JNK1-mediated phosphorylation of BcI-2 regulates starvation-induced autophagy

Starvation induces autophagy to preserve cellular homeostasis in virtually all eukaryotic organisms. However, the mechanisms by which starvation induces autophagy are not completely understood. In mammalian cells, the antiapoptotic protein, BcI-2, binds to Beclin 1 during nonstarvation conditions and inhibits its autophagy function. Here we show that starvation induces phosphorylation of cellular BcI-2 at residues T69, S70, and S87 of the nonstructured loop; BcI-2 dissociation from Beclin 1; and autophagy activation. In contrast, viral BcI-2, which lacks the phosphorylation site-containing nonstructured loop, fails to dissociate from Beclin 1 during starvation. Furthermore, the stress-activated signaling molecule, c-Jun N-terminal protein kinase 1 (JNK1), but not JNK2, mediates starvation-induced BcI-2 phosphorylation, BcI-2 dissociation from Beclin 1, and autophagy activation. Together, our findings demonstrate that JNK1-mediated multisite phosphorylation of BcI-2 stimulates starvation-induced autophagy by disrupting the BcI-2/Beclin 1 complex. These findings define a mechanism that cells use to regulate autophagic activity in response to nutrient status.