14-3-3 suppresses the nuclear localization of threonine 157-phosphorylated p27Kip1

Abstract

p27Kip1 (p27), a CDK inhibitor, migrates into the nucleus, where it controls cyclin-CDK complex activity for proper cell cycle progression. We report here that the classical bipartite-type basic amino-acid cluster and the two downstream amino acids of the C-terminal region of p27 function as a nuclear localization signal (NLS) for its full nuclear import activity. Importin a3 and a5, but not a1, transported p27 into the nucleus in conjunction with importin b, as evidenced by an in vitro transport assay. It is known that Akt phosphorylates Thr 157 of p27 and this reduces the nuclear import activity of p27. Using a pull-down experiment, 14-3-3 was identified as the Thr157-phosphorylated p27NLS-binding protein. Although importin a5 bound to Thr157-phosphorylated p27NLS, 14-3-3 competed with importin a5 for binding to it. Thus, 14-3-3 sequestered phosphorylated p27NLS from importin a binding, resulting in cytoplasmic localization of NLS-phosphorylated p27. These findings indicate that 14-3-3 suppresses importin a/b-dependent nuclear localization of Thr157-phosphorylated p27, suggesting implications for cell cycle disorder in Akt-activated cancer cells.

Cell proliferation and survival induced by Toll-like receptors is antagonized by type I IFNs

“…They are consistent with reports indicating that both type I and II IFN strongly repressed the activity of CDK2 and -4 in a number of cell types by decreasing their levels or by increasing CDK inhibitors such as p27 (14,39). During cell cycle regulation, p27 is degraded after a SCF Skp2 -dependent ubiquitination in the nucleus, whereas the newly synthesized p27 is retained in the cytoplasm through AKT or CDK/cyclin complexes (20,40). Here, we show that, whereas TLR5 induces p27 degradation and cytoplasmic retention through AKT, TLR3 and -4 induce the same effect on p27 through both CDK/cyclin-and AKT-dependent mechanisms.…”

Transgenic Mouse Proteomics Identifies New 14-3-3-associated Proteins Involved in Cytoskeletal Rearrangements and Cell Signaling

“…Here we describe the binding of 14-3-3 to a member of the chromatinremodeling SWI/SNF multiprotein complexes, SMARCB1, exclusively in the cytosol. We speculate that SMARCB1 could be retained in the cytoplasm depending on the activity of the 14-3-3 anchoring protein as it has been described for the cyclin-dependent kinase inhibitor p27(Kip1) (38) or the histone deacetylases HDAC4 and HDAC5 (21).…”

The crystal structure of the non-liganded 14-3-3σ protein: insights into determinants of isoform specific ligand binding and dimerization

“…Binding studies with recombinant 14-3-3 isoforms and p27 showed that 14-3-3β, ε, γ, τ and ζ isoforms, but not σ, bind to p27 and sequester p27 in the cytoplasm [17]. Also, CDC25C is not bound by 14-3-3σ, however by other 14-3-3 isoforms [11].…”

“…Interactions identified between other 14-3-3 isoforms and protein ligands do not necessarily apply to 14-3-3σ as distinct 14-3-3 isoforms show preferential or selective binding of ligands [16][17][18]. Binding studies with recombinant 14-3-3 isoforms and p27 showed that 14-3-3β, ε, γ, τ and ζ isoforms, but not σ, bind to p27 and sequester p27 in the cytoplasm [17].…”