Phosphorylation of β-catenin at serine 663 regulates its transcriptional activity

► Active PAK1(T423E) but not inactive PAK1(K299R) interacted with and phosphorylated β-catenin. ► PAK1 phosphorylated β-catenin at serine 663 (S663) in addition to S675. ► S663 phosphorylation is observed in colon cancer cell lines which show a higher PAK1 activity. ► S663 phosphorylation was important in regulation of the transcriptional activity of β-catenin.