The Role of Molecular Chaperones in Extracellular Vesicles

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The Role of Molecular Chaperones in Extracellular Vesicles*******Overview. In cells, protein folding and protein degradation are tightly regulated by several families of molecular chaperones. Chaperones safeguard all cells by binding to unfolded protein molecules to facilitate either their correct folding or removal. If the chaperone safeguard ‘falls short' and proteostasis is not maintained, cell dysfunction and death ensues.*******The basic chaperone machinery is conserved throughout all three kingdoms. The Hsp70/Hsc70 (70-kDa heat shock protein and cognate protein) chaperone family constitutes one of the most abundant and highly conserved chaperone families and has a broad range of cellular roles involving a large number of target proteins. By virtue of their ability to bind and sequester unfolded regions of a variety of substrate proteins, Hsp70s are able to re-fold and return their “client proteins” to their functionally competent states. Hsp70s don't function alone in this capacity. J proteins serve as molecular switches for Hsp70s by specifying the client proteins to be targeted.*******Recent work from our group has documented that select J protein chaperones are exported from cells in extracellular vesicles. It has been widely assumed that J protein chaperone-mediated folding occurs inside cells and our observation is unexpected. The biological function of J proteins in extracellular vesicles is an open question. In this proposal, we will perform studies to discern the role of J proteins in the release process.*******We will evaluate extracellular vesicle J proteins in two specific aims.**********Specific Aim 1. How do J proteins control the lipid content of extracellular vesicles?****In aim 1, we will shed light on which J proteins influence the lipids packaged into extracellular vesicles and the molecular events underlying this lipid export.**********Specific Aim 2. To determine if secreted J proteins ‘decide' the protein cargo of extracellular vesicles.****Intracellularly J proteins serve as molecular switches for Hsp70s by specifying the client proteins to be targeted, increasing ATP hydrolysis and determining whether client proteins are folded or degraded. In aim 2 we will establish if J proteins also ‘decide' whether client proteins are ‘packed' into extracellular vesicles for export.**********Significance. Surprisingly little is known about J proteins in extracellular vesicles. The core of this proposal will address how J protein chaperones are exported and more specifically how J proteins regulate lipid and protein content of extracellular vesicles. Proteostasis is essential for the survival of all cells. The proteostasis system that operates outside the cell to ensure the stability and fidelity of protein conformation and function still remains for the most part ‘a black box'. The experiments proposed here will provide a framework to begin to elucidate the role of J proteins in cell-cell signaling.***