Disruption of phactr-1 pathway triggers pro-inflammatory and pro-atherogenic factors: New insights in atherosclerosis development.

Significant interest has recently emerged for phosphatase and actin regulatory protein (PHACTR1) gene in heart diseases prognosis. However, the functional role of phactr-1 protein remains elusive in heart related-diseases such as atherosclerosis, coronary artery calcification, ischaemic stroke, coronary artery stenosis and early-onset myocardial infarction. Phactr-1 is directly regulated by vascular endothelial growth factor A165 (VEGF-A165) through VEGF receptor 1 (VEGR-1) and Neuropilin-1 (NRP-1). Using an antagonist peptide approach to inhibit the interaction of VEGF-A165 to NRP-1 and VEGF-R1, we highlighted the importance of both cysteine residues located at the end of VEGF-A165 exon-7 and at the exon-8 to generate functional peptides, which decreased Phactr-1 expression. Here, we report original data showing Phactr-1 down-expression induces the expression of Matrix Metalloproteinase (MMP) regulators such as Tissue inhibitor of metalloproteinase (TIMP-1/-2) and Reversion-inducing-cysteine-rich protein with kazal motifs (RECK). Furthermore, focal adhesion kinases (FAK/PYK2/PAXILLIN) and metabolic stress (AMPK/CREB/eNOS) pathways were inhibited in endothelial cells. Moreover, the decrease of phactr-1 expression induced several factors implicated in atherosclerotic events such as oxidized low-density lipoprotein receptors (CD36, Clusterin, Cadherin-13), pro-inflammatory proteins including Thrombin, Thrombin receptor 1 (PAR-1), A Disintegrin And Metalloprotease domain-9/-17 (ADAM-9/-17), Trombospondin-2 and Galectin-3. Besides, Phactr-1 down-expression also induces emerging atherosclerosis biomarkers such as semicarbazide-sensitive amine oxidase (SSAO) and TGF-beta-inducible gene h3 (ßIG-H3). In this report, we show for the first time the direct evidence of the phactr-1 biological function in the regulation of pro-atherosclerotic molecules. This intriguing result strengthened heart diseases PHACTR-1 single-nucleotide polymorphisms (SNP) correlation. Taken together, our result highlighted the pivotal role of phactr-1 protein in the pathogenesis of atherosclerosis.

Neuropilin-1 regulates a new VEGF-induced gene, Phactr-1, which controls tubulogenesis and modulates lamellipodial dynamics in human endothelial cells.

Recently, we identified a new Vascular Endothelial Growth Factor (VEGF)-A(165)-induced gene Phactr-1, (Phosphatase Actin Regulator-1). We reported that Phactr-1 gene silencing inhibited tube formation in human umbilical endothelial cells (HUVECs) indicating a key role for Phactr-1 in tubulogenesis in vitro. In this study, we investigated the role of Phactr-1 in several cellular processes related to angiogenesis. We found that neuropilin-1 (NRP-1) and VEGF-R1 depletion inhibited Phactr-1 mRNA expression while NRP-2 and VEGF-R2 depletion had no effect. We described a new interaction site of VEGF-A(165) to VEGF-R1 in peptides encoded by exons 7 and 8 of VEGF-A(165). The specific inhibition of VEGF-A(165) binding on NRP-1 and VEGF-R1 by ERTCRC and CDKPRR peptides decreased the Phactr-1 mRNA levels in HUVECs indicating that VEGF-A(165)-dependent regulation of Phactr-1 expression required both NRP-1 and VEGF-R1 receptors. In addition, upon VEGFA(165)-stimulation Phactr-1 promotes formation and maintenance of cellular tubes through NRP-1 and VEGFR1. Phactr-1 was previously identified as protein phosphatase 1 (PP1) α-interacting protein that possesses actin-binding domains. We showed that Phactr-1 depletion decreased PP1 activity, disrupted the fine-tuning of actin polymerization and impaired lamellipodial dynamics. Taken together our results strongly suggest that Phactr-1 is a key component in the angiogenic process.

Depletion of the novel protein PHACTR-1 from human endothelial cells abolishes tube formation and induces cell death receptor apoptosis.

Using suppression subtractive hybridisation (SSH), we identified a hitherto unreported gene PHACTR-1 (Phosphatase Actin Regulating Protein-1) in Human Umbilical Vascular Endothelial Cells (HUVECs). PHACTR-1 is an actin and protein phosphatase 1 (PP1) binding protein which is reported to be highly expressed in brain and which controls PP1 activity and F-actin remodelling. We have also reported that its expression is dependent of Vascular Endothelial Growth Factor (VEGF-A(165)). To study its function in endothelial cells, we used a siRNA strategy against PHACTR-1. PHACTR-1 siRNA-treated HUVECs showed a major impairment of tube formation and stabilisation. PHACTR-1 depletion triggered apoptosis through death receptors DR4, DR5 and FAS, which was reversed using death receptor siRNAs or with death receptor-dependent caspase-8 siRNA. Our findings suggest that PHACTR-1 is likely to be a key regulator of endothelial cell function properties. Because of its central role in the control of tube formation and endothelial cell survival, PHACTR-1 may represent a new target for the development of anti-angiogenic therapy.

p120-Ras GTPase activating protein (RasGAP): a multi-interacting protein in downstream signaling.

p120-RasGAP (Ras GTPase activating protein) plays a key role in the regulation of Ras-GTP bound by promoting GTP hydrolysis via its C-terminal catalytic domain. The p120-RasGAP N-terminal part contains two SH2, SH3, PH (pleckstrin homology) and CaLB/C2 (calcium-dependent phospholipid-binding domain) domains. These protein domains allow various functions, such as anti-/pro-apoptosis, proliferation and also cell migration depending of their distinct partners. The p120-RasGAP domain participates in protein-protein interactions with Akt, Aurora or RhoGAP to regulate functions described bellow. Here, we summarize, in angiogenesis and cancer, the various functional roles played by p120-RasGAP domains and their effector partners in downstream signaling.