Dualistic role of ZEB1 and ZEB2 in tumor progression.

It is generally accepted that ZEB1 and ZEB2 act as master regulators of the epithelial-mesenchymal transition, which arguably is the key mechanism of metastasis. Accordingly, they are deemed as negative predictors of the survival of cancer patients by promoting the emergence of secondary foci of the disease. Paradoxically, in some types of cancer types the opposite effect is observed, i.e. ZEB1 and ZEB2 are associated with better prognosis for cancer patients. In this review, we discuss the hypothesis that the tumorigenic effects of ZEB1/ZEB2 can be different in various tissues depending on the initial status of these proteins in the corresponding healthy tissues. Emerging evidence suggests that ZEB1 and ZEB2 are constitutively expressed in several healthy tissues, performing vital functions. Consequently, reducing the expression of ZEB1 and ZEB2 could negatively affect these tissues causing various diseases, including cancer. Finally, the dualistic role of ZEB1 and ZEB2 as immune modulators and their effect on tumor microenvironment is also discussed.