Hirofumi Kondoh

Mouse Fibroblast Expressing Human Tyrosinase with DHICA-Oxidase Activity Produces Predominantly Pheomelanin Deposit in Lysosome

Abstract The melanogenic gene-transfected cell system serves as a useful tool for the study of the symphonic relation between melanin synthesis and intracellular organelles such as melanosomes in melanocytes. We constructed melanin-producing mouse fibroblasts by transfection of human tyrosinase cDNA to investigate the intracellular changes caused by tyrosinase expression. DHICA-oxidase (5,6-dihydroxyindole-2-carboxylic acid oxidase) activity without TRP-1 (Tyrosinase Related Protein-1) expression in the cells suggested that human tyrosinase also possesses a DHICA-oxidase activities different from mouse tyrosinase, Electron microscopic observation indicated that melanin-deposit organelles have some lysosomal features. These properties of melanin-deposit organelles in tyrosinase expressing fibroblasts provide one evidence for the hypothesis that melanosome is the specialized lysosome in melanocytes.

Current Clinical Paradigms in Melanoma BNCT

At the last ISNCT meeting in Zurich (September, 1996), we presented our new findings on melanogenic gene transfer, converting fibroblasts to actively melanin synthesizing cells, and proposed applying this gene transfer to BNCT, called gBNCT, as a way of attacking a wider range of cancers.1