J
    2. Goldstein JL
    3. Hammer RE
    4. Moon YA
    5. Brown MS
    6. Horton JD

    (2001) Decreased lipid synthesis in livers of mice with disrupted Site-1 protease gene

    PNAS 98:13607–13612.

    https://doi.org/10.1073/pnas.201524598

    • PubMed
    • Google Scholar
33. 1. Yang C
    2. McDonald JG
    3. Patel A
    4. Zhang Y
    5. Umetani M
    6. Xu F
    7. Westover EJ
    8. Covey DF
    9. Mangelsdorf DJ
    10. Cohen JC
    11. Hobbs HH

    (2006) Sterol intermediates from cholesterol biosynthetic pathway as liver X receptor ligands

    Journal of Biological Chemistry 281:27816–27826.

    https://doi.org/10.1074/jbc.M603781200

    • PubMed
    • Google Scholar

Author details

1. Shunxing Rong

   Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States

   Contribution

   SRo, Conceptualization, Data curation, Formal analysis, Validation, Investigation, Visualization, Methodology, Writing—original draft, Writing—review and editing

   Competing interests

   The authors declare that no competing interests exist.

   "This ORCID iD identifies the author of this article:" 0000-0002-4948-7222

2. Víctor A Cortés

   Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States

   Present address

   Department of Nutrition, Diabetes and Metabolism, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile

   Contribution

   VAC, Data curation, Formal analysis, Validation, Methodology

   Competing interests

   The authors declare that no competing interests exist.

3. Shirya Rashid

   Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States

   Present address

   Department of Public Health, North South University, Bashundhara, Dhaka, Bangladesh

   Contribution

   SRa, Data curation, Methodology, Writing—original draft

   Competing interests

   The authors declare that no competing interests exist.

4. Norma N Anderson

   Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States

   Contribution

   NNA, Data curation, Formal analysis, Supervision, Validation, Methodology

   Competing interests

   The authors declare that no competing interests exist.

5. Jeffrey G McDonald

   Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States

   Contribution

   JGM, Data curation, Formal analysis, Methodology

   Competing interests

   The authors declare that no competing interests exist.

6. Guosheng Liang

   Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States

   Contribution

   GL, Data curation, Formal analysis, Supervision, Investigation, Methodology

   Competing interests

   The authors declare that no competing interests exist.

7. Young-Ah Moon

   Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States

   Present address

   Department of Biomedical Sciences, Inha University College of Medicine, Nam-gu Iuncheon, Korea

   Contribution

   Y-AM, Conceptualization, Resources, Data curation, Supervision, Validation, Investigation, Methodology, Writing—original draft

   Competing interests

   The authors declare that no competing interests exist.

8. Robert E Hammer

   Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States

   Contribution

   REH, Resources, Methodology

   Competing interests

   The authors declare that no competing interests exist.

9. Jay D Horton

   1. Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States
   2. Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, United States

   Contribution

   JDH, Conceptualization, Data curation, Formal analysis, Supervision, Funding acquisition, Investigation, Methodology, Project administration, Writing—review and editing

   For correspondence

   Jay.Horton@utsouthwestern.edu

   Competing interests

   The authors declare that no competing interests exist.

   "This ORCID iD identifies the author of this article:" 0000-0002-7778-1074

• 5,704

  views

• 1,070

  downloads

• 94

  citations

Views, downloads and citations are aggregated across all versions of this paper published by eLife.