The Biology of Inositol Polyphosphate Signaling

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DESCRIPTION (provided by applicant): The long-term goal of this grant is the elucidation of inositol polyphosphate (IP) signaling pathways and determination of the mechanisms by which cells use them to elicit selective intracellular responses. We have taken a molecular approach to understanding these pathways, and have collectively cloned and identified the function of numerous enzymes involved in the metabolism of IP messengers. This proposal focuses on the inositol polyphosphate kinases (IPKs) that we discovered are involved in the conversion of inositol 1,4,5- trisphosphate (IP3) to higher IP messengers (such as IP4, IP5, IP6 and inositol pyrophosphates - PP-IPs). Our studies of the IPKs, supported by this grant in previous years, have led to the definition of novel messenger roles for these lipid-derived IP chemical codes in the regulation of gene expression/transcription, mRNA export, telomere maintenance, organism development and most recently a role for inositol pyrophosphates in nutrient signaling. In this proposal we will focus primarily on two kinases, IPMK (also referred to as IPK2) and the newly discovered VIP1, a novel IP6/IP7 kinase, another IPK implicated in the control of gene expression in response to nutrient change and cell morphology. We seek to accomplish two major objectives: 1) elucidate the mechanisms of IPMK-mediated control of gene expression, growth control and cell death; and 2) understand the roles of diphosphoinositol phosphates, also known as inositol pyrophosphates, through studies of the exciting new evolutionarily conserved VIP1-like class of IP6/IP7 kinase. Overall, this work will further characterize IPK-dependent signaling pathways and the receptors that decode these important cellular regulators. We envision that the IPKs modulate an IP code. By analogy to a nucleotide code, we suggest that each IP species represents a base. Thus far over 20 IP bases generated by IPKs have been identified in cells and the number continues to grow. Through altering the patterns and levels of each IP base, we suggest that a cell may generate a combinatorially complex dynamic code capable of enhancing signaling specificity. Our studies of the IP code will likely provide new insights into organism development, cellular growth control and nutrient adaptation with relevance to public health. Public Health Relevance: Our proposal seeks to elucidate lipid-derived inositol phosphate cellular signal transduction pathways. Defects in the kinases and phosphatases that regulate an inositol phosphate signaling code result in human disease and defects in growth control, adaptation and organism development. Understanding these essential enzymes will provide significant insights into human cell biology and improve public health through basic science research.