The central role of the PACS family of proteins in cellular organization

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Background The movement of many proteins within cells is ensured by the membrane trafficking machinery. This machinery enables the correct subcellular localization of proteins which guarantees proteins fulfill their cellular functions. Overall, membrane trafficking maintains cellular homeostasis. This proposal is centered on the membrane trafficking regulator proteins Phosphofurin Acid Cluster Sorting (PACS) 1 and 2. The PACS proteins form key interactions with multiple cellular proteins termed cargo and shuttle the latter cargo to the correct subcellular location. The importance and diversity of PACS-1 and PACS-2 trafficking events demonstrates the central role these proteins play in trafficking. Indeed, PACS-1 trafficking is implicated in the formation of primary cilia, the delivery of activating molecules to specific cellular compartments and the conversion of inactive precursor proteins to active proteins, amongst other functions. Conversely, PACS-2 trafficking events can function during key cellular events such as maintaining cellular calcium levels and modulating cellular death pathways. Hypothesis We hypothesize that PACS proteins are central organizers of the cell by orchestrating multiple protein-protein interactions to enable trafficking of itinerant cargo to precise subcellular locales. Proper trafficking of proteins is critical for them to subsequently perform their functions. We further hypothesize that defining how novel PACS:protein interactions function will shed significant insight into defining the central role of PACS proteins in cellular organization. Progress My laboratory has identified a novel trafficking pathway that is controlled by PACS-1. This pathway is implicated in the delivery of hormones to a specific subcellular location, the dense core secretory granule. In addition, my laboratory has defined the full range of PACS-1 & PACS-2 interacting partners which has revealed an unexpected concentration of PACS roles in the nucleus. Overall, we will study these mechanisms aided by a variety of techniques that we have perfected and developed during the previous funding period. Aims Elucidating the roles of PACS-1 & PACS-2 in multiple membrane trafficking pathways is the overarching aim of this research program. Aim1: Defining the role of PACS-1 in the sorting of cargo to dense core secretory granules. Aim 2: Defining the role of PACS-1 in the secretion of cargo from the dense core secretory granule. Aim 3: Defining the protein-protein interactions and roles of PACS-1 and PAC-2 in the nucleus Significance This discovery-based research program will address important and unique questions concerning the pathways that are governed by the central membrane trafficking regulator PACS proteins. Our long-term plans are centered on exploring the full range of PACS-1 and PACS-2 cargo that we have discovered during the previous funding period.