Substrate Stiffness Mediated Metastasis Like Phenotype of Colon Cancer Cells is Independent of Cell to Gel Adhesion

Growing experimental evidences suggest that cells can feel and respond to the mechanical stiffness of the substrate on which they adhere. Human colon carcinoma (HCT-8) cells can exhibit a dissociative, metastasis-like phenotype (MLP) in vitro when cultured on extra-cellular matrix (ECM) coated polyacrylamide (PA) hydrogels with appropriate mechanical stiffness (20-47 kPa), but not on very stiff (3.6 GPa) polystyrene substrates. In this study, we ask the question whether similar morphological transition occurs on cell-cell adhesion molecule, i.e., E-cadherin coated PA gels and if so, how the actin cytoskeleton and focal adhesions compare with ECM mediated response on gels. First, we culture the HCT-8 cells on E-cadherin coated PA gels of specific mechanical stiffness (20 kPa) and very stiff glass (similar to 70 GPa) substrates. Interestingly, HCT-8 cells show the distinct dissociative in vitro MLP on 20 kPa gel only (not on stiff glass) on sixth day of culture; slightly earlier than the control (ECM/fibronectin coated 20 kPa gels). The complete inhibition of MLP on E-cadherin coated gels by pharmacological agent, blebbistatin, implicates the involvement of non-muscle myosin II activity in MLP. Confocal laser scanning microscopy and quantitative image analysis results suggest that the actin cytoskeletal architecture was characteristically different near the gel surface of E-cadherin and fibronectin coated gels of similar stiffness before dissociation. Conversely, identical cortical actin only structure was observed in the dissociated cells in both cases. Overall, these results suggest that MLP of HCT-8 cells on PA gels is independent of cell to gel adhesion in 2D in vitro culture.