Id2 Complexes with the SNAG Domain of Snai1 Inhibiting Snai1-Mediated Repression of Integrin β4

The epithelial-mesenchymal transition (EMT) is a fundamental process that underlies development and cancer. Although the EMT involves alterations in the expression of specific integrins that mediate stable adhesion to the basement membrane, such as alpha 6 beta 4, the mechanisms involved are poorly understood. Here, we report that Snai1 inhibits beta 4 transcription by increasing repressive histone modification (trimethylation of histone H3 at K27 [H3K27Me3]). Surprisingly, Snai1 is expressed and localized in the nucleus in epithelial cells, but it does not repress beta 4. We resolved this paradox by discovering that Id2 complexes with the SNAG domain of Snai1 on the beta 4 promoter and constrains the repressive function of Snai1. Disruption of the complex by depleting Id2 resulted in Snai1-mediated beta 4 repression with a concomitant increase in H3K27Me3 modification on the beta 4 promoter. These findings establish a novel function for Id2 in regulating Snai1 that has significant implications for the regulation of epithelial gene expression.