Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina 29403, USA.
J Biol Chem. 2012 Mar 16;287(12):9280-9. doi: 10.1074/jbc.M111.313445. Epub 2012 Jan 25.
Targets of bioactive sphingolipids in Saccharomyces cerevisiae were previously identified using microarray experiments focused on sphingolipid-dependent responses to heat stress. One of these heat-induced genes is the serine deamidase/dehydratase Cha1 known to be regulated by increased serine availability. This study investigated the hypothesis that sphingolipids may mediate the induction of Cha1 in response to serine availability. The results showed that inhibition of de novo synthesis of sphingolipids, pharmacologically or genetically, prevented the induction of Cha1 in response to increased serine availability. Additional studies implicated the sphingoid bases phytosphingosine and dihydrosphingosine as the likely mediators of Cha1 up-regulation. The yeast protein kinases Pkh1 and Pkh2, known sphingoid base effectors, were found to mediate CHA1 up-regulation via the transcription factor Cha4. Because the results disclosed a role for sphingolipids in negative feedback regulation of serine metabolism, we investigated the effects of disrupting this mechanism on sphingolipid levels and on cell growth. Intriguingly, exposure of the cha1Δ strain to high serine resulted in hyperaccumulation of endogenous serine and in turn a significant accumulation of sphingoid bases and ceramides. Under these conditions, the cha1Δ strain displayed a significant growth defect that was sphingolipid-dependent. Together, this work reveals a feedforward/feedback loop whereby the sphingoid bases serve as sensors of serine availability and mediate up-regulation of Cha1 in response to serine availability, which in turn regulates sphingolipid levels by limiting serine accumulation.
先前使用微阵列实验鉴定了酿酒酵母中生物活性神经鞘脂的靶标，这些实验集中在神经鞘脂依赖性对热应激的反应上。这些热诱导基因之一是丝氨酸脱氨酶/脱水酶 Cha1，已知其受到丝氨酸可用性的调节。本研究假设神经鞘脂可能介导丝氨酸可用性对 Cha1 的诱导。结果表明，通过药理学或遗传学抑制神经鞘脂的从头合成，可防止 Cha1 对增加的丝氨酸可用性的诱导。进一步的研究表明，鞘氨醇碱基植物鞘氨醇和二氢鞘氨醇可能是 Cha1 上调的中介物。已知的鞘氨醇碱基效应物酵母蛋白激酶 Pkh1 和 Pkh2 被发现通过转录因子 Cha4 介导 CHA1 的上调。由于结果揭示了神经鞘脂在丝氨酸代谢负反馈调节中的作用，我们研究了破坏这种机制对神经鞘脂水平和细胞生长的影响。有趣的是，暴露于高丝氨酸的 cha1Δ 菌株导致内源性丝氨酸的过度积累，进而导致鞘氨醇碱基和神经酰胺的显著积累。在这些条件下，cha1Δ 菌株表现出明显的生长缺陷，这是依赖于神经鞘脂的。总之，这项工作揭示了一个前馈/反馈回路，其中鞘氨醇碱基作为丝氨酸可用性的传感器，介导 Cha1 对丝氨酸可用性的上调，这反过来又通过限制丝氨酸积累来调节神经鞘脂水平。
