The Substrate of Greatwall Kinase, Arpp19, Controls Mitosis by Inhibiting Protein Phosphatase 2A

Abstract

Initiation and maintenance of mitosis require the activation of protein kinase cyclin B-Cdc2 and the inhibition of protein phosphatase 2A (PP2A), which, respectively, phosphorylate and dephosphorylate mitotic substrates. The protein kinase Greatwall (Gwl) is required to maintain mitosis through PP2A inhibition. We describe how Gwl activation results in PP2A inhibition. We identified cyclic adenosine monophosphate-regulated phosphoprotein 19 (Arpp19) and α-Endosulfine as two substrates of Gwl that, when phosphorylated by this kinase, associate with and inhibit PP2A, thus promoting mitotic entry. Conversely, in the absence of Gwl activity, Arpp19 and α-Endosulfine are dephosphorylated and lose their capacity to bind and inhibit PP2A. Although both proteins can inhibit PP2A, endogenous Arpp19, but not α-Endosulfine, is responsible for PP2A inhibition at mitotic entry in Xenopus egg extracts.

Genome-wide siRNA Screen Identifies the Radiosensitizing Effect of Downregulation of MASTL and FOXM1 in NSCLC

“…The radiosensitizing effect of MASTL knockdown did not seem to be driven by ENSA, the currently known substrate for MASTL (22,33), as we could not confirm an altered phosphorylation state of this protein after MASTL knockdown. Our phosphoproteomics analysis further suggests that the initial phosphorylation of DNA damage response proteins is not altered in irradiated cells with lowered MASTL expression.…”

LB100, a small molecule inhibitor of PP2A with potent chemo- and radio-sensitizing potential

“…In particular, PP2A is regulated by Greatwall kinase (called microtubule-associated serine/threonine kinase-like [Mastl] in mammals), which when depleted is associated with severe mitotic defects. 21,22 Greatwall has been shown to inhibit PP2A via the small proteins, a-endosulphine (ENSA) and cyclic AMP-regulated phosphoprotein 19 (ARPP19), 23,24 relieving PP2A-mediated dephosphorylation of various Cdk1 substrates and promoting mitotic progression. 25,26 PP2A also negatively regulates Cdk1 through activating wee1 and myt1 and inhibiting cdc25 through dephosphorylation.…”

Role for regulated phosphatase activity in generating mitotic oscillations in Xenopus cell-free extracts

“…PP2A:B55δ activity is indirectly repressed by Cdk1:CycB, which could account for the slow rate of APC/C dephosphorylation in M phase required by Ciliberto's model. Other data suggest roles for PP2A:B55δ in Wee1 activation and Cdc25 inactivation (27,29,30). Altogether, these data suggest an active role for PP2A:B55δ in the control of entry into and exit from mitosis.…”