Identification of extracellular matrix ligands for the heparan sulfate proteoglycan agrin

Agrin is a major brain heparan sulfate proteoglycan which is expressed in n early all basal laminae and in early axonal pathways of the developing cent ral nervous system. To further understand agrin's function during nervous s ystem development, we have examined agrin's ability to interact with severa l heparin-binding extracellular matrix proteins. Our data show that agrin b inds FGF-S and thrombospondin by a heparan sulfate-dependent mechanism, mer osin and laminin by both heparan sulfate-dependent and -independent mechani sms, and tenascin solely via agrin's protein core. Furthermore, agrin's hep aran sulfate side chains encode a specificity in interactions with heparin- binding molecules since fibronectin and the cell adhesion molecule L1 do no t bind agrin. Surface plasmon resonance studies (BIAcore) reveal a high aff inity for agrin's interaction with FG;F-S and merosin (2.5 and 1.8 nM, resp ectively). Demonstrating a biological significance for these interactions, FGF-8, laminin, and tenascin copurify with immunopurified agrin and immunoh istochemistry reveals a partial codistribution of agrin and its ECM ligands in the chick developing visual system. These studies and our previous stud ies, showing that merosin and NCAM also colocalize with agrin, provide evid ence that agrin plays a crucial role in the function of the extracellular m atrix and suggest a role for agrin in axon pathway development, (C) 1999 Ac ademic Press.