Metastatic breast tumor cells display an epithelial–mesenchymal transition (EMT) that increases cell motility, invasion, and dissemination. Although the transcription factor Twist1 has been shown to contribute to EMT and cancer metastasis, the signaling pathways regulating Twist1 activity are poorly understood. Here, we show that Twist1 is ubiquitously phosphorylated in 90% of 1,532 invasive...