Amplification of Chromosome 1q Genes Encoding the Phosphoinositide Signalling Enzymes PI4KB, AKT3, PIP5K1A and PI3KC2B in Breast Cancer

Little is known about the possible oncogenic roles of genes encoding for the phosphatidylinositol 4-kinases, a family of enzymes that regulate an early step in phosphoinositide signalling. To address this issue, the mutational status of all four human phosphatidylinositol 4-kinases genes was analyzed across 852 breast cancer samples using the COSMIC data resource. Point mutations in the phosphatidylinositol 4-kinase genes were uncommon and appeared in less than 1% of the patient samples however, 62% of the tumours had increases in gene copy number for PI4KB which encodes the phosphatidylinositol 4-kinase IIIbeta isozyme. Extending this analysis to subsequent enzymes in the phosphoinositide signalling cascades revealed that the only PIP5K1A, PI3KC2B and AKT3 genes exhibited similar patterns of gene copy number variation. By comparison, gene copy number increases for established oncogenes such as EGFR and HER2/Neu were only evident in 20% of the samples. The PI4KB, PIP5K1A, PI3KC2B and AKT3 genes are related in that they all localize to chromosome 1q which is often structurally and numerically abnormal in breast cancer. These results demonstrate that a gene quartet encoding a potential phosphoinositide signalling pathway is amplified in a subset of breast cancers.