Abstract
Carnitine palmitoyltransferase 1 (CPT1) catalyzes the first step in long-chain fatty acid import into mitochondria, and it is believed to be rate limiting for β-oxidation of fatty acids. However, in muscle, other proteins may collaborate with CPT1. Fatty acid translocase/CD36 (FAT/CD36) may interact with CPT1 and contribute to fatty acid import into mitochondria in muscle. Here, we demonstrate that another membrane-bound fatty acid binding protein, fatty acid transport protein 1 (FATP1), collaborates with CPT1 for fatty acid import into mitochondria. Overexpression of FATP1 using adenovirus in L6E9 myotubes increased both fatty acid oxidation and palmitate esterification into triacylglycerides. Moreover, immunocytochemistry assays in transfected L6E9 myotubes showed that FATP1 was present in mitochondria and coimmunoprecipitated with CPT1 in L6E9 myotubes and rat skeletal muscle in vivo. The cooverexpression of FATP1 and CPT1 also enhanced mitochondrial fatty acid oxidation, similar to the cooverexpression of FAT/CD36 and CPT1. However, etomoxir, an irreversible inhibitor of CPT1, blocked all these effects. These data reveal that FATP1, like FAT/CD36, is associated with mitochondria and has a role in mitochondrial oxidation of fatty acids.
Highlights
Carnitine palmitoyltransferase 1 (CPT1) catalyzes the first step in long-chain fatty acid import into mitochondria, and it is believed to be rate limiting for -oxidation of fatty acids
These data indicate that other factors independent of CPT1/malonyl-CoA interaction could be involved in the control of fatty acid oxidation in these cells
We examined the effect of FAT/CD36 overexpression in L6E9 myotubes, a protein that has already been shown to have a role in fatty acid oxidation in muscle [12]
Summary
Carnitine palmitoyltransferase 1 (CPT1) catalyzes the first step in long-chain fatty acid import into mitochondria, and it is believed to be rate limiting for -oxidation of fatty acids. We examined the effect of FAT/CD36 overexpression in L6E9 myotubes, a protein that has already been shown to have a role in fatty acid oxidation in muscle [12]. Acyl-CoA synthetase activity increased by 30% and 70% in total and mitochondrial extracts, respectively, in FATP1-overexpressing L6E9 myotubes compared with LacZ control cells (control values: 2.99 ± 0.16 and 3.91 ± 0.37 nmol palmitoyl-CoA/mg protein × min in total and mitochondrial extracts, respectively; Fig. 2C).
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