FOXO4
Also known as: Forkhead box O4, AFX, AFX1, MLLT7, FOXO4 protein
Not an approved product; no studies of exogenous administration found
5 notable studies · 7 references
TLDR
FOXO4 is a natural intracellular forkhead transcription factor, switched off by insulin/Akt signaling and switched on by oxidative stress, that helps senescent cells survive by binding p53; it is the biological target behind the separate FOXO4-DRI peptide, but no studies have tested FOXO4 protein itself as a treatment and it is not approved for any use.
At a Glance
Classification: Endogenous intracellular transcription factor of the forkhead box O (FOXO) family (about 500 amino acids); downstream target of PI3K-Akt signaling; regulator of stress resistance, cell-cycle arrest, apoptosis and senescence
FOXO4 is a natural human protein, a transcription factor that turns genes on and off inside the cell nucleus. It belongs to the FOXO family (FOXO1, FOXO3, FOXO4, FOXO6), the human relatives of the worm longevity gene daf-16. The FOXO4 gene was first cloned as AFX, a gene fused to MLL in certain acute leukemias. FOXO4 is controlled by: • Insulin and growth-factor signaling: the kinase Akt (PKB) phosphorylates and switches it off • Oxidative stress: Ral and JNK signaling switch it on. In senescent ("zombie") cells, FOXO4 binds p53 and helps keep those cells alive. That finding led to FOXO4-DRI, a separate synthetic peptide designed to break that interaction. This profile covers the FOXO4 protein itself, not FOXO4-DRI. No studies were found in which FOXO4 protein was given as a treatment, and no FOXO4 product is approved.
What Is FOXO4?
FOXO4 (this profile) → the full-length natural transcription factor, about 500 amino acids, working inside cells FOXO4-DRI → a short synthetic peptide made of D-amino acids in reverse order (retro-inverso), based on part of FOXO4, designed to disrupt FOXO4-p53 binding in senescent cells They are not interchangeable. FOXO4 protein is a large intracellular regulator; there is no established way for injected FOXO4 protein to reach the nucleus of target cells.
What Are Researchers Studying?
Insulin / Akt signaling
Akt (PKB) phosphorylates FOXO4 (AFX) both in vitro and in cells, and this phosphorylation blocks its transcriptional activity. This linked the insulin-PI3K-Akt pathway directly to a human daf-16 relative.
Oxidative stress response
Low-level oxidative stress (H2O2) activates the small GTPase Ral, leading to JNK-dependent phosphorylation of FOXO4 at threonines 447 and 451, moving it into the nucleus and switching it on. FOXOs regulate antioxidant genes such as manganese superoxide dismutase and catalase.
Senescence
FOXO4 levels are raised in senescent cells, where it holds p53 in the nucleus and prevents the cells from dying. A FOXO4-derived peptide that blocks this interaction caused senescent cells to die and improved fitness, fur density and kidney function in aged mice. A review summarizes how the FOXO4-p53 interaction regulates senescence.
Tumor suppression and development
Mice lacking FOXO4 alone are viable with no consistent abnormalities, but deleting FoxO1, FoxO3 and FoxO4 together causes thymic lymphomas and hemangiomas, showing the FOXOs act as redundant tumor suppressors.
How Does It Work?
Growth-factor / insulin signaling ↓ PI3K → Akt phosphorylates FOXO4 ↓ FOXO4 exported from nucleus → genes switched off. Oxidative stress ↓ Ral → JNK phosphorylates FOXO4 ↓ FOXO4 enters nucleus → stress-resistance, cell-cycle-arrest and apoptosis genes switched on. In senescent cells ↓ FOXO4 binds p53 in the nucleus ↓ restrains p53-driven apoptosis, helping senescent cells survive.
What Does the Research Show?
Human research
NONE for FOXO4 as an administered compound. Human data are genetic and cellular (for example, the AFX gene fusion in acute leukemia).
Animal research
MODERATE: knockout-mouse studies define FOXO4's in-vivo role; the FOXO4-DRI mouse study concerns the separate peptide.
In-vitro research
HIGH: extensive cell-signaling work on FOXO4 regulation by Akt, Ral/JNK and p53.
Notable Studies
Cloning and characterization of AFX, the gene that fuses to MLL in acute leukemias with a t(X;11)(q13;q23)
in-vitroJournal: Oncogene. Cloned the full AFX (FOXO4) gene: two exons encoding a 501-amino-acid forkhead-family protein, expressed in normal B and T cells, with MLL/AFX and AFX/MLL fusion transcripts present in a leukemia cell line and patient sample.
Limitations: Gene characterization study; does not address function or therapy.
View publication →Direct control of the Forkhead transcription factor AFX by protein kinase B
in-vitroJournal: Nature. Protein kinase B (Akt) phosphorylated AFX, a human ortholog of C. elegans daf-16, in vitro and in cells, inhibiting its transcriptional activity and defining a PI3K-to-nucleus signaling pathway.
Limitations: Cell-based mechanistic study.
View publication →FOXO transcription factor activation by oxidative stress mediated by the small GTPase Ral and JNK
in-vitroJournal: EMBO Journal. Low-level H2O2 activated Ral, leading to JNK-dependent phosphorylation of FOXO4 at Thr447 and Thr451, nuclear translocation and transcriptional activation; TNF-α used the same pathway.
Limitations: Cell-culture signaling study.
View publication →Disruption of forkhead transcription factor (FOXO) family members in mice reveals their functional diversification
animalJournal: Proceedings of the National Academy of Sciences of the USA. Foxo1-null embryos died from defective vascular development, while Foxo3a- and Foxo4-null mice were viable; histology of Foxo4-null mice found no consistent abnormalities.
Limitations: Single-gene knockouts may be masked by FOXO redundancy.
View publication →Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging
animalJournal: Cell. Identified FOXO4 as a key factor keeping senescent cells alive through binding p53. A FOXO4 peptide designed to disrupt this interaction caused p53 nuclear exclusion and apoptosis in senescent cells and improved fitness, fur density and kidney function in fast-aging and naturally aged mice.
Limitations: Mouse and cell study; the intervention was the FOXO4-DRI peptide, not FOXO4 protein; early findings needing independent replication.
View publication →What We Still Don't Know
• Any effect of administering FOXO4 protein (no such studies found) • Whether exogenous FOXO4 could enter cells and nuclei in a meaningful way • Whether raising or lowering FOXO4 activity would be beneficial or harmful in people, given its roles in both stress resistance and cancer biology • How FOXO4's functions differ from those of FOXO1 and FOXO3 in human tissues • Identity of any research-market product labeled "FOXO4" as distinct from FOXO4-DRI
Related Compounds
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Sources & References
- Borkhardt A et al. Cloning and characterization of AFX, the gene that fuses to MLL in acute leukemias with a t(X;11)(q13;q23). Oncogene. 1997.
- Kops GJ et al. Direct control of the Forkhead transcription factor AFX by protein kinase B. Nature. 1999.
- Essers MA et al. FOXO transcription factor activation by oxidative stress mediated by the small GTPase Ral and JNK. EMBO Journal. 2004.
- Hosaka T et al. Disruption of forkhead transcription factor (FOXO) family members in mice reveals their functional diversification. Proceedings of the National Academy of Sciences of the USA. 2004.
- Baar MP et al. Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging. Cell. 2017.
- Bourgeois B, Madl T. Regulation of cellular senescence via the FOXO4-p53 axis. FEBS Lett. 2018.
- Paik JH, et al. FoxOs are lineage-restricted redundant tumor suppressors and regulate endothelial cell homeostasis. Cell. 2007.
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