SUMMARY Endothelial cells (ECs) form cell-cell adhesive junctional structures maintaining vascular integrity. This barrier is dynamically regulated by vascular endothelial growth factor (VEGF) receptor signaling. We created an inducible knockin mouse model to study the contribution of the integrin-associated focal adhesion tyrosine kinase (FAK) signaling on vascular function. Here we show that genetic or pharmacological FAK inhibition in ECs prevents VEGF-stimulated permeability downstream of VEGF receptor or Src tyrosine kinase activation in vivo. VEGF promotes tension-independent FAK activation, rapid FAK localization to cell-cell junctions, binding of the FAK FERM domain to the vascular endothelial cadherin (VE-cadherin) cytoplasmic tail, and direct FAK phosphorylation of β-catenin at tyrosine-142 (Y142) facilitating VE-cadherin-β-catenin dissociation and EC junctional breakdown. Kinase inhibited FAK is in a closed conformation that prevents VE-cadherin association and limits VEGF-stimulated β-catenin Y142 phosphorylation. Our studies establish a role for FAK as an essential signaling switch within ECs regulating adherens junction dynamics.

Endothelial cell focal adhesion kinase is a key intermediate between c-Src and the regulation of endothelial cell barrier function in the control of tumor metastasis.

Several hundred million tons of toxic mercurials are dispersed in the biosphere. Microbes can detoxify organo-mercurials and mercury salts through sequential action of two enzymes, organomercury lyase and mercuric ion reductase (MerA). The latter, a homodimer with homology to the FAD-dependent disulphide oxidoreductases, catalyses the reaction NADPH + Hg(II)----NADP+ + H+ + Hg(0), one of the very rare enzymic reactions with metal substrates. Human glutathione reductase serves as a reference molecule for FAD-dependent disulphide reductases and between its primary structure and that of MerA from Tn501 (Pseudomonas), Tn21 (Shigella), p1258 (Staphylococcus) and Bacillus, 25-30% of the residues have been conserved. All MerAs have a C-terminal extension about 15 residues long but have very varied N termini. Although the enzyme from Streptomyces lividans has no addition, from Pseudomonas aeruginosa Tn501 and Bacillus sp. strain RC607 it has one and two copies respectively of a domain of 80-85 residues, highly homologous to MerP, the periplasmic component of proteins encoded by the mer operon. These domains can be proteolytically cleaved off without changing the catalytic efficiency. We report here the crystal structure of MerA from the Gram-positive bacterium Bacillus sp. strain RC607. Analysis of its complexes with nicotinamide dinucleotide substrates and the inhibitor Cd(II) reveals how limited structural changes enable an enzyme to accept as substrate what used to be a dangerous inhibitor. Knowledge of the mode of mercury ligation is a prerequisite for understanding this unique detoxification mechanism.

Tumor cells can grow in an anchorage-independent manner. This is mediated in part through survival signals that bypass normal growth restraints controlled by integrin cell surface receptors. Focal adhesion kinase (FAK) is a cytoplasmic protein-tyrosine kinase that associates with integrins and modulates various cellular processes including growth, survival, and migration. As increased FAK expression and tyrosine phosphorylation are associated with tumor progression, inhibitors of FAK are being tested for anti-tumor effects. Here, we analyze PND-1186, a substituted pyridine reversible inhibitor of FAK activity with a 50% inhibitory concentration (IC50) of 1.5 nM in vitro. PND-1186 has an IC50 of ~100 nM in breast carcinoma cells as determined by anti-phospho-specific immunoblotting to FAK Tyr-397. PND-1186 did not alter c-Src or p130Cas tyrosine phosphorylation in adherent cells, yet functioned to restrain cell movement. Whereas 1.0 µM PND-1186 (>5-fold above IC50) had limited effects on cell proliferation, under non-adherent conditions or when grown as spheroids or colonies in soft agar, 0.1 µM PND-1186 blocked FAK and p130Cas tyrosine phosphorylation, promoted caspase-3 activation, and triggered cell apoptosis. PND-1186 inhibited 4T1 breast carcinoma subcutaneous tumor growth correlated with elevated tumor cell apoptosis and caspase 3 activation. Addition of PND-1186 to the drinking water of mice was well tolerated and inhibited ascites-associated ovarian carcinoma tumor growth associated with the inhibition of FAK tyrosine phosphorylation. Our results with low-level PND-1186 treatment support the conclusion that FAK activity selectively promotes tumor cell survival in three-dimensional environments.

Tumor metastasis is a leading cause of cancer-related death. Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase recruited to integrin-mediated matrix attachment sites where FAK activity is implicated in the control of cell survival, migration, and invasion. Although genetic studies support the importance of FAK activity in promoting tumor progression, it remains unclear whether pharmacological FAK inhibition prevents tumor metastasis. Here, we show that the FAK inhibitor PND-1186 blocks FAK Tyr-397 phosphorylation in vivo and exhibits anti-tumor efficacy in orthotopic breast carcinoma mouse tumor models. PND-1186 (100 mg/kg intraperitoneal, i.p.) showed promising pharmacokinetics (PK) and inhibited tumor FAK Tyr-397 phosphorylation for 12 hours. Oral administration of 150 mg/kg PND-1186 gave a more sustained PK profile verses i.p., and when given twice daily, PND-1186 significantly inhibited sygeneic murine 4T1 orthotopic breast carcinoma tumor growth and spontaneous metastasis to lungs. Moreover, low-level 0.5 mg/ml PND-1186 ad libitum administration in drinking water prevented oncogenic KRAS- and BRAF-stimulated MDA-MB-231 breast carcinoma tumor growth and metastasis with inhibition of tumoral FAK and p130Cas phosphorylation. Although PND-1186 was not cytotoxic to cells in adherent culture, tumors from animals receiving PND-1186 exhibited increased TUNEL staining, decreased leukocyte infiltrate and reduced tumor-associated splenomegaly. In vitro, PND-1186 reduced tumor necrosis factor-α triggered interleukin-6 cytokine expression, indicating that FAK inhibition may impact tumor progression via effects on both tumor and stromal cells. As oral administration of PND-1186 also decreased experimental tumor metastasis, PND-1186 may therefore be useful clinically to curb breast tumor progression.