Regulation of Nur77 nuclear export by c-Jun N-terminal kinase and Akt.
Proapoptotic nuclear receptor family member Nur77 translocates from the nucleus to the mitochondria, where it interacts with Bcl-2 to trigger apoptosis. Nur77 translocation is induced by certain apoptotic stimuli, including the synthetic retinoid-related 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalenecarboxylic acid (AHPN)/CD437 class. In this study, we investigated the molecular mechanism by which AHPN/CD437 analog (E)-4-[3-(1-adamantyl)-4-hydroxyphenyl]-3-chlorocinnamic acid (3-Cl-AHPC) induces Nur77 nuclear export. Our results demonstrate that 3-Cl-AHPC effectively activated Jun N-terminal kinase (JNK), which phosphorylates Nur77. Inhibition of JNK activation by a JNK inhibitor suppressed 3-Cl-AHPC-induced Nur77 nuclear export and apoptosis. In addition, several JNK upstream activators, including the phorbol ester TPA, anisomycin and MAPK kinase kinase-1 (MEKK1), phosphorylated Nur77 and induced its nuclear export. However, Nur77 phosphorylation by JNK, although essential, was not sufficient for inducing Nur77 nuclear export. Induction of Nur77 nuclear export by MEKK1 required a prolonged MEKK1 activation and was attenuated by Akt activation. Expression of constitutively active Akt prevented MEKK1-induced Nur77 nuclear export. Conversely, transfection of dominant-negative Akt or treatment with a phosphatidylinositol 3-kinase (PI3-K) inhibitor accelerated MEKK1-induced Nur77 nuclear export. Furthermore, mutation of an Akt phosphorylation residue Ser351 in Nur77 abolished the effect of Akt or the PI3-K inhibitor. Together, our results demonstrate that both activation of JNK and inhibition of Akt play a role in translocation of Nur77 from the nucleus to the cytoplasm.
Pubmed ID: 16434970 RIS Download
Adamantane | Anisomycin | Apoptosis | Cell Line, Tumor | Cell Nucleus | Cinnamates | DNA-Binding Proteins | Enzyme Activation | Flavonoids | Humans | Imidazoles | JNK Mitogen-Activated Protein Kinases | MAP Kinase Kinase 7 | MAP Kinase Kinase Kinase 1 | Mutagenesis, Site-Directed | Nuclear Receptor Subfamily 4, Group A, Member 1 | Phosphatidylinositol 3-Kinases | Phosphorylation | Protein Processing, Post-Translational | Protein Transport | Proto-Oncogene Proteins c-akt | Proto-Oncogene Proteins c-bcl-2 | Pyridines | Receptors, Cytoplasmic and Nuclear | Receptors, Steroid | Recombinant Fusion Proteins | Tetradecanoylphorbol Acetate | Transcription Factors