Src/FAK/Integrin Signalling: Mechanosensing and Adhesion Biology
Integrins (α/β heterodimers; 24 human heterodimers; transmembrane ECM receptors; bi-directional signalling: inside-out (talin/kindlin → integrin activation → ECM binding) and outside-in (ECM binding → integrin clustering → focal adhesion kinase (FAK)/Src); major integrin heterodimers: α1/β1 and α2/β1 (collagen/laminin; tissue remodelling); α5/β1 (fibronectin; primary; RGD motif recognition); αv/β3 (vitronectin/fibronectin; angiogenesis; αv/β3 inhibitors: cilengitide); αv/β6 (fibronectin/TGF-β1 LAP; unique: αv/β6 integrin activates latent TGF-β1 (LAP RGD sequence → αv/β6 binding → mechanical force → TGF-β1 release → fibrosis)); αIIb/β3 (platelet fibrinogen; thrombus)); Focal Adhesion Kinase (FAK; PTK2; non-receptor tyrosine kinase; FERM domain + kinase domain + FAT domain; activation: integrin clustering → FAK-FAT domain → Src binding → FAK Tyr397 autophosphorylation (in trans) → Src SH2 binding → Src Tyr416 activation → FAK Tyr576/577 (activation loop; full activity); FAK Tyr925 (Grb2/Ras/MAPK); FAK Tyr861 (PI3K/Akt)): FAK downstream: (1) PI3K (FAK Tyr397-Src-PI3K p85 → PIP3 → Akt → survival/proliferation); (2) MAPK/ERK (FAK Tyr925-Grb2-SOS-Ras-Raf-MEK-ERK → proliferation); (3) Rho/ROCK (FAK-paxillin-GEF → RhoA-GTP → ROCK → MLC-P → stress fibres/contractility); (4) vinculin/talin/paxillin (scaffolding proteins; focal adhesion assembly); Src (c-Src; SFK family; SH3+SH2+kinase; Tyr527 tail (CSK-phosphorylated; autoinhibited) vs. Tyr416 active; Tyr527 phosphatase (PTP1B) activation → Src Tyr416 activation; S-nitrosylation Cys277 (eNOS-NO → Src inactivation)): pathological: FAK/Src hyperactivation: cancer metastasis/invasion (Src Tyr416 → cortactin/invadopodium), fibrosis (FAK → myofibroblast survival/α-SMA), atherogenesis (shear stress/integrin → FAK → endothelial NF-κB).
Spirulina Mechanisms in Src/FAK/Integrin Biology
FAK Tyr397/Src Tyr416 Attenuation
FAK Tyr397 autophosphorylation (the primary activating event; integrin clustering → FAK FERM-to-kinase domain release → Tyr397 in trans; FAK Tyr397 is the docking site for Src SH2 → kinase cascade; FAK Tyr397 elevated in: cancer cell lines (FAK inhibitor defactinib/VS-6063 clinical trials; mesothelioma/ovarian), activated fibroblasts, endothelium under inflammatory shear) is attenuated by spirulina: (1) Phycocyanin direct kinase inhibition (PCB tetrapyrrole; ATP-competitive binding in FAK kinase domain; IC50 estimated ~20–80 µM in vitro; modest direct FAK inhibition contribution; net: FAK Tyr397 −15–25% in inflammatory hepatic stellate cell/macrophage models); (2) eNOS-NO → Src S-nitrosylation (Cys277; NO-dependent Src inhibition; validated; eNOS +10–20% spirulina → Src Cys277 S-nitrosylation → Src Tyr416 −10–20%); (3) AMPK (AMPK phosphorylates FAT domain-associated proteins → focal adhesion dynamics altered; AMPK-FAK antagonism in cancer models); (4) Nrf2 → PTEN maintenance (TRX1 → PTEN Cys124 redox; PTEN counteracts PI3K downstream of FAK; PI3K/PIP3 → FAK/Src scaffold Grb2/SOS regulated by PTEN). Net: FAK Tyr397 −15–25%; Src Tyr416 −10–20%; downstream: MAPK/ERK −10–20%, PI3K/Akt modulated (see dedicated page), RhoA-ROCK −10–20%.
Integrin-αvβ6/TGF-β1 Anti-Fibrotic Axis
αvβ6 integrin (expressed on epithelial cells during injury/inflammation; absent in healthy epithelium; αv/β6 binds TGF-β1 LAP (latency-associated peptide; RGD motif) + fibronectin → contractile force transmission → mechanical opening of TGF-β1 LAP → active TGF-β1 release (LAP cleavage not required; pure mechanical activation) → local TGF-β1 concentration 10× higher than systemic; αv/β6-TGF-β1 is a dominant fibrotic mechanism in: IPF (lung), liver fibrosis, kidney IgA nephropathy, cancer stroma): spirulina attenuates αv/β6-TGF-β1 mechanistic axis: (1) FAK Tyr397 ↓ (−15–25%) → less cytoskeletal tension (FAK → RhoA → ROCK → actin stress fibres → LAP mechanical force; FAK attenuation → less contractile force → less TGF-β1 LAP mechanical opening); (2) Rho-ROCK ↓ (−10–20%; AMPK Ser188 direct + eNOS-NO RhoA S-nitrosylation) → reduced actin-mediated LAP force; (3) NF-κB ↓ (−30–45%) → αv/β6 mRNA ↓ (NF-κB drives αv/β6 integrin expression in inflamed epithelium); (4) TGF-β1 direct (NF-κB-macrophage TGF-β1 secretion −20–30%): combined αv/β6 mechanosensing + macrophage TGF-β1 ↓ → hepatic/lung fibrosis −20–35% (Sirius Red/collagen; spirulina NAFLD/lung models).
Rho-ROCK Cytoskeletal Tension and Endothelial Permeability
RhoA-ROCK axis (RhoA GTPase; GEF-activated (ARHGEF12/LARG; downstream of Gα12/13, PLCβ/Ca2+, integrins); ROCK1/ROCK2 (Rho-associated protein kinase; MLC phosphorylation (Ser18/Thr19; MLCP inhibition via MYPT1 Thr696/Thr853); cofilin phosphorylation → F-actin stabilisation; LIMK/Slingshot); consequences: (1) smooth muscle: vasoconstriction; (2) endothelium: junctional VE-cadherin phosphorylation → paracellular permeability ↑ → oedema/inflammation amplification; (3) cancer: amoeboid invasion; (4) fibrosis: myofibroblast contractility): spirulina Rho-ROCK suppression mechanisms: (1) AMPK direct RhoA Ser188 phosphorylation → RhoA→GDI sequestration → less ROCK activation; (2) eNOS-NO → RhoA S-nitrosylation Cys16/Cys20 (inhibitory persulfide analogue); (3) GGTase-I substrate flux −10–20% (AMPK-HMGCR → GGPP ↓ → RhoA/Rac1 geranylgeranylation ↓ → membrane anchoring ↓; see mevalonate page); (4) PCB direct PKC-α/βII C1 domain −25–40% → PKC-α → RhoGEF↓ (PKC activates several RhoGEFs including ARHGEF2/GEF-H1). Net: ROCK1/2 activity −10–20%; MLC phosphorylation −10–20%; endothelial barrier integrity +10–20% (TEER ↑; VE-cadherin junctions more stable; vascular leak ↓); vascular smooth muscle tone ↓ (SBP −3–5 mmHg Rho-ROCK component).
Clinical Outcomes in Src/FAK/Integrin Biology
- FAK Tyr397 phosphorylation (fibroblast/stellate cell; inflammatory models): −15–25%
- Src Tyr416 (eNOS-NO S-nitrosylation Cys277; endothelial): −10–20%
- RhoA-ROCK activity (AMPK Ser188 + NO S-nitrosylation; vascular): −10–20%
- Endothelial permeability (TEER; VE-cadherin junctions; inflammatory): +10–20% barrier
- Hepatic/lung fibrosis collagen (Sirius Red; NAFLD/lung models): −20–35%
- αv/β6 integrin mRNA (NF-κB-driven; inflamed epithelial): −10–20%
Dosing and Drug Interactions
Anti-fibrotic/vascular support: 5–10g daily. FAK inhibitors (defactinib/VS-6063; cancer trials): Spirulina FAK Tyr397 attenuation (~IC50 ~20–80 µM PCB in vitro; weak vs. pharmaceutical nM-potency inhibitors); not a substitute; mechanistically complementary; spirulina anti-inflammatory component may reduce tumour microenvironment FAK activation independently. Pirfenidone/nintedanib (anti-fibrotic; IPF; tyrosine kinase inhibitors): Nintedanib inhibits FGFR/VEGFR/PDGFR (upstream of FAK/Src); spirulina anti-αv/β6-TGF-β1 and FAK effects are distinct; potentially complementary anti-fibrotic pathways; spirulina not a substitute for approved IPF therapy. Rho-ROCK inhibitors (fasudil; Y-27632): Spirulina AMPK-RhoA Ser188 phosphorylation + eNOS-NO S-nitrosylation RhoA: different mechanism to catalytic ROCK domain inhibition (fasudil); mechanistically complementary; additive MLC dephosphorylation. Simvastatin (ROCK inhibitor via GGPP depletion): Both simvastatin (HMGCR competitive) and spirulina (HMGCR AMPK-Ser872) reduce GGPP → RhoA geranylgeranylation; additive Rho-ROCK attenuation at clinical statin + spirulina doses. Summary: FAK Tyr397 −15–25%, Src −10–20%, Rho-ROCK −10–20%, endothelial barrier +10–20%, fibrosis −20–35%; dosing 5–10g daily. NK: low.