ABSTRACT
The epithelial to mesenchymal transition (EMT) consists of a rapid change of cell phenotype, characterized by the loss of epithelial characteristics and the acquisition of a more invasive phenotype. Transcription factors regulating EMT (Snail, Twist and Zeb) are extremely labile proteins, rapidly degraded by the proteasome system. In this review we analyze the current mechanisms controlling degradation of EMT transcription factors, focusing on the role of new E3 ubiquitin-ligases involved in EMT. We also summarize the regulation of the stability of these EMT transcription factors, specially observed in different stress conditions, such as hypoxia, chemotherapeutic drugs, oxidative stress or γ-irradiation.
Subject(s)
Epithelial-Mesenchymal Transition , Transcription Factors/metabolism , Ubiquitin-Protein Ligases/metabolism , Animals , Basic Helix-Loop-Helix Transcription Factors/metabolism , Cell Line, Tumor , Homeodomain Proteins/metabolism , Humans , Mice , Phenotype , Protein Stability , Signal Transduction , Snail Family Transcription Factors , Stress, PhysiologicalABSTRACT
Snail1 is a transcriptional factor essential for triggering epithelial-to-mesenchymal transition. Moreover, Snail1 promotes resistance to apoptosis, an effect associated to PTEN gene repression and Akt stimulation. In this article we demonstrate that Snail1 activates Akt at an additional level, as it directly binds to and activates this protein kinase. The interaction is observed in the nucleus and increases the intrinsic Akt activity. We determined that Akt2 is the isoform interacting with Snail1, an association that requires the pleckstrin homology domain in Akt2 and the C-terminal half in Snail1. Snail1 enhances the binding of Akt2 to the E-cadherin (CDH1) promoter and Akt2 interference prevents Snail1 repression of CDH1 gene. We also show that Snail1 binding increases Akt2 intrinsic activity on histone H3 and have identified Thr45 as a residue modified on this protein. Phosphorylation of Thr45 in histone H3 is sensitive to Snail1 and Akt2 cellular levels; moreover, Snail1 upregulates the binding of phosphoThr45 histone H3 to the CDH1 promoter. These results uncover an unexpected role of Akt2 in transcriptional control and point out to phosphorylation of Thr45 in histone H3 as a new epigenetic mark related to Snail1 and Akt2 action.
