MULTIPLE HEPARAN-SULFATE CHAINS ARE REQUIRED FOR OPTIMAL SYNDECAN-1 FUNCTION

Syndecans have three highly conserved sites available for heparan sulf ate attachment. To determine if all three sites are required for norma l function, a series of mutated syndecans having two, one, or no hepar an sulfate chains were expressed in ARH-77 cells. Previously, we demon strated that expression of wild-type syndecan-1 on these myeloma cells mediates cell-matrix and cell-cell adhesion and inhibits cell invasio n into collagen gels. Here we show that to optimally mediate each of t hese activities, all three sites of heparan sulfate attachment are req uired. Generally, an increasing loss of syndecan-1 function occurs as the number of heparan sulfate attachment sites decreases. This loss of function is Plot the result of a decrease in either the total amount of cell surface heparan sulfate or syndecan-1 core protein. In regard to cell invasion, cells expressing syndecan-1 bearing a single heparan sulfate attachment site exhibit a hierarchy of function based upon th e position of the site within the core protein; the presence of an ava ilable attachment site at serine 47 confers the greatest level of acti vity, while serine 37 contributes little to syndecan-1 function. Howev er, when all three heparan sulfate chains are present, significantly g reater biological activity is observed than is predicted by the sum of the activities occurring when the chains act individually, This syner gy provides a functional basis for the evolutionary conservation of th e three heparan sulfate attachment sites on syndecans and supports the idea that molecular heterogeneity, which is characteristic of proteog lycans, contributes to their functional diversity.