Cell surface-associated and released proteolytic activities of bovine aorta endothelial cells

Inhibition of cell proliferation and protease activity by cartilage factors and heparin

Proliferating rat smooth muscle cells and fibroblasts have membrane-associated protease activity. High concentrations of heparin inhibited membrane-associated protease activity and cell proliferation, while low concentration of heparin promoted smooth muscle cell proliferation. The inhibition of protease activity and proliferation was abolished when heparin was treated with protamine sulfate or when acid treated fetal calf serum was used. Heparin required the presence of an acid labile factor(s) in serum for the inhibition of protease activity and proliferation. Heparin and antithrombin III in the presence of acid-treated fetal calf serum did not inhibit cell proliferation or protease activity. Cartilage factors isolated from bovine nasal cartilage containing trypsin inhibitory activity, but not papain inhibitory activity, inhibited rat smooth muscle and fibroblast proliferation and surface associated protease activity. The cartilage factors did not require acid-labile components in the fetal calf serum for the inhibitory activity. The inhibitory activity due to heparin and cartilage factors was not permanent under our experimental condition. Protein synthesis was not inhibited by heparin or the cartilage factors. In rat smooth muscle cells and fibroblasts, the expression of surface-associated protease activity was related to the proliferative state of the cells. Surface protease activity was only present on proliferating cells. When surface protease activity was inhibited by high concentrations of heparin in the presence of an acid-labile serum component(s) or cartilage factors, cell proliferation was also inhibited.

Hydrolysis of an exogenous 125I-labelled protein by rat yolk sacs. Evidence for intracellular degradation within lysosomes

When added to the serum-free medium in which 17.5-day rat yolk sacs were incubated, formaldehyde-denatured 125I-labelled bovine serum albumin was rapidly degraded. More than 80% of the radiolabelled digestion products appearing in the incubation medium consisted of [125I]iodo-L-tyrosine; larger digestion products were found only in association with the yolk-sac tissue. In the early stages of an incubation, low-molecular-weight digestion products began to appear in the incubation medium only after they could be detected within the tissue, and progressive association of trichloroacetic acid-insoluble radioactivity with the tissue preceded both these events. None of the observed proteolysis could be attributed to proteinases released into the incubation medium. Tissue-associated acid-insoluble radioactivity showed a lysosomal distribution on sub-cellular fractionation, and cell-free homogenates of yolk sacs degraded albumin only at acid pH values. Progressively decreasing the rat of pinosome formation (either by progressively lowering the incubation temperature or by the use of increasing concentrations of the metabolic inhibitor rotenone) caused a corresponding decrease in the rate of degradation of albumin. These findings indicate that, in vitro, formaldehyde-denatured 125I-labelled bovine serum albumin is digested by rat yolk sacs exclusively intracellularly, within lysosomes.

Distribution and movement of anionic cell surface sites in cultured human vascular endothelial cells

Cell surface anionic sites on primary and transformed cultures of human vascular endothelium were studied using cationized ferritin (CF) as an ultrastructural marker. The native distribution of anionic sites on the upper (free) surfaces of cells, fixed in situ with glutaraldehyde, was uniform. Binding of the polycationic ligand, CF, in unfixed cells induced redistribution of anionic sites. Rapid formation of discrete patches of CF particles was followed by reappearance of binding between patches, movement of surface-bound CF into intercellular clefts, and endocytosis, over the next 30 min. Aldehyde-fixed cells, detached from the culture surface, bound CF on both upper and lower surfaces. The distribution and mobility of negatively charged membrane components in vascular endothelium may have relevance for thrombosis, atherogenesis, and vascular permeability.