Effect of temperature on endocytosis and degradation of sulphated proteoglycans by cultured skin fibroblasts

Temperature up to 16‡C reduced endocytosis of [³⁵S]-proteoglycans by human skin fibroblasts to less than 15% of that at 37‡C. At temperatures between 20–26‡C endocytosis was more than 50%. At temperatures below 26‡C, the relative rate of degradation of endocytosed [³⁵S]-proteoglycans was several fold less than the rate of endocytosis. Codistribution of endocytosed [³⁵S]-proteoglycans and the lysosomal marker enzyme Β-hexosaminidase upon subcellular fractionation indicated that endocytotic vesicles containing [³⁵S]-proteoglycans had fused with lysosomes at 37‡C and at 16‡C. The prolonged halflives of endocytosed [³⁵S]-proteoglycans at 16–26‡C could not be explained merely by a temperature dependent reduction of catalytic activity of lysosomal enzymes participating in the degradation of sulphated proteoglycans.