| Long-chain fatty acids are complex, energy-rich compounds essential to all cells. We employ the lower eukaryotic Saccharomyces cerevisiae as a model to study fatty acid transport, activation, metabolism and gene regulation. We hypothesize ACSLs play pivotal roles in fatty acid trafficking and thus represent central players in the maintenance of intracellular lipid homeostasis. Disruption of FAA1 gene results in a deficiency in fatty acid transport and the downstream metabolism including fatty acid beta-oxidation and fatty acid-dependent gene transcription regulations. In addition to the well-characterized functions, we also noted yeast strains with deletions of FAA genes have reduced growth rates, are flocculent and have altered colony morphology. We observed reduced staining or vacuole fragmentation in faa1l, 4Delta and faal,2,3,4Delta cells using FM4-64 staining. We also observed increased free fatty acids but decreased phospholipids including PE, PI, PS and PC, and triglyceride synthesis in faa1,4Delta and faa1,2,3,4Delta strains. In a yeast two-hybrid library screen, we identified a specific interactor of Faa1p. Disruption of the YNM3 gene encoding Ynm3p resulted in increased fatty acid uptake, triglyceride and free fatty acids accumulation, and reduced expression of the fatty acid-responsive OLE1 gene. We propose that Ynm3p modulates fatty acid metabolism and gene regulation through attenuation of ACSL activities. We tested the role of Ynm3p in cell apoptosis and found that YB332 ynm3Delta strains had increased apoptosis. YB332 ynm3Delta also had strain-specific reduced growth rate, loss of the ability to grow in non-fermentable carbon source, and severely altered cellular morphology. Mammals express multiple isoforms of ACSLs (ACSL-1 and ACSL3-6) in various tissues. Four ACSLs from the rat were expressed in a yeast faa1,4Delta strain and their roles in fatty acid-dependent growth on cerulenin plate, fatty acid transport and trafficking were characterized. All four restored ACS activities yet varied in substrate preference. ACSL1, 4 and 6 were able to rescue fatty acid transport by vectorial acylation in a yeast faa1,4Delta strain. ACSL5 was unable to complement defects in fatty acid-dependent growth, transport and complex lipid synthesis in the yeast model system, consistent with its proposed role in mitochondrial lipid metabolism. |
