Cholesterol Biosynthesis from Lanosterol

Abstract

The cDNA encoding the 471-amino acid rat 7-dehydrocholesterol reductase (DHCR), an enzyme that has been implicated in both cholesterol biosynthesis and developmental abnormalities (e.g. Smith-Lemli-Opitz syndrome) in mammals, has been cloned and sequenced, and the primary structure of the enzyme has been deduced. The DHCR gene was mapped to chromosome 8q2.1 by fluorescence in situ hybridization. Rat DHCR, calculated molecular mass of 54.15-kDa polypeptide, shares a close amino acid identity with mouse and human DHCRs (96 and 87%, respectively) as compared with its other related proteins (e.g. fungal sterol ⌬ 14 -reductase) and exhibits high hydrophobicity (>68%) with 9 transmembrane domains. Five putative sterol-sensing domains were predicted to be localized in transmembrane domains 4 -8, which are highly homologous to those found in 3-hydroxymethylglutaryl-CoA reductase, sterol regulatory element-binding protein cleavage-activating protein, and patched protein. The polypeptide encoded by DHCR cDNA was expressed in yeast as a 55.45-kDa myctagged fusion protein, which was recognized with antimyc monoclonal antibody 9E10 and shown to possess full DHCR activity with respect to dependence on NADPH and sensitivity to DHCR inhibitors. Northern blot analysis indicates that the highest expression of DHCR mRNA was detected in liver, followed by kidney and brain. In rat brains, the highest level of mRNA encoding DHCR was detected in the midbrain, followed by the spinal cord and medulla. Feeding rats 5% cholestyramine plus 0.1% lovastatin in chow resulted in both approximately a 3-fold induction of DHCR mRNA and a 5-fold increase of the enzymic activity in the liver. When rats were fed 0.1% (w/w) AY-9944 (in chow) for 14-days, a complete inhibition of DHCR activity and a significant reduction in serum total cholesterol level were observed. However, the level of hepatic DHCR mRNA fell only slightly, suggesting that AY-9944 may act more rapidly at the protein level than at the level of transcription of the DHCR gene under these conditions.

Inactivation of liver X receptor β leads to adult-onset motor neuron degeneration in male mice

“…It is possible that only specific types of neurons depend on external cholesterol. Cholesterol homeostasis throughout the brain is not uniform, and the expression of enzymes involved in the cholesterol metabolism differs from region to region (41,42).…”

Cholesterol: Its Regulation and Role in Central Nervous System Disorders

“…The 3-hydroxy-3-methylglutaryl-coenzyme A reductase ( Hmgcr ; EC 2.3.3.10) is the rate limiting enzyme in cholesterol biosynthesis and the target of statin pharmacotherapy [18]. Besides cholesterol, the cholesterologenic pathway forms other important intermediates such as mevalonate, farnesyl pyrophosphate, squalene, and lanosterol [19]. The first enzymes of the isoprenoid/cholesterol biosynthetic pathway, that is, the conversion of acetyl-CoA to farnesyl pyrophosphate, are localized in the cytosol except for Hmgcr which, together with most enzymes involved in cholesterol synthesis, is localized in the endoplasmatic reticulum [20, 21].…”

Cholesterol Biosynthesis from Lanosterol

“…Dhcr7 mRNA was expressed mainly in liver and its regulation appeared to be controlled by tissue sterol contents as well as some cholesterogenic inhibitors (2,4). However, molecular cloning and the nature of sterol-mediated transcriptional control of the Dhcr7 gene in any species have not been reported previously.…”