Tyrosinase Degradation in Amelanotic Melanoma Cells is Mediated by Cytoplasmic Factors in Addition to Proteasome-Mediated Mechanism

Abstract

Tyrosinase, the rate-limiting enzyme of melanin synthesis pathway is under tight metabolic regulation. In this report, results on the pattern and rate of degradation of tyrosinase in amelanotic and melanotic B16 melanoma cells, the spontaneously formed two phenotypes of the same cell line, are presented. The results indicate that tyrosinase in amelanotic melanoma cells undergoes an increased ubiquitination and a proteasome-dependent rapid degradation as compared to that in melanotic melanoma cells. Further, the tyrosinase that is subjected to degradation is a mature Golgi form. The data also suggest that cytoplasmic factor(s) are involved in accelerated degradation of tyrosinase in amelanotic melanoma cells. In conclusion, the involvement of a post-Golgi mechanism of tyrosinase degradation particularly by hitherto unknown cytoplasmic factor(s) is the novelty of the present study.