Development of a novel PIG-A gene mutation assay based on a GPI-anchored fluorescent protein sensor

Accumulation of somatic mutations caused by both endogenous and exogenous exposures is a high risk for human health, in particular, cancer. Efficient detection of somatic mutations is crucial for risk assessment of different types of exposures. Due to its requirement in the process of attaching glycosylphatidylinositol- (GPI-) anchored proteins to the cell surface, the PIG-A gene located on the X-chromosome is used in both in vivo and in vitro mutation assays. Loss-of-function mutations in PIG-A lead to the elimination of GPI-anchored proteins such that they can no longer be detected on the cell surface by antibodies. Historically, mutation assays based on the PIG-A gene rely on the staining of these cell-surface proteins by antibodies; however, as with any antibody-based assay, there are major limitations, especially in terms of variability and lack of specific antibodies.

In the current study, we developed a modified PIG-A mutation assay that uses the expression of GPI-anchored fluorescent proteins (henceforth referred to as a GPI-sensor), whereby the presence of fluorescence on the cell membrane is dependent on the expression of wild-type PIG-A. Using our modified PIG-A mutation assay, we have achieved complete separation of wild type cells and spontaneously mutated cells, in which the presence of PIG-A mutations has been confirmed via proaerolysin resistance and gene sequencing.

This study establishes a novel PIG-A mutation assay using GPI-anchored fluorescent protein expression that eliminates the need for antibody-based staining. This GPI-sensor PIG-A mutation assay should be widely applicable for accurate and efficient testing of genotoxicity for use in many mammalian and vertebrate cells.