Parthenolide and DMAPT induce cell death in primitive CML cells through reactive oxygen species

Tyrosine kinase inhibitors (TKI) have become a first‐line treatment for chronic myeloid leuakemia (CML). TKIs efficiently target bulk CML cells; however, they are unable to eliminate the leukaemic stem cell (LSC) population that causes resistance and relapse in CML patients. In this study, we assessed the effects of parthenolide (PTL) and dimethyl amino parthenolide (DMAPT), two potent inhibitors of LSCs in acute myeloid leukaemia (AML), on CML bulk and CML primitive (CD34⁺lin^?) cells. We found that both agents induced cell death in CML, while having little effect on the equivalent normal hematopoietic cells. PTL and DMAPT caused an increase in reactive oxygen species (ROS) levels and inhibited NF‐κB activation. PTL and DMAPT inhibited cell proliferation and induced cell cycle arrest in G₀ and G₂ phases. Furthermore, we found cell cycle inhibition to correlate with down‐regulation of cyclin D1 and cyclin A. In summary, our study shows that PTL and DMAPT have a strong inhibitory effect on CML cells. Given that cell cycle arrest was not dependent on ROS induction, we speculate that this effect could be a direct consequence of NF‐κB inhibition and if this mechanism was to be evaded, PTL and DMAPT induced cell death would be potentiated.     

Hybridization in Trypanosoma congolense does not challenge the predominant clonal evolution model. A comment on Tihon et al., 2017, Mol. Ecol.

Tihon et al. have just published in Mol. Ecol. a fine genomic study on Trypanosoma congolense, agent of Animal African Trypanosomiasis. They present very convincing evidence that T. congolense underwent several hybridization events between distinct genetic lines in Zambia. They claim that their data challenge our predominant clonal evolution model (PCE) of micropathogens. We point out the main tenets of our model and show that Tihon et al.'s claim is based on a misinterpretation of the PCE model. Actually, their data strongly support PCE in T. congolense at a microevolutionary level.     

A Second Superoxide Dismutase Gene in the Medfly, Ceratitis Capitata

We report the first case of two Cu/Zn Sod genes (ccSod1 and ccSod2) that have been cloned and sequenced from an insect, the medfly, Ceratitis capitata. Biochemical evidence suggested the presence of two Sod genes in the medfly. The two genes are isolated using different molecular strategies: ccSod1 via cross-hybridization to a genomic library using a heterologous probe and ccSod2 from cDNA using a homologous probe generated by PCR. Sequence analysis shows that ccSod1 and ccSod2 are different genes. The inferred amino sequences show that all essential residues of the active site are strictly conserved, which suggests both genes encode functional Cu/Zn superoxide dismutase (SOD). Phylogenetic analysis by the maximum parsimony method with bootstrap resampling of previously known Cu/Zn SOD reveals two monophyletic groups, vertebrates and insects. The position of ccSOD2 in this phylogeny is undefined with respect to dipteran ccSOD1, vertebrate, plant, fungal, and extracellular Cu/Zn SOD, which suggests that the duplication detected in Ceratitis is ancient, perhaps as old as the origins of the arthropod phylum in the Cambrian more than 500 million years ago. In situ hybridization to polytene chromosomes places the genes on different chromosomes, which is consistent with an ancient gene duplication.     

ADH evolution and the phylogenetic footprint

The evolution of any given protein reflects the interplay between proximal selective forces involving the conservation of protein structure and function and more general populational factors that shape the action and efficiency of natural selection. In an attempt to address that interplay, we have analyzed patterns of amino acid replacement within a well-conserved molecule, alcohol dehydrogenase (ADH), in the Drosophilidae. A sliding window, moved along the protein sequence in order to quantify the extent of change at each amino acid position, reveals heterogeneous amounts of replacement across the molecule when all ADH sequences are analyzed simultaneously. Surprisingly, the replacement profile for ADH differs significantly in the melanogaster, mulleri, and Hawaiian subgroups, reflecting the imprint of the differing evolutionary histories of each of these assemblages on the evolution of this conservative molecule.Correspondence to: R.L. Dorit     

Intragenic duplication and divergence in the spectrin superfamily of proteins

Many structural, signaling, and adhesion molecules contain tandemly repeated amino acid motifs. The alpha-actinin/spectrin/dystrophin superfamily of F-actin-crosslinking proteins contains an array of triple alpha-helical motifs (spectrin repeats). We present here the complete sequence of the novel beta-spectrin isoform beta(Heavy)- spectrin (beta H). The sequence of beta H supports the origin of alpha- and beta-spectrins from a common ancestor, and we present a novel model for the origin of the spectrins from a homodimeric actin-crosslinking precursor. The pattern of similarity between the spectrin repeat units indicates that they have evolved by a series of nested, nonuniform duplications. Furthermore, the spectrins and dystrophins clearly have common ancestry, yet the repeat unit is of a different length in each family. Together, these observations suggest a dynamic period of increase in repeat number accompanied by homogenization within each array by concerted evolution. However, today, there is greater similarity of homologous repeats between species than there is across repeats within species, suggesting that concerted evolution ceased some time before the arthropod/vertebrate split. We propose a two-phase model for the evolution of the spectrin repeat arrays in which an initial phase of concerted evolution is subsequently retarded as each new protein becomes constrained to a specific length and the repeats diverge at the DNA level. This evolutionary model has general applicability to the origins of the many other proteins that have tandemly repeated motifs.      

The Neisseria type 2 IgA1 protease cleaves LAMP1 and promotes survival of bacteria within epithelial cells

Infection of human epithelial cells by Neisseria meningitidis (MC) and Neisseria gonorrhoeae (GC) increases the rate of degradation of LAMP1, a major integral membrane glycoprotein of late endosomes and lysosomes. Several lines of evidence indicate that the neisserial IgA1 protease is directly responsible for this LAMP1 degradation. LAMP1 contains an IgA1-like hinge region with potential cleavage sites for the neisserial type 1 and type 2 IgA1 proteases. Neisserial type 2 IgA1 protease cleaves purified LAMP1 in vitro . Unlike its wild-type isogenic parent, an iga ⁻ mutant of N. gonorrhoeae cannot affect LAMP1 turnover and its growth in epithelial cells is dramatically reduced. Thus, IgA1 protease cleavage of LAMP1 promotes intracellular survival of pathogenic Neisseria spp.     

Use of electrophoretic titration curves in the purification of a β-1-3 glucanase from Oerskovia xanthineolytica

A -1-3-glucanase from O. xanthineolytica was purified from a fermentation broth, in two chromatographic steps using information obtained from electrophoretic titration curves. Charge characteristic of proteins present were determined over a pH range of 3-9 and displayed a good correlation with the chromatographic behaviour observed using ionic exchange chromatography.This revised version was published online in October 2005 with corrections to the Cover Date.     

Higher‐order assemblies of oligomeric cargo receptor complexes form the membrane scaffold of the Cvt vesicle

Selective autophagy is the mechanism by which large cargos are specifically sequestered for degradation. The structural details of cargo and receptor assembly giving rise to autophagic vesicles remain to be elucidated. We utilize the yeast cytoplasm‐to‐vacuole targeting (Cvt) pathway, a prototype of selective autophagy, together with a multi‐scale analysis approach to study the molecular structure of Cvt vesicles. We report the oligomeric nature of the major Cvt cargo Ape1 with a combined 2.8 Å X‐ray and negative stain EM structure, as well as the secondary cargo Ams1 with a 6.3 Å cryo‐EM structure. We show that the major dodecameric cargo prApe1 exhibits a tendency to form higher‐order chain structures that are broken upon interaction with the receptor Atg19 in vitro. The stoichiometry of these cargo–receptor complexes is key to maintaining the size of the Cvt aggregate in vivo. Using correlative light and electron microscopy, we further visualize key stages of Cvt vesicle biogenesis. Our findings suggest that Atg19 interaction limits Ape1 aggregate size while serving as a vehicle for vacuolar delivery of tetrameric Ams1.     

Bee visitation rates to trees of Prockia crucis differing in flower number

Summary Annual flower production ranged over four orders of magnitude among individuals of the tropical tree Prockia crucis (Flacourtiaceae), but the number of visits per flower by bees did not increase with flower number. In a population in Jalisco, México, the trees flower for about one week each year, offering only pollen to the bees (mostly solitary species). In a small group of trees, the number of visits per flower was less on trees with greater flower production but in a large group visitation did not vary between trees. Pollen flow probably was not directed from large to small trees or vice versa, because the number of flowers per tree did not determine the schedule of visits. The ratio of pollinators to pollen thieves decreased rapidly through the day, while individuals of both groups foraged more rapidly. Most bee species were rare, and only a small subset of medium-sized to large bees were effective pollinators. Large and small groups of trees differed in the relationship between individual flower crop and abundance and diversity of both pollinators and thieves.