Regulation of Metal Ion Homeostasis by Channel Kinases

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DESCRIPTION (provided by applicant): The goal of this program is to uncover the mechanism of the regulation of metal ion homeostasis, particularly magnesium homeostasis in vertebrates through the investigation of the structure and function of channel kinases. Channel kinases, also know as "chanzymes" (channels plus enzymes) are recently discovered bifunctional molecules that consist of an ion channel fused to a protein kinase. Recent evidence suggests that channel kinases TRPM6 and TRPM7 play a key role in the regulation of metal ion homeostasis in vertebrates. Specifically, channel kinases have several major functions: 1) As magnesium channels they represent key regulators of magnesium homeostasis and may provide the major magnesium uptake mechanism in mammalian cells; 2) As trace metal ion channels, channel kinases may provide a major ion channel mechanism for cellular entry of trace metal ions such as manganese and zinc. In Project 1 (Andrea Fleig, PI), we will perform biophysical, molecular, and functional analysis of the TRPM7 and TRPM6 ion channels. We will investigate molecular determinants of channel permeation that provide selectivity for divalent metal ions. In Project 2 (Alexey Ryazanov, 4PI), we will investigate the physiological function and mechanism of activation of TRPM7 and TRPM6 kinases. We will determine sequence motifs recognized by these kinases and identify their physiological substrates. In Project 3 (Andrew Scharenberg, PI) we will investigate the role of TRPM7 in the regulation of magnesium homeostasis. We will identify signaling pathways through which TRPM7 mediates magnesium-dependent regulation of cell and organism growth. In Project 4 (John Stokes, PI), we will analyze the role of TRPM6 and TRPM7 in the regulation of magnesium homeostasis using knockout mouse models. We will determine how magnesium balance affects kidney function in mice deficient in TRPM6 or TRPM7. We will also develop mice with conditional and organ-specific knockouts of TRPM6 and TRPM7. These projects will be supported by an Administrative Core (Core A), and an Animal and Analytical Core (Core B). This work has a high degree of medical relevance considering that channel kinases are likely to play a role in such conditions as ischemia and stroke, and since mutations in channel kinases are causing diseases associated with metal ion imbalance.