Almaguer C, Mantella D, Perez E, Patton-Vogt J
Department of Biological Sciences, Duquesne University, Pittsburgh, Pennsylvania 15282, USA.
Eukaryot Cell. 2003 Aug;2(4):729-36. doi: 10.1128/EC.2.4.729-736.2003.
Glycerophosphoinositol is produced through deacylation of the essential phospholipid phosphatidylinositol. In Saccharomyces cerevisiae, the glycerophosphoinositol produced is excreted from the cell but is recycled for phosphatidylinositol synthesis when inositol is limiting. To be recycled, glycerophosphoinositol enters the cell through the permease encoded by GIT1. The transport of exogenous glycerophosphoinositol through Git1p is sufficiently robust to support the growth of an inositol auxotroph (ino1Delta). We now report that S. cerevisiae also uses exogenous phosphatidylinositol as an inositol source. Evidence suggests that phosphatidylinositol is deacylated to glycerophosphoinositol extracellularly before being transported across the plasma membrane by Git1p. A genetic screen identified Pho86p, which is required for targeting of the major phosphate transporter (Pho84p) to the plasma membrane, as affecting the utilization of phosphatidylinositol and glycerophosphoinositol. Deletion of PHO86 in an ino1Delta strain resulted in faster growth when either phosphatidylinositol or glycerophosphoinositol was supplied as the sole inositol source. The incorporation of radiolabeled glycerophosphoinositol into an ino1Delta pho86Delta mutant was higher than that into wild-type, ino1Delta, and pho86Delta strains. All strains accumulated the most GIT1 transcript when incubated in media limited for inositol and phosphate in combination. However, the ino1Delta pho86Delta mutant accumulated approximately threefold more GIT1 transcript than did the other strains when incubated in inositol-free media containing either high or low concentrations of P(i). Deletion of PHO4 abolished GIT1 transcription in a wild-type strain. These results indicate that the transport of glycerophosphoinositol by Git1p is regulated by factors affecting both inositol and phosphate availabilities and suggest a regulatory connection between phosphate metabolism and phospholipid metabolism.
甘油磷酸肌醇是通过必需磷脂磷脂酰肌醇的脱酰作用产生的。在酿酒酵母中,产生的甘油磷酸肌醇从细胞中排出,但当肌醇有限时会被循环用于磷脂酰肌醇的合成。为了被循环利用,甘油磷酸肌醇通过由GIT1编码的通透酶进入细胞。外源性甘油磷酸肌醇通过Git1p的转运足够强大,以支持肌醇营养缺陷型(ino1Delta)的生长。我们现在报告酿酒酵母也使用外源性磷脂酰肌醇作为肌醇来源。有证据表明,磷脂酰肌醇在被Git1p转运穿过质膜之前在细胞外脱酰为甘油磷酸肌醇。一项遗传筛选确定,主要磷酸盐转运体(Pho84p)靶向质膜所需的Pho86p会影响磷脂酰肌醇和甘油磷酸肌醇的利用。在ino1Delta菌株中缺失PHO86,当磷脂酰肌醇或甘油磷酸肌醇作为唯一的肌醇来源提供时,会导致生长更快。放射性标记的甘油磷酸肌醇掺入ino1Delta pho86Delta突变体的量高于掺入野生型、ino1Delta和pho86Delta菌株的量。当在同时限制肌醇和磷酸盐的培养基中培养时,所有菌株积累的GIT1转录本最多。然而,当在含有高浓度或低浓度P(i)的无肌醇培养基中培养时,ino1Delta pho86Delta突变体积累的GIT1转录本比其他菌株多大约三倍。在野生型菌株中缺失PHO4会消除GIT1转录。这些结果表明,Git1p介导的甘油磷酸肌醇转运受影响肌醇和磷酸盐可用性的因素调节,并提示磷酸盐代谢与磷脂代谢之间存在调节联系。