title: Endocytosis of proteoheparan sulfate by cultured skin fibroblasts.
abstract: Endocytosis by cultured human skin fibroblasts of 35SO4(2-)-labeled proteoheparan sulfate from fibroblast secretions was quantitatively investigated. At a constant dose of proteoheparan sulfate, uptake and subsequent intracellular degradation but not binding to the cell membrane increased with time. Compared with the endocytosis of total secreted proteoglycans containing predominantly a small proteodermatan sulfate, uptake of proteoheparan sulfate was 5- to 20-fold lower. Nevertheless, uptake of the latter proteoglycan was saturable. Maximally, about 6 nmol of disaccharide units could be internalized per h and mg cell protein. For half-maximal uptake 170 microM concentration of disaccharide units was required. Free heparan sulfate chains were competitive inhibitors of the endocytosis of proteoheparan sulfate, the Ki being 75 microM with respect to disaccharide units. 35SO4(2-)-Labeled heparan sulfate chains prepared from the proteoglycan by a beta-elimination reaction were endocytosed with similar kinetics. However, the maximal rate of endocytosis of free chains as well as the concentration required for half-maximal uptake were both about half as low as in case of proteoheparan sulfate. These results suggest that the recognition marker for receptor-mediated endocytosis of proteoheparan sulfate resides in its glycosaminoglycan moiety. The proteoglycan used for uptake studies exhibited considerable molecular diversity due to a varying number of bound heparan sulfate chains. However, all proteoheparan sulfate species contained predominantly a core protein of Mr = 30 000 and a minor one with an Mr = 17 000.
mesh_terms: D002478:Cells, Cultured; D011508:Chondroitin Sulfate Proteoglycans / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004705:Endocytosis; D005347:Fibroblasts / Q000378:metabolism; D006025:Glycosaminoglycans / Q000378:metabolism*; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate / Q000378:metabolism*; D006801:Humans; D008970:Molecular Weight; D011509:Proteoglycans / Q000378:metabolism*; D012867:Skin / Q000166:cytology* / Q000378:metabolism; D013997:Time Factors
chemical_list: D011508:Chondroitin Sulfate Proteoglycans; D006025:Glycosaminoglycans; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate; D011509:Proteoglycans