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 pr oteins 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 th e marine amoeba Neoparamoeba aestuarina. In addition, elevated levels of GRGDSPK cause cells to alter their shapes from those with digitifor m subpseudopodia to rounded cells with small lobed pseudopodia. These cells detach from the substratum. These results are specific for the R GD sequence, because incubation in GRGESPK solution at the same concen trations had no effect on cell attachment or structure. From these dat a we suggest that the structural adhesion molecules identified in vert ebrates show amino acid homologies with those found in unicellular pro tozoa.