A characterization of the expression, regulation, and function of the mouse voltage-sensitive phosphatase, Mm-VSP

Abstract

Voltage-sensitive phosphatases (VSPs) are proteins that directly couple changes in membrane electrical potential to changes in the enzymatic activity of a lipid phosphatase domain. The best characterized activity of VSPs so far is dephosphorylation of the lipid substrates phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2), and phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3). These phospholipid signals regulate many important cellular signaling cascades that have been implicated in numerous diseases, and regulated electrical signaling is also known to play a crucial role in an equally broad variety of cell signaling events and diseases. Given that VSPs are uniquely able to directly couple these two signaling mechanisms, there is a clear biomedical motivation to fully understand the roles that VSPs play in cell signaling. Great progress has been made using VSPs as tools to investigate phosphoinositide signaling pathways and to investigate structural mechanisms of electrochemical coupling in cells. However despite these advancements, the mammalian members of the VSP family remain poorly characterized relative to their non-mammalian counterparts, and very little is known about the cell signaling roles that any VSP proteins serve. To address this gap in knowledge, I have characterized the expression, regulation, and activity of the VSP family member from mouse, giving particular attention to a possible role in the central nervous system. This dissertation will begin with a summary of the current state of understanding of both mammalian and non-mammalian VSPs, and then discuss what I have recently learned about the properties of the mouse VSP. In particular, I have demonstrated that the mouse protein is expressed in the central nervous system, where its expression is developmentally regulated at both the mRNA and protein levels. I have also shown that the mouse protein's transmembrane segments function as a voltage sensing domain, and that the phosphatase domain is capable of reducing the concentration of PI(4,5)P2 at the plasma membrane. These properties of the mouse VSP are distinct from the reported properties of the non-mammalian VSPs, suggesting interesting and unique physiological roles for the VSPs from mammals.