Autocatabolism of surface macromolecules shed by human melanoma cells.

The fate of cell surface macromolecules released by human melanoma cells in vitro was studied. Labeled surface macromolecules released by lactoperoxidase-radioiodinated melanoma cells were incubated cells. It was found that some of these macromolecules were autocatabolized to acid-soluble fragments by the cells which had released them. Degradation did not occur in the absence of cells, was almost completely inhibited at 4 degrees, and was partially suppressed by cytochalasin B (10 micrograms/ml) and by some inhibitors of energy production, i.e., iodoacetamide (10(-4) M) and a combination of 2-deoxyglucose (18 mg/ml) and 2,4-dinitrophenol (10(-4) M). Radioiodinated surface macromolecules were degraded much more rapidly than radioiodinated serum proteins. Thus, degradation required the presence of cells, was in part an active process, and was selective. These results suggest that one of the pathways for the turnover of surface macromolecules on tumor cells is shedding followed by autocatabolism of the shed material by the cells which they have released.