Different thresholds of ZEB1 are required for Ras-mediated tumour initiation and metastasis.

Ras pathway mutation is frequent in carcinomas where it induces expression of the transcriptional repressor ZEB1. Although ZEB1 is classically linked to epithelial-mesenchymal transition and tumour metastasis, it has an emerging second role in generation of cancer-initiating cells. Here we show that Ras induction of ZEB1 is required for tumour initiation in a lung cancer model, and we link this function to repression Pten, whose loss is critical for emergence of cancer-initiating cells. These two roles for ZEB1 in tumour progression can be distinguished by their requirement for different levels of ZEB1. A lower threshold of ZEB1 is sufficient for cancer initiation, whereas further induction is necessary for tumour metastasis.