Ndfip 1 regulates nuclear Pten import in vivo to promote neuronal survival following cerebral ischemia

PTEN (phosphatase and tensin homologue deleted on chromosome TEN) is the major negative regulator of signaling by phosphatidylinositol 3-kinase (PI 3-K), thereby playing a central role in controlling many important cellular activities regulated by this pathway, including cell division, cell growth, cell survival, and DNA damage (Chalhoub and Baker, 2009). PTEN exerts its negative effect through its phosphatase activity on the plasma membrane lipid phosphatidylinositol 3,4,5-triphosphate (PIP3), reducing levels of phosphorylated Akt (pAkt; Maehama and Dixon, 1998; Stambolic et al., 1998). Thus, loss of PTEN, as demonstrated by genetic inactivation in human cancer or mouse knockout (KO) models, causes constitutive activation of Akt in cells, resulting in dysregulated cell proliferation, growth, and survival, which are hallmarks of tumorigenesis (Hobert and Eng, 2009; Nardella et al., 2010). PTEN can be found in both the cytoplasm and nucleus of many cell and tissue types, and its aberrant localization has been implicated in disease. The nucleocytoplasmic distribution of PTEN has been proposed to affect its tumorsuppressive function both within and outside the PI 3-K pathway (Planchon et al., 2008). However, it has remained unclear what physiological stimulus can drive PTEN into the nucleus and under what in vivo circumstances this can occur. In the brain, PTEN is required for multiple aspects of neuronal function and development, including maintenance of neuron structure, size, synaptic plasticity, and survival (Endersby PTEN (phosphatase and tensin homologue deleted on chromosome TEN) is the major negative regulator of phosphatidylinositol 3-kinase signaling and has cell-specific functions including tumor suppression. Nuclear localization of PTEN is vital for tumor suppression; however, outside of cancer, the molecular and physiological events driving PTEN nuclear entry are unknown. In this paper, we demonstrate that cytoplasmic Pten was translocated into the nuclei of neurons after cerebral ischemia in mice. Critically, this transport event was dependent on a surge in the Nedd4 family–interacting protein 1 (Ndfip1), as neurons in Ndfip1-deficient mice failed to import Pten. Ndfip1 binds to Pten, resulting in enhanced ubiquitination by Nedd4 E3 ubiquitin ligases. In vitro, Ndfip1 overexpression increased the rate of Pten nuclear import detected by photobleaching experiments, whereas Ndfip1/ fibroblasts showed negligible transport rates. In vivo, Ndfip1 mutant mice suffered larger infarct sizes associated with suppressed phosphorylated Akt activation. Our findings provide the first physiological example of when and why transient shuttling of nuclear Pten occurs and how this process is critical for neuron survival. Ndfip1 regulates nuclear Pten import in vivo to promote neuronal survival following cerebral ischemia