title: Evidence for AKT-independent regulation of FOXO1 and FOXO3 in haematopoietic stem and progenitor cells.
abstract: Transcription factors FOXOs (1, 3, 4) are essential for the maintenance of haematopoietic stem cells. FOXOs are evolutionary conserved substrates of the AKT serine threonine protein kinase that are also phosphorylated by several kinases other than AKT. Specifically, phosphorylation by AKT is known to result in the cytosolic localization of FOXO and subsequent inhibition of FOXO transcriptional activity. In addition to phosphorylation, FOXOs are regulated by a number of other post-translational modifications including acetylation, methylation, redox modulation, and ubiquitination that altogether determine these factors' output. Cumulating evidence raises the possibility that in stem cells, including in haematopoietic stem cells, AKT may not be the dominant regulator of FOXO. To address this question in more detail, we examined gene expression, subcellular localization, and response to AKT inhibition of FOXO1 and FOXO3, the main FOXO expressed in HSPCs (haematopoietic stem and progenitor cells). Here we show that while FOXO1 and FOXO3 transcripts are expressed at similar levels, endogenous FOXO3 protein is mostly nuclear compared to the cytoplasmic localization of FOXO1 in HSPCs. Furthermore, inhibition of AKT does not enhance nuclear localization of FOXO1 nor FOXO3. Nonetheless AKT inhibition in the context of loss of NAD-dependent SIRT1 deacetylase modulates FOXO3 localization in HSPCs. Together, these data suggest that FOXO3 is more active than FOXO1 in primitive haematopoietic stem and multipotent progenitor cells. In addition, they indicate that upstream regulators other than AKT, such as SIRT1, maintain nuclear FOXO localization and activity in HSPCs.
authors.affiliation: a Department of Developmental & Regenerative Biology , Icahn School of Medicine at Mount Sinai , New York , NY , USA.|b Developmental and Stem Cell Biology Multidisciplinary Training Area, Icahn School of Medicine at Mount Sinai , New York , NY , USA.
authors.forename: Raymond
authors.initials: R
authors.lastname: Liang
authors.affiliation: a Department of Developmental & Regenerative Biology , Icahn School of Medicine at Mount Sinai , New York , NY , USA.
authors.forename: Pauline
authors.initials: P
authors.lastname: Rimmelé
authors.affiliation: a Department of Developmental & Regenerative Biology , Icahn School of Medicine at Mount Sinai , New York , NY , USA.
authors.forename: Carolina L
authors.initials: CL
authors.lastname: Bigarella
authors.affiliation: a Department of Developmental & Regenerative Biology , Icahn School of Medicine at Mount Sinai , New York , NY , USA.
authors.forename: Safak
authors.initials: S
authors.lastname: Yalcin
authors.affiliation: a Department of Developmental & Regenerative Biology , Icahn School of Medicine at Mount Sinai , New York , NY , USA.|b Developmental and Stem Cell Biology Multidisciplinary Training Area, Icahn School of Medicine at Mount Sinai , New York , NY , USA.|c Department of Medicine , Division of Hematology and Medical Oncology, Icahn School of Medicine at Mount Sinai , New York , NY , USA.|d Black Family Stem Cell Institute, Icahn School of Medicine at Mount Sinai , New York , NY , USA.|e Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai , New York , NY , USA.
authors.forename: Saghi
authors.initials: S
authors.lastname: Ghaffari
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D000071161:Forkhead Box Protein O1 / Q000235:genetics* / Q000378:metabolism; D000071316:Forkhead Box Protein O3 / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009025:Morpholines / Q000494:pharmacology; D010766:Phosphorylation; D061251:Primary Cell Culture; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D056564:Sirtuin 1 / Q000172:deficiency / Q000235:genetics*
chemical_list: D002867:Chromones; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; C474033:FoxO3 protein, mouse; C467200:Foxo1 protein, mouse; D009025:Morpholines; D012333:RNA, Messenger; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D051057:Proto-Oncogene Proteins c-akt; C470545:Sirt1 protein, mouse; D056564:Sirtuin 1
keywords: AKT; FOXO; FOXO1; FOXO3; SIRT1; Sirtuins; acetylation; deacetylation; hematopoietic stem and progenitor cells