ID: h-c1aec6a4
Hypothesis
Neuron-Specific Expression of Autophagy Inhibitory Phosphatases (PP2A/Bβ1)
Neurons uniquely express the PP2A Bβ1 regulatory subunit forming a phosphatase complex that selectively dephosphorylates and activates ULK1 at Ser757 but not Ser317, creating a dominant-negative ULK1 activation state refractory to most a.
EvidencePending (0%)📖 0 cit🗣 1 debates✓ 3 support✗ 2 oppose
✓ All Quality Gates Passed
🧪 Overview
Neurons uniquely express the PP2A Bβ1 regulatory subunit forming a phosphatase complex that selectively dephosphorylates and activates ULK1 at Ser757 but not Ser317, creating a dominant-negative ULK1 activation state refractory to most autophagy induction strategies. SKEPTIC critique weakened this by noting PPP2R2B is 'neuron-enriched' not 'neuron-exclusive', and the selective dephosphorylation specificity lacks structural validation. DOMAIN_EXPERT identifies this as high-risk requiring structural data on PP2A-Bβ1:ULK1 interface before clinical investment.
🧬 Mechanism
🧬 Curated Mechanism Pathway
Curated pathway from expert analysis
flowchart TD
A["PPP2R2B PP2A Regulatory<br/>B55alpha Subunit"]
B["PP2A Heterotrimeric Complex<br/>Catalytic and Scaffold"]
C["Tau Dephosphorylation<br/>Ser262/396 Sites"]
D["AKT and MYC Regulation<br/>Cell Survival Signaling"]
E["PPP2R2B Methylation<br/>LEAVES.1 Long Noncoding RNA"]
F["PPP2R2B Silencing<br/>Hyperphosphorylated Tau Accumulation"]
G["PP2A Activators<br/>DT-061 or Peptide Activators"]
A --> B
B --> C
B --> D
E -.->|"reduces"| B
F -.->|"causes"| C
G -.->|"restores"| B
style A fill:#1a237e,stroke:#4fc3f7,color:#4fc3f7
style F fill:#b71c1c,stroke:#ef9a9a,color:#ef9a9a
style G fill:#1b5e20,stroke:#81c784,color:#81c784⚖️ Evidence
⚖️ Evidence Matrix3 supports2 contradicts
Supports
Oxidative stress promotes autophagic cell death in human neuroblastoma cells with ectopic transfer of mitochondrial PPP2R2B (Bbeta2).
Contradicts
AMPK activators successfully induce autophagy in neurons, suggesting ULK1-S757 dephosphorylation is not insurmountable barrier
Contradicts
LB-100 potentiates autophagy in cancer, not neurons—cross-tissue generalization unwarranted
📖 Linked Papers
No linked papers recorded for this hypothesis yet.
🏥 Translation
🧬 3D Protein Structure — PPP2R2B
No curated PDB or AlphaFold mapping for PPP2R2B yet. Search RCSB →
🧠 GTEx v10 Brain ExpressionJSON
Median TPM across 13 brain regions for PPP2R2B, ULK1 complex from GTEx v10.
💉 Clinical Trials
No clinical trials data linked to this hypothesis yet.
No curated ClinVar variants loaded for this hypothesis.
Run scripts/backfill_clinvar_variants.py to fetch P/LP/VUS variants.
No DepMap CRISPR Chronos data found for PPP2R2B, ULK1 complex.
Run python3 scripts/backfill_hypothesis_depmap.py to populate.
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🔮 Predictions
🔎 Predictions vs Observations2 predictions · 0 with recorded observations
| Prediction | Predicted | Observed | Status | Conf |
|---|---|---|---|---|
| IF the PP2A-Bβ1 holoenzyme selectively dephosphorylates ULK1 at Ser757 while sparing Ser317 (as hypothesized), THEN in vitro phosphatase assays using purified recombinant PP2A-Bβ1 complex incubated wi | PP2A-Bβ1 will dephosphorylate ULK1 Ser757 at least twice as fast as Ser317 in vitro, confirming substrate selectivity | — no observation — | pending | 0.35 |
| IF neuronal expression of PP2A-Bβ1 creates a dominant-negative ULK1 state refractory to mTOR inhibition, THEN siRNA-mediated knockdown of PPP2R2B (≥70% knockdown efficiency) in primary mouse cortical | PPP2R2B knockdown will restore autophagy sensitivity to mTOR inhibition, with rapamycin increasing LC3-II/LC3-I ratio in neurons to levels comparable to PPP2R2B | — no observation — | pending | 0.40 |
🔮 Falsifiable Predictions (2)
pendingconf 40%
IF neuronal expression of PP2A-Bβ1 creates a dominant-negative ULK1 state refractory to mTOR inhibition, THEN siRNA-mediated knockdown of PPP2R2B (≥70% knockdown efficiency) in primary mouse cortical neurons will restore rapamycin-induced ULK1 Ser757 dephosphorylation and increase LC3-II/LC3-I ratio
Predicted outcome: PPP2R2B knockdown will restore autophagy sensitivity to mTOR inhibition, with rapamycin increasing LC3-II/LC3-I ratio in neurons to levels comparable
Falsification: If ULK1 Ser757 phosphorylation remains refractory to rapamycin after PPP2R2B knockdown (phospho-Ser757 signal unchanged within 10%), or if LC3-II/LC3-I ratio fails to increase ≥1.5-fold, the dominant-
pendingconf 35%
IF the PP2A-Bβ1 holoenzyme selectively dephosphorylates ULK1 at Ser757 while sparing Ser317 (as hypothesized), THEN in vitro phosphatase assays using purified recombinant PP2A-Bβ1 complex incubated with dual-phosphorylated ULK1 substrate should show ≥2-fold greater dephosphorylation at Ser757 versus
Predicted outcome: PP2A-Bβ1 will dephosphorylate ULK1 Ser757 at least twice as fast as Ser317 in vitro, confirming substrate selectivity
Falsification: If Ser757 and Ser317 are dephosphorylated at similar rates (ratio <1.5), or if Ser317 is dephosphorylated preferentially over Ser757, the selective specificity claim is falsified and the hypothesis we
▸Metadatasource: v1_phase_c_backfill · origin_type: gap_debate
| source | v1_phase_c_backfill |
| origin_type | gap_debate |
| _schema_version | 1 |
📊 Evidence Profile
Evidence Balance
+0%
Certainty
0%
Debates
0
Incoming
0
Outgoing
0
0 supporting
0 contradicting
0 neutral
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