14-3-3 Binding to Pim-phosphorylated Ser166 and Ser186 of human Mdm2--Potential interplay with the PKB/Akt pathway and p14(ARF).

Here we show that 14-3-3 proteins bind to Pim kinase-phosphorylated Ser166 and Ser186 on the human E3 ubiquitin ligase mouse double minute 2 (Mdm2), but not protein kinase B (PKB)/Akt-phosphorylated Ser166 and Ser188. Pim-mediated phosphorylation of Ser186 blocks phosphorylation of Ser188 by PKB, indicating potential interplay between the Pim and PKB signaling pathways in regulating Mdm2. In cells, expression of Pim kinases promoted phosphorylation of Ser166 and Ser186, interaction of Mdm2 with endogenous 14-3-3s and p14(ARF), and also increased the amount of Mdm2 protein by a mechanism that does not require Pim kinase activities. The implications of these findings for regulation of the p53 pathway, oncogenesis and drug discovery are discussed.