Carotenoid cleavage products modify respiratory burst and induce apoptosis of human neutrophils

Carotenoid supplementation in the treatment of diseases associated with oxidative stress has been recently questioned because of the cell damage and the increased risk of lung cancer in male smokers. Because of the complex role of neutrophils in lung diseases, we investigated whether carotenoid derivatives could affect respiratory burst and apoptosis of human neutrophils purified from peripheral blood. Stimulation of superoxide production was induced by nanomolar and micromolar concentrations of carotenoid cleavage products with aliphatic chains of different length, but not by carotenoids lacking the carbonyl moiety. The stimulatory effect of carotenoid cleavage products was observed in cells activated by phorbol myristate acetate (PMA), while a slight inhibition of superoxide production was noticed with cells activated by the chemotactic tripeptide N-formyl-Met-Leu-Phe (f-MLP). At higher concentrations, carotenoid cleavage products inhibited superoxide production in the presence of both PMA and f-MLP. In the presence of 20 microM carotenoid cleavage products, inhibition of superoxide production was accompanied by DNA fragmentation and increased level of intracellular caspase-3 activity.     

Genistein can modulate channel function by a phosphorylation-independent mechanism: importance of hydrophobic mismatch and bilayer mechanics

Genistein, a generic tyrosine kinase inhibitor, has been used extensively as a tool to investigate the possible regulation of membrane function by tyrosine phosphorylation. Genistein, in micromolar concentrations, alters the function of numerous ion channels and other membrane proteins, but only in few cases has it been demonstrated that the changes in membrane protein (ion channel) function are due to changes in a protein's phosphorylation status. The major common denominator characterizing proteins that are modulated by genistein seems to be that they are imbedded into, and span, the bilayer component of the plasma membrane. We therefore explored whether genistein could alter ion channel function by a bilayer-mediated mechanism and examined genistein's effect on gramicidin A (gA) channels in planar phospholipid bilayers. gA channels form by transmembrane dimerization of two nonconducting subunits, and genistein potentiates gA channel activity by increasing the appearance rate and prolonging the lifetime of bilayer-spanning gA dimers. That is, genistein shifts the equilibrium between nonconducting monomers and conducting dimers in favor of the bilayer-spanning dimers; the changes in channel activity therefore cannot be due to changes in bilayer fluidity. To obtain further insights into the mechanism underlying this modulation of gA channel function, we examined the effects of genistein on channels formed by gA analogues that differ in amino acid sequence. For a given channel length, the effects of genistein on gA dimerization do not depend on the specific sequence, or the chirality, of the channel-forming gA analogues. In contrast, when we change the channel length (by decreasing or increasing the number of amino acid residues in the sequence), or the bilayer thickness (by changing methylene groups in the acyl chains), the magnitude of genistein's effect increases with increasing hydrophobic mismatch between the channel length and the bilayer thickness. These results strongly suggest that genistein alters bilayer mechanical properties, which in turn modulates channel function. This bilayer-mediated mechanism is likely to apply to other pharmacological reagents and membrane proteins.     

Evidence of a leading role for VEGF in Bartonella henselae-induced endothelial cell proliferations

Bartonella henselae causes the vasculoproliferative disorders bacillary angiomatosis (BA) and bacillary peliosis (BP). The pathomechanisms of these tumorous proliferations are unknown. Our results suggest a novel bacterial two-step pathogenicity strategy, in which the pathogen triggers growth factor production for subsequent proliferation of its own host cells. In fact, B. henselae induces host cell production of the angiogenic factor vascular endothelial growth factor (VEGF), leading to proliferation of endothelial cells. The presence of B. henselae pili was associated with host cell VEGF production, as a Pil- mutant of B. henselae was unable to induce VEGF production. In turn, VEGF-stimulated endothelial cells promoted the growth of B. henselae. Immunohistochemistry for VEGF in specimens from patients with BA or BP revealed increased VEGF expression in vivo. These findings suggest a novel bacteria-dependent mechanism of tumour growth.     

Sutural loosening and skeletal flexibility during growth: determination of drop-like shapes in sea urchins

The shape of sea urchins may be determined mechanically by patterns of force analogous to those that determine the shape of a water droplet. This mechanical analogy implies skeletal flexibility at the time of growth. Although comprised of many rigid calcite plates, sutural collagenous ligaments could confer such flexibility if the sutures between plates loosened and acted as joints at the time of growth. We present experimental evidence of such flexibility associated with weight gain and growth. Over 13-, 4-, and 2-week periods, fed urchins (Strongylocentrotus droebachiensis) gained weight and developed looser sutures than unfed urchins that maintained or lost weight. Further, skeletons of fed urchins force-relaxed more than did those of unfed urchins and urchins with loose sutures force-relaxed more than those with tight sutures. Urchins (Strongylocentrotus franciscanus) fed for two and a half weeks, gained weight, also had looser skeletons and deposited calcite at sutural margins, whereas unfed ones did not. In field populations of S. droebachiensis the percentage having loose sutures varied with urchin diameter and reflected their size-specific growth rate. The association between feeding, weight gain, calcite deposition, force relaxation and sutural looseness supports the hypothesis that urchins deform flexibly while growing, thus determining their drop-like shapes.     

Anaphase specific auto-cleavage of separase

Sister-chromatid separation is triggered by a specific proteolytic cleavage of chromosomal cohesins catalyzed by the endopeptidase separase. Prior to anaphase, separase is inhibited independently by affinity binding to securin and by specific inhibitory phosphorylation. Here we show that separase itself is also subjected to proteolytic cleavages at three adjacent sites. The cleavages are auto-catalyzed and occur specifically at anaphase coincident with separase activation. The cleaved fragments remain associated with each other and are catalytically active. Mapping of the cleavage sites reveals that all three sites are conserved in vertebrates underlining a significant function for this regulation.     

Conformational control through translocational regulation: a new view of secretory and membrane protein folding

We suggest a new view of secretory and membrane protein folding that emphasizes the role of pathways of biogenesis in generating functional and conformational heterogeneity. In this view, heterogeneity results from action of accessory factors either directly binding specific sequences of the nascent chain, or indirectly, changing the environment in which a particular domain is synthesized. Entrained by signaling pathways, these variables create a combinatorial set of necessary-but-not-sufficient conditions that enhance synthesis and folding of particular alternate, functional, conformational forms. We therefore propose that protein conformation is productively regulated by the cell during translocation across the endoplasmic reticulum (ER), a concept that may account for currently poorly understood aspects of physiological function, natural selection, and disease pathogenesis.     

Yop fusions to tightly folded protein domains and their effects on Yersinia enterocolitica type III secretion

Yersinia enterocolitica organisms secrete Yop proteins via the type III pathway. Translational fusion of yop genes to ubiquitin or dihydrofolate reductase results in hybrid proteins that cannot be secreted. The folding of hybrids prevents their own transport, but it does not hinder the type III secretion of other Yops.     

Anchoring of surface proteins to the cell wall of Staphylococcus aureus. III. Lipid II is an in vivo peptidoglycan substrate for sortase-catalyzed surface protein anchoring

Surface proteins of Staphylococcus aureus are anchored to the cell wall peptidoglycan by a mechanism requiring a C-terminal sorting signal with an LPXTG motif. Surface proteins are first synthesized in the bacterial cytoplasm and then transported across the cytoplasmic membrane. Cleavage of the N-terminal signal peptide of the cytoplasmic surface protein P1 precursor generates the extracellular P2 species, which is the substrate for the cell wall anchoring reaction. Sortase, a membrane-anchored transpeptidase, cleaves P2 between the threonine (T) and the glycine (G) of the LPXTG motif and catalyzes the formation of an amide bond between the carboxyl group of threonine and the amino group of cell wall cross-bridges. We have used metabolic labeling of staphylococcal cultures with [(32)P]phosphoric acid to reveal a P3 intermediate. The (32)P-label of immunoprecipitated surface protein is removed by treatment with lysostaphin, a glycyl-glycine endopeptidase that separates the cell wall anchor structure. Furthermore, the appearance of P3 is prevented in the absence of sortase or by the inhibition of cell wall synthesis. (32)P-Labeled cell wall anchor species bind to nisin, an antibiotic that is known to form a complex with lipid II. Thus, it appears that the P3 intermediate represents surface protein linked to the lipid II peptidoglycan precursor. The data support a model whereby lipid II-linked polypeptides are incorporated into the growing peptidoglycan via the transpeptidation and transglycosylation reactions of cell wall synthesis, generating mature cell wall-linked surface protein.     

Direct and quantitative single-cell analysis of human immunodeficiency virus type 1 reactivation from latency

The ability of human immunodeficiency virus type 1 (HIV-1) to establish latent infections in cells has received renewed attention owing to the failure of highly active antiretroviral therapy to eradicate HIV-1 in vivo. Despite much study, the molecular bases of HIV-1 latency and reactivation are incompletely understood. Research on HIV-1 latency would benefit from a model system that is amenable to rapid and efficient analysis and through which compounds capable of regulating HIV-1 reactivation may be conveniently screened. We describe a novel reporter system that has several advantages over existing in vitro systems, which require elaborate, expensive, and time-consuming techniques to measure virus production. Two HIV-1 molecular clones (NL4-3 and 89.6) were engineered to express enhanced green fluorescent protein (EGFP) under the control of the viral long terminal repeat without removing any viral sequences. By using these replication-competent viruses, latently infected T-cell (Jurkat) and monocyte/macrophage (THP-1) lines in which EGFP fluorescence and virus expression are tightly coupled were generated. Following reactivation with agents such as tumor necrosis factor alpha, virus expression and EGFP fluorescence peaked after 4 days and over the next 3 weeks each declined in a synchronized manner, recapitulating the establishment of latency. Using fluorescence microscopy, flow cytometry, or plate-based fluorometry, this system allows immediate, direct, and quantitative real-time analysis of these processes within single cells or in bulk populations of cells. Exploiting the single-cell analysis abilities of this system, we demonstrate that cellular activation and virus reactivation following stimulation with proinflammatory cytokines can be uncoupled.