From the Department of Biological Sciences, Duquesne University, Pittsburgh, Pennsylvania 15282 and.
the Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260.
J Biol Chem. 2014 Nov 7;289(45):31591-604. doi: 10.1074/jbc.M114.581157. Epub 2014 Sep 25.
Ypk1, the yeast homolog of the human serum- and glucocorticoid-induced kinase (Sgk1), affects diverse cellular activities, including sphingolipid homeostasis. We now report that Ypk1 also impacts the turnover of the major phospholipid, phosphatidylcholine (PC). Pulse-chase radiolabeling reveals that a ypk1Δ mutant exhibits increased PC deacylation and glycerophosphocholine production compared with wild type yeast. Deletion of PLB1, a gene encoding a B-type phospholipase that hydrolyzes PC, in a ypk1Δ mutant curtails the increased PC deacylation. In contrast to previous data, we find that Plb1 resides in the ER and in the medium. Consistent with a link between Ypk1 and Plb1, the levels of both Plb1 protein and PLB1 message are elevated in a ypk1Δ strain compared with wild type yeast. Furthermore, deletion of PLB1 in a ypk1Δ mutant exacerbates phenotypes associated with loss of YPK1, including slowed growth and sensitivity to cell wall perturbation, suggesting that increased Plb1 activity buffers against the loss of Ypk1. Because Plb1 lacks a consensus phosphorylation site for Ypk1, we probed other processes under the control of Ypk1 that might be linked to PC turnover. Inhibition of sphingolipid biosynthesis by the drug myriocin or through utilization of a lcb1-100 mutant results in increased PLB1 expression. Furthermore, we discovered that the increase in PLB1 expression observed upon inhibition of sphingolipid synthesis or loss of Ypk1 is under the control of the Crz1 transcription factor. Taken together, these results suggest a functional interaction between Ypk1 and Plb1 in which altered sphingolipid metabolism up-regulates PLB1 expression via Crz1.
Ypk1 是酵母中与人血清和糖皮质激素诱导的激酶(Sgk1)同源的蛋白,影响多种细胞活动,包括神经酰胺稳态。我们现在报告 Ypk1 也会影响主要磷脂,磷脂酰胆碱(PC)的周转率。脉冲追踪放射性标记显示,与野生型酵母相比,ypk1Δ 突变体表现出 PC 脱酰基化和甘油磷酸胆碱生成增加。在 ypk1Δ 突变体中缺失编码 B 型磷脂酶的 PLB1 基因可减少增加的 PC 脱酰基化。与之前的数据相反,我们发现 Plb1 存在于内质网和介质中。与 Ypk1 和 Plb1 之间的联系一致,与野生型酵母相比,ypk1Δ 菌株中 Plb1 蛋白和 PLB1 基因的水平均升高。此外,在 ypk1Δ 突变体中缺失 PLB1 会加剧与 YPK1 缺失相关的表型,包括生长缓慢和对细胞壁扰动的敏感性,这表明增加的 Plb1 活性可以缓冲 Ypk1 的缺失。由于 Plb1 缺乏 Ypk1 的共识磷酸化位点,我们研究了其他受 Ypk1 控制的可能与 PC 周转率相关的过程。通过药物米屈肼抑制鞘脂生物合成或通过利用 lcb1-100 突变体导致 PLB1 表达增加。此外,我们发现,在抑制鞘脂合成或失去 Ypk1 时观察到的 PLB1 表达增加受 Crz1 转录因子的控制。总之,这些结果表明 Ypk1 和 Plb1 之间存在功能相互作用,改变的鞘脂代谢通过 Crz1 上调 PLB1 表达。