title: The phosphatidylglycerol/cardiolipin biosynthetic pathway is required for the activation of inositol phosphosphingolipid phospholipase C, Isc1p, during growth of Saccharomyces cerevisiae.
abstract: Inositolsphingolipid phospholipase C (Isc1p) is the Saccharomyces cerevisiae member of the extended family of neutral sphingomyelinases that regulates the generation of bioactive ceramides. Recently, we reported that Isc1p is post-translationally activated in the post-diauxic phase of growth and that it localizes to mitochondria (Vaena de Avalos, S., Okamoto, Y., and Hannun, Y. A. (2004) J. Biol. Chem. 279, 11537-11545). In this study the in vivo mechanisms of activation and function of Isc1p were investigated. Deletion of ISC1 resulted in markedly lower growth in non-fermentable carbon sources. Interestingly, the growth defect of isc1Delta strains resembled that of pgs1Delta strains, lacking the committed step in the synthesis of phosphatidylglycerol (PG) and cardiolipin (CL), which were shown to activate Isc1p in vitro. Therefore, the role of Pgs1p in activation of Isc1p in vivo was investigated. The results showed that in the pgs1Delta strain, the growth-dependent activation of Isc1p was impaired as was the ISC1-dependent increase in the levels of phytoceramide during the post-diauxic phase, demonstrating that the activation of Isc1p in vivo is dependent on PGS1 and on the mitochondrial phospholipids PG/CL. Mechanistically, loss of Isc1p resulted in lower levels of mitochondrial cytochrome c oxidase subunits cox3p and cox4p, previously established targets of both PG and CL (Ostrander, D. B., Zhang, M., Mileykovskaya, E., Rho, M., and Dowhan, W. (2001) J. Biol. Chem. 276, 25262-25272), thus suggesting that Isc1p mediates at least some functions downstream of PG/CL. This study provides the first evidence for the mechanism of in vivo activation and function of Isc1p. A model with endogenous PG/CL as the in vivo activator of Isc1p is proposed.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
authors.forename: Silvia
authors.initials: S
authors.lastname: Vaena de Avalos
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Su
authors.forename: Mei
authors.initials: M
authors.lastname: Zhang
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Okamoto
authors.forename: William
authors.initials: W
authors.lastname: Dowhan
authors.forename: Yusuf A
authors.initials: YA
authors.lastname: Hannun
mesh_terms: D010717:CDPdiacylglycerol-Serine O-Phosphatidyltransferase / Q000502:physiology; D002308:Cardiolipins / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000032:analysis; D004789:Enzyme Activation; D008565:Membrane Proteins / Q000032:analysis; D008928:Mitochondria / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000378:metabolism*; D010740:Phospholipases / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D010738:Type C Phospholipases
chemical_list: D002308:Cardiolipins; D008565:Membrane Proteins; D010715:Phosphatidylglycerols; D029701:Saccharomyces cerevisiae Proteins; C093750:COX3 protein, S cerevisiae; D003576:Electron Transport Complex IV; D010717:CDPdiacylglycerol-Serine O-Phosphatidyltransferase; C084652:PGS1 protein, S cerevisiae; D010740:Phospholipases; C419391:ISC1 protein, S cerevisiae; D010738:Type C Phospholipases