ALKBH4

ALKBH4 is an Fe(II)/2-oxoglutarate-dependent dioxygenase that governs actomyosin contractility through site-specific protein demethylation (PMID:23673617, PMID:21166655). It is a catalytically active enzyme whose iron requirement depends on coordination at a histidine-carboxylate site (PMID:21166655), and its defining substrate is monomethylated lysine-84 on actin (K84me1): by removing this mark, ALKBH4 enables non-muscle myosin II to engage actin, since myosin II binds only unmethylated actin (PMID:23673617). Through this activity ALKBH4 localizes to the actomyosin contractile ring and midbody and is required for proper cytokinesis and cell migration, with loss causing multinucleation and cleavage furrow disorganization that is rescued only by catalytically active enzyme (PMID:23673617). This function extends to development and reproduction: ALKBH4 controls contractile ring formation during zebrafish epiboly in cooperation with its partner Attractin (PMID:28924386) and is essential for synaptonemal complex formation during meiotic prophase I in spermatocytes (PMID:25153837). Beyond actin, ALKBH4 has been linked to chromatin and RNA regulation, where it competes with WDR5 to lower H3K4me3 at target promoters (PMID:32478065, PMID:38902235), modulates DNMT1-dependent cytosine methylation (PMID:34951099), demethylates 6mA DNA (PMID:37207134), and influences tRNA-derived small RNA biogenesis and translational efficiency (PMID:37507018, PMID:42052838), and it sustains GPX4 levels to confer ferroptosis resistance in a demethylase-dependent manner (PMID:42207440). The unifying biochemical principle across these activities is its 2-oxoglutarate/Fe(II) dioxygenase catalysis (PMID:23673617, PMID:21166655), though the substrate basis for its nuclear and RNA-associated roles is less defined than its actin demethylase function.

1. 2011 High

   Established that ALKBH4 is a genuine catalytically active enzyme before any substrate was known, defining its cofactor requirements.

   Evidence EPR/UV-visible spectroscopy, Fe(II)-binding mutagenesis, and in vitro 2-oxoglutarate decarboxylation assay on recombinant protein

   PMID:21166655

   Open questions at the time

   • No physiological substrate identified at this stage
   • Function of the conserved N-terminal cysteine-rich motif unresolved
2. 2013 High

   Identified actin K84me1 as the physiological substrate and connected ALKBH4 demethylase activity to myosin II engagement and cytokinesis, defining its core cellular function.

   Evidence In vitro demethylation assay, active-site mutagenesis, Co-IP, immunofluorescence, reconstitution rescue, and Alkbh4 knockout mice

   PMID:23673617

   Open questions at the time

   • Structural basis of substrate recognition not resolved
   • Embryonic lethality of full knockout limits in vivo dissection
3. 2012 Low

   Raised the possibility of a nuclear/chromatin-associated role by identifying chromatin and transcription-related interactors.

   Evidence Yeast two-hybrid screen with nuclear co-localization by immunofluorescence

   PMID:23145062

   Open questions at the time

   • Yeast two-hybrid only, no reciprocal Co-IP or functional validation
   • Interactions not linked to a demethylation activity
4. 2014 Medium

   Extended ALKBH4 function to meiosis, showing it is required for synaptonemal complex establishment in spermatocytes.

   Evidence Inducible Alkbh4 knockout mice, histology of spermatogenesis, immunofluorescence localization to nucleolar structures

   PMID:25153837

   Open questions at the time

   • Molecular substrate underlying the meiotic phenotype not identified
   • Relationship to actin demethylase activity unclear
5. 2017 Medium

   Demonstrated conservation of the actomyosin-regulatory role in vivo and identified Attractin as a functional partner that prefers the active enzyme.

   Evidence Zebrafish CRISPR maternal mutants, morpholino knockdown, immunofluorescence, yeast two-hybrid

   PMID:28924386

   Open questions at the time

   • Mechanism by which Atrn modulates demethylation not defined
   • Direct biochemical interaction not validated reciprocally
6. 2020 Medium

   Introduced a chromatin-regulatory mechanism in which ALKBH4 competes with WDR5 to lower H3K4me3 at promoters, linking it to cancer metastasis.

   Evidence Reciprocal Co-IP, ChIP, shRNA knockdown, invasion assays, and in vivo metastasis model in colorectal cancer

   PMID:32478065

   Open questions at the time

   • Whether demethylase catalytic activity is required for WDR5 competition unclear
   • Single lab, single cancer context
7. 2022 Medium

   Expanded substrate scope to nucleic acids, proposing ALKBH4 as a 6mA DNA demethylase whose stability is regulated by arsenic-modulated autophagy.

   Evidence Western blot, genetic ablation, in vitro transformation, xenograft, and autophagy inhibition

   PMID:37207134

   Open questions at the time

   • Direct enzymatic demethylation of 6mA not shown biochemically in the abstract
   • Relationship to actin substrate undefined
8. 2022 Medium

   Showed an indirect route to DNA cytosine methylation control via regulation of DNMT1 protein levels and downstream promoter methylation.

   Evidence Quantitative proteomics of knockout cells, Western blot, bisulfite sequencing in HEK293T

   PMID:34951099

   Open questions at the time

   • Mechanism by which ALKBH4 controls DNMT1 levels not defined
   • Indirect effect, no direct substrate
9. 2023 Medium

   Linked ALKBH4 to tRNA uridine modification and translational efficiency, broadening its activity to RNA metabolism.

   Evidence RNA binding assay, identification of a modified uridine, in vitro translation efficiency assay

   PMID:37507018

   Open questions at the time

   • Limited orthogonal validation of the RNA modification activity
   • In vivo relevance not established
10. 2024 Medium

    Connected the H3K4me3-lowering activity to suppression of GSDME transcription and pyroptosis resistance in gastric cancer.

    Evidence ChIP at GSDME promoter, knockdown/overexpression, proliferation and pyroptosis assays

    PMID:38902235

    Open questions at the time

    • Direct catalytic mechanism on H3K4me3 not shown
    • Single cancer model
11. 2026 Medium

    Established a demethylase-dependent role in sustaining GPX4 and conferring ferroptosis resistance in breast cancer.

    Evidence Knockdown, GPX4 overexpression rescue, ferroptosis markers, catalytically inactive mutant, xenograft

    PMID:42207440

    Open questions at the time

    • Molecular substrate connecting ALKBH4 to GPX4 levels unknown
    • Single lab
12. 2026 Medium

    Placed 5'-tsRNAGlu biogenesis downstream of ALKBH4 in a tumor-suppressive, translation-modulating axis in NSCLC.

    Evidence Proliferation/colony assays, flow cytometry, polysome profiling, Northern blot, RNA pulldown/IP, luciferase reporter, epistasis with tsRNA knockdown

    PMID:42052838

    Open questions at the time

    • Direct enzymatic step in tsRNA biogenesis not defined
    • Reconciliation with tumor-promoting roles in other cancers unresolved

• It remains unresolved how a single 2-oxoglutarate/Fe(II) dioxygenase mechanism accommodates substrates as diverse as actin lysine, 6mA DNA, and tRNA uridine, and which substrate underlies each cellular and disease phenotype.
• No unifying structural or substrate-specificity model across protein, DNA, and RNA activities
• Context-dependent tumor-suppressive versus tumor-promoting roles not reconciled
• Catalytic requirement not directly tested for several nuclear/RNA functions