High FOXO3a expression is associated with a poorer prognosis in AML with normal cytogenetics

Xing

Proc. Natl. Acad. Sci. U.S.A.

et al. 2012

To ensure genome stability, DNA must be replicated once and only once during each cell cycle. Cdt1 is tightly regulated to make sure that cells do not rereplicate their DNA. Multiple regulatory mechanisms operate to ensure degradation of Cdt1 in S phase. However, little is known about the positive regulators of Cdt1 under physiological conditions. Here we identify FOXO3 as a binding partner of Cdt1. FOXO3 forms a protein complex with Cdt1, which in turn blocks its interaction with DDB1 and PCNA. Conversely, FOXO3 depletion facilitated the proteolysis of Cdt1 in unperturbed cells. Intriguingly, FOXO3 deficiency resulted in impaired S-phase entry and reduced cell proliferation. We provide data that FOXO3 knockdown mimics Cdt1 down-regulation and affects G1/S transitions. Our results demonstrate a unique role of FOXO3 in binding to Cdt1 and maintaining its level required for cell cycle progression.I n eukaryotic cells, DNA replication initiates from thousands of replication origins. Each origin acquires replication competence through the assembly of a prereplication complex (pre-RC) occurring in late mitosis and early G1 (1-3). Pre-RCs are assembled at the origins of DNA replication through the sequential loading of the initiation factors ORC, Cdc6, Cdt1, and MCM2-7 (4). In S phase, pre-RCs are sequentially acted on by two protein kinases, Cdc7 and Cdk2, which promote recruitment of proteins required for helicase activation and replisome assembly, leading to origin unwinding and DNA synthesis. To ensure that no replication origin fires more than once, the assembly of the replication apparatus at origins is tightly regulated by the cell cycle machinery. Among the most important of these regulatory mechanisms are the degradation of Cdt1 during S phase and the sequestration of Cdt1 by the geminin protein (5-7). Phosphorylation of Cdt1 by Cdk2 promotes its binding to SCF-Skp2 E3 ubiquitin ligase (8-10), which results in its degradation in S phase. In addition to the Skp2 pathway, PCNA/ DDB1/Cul4-dependent signaling was found to degrade Cdt1 during S phase via the interaction of Cdt1 with PCNA (11-15). Recently, APC/C Cdh1 was proposed as a third ubiquitin ligase regulating Cdt1 degradation (16). Cdt1 is also targeted for degradation after DNA damage to stop licensing of new origins until after DNA repair. Both the SCF-Skp2 complex and the Cul4-DDB1 complex have been reported to induce degradation of Cdt1 after UV irradiation (17,18).FOXO transcription factors are critical for the regulation of cell cycle arrest, cell death, and DNA damage repair. Ample evidence has suggested that FOXO exerts a negative effect on cell cycle progression. In dividing cells, overexpression of the active form of FOXO family members promotes cell cycle arrest at the G1/S boundary. Target genes that mediate FOXO-induced cell cycle arrest are the Cdk inhibitors p27KIP1 and p21 (in the presence of TGF-β), the Rb family member p130, and cyclin D1 and D2. The ectopically expressed active form of FOXO factors can cause G1 arrest both by up-regulat...

Section: Discussionmentioning

confidence: 99%

Regulation of cell cycle progression by forkhead transcription factor FOXO3 through its binding partner DNA replication factor Cdt1

Xing

Proc. Natl. Acad. Sci. U.S.A.

et al. 2012

“…Restoring FOXO3a tumor suppressive functions may therefore induce the killing of leukemic cells and could thus represent an attractive perspective in AML therapy. Nevertheless, although it has been recently reported that high levels of FOXO3a mRNA 26 and the phosphorylation of FOXO3a 27 represent adverse prognostic factors in AML, little is currently known about the cellular functions of the FOXOs in this cancer. Hence, we have in our current study further analyzed FOXO3a activity in AML cells and its regulation by the PI3K/Akt, ERK/MAPK, and IKK signaling pathways.…”

Section: Introductionmentioning

confidence: 99%

IκB kinase overcomes PI3K/Akt and ERK/MAPK to control FOXO3a activity in acute myeloid leukemia

Chapuis

Park

Léotoing

et al. 2010

Blood

The FOXO transcription factors are involved in multiple signaling pathways and have tumor-suppressor functions. In acute myeloid leukemia (AML), deregulation of oncogenic kinases, including Akt, extra-signal-regulated kinase, or IB kinase, is frequently observed, which may potentially inactivate FOXO activity. We therefore investigated the mechanism underlying the regulation of FOXO3a, the only FOXO protein constantly expressed in AML blast cells. We show that in both primary AML samples and in a MV4-11/ FOXO3a-GFP cell line, FOXO3a is in a constant inactive state due to its cytoplasmic localization, and that neither PI3K/Akt nor extra-signal-regulated kinase-specific inhibition resulted in its nuclear translocation. In contrast, the anti-Nemo peptide that specifically inhibits IKK activity was found to induce FOXO3a nuclear localization in leukemic cells. IntroductionAcute myeloid leukemia (AML) is a clonal hematopoietic stem cell disorder characterized by differentiation arrest and inappropriate proliferation and survival of immature myeloid progenitors. As the global prognosis for this disease remains particularly poor, major efforts have been made to both characterize the deregulated signal transduction pathways in AML cells 1 and to develop targeted therapies against these aberrant signals.The human FOXO transcription factors, which include FOXO1, FOXO3a, FOXO4, and FOXO6, 2 function as tumor suppressors by up-regulating genes involved in the control of the cell cycle (p27 and p21 Cip16 ) or in the induction of apoptosis (Fas ligand [Fas-L] 7 and Bim 5,8 ). The activity of the FOXO transcription factors is mainly regulated through posttranslational modifications (PTMs), resulting in changes in the subcellular localization of these proteins. Accordingly, activation of the PI3K/Akt signaling pathway downstream of growth factor receptors negatively regulates FOXO proteins. Indeed, by phosphorylating FOXO3a at 3 conserved sites (T 32 , S 253 , and S 315 ), Akt creates binding sites for the 14-3-3 chaperone proteins and thereby allows active export and sequestration of FOXO3a in the cytoplasm. 7 Nevertheless, in addition to Akt, other kinases, such as the serum and glucocorticoidinducible kinase (SGK), casein kinase (CK1), dual tyrosine phosphorylated regulated kinase 1 (DYRK1), extra-signal-regulated kinases 1 and 2 (ERK1/2) and IB Kinase ␤ (IKK␤) can also phosphorylate FOXOs and therefore regulate their subcellular localization. 9 The activity of FOXOs is also regulated by ubiquitindependant protein degradation. Phosphorylation of FOXO1 by Akt (most notably on S 256 ) is necessary for its Skp2-mediated polyubiquitination and proteasome degradation. 10 Another E3 ubiquitin ligase, MDM2, has been reported to mediate FOXO3a ubiquitination and degradation after ERK-dependent phosphorylations. 11 Recently, perturbation of FOXO functions have been observed in a number of human cancers 12,13 thus emphasizing the tumorsuppressive roles of these transcription factors. Inactivation of FOXO proteins can occur throu...

Journal of Biological Chemistry

“…Depletion of FOXO3 reduced G 1 /S transition and cell proliferation in MCF7 breast cancer cells and H1299 lung cancer cells (27). Elevated FOXO3 expression is associated with poor prognosis in patients with acute myeloid leukemia exhibiting normal cytogenetics, and genetic ablation of FOXO3 reduces disease burden in a murine model of chronic myeloid leukemia (28,29). Another recent study has revealed that FOXO inhibition triggers myeloid cell maturation and acute myeloid leukemia cell death (30).…”

mentioning

confidence: 99%

GSK3 Protein Positively Regulates Type I Insulin-like Growth Factor Receptor through Forkhead Transcription Factors FOXO1/3/4

Huo

Liu

Shao

et al. 2014

Background: Glycogen synthase kinase-3 (GSK3) and the O subfamily of forkhead/winged helix transcription factors (FOXO) have pro-tumor or anti-tumor roles in human cancers. Results: GSK3 up-regulates type I insulin-like growth factor receptor (IGF-IR) expression and IGF-I-induced hepatoma cell proliferation through FOXO1/3/4. Conclusion: GSK3 and FOXO promote hepatoma cell proliferation through IGF-IR. Significance: These findings inform how GSK3 and FOXO promote cell proliferation.