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Journal of Lipid Research, Vol. 44, 1751-1762, September 2003 Sterol carrier protein-2/sterol carrier protein-x expression differentially alters fatty acid metabolism in L cell fibroblasts
Department of Physiology and Pharmacology, Texas A&M University, TVMC College Station, TX 77843-4466
1 To whom correspondence should be addressed. e-mail: fschroeder{at}cvm.tamu.edu Sterol carrier protein-2 (SCP-2) and SCP-x are ubiquitous proteins found in all mammalian tissues. Although both proteins interact with fatty acids, their relative contributions to the uptake, oxidation, and esterification of straight-chain (palmitic) and branched-chain (phytanic) fatty acids in living cells has not been resolved. Therefore, the effects of each gene product on fatty acid metabolism was individually examined. Based on the following, SCP-2 and SCP-x did not enhance the uptake/translocation of fatty acids across the plasma membrane into the cell: i) a 2-fold increase in phytanic and palmitic acid uptake was observed at long incubation times in SCP-2- and SCP-x-expressing cells, but no differences were observed at initial time points; ii) uptake of 2-bromo-palmitate, a nonoxidizable, poorly metabolizable fatty acid analog, was unaffected by SCP-2 or SCP-x overexpression; and iii) SCP-2 and SCP-x expression did not increase targeting of radiolabeled phytanic and palmitic acid to the unesterified fatty acid pool. Moreover, SCP-2 and SCP-x expression enhanced fatty acid uptake by stimulating the intracellular metabolism via fatty acid oxidation and esterification. In summary, these data showed for the first time that SCP-2 and SCP-x stimulate oxidation and esterification of branched-chain as well as straight-chain fatty acids in intact cells.
Abbreviations: CE, cholesteryl ester; DG, diacylglyceride; FA, fatty acid; L-FABP, liver fatty acid binding protein; MG, monoacylglyceride; PI, phosphatidylinositol; PL, phospholipid; PS, phosphatidylserine; SCP, sterol carrier protein; TG, triacylglyceride Supplementary key words phytanic acid palmitic acid 2-bromopalmitate fatty acid oxidation fatty acid uptake
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