The Greatwall-Endosulfine Switch Accelerates Autophagic Flux during the Cell Divisions Leading to G1 Arrest and Entry into Quiescence in Fission Yeast

Entry into quiescence in the fission yeast Schizosaccharomyces pombe is induced by nitrogen starvation. In the absence of nitrogen, proliferating fission yeast cells divide twice without cell growth and undergo cell cycle arrest in G1 before becoming G0 quiescent cells. Under these conditions, autophagy is induced to produce enough nitrogen for the two successive cell divisions that take place before the G1 arrest. In parallel to the induction of autophagy, the Greatwall–Endosulfine switch is activated upon nitrogen starvation to down-regulate protein phosphatase PP2A/B55 activity, which is essential for cell cycle arrest in G1 and implementation of the quiescent program. Here we show that, although inactivation of PP2A/B55 by the Greatwall–Endosulfine switch is not required to promote autophagy initiation, it increases autophagic flux at least in part by upregulating the expression of a number of autophagy-related genes.This work was funded by the Spanish Ministry of Science and Innovation-MICINN (grants BFU2017-88335-R and PID2020-117218RB-I00) and from the Castile and Leon government (grants CSI151U13 and CSI259P20 and IBFG Unit of Excellence programs CLU-2017-03 and CL-EI-2021-08 co-funded by the P.O. Feder of Castile and Leon 14-20 and European Union ERDF “Europe drives our growth”). N.G.-B., A.V.B. and D.G.-Á. were funded by FPU15/03654, BES-2015-073171, PRE2018-084956 predoctoral training contracts. R.L.-S.S. was funded by a predoctoral fellowship from the Castile and Leon governments