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Lipid traffic to peroxisomes from the yeast Saccharomyces cerevisiae
Chemistry and Physics of Lipids 154S (2008) S61–S63
Contents lists available at ScienceDirect
Chemistry and Physics of Lipids journal homepage: www.elsevier.com/locate/chemphyslip
Abstracts
Posters session 7: Lysosomal lipid metabolism (PO 108–114)
PO 108
PO 109
Lipid traffic to peroxisomes from the yeast Saccharomyces cerevisiae
Perturbation of intracellular acyl-CoA metabolism induces the unfolded protein response pathway and autophagy in Saccharomyces cerevisiae
M. Connerth 1 , J. Schatte 1 , G. Zellnig 2 , A. Hermetter 1 , G. Daum 1 1
Institute of Biochemistry, Graz University of Technology, Petersgasse 12/2, 8010 Graz, Austria 2 Institute of Plant Science, Karl Franzens University Graz, Austria Peroxisomes are small ubiquitous organelles present in all eukaryotic cells. They play an essential role in various cellular processes including -oxidation of fatty acids. In contrast to mammalian cells, where -oxidation takes place in mitochondria and peroxisomes, in the yeast fatty acids are exclusively degraded in the latter organelle. Therefore, growth defects on oleic acid supplemented media serve as indication for peroxisomal dysfunction. Induction of peroxisomal proliferation also requires efficient intracellular fatty acid supply to this organelle. When yeast cells were grown in the presence of exogenous oleic acid as the only carbon source, peroxisomes were formed, but at the same time storage lipid particles/droplets (LP) increased in size and abundance. Studies employing mutants defective in neutral lipid turnover indicated that oleic acid was primarily incorporated into triacylglycerols (TAG) and only to a minor extent into steryl esters (STE). Interestingly, TAG turnover in cells grown on oleic acid did not come to a halt in a mutant deficient of all three known TAG lipases Tgl3p, Tgl4p and Tgl5p. This result indicated that additional TAG mobilizing pathway(s) may exist which take over TAG degradation if required, e.g., for providing substrates for peroxisomal -oxidation. Recent experiments in vitro and in vivo identified candidate gene products which may be involved in this process. Current investigations are aimed at the elucidation of the complex network of fatty acid trafficking that is prerequisite to the induction of yeast peroxisomes. Acknowledgements: Supported by FWF projects 17321 and W901-B05 (DK Molecular Enzymology) to G.D.
Søren Feddersen, Nils J. Færgeman Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark Eukaryotic cells have developed several strategies to respond and adapt to changes in their intracellular and extracellular environment. The unfolded protein response (UPR) pathway is activated following accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER), whereas autophagy mainly is a response to the stress of nutrient limitation. In the present study, we demonstrate that perturbation of fatty acid synthesis and transport either through inhibition of fatty acid synthase (FAS) or by depleting cells for the acyl-CoA binding protein, Acb1p, leads to induction of Hac1p, a transcription factor regulating the unfolded protein response and membrane biogenesis, as well as Hac1p target genes incl. KAR2 and PDI1. Under similar conditions, we find a massive upregulation of pre-autophagosomal structure (PAS) formation, indicative of upregulation of autophagy. Supplementation with exogenous fatty acids suppresses induction of both the UPR pathway and autophagy in cells lacking Acb1p. Activation of the Ras-cAMP signalling pathway by overexpressing TPK1 or the RAS1val19 allele in Acb1p-depleted cells reduced the number of pre-autophagosomal structures to wild type levels. This and the facts that Acb1p-depleted cells are hypersensitive to the immunosuppressive drug rapamycin and accumulate the transcription factor Msn2p in the nucleus, indicate that perturbation of intracellular acyl-CoA metabolism leads to a starvation response that upregulate autophagy, which involves both Ras-cAMP and TOR1 signalling. doi:10.1016/j.chemphyslip.2008.05.168
doi:10.1016/j.chemphyslip.2008.05.167
0009-3084/$ – see front matter
Contents lists available at ScienceDirect
Chemistry and Physics of Lipids journal homepage: www.elsevier.com/locate/chemphyslip
Abstracts
Posters session 7: Lysosomal lipid metabolism (PO 108–114)
PO 108
PO 109
Lipid traffic to peroxisomes from the yeast Saccharomyces cerevisiae
Perturbation of intracellular acyl-CoA metabolism induces the unfolded protein response pathway and autophagy in Saccharomyces cerevisiae
M. Connerth 1 , J. Schatte 1 , G. Zellnig 2 , A. Hermetter 1 , G. Daum 1 1
Institute of Biochemistry, Graz University of Technology, Petersgasse 12/2, 8010 Graz, Austria 2 Institute of Plant Science, Karl Franzens University Graz, Austria Peroxisomes are small ubiquitous organelles present in all eukaryotic cells. They play an essential role in various cellular processes including -oxidation of fatty acids. In contrast to mammalian cells, where -oxidation takes place in mitochondria and peroxisomes, in the yeast fatty acids are exclusively degraded in the latter organelle. Therefore, growth defects on oleic acid supplemented media serve as indication for peroxisomal dysfunction. Induction of peroxisomal proliferation also requires efficient intracellular fatty acid supply to this organelle. When yeast cells were grown in the presence of exogenous oleic acid as the only carbon source, peroxisomes were formed, but at the same time storage lipid particles/droplets (LP) increased in size and abundance. Studies employing mutants defective in neutral lipid turnover indicated that oleic acid was primarily incorporated into triacylglycerols (TAG) and only to a minor extent into steryl esters (STE). Interestingly, TAG turnover in cells grown on oleic acid did not come to a halt in a mutant deficient of all three known TAG lipases Tgl3p, Tgl4p and Tgl5p. This result indicated that additional TAG mobilizing pathway(s) may exist which take over TAG degradation if required, e.g., for providing substrates for peroxisomal -oxidation. Recent experiments in vitro and in vivo identified candidate gene products which may be involved in this process. Current investigations are aimed at the elucidation of the complex network of fatty acid trafficking that is prerequisite to the induction of yeast peroxisomes. Acknowledgements: Supported by FWF projects 17321 and W901-B05 (DK Molecular Enzymology) to G.D.
Søren Feddersen, Nils J. Færgeman Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark Eukaryotic cells have developed several strategies to respond and adapt to changes in their intracellular and extracellular environment. The unfolded protein response (UPR) pathway is activated following accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER), whereas autophagy mainly is a response to the stress of nutrient limitation. In the present study, we demonstrate that perturbation of fatty acid synthesis and transport either through inhibition of fatty acid synthase (FAS) or by depleting cells for the acyl-CoA binding protein, Acb1p, leads to induction of Hac1p, a transcription factor regulating the unfolded protein response and membrane biogenesis, as well as Hac1p target genes incl. KAR2 and PDI1. Under similar conditions, we find a massive upregulation of pre-autophagosomal structure (PAS) formation, indicative of upregulation of autophagy. Supplementation with exogenous fatty acids suppresses induction of both the UPR pathway and autophagy in cells lacking Acb1p. Activation of the Ras-cAMP signalling pathway by overexpressing TPK1 or the RAS1val19 allele in Acb1p-depleted cells reduced the number of pre-autophagosomal structures to wild type levels. This and the facts that Acb1p-depleted cells are hypersensitive to the immunosuppressive drug rapamycin and accumulate the transcription factor Msn2p in the nucleus, indicate that perturbation of intracellular acyl-CoA metabolism leads to a starvation response that upregulate autophagy, which involves both Ras-cAMP and TOR1 signalling. doi:10.1016/j.chemphyslip.2008.05.168
doi:10.1016/j.chemphyslip.2008.05.167
0009-3084/$ – see front matter