Targeting of cytoskeletal linker proteins to focal adhesion complexes is reduced in fibroblasts adhering to laminin-1 when compared to fibronectin

Cellular interactions with the extracellular matrix determine to a large ex tent cell behavior, including cell migration. These interactions take place at specialized cellular structures, the focal adhesions, which have a subs trate-specific morphology. To determine the molecular and functional releva nce of this observation, the composition of isolated focal adhesions develo ped by fibroblasts adhering to fibronectin or laminin-1 was analyzed by ind irect immunofluorescence and immunoblotting with or without stabilization o f the structures by cross-linking. In the absence of cross-linking, integri ns, talin, vinculin and, to a lower extent, paxillin remained associated wi th the focal adhesions formed on both substrates, indicating a tight associ ation of these proteins with the extracellular matrix support. By contrast, alpha-actinin, FAK, and actin were apparently loosely maintained within fo cal adhesions and were found associated to these structures only after stab ilization by crosslinking. Interestingly, although both substrates induced clustering and aggregation of all these proteins, their relative concentrat ion, with the exception of alpha-actinin, was lower within the focal adhesi ons formed on laminin-1 than in those formed on fibronectin. Moreover, as a ssessed in migration assays, the locomotory speed of fibroblasts was higher on laminin-1 than on fibronectin. Altogether these results indicate that i ntegrins involved in cellular interactions with fibronectin or laminin-1 tr igger the formation of focal adhesion structures which differ by molecular organization, concentration in several adhesion plaque components, and func tion.