Phosphoinositide signaling lipids are essential for several cellular processes. The requirement for a phosphoinositide is conventionally studied by depleting the corresponding lipid kinase. However, there are very few reports on the impact of elevating phosphoinositides. That phosphoinositides are dynamically elevated in response to stimuli suggests that, in addition to being required, phosphoinositides drive downstream pathways. To test this hypothesis, we elevated the levels of phosphatidylinositol-3-phosphate (PI3P) by generating hyperactive alleles of the yeast phosphatidylinositol 3-kinase, Vps34. We find that hyperactive Vps34 drives certain pathways, including PI(3,5)P₂ synthesis and retrograde transport from the vacuole. This demonstrates that PI3P is rate limiting in some pathways. Interestingly, hyperactive Vps34 does not affect ESCRT function. Thus, elevating PI3P does not always increase the rate of PI3P-dependent pathways. Elevating PI3P can also delay a pathway. Elevating PI3P slowed late steps in autophagy, in part by delaying the disassembly of autophagy proteins from mature autophagosomes as well as delaying fusion of autophagosomes with the vacuole. This latter defect is likely due to a more general defect in vacuole fusion, as assessed by changes in vacuole morphology. These studies suggest that stimulus-induced elevation of phosphoinositides provides a way for these stimuli to selectively regulate downstream processes.

磷酸肌醇信号脂质是几个细胞过程是必不可少的。对于磷酸肌醇的要求通常通过消耗相应的脂质激酶的研究。不过，也有对提升磷酸肌醇的影响很少报道。即磷酸肌醇在响应动态地升高到刺激表明，除了被要求，磷酸肌醇驱动下游途径。为了检验这一假设，我们通过产生酵母磷脂酰肌醇3-激酶，VPS34的活动过度的等位基因升高磷脂酰肌醇-3-磷酸酯（PI3P）的水平。我们发现，活跃的VPS34驱动某些途径，包括PI（3,5）p ₂从液泡合成和逆行运输。这表明 PI3P 在某些途径中是限速的。有趣的是，过度活跃的 Vps34 不影响 ESCRT 功能。因此，提升PI3P并不总是增加PI3P依赖途径的速度。升降PI3P也可以推迟途径。升降PI3P减缓了自噬后期步骤，部分由自噬体成熟延迟拆卸自噬蛋白质以及延缓自噬体的融合与液泡。这后一种缺陷可能是由于在液泡融合更一般的缺陷，通过在液泡形态变化评估的。这些研究表明，磷酸肌醇的刺激措施引发的海拔为这些刺激选择性调节下游流程的方式。