TRANSGLUTAMINASE-MEDIATED PROCESSING OF FIBRONECTIN BY ENDOTHELIAL-CELL MONOLAYERS

We studied the interaction of [I-125]fibronectin with human umbilical vein endothelial cells. Endothelial cell monolayers cross-linked [I-12 5]fibronectin which had been preadsorbed to gelatin-coated dishes. The cross-linking of the substrate-immobilized [I-125]fibronectin was med iated by cell-associated tissue transglutaminase and occurred more rap idly during the first 30 min after endothelial cell seeding but also c ontinued for several hours after the cells were fully spread. The proc essing of the [I-125]fibronectin was associated with the basolateral s urface of the endothelial cell, as demonstrated by the finding that cr oss-linking did not occur when [I-125] fibronectin was presented to th e apical surface of confluent monolayers. Transglutaminase activity wa s not necessary for attachment and spreading of HUVEC on a fibronectin /gelatin matrix. The presence of a nonpeptidyl transglutaminase inacti vator rendered the cells more susceptible to detachment by trypsin and destabilized the association of fibronectin with the subendothelial e xtracellular matrix. Thus, endothelial cells process fibronectin into cross-linked multimers due to the expression of tissue transglutaminas e at the basal surface of the cell. This process may serve to stabiliz e the extracellular matrix and to firmly anchor the cells to the basem ent membrane.