Three glucuronate-rich dermatan sulfate proteoglycan (DS-PG) subclasses were isolated and previously characterized from bovine aortic endothelial cell cultures (Kinsella, M. G., and Wight, T. N. (1988) J. Biol. Chem. 263, 19222-19231). In the present study, pulse-chase experiments indicate that the DS-PG of highest apparent Mr (approximately 1 x 10(6)), denoted previously as HMW-DS, is a relatively stable component of the endothelial extracellular matrix and is formed at the expense of lower Mr DS-PG species. The formation of HMW-DS is reduced in a dose-dependent manner in the presence of dansylcadaverine, an inhibitor of transglutaminase-catalyzed protein cross-linking, but not when the activity of other cross-linking enzymes such as lysyl oxidase is inhibited. The putative DS-PG precursor to HMW-DS accumulates during inhibition of cross-linking only when lysosomal degradation is also inhibited by ammonium chloride, suggesting that the precursor is degraded rapidly in the absence of cross-linking. HMW-DS is precipitable from endothelial cell monolayer extracts with antibodies against fibronectin, a known transglutaminase substrate. Thus, we conclude that the stability of HMW-DS in the subendothelial matrix in culture depends upon the cross-linking of a low Mr DS-PG precursor to matrical protein(s), including fibronectin, resulting in the formation of a DS-PG subclass of high apparent molecular mass.