Cdc2-cyclin B phosphorylates p70 S6 kinase on Ser411 at mitosis.
The carboxyl terminus of p70 S6 kinase (p70(s6k)) has a set of Ser and Thr residues (Ser411, Ser418, Ser424, and Thr421) phosphorylated in vivo by an unidentified kinase(s). These Ser/Thr sites are immediately followed by proline, a motif that is commonly seen in the substrates of cyclin-dependent kinases (Cdk) and mitogen-activated protein kinases. A previous study has shown that Cdc2 (Cdk1) indeed phosphorylates these p70(s6k) Ser/Thr residues in vitro. Here, we demonstrate that Cdc2-cyclin B complex phosphorylates Ser411 in the KIRSPRR sequence, whereas other Cdk-cyclin complexes including those containing Cdk2, Cdk4, or Cdk6 do not. Additionally, Ser411 phosphorylation in vivo was increased at mitosis in parallel with Cdc2 activation, and it was suppressed by a dominant negative form of Cdc2. These data indicate that p70(s6k) is a physiological substrate of Cdc2-cyclin B in mitosis. Since the activity of p70(s6k) is low during mitosis, Cdc2-cyclin B may play a role in inactivating p70(s6k) during mitosis, where protein synthesis is suppressed.[1]References
- Cdc2-cyclin B phosphorylates p70 S6 kinase on Ser411 at mitosis. Papst, P.J., Sugiyama, H., Nagasawa, M., Lucas, J.J., Maller, J.L., Terada, N. J. Biol. Chem. (1998) [Pubmed]
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