Catabolism of heparan sulfate proteoglycans in Drosophila cell lines

We have studied intracellular catabolism of heparan sulfate proteoglycans (HSPGs) in Drosophila cell lines, Kc and S2, by a series of pulse-chase experiments using [(35)S]sulfate as a precursor in metabolic labeling experiments. HSPGs in culture medium and cell layer were separately purified by serial chromatographic procedures using Q-Sepharose and Superose 6 for characterization. Analysis of intact HSPG on Superose 6 chromatography revealed that Kc and S2 cells synthesize one major molecular species with slightly differing in sizes (estimated to be 54kDa in Kc and 78kDa in S2 cells). Analysis of glycosaminoglycans for (35)S-labeled macromolecules showed that the majority of (35)S-labeled macromolecules in Kc and S2 cells are HSPGs ( approximately 60% and approximately 80%, respectively). Results from continuous labeling and 2h pulse labeling-chase experiments revealed that, in both cell lines, the intact HSPGs were degraded in multiple phases; the degradation of HSPG was rapid in the early phase (with half-lives of approximately 6h in Kc and approximately 3h in S2 cells) and slow in the later phase (with half-lives >80h in both Kc and S2 cells). The rapid degradation appeared similar to that observed for glycosylphosphatidylinositol-anchored HSPGs (glypicans) in mammalian cell cultures. While the slow degradation appeared similar to that observed for transmembrane HSPGs (syndecans) in mammalian cell cultures. These experiments suggested that vertebrates and invertebrates shared common mechanisms for intracellular HSPG catabolism.