Sensitivity to antitubulin chemotherapeutics is regulated by MCL1 and FBW7

Microtubules have pivotal roles in fundamental cellular processes and are targets of antitubulin chemotherapeutics. Microtubule-targeted agents such as Taxol and vincristine are prescribed widely for various malignancies, including ovarian and breast adenocarcinomas, non-small-cell lung cancer, leukaemias and lymphomas. These agents arrest cells in mitosis and subsequently induce cell death through poorly defined mechanisms. The strategies that resistant tumour cells use to evade death induced by antitubulin agents are also unclear. Here we show that the pro-survival protein MCL1 (ref. 3) is a crucial regulator of apoptosis triggered by antitubulin chemotherapeutics. During mitotic arrest, MCL1 protein levels decline markedly, through a post-translational mechanism, potentiating cell death. Phosphorylation of MCL1 directs its interaction with the tumour-suppressor protein FBW7, which is the substrate-binding component of a ubiquitin ligase complex. The polyubiquitylation of MCL1 then targets it for proteasomal degradation. The degradation of MCL1 was blocked in patient-derived tumour cells that lacked FBW7 or had loss-of-function mutations in FBW7, conferring resistance to antitubulin agents and promoting chemotherapeutic-induced polyploidy. Additionally, primary tumour samples were enriched for FBW7 inactivation and elevated MCL1 levels, underscoring the prominent roles of these proteins in oncogenesis. Our findings suggest that profiling the FBW7 and MCL1 status of tumours, in terms of protein levels, messenger RNA levels and genetic status, could be useful to predict the response of patients to antitubulin chemotherapeutics.     

New central stimulants

Zusammenfassung Mit 2-Piperidyl(1)-3-phenylpropanol (CN₂) wird an Mäusen, Ratten und Hunden eine deutliche zentralstimulierende Wirkung festgestellt. An anästhesierten Katzen und Hunden blockiert CN₂ die vasopressive Wirkung des Amphetamins und Ephedrins und verstärkt diejenige der Catecholamine.     

Biomimetic synthesis and optimization of cyclic peptide antibiotics

Molecules in nature are often brought to a bioactive conformation by ring formation (macrocyclization). A recurrent theme in the enzymatic synthesis of macrocyclic compounds by non-ribosomal and polyketide synthetases is the tethering of activated linear intermediates through thioester linkages to carrier proteins, in a natural analogy to solid-phase synthesis. A terminal thioesterase domain of the synthetase catalyses release from the tether and cyclization. Here we show that an isolated thioesterase can catalyse the cyclization of linear peptides immobilized on a solid-phase support modified with a biomimetic linker, offering the possibility of merging natural-product biosynthesis with combinatorial solid-phase chemistry. Starting from the cyclic decapeptide antibiotic tyrocidine A, this chemoenzymatic approach allows us to diversify the linear peptide both to probe the enzymology of the macrocyclizing enzyme, TycC thioesterase, and to create a library of cyclic peptide antibiotic products. We have used this method to reveal natural-product analogues of potential therapeutic utility; these compounds have an increased preference for bacterial over eukaryotic membranes and an improved spectrum of activity against some common bacterial pathogens.     

Homologous recombination in fission yeast: Absence of crossover interference and synaptonemal complex

The study of homologous recombination in the fission yeastSchizosaccharomyces pombe has recently been extended to the cytological analysis of meiotic prophase. Unlike in most eukaryotes no tripartite SC structure is detectable, but linear elements resembling axial cores of other eukaryotes are retained. They may be indispensable for meiotic recombination and proper chromosome segregation in meiosis I. In addition fission yeast shows interesting features of chromosome organization in vegetative and meiotic cells: Centromeres and telomeres cluster and associate with the spindle pole body. The special properties of fission yeast meiosis correlate with the absence of crossover interference in meiotic recombination. These findings are discussed. In addition homologous recombination in fission yeast is reviewed briefly.This article is dedicated to Urs Leupold, the founder of fission yeast genetics.     

In vitro suppression of UGA codons in a mitochondrial mRNA

Although both prokaryotic and eukaryotic messenger RNAs can be easily translated in heterologous protein-synthesizing systems, attempts to achieve correct synthesis of mitochondrial proteins by translation of mitochondrial mRNAs in such systems have failed. In general, the products of synthesis are of low molecular weight and presumably represent fragments of mitochondrial proteins. These fragments display a strong tendency to aggregate. Explanations have included the use by mitochondria of codons requiring a specialized tRNA population and the fortuitous occurrence within genes of purine-rich sequences resembling bacterial ribosome binding sites. In addition, the long 5'-leader sequences present in many mitochondrial (mt) RNAs may also contribute to difficulties in mRNA recognition by heterologous ribosomes. Recent sequence analysis of human mtDNA suggests that the genetic code used by mammalian mitochondria deviates in a number of respects from the 'universal' code, the most striking of these being the use of the UGA termination codon to specify tryptophan. That this may also apply in yeast mitochondria has been shown by Fox and Macino et al., thus providing an obvious and easily testable explanation for the inability of heterologous systems to synthesize full-length mitochondrial proteins. We confirm this explanation and describe here the in vitro synthesis of a full-length subunit II of yeast cytochrome c oxidase in a wheat-germ extract supplemented with a partially purified mitochondrial mRNA for this protein and a UGA-suppressor tRNA from Schizosaccharomyces pombe.     

Urinary excretion of renal brush border membrane enzymes in leprosy patientseffect of multidrug therapy

Renal function at the brush border membrane level has been studied using characteristic enzymes, such as alkaline phosphatase, leucine-aminopeptidase and gamma-glutamyl transpeptidase. Urinary enzyme studies were performed using leprosy patients, classified on the basis of bacteriological index (BI>3; n=20,BI<3; n=12, BI-ve; n=10) and compared with control subjects (n=10). The role of enzymuria in monitoring WHO-recommended multidrug therapy (MDT) has been evaluated in these patients. A significant increase in the enzyme activities (p<0.01), as well as significant (p<0.01) proteinurea in 24-hour urine samples of both the smear positive groups (BI>3,BI<3) prior to therapy compared to control subjects, indicates proximal tubular functional impairment at brush border membrane level. In the smear negative (BI-ve) grou, no significant difference was observed in enzyme activities as compared with the control group. In a follow-up study (BI>3; n=13, BI<3; n=4) the activities of all the enzymes decreased significantly in all the groups when compared to a corresponding untreated group. The follow-up study was not carried out on the smear negative group. The surprising finding was the differential behaviour of r-glutamyl transpeptidase, whose activity increased significantly (p<0.01) even after therapy inBI>3 group when compared with untreated patients. However in a detailed work-up including hepatic and renal function tests, the serum biochemistry was found to be normal both before and after therapy. Urinary excretion of brush border enzymes seems to be related to bacterial load, and their potential in studying the effect of MDT remains unclear.     

Antimony trichloride catalyzed reactions on terpenoids,a nucleophilic addition reaction on khusinol

Zusammenfassung Es wird eine neuartige Reaktion an einem Terpen beschrieben.     

Photodynamic effect of dye on frog muscle fibre using microelectrodes

Zusammenfassung Kurarisierte und nichtkurarisierte Frosch-Sartorii zeigten einen veränderlichen Grad der Depolarisation, wenn sie mit Bengalrot (1:25 000) gefärbt und durch scharf zentriertes Licht einer 300-Watt-Tungsten-Lampe beleuchtet wurden. Die Depolarisation wurde niemals im äusseren Natrium und ohne Sauerstoff beobachtet.     

Involvement of nucleotide-excision repair in msh2 pms1-independent mismatch repair

Nucleotide-excision repair (NER) and mismatch repair (MMR) are prominent examples of highly conserved DNA repair systems which recognize and replace damaged and/or mispaired nucleotides in DNA. In humans, inheritable defects in components of the NER system are associated with severe diseases such as xeroderma pigmentosum (XP) and Cockayne syndrome (CS), whereas inactivation of MMR is accompanied by predisposition to certain types of cancer. In Schizosaccharomyces pombe, the msh2- and pms1-dependent long-patch MMR system efficiently corrects small insertion/deletion loops and all base-base mismatches, except C/C. Up to 70% of C/C mismatches generated in recombination intermediates, and to a lesser extent also other base-base mismatches, are thought to undergo correction by a minor, short-patch excision repair system. We identify here the NER genes rhpl4, swi10 and rad16 as components of this repair pathway and show that they act independently of msh2 and pms1.