Protein phosphatase 2A (PP2A) holoenzyme is a heterotrimeric complex, consisting of
A, B and C subunits. The catalytic subunit PP2A-C (microtubule star/mts) binds to
the C-terminal part of the scaffold protein PP2A-A (PP2A-29B). In Drosophila, there
are three different forms of B subunits (widerborst/wdb, twins/tws and PP2A-B'), which
determine the subcellular localization and substrate specificity of the holoenzyme.
Previous studies demonstrated that PP2A is involved in the control of TOR-dependent
autophagy both in yeast and mammals. Furthermore, in Drosophila, wdb genetically interacts
with the PtdIns3K/PTEN/Akt signaling cascade, which is a main upstream regulatory
system of dTOR. Here we demonstrate that in Drosophila, two different PP2A complexes
(containing B' or wdb subunit) play essential roles in the regulation of starvation-induced
autophagy. The PP2A-A/wdb/C complex acts upstream of dTOR, whereas the PP2A-A/B'/C
complex functions as a target of dTOR and may regulate the elongation of autophagosomes
and their subsequent fusion with lysosomes. We also identified three Drosophila Atg
orthologs (Atg14, Atg17 and Atg101), which represent potential targets of the PP2A-A/B'/C
complex during autophagy.
