title: Regulation of α-endosulfine, an inhibitor of protein phosphatase 2A, by multisite phosphorylation.
abstract: Progression into M phase requires inhibition of heterotrimeric PP2A containing the regulatory B55 subunit (PP2A-B55) as well as the activation of cyclin-dependent kinase 1 (Cdk1). α-endosulfine (ENSA)/cyclic AMP-regulated 19 kDa phosphoprotein (ARPP-19) family proteins phosphorylated at S67 by Greatwall kinase bind and inhibit PP2A-B55. This study shows that endogenous kinases phosphorylate not only S67 but also two additional sites in ENSA (T28 and S109) with different kinetics at different cell-cycle stages in Xenopus laevis intact cells and cell-free egg extracts. When assayed in vitro, these phosphorylations had qualitatively and/or quantitatively different effects on inhibition of PP2A-B55 by ENSA. Structural analyses revealed that the most-conserved middle region of ENSA containing S67 physically interacts with PP2A-B55 at the interface of the B55 and C subunits, where the catalytic centre of PP2A is located. As non-phosphorylated ENSA has an intrinsic potential for PP2A-B55 inhibition, these three phosphorylations differentially affect physical interaction of the middle region of ENSA with PP2A-B55. These results suggest that the two additional phosphorylation sites together with S67 allow ENSA to function as a 'stepwise tuner' for PP2A-B55, which may be regulated by multiple cellular signals, rather than a simple 'on/off' switch.
authors.affiliation: Priority Organization for Innovation and Excellence, Kumamoto University, Japan; Precursory Research for Embryonic Science and Technology (PRESTO) Program, Japan Science and Technology Agency, Tokyo, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Mochida
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C075663:endosulfine; D054648:Protein Phosphatase 2
keywords: cell cycle; cyclin-dependent kinase; greatwall kinase; protein kinase A; protein phosphatase 2A