title: The peptidyl-isomerase Pin1 regulates p27kip1 expression through inhibition of Forkhead box O tumor suppressors.
abstract: The Forkhead box O (FOXO) protein family is an evolutionarily conserved subclass of transcription factors recently identified as bona fide tumor suppressors. Preventing the accumulation of cellular damage due to oxidative stress is thought to underlie its tumor-suppressive role. Oxidative stress, in turn, also feedback controls FOXO4 function. Regulation of this process, however, is poorly understood but may be relevant to the ability of FOXO to control tumor suppression. Here, we characterize novel FOXO4 phosphorylation sites after increased cellular oxidative stress and identify the isomerase Pin1, a protein frequently found to be overexpressed in cancer, as a critical regulator of p27(kip1) through FOXO4 inhibition. We show that Pin1 requires these phosphorylation events to act negatively on FOXO4 transcriptional activity. Consistent with this, oxidative stress induces binding of Pin1 to FOXO, thereby attenuating its monoubiquitination, a yet uncharacterized mode of substrate modulation by Pin1. We have previously shown that monoubiquitination is involved in controlling nuclear translocation in response to cellular stress, and indeed, Pin1 prevents nuclear FOXO4 accumulation. Interestingly, Pin1 acts on FOXO through stimulation of the activity of the deubiquitinating enzyme HAUSP/USP7. Ultimately, this results in decreased transcriptional activity towards target genes, including the cell cycle arrest gene p27(kip1). Notably, in a primary human breast cancer panel, low p27(kip1) levels inversely correlated with Pin1 expression. Thus, Pin1 is identified as a novel negative FOXO regulator, interconnecting FOXO phosphorylation and monoubiquitination in response to cellular stress to regulate p27(kip1).
authors.affiliation: Department of Metabolic and Endocrine Diseases and Netherlands Metabolomics Centre, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Arjan B
authors.initials: AB
authors.lastname: Brenkman
authors.forename: Peter L J
authors.initials: PL
authors.lastname: de Keizer
authors.forename: Niels J F
authors.initials: NJ
authors.lastname: van den Broek
authors.forename: Petra
authors.initials: P
authors.lastname: van der Groep
authors.forename: Paul J
authors.initials: PJ
authors.lastname: van Diest
authors.forename: Armando
authors.initials: A
authors.lastname: van der Horst
authors.forename: Alida M M
authors.initials: AM
authors.lastname: Smits
authors.forename: Boudewijn M T
authors.initials: BM
authors.lastname: Burgering
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001943:Breast Neoplasms / Q000201:enzymology / Q000378:metabolism; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000096:biosynthesis* / Q000235:genetics; D051858:Forkhead Transcription Factors; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D051379:Mice; D016297:Mutagenesis, Site-Directed; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D019696:Peptidylprolyl Isomerase / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D043222:Ubiquitin Thiolesterase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000076084:Ubiquitin-Specific Peptidase 7; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D018797:Cell Cycle Proteins; C108803:FOXO4 protein, human; D051858:Forkhead Transcription Factors; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D014157:Transcription Factors; D050760:Cyclin-Dependent Kinase Inhibitor p27; D006861:Hydrogen Peroxide; C464569:USP7 protein, human; D043222:Ubiquitin Thiolesterase; D000076084:Ubiquitin-Specific Peptidase 7; C000606846:PIN1 protein, human; D019696:Peptidylprolyl Isomerase; C000606850:Pin1 protein, mouse