Beclin-phosphatidylinositol 3-kinase complex functions at the trans-Golgi network.

Autophagy is an intracellular bulk protein degradation system. Beclin is known to be involved in this process; however, its role is unclear. In this study, we showed that Beclin was co-immunoprecipitated with phosphatidylinositol (PtdIns) 3-kinase, which is also required for autophagy, suggesting that Beclin is a component of the PtdIns 3-kinase complex. Quantitative analyses using a cross-linker showed that all Beclin forms a complex with PtdIns 3-kinase, whereas approximately 50% of PtdIns 3-kinase remains free from Beclin. Indirect immunofluorescence microscopy demonstrated that the majority of Beclin and PtdIns 3-kinase localize to the trans-Golgi network (TGN). Some PtdIns 3-kinase is also distributed in the late endosome. These results suggest that Beclin and PtdIns 3-kinase control autophagy as a complex at the TGN.