Control of extracellular matrix assembly by syndecan-2 proteoglycan

Extracellular matrix (ECM) deposition and organization is maintained by tra nsmembrane signaling and integrins play major roles. We now show that a sec ond transmembrane component, syndecan-2 heparan sulfate proteoglycan, is pi votal in matrix assembly. Chinese Hamster Ovary (CHO) cells were stably tra nsfected with full length (S2) or truncated syndecan-2 lacking the C-termin al 14 amino acids of the cytoplasmic domain (S2 Delta S). No differences in the amount of matrix assembly were noted with S2 cells, but those expressi ng S2 Delta S could not assemble laminin or fibronectin into a fibrillar ma trix. The loss of matrix formation was not caused by a failure to synthesiz e or externalize ECM components as determined by metabolic labeling or due to differences in surface expression of alpha(5) or beta(1) integrin. The m atrix assembly defect was at the cell surface, since S2 Delta S cells also lost the ability to rearrange laminin or fibronectin substrates into fibril s and to bind exogenous fibronectin. Transfection of activated alpha(Iib)al pha(L Delta)beta(3) integrin into alpha(5)-deficient CHO B2 cells resulted in reestablishment of the previously lost fibronectin matrix. However, cotr ansfection of this cell line with S2 Delta S could override the presence of activated integrins. These results suggest a regulatory role for syndecan- 2 in matrix assembly, along with previously suggested roles for activated i ntegrins.