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 recent discovery showing that non-centrosomal MTs are
both sufficient and required to drive polarized cell migration has established a paradigm shift, suggesting that non-
centrosomal MTs are primed to function in a way that is distinct from MTs nucleated by the centrosome. The 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. One targeted MT effector protein, MCAK, is locally inhibited by Rac1 to
promote leading-edge MT growth and cell polarity, and MCAKs effects on MT dynamics are sensitive to myosin-II
contractility. Despite this knowledge, how Rac1 and myosin-II contribute to the organization of FAs, MTs, and actin is
not well understood. Preliminary evidence demonstrates that FA-associated MTs are predominantly of non-centrosomal
origin and that Rac1 activity enhances the association of two different families of MAPs, CAMSAPs and septins, which
increase non-centrosomal MT growth into FAs. Here, we will test the hypothesis that Rac1 and myosin-II promote the
association of CAMSAP and septins with non-centrosomal MTs, which inhibits MCAK-mediated MT disassembly and
drives MT-FA interactions. Our approach will incorporate a team of undergraduate researchers using fluorescence
microscopy of live endothelial cells to determine: (1) how Rac1 and myosin-II regulate CAMSAP and septin interactions
with non-centrosomal MTs, (2) how MCAK disassembly of non-centrosomal MTs controls MT dynamics and FA size,
and (3) how septins promote MT growth into FAs. These investigations will provide critical advances to the field of cell
migration by functionally linking Rac1 and myosin-II with cytoskeletal effector proteins that control non-centrosomal MT
growth into FAs and the regulation of cell migration in health and disease.
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