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

Autophagy is an intracellular bulk protein degradation system. Beclin is kn own to be involved in this process; however, its role is unclear. In this s tudy, we showed that Beclin was co-immunoprecipitated with phosphatidylinos itol (PtdIns) 3-kinase, which is also required for autophagy, suggesting th at Beclin is a component of the PtdIns 3-kinase complex. Quantitative analy ses using a cross-linker showed that all Beclin forms a complex with PtdIns 3-kinase, whereas similar to 50% of PtdIns 3-kinase remains free from Becl in. Indirect immunofluorescence microscopy demonstrated that the majority o f Beclin and PtdIns 3-kinase localize to the trans-Golgi network (TGN). Som e PtdIns 3-kinase is also distributed in the late endosome. These results s uggest that Beclin and PtdIns 3-kinase control autophagy as a complex at th e TGN.