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)-A₁₆₅-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-A₁₆₅ to VEGF-R1 in peptides encoded by exons 7 and 8 of VEGF-A₁₆₅. The specific inhibition of VEGF-A₁₆₅ binding on NRP-1 and VEGF-R1 by ERTCRC and CDKPRR peptides decreased the Phactr-1 mRNA levels in HUVECs indicating that VEGF-A₁₆₅-dependent regulation of Phactr-1 expression required both NRP-1 and VEGF-R1 receptors. In addition, upon VEGFA₁₆₅-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.     

Toxic effects of amyloid fibrils on cell membranes: the importance of ganglioside GM1

The interaction of amyloid aggregates with the cell plasma membrane is currently considered among the basic mechanisms of neuronal dysfunction in amyloid neurodegeneration. We used amyloid oligomers and fibrils grown from the yeast prion Sup35p, responsible for the specific prion trait [PSI(+)], to investigate how membrane lipids modulate fibril interaction with the membranes of cultured H-END cells and cytotoxicity. Sup35p shares no homology with endogenous mammalian polypeptide chains. Thus, the generic toxicity of amyloids and the molecular events underlying cell degeneration can be investigated without interference with analogous polypeptides encoded by the cell genome. Sup35 fibrils bound to the cell membrane without increasing its permeability to Ca(2+). Fibril binding resulted in structural reorganization and aggregation of membrane rafts, with GM1 clustering and alteration of its mobility. Sup35 fibril binding was affected by GM1 or its sialic acid moiety, but not by cholesterol membrane content, with complete inhibition after treatment with fumonisin B1 or neuraminidase. Finally, cell impairment resulted from caspase-8 activation after Fas receptor translocation on fibril binding to the plasma membrane. Our observations suggest that amyloid fibrils induce abnormal accumulation and overstabilization of raft domains in the cell membrane and provide a reasonable, although not unique, mechanistic and molecular explanation for fibril toxicity.     

Solution structure of the immunodominant domain of protective antigen GNA1870 of Neisseria meningitidis

GNA1870, a 28-kDa surface-exposed lipoprotein of Neisseria meningitidis recently discovered by reverse vaccinology, is one of the most potent antigens of Meningococcus and a promising candidate for a universal vaccine against a devastating disease. Previous studies of epitope mapping and genetic characterization identified residues critical for bactericidal response within the C-terminal domain of the molecule. To elucidate the conformation of protective epitopes, we used NMR spectroscopy to obtain the solution structure of the immunodominant 18-kDa C-terminal portion of GNA1870. The structure consists of an eight-stranded antiparallel beta-barrel overlaid by a short alpha-helix with an unstructured N-terminal end. Residues previously shown to be important for antibody recognition were mapped on loops facing the same ridge of the molecule. The sequence similarity of GNA1870 with members of the bacterial transferrin receptor family allows one to predict the folding of this class of well known bacterial antigens, providing the basis for the rational engineering of high affinity B cell epitopes.     

Redox regulation of beta-actin during integrin-mediated cell adhesion

Redox sensitivity of actin toward an exogenous oxidative stress has recently been reported. We report here the first evidence of in vivo actin redox regulation by a physiological source of reactive oxygen species, specifically those species generated by integrin receptors during cell adhesion. Actin oxidation takes place via the formation of a mixed disulfide between cysteine 374 and glutathione; this modification is essential for spreading and for cytoskeleton organization. Impairment of actin glutathionylation, either through GSH depletion or expression of the C374A redox-insensitive mutant, greatly affects cell spreading and the formation of stress fibers, leading to inhibition of the disassembly of the actinomyosin complex. These data suggest that actin glutathionylation is essential for cell spreading and cytoskeleton organization and that it plays a key role in disassembly of actinomyosin complex during cell adhesion.     

Functional conservation of MADS-box factors controlling floral organ identity in rice and Arabidopsis

Studies on MADS-box genes in Arabidopsis and other higher eudicotyledonous flowering plants have shown that they are key regulators of flower development. Since Arabidopsis and monocotyledonous rice are distantly related plant species it is interesting to investigate whether the floral organ identity factors have been conserved in their functions, and if not, to understand the differences. Arabidopsis and rice are very suitable for these studies since they are both regarded as models for plant functional genomics. Both their genomes are sequenced and tools are available for the analysis of gene function. These developments have accelerated experiments and increased our knowledge on rice gene function. Therefore it is the right moment to perform a comparative analysis on MADS-box factors controlling floral organ identity as reported in this review.     

High-level production and covalent immobilization of Providencia rettgeri penicillin G acylase (PAC) from recombinant Pichia pastoris for the development of a novel and stable biocatalyst of industrial applicability

A complete, integrated process for the production of an innovative formulation of penicillin G acylase from Providencia rettgeri(rPAC(P.rett))of industrial applicability is reported. In order to improve the yield of rPAC, the clone LN5.5, carrying four copies of pac gene integrated into the genome of Pichia pastoris, was constructed. The proteinase activity of the recombinant strain was reduced by knockout of the PEP4 gene encoding for proteinase A, resulting in an increased rPAC(P.rett) activity of approximately 40% (3.8 U/mL vs. 2.7 U/mL produced by LN5.5 in flask). A high cell density fermentation process was established with a 5-day methanol induction phase and a final PAC activity of up to 27 U/mL. A single step rPAC(P.rett) purification was also developed with an enzyme activity yield of approximately 95%. The novel features of the rPAC(P.rett) expressed in P.pastoris were fully exploited and emphasized through the covalent immobilization of rPAC(P.rett). The enzyme was immobilized on a series of structurally correlated methacrylic polymers, specifically designed and produced for optimizing rPAC(P.rett) performances in both hydrolytic and synthetic processes. Polymers presenting aminic functionalities were the most efficient, leading to formulations with higher activity and stability (half time stability >3 years and specific activity ranging from 237 to 477 U/g (dry) based on benzylpenicillin hydrolysis). The efficiency of the immobilized rPAC(P.rett) was finally evaluated by studying the kinetically controlled synthesis of beta-lactam antibiotics (cephalexin) and estimating the synthesis/hydrolysis ratio (S/H), which is a crucial parameter for the feasibility of the process.     

Smooth muscle cell injury after cryopreservation of human thoracic aortas

The cryopreservation protocol we use for arterial reconstructive surgery has been studied to evaluate smooth muscle cell (SMC) structural integrity and viability before implantation. Samples of human thoracic aortas (HTA) were harvested from five multi-organ donors. Sampling included unfrozen and cryopreserved specimens. Cryopreservation was performed using RPMI with human albumin and 10% Me(2)SO in a controlled-rate freezing apparatus. Thawing was accomplished by submerging bags in a water bath (39 degrees C) followed by washings in cooled saline. In situ cell preservation as investigated by light and transmission electron microscopy showed that SMCs from cryopreserved HTA had nuclear and cytoplasmic changes. A TUNEL assay, performed to detect DNA fragmentation in situ, showed increased SMC nuclear positivity in cryopreserved HTA when compared to unfrozen samples. 7-AAD flow cytometry assay of cells derived from cryopreserved HTA showed that an average of 49+/-16% cells were unlabeled after cryopreservation. Organ cultures aimed to study cell ability to recover cryopreservation damage showed a decreasing number of SMCs from day 4 to day 15 in cryopreserved HTA. In conclusion, the cryopreservation protocol applied in this study induces irreversible damage of a significant fraction of arterial SMCs.     

YCA1 participates in the acetic acid induced yeast programmed cell death also in a manner unrelated to its caspase-like activity

Yeast cells lacking the metacaspase-encoding gene YCA1 (Δyca1) were compared with wild-type (WT) cells with respect to the occurrence, nature and time course of acetic-acid triggered death. We show that Δyca1 cells undergo programmed cell death (PCD) with a rate lower than that of the WT and that PCD in WT cells is caused at least in part by the caspase activity of Yca1p. Since in Δyca1 cells this effect is lost, but z-VAD-fmk does not prevent both WT and Δyca1 cell death, PCD in WT cells occurs via a Yca1p caspase and a non-caspase route with similar characteristics.