Loss of an Actin Crosslinker Uncouples Cell Spreading from Cell Stiffening on Gels with a Gradient of Stiffness

Abstract

We show the essential function of an actin crosslinker, filamin A, in cell responses to mechanical stimuli by measuring the stiffness, spreading area of A7 and M2 cells cultured on substrates with stiffness gradients created by microfluidics. M2 melanoma cells, null for filamin A, do not alter their adherent area in response to increased substrate stiffness when they link to the substrate only through collagen receptors, but change adherent area normally when bound through fibronectin receptors. In contrast, filamin A-replete A7 cells change adherent area on both substrates and respond more strongly to collagen I-coated gels than to fibronectin-coated gels. A7 cells alter their stiffness, as measured by atomic force microscopy, to match the elastic modulus of the substrate immediately adjacent to them on the gradient. M2 cells, in contrast, maintain a constant stiffness on all substrates that is as low as that of A7 cells on the softest gels achievable (1000 Pa). Comparing the responses of these cell types to different adhesive substrates, we found that cell spreading and stiffening can be uncoupled.