NORMAL TYROSINE TRANSPORT AND ABNORMAL TYROSINASE ROUTING IN PINK-EYED DILUTION MELANOCYTES

The pink-eyed dilution phenotype in mice arises from mutations in the p gene; in humans, analogous mutations in the P gene result in oculocu taneous albinism type 2, Although the molecular mechanisms which under lie this phenotype remain obscure, it has been postulated that mutatio ns in p result in defective tyrosine transport into murine melanosomes , resulting in hypopigmentation and diminished coat color. However, we previously reported no difference in melanosomal tyrosine transport i n unpigmented, melanoblast-like pink-eyed dilution (p(cp)/p(cp)), and in pigmented (melan-a) murine melanocytes. In this study, we utilized melan-p1 cells, more differentiated pink-eyed dilution (p(cp)/p(25H)) melanocytes which can be induced to produce melanin, to characterize t he melanogenic lesion(s) more definitively. Uptake of [H-3]tyrosine in to melan-a melanosomes did not differ significantly from uptake into m elanosomes derived from melan-p1 melanocytes, further arguing against its critical role as a tyrosine transporter. Pink-eyed dilution melano cytes incubated in high tyrosine concentrations became extremely pigme nted as they became confluent and secreted large amounts of black mate rial into the medium. Total cellular tyrosinase activity in melan-p1 m elanocytes was significantly higher than that in melan-a melanocytes ( which are wild-type at the p locus), but the localization of tyrosinas e to melanosomes was impaired in melan-p1 melanocytes compared to mela n-a melanocytes. These results indicate that mechanisms other than def icient tyrosine transport are involved in the pink-eyed dilution pheno type and that this protein may serve a chaperone-like or stabilizing f unction in melanocytes. (C) 1998 Academic Press.