Affinage

PJA2

E3 ubiquitin-protein ligase Praja-2 · UniProt O43164

Length
708 aa
Mass
78.2 kDa
Annotated
2026-04-28
19 papers in source corpus 16 papers cited in narrative 16 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PJA2 is a RING-domain E3 ubiquitin ligase that controls the amplitude and duration of multiple signalling pathways by ubiquitylating a diverse set of substrates for either proteasomal degradation or non-degradative regulatory modification. PJA2 attenuates cAMP/PKA signalling by degrading PKA regulatory subunits upon cAMP stimulation (PMID:21423175), suppresses Hippo signalling through MOB1 degradation (PMID:23652010), limits MAPK/ERK output by targeting the scaffold KSR1 (PMID:27195677), restrains Wnt/β-catenin signalling via TCF/LEF1 degradation (PMID:30021253), negatively regulates type I interferon signalling through non-degradative ubiquitylation of TYK2/JAK1 (PMID:38802340), promotes primary ciliogenesis by degrading OFD1 at the centrosome (PMID:33934390), facilitates EGFR endocytosis by ubiquitylating the AP2 adapter complex (PMID:38379085), and drives P-body assembly and translational repression through non-proteolytic ubiquitylation of the RNA helicase DDX6 (PMID:40148504). PJA2 itself is regulated at transcriptional and post-transcriptional levels, including PKA-mediated phosphorylation that activates its ligase function (PMID:21423175), epigenetic silencing via KDM5A-mediated H3K4me3 removal at its promoter (PMID:34372882), and FTO-dependent m6A demethylation that stabilizes its mRNA (PMID:34484859). Through these activities PJA2 functions as a versatile signalling rheostat in processes spanning long-term memory, ciliogenesis, receptor trafficking, innate immunity, macrophage polarization, and tumour suppression (PMID:21423175, PMID:33934390, PMID:38802340, PMID:38379085).

Mechanistic history

Synthesis pass · year-by-year structured walk · 14 steps
  1. 2011 High

    Establishing PJA2 as a cAMP-responsive E3 ligase that degrades PKA regulatory subunits resolved how cells terminate PKA holoenzyme reassembly and sustain catalytic activity during prolonged cAMP signalling, linking ubiquitin-dependent proteolysis to long-term memory formation.

    Evidence Co-IP, ubiquitylation assays, proteasome inhibitor rescue, PKA phosphorylation mapping, and mouse long-term memory assays

    PMID:21423175

    Open questions at the time
    • Whether PKA phosphorylation of PJA2 is required for all subsequent substrate interactions or is context-specific
    • Structural basis for PJA2–R subunit recognition
  2. 2013 High

    Identifying MOB1 as a PJA2 substrate established the ligase as a negative regulator of Hippo signalling and showed that PJA2-mediated proteolysis sustains glioblastoma growth, broadening its substrate repertoire beyond the PKA axis.

    Evidence Reciprocal Co-IP, in vitro ubiquitylation, proteasome inhibitor rescue, and in vivo xenograft tumour model

    PMID:23652010

    Open questions at the time
    • Whether PJA2 targets additional Hippo pathway components
    • Upstream signal that triggers MOB1 ubiquitylation
  3. 2014 High

    Demonstration that PJA2 operates within a SIK2–p35 complex to ubiquitylate phosphorylated p35 upon glucose stimulation revealed a phosphorylation-primed degron mechanism coupling nutrient sensing to insulin secretion.

    Evidence AP-MS complex identification, in vitro ubiquitylation, β-cell-specific SIK2 knockout mouse with insulin secretion phenotype

    PMID:24561619

    Open questions at the time
    • Direct in vivo confirmation using β-cell-specific PJA2 knockout
    • Whether PJA2 ubiquitylates additional CDK5-related substrates in β-cells
  4. 2016 High

    Showing that PJA2 ubiquitylates the Ras/MAPK scaffold KSR1 for degradation established a direct mechanism for attenuating ERK signalling intensity and linked this axis to embryonic stem cell pluripotency maintenance.

    Evidence Co-IP, in vitro ubiquitylation, proteasome inhibitor rescue, ERK phosphorylation readouts, ESC differentiation assays

    PMID:27195677

    Open questions at the time
    • Whether KSR2 is similarly targeted
    • Structural determinants of KSR1 recognition by PJA2
  5. 2017 Medium

    Discovery that PJA2 attaches atypical, non-degradative polyubiquitin chains to HIV-1 Tat—requiring prior Tat–P-TEFb binding—revealed a non-proteolytic ubiquitylation mode of PJA2 and a role in viral transcription elongation.

    Evidence RNAi screen, ubiquitylation assay with linkage analysis, ubiquitin acceptor site mutagenesis, HIV transcription elongation reporter

    PMID:28345603

    Open questions at the time
    • Specific ubiquitin chain linkage types remain incompletely defined
    • Independent replication in primary CD4+ T cells
    • Whether PJA2 affects latency reversal
  6. 2017 Medium

    Identification of MFHAS1 as a non-degradative substrate showed PJA2 can positively regulate innate immune signalling (TLR2–JNK/p38) and macrophage M1 polarization through ubiquitylation that does not lead to target destruction.

    Evidence In vitro pulldown, Co-IP, ubiquitylation assay, macrophage polarization readouts

    PMID:28471450

    Open questions at the time
    • Ubiquitin chain type on MFHAS1 not determined
    • In vivo confirmation of PJA2-dependent macrophage polarization
  7. 2018 Medium

    Demonstration that PJA2 ubiquitylates TCF/LEF1 for degradation extended its reach to Wnt/β-catenin signalling and embryonic stem cell fate decisions.

    Evidence Co-IP, ubiquitylation assay, Wnt reporter assay, gain/loss-of-function in stem cells

    PMID:30021253

    Open questions at the time
    • Which TCF/LEF family member is preferentially targeted
    • Independent replication outside the original lab
  8. 2021 High

    Reconstitution of a centrosomal PJA2–TBC1D31–PKA–OFD1 complex, and showing that PKA phosphorylation of OFD1 triggers its PJA2-mediated degradation to enable ciliogenesis, established a GPCR–cAMP–ubiquitin axis at the centrosome governing primary cilium formation.

    Evidence Co-IP, PLA, in vitro ubiquitylation, S735A OFD1 mutagenesis, ciliogenesis assays, in vivo Medaka fish model

    PMID:33934390

    Open questions at the time
    • Whether PJA2 targets other centrosomal ciliogenesis regulators
    • Human ciliopathy genetic evidence linking PJA2
  9. 2021 Medium

    Convergent studies on KSR1 in gastric cancer confirmed PJA2's tumour-suppressive role through ERK attenuation and uncovered upstream epigenetic regulation of PJA2 expression by KDM5A-mediated H3K4me3 removal and FTO-dependent m6A demethylation of PJA2 mRNA, placing PJA2 within transcriptional and epitranscriptomic regulatory circuits.

    Evidence ChIP, dual-luciferase reporter, CHX chase, m6A methylation and mRNA stability assays, xenograft models

    PMID:33461174 PMID:34372882 PMID:34484859

    Open questions at the time
    • Functional interplay between epigenetic and epitranscriptomic PJA2 regulation in the same cell type
    • In vivo confirmation in genetic mouse models of gastric/pancreatic cancer
  10. 2024 High

    Identification of the AP2 adapter complex as a PJA2 substrate linked the ligase to receptor endocytosis: PJA2 loss impairs EGFR clearance, amplifies mitogenic signalling, and phenocopies vascular and epithelial alterations in knockout mice, establishing PJA2 as a gatekeeper of RTK surface levels.

    Evidence Co-IP, ubiquitylation assay, endocytosis assay, PJA2 knockout mouse with EGFR/VEGFR readouts

    PMID:38379085

    Open questions at the time
    • Whether PJA2 regulates endocytosis of RTKs other than EGFR
    • Specific ubiquitin chain linkage on AP2 subunits
  11. 2024 High

    Proximity proteomics and functional screening identified TYK2 and JAK1 as PJA2 substrates undergoing non-degradative ubiquitylation that limits TYK2 phosphorylation, establishing PJA2 as a negative regulator of type I interferon/STAT signalling.

    Evidence TurboID proximity labeling–AP-MS, RNAi screen, Co-IP, ubiquitination and phosphorylation assays

    PMID:38802340

    Open questions at the time
    • Ubiquitin chain topology on TYK2/JAK1
    • In vivo consequence of PJA2 loss for antiviral immunity
  12. 2025 High

    Discovery that PJA2 non-proteolytically ubiquitylates the P-body helicase DDX6 in response to cAMP/GPCR signalling, driving P-body assembly and translational repression, revealed a new role in post-transcriptional gene regulation; an ubiquitylation-defective DDX6 mutant sustained glioblastoma growth, linking this axis to cellular senescence.

    Evidence Co-IP, in vitro ubiquitylation, DDX6 ubiquitylation-site mutagenesis, polysome profiling, P-body imaging, senescence assays

    PMID:40148504

    Open questions at the time
    • Identity of translationally repressed mRNAs critical for senescence
    • Whether PJA2 targets other P-body components
  13. 2025 High

    Mapping PJA2's RING-B-box domain as the HDAC2-binding interface and Lys90 of HDAC2 as the ubiquitylation site, with consequent de-repression of IFIT innate immune genes, connected PJA2 to chromatin-level regulation of interferon-stimulated genes and colorectal cancer suppression.

    Evidence Co-IP, PLA, domain-deletion mutagenesis, site-specific ubiquitylation (K90), ChIP, RNA-seq, AOM/DSS mouse CRC model

    PMID:39928532

    Open questions at the time
    • Whether other HDACs are PJA2 substrates
    • Crystal structure of PJA2 RBD–HDAC2 interface
  14. 2025 Medium

    Identification of CHRM3 as a PJA2 substrate whose ubiquitylation-dependent degradation suppresses TGFβ–pSMAD3 signalling extended PJA2's reach to GPCR turnover and gastric cancer progression.

    Evidence Mass spectrometry, Co-IP, ubiquitination/degradation assays, ΔRING mutant rescue, patient-derived organoids, xenograft metastasis model

    PMID:40858831

    Open questions at the time
    • Whether PJA2 degrades other muscarinic receptors
    • Independent replication outside the original study
    • Ubiquitylation site(s) on CHRM3 not mapped

Open questions

Synthesis pass · forward-looking unresolved questions
  • Despite extensive substrate cataloguing, no crystal or cryo-EM structure of PJA2 exists; the basis for its remarkably broad substrate selectivity, the determinants specifying degradative versus non-degradative ubiquitin chain assembly, and the in vivo physiological consequences of whole-organism PJA2 loss in mammals remain incompletely defined.
  • No structural model of PJA2 or any PJA2–substrate complex
  • Rules governing chain-type selectivity (K48 vs. K63 vs. atypical) unknown
  • Comprehensive phenotyping of PJA2 knockout mice beyond kidney reported only for AP2/EGFR axis

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 14 GO:0016874 ligase activity 10
Localization
GO:0005829 cytosol 3 GO:0005634 nucleus 2 GO:0005815 microtubule organizing center 1
Pathway
R-HSA-392499 Metabolism of proteins 13 R-HSA-162582 Signal Transduction 9 R-HSA-1643685 Disease 5 R-HSA-168256 Immune System 3 R-HSA-1852241 Organelle biogenesis and maintenance 1 R-HSA-5653656 Vesicle-mediated transport 1
Partners
AP2A1DDX6HDAC2KSR1MOB1AOFD1PRKAR1ATYK2
Complex memberships
PJA2–SIK2–p35 complexPJA2–TBC1D31–PKA–OFD1 centrosomal complex

Evidence

Reading pass · 16 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2011 Praja2 (PJA2) forms a stable complex with PKA regulatory (R) subunits and is phosphorylated by PKA. Rising cAMP levels promote praja2-mediated ubiquitylation and subsequent proteasomal degradation of R subunits, leading to sustained catalytic subunit activity and downstream substrate phosphorylation. This mechanism is required for efficient nuclear cAMP signalling and PKA-mediated long-term memory. Co-immunoprecipitation, ubiquitylation assays, proteasome inhibitor experiments, in vivo mouse memory assays, loss-of-function knockdown with defined phosphorylation readouts Nature cell biology High 21423175
2013 Praja2 ubiquitylates and targets MOB1 (Mob), a core component of NDR/LATS kinases and positive regulator of the Hippo cascade, for proteasomal degradation. This attenuates Hippo signalling and sustains glioblastoma growth in vivo. Co-immunoprecipitation, in vitro ubiquitylation assay, proteasome inhibitor experiments, in vivo xenograft tumor model, knockdown with defined Hippo pathway readouts Nature communications High 23652010
2014 PJA2 forms a complex with the AMPK-related kinase SIK2 and the CDK5 activator p35. Following glucose stimulation, SIK2 phosphorylates p35 at Ser91, which triggers p35 ubiquitylation by PJA2 and promotes insulin secretion. β-cell-specific SIK2 knockout leads to p35 accumulation and impaired secretion. Affinity purification-mass spectrometry (AP-MS), Co-immunoprecipitation, in vitro ubiquitylation assay, β-cell-specific knockout mouse, glucose-stimulated insulin secretion assay Nature cell biology High 24561619
2016 Praja2 acts as the E3 ubiquitin ligase that polyubiquitylates KSR1, a scaffold of the Ras/MAPK pathway, leading to its proteasomal degradation. This attenuates ERK1/2 signalling downstream of receptor stimulation, controls cancer cell growth, and is required for maintenance of mouse embryonic stem cell pluripotency. Co-immunoprecipitation, in vitro ubiquitylation assay, proteasome inhibitor rescue, overexpression/knockdown with ERK phosphorylation and colony formation readouts, mouse ESC differentiation assays Cell death & disease High 27195677
2017 PJA2 ubiquitylates the HIV-1 Tat protein with atypical, non-degradative polyubiquitin chain linkages, specifically regulating the transcription elongation step of HIV transcription. Ubiquitin acceptor sites on Tat and the ubiquitin linkage type are both variable. Proper chain assembly by PJA2 requires Tat to first bind P-TEFb. RNAi knockdown screen, in vivo ubiquitylation assay, mutational mapping of ubiquitin acceptor lysines, HIV transcription elongation reporter assay, viral replication assay Scientific reports Medium 28345603
2017 Praja2 directly binds MFHAS1 (confirmed by pulldown and co-immunoprecipitation) and promotes its non-degradative ubiquitylation. This ubiquitylation positively regulates TLR2-mediated JNK/p38 pathway activation and promotes M1 macrophage polarization. In vitro pulldown, co-immunoprecipitation, in situ immunostaining colocalization, ubiquitylation assay, macrophage polarization assays with pathway readouts Cell death & disease Medium 28471450
2018 Pja2 binds TCF/LEF1 transcription factors and promotes their ubiquitylation-dependent degradation, thereby downregulating Wnt/β-catenin signalling activity and influencing embryonic stem cell differentiation. Co-immunoprecipitation, ubiquitylation assay, Wnt reporter assay, gain- and loss-of-function in stem cells International journal of stem cells Medium 30021253
2021 Praja2 assembles a novel centrosomal complex with TBC1D31, PKA, and OFD1. Upon GPCR-cAMP stimulation, PKA phosphorylates OFD1 at Ser735, triggering OFD1 ubiquitylation and proteasomal degradation by praja2. This pathway is essential for primary ciliogenesis; a non-phosphorylatable OFD1 mutant dramatically affects cilium morphology. Disruption of this network impairs ciliogenesis in Medaka fish. Co-immunoprecipitation, proximity ligation assay, in vitro ubiquitylation assay, site-directed mutagenesis (S735A OFD1), GPCR-cAMP stimulation, ciliogenesis assays, in vivo Medaka zebrafish model The EMBO journal High 33934390
2021 PJA2 reduces KSR1 protein levels through ubiquitylation and degradation, which inhibits MEK-ERK signalling in gastric cancer cells. Overexpression of praja2 suppresses cancer cell proliferation, migration, and invasion, and inhibits tumor growth in vivo via the KSR1-MEK-ERK axis. Co-immunoprecipitation, ubiquitylation assay, proteasome inhibitor rescue (MG132), in vitro proliferation/migration/invasion assays, in vivo xenograft model Aging Medium 33461174
2021 PJA2 ubiquitylates KSR1, promoting its degradation. In the KDM5A-PJA2-KSR1 axis in gastric cancer macrophages, KDM5A suppresses PJA2 expression by removing H3K4me3 from the PJA2 promoter, thereby stabilizing KSR1 and promoting macrophage M2 polarization. ELK4 drives this axis through transcriptional activation of KDM5A. Dual luciferase reporter assay, ChIP assay, Co-immunoprecipitation, cycloheximide chase for KSR1 stability, gain- and loss-of-function assays, xenograft model Journal of translational medicine Medium 34372882
2021 FTO demethylates m6A modification on PJA2 mRNA, reducing its decay and restoring PJA2 expression. Increased PJA2 suppresses Wnt signalling and restrains proliferation, invasion, and metastasis of pancreatic cancer cells. m6A methylation assay, mRNA stability assay, Wnt signalling reporter, gain- and loss-of-function with proliferation/invasion readouts Molecular therapy. Nucleic acids Medium 34484859
2024 Praja2 forms a complex with the AP2 adapter complex and ubiquitylates it, contributing to EGFR endocytosis and clearance. Downregulation of praja2 by oncomiRs impairs EGFR endocytosis, amplifies downstream mitogenic signalling, and promotes kidney cancer cell growth. Genetic ablation of praja2 in mice upregulates EGFR and VEGFR and induces epithelial and vascular alterations in kidney tissue. Co-immunoprecipitation, ubiquitylation assay, endocytosis assay, oncomiR overexpression, praja2 restoration experiments, praja2 knockout mouse model with RTK readout Communications biology High 38379085
2024 PJA2 interacts with TYK2 and JAK1 within the type I IFN signalling cascade, promotes their non-degradative ubiquitination, and limits the activating phosphorylation of TYK2, thereby restraining downstream STAT signalling and acting as a negative regulator of IFN signalling. TurboID proximity labeling coupled with affinity purification-mass spectrometry, functional RNAi screen, co-immunoprecipitation, ubiquitination assays, phosphorylation assays for TYK2/STAT Nature communications High 38802340
2025 Praja2 forms a multimeric complex with the RNA helicase DDX6 and promotes non-proteolytic polyubiquitylation of DDX6 in response to cAMP/GPCR signalling, inducing P-body assembly and translational repression of target RNAs. Genetic inactivation of praja2 reshapes DDX6/mRNA complexes and polysomes, promoting cellular senescence and GBM growth arrest. An ubiquitylation-defective DDX6 mutant suppresses P-body assembly and sustains GBM growth. Co-immunoprecipitation, in vitro ubiquitylation assay, site-directed mutagenesis (ubiquitylation-defective DDX6), polysome profiling, P-body imaging, cAMP stimulation, loss-of-function with senescence readout EMBO reports High 40148504
2025 PJA2 recognizes HDAC2 via its RING-B-box domain (RBD), binds the N-terminal of HDAC2, and facilitates its ubiquitylation at Lys90, promoting HDAC2 degradation. This de-represses the IFIT family of interferon-induced genes, suppressing colorectal cancer progression. HDAC2 reciprocally regulates PJA2 expression, forming a positive feedback loop. Co-immunoprecipitation, proximity ligation assay, ubiquitylation assay, ChIP, RNA-seq, AOM/DSS mouse CRC model, colony formation assay, domain-deletion mutagenesis Advanced science High 39928532
2025 PJA2 (RING E3 ligase) directly interacts with CHRM3 (muscarinic acetylcholine receptor M3), ubiquitinates it, and promotes its degradation, thereby suppressing downstream TGFβ-pSMAD3 signalling and gastric tumor cell progression. The catalytically dead ΔRING PJA2 mutant cannot suppress CHRM3-driven organoid growth. Mass spectrometry, co-immunoprecipitation, ubiquitination assay, degradation assay, patient-derived organoids, ΔRING mutant rescue, xenograft metastasis model British journal of cancer Medium 40858831

Source papers

Stage 0 corpus · 19 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2013 Proteolysis of MOB1 by the ubiquitin ligase praja2 attenuates Hippo signalling and supports glioblastoma growth. Nature communications 102 23652010
2011 Control of PKA stability and signalling by the RING ligase praja2. Nature cell biology 78 21423175
2014 Role of the SIK2-p35-PJA2 complex in pancreatic β-cell functional compensation. Nature cell biology 69 24561619
2017 Ubiquitylation of MFHAS1 by the ubiquitin ligase praja2 promotes M1 macrophage polarization by activating JNK and p38 pathways. Cell death & disease 63 28471450
2021 ELK4 promotes the development of gastric cancer by inducing M2 polarization of macrophages through regulation of the KDM5A-PJA2-KSR1 axis. Journal of translational medicine 41 34372882
2021 The TBC1D31/praja2 complex controls primary ciliogenesis through PKA-directed OFD1 ubiquitylation. The EMBO journal 33 33934390
2017 PJA2 ubiquitinates the HIV-1 Tat protein with atypical chain linkages to activate viral transcription. Scientific reports 27 28345603
2021 m6A demethylase FTO suppresses pancreatic cancer tumorigenesis by demethylating PJA2 and inhibiting Wnt signaling. Molecular therapy. Nucleic acids 26 34484859
2016 praja2 regulates KSR1 stability and mitogenic signaling. Cell death & disease 25 27195677
2012 Expression of the ring ligase PRAJA2 in thyroid cancer. The Journal of clinical endocrinology and metabolism 18 22948757
2018 Pja2 Inhibits Wnt/β-catenin Signaling by Reducing the Level of TCF/LEF1. International journal of stem cells 16 30021253
2021 Praja2 suppresses the growth of gastric cancer by ubiquitylation of KSR1 and inhibiting MEK-ERK signal pathways. Aging 12 33461174
2019 CD1d- and PJA2-related immune microenvironment differs between invasive breast carcinomas with and without a micropapillary feature. BMC cancer 11 30651076
2024 Proximal protein landscapes of the type I interferon signaling cascade reveal negative regulation by PJA2. Nature communications 8 38802340
2024 Downregulation of praja2 restrains endocytosis and boosts tyrosine kinase receptors in kidney cancer. Communications biology 7 38379085
2025 PJA2 Suppresses Colorectal Cancer Progression by Controlling HDAC2 Degradation and Stability. Advanced science (Weinheim, Baden-Wurttemberg, Germany) 6 39928532
2024 ZC3H13 promotes autophagy in bladder cancer through m6A methylation modification of PJA2 and ubiquitination of KSR1. Human cell 4 39614918
2025 Praja2 controls P-body assembly and translation in glioblastoma by non-proteolytic ubiquitylation of DDX6. EMBO reports 2 40148504
2025 Aberrant PJA2-CHRM3 signaling creates a therapeutic vulnerability in gastric tumor. British journal of cancer 0 40858831