Understanding the molecular alterations that confer cancer cells with motile, metastatic properties is needed to improve patient survival. Here we report that p38γ MAPK regulates breast cancer cell motility and metastasis, in part by controlling expression of the metastasis-associated small GTPase RhoC. This p38γ-RhoC regulatory connection was mediated by a novel mechanism of modulating RhoC ubiquitination. This relationship persisted across multiple cell lines and in clinical breast cancer specimens. Using a computational mechanical model based on the finite element method, we demonstrated that p38γ-mediated cytoskeletal changes are sufficient to control cell motility. This model predicted novel dynamics of leading edge actin protrusions, which were experimentally verified and established to be closely related to cell shape and cytoskeletal morphology. Clinical relevance was supported by evidence that elevated expression of p38γ associated with lower overall survival of breast cancer patients. Taken together, our results offer a detailed characterization of how p38γ contributes to breast cancer progression, presents a new mechanics-based analysis of cell motility, and discovers a leading edge behavior in motile cells to accommodate modified cytoskeletal architecture. In summary, these findings not only identify a novel mechanism for regulating RhoC expression but also advance p38γ as a candidate therapeutic target.

We apply a recently developed model of cytoskeletal force generation to study a cell's intrinsic contractility, as well as its response to external loading. The model is based on a nonequilibrium thermodynamic treatment of the mechanochemistry governing force in the stress fiber-focal adhesion system. Our computational study suggests that the mechanical coupling between the stress fibers and focal adhesions leads to a complex, dynamic, mechanochemical response. We collect the results in response maps whose regimes are distinguished by the initial geometry of the stress fiber-focal adhesion system, and by the external load on the cell. The results from our model connect qualitatively with recent studies on the force response of smooth muscle cells on arrays of polymeric microposts.

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spacing and a height of 4-12 mm. In this range forces of 1-50 nN per pillar are measured. The PDMS pillars were stamped with partly fluorescently labeled fibronectin that allowed us to accurately determine the pillar deflections. Subsequently, 3T3 mouse fibroblasts were seeded onto the pillars. Immunostaining was employed using standard procedures to visualize the actin cytoskeleton and focal adhesion complexes. The actin cytoskeleton, focal adhesions and pillar deflections were imaged with a confocal spinning disk setup. From these results, we quantified the degree of co-orientation of focal adhesion elongation with force direction and the increase in stress fiber-and focal adhesion size with forces in the range of 1-15 nN.

Background: We consider a focal adhesion to be made up of molecular complexes, each consisting of a ligand, an integrin molecule, and associated plaque proteins. Free energy changes drive the binding and unbinding of these complexes and thereby controls the focal adhesion's dynamic modes of growth, treadmilling and resorption.