title: Suppressor analysis points to the subtle role of the LAG1 ceramide synthase gene in determining yeast longevity.
abstract: Individual yeast cells display a finite replicative capacity. LAG1 was identified as a gene that is differentially expressed during the yeast replicative life span and was shown to play a role in determining yeast longevity. This gene is not essential, but simultaneous deletion of LAG1 and its close homologue LAC1 is lethal. Lag1p and Lac1p have been found to be an essential component of ceramide synthase. In this study, multicopy suppressors of the lethality of a lag1delta lac1delta double mutant were isolated to help clarify the role of LAG1 in yeast longevity. The two multicopy suppressors YBR183w (YPC1) and YPL087w (YDC1) encode ceramidases unrelated to Lag1p and Lac1p, which were previously found to support the reverse reaction of ceramide synthesis. Multiple copies of YPC1 were much more efficient than YDC1 in rescuing cell growth. They were also much more effective in rescuing the life span of a lag1delta lac1delta double mutant, sustaining a life span approaching that obtained by the restoration of LAG1 expression. Neither deletion of LAC1 nor overexpression of YPC1 had a detectable effect on wild-type life span. However, the overexpression of LAG1 had a bimodal effect on longevity, with moderate expression resulting in increased longevity and with higher expression curtailing life span. These results suggest that subtle changes in ceramide/sphingolipid metabolism are important in determining yeast longevity. They also indicate that Lag1p plays a special role in this relationship. Homologues of Lag1p have been identified in higher eukaryotes, including human, raising the possibility that ceramide and other sphingolipid metabolites play a wider role in biological aging.
authors.affiliation: Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1901 Perdido St., Box P7-2, New Orleans 70112, USA.
authors.forename: James C
authors.initials: JC
authors.lastname: Jiang
authors.forename: Paul A
authors.initials: PA
authors.lastname: Kirchman
authors.forename: Meghan
authors.initials: M
authors.lastname: Allen
authors.forename: S Michal
authors.initials: SM
authors.lastname: Jazwinski
mesh_terms: D000375:Aging / Q000235:genetics*; D000595:Amino Acid Sequence; D004305:Dose-Response Relationship, Drug; D005690:Galactose / Q000494:pharmacology; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000235:genetics*; D010957:Plasmids; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*; D016415:Sequence Alignment
chemical_list: C087436:LAG1 protein, S cerevisiae; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D010088:Oxidoreductases; C108138:dihydroceramide desaturase; D005690:Galactose