Fig. 4. Regulation of autophagy in Drosophila by PI 3-kinases. Autophagy is known to be regulated by both the class I and the class III PI 3-kinases. The class III PI 3-kinase is required for autophagy through producing PtdIns(3)P via the autophagy-specific complex containing Beclin-1, Vps15 and hVps34. (In yeast, an additional accessory protein, Vps14, has been shown to be part of the complex.) By contrast, the class I PI 3-kinase inhibits autophagy by activating the Akt/PKB pathway. The insect hormone ecdysone acts through nuclear receptors and triggers programmed autophagy in the Drosophila fat body by downregulating the class I PI 3-kinase pathway through an unknown mechanism. The overexpression of the PI 3-phosphatase PTEN mimics this effect.