Repression of PTEN Phosphatase by Snail1 Transcriptional Factor during Gamma Radiation-Induced Apoptosis

Abstract

The product of the Snail1 gene is a transcriptional repressor required for triggering the epithelial-to-mesenchymal transition. Furthermore, ectopic expression of Snail1 in epithelial cells promotes resistance to apoptosis. In this study, we demonstrate that this resistance to γ radiation-induced apoptosis caused by Snail1 is associated with the inhibition of PTEN phosphatase. In MDCK cells, mRNA levels of the p53 target gene PTEN are induced after γ radiation; the transfection of Snail1 prevents this up-regulation. Decreased mRNA levels of PTEN were also detected in RWP-1 cells after the ectopic expression of this transcriptional factor. Snail1 represses and associates to the PTEN promoter as detected both by the electrophoretic mobility shift assay and chromatin immunoprecipitation experiments performed with either endogenous or ectopic Snail1. The binding of Snail1 to the PTEN promoter increases after γ radiation, correlating with the stabilization of Snail1 protein, and prevents the association of p53 to the PTEN promoter. These results stress the critical role of Snail1 in the control of apoptosis and demonstrate the regulation of PTEN phosphatase by this transcriptional repressor.

ACKNOWLEDGMENTS

We greatly appreciate the advice and help of Gabriel Gil. We also thank Marta Garrido and Álvaro Jansà for technical assistance, Isabel Puig and Lionel Larue for PTEN cDNA, and Lauro Sumoy for his help in the interpretation of the ChIP-on-ChIP experiments.

This study was supported by grants from the Ministerio de Ciencia y Tecnología to A.G.H. (SAF2003-02324 and SAF2006-00339), from the American Cancer Society to S.A.M. (PF-04-245-01-DDC), and from the NIH to T.G. (HD034883). Partial support from Instituto Carlos III (RTICCC and C03710) and from the Generalitat de Catalunya (2005SGR00970) is also appreciated. M.E, N.H., and P.V. are recipients of predoctoral fellowships from the Ministerio de Educación. S.P. was supported by a La Cierva contract.