Deciphering the New Role of the Greatwall/PP2A Pathway in Cell Cycle Control

Mitotic division is induced by protein phosphorylation. For a long time the supported hypothesis was that mitotic entry and exit were the exclusive result of cyclin B-Cdk1 kinase activation and inactivation, whereas the phosphatase activity required to dephosphorylate mitotic substrates was thought to be constant during mitosis. Recent data demonstrate that phosphatase activity must also be tightly regulated to promote correct cell division. Here we describe the new pathway involved in phosphatase regulation and the questions that this discovery raises concerning the classic view of cell cycle regulation.