Dephosphorylation and inactivation of Akt/PKB is counteracted by protein kinase CK2 in HEK 293T cells
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Akt (PKB) is a critical kinase in cell-survival pathways. Its activity depends on the phosphorylation of Thr308 and Ser473, by PDK1 and mTORC2, respectively. We found that Akt can be further stimulated through phosphorylation of Ser129 by another kinase, CK2. Here we show that phosphorylation of Akt at Ser129 also facilitates its association with Hsp90 chaperone, thus preventing Thr308 dephosphorylation. This is supported by the following observations: (1) phospho-Thr308 decreases when Ser129 is mutated to alanine, (2) this decrease is abolished by cell treatment with okadaic acid (to inactivate PP2A) or geldanamycin (to inactivate Hsp90), (3) phosphorylation of Ser129 neither enhances the activity of PDK1 nor hampers the in vitro activity of PP2A on Thr308, but increases the Hsp90 association to Akt. These data support the view that the antiapoptotic potential of CK2 is at least in part mediated by its ability to maintain Akt in its active form.
KeywordsCK2 CKII Akt PKB Casein kinase 2
We thank the protein production team of the Division of Signal Transduction Therapy at the University of Dundee, Scotland (coordinated by Hilary McLauchlan and James Hastie), for providing inactive Akt and active PDK1; Dr. S. Sarno (Padova, Italy) for providing recombinant CK2; Dr. P. Csermely and Dr. C. Soti (Budapest, Hungary) for providing recombinant Hsp90; Dr. P. Agostinis (Leuven, Belgium) for providing PP2A; and Dr. O. Marin (Padova, Italy) for the synthesis of Ser129 peptide and phospho-peptide. This work was supported by grants from the University of Padova (Progetto Ateneo 2005 to M.R.) and the Italian Ministry of University and Research (PRIN-2007 to M.R.) and from AIRC and EC (PRO-KINASERESEARCH 503467 to L.A.P.).