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Mechanism of autodegradation of cell-surface macromolecules shed by human melanoma cells
Abstract:
The mechanism of autodegradation of cell-surface macromolecules shed by human melanoma cells was studied by incubating radio-iodinated shed macromolecules with unlabeled sister cells and measuring the appearance of acid-soluble radioactivity. After a preliminary latent period of 1-3 h, degradation continually increased up to 24 h and was concentration-dependent. By contrast, binding to cells was very rapid reaching half-maximal value within 15 min. Autodegradation was markedly reduced (44-82%) by pharmacological agents which interfere with endocytosis or lysosomal enzyme activity, including drugs which inhibit receptor migration into coated pits (dansylcadaverine), endocytosis and intracellular transport (colchicine, cytochalasin B, and monensin), and the activity of lysosomal enzymes (chloroquine, ammonium chloride, leupeptin). Degradation was almost totally suppressed (95%) at 4 degrees C. These data suggest that surface macromolecules shed by melanoma cells are autodegraded in part by re-uptake into melanoma cells followed by degradation in lysosomes.
Insights
Human melanoma cells can degrade their own shed macromolecules through a process involving cellular re-uptake and lysosomal breakdown. This study investigates the mechanism of melanoma cell autodegradation.
Area of Science:
- Cell Biology
- Biochemistry
- Oncology
Background:
- Melanoma cells shed macromolecules into their environment.
- The fate and degradation mechanisms of these shed molecules are not fully understood.
Purpose of the Study:
- To investigate the mechanism of autodegradation of cell-surface macromolecules shed by human melanoma cells.
- To determine the role of cellular uptake and lysosomal pathways in this process.
Main Methods:
- Radio-iodinated shed melanoma macromolecules were incubated with unlabeled sister cells.
- Appearance of acid-soluble radioactivity was measured to quantify degradation.
- Pharmacological agents affecting endocytosis and lysosomal activity were used to probe the mechanism.
- Experiments were conducted at different temperatures (4°C vs. 37°C).
Main Results:
- Autodegradation showed a latent period (1-3 h) followed by increased degradation up to 24 h.
- Degradation was concentration-dependent and binding to cells was rapid (half-maximal at 15 min).
- Pharmacological agents inhibiting endocytosis (dansylcadaverine, colchicine, cytochalasin B, monensin) and lysosomal activity (chloroquine, ammonium chloride, leupeptin) significantly reduced degradation (44-82%).
- Degradation was almost completely suppressed at 4°C (95%).
Conclusions:
- Melanoma cell-surface macromolecules are subject to autodegradation.
- This process involves re-uptake of shed molecules by melanoma cells.
- Lysosomal pathways are critical for the degradation of these macromolecules.
- The findings suggest a mechanism for recycling or clearing shed cellular components by melanoma cells.