Cholesterol Biosynthesis: Lanosterol to Cholesterol

Risley, John M.

doi:10.1021/ed079p377

Cited by 46 publications

(35 citation statements)

References 35 publications

(57 reference statements)

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“…The metabolic acidosis resulting from methanol poisoning is caused by the accumulation of formic acid (formate plus hydrogen ions) (17). Finally, formate is also produced in the endoplasmic reticulum during cholesterol synthesis (during the conversion of lanosterol to cholesterol) (28) and in peroxisomes during the ␣-oxidation of phytanic acid (39) and 2-hydroxy fatty acids (8). We are unaware of any study that has attempted to quantify the different sources of formate.…”

Section: E65mentioning

confidence: 99%

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration

Lamarre

Molloy

Reinke

et al. 2012

American Journal of Physiology-Endocrinology and Metabolism

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Lamarre SG, Molloy AM, Reinke SN, Sykes BD, Brosnan ME, Brosnan JT. Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration. 1 H-NMR metabolomic analysis of sera from vitamin B12-deficient rats. In addition to the expected increases in methylmalonate and homocysteine (Hcy), we observed an approximately sevenfold increase in formate levels, from 64 M in control rats to 402 M in vitamin B 12-deficient rats. Urinary formate was also elevated. This elevation of formate could be attributed to impaired one-carbon metabolism since formate is assimilated into the one-carbon pool by incorporation into 10-formyl-THF via the enzyme 10-formyl-THF synthase. Both plasma and urinary formate were also increased in folate-deficient rats. Hcy was elevated in both the vitamin B12-and folate-deficient rats. Although plasma Hcy was also elevated, plasma formate was unaffected in vitamin B6-deficient rats (impaired transsulfuration pathway). These results were in accord with a mathematical model of folate metabolism, which predicted that reduction in methionine synthase activity would cause increased formate levels, whereas reduced cystathionine ␤-synthase activity would not. Our data indicate that formate provides a novel window into cellular folate metabolism, that elevated formate can be a useful indicator of deranged one-carbon metabolism and can be used to discriminate between the hyperhomocysteinemia caused by defects in the remethylation and transsulfuration pathways. VITAMIN B 12 DEFICIENCY RESULTS IN A WIDE SPECTRUM of hematologic and neuropsychiatric disorders. The detection of vitamin B 12 deficiency has traditionally been based on low serum vitamin B 12 levels, with supportive clinical evidence of disease. It is now recognized that serum vitamin B 12 may be insufficient to detect a deficiency, especially in the case of elderly subjects without hematologic abnormalities. The measurement of metabolites such as homocysteine (Hcy) and methylmalonic acid (MMA) has been shown to be more sensitive in diagnosing vitamin B 12 deficiency (33, 34). In a search for novel biomarkers of vitamin B 12 deficiency, we fed rats a vitamin B 12 -deficient diet and subjected their sera to 1 H-NMR metabolomic analysis. Together with the expected increased concentrations of Hcy and MMA, we found an approximately sevenfold increase in both serum and urinary formate concentrations in the vitamin B 12 -deficient animals.We confirmed that elevated formate would also be found in folate-deficient rats, since impaired folate metabolism (via the methylfolate trap) is a well-recognized consequence of vitamin B 12 deficiency (12, 31, 32) and because formate is incorporated into 10-formyl-tetrahydrofolate (THF) via 10-formyl-THF synthase (37). Both folate and vitamin B 12 deficiencies are characterized by elevated plasma Hcy. A deficiency of pyridoxal (vitamin B 6 ) also causes elevated plasma Hcy, which becomes more pronounced after methionine loading (18). This is due to impaired removal of Hcy ...

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Section: E65mentioning

confidence: 99%

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration

Lamarre

Molloy

Reinke

et al. 2012

American Journal of Physiology-Endocrinology and Metabolism

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“…Cholesterol biosynthesis in modern organisms is a long biochemical pathway that employs the following four O 2 -dependent enzymes: (i) squalene epoxidase, (ii) lanosterol 14-␣-methyl demethylase cytochrome P450, (iii) sterol-4-␣-methyl oxidase, and (iv) lathosterol oxidase (49). These O 2 -dependent enzymes perform reactions that, although not currently known to occur biochemically in anaerobic organisms, could feasibly occur without O 2 .…”

Section: Biomarker Counterevidence For Archean Omentioning

confidence: 99%

The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis

Kopp

Kirschvink

Hilburn

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

492

299

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Although biomarker, trace element, and isotopic evidence have been used to claim that oxygenic photosynthesis evolved by 2.8 giga-annum before present (Ga) and perhaps as early as 3.7 Ga, a skeptical examination raises considerable doubt about the presence of oxygen producers at these times. Geological features suggestive of oxygen, such as red beds, lateritic paleosols, and the return of sedimentary sulfate deposits after a Ϸ900-million year hiatus, occur shortly before the Ϸ2.3-2.2 Ga Makganyene ''snowball Earth'' (global glaciation). The massive deposition of Mn, which has a high redox potential, practically requires the presence of environmental oxygen after the snowball. New age constraints from the Transvaal Supergroup of South Africa suggest that all three glaciations in the Huronian Supergroup of Canada predate the Snowball event. A simple cyanobacterial growth model incorporating the range of C, Fe, and P fluxes expected during a partial glaciation in an anoxic world with high-Fe oceans indicates that oxygenic photosynthesis could have destroyed a methane greenhouse and triggered a snowball event on timescales as short as 1 million years. As the geological evidence requiring oxygen does not appear during the Pongola glaciation at 2.9 Ga or during the Huronian glaciations, we argue that oxygenic cyanobacteria evolved and radiated shortly before the Makganyene snowball.oxygen ͉ Makganyene glaciation ͉ Huronian glaciations ͉ cyanobacteria

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“…Deficiency of 17b-hydroxysteroid dehydrogenase type7 (Hsd17b7), an enzyme recently shown to be involved in cholesterol biosynthesis in yeast (Marijanovic et al, 2003) was shown to be responsible for the cholesterol auxotrophy. Hsd17b7 encodes a 3-ketoreductase and is utilized twice in the conversion of lanosterol to lathosterol during cholesterol biosynthesis (Risley, 2002). In a natural revertant, Hsd17b7 was expressed 15 fold higher compared to the parental wild type cells.…”

Section: Introductionmentioning

confidence: 99%

Reverting cholesterol auxotrophy of NS0 cells by altering epigenetic gene silencing

Seth

Öztürk

2006

Biotechnol. Bioeng.

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NS0 is a cholesterol-requiring mouse myeloma cell line widely used in the production of recombinant antibodies. We have previously reported that the deficiency of 17beta-hydroxysteroid dehydrogenase type7 (Hsd17b7) is responsible for the cholesterol auxotrophy of NS0 cells. Here we demonstrate DNA methylation to be the mechanism underlying transcriptional suppression of Hsd17b7 in cholesterol dependent NS0 cells. Analysis of the DNA methylation pattern revealed methylation of the CpG-rich region upstream of the Hsd17b7 transcription start site in NS0 cells. This is in contrast to the unmethylated status of this sequence in a naturally isolated cholesterol independent revertant cell population (NS0_r). This transcriptional repression was relieved after treating cells with the demethylating drug, 5-azacytidine. Drug treatment also gave rise to high frequency cholesterol-independent variants. Characterization of revertants revealed substantially elevated transcript level of 17beta-hydroxysteroid dehydrogenase type7 (Hsd17b7) gene along with hypomethylation of the CpG-rich region. These results affirm that deficiency of Hsd17b7 causes cholesterol dependence of NS0 cells. Furthermore, induction of cholesterol independence by altering DNA methylation pattern alludes to the role of epigenetics in the metabolic adaptation of NS0 cells. With the widespread use of NS0 cells, this finding will have a significant impact on the optimization of recombinant antibody production processes.

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Cholesterol Biosynthesis: Lanosterol to Cholesterol

Cited by 46 publications

References 35 publications

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration

The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis

Reverting cholesterol auxotrophy of NS0 cells by altering epigenetic gene silencing

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