Heparin/Heparan Sulfate (HP/HS) Interacting Protein (HIP) Supports Cell Attachment and Selective, High Affinity Binding of HP/HS
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abstract
Heparin/heparan sulfate (HP/HS), HS proteoglycans, and their binding proteins play important roles in a variety of biological processes. Previously, we identified a novel cell surface HP/HS interacting protein (HIP) from human uterine epithelia and a variety of other human epithelial and endothelial cells and cell lines (Liu, S., Smith, S. E., Julian, J., Rohde, L. H., Karin, N. J., and Carson, D. D. (1996) J. Biol. Chem. 271, 11817-11823; Rohde, L. H., Julian, J., Babaknia, A., and Carson, D. D. (1996) J. Biol. Chem. 271, 11824-11830). In the current studies, we have purified and characterized HIP from HEC cells, a human uterine epithelial cell line, as well as recombinant HIP from a bacterial expression system. HIP supports attachment of the human trophoblastic cell line, JAR, in a HS-dependent fashion. Predigestion of JAR cells with a mixture of heparitinases, but not chondroitinase AC, abolished cell attachment to HIP. In addition, JAR cell attachment to HIP is highly sensitive to HP inhibition and much more selective for HP/HS than other glycosaminoglycans. Dermatan sulfate displays partial inhibitory activity as well, consistent with the observation that chondroitinase ABC digestion partially reduces JAR cell attachment to HIP. Solid-phase binding assays indicate HIP binds [3H]HP with high affinity (apparent KD = 8 nM). Furthermore, HIP bound cell surface/extracellular matrix-associated HS, expressed by RL95 cells, a human uterine epithelial cell line. Anti-HIP antibody generated against a synthetic peptide derived from a putative HP/HS-binding motif resident within HIP inhibited about half of [3H]HP binding to HIP, indicating that this domain is a functional HP-binding domain of HIP. Similarly, this same synthetic peptide motif of HIP could block about 50% of [3H]HP binding to HIP; however, this peptide almost completely inhibited cell attachment to HIP, suggesting a critical role, in this regard. Collectively, these results suggest that HIP can function as a HP/HS-binding cell-cell/cell-matrix adhesion molecule.
