Release of surface macromolecules by human melanoma and normal cells

Viable human melanoma cells are known to rapidly release cell surface macromolecules and tumor-associated antigens. To study whether this is a phenomenon related to malignant transformation, the release of surface macromolecules by human and murine melanoma cells was compared to that by normal allogeneic cells. Following lactoperoxidase radioiodination of cell surfaces, it was found that the proportion of labeled macromolecules released by human melanoma cells in 3 hr (60.0 +/- 9.9% (S.D.)] did not differ significantly from that released in the same time by normal allogeneic keratinocytes (56.0 +/- 10.0%) or fibroblasts (42.1 +/- 11.1%). Likewise in mice, the release of labeled surface macromolecules by B16 melanoma cells (36% in 3 hr) was no faster than that by normal syngeneic fibroblasts (56% in 3 hr). Control experiments excluded the possibilities that release was the result of cell death or of artifacts of the radioiodination procedure or that it represented release of fetal calf serum proteins adhering to the cells. These results suggest that rapid release of membrane macromolecules is not an expression of malignant transformation but rather a normal process which involves a major portion of macromolecules on the external surface of melanoma and normal cells and which occurs at a similar rate in both instances.