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.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK081367-04
Application #
8293227
Study Section
Special Emphasis Panel (ZRG1-BCMB-B (02))
Program Officer
Silva, Corinne M
Project Start
2009-05-01
Project End
2014-04-30
Budget Start
2012-05-01
Budget End
2014-04-30
Support Year
4
Fiscal Year
2012
Total Cost
$319,440
Indirect Cost
$106,268
Name
Wayne State University
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
001962224
City
Detroit
State
MI
Country
United States
Zip Code
48202
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Deranieh, Rania M; He, Quan; Caruso, Joseph A et al. (2013) Phosphorylation regulates myo-inositol-3-phosphate synthase: a novel regulatory mechanism of inositol biosynthesis. J Biol Chem 288:26822-33
Chang, Pishan; Orabi, Benoit; Deranieh, Rania M et al. (2012) The antiepileptic drug valproic acid and other medium-chain fatty acids acutely reduce phosphoinositide levels independently of inositol in Dictyostelium. Dis Model Mech 5:115-24
Deranieh, Rania M; Greenberg, Miriam L (2009) Cellular consequences of inositol depletion. Biochem Soc Trans 37:1099-103