Microtubules Mechanically Regulate Cell Adhesion Strengthening Via Cell Shape

Cell adhesion strengthening is a complex mechanical and biochemical process involving receptor binding, cytoskeletal reorganization, and morphological changes. Actin-myosin contractility has been established to drive focal adhesion assembly and adhesion strengthening; yet while microtubules are believed to balance contractile elements, their role in adhesion strength has not been investigated. A hydrodynamic adhesion assay and micropatterned surfaces to control cell shape were used to analyze the interdependent effects of microtubule inhibition and serum-modulated cytoskeletal tension on adhesion strength. Microtubule disruption enhanced contractility and focal adhesion assembly in serum, however only serum free conditions made cells susceptible to microtubule disruption in terms of spreading, morphology and adhesion strength. Forcing cells to remain spherical by micropatterning resulted in reduced adhesion strength after microtubule disruption in the presence of serum, and the temporal evolution of adhesion strength of spreading cells was observed to be strongly regulated by microtubules. Together these results, along with previous studies of contractility, establish that a tightly controlled intracellular force balance is required for the cell to reach its maximum adhesion strength and that cells are more sensitive to perturbations before they are fully spread.