Use of non-melanocytic HEK293 cells stably expressing human tyrosinase for the screening of anti-melanogenic agents.

Tyrosinase (TYR) from mushrooms has been inappropriately used in the screening assay for hypopigmenting agents even though its biochemical properties are different from those of human TYR. Cell-free extracts of human epidermal melanocyes (HEMs) could be another choice for the assay, but HEMs grow too slowly to get a sufficient amount of cell-free extracts. In the present study, human embryonic kidney (HEK) 293 cells were transfected with a human TYR construct to establish a cell line that grows rapidly and expresses human TYR constitutively. Cell-free extracts of the established cell line, HEK293-TYR, were tentatively used in the screening assays for 11 phenylpropanoids that have chemical structures similar to that of L-tyrosine, the substrate of TYR. Of the 11 compounds, the strongest inhibition of TYR activity was shown by p-coumaric acid (IC50, 3 μM), followed by 3-(4-hydroxyphenyl)propionic acid (50 μM) and 3-(4-hydroxyphenyl)lactic acid (70 μM). The results indicate that p-coumaric acid has an optimal chemical structure for the inhibition of TYR. The effects of these phenylpropanoids on melanin synthesis in HEMs correlated well with their effects on TYR activity in vitro. This study demonstrated that HEK293-TYR cells can be a good source of the human TYR enzymes needed in the screening assay of anti-melanogenic agents.