title: The B55α-containing PP2A holoenzyme dephosphorylates FOXO1 in islet β-cells under oxidative stress.
abstract: The FOXO1 (forkhead box O1) transcription factor influences many key cellular processes, including those important in metabolism, proliferation and cell death. Reversible phosphorylation of FOXO1 at Thr(24) and Ser(256) regulates its subcellular localization, with phosphorylation promoting cytoplasmic localization, whereas dephosphorylation triggers nuclear import and transcriptional activation. In the present study, we used biochemical and molecular approaches to isolate and link the serine/threonine PP2A (protein phosphatase 2A) holoenzyme containing the B55α regulatory subunit, with nuclear import of FOXO1 in pancreatic islet β-cells under oxidative stress, a condition associated with cellular dysfunction in Type 2 diabetes. The mechanism of FOXO1 dephosphorylation and nuclear translocation was investigated in pancreatic islet INS-1 and βTC-3 cell lines subjected to oxidative stress. A combined chemical cross-linking and MS strategy revealed the association of FOXO1 with a PP2A holoenzyme composed of the catalytic C, structural A and B55α regulatory subunits. Knockdown of B55α in INS-1 cells reduced FOXO1 dephosphorylation, inhibited FOXO1 nuclear translocation and attenuated oxidative stress-induced cell death. Furthermore, both B55α and nuclear FOXO1 levels were increased under hyperglycaemic conditions in db/db mouse islets, an animal model of type 2 diabetes. We conclude that B55α-containing PP2A is a key regulator of FOXO1 activity in vivo.
authors.affiliation: Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
authors.forename: Ling
authors.initials: L
authors.lastname: Yan
authors.forename: Shuangli
authors.initials: S
authors.lastname: Guo
authors.forename: Marie
authors.initials: M
authors.lastname: Brault
authors.forename: Jamie
authors.initials: J
authors.lastname: Harmon
authors.forename: R Paul
authors.initials: RP
authors.lastname: Robertson
authors.forename: Rizwan
authors.initials: R
authors.lastname: Hamid
authors.forename: Roland
authors.initials: R
authors.lastname: Stein
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D050417:Insulin-Secreting Cells / Q000201:enzymology / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D018384:Oxidative Stress / Q000502:physiology*; D010766:Phosphorylation / Q000502:physiology; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D051381:Rats; D015854:Up-Regulation / Q000502:physiology
chemical_list: D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D007527:Isoenzymes; C512974:PPP2R2A protein, human; D054648:Protein Phosphatase 2