Glycosylation of tyrosinase is a determinant of melanin production in cultured melanoma cells

Abstract

The majority of malignant melanoma cell types are able to produce melanin and the degree of melanin synthesis in various types of cultured cell line differs. In this study, we evaluated three types of cultured cell line, MNT-1, HM3KO and G-361, with differing melanin production levels. The level was greatest in the MNT-1 cells, lower in the HM3KO cells and lowest in the G-361 cells. In addition, a positive correlation between melanin production and tyrosinase activity was observed. The molecular masses of tyrosinases from HM3KO and G-361 cells were marginally lower than those from MNT-1 cells. Glycosylation inhibitor treatment on MNT-1 cells caused decreases in the molecular mass of tyrosinase, its activity and melanin production. An immunoprecipitation assay using anti-tyrosinase indicated that the immature glycosylated tyrosinases were associated with a type of chaperone, Hsp70. The interaction between tyrosinase and Hsp70 was also detected in HM3KO and G-361 cells. The results indicated that the immature glycosylation of tyrosinase has a critical effect on the melanin-producing ability of melanoma cells.