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  • 1
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    Online Resource
    α-Tocopherol transfer protein stimulates the secretion of α-tocopherol from a cultured liver cell line through a brefeldin A-insensitive pathway
    Proceedings of the National Academy of Sciences ; 1997
    In:  Proceedings of the National Academy of Sciences Vol. 94, No. 23 ( 1997-11-11), p. 12437-12441
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 94, No. 23 ( 1997-11-11), p. 12437-12441
    Abstract: Vitamin E (α-tocopherol) is a fat-soluble antioxidant that is transported by plasma lipoproteins in the body. α-Tocopherol taken up by the liver with lipoprotein is thought to be resecreted into the plasma in very low density lipoprotein (VLDL). α-Tocopherol transfer protein (αTTP), which was recently identified as a product of the causative gene for familial isolated vitamin E deficiency, is a cytosolic liver protein and plays an important role in the efficient recycling of plasma vitamin E. To throw light on the mechanism of αTTP-mediated α-tocopherol transfer in the liver cell, we devised an assay system using the hepatoma cell line McARH7777. Using this system, we found that the secretion of α-tocopherol was more efficient in cells expressing αTTP than in matched cells lacking αTTP. Brefeldin A, which effectively inhibits VLDL secretion by disrupting the Golgi apparatus, had no effect on α-tocopherol secretion, indicating that αTTP-mediated α-tocopherol secretion is not coupled to VLDL secretion. Among other agents tested, only 25-hydroxycholesterol, a modulator of cholesterol metabolism, inhibited α-tocopherol secretion. This inhibition is most likely mediated by oxysterol-binding protein. These results suggest that αTTP present in the liver cytosol functions to stimulate secretion of cellular α-tocopherol into the extracellular medium and that the reaction utilizes a novel non-Golgi-mediated pathway that may be linked to cellular cholesterol metabolism and/or transport.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.94.23.12437
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 1997
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    detail.hit.zdb_id: 1461794-8
    SSG: 11
    SSG: 12
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  • 2
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    Online Resource
    Supernatant protein factor, which stimulates the conversion of squalene to lanosterol, is a cytosolic squalene transfer protein and enhances cholesterol biosynthesis
    Proceedings of the National Academy of Sciences ; 2001
    In:  Proceedings of the National Academy of Sciences Vol. 98, No. 5 ( 2001-02-27), p. 2244-2249
    Details
    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
    URL: Article
    DOI: 10.1073/pnas.041620398
    RVK:
    TA 1000
    RVK:
    WA 15000
    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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  • 3
    Online Resource
    Online Resource
    Type II platelet-activating factor-acetylhydrolase is essential for epithelial morphogenesis in Caenorhabditis elegans
    Proceedings of the National Academy of Sciences ; 2004
    In:  Proceedings of the National Academy of Sciences Vol. 101, No. 36 ( 2004-09-07), p. 13233-13238
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 101, No. 36 ( 2004-09-07), p. 13233-13238
    Abstract: Type II platelet-activating factor-acetylhydrolase [PAF-AH (II)] is an N-myristoylated enzyme that contains a lipase/esterase catalytic motif and selectively hydrolyzes the sn -2 acetyl ester of PAF and other short-chain acyl groups attached to phosphoglycerides. However, the physiological role of this enzyme remains to be elucidated. PAF-AH (II) is conserved in a variety of species ranging from a simple multicellular organism, Caenorhabditis elegans , to mammals. C. elegans possesses two homologous PAF-AH (II) genes, named paf-1 and paf-2 . In this study, we generated these two loss-of-function mutants to elucidate the in vivo PAF-AH (II) function. Surprisingly, mutants of paf-2 , a major isoform of C. elegans PAF-AH (II)s, exhibits gross defects in epithelial sheet formation, resulting in unsuccessful subsequent morphogenesis with complete penetrance. Moreover, paf-2 RNA interference worms show a variable abnormal morphology, including ectopic protrusions and a lumpy shape at the late embryonic and early larval stages due to epithelial organization defects. Consistent with these phenotypes, PAF-AH (II) is predominantly expressed in epithelial cells of C. elegans . This study demonstrates that PAF-AH (II) is essential for epithelial morphogenesis.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0405507101
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2004
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
    SSG: 11
    SSG: 12
    Location Call Number Limitation Availability
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  • 4
    Online Resource
    Online Resource
    Identification of a PDZ-domain-containing protein that interacts with the scavenger receptor class B type I
    Proceedings of the National Academy of Sciences ; 2000
    In:  Proceedings of the National Academy of Sciences Vol. 97, No. 12 ( 2000-06-06), p. 6538-6543
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 97, No. 12 ( 2000-06-06), p. 6538-6543
    Abstract: The scavenger receptor class B type I (SR-BI) mediates the selective uptake of cholesteryl esters from high-density lipoprotein (HDL) and cholesterol secretion into bile in the liver. In this study, we identified an SR-BI-associated protein from rat liver membrane extracts by using an affinity chromatography technique. This protein of 523 amino acids contains four PDZ domains and associates with the C terminus of SR-BI by using its N-terminal first PDZ domain. Therefore, we denoted this protein as CLAMP ( C -terminal l inking a nd m odulating p rotein). CLAMP was located mostly in the sinusoidal membranes, whereas SR-BI was detected in both sinusoidal and canalicular membranes. After the solubilization of the liver membranes with Triton X-100, SR-BI was immunoprecipitated with anti-CLAMP monoclonal antibody, suggesting the association of these proteins in vivo . By coexpressing SR-BI with CLAMP in Chinese hamster ovary cells, we observed ( i ) the increase in the expression level of SR-BI, ( ii ) the reduction in the deacylation rate of the cholesteryl esters taken up from HDL, and ( iii ) the change in the intracellular distribution of fluorescent lipid 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine percholate taken up from HDL. Taken together, these data suggest that CLAMP, a four-PDZ-domain-containing protein, is associated with SR-BI in the liver sinusoidal plasma membranes and may modulate the intracellular transport and metabolism of cholesteryl esters taken up from HDL.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.100114397
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2000
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
    SSG: 11
    SSG: 12
    Location Call Number Limitation Availability
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