Bacillus sphaericus Binary Toxin Elicits Host Cell Autophagy as a Response to Intoxication

Bacillus sphaericus strains that produce the binary toxin (Bin) are highly toxic to Culex and Anopheles mosquitoes, and have been used since the late 1980s as a biopesticide for the control of these vectors of infectious disease agents. The Bin toxin produced by these strains targets mosquito larval midgut epithelial cells where it binds to Cpm1 (Culex pipiens maltase 1) a digestive enzyme, and causes severe intracellular damage, including a dramatic cytoplasmic vacuolation. The intoxication of mammalian epithelial MDCK cells engineered to express Cpm1 mimics the cytopathologies observed in mosquito enterocytes following Bin ingestion: pore formation and vacuolation. In this study we demonstrate that Bin-induced vacuolisation is a transient phenomenon that affects autolysosomes. In addition, we show that this vacuolisation is associated with induction of autophagy in intoxicated cells. Furthermore, we report that after internalization, Bin reaches the recycling endosomes but is not localized either within the vacuolating autolysosomes or within any other degradative compartment. Our observations reveal that Bin elicits autophagy as the cell's response to intoxication while protecting itself from degradation through trafficking towards the recycling pathways

The Ubiquitin/Proteasome System Mediates Entry and Endosomal Trafficking of Kaposi's Sarcoma-Associated Herpesvirus in Endothelial Cells

Ubiquitination, a post-translational modification, mediates diverse cellular functions including endocytic transport of molecules. Kaposi's sarcoma-associated herpesvirus (KSHV), an enveloped herpesvirus, enters endothelial cells primarily through clathrin-mediated endocytosis. Whether ubiquitination and proteasome activity regulates KSHV entry and endocytosis remains unknown. We showed that inhibition of proteasome activity reduced KSHV entry into endothelial cells and intracellular trafficking to nuclei, thus preventing KSHV infection of the cells. Three-dimensional (3-D) analyses revealed accumulation of KSHV particles in a cytoplasmic compartment identified as EEA1+ endosomal vesicles upon proteasome inhibition. KSHV particles are colocalized with ubiquitin-binding proteins epsin and eps15. Furthermore, ubiquitination mediates internalization of both KSHV and one of its receptors integrin β1. KSHV particles are colocalized with activated forms of the E3 ligase c-Cbl. Knock-down of c-Cbl or inhibition of its phosphorylation reduced viral entry and intracellular trafficking, resulting in decreased KSHV infectivity. These results demonstrate that ubiquitination mediates internalization of both KSHV and one of its cognate receptors integrin β1, and identify c-Cbl as a potential E3 ligase that facilitates this process

Phase I study of oral CP-4126, a gemcitabine derivative, in patients with advanced solid tumors

<p>CP-4126 is a gemcitabine (2',2'-difluorodeoxycytidine; dFdC) 5' elaidic acid ester. The purpose of this dose-escalating study was to assess safety, pharmacokinetics (PK) and preliminary antitumor activity of the oral formulation and to determine the recommended dose (RD) for phase II studies. The study had a two-step design: a non-randomized dose-escalating step I with oral CP-4126 alone, followed by a randomized, cross-over step II that compared oral CP-4126 with dFdC i.v.. CP-4126 was given on days 1,8,15 in a 4-week schedule with increasing doses until the RD was established. 26 patients with different solid tumours were enrolled in step I at seven dose levels (100-3,000 mg/day). The most frequent drug-related AEs were fatigue and dysgeusia, the majority being grade 1-2. One patient experienced a dose limiting toxicity after one dose of CP-4126 at 1,300 mg/day (ASAT grade 3). PK of CP-4126 could not be determined. The metabolites dFdC and dFdU obeyed dose-dependent pharmacokinetics. Exposures to dFdC were about ten-fold lower compared to exposures after comparable doses of dFdC i.v.. Nine patients reached stable disease as best response, whereby in one patient with vaginal carcinoma a 25 % reduction of tumor volume was reached. This study demonstrates that CP-4126 can be safely administered orally to patients up to 3,000 mg/day in a d1,8,15 q4w schedule with a tolerable safety profile. CP-4126 acts as a prodrug for dFdC when given orally, but because of the poor absorption and the rapid pre-systemic metabolism the study was terminated early and no RD could be determined.</p>