Detection in human melanoma cell lines of particles with some properties in common with RNA tumour viruses

Abstract

Abstract Six established lines of malignant melanoma cells produced particles having a buoyant density of 1.14 to 1.18 g/ml and containing RNA with a component of approximately 70S. Fractions containing these particles showed RNase‐sensitive DNA polymerase activity, and in simultaneous assays the DNA product was found to be associated with 70S RNA. Similar results were obtained in control studies with two known oncornaviruses (Rauscher and WM1‐B mouse leukaemia viruses), but not with particles from three normal human fibroblast strains. Filtration studies showed that the uridine‐labelled particles from four melanoma cell lines, as well as the materials from two melanoma lines active in the simultaneous assay, were largely retained by filters with an average pore diameter of 100–650 nm. In negative‐stained preparations of 1.14 to 1.18g/ml fractions from four melanoma lines, a small number of virus‐like particles about 125 nm in diameter were detected, as well as smaller amorphous material and minute ring‐like structures about 12–14 nm in diameter. The evidence strongly suggests the production by these cultured malignant melanoma cells of particles with properties closely resembling those of oncornaviruses. Although evidence was found of similar virus‐like particles in a malignant melanoma biopsy, their role in the aetiology of malignant melanoma remains unknown.