Identification of acyl-CoA synthetases involved in the mammalian sphingosine 1-phosphate metabolic pathway

Abstract

2 Highlights• Eight ACSs exhibited activities toward the S1P metabolite trans-2-hecadecenoic acid.• ACS isozymes involved in S1P metabolism were localized in the ER.• Inhibition of ACSs caused accumulation of trans-2-hexadecenoic acid. 3 ABSTRACTSphingosine 1-phosphate (S1P) plays important roles both as a bioactive lipid molecule and an intermediate of the sphingolipid-to-glycerophospholipid metabolic pathway. To identify human acyl-CoA synthetases (ACSs) involved in S1P metabolism, we cloned all 26 human ACS genes and examined their abilities to restore deficient sphingolipid-to-glycerophospholipid metabolism in a yeast mutant lacking two ACS genes, FAA1 and FAA4. Here, in addition to the previously identified ACSL family members (ACSL1, 3, 4, 5, and 6), we found that ACSVL1, ACSVL4, and ACSBG1 also restored metabolism. All 8 ACSs were localized either exclusively or partly to the endoplasmic reticulum (ER), where S1P metabolism takes place. We previously proposed the entire S1P metabolic pathway from results obtained using yeast cells, i.e., S1P is metabolized totrans-2-hexadecenoyl-CoA, and palmitoyl-CoA. However, as S1P is not a naturally occurring long-chain base 1-phosphate in yeast, the validity of this pathway required further verification using mammalian cells. In the present study, we treated HeLa cells with the ACS inhibitor triacsin C and found that inhibition of ACSs resulted in accumulation of trans-2-hexadecenoic acid as in ACS mutant yeast. From these results, we conclude that S1P is metabolized by a common pathway in eukaryotes.

Phytosphingosine degradation pathway includes fatty acid α-oxidation reactions in the endoplasmic reticulum

“…Of the ACS subfamilies, the ACSL subfamily, consisted of ACSL1, ACSL3, ACSL4, ACSL5, and ACSL6, is mainly responsible for the conversion of long-chain FAs to acyl-CoAs (39). We previously revealed that ACSL1, ACSL3, ACSL4, ACSL5, ACSL6, ACSVL1, ACSVL4, and ACSBG1 are involved in the DHS and SPH degradation pathways (21,22). It is likely that these ACSs are also involved in the PHS degradation pathway.…”

“…We speculate that the differences in the localization of HACL1 (peroxisome) and HACL2 (ER) determines the degree of their contribution to the PHS degradation pathway. All of the enzymes acting downstream of PHS 1-phosphate, i.e., SGPL1, ALDH3A2, and ACSLs, are all localized in the ER (22,35,40): In other words, PHS degradation occurs in the ER. In Hacl2-deficient cells, unmetabolized 2-OH C16:0-CoA in the ER may be unusually delivered to peroxisomes and is subjected to the C1 removal reaction by HACL1.…”

“…The saturated LCB dihydrosphingosine (DHS) also exists ubiquitously but at lower levels than SPH. We recently determined the entire degradation pathways of SPH and DHS (21)(22)(23) (Fig. S1B).…”

Dual Functions of the Trans-2-Enoyl-CoA Reductase TER in the Sphingosine 1-Phosphate Metabolic Pathway and in Fatty Acid Elongation

“…Because trans-2-hexadecenoyl-CoA is classified as a trans-2-enoyl-CoA, the enzyme involved is trans-2-enoyl-CoA reductase. All known enzymes involved in the S1P metabolic pathway are localized in the endoplasmic reticulum (20,(31)(32)(33). Therefore, we expected the candidate trans-2-enoyl-CoA reductase to be localized in the endoplasmic reticulum.…”

“…1A) (6). We also identified the fatty aldehyde dehydrogenase ALDH3A2 and some members of acyl-CoA synthetases (ACSL1-6, ACSBG1, and ACSVL1 and -4) as genes responsible for the oxidation of trans-2-hexadecenal and addition of CoA to trans-2-hexadecenoic acid, respectively (6,20). Mutations in the ALDH3A2 gene cause the neurocutaneous disorder Sjögren-Larsson syndrome (21), which implies a link between S1P metabolism and this condition (6,8).…”