Isolation and properties of amelanotic variants of a hamster melanoma

Abstract

Stable amelanotic variants, isolated from a line of pigmented Syrian hamster melanoma cells, show a constant association of (1) dopa oxidase deficiency, (2) flattened epithelial or fibroblast morphology, (3) anchorage dependence, and (4) a long latent period in tumor formation, each of these properties distinguishing them from the dopa-oxidase-positive, anchorage-independent, highly malignant pigmented cells of origin. One of the variants is shown to have the properties of a pleiotropic conditional “mutant” since its cells show the simultaneous but transitory restoration of pigmentation and melanoma-like morphology when cloned at alkaline pH. Cells of this variant have been hybridized with pigmented cells, derived both from the line of origin and from a mouse melanoma. Hybrids from the first cross show all of the properties characteristic of the pigmented parental cells, but produce segregants reexpressing the ensemble of properties of the amelanotic variant, while those of the second cross show extinction (followed by reexpression) of pigmentation. It is therefore concluded that cells of the amelanotic variant produce a factor capable of extinguishing dopa oxidase activity, as revealed directly by the properties of the hamster-mouse hybrids and indirectly by the amelanotic segregants of the hamster-hamster hybrids.