Ultrastructural localization and internalization of proteoglycan epitopes in a human non-Hodgkin (B) lymphoma

In a human non-Hodgkin (B) lymphoma xenograft (HT-117) heparan sulphate (HS) proved to be the main cell surface glycosaminoglycan, in contrast to the chondroitin sulphate dominance in normal lymphoid cells. Using anti-proteoglycan (PG) antibodies and immunoelectronmicroscopy, two heparan sulphate proteoglycans (transferrin receptor (TfR) and fibroblast membrane type) and one chondroitin sulphate proteoglycan (articular cartilage type) molecule were co-localized as random clusters on the surface of these lymphoma cells. Double labelling revealed that during internalization, which occurred via endosomes avoiding the lysosomal system, the different proteoglycan (PG) antigens became separated. The TfR and fibroblast membrane type HSPG epitopes reappeared on plasmalemmal vesicles derived most probably from the multivesicular endosomes, representing a unique form of exocytosis. It is suggested that different cell membrane PGs are integrated into subunits of yet unknown function in these human non-Hodgkin (B) lymphoma cells.