PIK3CA and malignant colon neoplasm: To further determine whether the difference in colon cancer cell sensitivity to MEK inhibitors is a result of decreased β-catenin expression, we first examined the effect of β-catenin overexpression on MEK inhibitor-treated colon cancer cells that express wild-type PIK3CA. Briefly, a pcDNA3.1 plasmid containing wild-type β-catenin cDNA with an HA tag was constructed.