Nocodazole Induced Suicidal Death of Human Erythrocytes

Background: The microtubule assembly inhibitor nocodazole has been shown to trigger caspase-independent mitotic death and caspase dependent apoptosis. Similar to apoptosis of nucleated cells, erythrocytes may undergo eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Stimulators of eryptosis include increase of cytosolic Ca2+ activity ([Ca2+]i), oxidative stress and ceramide. The present study explored, whether and how nocodazole induces eryptosis. Methods: Flow cytometry was employed to determine phosphatidylserine exposure at the cell surface from annexin-V-binding, cell volume from forward scatter, [Ca2+]i from Fluo3-fluorescence, the abundance of reactive oxygen species (ROS) from 2\u2032,7\u2032-dichlorodihydrofluorescein (DCF) diacetate dependent fluorescence as well as ceramide surface abundance utilizing specific antibodies. Tubulin abundance was quantified by TubulinTracker\u2122 Green reagent and visualized by confocal microscopy. Results: A 48 hours exposure of human erythrocytes to nocodazole ( 65 30 \u3bcg/ml) significantly increased the percentage of annexin-V-binding cells without significantly modifying average forward scatter. Nocodazole significantly increased Fluo3-fluorescence, significantly increased DCF fluorescence and significantly increased ceramide surface abundance. The effect of nocodazole on annexin-V-binding was significantly blunted, but not abolished by removal of extracellular Ca2+ and was not modified in the presence of Caspase 3 inhibitor zVAD (1 \u3bcM). Nocodazole treatment reduced the content of total tubulin. Conclusions: Nocodazole triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect in part due to stimulation of Ca2+ entry, oxidative stress and ceramide

The Genome of a Pathogenic Rhodococcus: Cooptive Virulence Underpinned by Key Gene Acquisitions

We report the genome of the facultative intracellular parasite Rhodococcus equi, the only animal pathogen within the biotechnologically important actinobacterial genus Rhodococcus. The 5.0-Mb R. equi 103S genome is significantly smaller than those of environmental rhodococci. This is due to genome expansion in nonpathogenic species, via a linear gain of paralogous genes and an accelerated genetic flux, rather than reductive evolution in R. equi. The 103S genome lacks the extensive catabolic and secondary metabolic complement of environmental rhodococci, and it displays unique adaptations for host colonization and competition in the short-chain fatty acid–rich intestine and manure of herbivores—two main R. equi reservoirs. Except for a few horizontally acquired (HGT) pathogenicity loci, including a cytoadhesive pilus determinant (rpl) and the virulence plasmid vap pathogenicity island (PAI) required for intramacrophage survival, most of the potential virulence-associated genes identified in R. equi are conserved in environmental rhodococci or have homologs in nonpathogenic Actinobacteria. This suggests a mechanism of virulence evolution based on the cooption of existing core actinobacterial traits, triggered by key host niche–adaptive HGT events. We tested this hypothesis by investigating R. equi virulence plasmid-chromosome crosstalk, by global transcription profiling and expression network analysis. Two chromosomal genes conserved in environmental rhodococci, encoding putative chorismate mutase and anthranilate synthase enzymes involved in aromatic amino acid biosynthesis, were strongly coregulated with vap PAI virulence genes and required for optimal proliferation in macrophages. The regulatory integration of chromosomal metabolic genes under the control of the HGT–acquired plasmid PAI is thus an important element in the cooptive virulence of R. equi