Abstract

Cell cycle progression is controlled by the sequential and ordered phosphorylation of cell phase specific substrates. This phosphorylation is the result of the balance between cyclin/cdk kinases and their counteracting phosphatases. PP2A -B55 is one of these phosphatases. During the cell cycle, the activity of PP2A -B55 is regulated by the Greatwall (Gwl) kinase and their substrates Arpp19 and ENSA . The phosphorylation of Arpp19 and ENSA by Gwl promotes their binding to PP2A -B55 and the inhibition of this phosphatase. How this binding results in the inhibition of this enzyme is not known. Moreover, how this pathway can induce the correct temporal and spatial inactivation of PP2A -B55 required for the ordered dephosphorylation of the cell cycle substrates is elusive. Using Xenopus egg extract model, we shed light in the molecular mechanisms defining the PP2A -B55 inhibitory activity of Arpp19 and ENSA . Moreover, we also identified a differential role of the two PP2A -B55 inhibitors. Notably, our “in cellulo” and “in vivo” data demonstrate that the ENSA protein participates to the correct phosphorylation of S phase substrates while Arpp19 plays an essential role to promote the ordered substrate dephosphorylation pattern required for a correct mitotic exit.