Vesicular transport between organelles involves coat protein-mediated formation of buds that recruit scission factors such as dynamin to release vesicles into the cytoplasm. Formation of intralumenal vesicles in multivesicular bodies (MVBs) of the endolysosomal pathway (and the related processes of viral budding and abscission at the end of cytokinesis) is topologically opposite to this, with cytosolic factors promoting release of vesicles into the endosomal lumen or extracellular space. Because cytosolic factors drive both reactions, but operate in one case from outside and in the other from inside the neck connecting a vesicle to its donor membrane, fundamentally different mechanisms must be involved. A conceptual framework for how outwardly directed membrane scission proceeds invokes sequential recruitment of ESCRT (endosomal sorting complex required for transport) components to delineate, deform, and ultimately release vesicles into the endosomal lumen. We are studying how the ESCRT machinery and its AAA+ ATPase VPS4 drive and regulate vesicle formation. We are also interested in how ESCRTs and VPS4 modulate the trafficking (and downregulation) of signaling receptors and the biogenesis of secreted exosomes.Functional Analysis of TorsinA and its Role in DYT1 Dystonia
The endoplasmic reticulum (ER) is the largest and most heterogeneous organelle in the cell and includes the nuclear envelope (NE). TorsinA is an AAA+ ATPase in the lumen of the ER and NE which when mutated causes early onset (DYT1) dystonia, a devastating non-degenerative neurological movement disorder. Although many possibilities have been considered for the action of torsinA and related enzymes, their function remains poorly defined creating a significant roadblock to developing targeted treatments for dystonia. Our goal is to clarify the cellular function and disease-linked dysfunction of torsinA. We have previously found that the distribution of torsinA within the ER is regulated and likely to play an important role in controlling its activity. We are working to understand the molecular mechanisms responsible for distributing torsinA within the ER and NE, to define torsinA’s substrates, to determine how these are affected by torsinA, and to establish how disease-associated mutations change torsinA structure and function. Current work suggests that torsinA modulates components of the LINC complexes that bridge the nuclear envelope to connect nucleus to cytoskeleton.