Glycosaminoglycans promote HARP/PTN dimerization

Heparin affin regulatory peptide (HARP), also called pleiotrophin (PTN), is a secreted polypeptide which binds to heparin and plays a key role in cell ular growth and differentiation. In order to assess the determinants potent ially important to its biological activity, we tested the ability of HARP t o oligomerize, a process involved in mitogenic activity of the heparin-bind ing fibroblast growth factor. Using dissuccinimidyl suberate cross-linking experiments and affinity chromatography, we report that human HARP forms no ncovalent dimers, Dimerization is dependent on the presence of heparin or o ther sulfated glycosaminoglycans, as chlorate treatment of cells inhibits t his process. In vitro, different glycosaminoglycans, such as dermatan sulfa te and chondroitin sulfate-C, also in duce a dimer assembly of HARP, The re levance of this process was supported by experiments demonstrating that HAR P is secreted as a dimer in conditioned medium of NIH-3T3 cells that overex pressed this growth factor and is also associated to the cell surface or to the extracellular matrix. (C) 1999 Academic Press.