The dependence of fibrillar adhesions in human fibroblasts on substratum chemistry

Little is known about the influence of substratum properties and composition on the ability of cells to translocate α5β1 integrins and to form fibrillar adhesion. We have examined the impact of self-assembled monolayers (SAMs) bearing different functional end groups (amines (NH2) or carboxylic acids (COOH)) on the presence of fibrillar adhesions in human fibroblasts attached to fibronectin-coated SAMs. Most of the fibroblasts incubated in serum-free medium for 2 h on COOH showed segregation of focal contact components (αv integrin subunits, phosphotyrosine proteins) and fibrillar adhesions (α5 integrin subunits, tensin) while the majority of cells plated on NH2 did not. Analysis of fibronectin fibril formation confirmed also that human fibroblasts plated on COOH formed matrix fibrils significantly better. The surface-associated α5 to αv integrin ratio was smaller in cells on COOH than on NH2 due to a decreased α5 integrin binding. In addition, human fibroblasts migrated more readily on COOH in comparison to NH2 which points to a different binding strength of integrins to the substratum. Overall, the results indicate that the molecular composition of substrata has a strong influence on FN matrix formation by promoting or inhibiting segregation of focal and fibrillar adhesions.