Abstract
Glycosylphosphatidylinositol (GPI) acts as a membrane anchor and a post-translational modifier for more than 150 proteins (called GPI-anchored proteins: GPI-APs). However, little study has been done to explore the role of GPI-APs in melanocytes. In this report, we examined the expression of the genes, which play essential roles in GPI synthesis and GPI anchoring, in 13 different normal human epidermal melanocytes (NHEMs) derived from light to dark skin, for which the tyrosinase (TYR) activity had already been investigated. Then, we clarified that the mRNA expressions of phosphatidylinositol glycan, class K gene (PIGK) were significantly in inverse correlation with TYR activities in NHEMs. In addition, a microsatellite polymorphism located in the predicted promoter region of PIGK was strongly correlated with PIGK mRNA expression in NHEMs. We failed to demonstrate direct interaction between the expression of PIGK and TYR by transient knockdown of PIGK in NHEMs. Also, there was no correlation between the presence of the microsatellite polymorphism and variations in the melanin index of 105 Japanese females. However, our data indicated that inadequate protein-GPI anchoring caused by suppression of PIGK might affect the expression or function of some GPI-APs associated with tyrosinase activity.
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