Tyrosinase Protein Levels Research Articles

Role of Tyrosinase as the Determinant of Pigmentation in Cultured Human Melanocytes

Variations in human pigmentation among different racial groups are due to differences in the production and deposition of melanin in the skin. Although melanin synthesis is known to be controlled by the rate-limiting enzyme tyrosinase, the role of this enzyme as the principal determinant of skin pigmentation is unclear. Results from studies with human melanocyte cultures derived from different racial skin types reveal an excellent correlation between the melanin content of melanocyte cultures and the in situ activity of tyrosinase. Melanocytes derived from black skin have up to 10 times more tyrosinase activity and produce up to 10 times more melanin than melanocytes derived from white skin. However, the higher level of tyrosinase activity in melanocytes derived from black skin is not due to a greater abundance of tyrosinase. Results from immunotitration experiments and Western immunoblots reveal that the number of tyrosinase molecules present in white-skin melanocytes may equal the number found in highly pigmented black skin types. Moreover, approximately equivalent levels of tyrosinase mRNA are present in white and black skin cell strains. In contrast, melanocytes derived from red-haired neonates with low tyrosinase activity contain low numbers of tyrosinase molecules and low levels of tyrosinase mRNA. These results show that tyrosinase activity and melanin production in most light-skinned people is controlled primarily by a post-translational regulation of pre-existing enzyme and not by regulating tyrosinase gene activity. In contrast, melanocytes from red-haired (type I) people have low levels of tyrosinase protein and mRNA, suggesting that transcriptional activity of the tyrosinase gene is suppressed.

L-tyrosine induces tyrosinase expression via a posttranscriptional mechanism

Exposure of hamster amelanotic melanoma cells to L-tyrosine caused a time-dependent increase of tyrosinase protein concentrations, tyrosinase activity and level of cell pigmentation. In contrast, Northern blot analysis using mouse tyrosinase cDNA showed a steady level of tyrosinase mRNA. Thus in hamster melanoma cells the stimulation of intracellular tyrosinase concentration by L-tyrosine is mediated mainly via a posttranscriptional mechanism.

Tyrosinase Expression and Melanogenesis in Melanotic and Amelanotic B16 Mouse Melanoma Cells

Tyrosinase activity, abundance, and mRNA transcription were examined in three sublines of the B16 mouse melanoma. Tyrosinase activity and melanin content were highest in the B16-F1 cells, slightly less in the B16-F10, and markedly lower in the B16-F10-DD cells. No differences in the level of tyrosinase mRNA or protein were found in the three different sublines. Thus, the differences in tyrosinase expression arise from the post-translational modification of the enzyme causing its activation or inhibition.