In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 98, No. 5 ( 2001-02-27), p. 2244-2249
Abstract:
Squalene epoxidase, a membrane-associated enzyme that converts
squalene to squalene 2,3-oxide, plays an important role in the maintenance of cholesterol homeostasis. In 1957, Bloch and colleagues
identified a factor from rat liver cytosol termed “supernatant protein factor (SPF),” which promotes the squalene epoxidation
catalyzed by rat liver microsomes with oxygen, NADPH, FAD, and phospholipid [Tchen, T. T. & Bloch, K. (1957) J.
Biol. Chem. 226, 921–930]. Although purification of SPF by 11,000-fold was reported, no information is so far available on the
primary structure or biological function of SPF. Here we report the cDNA cloning and expression of SPF from rat and human. The encoded
protein of 403 amino acids belongs to a family of cytosolic lipid-binding/transfer proteins such as α-tocopherol transfer
protein, cellular retinal binding protein, yeast phosphatidylinositol transfer protein (Sec14p), and squid retinal binding protein.
Recombinant SPF produced in Escherichia coli enhances
microsomal squalene epoxidase activity and promotes intermembrane transfer of squalene in vitro . SPF mRNA is expressed
abundantly in the liver and small intestine, both of which are important sites of cholesterol biosynthesis. SPF is expressed
significantly in isolated hepatocytes, but the expression level was markedly decreased after 48 h of in vitro culture.
Moreover, SPF was not detectable in most of the cell lines tested, including HepG2 and McARH7777 hepatomas. Transfection of SPF cDNA
in McARH7777 significantly stimulated de novo cholesterol biosynthesis. These data suggest that SPF is a
cytosolic squalene transfer protein capable of regulating cholesterol biosynthesis.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.041620398
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2001
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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