TBK1-PAK1IP1-PAK1 signaling pathway analysis

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

Human aortic endothelial cells (HAOECs) or HUVECs

Culture in EBM-2 + EGM-2 MV supplements

Serum-starve (0.5% FBS) overnight before treatments

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

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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

Human aortic endothelial cells (HAOECs) or HUVECs

Culture in EBM-2 + EGM-2 MV supplements

Serum-starve (0.5% FBS) overnight before treatments

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

Lyse cells in NP-40 buffer with proteasome/phosphatase inhibitors

Immunoprecipitate TBK1: anti-TBK1 antibody + Protein A/G beads

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

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

Western blot panel:

• pTBK1 (S172), total TBK1
• pPAK1 (T423), total PAK1
• PAK1IP1
• Downstream: pERK, pAKT, pFAK, pSRC
• Loading control: β-actin, GAPDH

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

TBK1 phosphorylates PAK1IP1: Phosphorylation reduces PAK1IP1 stability/inhibitory activity

TBK1 activation increases PAK1 activity: Loss of PAK1IP1-mediated inhibition

Cytoskeletal remodeling: TBK1 activation promotes stress fiber formation

Enhanced migration: TBK1-PAK1 axis required for endothelial migration

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

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