Lead inhibits the core protein synthesis of a large heparan sulfate proteoglycan perlecan by proliferating vascular endothelial cells in culture

Abstract

We characterized proteoglycans synthesized by growing cultured bovine aortic endothelial cells after exposure to lead. Lead significantly decreased the incorporation of both [ 3H]glucosamine and [ 35S]sulfate into glycosaminoglycans accumulated in the cell layer and the conditioned medium of the cells in a dose-dependent manner. Proteoglycans metabolically labeled with [ 35S]sulfate in the presence of lead were separated into heparan sulfate proteoglycans (HSPGs) and more highly charged chondroitin/dermatan sulfate proteoglycans by DEAE-Sephacel ion-exchange chromatography. It was found that lead markedly inhibited the synthesis of HSPGs. Sepharose CL-4B molecular sieve gel filtration showed that the marked decrease by lead occurred in the high molecular weight subclass of HSPGs. However, the length of heparan sulfate chains (approximately 50 kDa) was unchanged when analyzed by Sepharose CL-6B chromatography. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis analysis of core proteins showed that lead reduced the accumulation of a high molecular weight (approximately 400 kDa) HSPG core protein in the cell layer and the conditioned medium; the core protein was identified as a perlecan core by Western blot analysis. It is suggested that lead inhibits the synthesis of the perlecan core protein in growing endothelial cells without a change of heparan sulfate chain length. The present data support the hypothesis that inhibition of endothelial cell proliferation by lead may result from a lower response of the cells to endogenous basic fibroblast growth factor whose binding to the receptor is strongly promoted by heparan sulfate chains of perlecan.