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Protein kinase Cδ regulates nuclear export of FOXO1 through phosphorylation of the chaperone 14-3-3ζ.
Diabetologia 58, 2819-2831 (2015)
AIMS/HYPOTHESIS: Forkhead box protein O1 (FOXO1) is a transcription factor essential for beta cell fate. Protein kinase B-dependent phosphorylation of FOXO1 at S256 (P-FOXO1) enables its binding to 14-3-3 dimers and nuclear export. Dephosphorylated FOXO1 enters nuclei and activates pro-apoptotic genes. Since our previous observations suggest that protein kinase C delta (PKCδ) induces nuclear accumulation of FOXO1, the underlying mechanism was examined. METHODS: In human islets, genetically modified mice and INS-1E cells apoptosis was assessed by TUNEL staining. Subcellular translocation of proteins was examined by confocal microscopy and signalling pathways were analysed by western blotting and overlay assay. RESULTS: In PKCδ-overexpressing (PKCδ-tg) mouse islet cells and INS-1E cells FOXO1 accumulated in nuclei, surprisingly, as P-FOXO1. PKCδ-tg decelerated IGF-1-dependent stimulation of nuclear export, indicating that changes in export caused nuclear retention of P-FOXO1. Nuclear accumulation of P-FOXO1 was accompanied by increased phosphorylation of 14-3-3ζ at S58 and reduced dimerisation of 14-3-3ζ. Palmitic acid further augmented phosphorylation of 14-3-3ζ and triggered nuclear accumulation of FOXO1 in both INS-1E and human islet cells. Furthermore, the overexpression of a phosphomimicking mutant of 14-3-3ζ (S58D) enhanced nuclear FOXO1. In accordance with the nuclear accumulation of P-FOXO1, PKCδ overexpression alone did not increase apoptotic cell death. Additionally, insulin secretion and glucose homeostasis in PKCδ-overexpressing mice remained unaffected. CONCLUSIONS/INTERPRETATION: These results suggest that PKCδ-mediated phosphorylation of 14-3-3ζ contributes to the nuclear retention of FOXO1, even when FOXO1 is phosphorylated as under non-stress conditions. P-FOXO1 does not induce pro-apoptotic genes, but may rather exert beneficial effects on beta cells.
Impact Factor
Scopus SNIP
Web of Science
Times Cited
Times Cited
Scopus
Cited By
Cited By
Altmetric
6.671
1.923
17
19
Anmerkungen
Besondere Publikation
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Publikationstyp
Artikel: Journalartikel
Dokumenttyp
Wissenschaftlicher Artikel
Schlagwörter
14-3-3 Zeta ; Apoptosis ; Foxo1 ; Insulin Secreting Beta Cells ; Jnk ; Palmitate ; Pkc Delta
Sprache
englisch
Veröffentlichungsjahr
2015
HGF-Berichtsjahr
2015
ISSN (print) / ISBN
0012-186X
e-ISSN
1432-0428
Zeitschrift
Diabetologia
Quellenangaben
Band: 58,
Heft: 12,
Seiten: 2819-2831
Verlag
Springer
Verlagsort
Berlin ; Heidelberg [u.a.]
Begutachtungsstatus
Peer reviewed
POF Topic(s)
90000 - German Center for Diabetes Research
Forschungsfeld(er)
Helmholtz Diabetes Center
PSP-Element(e)
G-502400-002
G-502400-001
G-502400-001
PubMed ID
26363783
WOS ID
WOS:000364221200016
Erfassungsdatum
2015-10-08