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PP1-mediated dephosphorylation of phosphoproteins at mitotic exit is controlled by inhibitor-1 and PP1 phosphorylation


Loss of cell division cycle 2 (Cdc2, also known as Cdk1) activity after cyclin B degradation is necessary, but not sufficient, for mitotic exit. Proteins phosphorylated by Cdc2 and downstream mitotic kinases must be dephosphorylated. We report here that protein phosphatase-1 (PP1) is the main catalyst of mitotic phosphoprotein dephosphorylation. Suppression of PP1 during early mitosis is maintained through dual inhibition by Cdc2 phosphorylation and the binding of inhibitor-1. Protein kinase A (PKA) phosphorylates inhibitor-1, mediating binding to PP1. As Cdc2 levels drop after cyclin B degradation, auto-dephosphorylation of PP1 at its Cdc2 phosphorylation site (Thr 320) allows partial PP1 activation. This promotes PP1-regulated dephosphorylation at the activating site of inhibitor-1 (Thr 35) followed by dissociation of the inhibitor-1–PP1 complex and then full PP1 activation to promote mitotic exit. Thus, Cdc2 both phosphorylates multiple mitotic substrates and inhibits their PP1-mediated dephosphorylation.

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Figure 1: Dephosphorylation of mitotic phosphoproteins by okadaic acid-sensitive phosphatase activity.
Figure 2: PP1 is required for the dephosphorylation of substrates at mitotic, but not meiotic, exit.
Figure 3: Cdc2 regulation of PP1 prevents premature substrate dephosphorylation in mitosis.
Figure 4: PP1 auto-dephosphorylation and inhibitor-1 dephosphorylation control PP1-regulated Cdc2 substrate dephosphorylation.
Figure 5: Cell-cycle regulation of inhibitor-1.


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This work was supported by NIH grants to S.K. (RO1 GM67225) and A.C.N. (DA10044).

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J.Q.W., J.Y.G., WT., A.C.N. and S.K. designed the experiments; J.Q.W., J.Y.G., W.T., C.Y. and C.C. performed experiments; A.C.N. contributed reagents; C.D.F. analysed data; J.Q.W. and S.K. wrote and J.Y.G., W.T. and A.C.N. edited the manuscript.

Corresponding author

Correspondence to Sally Kornbluth.

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The authors declare no competing financial interests.

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Wu, J., Guo, J., Tang, W. et al. PP1-mediated dephosphorylation of phosphoproteins at mitotic exit is controlled by inhibitor-1 and PP1 phosphorylation. Nat Cell Biol 11, 644–651 (2009).

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