PIK3CA hypomethylation plays a key role in activation of the PI3K/AKT pathway in esophageal cancer in Chinese patients

Aim: To investigate the role of PIK3CA oncogene in tumorigenesis and development of esophageal cancer in Chinese patients at the levels of genetic mutation and epigenetics. Methods: Seventy six esophageal tumor samples and corresponding adjacent normal tissues were collected, and the genomic DNA was extracted. Mutations in the 9th and 20th exons of PIK3CA gene were detected using conventional sequencing. PIK3CA methylation rates in two selected CpG islands (CpG island 1 and 2) were detected using sub-bisulfate modified sequencing. P110 alpha and pAKT expression levels were detected with Western blotting. Results: In PIK3CA gene of the tumor tissues, G1633C (E545Q) mutation was detected in the 9th exon with a rate of 3.95% (3/76), whereas mutation was not found in the 20th exon. Nor mutation did occur in PIK3CA gene of the adjacent normal tissues. The methylation rate of the CpG island 1 had no significant difference between the tumor and adjacent tissues (0.77%+/-0.009% vs 0.89%+/-0.008%), but the methylation rate of the CpG island 2 in the esophageal tumors was significantly lower than that in the adjacent tissues (6.00%+/-2.80% vs 10.45%+/-5.51%). Furthermore, the rate of methylation of the CpG island 2 in TNM stage III and IV esophageal cancer (3.84%+/-2.08%) was significantly lower than in stage I (8.52%+/-2.55%) and stage II (6.42%+/-2.36%). PIK3CA gene hypomethylation in esophageal cancer was significantly correlated with high expression of p110 alpha. Conclusion: PIK3CA gene hypomethylation plays a key role in the tumorigenesis and development of esophageal cancer in Chinese patients, while the mutations of PIK3CA gene have little effect on the development of esophageal cancer.