E-cadherin dis-engagement activates the Rap1 GTPase

E-cadherin based adherens junctions are finely regulated by multiple cellular signaling events. Here we show that the Ras-related Rap1 GTPase is enriched in regions of nascent cell-cell contacts and strengthens E-cadherin junctions: constitutively active Rap1 expressing MDCK cells exhibit increased junctional contact and resisted calcium depletion-induced cell-cell junction disruption. E-cadherin disengagement activated Rap1 and this correlated with E-cadherin association with the Rap GEFs, C3G and PDZ-GEF I. PDZ-GEF I associated with E-cadherin and beta-catenin whereas C3G interaction with E-cadherin did not involve beta-catenin. Knockdown of PDZ-GEF I in MDCK cells decreased Rap1 activity following E-cadherin junction disruption. We hereby show that Rap1 plays a role in the maintenance and repair of E-cadherin junctions and is activated via an "outside-in" signaling pathway initiated by E-cadherin and mediated at least in part by PDZ-GEF I.     

Light-regulated nuclear localization of phytochromes

Phytochrome is a soluble protein that regulates various responses of plants to light. Not all but most of the phytochrome responses are accompanied by changes in the pattern of gene expression. Upon light activation, phytochrome is imported into the nucleus by the nuclear localization activity of the carboxy-terminal half of the molecule. In darkness, the amino-terminal chromophoric domain suppresses this activity to retain the molecule in the cytoplasm. In the nucleus, light-activated phytochrome forms speckles whose biological function remains unclear.     

Internalization of Tissue Factor‐Rich Microvesicles by Platelets Occurs Independently of GPIIb‐IIIa,and Involves CD36 Receptor,Serotonin Transporter and Cytoskeletal Assembly

Platelets are important in hemostasis, but also detect particles and pathogens in the circulation. Phagocytic and endocytic activities of platelets are widely recognized; however, receptors and mechanisms involved remain poorly understood. We previously demonstrated that platelets internalize and store phospholipid microvesicles enriched in human tissue factor (TF+MVs) and that platelet‐associated TF enhances thrombus formation at sites of vascular damage. Here, we investigate the mechanisms implied in the interactions of TF+MVs with platelets and the effects of specific inhibitory strategies. Aggregometry and electron microscopy were used to assess platelet activation and TF+MVs uptake. Cytoskeletal assembly and activation of phosphoinositide 3‐kinase (PI3K) and RhoA were analyzed by western blot and ELISA. Exposure of platelets to TF+MVs caused reversible platelet aggregation, actin polymerization and association of contractile proteins to the cytoskeleton being maximal at 1 min. The same kinetics were observed for activation of PI3K and translocation of RhoA to the cytoskeleton. Inhibitory strategies to block glycoprotein IIb‐IIIa (GPIIb‐IIIa), scavenger receptor CD36, serotonin transporter (SERT) and PI3K, fully prevented platelet aggregation by TF+MVs. Ultrastructural techniques revealed that uptake of TF+MVs was efficiently prevented by anti‐CD36 and SERT inhibitor, but only moderately interfered by GPIIb‐IIIa blockade. We conclude that internalization of TF+MVs by platelets occurs independently of receptors related to their main hemostatic function (GPIIb‐IIIa), involves the scavenger receptor CD36, SERT and engages PI3‐Kinase activation and cytoskeletal assembly. CD36 and SERT appear as potential therapeutic targets to interfere with the association of TF+MVs with platelets and possibly downregulate their prothrombotic phenotype. J. Cell. Biochem. 117: 448–457, 2016. © 2015 Wiley Periodicals, Inc.     

Chemokine receptor CXCR7 mediates human endothelial progenitor cells survival, angiogenesis, but not proliferation

Stromal cell-derived factor 1 (SDF-1) is a critical regulator of endothelial progenitor cells (EPCs) mediated physiological and pathologic angiogenesis. It was considered to act via its unique receptor CXCR4 for a long time. CXCR7 is a second, recently identified receptor for SDF-1, and its role in human EPCs is unclear. In present study, CXCR7 was found to be scarcely expressed on the surface of human EPCs derived from cord blood, but considerable intracellular CXCR7 was detected, which differs from that on EPCs derived from rat bone marrow. CXCR7 failed to support SDF-1 induced human EPCs migration, proliferation, or nitric oxide (NO) production, but mediated human EPCs survival exclusively. Besides that, CXCR7 mediated EPCs tube formation along with CXCR4. Blocking CXCR7 with its antagonist CCX733 impaired SDF-1/CXCR4 induced EPCs adhesion to active HUVECs and trans-endothelial migration. Those results suggested that CXCR7 plays an important role in human cord blood derived EPCs in response to SDF-1.