Tyrosinase transfection produces melanin synthesis and growth retardation in glioma cells

Tyrosinase is the key enzyme in melanin biosynthesis in pigmented cells. We transfected 9L rat glioma cells with human tyrosinase cDNA that had been c loned in a high expression vector. Stable transfectants were selected by th eir resistance to the antibiotic G418, More than a dozen G418-resistant clo nes were isolated and were screened for tyrosinase expression using dopa-ox idase activity. The clone with the highest tyrosinase activity was selected and expanded for further studies. Northern blot analyses of total RNA from cells showed that the transfected cells had relatively more tyrosinase tra nscript than SK-MEL-23 human melanotic melanoma cells. The melanin content of the transfected cells was dependent on the concentration of L-tyrosine i n the culture medium. In addition, the growth of transfected cells was inhi bited when grown in a medium containing high concentrations of L-tyrosine. These results suggest that tyrosinase activity is cytotoxic in a substrate- dependent manner. This may have far reaching therapeutic use for glioma tum ours. (C) 1998 Lippincott Williams & Wilkins.