HUMAN TYROSINASE-RELATED PROTEIN-1 (TRP-1) DOES NOT FUNCTION AS A DHICA OXIDASE ACTIVITY IN CONTRAST TO MURINE TRP-1

Tyrosinase related protein-1 is a melanocyte specific protein and a me mber of the tyrosinase gene family which also includes tyrosinase and TRP-2 (DOPAchrome tautomerase). In murine melanocytes, TRP-1 functions as a 5,6-dihydroxyindole-2-carboxylic acid [DHICA] oxidase during the biosynthetic conversion of tyrosine to eumelanin and mutations affect ing TRP-1 result in the synthesis of brown rather than black pelage co loration. In this study, we examined the putative DHICA oxidase activi ty of TRP-1 in human melanocytes using several approaches. We first ut ilized a line of cultured melanocytes established from a patient with a form of oculocutaneous albinism completely lacking expression of TRP -1 (OCA3). This line of melanocytes endogenously exhibited the same am ount of DHICA oxidase activity as control melanocytes expressing TRP-1 . In other experiments, cultured human fibroblasts were transfected wi th a cDNA for TRP-1, in either the sense or antisense direction, or wi th the retroviral vector alone. TRP-1 expression was induced in fibrob lasts transfected with the TRP-1 cDNA in the sense direction only. Alt hough TRP-1 was expressed by sense-transfected cells, there was no sig nificant DHICA oxidase activity above controls. These results demonstr ate that human TRP-1 does not use DHICA as a substrate for oxidation.