Uptake of Proteoglycans and Sulfated Glycosaminoglycans by Cultured Skin Fibroblasts

Pinocytosis and degradation of [ 35 S]proteoglycans [ 35 S]glycosaminoglycan chains were studied in cultured skin fibroblasts. Proteoglycans were obtained from fibroblast secretions, glycosaminoglycan chains either by β ‐elimination of proteoglycans or from secretions of fibroblasts grown in the presence of d ‐xylose or P ‐nitrophenyl‐ β ‐ d ‐xyloside, respectively. The following results were obtained. The uptake of proteoglycans as well as of glycosaminoglycan chains is dose‐dependent and follows saturation kinetics. The maximal rate of pinocytosis og glycosaminoglycan chains induced by xylose and P ‐nitrophenyl‐β‐ d ‐xyloside is only about 25% of that of proteoglycans as determined on the basis of the sulfate content. On a molar basis the maximal uptake rate for proteoglycans is 10‐fold lower than for free glycosaminoglycan chains, but proteoglycans have a higher affinity than chains for the proposed receptors. Uptake is followed by degradation. Its relative proportion is inversely related to the amount of endocytosed material. Unlabeled proteoglycans compete for the uptake of [ 35 S]proteoglycans, but protein‐free proteoglycan chains are inefficient competitors at the doses used. In case of [ 35 S]glycosaminoglycans induced by xylose and P ‐nitrophenyl‐β‐ d ‐xyloside, competition for uptake occurs by the addition of unlabeled glycosaminoglycan chains and of hybrid chondroitin‐sulfate‐dermatan‐sulfate decasaccharides, but not by the addition of smaller saccharide fragments.