A single nucleotide polymorphism in the human PIGK gene associates with low PIGK expression in colorectal cancer patients

Colorectal cancer (CRC) represents one of the highest incidences of cancers worldwide. Phosphatidylinositol glycan, class K (PIGK), is a crucial member of the glycosyl-phosphatidylinositol transamidase (GPIT) protein complex that attaches a diverse group of macromolecules to the plasma membrane of eukaryotes. However, the precise role of PIGK in tumorigenesis remains largely unknown. Recently, we reported low expression of PIGK protein in primary tumors compared to paired normal tissues of colorectal cancer (CRC) patients. To understand the mechanism underlying this phenomenon, we performed sequencing of all 10 exons of the PIGK gene in 45 CRC patients. Corresponding PIGK protein expression was also evaluated in these patients by immunohistochemistry. No mutation was detected in the coding regions, however, we found a single nucleotide polymorphism (C/C→C/G or G/G; rs1048575) in the 3'UTR of the PIGK gene in 67% (30/45) of the patients. Most of the patients (22/26, 85%) with the altered alleles were of Jewish origin. In comparison, 47% (8/17) of the Arabian patients exhibited the altered C/G alleles. We observed a significantly low (p