Davidson, M. W. | bioRxiv Science

bioRxiv2018

Spindly is Required for Rapid Migration of Human Cells.

Dynein is the sole minus-end directed microtubule motor found in animals. It has roles in cell division, membrane trafficking, and cell migration. Together with dynactin, dynein regulates centrosomal orientation to establish and maintain cell polarity, controls focal adhesion turnover and anchors microtubules at the leading edge. In higher eukaryotes, dynein/dynactin requires additional components such as Bicaudal D to form an active motor complex and for regulating its cellular localization. Spindly is a protein that targets dynein/dynactin to kinetochores in mitosis and can activate its motility in vitro. However, no role for Spindly in interphase dynein/dynactin function has been found. We show that Spindly binds to the cell cortex and microtubule tips and colocalizes with dynein/dynactin at the leading edge of migrating U2OS cells and primary fibroblasts. U2OS cells that lack Spindly migrated slower in 2D than control cells, although centrosome polarization appeared to happen properly in the absence of Spindly. Re-expression of Spindly rescues migration, but the expression of a mutant, which is defective for dynactin binding, failed to rescue this defect. Taken together, these data demonstrate that Spindly plays an important role in mediating a subset of dynein/dynactins function in cell migration.

cell biology↗

bioRxiv2017

A Cautionary Tail: Changes in Integrin Behavior with Labeling

Genetic expression of fluorescently labeled proteins is essential to visualizing dynamic behavior within live cells. Recent advances in microscopy have increased resolution to the level where it is now possible to capture individual molecules interacting. However, the criteria for determining whether a fluorescent label perturbs protein function have not undergone a corresponding increase in resolution. The effects of protein labeling on cell function are still judged by whether populations of protein localize and interact with known binding partners. Here we use integrins, bidirectional signal adhesion molecules that regulate interactions between the extracellular matrix and the cytoskeleton through a well-defined series of conformational changes to show that not all labeling strategies are the same. We found that labeling the beta subunit decreased the mobility of individual integrin molecules and the protrusive activity of the entire cell. While integrins with labeled alpha subunits behaved similarly to unlabeled integrins, labeling the beta subunit increased the size of adhesions by elevating integrin affinity and exposing the ligand induced binding domain to change the molecule conformation. Thus, our single molecule and cellular data indicate that the ability of labeled proteins to localize and interact with known binding partners does not guarantee it does not alter protein function. We propose that the behaviors of individual molecules rather than the ensemble behavior of populations need to be considered as criteria to determine if a probe is non-perturbative.

cell biology↗