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Somatic mutation and gain of copy number of PIK3CA in human breast cancer

DOI: 10.1186/bcr1262

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Abstract:

Fifteen breast cancer cell lines and 92 primary breast tumors (33 with matched normal tissue) were used to check somatic mutation and gene copy number of PIK3CA. For the somatic mutation study, we specifically checked exons 1, 9, and 20, which have been reported to be hot spots in colon cancer. For the analysis of the gene copy number, we used quantitative real-time PCR and fluorescence in situ hybridization. We also treated several breast cancer cells with the PIK3CA inhibitor LY294002 and compared the apoptosis status in cells with and without PIK3CA mutation.We identified a 20.6% (19 of 92) and 33.3% (5 of 15) PIK3CA somatic mutation frequency in primary breast tumors and cell lines, respectively. We also found that 8.7% (8 of 92) of the tumors harbored a gain of PIK3CA gene copy number. Only four cases in this study contained both an increase in the gene copy number and a somatic mutation. In addition, mutation of PIK3CA correlated with the status of Akt phosphorylation in some breast cancer cells and inhibition of PIK3CA-induced increased apoptosis in breast cancer cells with PIK3CA mutation.Somatic mutation rather than a gain of gene copy number of PIK3CA is the frequent genetic alteration that contributes to human breast cancer progression. The frequent and clustered mutations within PIK3CA make it an attractive molecular marker for early detection and a promising therapeutic target in breast cancer.Phosphatidylinositol 3-kinases (PI3Ks) are a group of lipid kinases composed of 85-kDa and 110-kDa subunits. The 85-kDa subunit lacks PI3K activity and acts as adaptor, coupling the 110-kDa subunit (P110) to activated protein tyrosine kinases and generating second messengers by phosphorylating membrane inositol lipids at the D3 position. The resulting phosphatidylinositol derivatives then permit activation of downstream effectors that are involved in cell proliferation, survival, metabolism, cytoskeletal reorganization, and membrane trafficking [1,2].PIK3CA, the g

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