Mechanisms of compartmentalized signaling in electrically excitable cells

PROJECT SUMMARY We often think of action potentials as a way for cells to quickly send signals over long distances and release substances like neurotransmitters. This perspective overlooks the crucial role of electrical signals in triggering intracellular biochemical processes, including gene expression. Our research has identified that endoplasmic reticulum (ER)-plasma membrane (PM) junctions in the neuronal soma act as specialized sites for this electrical- biochemical coupling. These ER-PM junctions are molecularly complex, exhibiting diverse architectures, protein compositions, and distributions, indicating that they serve distinct cellular functions. Our lab's long-term goal is to understand how electrical signals are translated into specific biochemical responses, such as activating gene expression programs. We propose that ER-PM junctions are central to translating membrane depolarizations into intracellular signaling events, and our work is focused on discovering the mechanisms underlying their assembly and function. Building on our previous work in defining the proteome and physiological roles of these junctions in mammalian neurons, our five-year goal is to investigate the regulatory mechanisms governing their organization, with a particular emphasis on cAMP-dependent protein kinase (PKA) signaling. First, we aim to define the signaling interactions at PKA-containing ER-PM junctions, focusing on how distinct A-kinase anchoring proteins (AKAPs) recruit additional scaffolding proteins and shape the composition of these signaling complexes. We will use genetic and biochemical approaches to map enzyme substrates targeted to these sites and identify how these enzymes influence somatic signaling pathways. Secondly, we will examine how AKAP- enzyme signaling complexes are structurally organized, especially how conserved, disease-linked domains within AKAPs direct the formation of specific complexes at ER-PM junctions. A key aspect of our research will be to determine how PKA’s kinase activity versus its role in organizing ER-PM junctions affects signaling outcomes. By identifying the molecular components and pathways involved, this research aims to clarify the roles of ER-PM junctions in neurons and uncover principles applicable to similar structures in other cell types. Such knowledge will improve our understanding of how electrically excitable cells fine-tune their signaling systems to regulate processes like gene expression.