Evolution of cell adhesion systems: evidence for Arg-Gly-Asp-mediated adhesion in the protozoan Neoparamoeba aestuarina.

Developmental processes in multicellular organisms require structural elements, such as adhesion molecules, to stabilize cells at functional positions. In vertebrates, a series of extracellular matrix proteins, e.g. fibronectin and laminin, are involved in cell adhesion. These proteins contain Arg-Gly-Asp [RGD] at their binding sites. Here we show that at concentrations above 2 mM the peptide GRGDSPK, comprising the tripeptide RGD (Arg-Gly-Asp), prevents the adhesiveness of cells of the marine amoeba Neoparamoeba aestuarina. In addition, elevated levels of GRGDSPK cause cells to alter their shapes from those with digitiform subpseudopodia to rounded cells with small lobed pseudopodia. These cells detach from the substratum. These results are specific for the RGD sequence, because incubation in GRGESPK solution at the same concentrations had no effect on cell attachment or structure. From these data we suggest that the structural adhesion molecules identified in vertebrates show amino acid homologies with those found in unicellular protozoa.