The regulation of tyrosinase-related protein (TRP)-1 and TRP-2 gene expression was studied to
understand the action mechanism of Imoniga ginger on melanogenic inhibition. There was no significant difference
in the expression of TRP-2 by the addition of the extract, but the expression of TRP-1 decreased in the presence of
0.001% and 0.003% extracts ( Figure 13). Furthermore, the expression level of tyrosinase mRNA exhibited dosedependent decrease in the presence of 0.001% and 0.005% Imoniga ginger extract, while no specific effect of the
addition of the extract was observed on glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA expression. Promoter assays were performed by constructing luciferase reporter plasmid, which combined human
tyrosinase promoter region to a vector (Pica Gene Basic Vector2 or PGv-B2). Tyrosinase promoter activity was
significantly decreased by the addition of the extracts. As described above, Imoniga ginger extract had no direct
inhibitory effect on tyrosinase activity, unlike common melanogenesis inhibitors based on tyrosinase inhibitory
action, such as Chinese tamarisk. In addition, it was inferred that the extract had an inhibitory effect related to
the expression or posttranslational modification of tyrosinase from the fact that tyrosinase activity inside the cell
decreased. Furthermore, it was demonstrated to cause the amount of the tyrosinase protein to decrease, resulting
in a decrease in tyrosinase mRNA expression and promoter activity. These results suggested that the action
mechanism of this extract would be a transcriptional suppression of tyrosinase gene. The decrease in TRP-1
suggested that microphthalmia-associated transcription factor (MITF) regulating TRP-1 expression would be
influenced by the extracts. On the other hand, TRP-2 was not affected by the extracts, which would be consistent
with the reported theory that TRP-2, unlike TRP-1, is not involved in the control of the MITF expression.