MOLECULAR APPROACH TO THE NUCLEO-MELANOSOMAL INTERACTION IN HUMAN-MELANOMA CELLS

This paper presents evidence that L-tyrosine oxidation products and 5, 6-dihydroxyindole, an intermediate of melanin synthesis bind to and mo dify DNA structure, as tested by extracting cell DNA, using topoisomer ase I and denaturation assays. When supercoiled plasmid pCU18 or pBR32 2 DNAs are treated with 5,6-dihydroxyindole the supercoiled species di sappear and are converted to species less mobile in a gel retardation test with respect to relaxed DNA. 5,6-Dihydroxyindole causes an easier acid denaturation of the double helix. The results, that are dose dep endent,would point to both intercalation and cross-linking of DNA by 5 ,6-dihydroxyindole and its oxidation product(s). H-3-L-tyrosine derivi ng radioactivity, bound to nuclear DNA, is higher at low pH, (5.6) if compared to pH 6.8. The highest radioactivity bound to cell DNA is fou nd during the transition from the amelanotic to the melanotic phenotyp e in human melanoma cell lines. As a control, the binding of 3H-L-tyro sine radioactivity to human prostate fibroblast DNA was investigated.