A NOVEL MECHANISM OF REGULATION OF INOSITOL BIOSYNTHESIS IN YEAST

说明(申请人提供)：肌醇是一种重要的代谢物，在调节细胞信号通路中起着重要作用。在酵母中，肌醇影响700多个基因的转录。此外，许多肌醇磷酸和肌醇肌醇是控制重要细胞通路的信号分子。因此，肌醇动态平衡必须受到高度的调控。大量研究表明，肌醇的生物合成受控于编码肌醇3-磷酸合成酶(MIPS)的INO1基因的转录水平。然而，肌醇水平的调节不能仅仅通过调节INO1的表达来解释，因为导致肌醇耗竭的几种生理条件的特征是尽管INO1的表达增加，但肌醇合成减少。事实上，初步研究表明，MIPS活性的降低是由于MIPS蛋白的磷酸化，而不是INO1mRNA的减少。有趣的是，抑制肌醇合成会扰乱液泡功能和V-ATPase活性。基于这些发现，这项拟议的研究将解决这样的假设，即肌醇稳态由MIPS的磷酸化控制，肌醇耗竭导致空泡功能和ATPase活性的扰动。V-ATPase是一种高度保守的泵，对于将分子运输到酸性细胞器是必不可少的。在突触小泡中，V-ATPase活性驱动神经递质的摄取。因此，肌醇耗竭药物对V-ATPase的干扰有望对神经传递产生重要影响。具体目标将解决以下问题：1)MIPS磷酸化的潜在机制是什么？2)肌醇耗竭是如何导致空泡功能紊乱的？3)人类细胞中MIPS的控制机制是什么？这项研究将首次描述一种新的调节机制，它控制肌醇的动态平衡，并将这种调节与空泡功能和V-ATPase活性联系起来。这项研究还将解决我们对肌醇合成是如何在人类细胞中调节的理解上的严重差距。由于含有肌醇的化合物涉及神经和精神疾病、肌肉疾病、癌症和糖尿病等各种疾病，这些研究的结果将对理解对人类健康至关重要的调控途径产生强大的影响。公共卫生相关性：这项拟议的研究将阐明一种控制肌醇稳态的新分子机制，以及这一调控的细胞后果。肌醇是一种重要的代谢感受器，在调节细胞信号通路中起着重要作用。由于含有肌醇的化合物涉及神经和精神疾病、肌肉疾病、癌症和糖尿病等各种疾病，这些研究的结果将对理解对人类健康至关重要的调控途径产生强大的影响。

DESCRIPTION (provided by applicant): Inositol is an essential metabolite that plays a fundamental role in regulating cellular signaling pathways. In yeast, inositol affects the transcription of over 700 genes. In addition, many inositol phosphates and phosphoinositides are signaling molecules that control essential cellular pathways. Therefore, inositol homeostasis must be highly regulated. Numerous studies have shown that inositol biosynthesis is controlled at the level of transcription of the INO1 gene, which encodes myo-inositol 3-phosphate synthase (MIPS). However, regulation of inositol levels cannot be explained solely by modulating INO1 expression, as several physiological conditions that lead to inositol depletion are characterized by decreased inositol synthesis in spite of an increase in INO1 expression. In fact, preliminary studies indicate that decreased MIPS activity results from phosphorylation of the MIPS protein, not from decreased INO1 mRNA. Interestingly, inhibition of inositol synthesis perturbs vacuole function and V-ATPase activity. Based on these findings, the proposed study will address the hypothesis that inositol homeostasis is controlled by the phosphorylation of MIPS, and that inositol depletion leads to perturbation of vacuolar function and ATPase activity. The V-ATPase is a highly conserved pump that is essential for the transport of molecules into acidic organelles. In synaptic vesicles, V-ATPase activity drives the uptake of neurotransmitters. Therefore, perturbation of the V-ATPase by inositol depleting drugs is expected to have important implications for neurotransmission. The specific aims will address the following questions: 1) What is the mechanism underlying the phosphorylation of MIPS? 2) How does inositol depletion lead to perturbation of vacuolar function? 3) What mechanisms control MIPS in human cells? This study will characterize for the first time a novel regulatory mechanism that controls inositol homeostasis and that links this regulation to vacuolar function and V-ATPase activity. This study will also address the serious gap in our understanding of how inositol synthesis is regulated in human cells. Because inositol-containing compounds are involved in disorders as diverse as neurological and psychiatric illnesses, myopathies, cancer, and diabetes, the outcome of these studies will have a powerful impact on understanding regulatory pathways crucial to human health. PUBLIC HEALTH RELEVANCE: The proposed study will elucidate a novel molecular mechanism of control of inositol homeostasis and the cellular consequences of this regulation. Inositol is an essential metabolic sensor that plays a fundamental role in regulating cellular signaling pathways. Because inositol-containing compounds are involved in disorders as diverse as neurological and psychiatric illnesses, myopathies, cancer, and diabetes, the outcome of these studies will have a powerful impact on understanding regulatory pathways crucial to human health.