Affinage

PHKG2

Phosphorylase b kinase gamma catalytic chain, liver/testis isoform · UniProt P15735

Length
406 aa
Mass
46.4 kDa
Annotated
2026-06-10
16 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 4/5 claims corpus-supported (80%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PHKG2 encodes the liver/testis-specific catalytic gamma subunit of phosphorylase kinase, the enzyme that activates glycogen phosphorylase to drive hepatic glycogen breakdown (PMID:8896567, PMID:34083142). It is the predominant catalytic gamma isoform in liver, erythrocytes, and non-muscle tissues, and its activity resides in a conserved catalytic core whose disruption by missense substitutions, frameshifts, and splice defects abolishes function (PMID:8896567, PMID:9245685). Loss-of-function mutations cause autosomal-recessive liver-specific phosphorylase kinase deficiency (GSD IX γ2), with knockout mice recapitulating decreased hepatic phosphorylase kinase activity, liver glycogen accumulation, and early fibrosis without glycogen build-up in muscle, brain, kidney, or heart, establishing the tissue-restricted role of the gene (PMID:34083142); severe truncating mutations correlate with progression to cirrhosis (PMID:9384616). Beyond glycogen metabolism, PHKG2 acts as a kinase in ferroptosis regulation, sitting downstream of TP53 (which activates it) and NRF2 (which represses it): it phosphorylates PPP1R3B to disrupt PPP1R3B–PP1C interaction and enhance PP1 activity, driving NRF2 dephosphorylation, nuclear export, and GPX4 suppression, and it also promotes ALOX5-dependent lipid peroxidation and ferritinophagy-driven iron release (PMID:36948350, PMID:39169204, PMID:40885710). In esophageal squamous cell carcinoma, PHKG2 phosphorylates IGF2BP3 at T225/T306 to enhance its phase separation and m6A-dependent stabilization of CXCL8 mRNA, promoting cisplatin resistance and an immunosuppressive microenvironment (PMID:42161921).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 1996 High

    Established that PHKG2 is the gene whose loss causes liver-specific phosphorylase kinase deficiency, identifying the functionally critical catalytic core of the gamma subunit.

    Evidence Sequencing of PHKG2 in patients with autosomal liver glycogenosis and the gsd rat, finding non-conservative substitutions at conserved catalytic residues and a frameshift

    PMID:8896567

    Open questions at the time
    • Catalytic mechanism and substrate specificity not biochemically dissected
    • Did not address tissue-specific regulation of the isoform
  2. 1997 Medium

    Showed that splice-disrupting mutations, not only coding mutations, can ablate PHKG2 function by removing the catalytic site.

    Evidence Exon-specific sequencing of a IVS4+1 g→a splice mutation causing exon 4 skipping and a premature stop in affected siblings

    PMID:9245685

    Open questions at the time
    • Single family
    • No direct enzyme activity quantification
  3. 1998 Medium

    Defined the genomic architecture of PHKG2 and linked truncating mutation severity to clinical progression toward cirrhosis.

    Evidence Genomic sequencing establishing 10-exon structure conserved with PHKG1, plus mutation identification in cirrhotic patients

    PMID:9384616

    Open questions at the time
    • Genotype–phenotype correlation based on limited patients
    • Mechanism linking enzyme loss to fibrosis not established
  4. 2021 High

    Provided definitive in vivo proof that PHKG2 encodes the liver-specific catalytic subunit required for hepatic glycogen breakdown, with strict tissue restriction.

    Evidence Phkg2-/- mouse with reduced liver phosphorylase kinase activity, hepatic glycogen accumulation, and early fibrosis, with no glycogen accumulation in other organs

    PMID:34083142

    Open questions at the time
    • Did not address non-metabolic roles
    • Mechanism of fibrosis development not resolved
  5. 2022 Medium

    Confirmed that newly identified clinical variants are loss-of-function by direct enzymatic readout.

    Evidence Phosphorylase b kinase activity assay on patient samples carrying F233S and R320DfsX5

    PMID:35549678

    Open questions at the time
    • Single case report
    • No structural rationale for activity loss
  6. 2023 Medium

    Introduced a non-metabolic role for PHKG2 in promoting ferroptosis via lipid peroxidation.

    Evidence Overexpression/knockdown in H. pylori-positive gastric cancer cells showing PHKG2 upregulates ALOX5 and enhances RSL3-induced ferroptosis

    PMID:36948350

    Open questions at the time
    • Mechanism connecting PHKG2 kinase activity to ALOX5 induction unknown
    • Cell-line only, abstract-level detail
  7. 2024 Medium

    Placed PHKG2 downstream of NRF2 transcriptional repression and tied it to ferritinophagy-driven iron release and radiotherapy sensitivity.

    Evidence Transcriptomics, in vitro overexpression/knockdown, iron and ferritinophagy assays, and in vivo tumor models in NSCLC

    PMID:39169204

    Open questions at the time
    • Direct NRF2 binding at PHKG2 promoter not shown
    • How PHKG2 mechanistically triggers ferritinophagy unresolved
  8. 2025 Medium

    Defined a kinase-based ferroptosis mechanism: TP53→PHKG2→PPP1R3B/PP1→NRF2 export→GPX4 suppression, identifying PPP1R3B as a PHKG2 substrate.

    Evidence Phosphorylation assays (PPP1R3B T225/T306), Co-IP showing disrupted PPP1R3B–PP1C interaction, NRF2 export and GPX4 transcription assays, and xenografts in HNSCC

    PMID:40885710

    Open questions at the time
    • Single lab
    • Direct PP1 dephosphorylation of NRF2 not reconstituted in vitro
  9. 2025 Medium

    Demonstrated that a deep intronic non-coding variant is causal for PHKG2 deficiency and is correctable by splice-switching oligonucleotides.

    Evidence WGS, short/long-read RNA-seq in patient blood, CRISPR-installed variant in HEK293T, and antisense oligonucleotide rescue (preprint)

    PMID:bio_10.1101_2025.05.14.654043

    Open questions at the time
    • Preprint, not peer-reviewed
    • Therapeutic rescue shown only in cell model
  10. 2026 Medium

    Extended PHKG2 kinase signaling to cancer immunoevasion and chemoresistance through IGF2BP3 phosphorylation and CXCL8 mRNA stabilization.

    Evidence CRISPR screen, phosphorylation assays (IGF2BP3 T225/T306), phase separation and mRNA stability assays, macrophage/T-cell assays, and prexasertib inhibition in ESCC

    PMID:42161921

    Open questions at the time
    • Single lab
    • Selectivity of prexasertib for PHKG2 not established

Open questions

Synthesis pass · forward-looking unresolved questions
  • How a single liver-glycogenolytic kinase acquires its diverse oncogenic substrates (PPP1R3B, IGF2BP3) and whether these roles operate in normal physiology remains unresolved.
  • No structural basis for substrate selectivity
  • No unifying model linking metabolic and ferroptosis/cancer functions
  • Physiological relevance of ferroptosis roles outside tumor contexts unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 4 GO:0016740 transferase activity 2
Pathway
R-HSA-5357801 Programmed Cell Death 3 R-HSA-1430728 Metabolism 2
Partners
Complex memberships
phosphorylase kinase

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1996 Mutations in PHKG2 (the testis/liver isoform of the phosphorylase kinase catalytic gamma subunit) cause autosomal liver-specific phosphorylase kinase deficiency. Non-conservative amino acid replacements (V106E, G189E, D215N) at highly conserved residues within the catalytic core of the kinase domain, as well as a frameshift mutation, abolish normal function; PHKG2 is identified as the predominant catalytic gamma subunit isoform in liver, erythrocytes, and non-muscle tissues. Sequencing of PHKG2 in human patients with autosomal liver glycogenosis and in the gsd rat strain; mutation analysis identifying frameshift and missense mutations in conserved catalytic core residues Nature genetics High 8896567
1997 A splice-site mutation (IVS4+1 g→a) in PHKG2 causes skipping of exon 4, resulting in a frameshift starting at nucleotide 272, a premature stop codon after 32 additional amino acids, and subsequent loss of the catalytic site, causing liver phosphorylase kinase deficiency. Exon-specific amplification and direct sequencing of PHKG2 genomic DNA; functional inference from loss of catalytic site due to frameshift Biochemical and biophysical research communications Medium 9245685
1998 The human PHKG2 gene spans 9.5 kb, is divided into 10 exons, and intron positions are highly conserved with PHKG1 (muscle isoform), indicating conserved gene structure between the two gamma subunit isoforms. Translation-terminating mutations (277delC and Arg44ter) in PHKG2 are associated with progression to liver cirrhosis, suggesting that the severity of PHKG2 loss-of-function correlates with cirrhosis risk. Genomic sequencing and gene structure determination; mutation identification in cirrhotic patients Human molecular genetics Medium 9384616
2021 Knockout of Phkg2 in mice (Phkg2-/- model) leads to significantly decreased liver phosphorylase kinase enzyme activity, increased liver glycogen accumulation, elevated liver:body weight ratio, elevated serum liver markers, and early liver fibrosis, with no glycogen accumulation in brain, muscle, kidney, or heart — establishing that PHKG2 encodes the liver-specific catalytic subunit of phosphorylase kinase responsible for hepatic glycogen breakdown. Targeted gene knockout mouse model; enzyme activity assays, glycogen content measurement, histology (H&E, Masson's Trichrome), serum liver markers, urinary Glc4 biomarker Molecular genetics and metabolism High 34083142
2022 Novel PHKG2 mutations F233S and R320DfsX5 each lead to a decrease in key phosphorylase b kinase enzyme activity, as demonstrated by functional experiments in patient-derived samples. Functional enzyme activity assay on patient samples with novel PHKG2 mutations BMC pediatrics Medium 35549678
2023 PHKG2 promotes RSL3-induced ferroptosis in H. pylori-positive gastric cancer cells by upregulating the lipoxygenase ALOX5 expression, thereby enhancing lipid peroxidation. Cell-based overexpression/knockdown experiments in gastric cancer cell lines; measurement of ferroptosis markers and ALOX5 expression Archives of biochemistry and biophysics Medium 36948350
2024 NRF2 transcriptionally represses PHKG2; overexpression of PHKG2 promotes ferritinophagy, elevates intracellular iron levels, and induces mitochondrial stress-dependent ferroptosis in NSCLC cells under radiotherapy. Targeting NRF2 upregulates PHKG2 and reverses radiotherapy resistance. High-throughput transcriptome sequencing, Lasso regression, in vitro overexpression/knockdown, ferritinophagy and iron level assays, mitochondrial function assays, in situ transplantation tumor models in vivo NPJ precision oncology Medium 39169204
2025 TP53 transcriptionally activates PHKG2; PHKG2 phosphorylates PPP1R3B at specific residues, disrupting its interaction with PP1C and thereby enhancing PP1 phosphatase activity; activated PP1 dephosphorylates NRF2, promoting NRF2 nuclear export and suppressing GPX4 transcription, which sensitizes HNSCC cells to ferroptosis. This defines a TP53/PHKG2–PP1–NRF2 signaling axis. In vitro and in vivo overexpression experiments; phosphorylation assays demonstrating PHKG2 phosphorylates PPP1R3B (T225, T306); co-immunoprecipitation showing disruption of PPP1R3B–PP1C interaction; NRF2 nuclear export assays; GPX4 transcription assays; lipid peroxidation measurement; xenograft tumor models Cell death & disease Medium 40885710
2026 PHKG2 mediates cisplatin resistance in ESCC by phosphorylating IGF2BP3 at residues T225 and T306; this phosphorylation enhances IGF2BP3 phase separation, stabilizing CXCL8 mRNA in an m6A-dependent manner; increased CXCL8 secretion then promotes M2 macrophage polarization and suppresses CD8+ T cell cytotoxicity. Pharmacological inhibition of PHKG2 by prexasertib curtails ESCC proliferation and enhances cisplatin sensitivity. CRISPR/Cas9 knockout library functional screening; transcriptomic profiling; in vitro phosphorylation assays identifying IGF2BP3 T225/T306 as PHKG2 substrates; phase separation assays; mRNA stability assays; macrophage polarization assays; in vivo validation; pharmacological inhibition with prexasertib Cell death & disease Medium 42161921
2025 A deep intronic variant in PHKG2 causes aberrant splicing (confirmed by short-read and long-read RNA-seq in patient blood and a CRISPR-edited HEK293T cell model), leading to PHKG2 deficiency consistent with GSD IX γ2. Antisense splice-switching oligonucleotides reverse the aberrant splicing in the cell model, demonstrating the causal role of this non-coding variant in PHKG2 dysfunction. Whole genome sequencing; short-read and long-read RNA-seq on patient blood; CRISPR-installed variant in HEK293T cells; antisense oligonucleotide rescue experiments bioRxivpreprint Medium bio_10.1101_2025.05.14.654043

Source papers

Stage 0 corpus · 16 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1996 Mutations in the testis/liver isoform of the phosphorylase kinase gamma subunit (PHKG2) cause autosomal liver glycogenosis in the gsd rat and in humans. Nature genetics 67 8896567
1998 Liver glycogenosis due to phosphorylase kinase deficiency: PHKG2 gene structure and mutations associated with cirrhosis. Human molecular genetics 50 9384616
2013 Variability of disease spectrum in children with liver phosphorylase kinase deficiency caused by mutations in the PHKG2 gene. Molecular genetics and metabolism 45 24389071
2003 Severe phenotype of phosphorylase kinase-deficient liver glycogenosis with mutations in the PHKG2 gene. Pediatric research 33 12930917
2013 Novel PHKG2 mutation causing GSD IX with prominent liver disease: report of three cases and review of literature. European journal of pediatrics 23 24326380
2023 PHKG2 regulates RSL3-induced ferroptosis in Helicobacter pylori related gastric cancer. Archives of biochemistry and biophysics 21 36948350
1997 Autosomal recessive liver phosphorylase kinase deficiency caused by a novel splice-site mutation in the gene encoding the liver gamma subunit (PHKG2). Biochemical and biophysical research communications 17 9245685
2018 PHKG2 mutation spectrum in glycogen storage disease type IXc: a case report and review of the literature. Journal of pediatric endocrinology & metabolism : JPEM 16 29360628
2024 Targeting Nrf2/PHKG2 axis to enhance radiosensitivity in NSCLC. NPJ precision oncology 12 39169204
2021 Characterization of liver GSD IX γ2 pathophysiology in a novel Phkg2-/- mouse model. Molecular genetics and metabolism 8 34083142
2020 Variability of clinical and biochemical phenotype in liver phosphorylase kinase deficiency with variants in the phosphorylase kinase (PHKG2) gene. Journal of pediatric endocrinology & metabolism : JPEM 8 32697758
2022 A very rare case report of glycogen storage disease type IXc with novel PHKG2 variants. BMC pediatrics 4 35549678
2026 Decoding genetic complexity in glycogen storage diseases: three novel variants in SLC37A4, GAA, and PHKG2 identified in an Iranian cohort. Neuromuscular disorders : NMD 0 41771245
2026 PHKG2 confers resistance of ESCC to cisplatin and enhances CXCL8-dependent immunosuppression to exacerbate tumorigenesis. Cell death & disease 0 42161921
2025 A novel sequence of the PHKG2 mutation associated with the first case of glycogen storage diseases type IXc in Syria: a case report and review of literature. Journal of medical case reports 0 40615918
2025 Transcriptional activation of PHKG2 by TP53 promotes ferroptosis through nuclear export of NRF2 in head and neck squamous cell carcinoma. Cell death & disease 0 40885710

Missed literature

Know a paper Affinage missed for PHKG2? Flag it for the maintainers and the community.

No submissions yet.