(77h) Focal Adhesion Maturation and Dynamics Regulate Cell-to-Cell Variability In EGF-Stimulated Migration

Cell migration plays an essential role in many biological processes, such as cancer metastasis, wound healing and immune response.  Cell migration is mediated in part through adhesion via focal adhesions (FAs), which are dynamic, macromolecular structures that serve as mechanical linkages and centers of intracellular signal transduction.  FAs exist in different maturation states, which have been traditionally tied to either protein composition or morphology.  Different maturation states regulate cell migration by either promoting local protrusion, quiescence or retraction.  Epidermal growth factor (EGF) is known to enhance migration rate; however it is not known how FA maturation contributes to this control.

Our first objective is to determine the response of a population of cells to different doses of EGF at the level of migration.  Our second objective is to use the cell-to-cell variability in migration rate at each EGF dose to understand which FA maturation and dynamics characteristics drive fast migration under EGF stimulation.  We expressed a GFP fusion protein that localizes to FAs of various maturation states, paxillin-GFP, and imaged cells using total internal reflection fluorescence (TIRF) microscopy.  Computer vision software was used to segment and track FA characteristics and quantify cell migration rate under different doses of EGF.

We found that there was considerable cell-to-cell variability in the effect of EGF on cell migration rate.  The mean speed of cells only increased slightly with increased dose of EGF, while the distribution widened, indicating subpopulations of cells that both migrated much faster and much slower than those at lower EGF concentrations.  We examined the FA characteristics, such as size, integrated intensity and lifetime under different doses of EGF and found that the average values and distributions of these characteristics were not significantly different among each concentration of EGF.  However, when we grouped cells according to migration rate and examined the FA characteristics, we found that these characteristics differed between slow and fast moving cells.  Slow cells had a higher probability of having both small and large FAs, while fast cells had a higher probability of having intermediate sized FAs.  Additionally, slow cells had FAs with high intensities while fast cells had FAs with low intensities.

These findings indicate that there is high cell-to-cell variability in the response of cell migration to EGF.  However, this variability can be leveraged to understand how cell migration rate is regulated by FA maturation and dynamics.  Interestingly, some maturation characteristics such as FA area may not contribute to enhanced cell migration in a monotonic fashion.  Rather, intermediate values of these characteristics may be optimized for fast cell migration.  By understanding how FA maturation and dynamics correlate with migration rate, we can manipulate the cell migration behavior through the intracellular regulation of FAs, providing a potential way to control migration in artificial matrices or during pathologies such as cancer metastasis.