Cancer cell invasion is driven by migration. Often this migration is directed by aligned collagen fibers, a process called contact guidance. Because of the strong link between directed migration and aligned collagen fiber orientation, extracellular matrix alignment has been suggested as a measurable to determine invasion potential. We have recently shown that different breast cancer cells respond to contact guidance cues differently. MDA-MB-231 cells, which migrate with a mesenchymal mode, sense contact guidance cues with high fidelity, but MTLn3 cells, which migrate with an amoeboid mode, do not sense contact guidance cues. Several studies have shown that modulating contractility and adhesion through Rho-family GTPases and integrin activation allows cells to switch between migrational modes. We were interested if this plasticity in migrational mode affects contact guidance.
In this study, we have used several different approaches for generating contact guidance cues including microcontact printing, soft lithography and epitaxial collagen growth to generate lines, ridges and aligned fibrils of collagen. In addition, we have used pharmacological inhibitors and genetic approaches to examine the role of Rac and Rho GTPases as well as the activation of b1 integrins in modulating contact guidance through focal adhesions and the cytoskeleton. Decreasing contractility by inhibiting Rho-kinase (Y-27632) or partially blocking b1 integrin activation (P5D2 antibody) in MDA-MB-231 cells diminished contact guidance fidelity on epitaxially growth collagen fibrils. One the other hand, increasing contractility (calyculin A (CA)) or activating integrins (MnCl2) increased contact guidance fidelity in MTLn3 on epitaxially growth collagen fibrils. Interestingly, speed was not altered. These changes in motility were explained by changes in F-actin stress fiber density and orientation, myosin light chain phosphorylation and focal adhesion dynamics and maturation. This suggests that the assessment of the cell's ability to generate and transmit force in combination with the organization of the extracellular matrix are important in determining whether contact guidance occurs leading to cancer cell invasion.
Figure1: Contact guidance efficiency is altered through contractility and adhesion. Cells were imaged over time using phase contrast microscopy in the presence of contractility inhibitors (Y-27632), contractility enhancers (calyculin A (CA)) and integrin activators (MnCl2).