Binding and degradation of proteoglycans by cultured arterial smooth muscle cells. I. Endocytosis and intracellular translocation of proteoglycan-gold conjugates.

Proteoglycans (Mr approximately 200 000) isolated from bovine arterial tissue were decorated with 17 nm diameter gold particles for tracing in electron microscopic thin sections and surface replicas. Lysine and arginine residues of their proteoglycan protein core are assumed to be essential for gold conjugation. The resulting proteoglycan-gold conjugates, which appear as pearl string-like gold strands of about 170 nm in length were used to visualize binding, endocytosis and intracellular translocation of proteoglycans by homologous cultured arterial smooth muscle cells. The proteoglycan-gold conjugates bind to coated as well as to non-coated cell surface membrane areas at 4 degrees C. This is followed by the formation of membrane invaginations. Postincubation at 37 degrees C leads to a time-dependent uptake of proteoglycan-gold conjugates via non-coated and coated vesicles which after fusion are translocated to multivesicular bodies and to large sized vesicles within 1 h. After conversion of these vesicles to lysosomal compartments the gold particles are uncoupled from the proteoglycans and are concentrated within residual vacuoles. From these vacuoles the gold particles are extruded. In contrast to the surface-bound proteoglycan-gold conjugates the released gold particles are condensed to bulky aggregates. The results, which include competition, inhibition and pulse chase experiments, extend biochemical data on endocytosis and degradation of proteoglycans.