Regulation of sterol 27-hydroxylase and an alternative pathway of bile acid biosynthesis in primary cultures of rat hepatocytes

Stravitz, R. Todd; Vlahčevič, Z. Reno; Russell, Terry; Heizer, Marcia L.; Avadhani, Narayan G.; Hylemon, Phillip B.

doi:10.1016/0960-0760(95)00282-0

Cited by 76 publications

(58 citation statements)

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“…While the cholesterol content of mitochondria has not been properly estimated because of PM contamination of those subcellular fractions, it appears that its level is quite low, thereby limiting the rate of synthesis of 27-HC. This supposition explains why bolstering the cholesterol in isolated mitochondria with cholesterol-cyclodextrin complexes promotes the production of 27-HC and why cyclodextrin itself has a similar effect in vitro: presumably it shuttles cholesterol present in contaminating PM fragments to the mitochondria (35)(36)(37). In keeping with these indirect fi ndings, we fi nd that, in intact cells, mitochondrial oxysterol production is greatly stimulated by augmenting PM cholesterol ( Fig.…”

Section: Effect Of Nonsterol Intercalators On 27-hc Productionsupporting

confidence: 71%

Regulation of fibroblast mitochondrial 27-hydroxycholesterol production by active plasma membrane cholesterol

Lange

Steck

et al. 2009

Journal of Lipid Research

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This study addresses the regulation of the biosynthesis of oxysterol signal molecules. Side chain oxysterols such as 24-, 25-, and 27-hydroxycholesterol (HC) are derived from cholesterol in the endoplasmic reticulum (ER) and mitochondria and trigger downregulation of the abundance of cell cholesterol through diverse pathways ( 1-4 ). In particular, the association of oxysterols with nuclear liver X receptors (LXR) promotes the expression of ATP-binding cassette (ABC) transport proteins that transfer excess cholesterol out of cells such as macrophages ( 5 ). Furthermore, because the oxysterol derivatives are more water-soluble than cholesterol, they readily exit cells and are transported via circulating lipoproteins to the liver for conversion to bile acids and excretion ( 6, 7 ). In addition, side-chain oxysterols promote the interaction of Insig proteins with sterol regulatory element-binding protein (SREBP) cleavage-activating protein-SREBP complexes; this action sequesters SREBP in the ER and, as a result, reduces the expression of genes for cholesterol accretion ( 8 ). By activating Insig, side-chain oxysterols also stimulate the proteolysis of hydroxy-3-methylglutaryl CoA reductase (HMGR) through a ubiquitination-proteasomal pathway ( 9, 10 ).The mechanism by which oxysterol biosynthesis is set according to the level of cell cholesterol so as to execute these homeostatic functions is obscure. Indeed, despite the cogency of the oxysterol hypothesis, the physiological relevance of the underlying in vitro fi ndings has long been debated ( 1, 11 ). To carry out its postulated role in vivo, oxysterol production should represent the level of cellular Abstract Side chain oxysterols are cholesterol derivatives thought to signal the abundance of cell cholesterol to homeostatic effector proteins. Here, we investigated how plasma membrane (PM) cholesterol might regulate 27-hydroxycholesterol (HC) biosynthesis in cultured fi broblasts. We showed that PM cholesterol was a major substrate for 27-HC production. Biosynthesis commenced within minutes of loading depleted cells with cholesterol, concurrent with the rapid inactivation of hydroxy-3-methylglutaryl CoA reductase (HMGR). 27-HC production rose ~ 30-fold in normal and Niemann-Pick C1 fi broblasts when PM cholesterol was increased by ~ 60%. 27-HC production was also stimulated by 1-octanol, which displaces PM cholesterol from its phospholipid complexes and thereby increases its activity (escape tendency) and elevates its intracellular abundance. Conversely, lysophosphatidylserine and U18666A inhibited 27-HC biosynthesis and the inactivation of HMGR, presumably by reducing the activity of PM cholesterol and, therefore, its circulation to mitochondria. We conclude that, in this in vitro system, excess ( Press, April 28, 2009 DOI 10.1194 Regulation of fi broblast mitochondrial 27-hydroxycholesterol production by active plasma membrane cholesterol Abbreviations: ER, endoplasmic reticulum; HC, hydroxycholesterol; HMGR, hydroxy-3-methylglutaryl CoA reductase; HPCD, 2-␤ -...

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Section: Effect Of Nonsterol Intercalators On 27-hc Productionsupporting

confidence: 71%

Regulation of fibroblast mitochondrial 27-hydroxycholesterol production by active plasma membrane cholesterol

Lange

Steck

et al. 2009

Journal of Lipid Research

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“…Although the decrease in bile acids inside the cells is not statistically significant, they do not increase either, further supporting the idea that the p38 kinase pathway has a direct effect on their synthesis. It should be noted that in primary hepatocytes ϳ50% of bile acid synthesis takes place through the acidic pathway in which 7␣-hydroxylase is not involved, thus the highest reduction in bile acid synthesis that can be seen suppressing 7␣-hydroxylase is 50% (31). The dramatic suppression of 7␣-hydroxylase expression that we observed (Fig.…”

Section: Discussionsupporting

confidence: 57%

Activation of Bile Acid Biosynthesis by the p38 Mitogen-activated Protein Kinase (MAPK)

Tavares-Sanchez

et al. 2007

Journal of Biological Chemistry

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Bile acids are required for intestinal absorption and biliary solubilization of cholesterol and lipids. In addition, bile acids play a crucial role in cholesterol homeostasis. One of the key enzymes in the bile acid biosynthetic pathways is cholesterol 7␣-hydroxylase/cytochrome P450 7␣-hydroxylase (7␣-hydroxylase), which is the rate-limiting and regulatory step of the "classic" pathway. Transcription of the 7␣-hydroxylase gene is highly regulated. Two nuclear receptors, hepatocyte nuclear factor 4␣ (HNF-4␣) and ␣ 1 -fetoprotein transcription factor, are required for both transcription and regulation by different physiological events. It has been shown that some mitogen-activated protein kinases, such as the c-Jun N-terminal kinase and the ERK, play important roles in the regulation of 7␣-hydroxylase transcription. In this study, we show evidence that the p38 kinase pathway plays an important role in 7␣-hydroxylase expression and hence in bile acid synthesis. Inhibition of p38 kinase activity in primary hepatocytes results in ϳ5-10-fold reduction of 7␣-hydroxylase mRNA. This suppression is mediated, at least in part, through HNF-4␣. Inhibition of p38 kinase activity diminishes HNF-4␣ nuclear protein levels and its phosphorylation in vivo and in vitro, and it renders a less stable protein. Induction of the p38 kinase pathway by insulin results in an increase in HNF-4␣ protein and a concomitant induction of 7␣-hydroxylase expression that is blocked by inhibiting the p38 pathway. These studies show a functional link between the p38 signaling pathway, HNF-4␣, and bile acid synthesis.

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“…In the present studies, the gene, as expected (57), was found to be induced by dexamethasone, a known inducer of the CYP3A family of cytochrome P-450s (28). In addition, CYP27A was shown to be upregulated by ␤-naphtoflavone, a known inducer of CYP1A1 and -1A2 (17).…”

Section: Discussionmentioning

confidence: 50%

High sensitivity of rat hepatic vitamin D₃-25 hydroxylaseCYP27Ato 1,25-dihydroxyvitamin D₃administration

Theodoropoulos

Demers

Petit

et al. 2003

American Journal of Physiology-Endocrinology and Metabolism

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High sensitivity of the rat hepatic vitamin D3-25 hydroxylase CYP27A to 1,25-dihydroxyvitamin D 3 administration. Am J Physiol Endocrinol Metab 284: E138-E147, 2003. First published October 1, 2002 10.1152 10. /ajpendo.00303.2002 is considered the main vitamin D3 (D3)-25 hydroxylase in humans. Our purpose was to evaluate the effect of the D3 nutritional and hormonal status on hepatic CYP27A mRNA, cellular distribution, transcription rate, and enzyme activity. Studies were carried out in normal and in D-depleted rats supplemented with D3, 25OHD3, or 1,25(OH)2D3. CYP27A exhibited a significant gender difference and was observed throughout the hepatic acinus not only in hepatocytes but also in sinusoidal endothelial, stellate, and Kupffer cells. Neither D3 nor 25OHD3 influenced CYP27A mRNA levels. However, 1,25(OH)2D3 repletion led to a 60% decrease in CYP27A mRNA, which was accompanied by a 46% decrease in mitochondrial D3-25 hydroxylase activity. The effect of 1,25(OH)2D3 was mediated by a significant decrease in CYP27A transcription, whereas its mRNA half-life remained unchanged. Our data indicate that CYP27A is present in hepatic parenchymal and sinusoidal cells and that the gene transcript is not influenced by the D3 nutritional status but is transcriptionally regulated by 1,25(OH)2D3 exposure.bile acid biosynthesis; Kupffer cells; stellate cells; hepatocytes; sinusoidal endothelial cells THE SECOSTEROID VITAMIN D 3 (D 3 ) of endogenous or exogenous origin has, in its native form, no biological activity. Once in circulation, D 3 is efficiently taken up by the liver (26) and hydroxylated at C-25 by a mitochondrial mixed-function oxidase CYP27A [C 27 sterol hydroxylase (EC 1.14.13.15)] (15). In humans, the enzyme is presumed to be the only D 3 -25 hydroxylase (51). However, a microsomal D 3 -25 hydroxylase has also been reported in rodents (11), chickens (12), and pigs (35), but only the porcine enzyme (which has been termed CYP2D25) has been cloned to date (34,44).CYP27A is a cytochrome P-450 that catalyzes the first step in the oxidation of the cholesterol side chain in the secondary "acidic" bile acid biosynthesis pathway (13). CYP27A is also able to hydroxylate D 3 and D 3 metabolites at position C-25 (51) as well as at other positions on the secosteroid side chain (29, 54). It has also been reported to be able to catalyze the 1␣-hydroxylation of 25-hydroxyvitamin D 3 (25OHD 3 ), albeit at a much lower rate than the transformation of D 3 into 25OHD 3 (3). However, unlike the tight regulation by the D 3 endocrine system associated with the renal 25-hydroxyvitamin D 3 -1␣-hydroxylase, the sensitivity of the gene encoding CYP27A to D 3 or to D 3 metabolites has not been characterized. The presence of regulatory mechanisms related to the D 3 status as a modulator of the 25-hydroxylation of the vitamin is, however, a widely accepted notion, which rests on the studies of DeLuca's group in the early 1970s (Bhattacharyya and DeLuca, Refs. 10, 12). Several laboratories have attempted to evaluate the mechanism(s) inv...

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Regulation of sterol 27-hydroxylase and an alternative pathway of bile acid biosynthesis in primary cultures of rat hepatocytes

Cited by 76 publications

References 51 publications

Regulation of fibroblast mitochondrial 27-hydroxycholesterol production by active plasma membrane cholesterol

Regulation of fibroblast mitochondrial 27-hydroxycholesterol production by active plasma membrane cholesterol

Activation of Bile Acid Biosynthesis by the p38 Mitogen-activated Protein Kinase (MAPK)

High sensitivity of rat hepatic vitamin D₃-25 hydroxylaseCYP27Ato 1,25-dihydroxyvitamin D₃administration

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Regulation of sterol 27-hydroxylase and an alternative pathway of bile acid biosynthesis in primary cultures of rat hepatocytes

Cited by 76 publications

References 51 publications

Regulation of fibroblast mitochondrial 27-hydroxycholesterol production by active plasma membrane cholesterol

Regulation of fibroblast mitochondrial 27-hydroxycholesterol production by active plasma membrane cholesterol

Activation of Bile Acid Biosynthesis by the p38 Mitogen-activated Protein Kinase (MAPK)

High sensitivity of rat hepatic vitamin D3-25 hydroxylaseCYP27Ato 1,25-dihydroxyvitamin D3administration

Contact Info

Product

Resources

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High sensitivity of rat hepatic vitamin D₃-25 hydroxylaseCYP27Ato 1,25-dihydroxyvitamin D₃administration