TBK1-PAK1IP1-PAK1 signaling pathway analysis

PRIMARY OUTCOME

mechanism of TBK1-mediated EndMT signaling

EXPECTED OUTCOMES

## Expected Outcomes ### Primary Outcomes 1. **TBK1-PAK1IP1 interaction:** Co-immunoprecipitation confirms physical interaction 2. **PAK1IP1 as TBK1 substrate:** In vitro kinase assay shows phosphorylation 3. **Inverse correlation:** TBK1 activation → decreased PAK1IP1 levels, increased PAK1 activity 4. **Phenotypic consequence:** TBK1 activation promotes stress fibers and migration ### Secondary Outcomes - PAK1IP1 degradation via proteasome (MG132 treatment stabilizes PAK1IP1) - Cross-talk with AKT and ERK pathways - Integrin signaling involvement (FAK phosphorylation) ### Null Result Interpretation - If no interaction, consider alternative scaffolding proteins - May require higher TBK1 activation (time course optimization) - Verify antibody specificity by knockout validation

SUCCESS CRITERIA

## Success Criteria ### Primary - [ ] Co-IP: TBK1-PAK1IP1 interaction confirmed in both directions - [ ] TBK1 phosphorylates PAK1IP1 in vitro (kinase assay positive) - [ ] TBK1 activation: PAK1IP1 protein reduced, PAK1 activity increased - [ ] TBK1 knockdown: PAK1IP1 accumulates, PAK1 activity decreases - [ ] Phenotype rescue: PAK1IP1 knockdown restores migration in TBK1-KD cells ### Secondary - [ ] Time course: peak PAK1IP1 phosphorylation at 30-60 min - [ ] Proteasome inhibition: MG132 stabilizes PAK1IP1 - [ ] Signaling cross-talk documented (AKT, ERK) ### Technical Quality Gates - [ ] Antibody specificity verified (input, IgG control, knockout validation) - [ ] Kinase assay: background subtracted, positive control included - [ ] Cell viability > 80% at all treatment concentrations - [ ] ≥3 biological replicates per condition

PROTOCOL

## Protocol: TBK1-PAK1IP1-PAK1 Signaling Pathway Analysis in Endothelial Cells ### Study Design Molecular study to characterize the TBK1-PAK1IP1-PAK1 signaling axis in endothelial cells. Investigate how TBK1 phosphorylation affects PAK1 inhibition by PAK1IP1 and downstream effects on cytoskeletal dynamics. ### Cell Culture and Treatment 1. Human aortic endothelial cells (HAOECs) or HUVECs 2. Culture in EBM-2 + EGM-2 MV supplements 3. Serum-starve (0.5% FBS) overnight before treatments 4. Treatments: - TBK1 agonist/activator (BTK inhibitor ibrutinib, 1 µM) or TBK1-specific agonist - TBK1 siRNA or CRISPR knockout - PAK1 activator (PTU, 50 µM) or PAK1 inhibitor (IPA-3, 5 µM) - PAK1IP1 overexpression plasmid or siRNA ### Immunoprecipitation Assays 1. Lyse cells in NP-40 buffer with proteasome/phosphatase inhibitors 2. Immunoprecipitate TBK1: anti-TBK1 antibody + Protein A/G beads 3. Wash, elute, and analyze: - Western blot for PAK1IP1 (co-IP interaction) - TBK1 autophosphorylation (pTBK1 S172) 4. Reciprocal IP: anti-PAK1IP1, blot for TBK1 and PAK1 ### Kinase Activity Assays 1. **TBK1 kinase assay:** - Immunoprecipitate TBK1, incubate with recombinant PAK1IP1 substrate - Measure 32P incorporation (radioactive) or ADP-Glo assay 2. **PAK1 kinase assay:** - Immunoprecipitate PAK1, use recombinant MBP or myelin basic protein as substrate - Measure kinase activity ### Signaling readouts 1. **Western blot panel:** - pTBK1 (S172), total TBK1 - pPAK1 (T423), total PAK1 - PAK1IP1 - Downstream: pERK, pAKT, pFAK, pSRC - Loading control: β-actin, GAPDH 2. **Cellular phenotypes:** - F-actin staining (phalloidin) for stress fibers and cortical actin - Cell migration (wound healing assay) - Cell adhesion assay (fibronectin-coated plates) ### Controls - **Negative control:** Non-targeting siRNA, empty vector transfection - **Positive control:** Known activator or inhibitor for each pathway component - **Time course:** 0, 15, 30, 60, 120 min to capture kinetic profile - **Specificity control:** Use multiple siRNAs or independent CRISPR clones ### Expected Outcomes 1. **TBK1 phosphorylates PAK1IP1:** Phosphorylation reduces PAK1IP1 stability/inhibitory activity 2. **TBK1 activation increases PAK1 activity:** Loss of PAK1IP1-mediated inhibition 3. **Cytoskeletal remodeling:** TBK1 activation promotes stress fiber formation 4. **Enhanced migration:** TBK1-PAK1 axis required for endothelial migration 5. **Cross-talk:** TBK1 may activate AKT and ERK downstream of PAK1 ### Success Criteria - [ ] Co-IP confirms TBK1-PAK1IP1 interaction (endogenous proteins) - [ ] TBK1 kinase activity increases PAK1IP1 phosphorylation in vitro - [ ] TBK1 knockdown increases PAK1IP1 protein levels (loss of phosphorylation/degradation) - [ ] PAK1IP1 knockdown phenocopies TBK1 activation - [ ] Rescue experiment: PAK1IP1 knockdown restores function in TBK1-deficient cells - [ ] ≥3 independent biological replicates per condition

LINKED HYPOTHESES

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