Abstract
Transport of dietary lipids into small-intestinal epithelial cells is pathologically and nutritionally important. However, lipid uptake remains an almost unexplored research area. Although we know that long-chain bases (LCBs), constituents of sphingolipids, can enter into cells efficiently, the molecular mechanism of LCB uptake is completely unclear. Here, we found that the yeast acyl-CoA synthetases (ACSs) Faa1 and Faa4 are redundantly involved in LCB uptake. In addition to fatty acid-activating activity, transporter activity toward long-chain fatty acids (LCFAs) has been suggested for ACSs. Both LCB and LCFA transports were largely impaired in faa1Δ faa4Δ cells. Furthermore, LCB and LCFA uptakes were mutually competitive. However, the energy dependency was different for their transports. Sodium azide/2-deoxy-D-glucose treatment inhibited import of LCFA but not that of LCB. Furthermore, the ATP-AMP motif mutation FAA1 S271A largely impaired the metabolic activity and LCFA uptake, while leaving LCB import unaffected. These results indicate that only LCFA transport requires ATP. Since ACSs do not metabolize LCBs as substrates, Faa1 and Faa4 are likely directly involved in LCB transport. Furthermore, we revealed that ACSs are also involved in LCB transport in mammalian cells. Thus, our findings provide strong support for the hypothesis that ACSs directly transport LCFAs.
Highlights
Transport of dietary lipids into small-intestinal epithelial cells is pathologically and nutritionally important
Our findings indicate that Faa[1] and Faa[4] are involved in both long-chain FAs (LCFAs) and long-chain bases (LCBs) uptakes
Triacsin C treatment caused reduced transports of both [3H]palmitic acid and [3H]DHS (Fig. 5g,h). These results indicate that the mammalian acyl-CoA synthetases (ACSs) acyl-CoA synthetase long-chain (ACSL) and ACSVL4 are involved in LCB uptake, in a similar way to their yeast counterparts
Summary
Transport of dietary lipids into small-intestinal epithelial cells is pathologically and nutritionally important. The ATP-AMP motif mutation FAA1 S271A largely impaired the metabolic activity and LCFA uptake, while leaving LCB import unaffected. These results indicate that only LCFA transport requires ATP. FA transport activities of ACS family members have not been verified experimentally using purified proteins due to technical difficulties inherent in such in vitro assays, leading to debates whether ACSs function only in FA activation or both in FA activation and FA transport[5,8] In the former case, ACSs would cause an apparent increase in LCFA uptake by trapping LCFAs as acyl-CoAs so they do not diffuse back to the extracellular spaces or by decreasing the intracellular LCFA concentration.
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