Regulation of Phosphatidylinositol 4-Kinase Activity: A Plant Perspective of Signal Transduction

多磷酸肌醇磷脂，磷脂酰肌醇单磷酸（PIP）存在于高等植物细胞的质膜中；然而，它们在信号转导中的作用尚不清楚。高等植物中PIP和PIP2水平相对较低。本实验室从胡萝卜细胞中分离出一种49 kDa的蛋白，该蛋白可激活磷脂酰肌醇（PI） 4-激酶，即合成PIP的酶。49 kDa PI激酶激活因子，被命名为PIK-A49，是一种多功能蛋白。它结合并捆绑肌动蛋白并具有翻译延伸因子-1- α活性。本研究基于PIK-A49在协调细胞内PIP代谢、肌动蛋白细胞骨架和蛋白质合成状态中发挥重要作用的工作假设。PIK-A49和PI激酶存在于胡萝卜细胞的质膜、肌动蛋白骨架和可溶性部分。在膜和细胞骨架PI激酶活性的变化已经观察到暴露胡萝卜细胞外部刺激的几秒钟内。无论PIP和PIP2是第二信使的前体还是直接的膜效应物，了解PIP和PIP2生物合成的调控机制对于了解它们在信号转导中的作用至关重要。本研究的目的是了解环境刺激下PIP生物合成的调节机制，以及PIP代谢的这些变化如何影响细胞生理。在这些研究中，胡萝卜悬浮培养细胞将被用作模型系统和两种刺激，一种增加PI - 4激酶活性，另一种降低PI - 4激酶活性。需要解决的具体问题是：PIK-A49激活PI - 4激酶的机制是什么？PIK-A49、PI激酶或f -肌动蛋白的分布是否在对刺激的反应中发生变化，如果有，是什么导致了分布的变化？这项工作为PIP代谢提供了一个不同的视角——一个专注于PIP合成的视角。此外，PIK-A49激活PI - 4激酶，结合并捆绑肌动蛋白，并具有延伸因子活性，这一事实为植物细胞在响应环境刺激时质膜、细胞骨架和蛋白质合成机制之间的串扰提供了一个新的维度。我们对植物感知环境信号的机制知之甚少。这位研究者已经证明，植物细胞外膜中的一种带负电荷的脂质在环境刺激下发生化学变化。这些脂质的生物合成是由一种激活蛋白调节的，这种激活蛋白也可以调节细胞骨架的结构和细胞内的蛋白质合成。这一发现表明，激活蛋白可能有助于将植物环境的变化从外膜传递到细胞的其余部分。本研究的目的是了解这些脂质的生物合成是如何被调节的，并确定激活蛋白是否作为传感器将环境信号传递到植物细胞内部

9304556 Boss The polyphosphorylated inositol phospholipids, phosphatidylinositol monophosphate (PIP) are present in the plasma membranes of higher plant cells; however, their functions in signal transduction are not well understood. PIP and PIP2 levels are relatively low in higher plants. This laboratory has isolated a 49 kDa protein from carrot cells that activates phosphatidylinositol (PI) 4-kinase, the enzyme that synthesizes PIP. The 49 kDa PI kinase activator, designated PIK-A49, is a multifunctional protein. It binds and bundles actin and has translational elongation factor-1-alpha activity. This research is based on the working hypothesis that PIK-A49 plays an important role in coordinating the status of PIP metabolism, the actin cytoskeleton, and protein synthesis within the cell. PIK-A49 and PI kinase are present in the plasma membrane, actin cytoskeleton and soluble fractions of carrot cells. Changes in the membrane and cytoskeletal PI kinase activity have been observed within seconds of exposing carrot cells to external stimuli. Whether PIP and PIP2 serve as precursors of second messengers or as direct membrane effectors, understanding the mechanism of regulation of PIP and PIP2 biosynthesis is essential in order to understand their roles in signal transduction. The goals of this research are to understand the mechanism of regulation of PIP biosynthesis in response to environmental stimuli and to understand how these changes in PIP metabolism might affect cell physiology. For these studies, carrot suspension culture cells will be used as a model system and two stimuli, one that increases PI 4-kinase activity and one that decreases PI 4-kinase activity. Specific questions to be addressed are: What is the mechanism of activation of PI 4-kinase by PIK-A49? Is there a change in the distribution of PIK-A49, PI kinase or F-actin in response to stimuli, and if so, what causes the change in distribution? This work provides a different perspective of PIP metabolism--one focused on PIP synthesis. In addition, the fact that the PIK-A49 activates PI 4-kinase, binds and bundles actin, and has elongation factor activity adds a new dimension to the potential for cross-talk among the plasma membrane, cytoskeleton, and protein synthesis machinery within plant cells during responses to environmental stimuli. %%% Little is known about the mechanisms used by plants to sense environmental signals. This investigator has shown that a subset of very negatively charged lipids in the outer membranes of plant cells undergo chemical changes in response to environmental stimuli. The biosynthesis of these lipids is regulated by an activator protein that can also regulate the structure of the cytoskeleton and protein synthesis within the cell. This finding suggested that the activator protein may serve to communicate the changes in the plant's environment from the outer membrane to the rest of the cell. The goals of this research are to understand how biosynthesis of these lipids is regulated and to determine whether the activator protein acts as a sensor to communicate environmental signals to the interior of the plant cell.***