Affinage

ENSA

Alpha-endosulfine · UniProt O43768

Length
121 aa
Mass
13.4 kDa
Annotated
2026-06-09
15 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

ENSA (alpha-endosulfine) is an intrinsically disordered protein that acts as the central effector of the Greatwall/MASTL-PP2A-B55 axis, converting mitotic kinase signaling into temporally ordered phosphatase control during cell division (PMID:24120663, PMID:34346186). Upon phosphorylation at Ser67 by Greatwall kinase, ENSA binds PP2A primarily through the A-subunit via a dock-and-coalesce mechanism and potently inhibits the PP2A-B55 holoenzyme (PMID:34346186). This MASTL-ENSA-PP2A/B55 module establishes two cyclin B thresholds during mitotic exit—the first licensing chromosome segregation and the second licensing cytokinesis—so that loss of ENSA/Greatwall uncouples PP2A-B55 from Cdk1-cyclin B activity and eliminates the ordered delay in substrate dephosphorylation (PMID:24120663). ENSA inhibition of PP2A-B55 is reversed when the RNA Pol II CTD phosphatase Fcp1 dephosphorylates ENSA, placing it within a phosphatase hierarchy that coordinates Greatwall, ENSA, and Cdk substrate dephosphorylation (PMID:24391510). Beyond mitotic exit, ENSA specifically controls S-phase duration by maintaining Treslin protein stability against ubiquitin-proteasome degradation, a role distinct from that of its paralog ARPP19, which is the paralog essential for mitotic progression and embryogenesis (PMID:28785014, PMID:30626720). The same axis promotes meiotic maturation in oocytes through inhibition of PP2A-B55δ (PPP2R2D) (PMID:24675883), operates in anucleate platelets where PKA/PKG provide additional regulatory input by phosphorylating ENSA at Ser109 (PMID:32085646), and modulates chemoresistance in oral squamous cell carcinoma in a MASTL-dependent manner (PMID:36247015). An earlier characterization established ENSA as a regulator of beta-cell K(ATP) channels that stimulates insulin secretion (PMID:10480622).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 1999 Medium

    Established the first biochemical activity attributed to ENSA, linking it to potassium channel regulation and insulin secretion before its mitotic role was known.

    Evidence Recombinant alpha-endosulfine in sulfonylurea binding competition, patch-clamp of cloned K(ATP) channels, and insulin secretion assays

    PMID:10480622

    Open questions at the time
    • Does not connect this channel-regulatory activity to the later PP2A-inhibitory function
    • Physiological relevance in vivo not established
    • No structural basis for channel interaction
  2. 2013 High

    Defined the core function of ENSA as a timer module that couples PP2A-B55 inhibition to Cdk1-cyclin B activity, answering how mitotic exit events are ordered in time.

    Evidence Mathematical modeling combined with ENSA/Greatwall depletion and PRC1 dephosphorylation readout of cytokinesis timing

    PMID:24120663

    Open questions at the time
    • Molecular basis of PP2A-B55 binding not resolved here
    • Did not distinguish ENSA from its paralog ARPP19
  3. 2014 High

    Resolved how the ENSA-PP2A inhibition is switched off, identifying Fcp1 as the specific phosphatase for ENSA/ARPP19 within a phosphatase hierarchy.

    Evidence Phospho-specific antibody monitoring during mitosis with Fcp1 and PP2A inhibition/depletion plus mathematical modeling

    PMID:24391510

    Open questions at the time
    • Does not establish how Fcp1 activity is timed during exit
    • Does not separate ENSA-specific from ARPP19-specific dephosphorylation
  4. 2014 High

    Extended the ENSA-PP2A axis to meiosis, showing ENSA promotes oocyte prophase I exit specifically through PP2A-B55delta.

    Evidence Morpholino ENSA depletion in mouse oocytes with okadaic acid rescue and ENSA+PPP2R2D double-depletion epistasis

    PMID:24675883

    Open questions at the time
    • Does not identify the upstream kinase activating ENSA in oocytes
    • B55delta specificity versus other B55 isoforms not fully dissected
  5. 2017 High

    Uncovered a non-mitotic role for ENSA in controlling S-phase length by stabilizing Treslin, expanding its function across cell-cycle phases.

    Evidence siRNA knockdown of Ensa in human cells, replication fork density measurement, and rescue by Treslin overexpression

    PMID:28785014

    Open questions at the time
    • The ubiquitin ligase acting on Treslin is not identified
    • Mechanistic link between ENSA/PP2A and Treslin stability not biochemically defined
  6. 2017 Medium

    Identified a regulated mechanism for dissociating Igo/ENSA from PP2A via Pkc1 phosphorylation of both Cdc55 and Igo/ENSA in yeast.

    Evidence MS phosphosite mapping, in vitro Pkc1 kinase assay, mutagenesis, and Co-IP of Igo2 with PP2A-Cdc55 in budding yeast

    PMID:28100785

    Open questions at the time
    • Conservation of this Pkc1-driven dissociation in mammalian ENSA not shown
    • Single-organism (yeast ortholog) evidence
  7. 2019 High

    Separated the functions of ENSA and ARPP19, showing ARPP19 is essential for mitosis and embryogenesis while ENSA is dedicated to S-phase control.

    Evidence Conditional Arpp19 and Ensa knockout mouse models, MEF viability, PP2A-B55 activity, and cell cycle analysis

    PMID:30626720

    Open questions at the time
    • Molecular basis for the non-redundancy between paralogs not defined
    • Why ENSA cannot compensate for ARPP19 in mitosis unexplained
  8. 2019 Medium

    Placed the ENSA-PP2A-B55 axis downstream of DNA damage checkpoint signaling, showing ATM/Chk repression of Greatwall releases ENSA from PP2A-B55 to drive mitotic slippage.

    Evidence siRNA depletion of PP2A-B55alpha/delta, Plk1/Cdk1 phospho-analysis, and Co-IP of Plk1 with PP2A-B55

    PMID:31072185

    Open questions at the time
    • Direct phosphorylation events linking ATM/Chk to Greatwall not shown here
    • Single Co-IP for Plk1-PP2A-B55 interaction
  9. 2020 Medium

    Demonstrated the MASTL-ENSA-PP2A/B55 pathway operates in anucleate platelets and identified PKA/PKG phosphorylation of ENSA at Ser109 as an additional regulatory input.

    Evidence Platelet proteomics, phospho-specific antibodies, recombinant MASTL/PKA/PKG assays, phospho-mutants, and platelet aggregation assays

    PMID:32085646

    Open questions at the time
    • Functional consequence of Ser109 phosphorylation on PP2A inhibition not fully resolved
    • Identity of the MASTL-related kinase in platelets uncertain
  10. 2021 High

    Provided the structural and biochemical mechanism of ENSA-PP2A inhibition, showing ENSA is disordered, binds primarily via the PP2A A-subunit, and requires Ser67 phosphorylation.

    Evidence NMR spectroscopy, SAXS, and binding affinity measurements against PP2A A-subunit and B56 isoforms

    PMID:34346186

    Open questions at the time
    • No co-crystal structure of the inhibited holoenzyme
    • Mechanism of B55-holoenzyme selectivity not fully resolved
  11. 2022 Medium

    Linked the MASTL-ENSA-PP2A axis to cancer chemoresistance, showing ENSA mediates MASTL-driven cisplatin survival in oral squamous cell carcinoma.

    Evidence Stable overexpression and CRISPR deletion of MASTL/ENSA in OSCC cell lines, cisplatin survival, caspase/DNA damage readouts, and xenograft with MASTL inhibitor

    PMID:36247015

    Open questions at the time
    • Direct PP2A substrate mediating chemoresistance not identified
    • Clinical relevance beyond cell lines and xenografts not established

Open questions

Synthesis pass · forward-looking unresolved questions
  • How ENSA's diverse contexts (channel regulation, S-phase, meiosis, platelets, nuclear translocation in ischemia) integrate with its canonical PP2A-B55 inhibitory function remains unresolved.
  • Whether nuclear translocation of ENSA in ischemic neurons reflects a PP2A-independent function is unknown
  • No unified model reconciling K(ATP) channel regulation with PP2A inhibition
  • Substrate-level consequences of ENSA-PP2A inhibition in non-dividing cells largely uncharacterized

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3 GO:0140096 catalytic activity, acting on a protein 1
Localization
GO:0005634 nucleus 1
Pathway
R-HSA-1640170 Cell Cycle 4 R-HSA-1474165 Reproduction 1 R-HSA-69306 DNA Replication 1
Partners
FCP1MASTLPKAPKGPP2APPP2R2D

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2013 The BEG (PP2A-B55/ENSA/Greatwall) pathway controls temporal order during mitotic exit in metazoans. ENSA/Greatwall act as a timer module that couples PP2A-B55 inhibition to Cdk1-cyclin B activity, creating two cyclin B thresholds: the first permits separase activation and chromosome segregation, and the second permits PP2A-B55 activation and initiation of cytokinesis. Removal of the ENSA/Greatwall module eliminates the second threshold and the associated delay in PRC1 dephosphorylation, uncoupling PP2A-B55 from Cdk1-cyclin B activity. Mathematical modeling combined with cell-based experiments; PRC1 used as model substrate; depletion of ENSA/Greatwall with phenotypic readout of cytokinesis timing Molecular cell High 24120663
2014 PP2A/B55 is required for Greatwall dephosphorylation at the essential Cdk site Thr194, while Ensa/ARPP19 dephosphorylation during mitotic exit is mediated specifically by the RNA Polymerase II CTD phosphatase Fcp1, establishing a hierarchy of phosphatases coordinating Greatwall, Ensa/ARPP19, and Cdk substrate dephosphorylation. Phospho-specific antibody monitoring of Greatwall, Ensa/ARPP19 and Cdk substrates during mitotic entry and exit; inhibition and depletion of Fcp1 and PP2A; mathematical modelling PLoS genetics High 24391510
2017 Ensa controls S-phase length by modulating Treslin protein levels via ubiquitin-proteasome degradation. Ensa knockdown causes dramatic S-phase extension and reduced replication fork density due to decreased Treslin levels; overexpression of Treslin fully rescues the extended S phase in Ensa-depleted cells, placing Ensa upstream of Treslin stability in a Gwl/Ensa-dependent pathway. siRNA knockdown of Ensa in human cells; rescue by Treslin overexpression; replication fork density measurement; ubiquitin-proteasome pathway implicated Nature communications High 28785014
2019 ARPP19, but not ENSA, is essential for mitotic division and mouse embryogenesis; ENSA is specifically required for controlling S-phase duration but not mitotic progression. In Arpp19-knockout MEFs, PP2A-B55 inhibition is impaired and the temporal pattern of mitotic dephosphorylation is perturbed; ENSA (still expressed) cannot compensate, establishing non-redundant roles for the two paralogs. Conditional knockout mouse models for Arpp19 and Ensa; MEF viability assay; PP2A-B55 activity measurement; cell cycle analysis The Journal of cell biology High 30626720
2014 ENSA plays a key role in exit from prophase I arrest in mouse oocytes by inhibiting PP2A containing the regulatory subunit PPP2R2D (B55δ). The majority of ENSA-deficient oocytes fail to exit prophase I arrest; this defect is rescued by okadaic acid (PP2A inhibitor) or by co-depletion of PPP2R2D, demonstrating that ENSA functions through PP2A-B55δ to promote meiotic maturation. Morpholino-mediated ENSA depletion in mouse oocytes; pharmacological PP2A inhibition (okadaic acid); double-depletion epistasis (ENSA + PPP2R2D) Cell cycle (Georgetown, Tex.) High 24675883
2021 ENSA is an intrinsically disordered protein containing three transient α-helical structures. It interacts with PP2A primarily via the A-subunit (with significantly stronger affinity to A-subunit than to any B56-subunit isoforms) and follows a dock-and-coalesce binding mechanism. Phosphorylation of ENSA at Ser67 by Greatwall kinase is required for PP2A inhibition. NMR spectroscopy, small-angle X-ray scattering (SAXS), and interaction assays (binding affinity measurements with PP2A A-subunit and B56-subunit isoforms) The FEBS journal High 34346186
2020 The MASTL-ENSA/ARPP19-PP2A/B55 pathway is present and functional in anucleate human platelets. ENSA-S67 is phosphorylated by MASTL (or a related kinase) converting it into a PP2A inhibitor, and ENSA-S109 is phosphorylated by PKA and PKG. PP2A inhibition by this pathway modulates thrombin-stimulated platelet aggregation and phosphorylation of VASP, Akt, p38 and ERK1/2. Proteomic identification of ENSA and PP2A subunits in platelets; phospho-specific antibodies; recombinant protein assays with MASTL, PKA, and PKG; phospho-mutant analysis; okadaic acid treatment; platelet aggregation assay Cells Medium 32085646
2019 During recovery from mitotic DNA damage, ATM and Chk1/2 repress Greatwall kinase, causing dissociation of ENSA from PP2A-B55 and PP2A activation. The activated PP2A-B55 (specifically B55α and B55δ) then dephosphorylates Plk1 and Cdk1, leading to mitotic slippage without normal cytokinesis. Depletion of PP2A-B55α/δ restored Plk1 phosphorylation and G1 progression. siRNA depletion of PP2A-B55α and/or B55δ; phosphorylation state analysis of Plk1 and Cdk1; Co-immunoprecipitation of Plk1 with PP2A-B55 Cell cycle (Georgetown, Tex.) Medium 31072185
2022 In oral squamous cell carcinoma (OSCC), the MASTL-ENSA-PP2A/B55 axis modulates cisplatin resistance. Stable MASTL overexpression promotes cell survival under cisplatin in an ENSA-dependent manner; deletion of MASTL or ENSA, or overexpression of B55α, sensitizes cisplatin response with increased DNA damage signaling and caspase activation. Stable overexpression and CRISPR deletion of MASTL and ENSA in OSCC cell lines; cisplatin survival assay; DNA damage and caspase activation readouts; mouse xenograft model with MASTL inhibitor GKI-1 Frontiers in cell and developmental biology Medium 36247015
2017 In budding yeast, Protein Kinase C (Pkc1) controls the binding of Igo/ENSA proteins to PP2A-Cdc55 by directly phosphorylating both Cdc55 and Igo/ENSA, with phosphorylation of Cdc55 contributing to Igo/ENSA dissociation from the complex. This establishes a mechanism for inactivating the Igo/ENSA-PP2A inhibitory interaction. Mass spectrometry phosphorylation mapping; in vitro kinase assay with Pkc1; site-directed mutagenesis of phosphorylation sites; Co-immunoprecipitation of Igo2 with PP2A-Cdc55 The Journal of biological chemistry Medium 28100785
1999 Human alpha-endosulfine (encoded by ENSA) functions as an endogenous regulator of beta-cell K(ATP) channels: recombinant alpha-endosulfine inhibits sulfonylurea binding to beta-cell membranes, reduces cloned K(ATP) channel currents, and stimulates insulin secretion from beta-cells. Recombinant protein assay: sulfonylurea binding competition, patch-clamp of cloned K(ATP) channels, insulin secretion assay Diabetes Medium 10480622
2013 Overexpressed ENSA interacts with MASTL and suppresses hepatic tumor growth in an established hepatic cell line and mouse model. Co-immunoprecipitation of ENSA with MASTL; overexpression in liver cancer cell line; mouse tumor model Biochemical and biophysical research communications Low 24211627
2017 In a rat stroke model, αEnsa (mammalian ENSA) shows nuclear translocation in ischemic neurons within hours of ischemic onset, and rapamycin treatment that reduces infarct size also enhances αEnsa nuclear translocation in affected neurons, suggesting TORC1-regulated subcellular redistribution of ENSA. Immunofluorescence localization in rat brain sections; in situ hybridization for ENSA mRNA; rapamycin pharmacological intervention with behavioral and histological readout Journal of neuropathology and experimental neurology Low 28922851

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2013 The BEG (PP2A-B55/ENSA/Greatwall) pathway ensures cytokinesis follows chromosome separation. Molecular cell 128 24120663
2022 Copy number amplification of ENSA promotes the progression of triple-negative breast cancer via cholesterol biosynthesis. Nature communications 59 35145111
2014 PP2A/B55 and Fcp1 regulate Greatwall and Ensa dephosphorylation during mitotic exit. PLoS genetics 52 24391510
2017 Ensa controls S-phase length by modulating Treslin levels. Nature communications 47 28785014
2019 ENSA and ARPP19 differentially control cell cycle progression and development. The Journal of cell biology 36 30626720
1999 Isolation, characterization, and chromosomal localization of the human ENSA gene that encodes alpha-endosulfine, a regulator of beta-cell K(ATP) channels. Diabetes 25 10480622
2020 The Cell Cycle Checkpoint System MAST(L)-ENSA/ARPP19-PP2A is Targeted by cAMP/PKA and cGMP/PKG in Anucleate Human Platelets. Cells 23 32085646
2019 Dephosphorylation of Plk1 occurs through PP2A-B55/ENSA/Greatwall pathway during mitotic DNA damage recovery. Cell cycle (Georgetown, Tex.) 14 31072185
2015 The mitotic PP2A regulator ENSA/ARPP-19 is remarkably conserved across plants and most eukaryotes. Biochemical and biophysical research communications 14 25666948
2017 Protein Kinase C Controls Binding of Igo/ENSA Proteins to Protein Phosphatase 2A in Budding Yeast. The Journal of biological chemistry 13 28100785
2022 The MASTL-ENSA-PP2A/B55 axis modulates cisplatin resistance in oral squamous cell carcinoma. Frontiers in cell and developmental biology 10 36247015
2014 α-endosulfine (ENSA) regulates exit from prophase I arrest in mouse oocytes. Cell cycle (Georgetown, Tex.) 10 24675883
2013 ENSA expression correlates with attenuated tumor propagation in liver cancer. Biochemical and biophysical research communications 8 24211627
2021 Interaction mechanism of endogenous PP2A inhibitor protein ENSA with PP2A. The FEBS journal 6 34346186
2017 α-Endosulfine (ARPP-19e) Expression in a Rat Model of Stroke. Journal of neuropathology and experimental neurology 2 28922851

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