PROCEEDINGS |
Excess deposition of extracellular matrix is associated with multiple diseases like interstitial fibrosis in liver cirrhosis, end stage renal disease and pulmonal fibrosis. The control of matrix assembly is, therefore, an important process. Integrins are pivotal in matrix assembly, with specific integrins governing the deposition of individual matrix components. We now show that the deposition of several matrix components is concurrently controlled through the transmembrane heparan sulfate proteoglycan, syndecan-2. Fibroblasts in culture form a fibrillar matrix containing both laminin and fibronectin. When cells are transfected with cDNA encoding the full length syndecan-2 core protein, this has no effect on matrix formation. In contrast, if cells are transfected with cDNA encoding a truncated syndecan-2 core protein that lacks the C-terminal 14 amino acids, they are incapable of forming an organized extracellular fibrillar array of either laminin or fibronectin. Metabolic labeling studies showed that this is not due to a defect in synthesis or secretion of either component, nor to down-regulation of integrin expression. Cells expressing truncated syndecan-2 also cannot reorganize an exogenous substrate into fibrils, unlike vector-only transfected cells or those overexpressing full length syndecan-2, indicating that the defect occurs at the cell membrane. Syndecan-2 cytoplasmic domain can be phosphorylated by protein kinase C, whose activity is needed for matrix synthesis, and we are investigating how this may control matrix assembly.