Control of cell polarity and migration by non-centrosomal microtubules - Project Summary/Abstract: The coordinated and regulated remodeling of the actin and microtubule (MT) cytoskeleton is required for cell migration for developmental processes and homeostatic maintenance, as well as during the body’s response to external insults and disease states including heart disease and tumor metastasis. During cell migration, actin filaments assemble and become linked to focal adhesion (FA) complexes, while MTs undergo dynamic instability that is locally controlled by MT- associated proteins (MAPs). These two processes enable cells to establish a leading-edge and a trailing-edge, and to migrate with directional persistence. Despite many advances in our understanding of the functional implications of MAPs on MTs and MT-FA interactions, it remains unknown how exactly MT organization is spatially and temporally coordinated with FAs to promote directional cell movement. A critical discovery, that non-centrosomal MTs are both sufficient and required to drive polarized cell migration, suggests that non-centrosomal MTs are primed to function in a way that is distinct from MTs nucleated by the centrosome. This finding underscores the need to determine how cytoskeletal proteins identify and regulate non-centrosomal versus centrosomal MT dynamics and effects on polarity and migration. This gap in knowledge impacts our understanding of fundamental processes, including how signaling molecules simultaneously regulate families of proteins to achieve complex tasks, such as guiding persistent cell migration. The small GTPase, Rac1, is a key signaling protein that is spatially controlled to promote FA formation, MT growth, and actin filament assembly, resulting in leading edge advance. Rac1 signaling is complemented by the molecular motor protein, myosin-II, which organizes actin stress fibers, promotes FA maturation, and generates forces that pull the trailing- edge of the cell forward. Thus, Rac1 and myosin-II are spatially and temporally controlled to drive directional cell movement. We recently discovered that another family or MAPs, termed septins, respond to Rac1activity by relocating adjacent to FAs, where septins reorient non-centrosomal MT polymerization into FAs and drive FA disassembly and directed migration. Collectively, these findings point to functionally and spatially distinct roles for centrosomal and non- centrosomal MT-mediated regulation of FA dynamics and directed cell motility. Here, we will test the hypothesis that Rac1 and myosin-II promote FA-localized membrane curvature to recruit septin, that polyglutamylation of non- centrosomal MTs promotes septin-MT interactions and FA disassembly, and that FA-tethered centrosomal MTs function to deliver matrix remodeling cargo to FAs. Our approach will incorporate a team of undergraduate researchers using fluorescence microscopy of live endothelial cells to determine: (1) how Rac1 signaling and actin-myosin contractility regulate septin localization adjacent to FAs, (2) how septins functionally distinguish centrosomal MTs from non- centrosomal MTs, and (3) whether/how centrosomal and non-centrosomal MTs work together to promote FA disassembly and directed cell migration. These investigations will provide critical advances to the field of cell migration by functionally linking Rac1 and myosin-II with cytoskeletal effector proteins that regulate centrosomal and non-centrosomal MT behaviors to control FA dynamics and cell migration in health and disease.
