Microsatellite polymorphism located immediately upstream of the phosphatidylinositol glycan, class K gene (PIGK) affects its expression, which correlates with tyrosinase activity in human melanocytes.

BACKGROUND: 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.

METHODS: The relationship between the mRNA expression of the genes which play essential roles in GPI anchoring system [phosphatidylinositol glycan, class A, and class K gene (PIGA, PIGK)] and melanogenesis-related genes (MITF, TYRP1, TYRP2, and TYR) as well as DOPA oxidase activities were evaluated in 13 different normal human epidermal melanocytes (NHEMs). A short tandem repeat (STR) polymorphism located in the predicted promoter region of PIGK was genotyped in the NHEMs. RNA interference experiment of PIGK was also conducted using one of the NHEMs.

RESULTS: PIGK mRNA expression in NHEMs were strongly in inverse correlation with TYR mRNA and DOPA oxidase activities. NHEMs with the STR polymorphism revealed a low level of PIGK expression. However, a transient knockdown of PIGK in NHEM failed to reveal significant changes in the expression of TYR mRNA and DOPA oxidase activity.

CONCLUSIONS: This report firstly demonstrated that inadequate protein-GPI anchoring caused by suppression of PIGK might affect the expression or function of some GPI-APs associated with tyrosinase activity.