Affinage

PJA2

E3 ubiquitin-protein ligase Praja-2 · UniProt O43164

Length
708 aa
Mass
78.2 kDa
Annotated
2026-06-10
20 papers in source corpus 16 papers cited in narrative 16 extracted findings
Cross-family judge vs UniProt: tie faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PJA2 (praja2) is a RING-type E3 ubiquitin ligase that integrates cAMP/PKA signaling with the proteostatic control of diverse signaling effectors (PMID:21423175). Anchored to PKA through stable binding of its regulatory (R) subunits, praja2 is itself phosphorylated by PKA and, upon cAMP elevation, ubiquitylates R subunits to drive their proteolysis, liberating catalytic subunit activity and sustaining nuclear cAMP signaling and PKA-dependent long-term memory (PMID:21423175). From this signaling hub praja2 ubiquitylates and degrades a series of substrates to tune growth and tumor-suppressor pathways: MOB1, attenuating Hippo signaling and sustaining glioblastoma growth (PMID:23652010); the Ras/MAPK scaffold KSR1, dampening ERK1/2 signaling in cancer cells and embryonic stem cells (PMID:27195677, PMID:33461174); and the muscarinic receptor CHRM3, suppressing TGFβ–pSMAD3 signaling in gastric cancer in a manner requiring an intact RING domain (PMID:40858831). Praja2 couples PKA phosphorylation to substrate destruction in a centrosomal complex with TBC1D31, PKA, and OFD1, where PKA phosphorylation of OFD1 at Ser735 licenses its praja2-dependent proteolysis to permit primary ciliogenesis (PMID:33934390). Beyond degradation, praja2 catalyzes non-degradative ubiquitylation: it modifies DDX6 downstream of GPCR-cAMP signaling to promote P-body assembly and translational repression (PMID:40148504), modifies MFHAS1 to potentiate TLR2-driven JNK/p38 signaling and M1 macrophage polarization (PMID:28471450), modifies AP2 adapter subunits to support receptor endocytosis and EGFR clearance (PMID:38379085), and modifies JAK1/TYK2 to restrain type I interferon STAT1/STAT2 signaling (PMID:38802340). Additional substrates include p35/CDK5R1, degraded downstream of SIK2 phosphorylation to drive insulin secretion and β-cell compensation (PMID:24561619), and HDAC2, degraded to relieve transcriptional repression of IFIT genes in colorectal cancer (PMID:39928532).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 2011 High

    Established praja2 as a PKA-associated E3 ligase that closes a feedback loop on cAMP signaling, answering how PKA activity is sustained after stimulation.

    Evidence Co-IP, in vivo phosphorylation, and ubiquitylation assays with a behavioral long-term memory readout

    PMID:21423175

    Open questions at the time
    • Ubiquitin chain linkage on R subunits not defined
    • Selectivity among PKA R subunit isoforms not resolved
  2. 2013 High

    Showed praja2 attenuates the Hippo tumor-suppressor cascade by degrading MOB1, extending its role to growth control in cancer.

    Evidence Co-IP, ubiquitylation and degradation assays, and in vivo glioblastoma xenograft models

    PMID:23652010

    Open questions at the time
    • Whether MOB1 degradation is cAMP/PKA-coupled not established
    • Direct E3 catalysis on MOB1 vs adapter-mediated not separated
  3. 2014 High

    Identified a SIK2–p35–praja2 axis linking glucose stimulation to ubiquitylation of p35, defining a physiological role in insulin secretion.

    Evidence AP-MS, Co-IP, in vitro ubiquitylation with site-directed mutagenesis, and β-cell-specific knockout mice

    PMID:24561619

    Open questions at the time
    • Degradative vs non-degradative fate of ubiquitylated p35 not detailed
    • How SIK2 phosphorylation creates the praja2 recognition signal unclear
  4. 2016 High

    Defined praja2 as the E3 ligase degrading the Ras/MAPK scaffold KSR1, linking it to ERK pathway attenuation and pluripotency control.

    Evidence Co-IP, in vivo ubiquitylation assays, and loss/gain-of-function in cancer cells and embryonic stem cells

    PMID:27195677

    Open questions at the time
    • Ubiquitylation acceptor lysines on KSR1 not mapped
    • Regulation of this event by upstream cAMP not addressed
  5. 2017 Medium

    Demonstrated that praja2 also performs non-degradative ubiquitylation, modifying MFHAS1 and HIV-1 Tat to regulate signaling and transcription rather than turnover.

    Evidence Pulldown/Co-IP for MFHAS1 with macrophage polarization assays; RNAi, ubiquitylation assays, and lysine/linkage mutagenesis for Tat with transcription elongation readouts

    PMID:28345603 PMID:28471450

    Open questions at the time
    • Ubiquitin chain topology on MFHAS1 not characterized
    • How non-degradative chains alter Tat or MFHAS1 function mechanistically unresolved
    • Single-lab findings
  6. 2018 Medium

    Extended substrate range to TCF/LEF1, implicating praja2 in downregulation of Wnt/β-catenin signaling.

    Evidence Co-IP, ubiquitylation assays, and Wnt reporter assays with overexpression/knockdown

    PMID:30021253

    Open questions at the time
    • Direct vs indirect ubiquitylation not separated
    • No in vivo confirmation
  7. 2021 High

    Showed praja2 couples PKA phosphorylation of OFD1 to its proteolysis within a centrosomal complex, defining a function in primary ciliogenesis.

    Evidence Co-IP, ubiquitylation assays, OFD1 S735A mutagenesis, cycloheximide chase, and a Medaka fish ciliogenesis model

    PMID:33934390

    Open questions at the time
    • Role of TBC1D31 in substrate presentation not fully defined
    • Connection to human ciliopathy disease not established in this corpus
  8. 2021 Medium

    Independently confirmed praja2-mediated KSR1 degradation in gastric cancer and connected loss of PJA2 to KSR1 accumulation and M2 macrophage polarization through an ELK4–KDM5A epigenetic axis.

    Evidence Co-IP, ubiquitylation and cycloheximide-chase assays, ChIP/luciferase reporters, and xenograft models

    PMID:33461174 PMID:34372882

    Open questions at the time
    • Whether KSR1 accumulation alone drives macrophage polarization not isolated
    • Single-lab transcriptional regulation circuit
  9. 2024 Medium

    Revealed praja2 functions in receptor endocytosis and interferon restraint, ubiquitylating AP2 adapter subunits to promote EGFR clearance and non-degradatively modifying JAK1/TYK2 to limit STAT activation.

    Evidence Co-IP, ubiquitylation/endocytosis assays and a knockout mouse for AP2/EGFR; TurboID proximity labeling MS, RNAi screen, and phosphorylation analysis for JAK1/TYK2

    PMID:38379085 PMID:38802340

    Open questions at the time
    • Direct AP2 subunit acceptor sites not mapped
    • Mechanism by which non-degradative JAK1/TYK2 ubiquitylation blocks activating phosphorylation unresolved
    • Single-lab studies
  10. 2025 Medium

    Expanded the non-degradative repertoire to DDX6 (P-body assembly and translational repression downstream of cAMP) and added degradative substrates HDAC2 (relief of IFIT repression) and CHRM3 (suppression of TGFβ signaling).

    Evidence Co-IP, ubiquitylation assays with defective mutants, polysome profiling for DDX6; domain mapping, K90 mutagenesis, PLA, ChIP, RNA-seq and AOM/DSS model for HDAC2; MS, ΔRING mutant, organoids and xenografts for CHRM3

    PMID:39928532 PMID:40148504 PMID:40858831

    Open questions at the time
    • How cAMP directs the degradative vs non-degradative outcome on different substrates not unified
    • Each substrate validated in a single lab
    • Tissue-specific selectivity of substrate choice unexplained
  11. 2026 Low

    Proposed praja2 degrades p53 via K48-linked polyubiquitination downstream of ERCC6L to promote lung adenocarcinoma metastasis.

    Evidence Co-IP and K48-linkage ubiquitylation assays with an ERCC6L-knockout metastasis model

    PMID:42063149

    Open questions at the time
    • No mutagenesis of PJA2 catalytic activity to prove direct effect
    • Acceptor lysines on p53 not mapped
    • Not independently confirmed

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unknown what molecular determinants direct praja2 between degradative and non-degradative ubiquitylation outcomes and how substrate selection is dictated across tissues and signaling contexts.
  • No structural model of praja2 RING engaging substrates
  • Ubiquitin chain linkage rules for distinct substrates not systematized
  • Determinants of cAMP-coupled vs cAMP-independent substrate choice undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 9 GO:0016740 transferase activity 6 GO:0016874 ligase activity 4
Localization
GO:0005815 microtubule organizing center 1
Pathway
R-HSA-392499 Metabolism of proteins 6 R-HSA-162582 Signal Transduction 5 R-HSA-1640170 Cell Cycle 2 R-HSA-168256 Immune System 2 R-HSA-5653656 Vesicle-mediated transport 1 R-HSA-8953854 Metabolism of RNA 1
Partners
DDX6HDAC2KSR1MOB1OFD1PRKAR (PKA R SUBUNITS)SIK2TYK2
Complex memberships
AP2 adapter complexSIK2–p35 complexTBC1D31–PKA–OFD1 centrosomal complexpraja2–PKA holoenzyme 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 the regulatory (R) subunits of PKA, is phosphorylated by PKA, and ubiquitylates R subunits, promoting their proteolysis upon cAMP elevation. This sustains catalytic subunit activity and is required for efficient nuclear cAMP signaling and PKA-mediated long-term memory. Co-immunoprecipitation, ubiquitylation assays, in vivo phosphorylation, loss-of-function with behavioral readout Nature cell biology High 21423175
2013 Praja2 ubiquitylates and degrades MOB1 (Mob), a core component of NDR/LATS kinase complexes and positive regulator of the Hippo tumor-suppressor cascade, thereby attenuating Hippo signaling and sustaining glioblastoma growth in vivo. Co-immunoprecipitation, ubiquitylation assays, in vivo degradation assays, in vivo xenograft/tumor models Nature communications High 23652010
2014 PJA2 forms a complex with the AMPK-related kinase SIK2 and the CDK5 activator p35 (CDK5R1). Following glucose stimulation, SIK2 phosphorylates p35 at Ser91, triggering p35 ubiquitylation by PJA2, which promotes insulin secretion. This SIK2-p35-PJA2 axis is essential for β-cell functional compensation and glucose homeostasis. Affinity purification-mass spectrometry, co-immunoprecipitation, in vitro ubiquitylation assay, site-directed mutagenesis, β-cell-specific knockout mouse model Nature cell biology High 24561619
2016 Praja2 acts as the E3 ligase that ubiquitylates KSR1, a scaffold protein of the Ras/MAP kinase pathway, leading to its polyubiquitination and proteolytic degradation, thereby attenuating ERK1/2 signaling. This mechanism controls cancer cell growth and maintenance of pluripotency in mouse embryonic stem cells. Co-immunoprecipitation, in vivo ubiquitylation assay, loss-of-function/overexpression in cancer cells and embryonic stem cells Cell death & disease High 27195677
2017 Praja2 ubiquitylates MFHAS1 via pulldown-confirmed direct binding, but promotes accumulation of ubiquitylated MFHAS1 without degrading it (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, functional macrophage polarization assays Cell death & disease Medium 28471450
2017 PJA2 ubiquitinates the HIV-1 Tat protein in a non-degradative manner at variable lysine residues with atypical polyubiquitin chain linkages, specifically regulating the transcription elongation step. Proper ubiquitin chain assembly by PJA2 requires that Tat first binds its P-TEFb cofactor. RNAi knockdown, in vivo ubiquitylation assay, site-directed mutagenesis of ubiquitin acceptor lysines, HIV transcription elongation assays, viral replication assays Scientific reports Medium 28345603
2018 Pja2 binds TCF/LEF1 transcription factors and ubiquitylates them, reducing their protein levels and thereby downregulating Wnt/β-catenin signaling activity. Co-immunoprecipitation, ubiquitylation assay, overexpression/knockdown with reporter assays for Wnt signaling International journal of stem cells Medium 30021253
2021 Praja2 assembles a centrosomal complex with TBC1D31, PKA, and the ciliopathy protein OFD1. Upon GPCR-cAMP stimulation, PKA phosphorylates OFD1 at Ser735, promoting OFD1 proteolysis through the praja2-ubiquitin-proteasome system. This pathway is essential for primary ciliogenesis, and a non-phosphorylatable OFD1 mutant impairs cilium morphology. Genetic disruption of TBC1D31/praja2/OFD1 axis impairs ciliogenesis in vivo in Medaka fish. Co-immunoprecipitation, in vivo ubiquitylation assay, site-directed mutagenesis (OFD1 S735A), in vivo Medaka fish ciliogenesis model, cycloheximide chase The EMBO journal High 33934390
2021 Praja2 promotes ubiquitylation and degradation of KSR1 in gastric cancer cells, inhibiting MEK-ERK signaling and suppressing tumor cell proliferation, migration, and invasion in vitro and tumor growth in vivo. Co-immunoprecipitation, ubiquitylation assay, overexpression/knockdown in cancer cells, in vivo xenograft model, pharmacological proteasome inhibition (MG132) Aging Medium 33461174
2021 ELK4 transcriptionally activates KDM5A, which removes H3K4me3 marks from the PJA2 promoter to suppress PJA2 expression. Reduced PJA2 leads to accumulation of KSR1 (its ubiquitination substrate), promoting M2 macrophage polarization and gastric cancer progression. Dual luciferase reporter, ChIP assay, co-immunoprecipitation, cycloheximide chase for KSR1 stability, gain/loss-of-function assays, xenograft model Journal of translational medicine Medium 34372882
2024 PJA2 interacts with TYK2 and JAK1 (identified by TurboID proximity labeling and confirmed functionally), promotes their non-degradative ubiquitination, and limits activating phosphorylation of TYK2, thereby restraining downstream STAT1/STAT2 signaling in the type I interferon pathway. TurboID proximity labeling coupled with affinity purification-mass spectrometry, RNAi functional screen, E3 ligase activity assay, phosphorylation analysis Nature communications Medium 38802340
2024 Praja2 forms a complex with the AP2 adapter complex, ubiquitylates it, and contributes to receptor endocytosis and clearance. Downregulation of praja2 in RCC by oncogenic miRNAs impairs endocytosis and clearance of EGFR, amplifying downstream mitogenic signaling. Genetic ablation of praja2 in mice upregulates EGFR and VEGFR and induces kidney epithelial and vascular alterations. Co-immunoprecipitation, ubiquitylation assay, in vivo endocytosis assay, genetic mouse knockout, oncomiR-mediated knockdown Communications biology Medium 38379085
2025 Praja2 forms a multimeric complex with the RNA helicase DDX6, which inhibits translation of target RNAs within P-bodies. GPCR-cAMP signaling induces non-proteolytic polyubiquitylation of DDX6 by praja2, promoting P-body assembly and translational repression. Genetic inactivation of praja2 or expression of an ubiquitylation-defective DDX6 mutant suppresses P-body assembly and promotes GBM growth. Co-immunoprecipitation, in vivo ubiquitylation assay, ubiquitylation-defective mutant, polysome profiling, genetic inactivation with cellular phenotype (senescence, growth arrest) EMBO reports Medium 40148504
2025 PJA2 recognizes HDAC2 via its RING-B-box domain, binds the N-terminal of HDAC2, and facilitates ubiquitination at lysine 90 (K90) of HDAC2, leading to its degradation. PJA2-mediated degradation of HDAC2 counteracts transcriptional repression of the IFIT family, suppressing colorectal cancer progression. Co-immunoprecipitation, proximity ligation assay, chromatin immunoprecipitation, RNA-seq, domain mapping, site-directed mutagenesis (K90), in vivo AOM/DSS mouse model Advanced science Medium 39928532
2025 PJA2 ubiquitinates and degrades CHRM3 (muscarinic acetylcholine receptor 3), suppressing downstream TGFβ-pSMAD3 signaling and tumor cell progression in diffuse-type gastric cancer. A catalytically dead ΔRING mutant of PJA2 fails to suppress CHRM3-driven tumor growth. Mass spectrometry, co-immunoprecipitation, ubiquitylation assay, degradation assay, RING-dead mutant, patient-derived organoids, xenograft model British journal of cancer Medium 40858831
2026 PJA2 mediates K48-linked polyubiquitination and subsequent proteasomal degradation of p53, thereby attenuating its tumor-suppressive function in lung adenocarcinoma. ERCC6L activates this PJA2-p53 axis to promote EMT and metastasis. Co-immunoprecipitation, ubiquitylation assay (K48-linkage specified), in vivo tumor/metastasis model with ERCC6L knockout Respiratory research Low 42063149

Source papers

Stage 0 corpus · 20 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 71 24561619
2017 Ubiquitylation of MFHAS1 by the ubiquitin ligase praja2 promotes M1 macrophage polarization by activating JNK and p38 pathways. Cell death & disease 64 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 43 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 28 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
2024 Proximal protein landscapes of the type I interferon signaling cascade reveal negative regulation by PJA2. Nature communications 11 38802340
2019 CD1d- and PJA2-related immune microenvironment differs between invasive breast carcinomas with and without a micropapillary feature. BMC cancer 11 30651076
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 1 40858831
2026 ERCC6L drives lung adenocarcinoma metastasis: a PJA2/p53 ubiquitination-dependent mechanism. Respiratory research 0 42063149

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