Disease relevance of FOXO4

• Interestingly, FOXO4 down-regulates the HIF-1 alpha protein levels, consistent with the lack of hypoxia responsiveness [1].
• FOXO3 and FOXO4 genes are fused to MLL gene in hematological malignancies [2].
• MLL-AFX is a fusion gene created by t(X;11) chromosomal translocations in a subset of acute leukemias of either myeloid or lymphoid derivation [3].
• We demonstrate here that forced expression of MLL-AFX enhances the self-renewal of hematopoietic progenitors in vitro and induces acute myeloid leukemias after long latencies in syngeneic recipient mice [3].
• It is noteworthy that the t(X;11)(q13;q23) in the KARPAS 45 cell line and in one acute nonlymphoblastic leukemia (ANLL) disrupts the forkhead domain of the AFX protein exactly at the same amino acids as does the t(2;13)(q35;q14) in case of the FKHR protein [4].

High impact information on FOXO4

• The Forkhead transcription factors AFX, FKHR and FKHR-L1 are orthologues of DAF-16, a Forkhead factor that regulates longevity in Caenorhabditis elegans [5].
• We conclude that AFX-like proteins are involved in cell-cycle regulation and that inactivation of these proteins is an important step in oncogenic transformation [5].
• In addition, phosphorylation of AFX by protein kinase B inhibits its transcriptional activity [6].
• The probable human orthologues of DAF-16, FKHR and AFX, may also act downstream of insulin signalling and cooperate with TGF-beta effectors in mediating metabolic regulation [7].
• Here we show that, in contrast to insulin signalling, low levels of oxidative stress generated by treatment with H2O2 induce the activation of FOXO4 [8].

Biological context of FOXO4

• AFX-like Forkhead transcription factors, which are controlled by phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) signaling, are involved in regulating cell cycle progression and cell death [9].
• The forkhead transcription factor FOXO4 induces the down-regulation of hypoxia-inducible factor 1 alpha by a von Hippel-Lindau protein-independent mechanism [1].
• These results indicate that phosphorylation at Thr32 and Ser197 is indispensable, whereas that at Ser262 is not critical, for regulation of the nuclear localization and transcriptional activity of FOXO4 [10].
• AFX (also called Foxo4), a member of mammalian FOXO forkhead transcription factors, is the homolog of DAF-16, which contributes longevity and oxidative stress in Caenorhabditis elegans [11].
• Taken together, these results demonstrate that CBP-induced acetylation of AFX is a novel modification mechanism by which AFX keeps the transcriptional activity mitigating in the nucleus [11].

Anatomical context of FOXO4

• AFX was recovered as a phosphoprotein from transfected COS-7 cells growing in the presence of FBS, and the phosphorylation was eliminated by wortmannin, a potent inhibitor of phosphatidylinositol (PI) 3-kinase [12].
• We have generated mouse myoblastic C2C12 cell lines in which expression of a constitutively active form of AFX (AFX-TM) is inducible by Cre-mediated recombination at loxP sites [13].
• The role of different alpha and gamma subunit subtypes in modulation of IGABA by ALP and AFX was investigated using recombinant GABAA receptor isoforms expressed in Xenopus oocytes [14].
• SUBJECTS AND METHODS: We studied 27 patients with amaurosis fugax (AFX), branch retinal artery occlusion (BRAO), central retinal artery occlusion (CRAO) and anterior ischaemic optic neuropathy (AION) [15].

Associations of FOXO4 with chemical compounds

• Furthermore, TSA suppressed the expression of p27kip1 gene induced by AFX in HEK293T cells [11].
• Here, we show that CREB-binding protein (CBP) interacts with AFX via CH1 region and acetylates it at the three lysine residues (K186, K189, and K408) [11].
• Upon treatment of cells with H2O2, the small GTPase Ral is activated and this results in a JNK-dependent phosphorylation of FOXO4 on threonine 447 and threonine 451 [8].
• Here, we applied the FOXO4 gene as a novel anticancer agent for HER2-overexpressing cells under the control of a tetracycline (tet)-regulated gene expression system [16].
• Furthermore, naltrindole treatment not only reduced the phosphorylation of the Akt/PKB upstream kinase phosphoinositide-dependent kinase-1, but also its downstream effectors glycogen synthase kinase-3beta and the Forkhead transcription factors AFX and FKHR [17].

Physical interactions of FOXO4

• Although AFX interacts with the KIX domain of CBP, it does not interact with SRC and does not respond to glucocorticoids or insulin [18].
• In contrast, mammalian SIRT1 was found to bind to FOXO4, catalyze its deacetylation in an NAD-dependent manner, and thereby increase its transactivation activity [19].

Regulatory relationships of FOXO4

• The activity of FOXO4 is suppressed or enhanced by SIRT1 inhibitor, nicotinamide, or its activator, resveratrol, respectively [19].
• The forkhead transcription factor AFX activates apoptosis by induction of the BCL-6 transcriptional repressor [20].

Other interactions of FOXO4

• Regulation of intracellular localization and transcriptional activity of FOXO4 by protein kinase B through phosphorylation at the motif sites conserved among the FOXO family [10].
• Compared to the coexpression of CBP wild-type, a HAT activity-deficient mutant (DeltaHAT) efficiently leads the cooperative activation of AFX transcription in HepG2 cells [11].
• Furthermore, 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR), an AMP-activated protein kinase activator, repressed AFX zeta-dependent reporter activation [21].
• In one such case, RT-PCR analysis of candidate partners identified a fusion of PAX3 to AFX, which is highly similar in structure and function to FKHR [22].
• Therefore, AF6q21, AFX, and FKHR could define a new FH subfamily particularly involved in human malignancies [23].

Analytical, diagnostic and therapeutic context of FOXO4

• Analytical gel filtration and sedimentation equilibrium experiments indicate that doubly phosphorylated FOXO4 and 14-3-3zeta form a complex with 1:2 molar stoichiometry and a K(D) of less than 30 nM [24].
• With the exception of AFX, the use of anti-S100A6 does not appear to offer added benefit over anti-factor XIIIa in the differential diagnosis of fibrohistiocytic lesions [25].

References