Interactions of the natural product kendomycin and the 20S proteasome

Natural products are a valuable source for novel lead structures in drug discovery, but for the majority of isolated bioactive compounds, the cellular targets are unknown. The structurally unique ansa-polyketide kendomycin (KM) was reported to exert its potent cytotoxic effects via impairment of the ubiquitin proteasome system, but the exact mode of action remained unclear. Here, we present a systematic biochemical characterization of KM–proteasome interactions in vitro and in vivo, including complex structures of wild type and mutant yeast 20S proteasome with KM. Our results provide evidence for a polypharmacological mode of action for KM's cytotoxic effect on cancer cells.     

Experiences of Borna disease virus infection in Sweden

In the early 1970s a fatal neurological disorder in cats was reported in the areas around Lake M?laren in central Sweden. The major signs were hind-leg ataxia, as well as absence or marked decrease in postural reactions and in some cases behavioural changes. The pathology of the disorder was characterized as a non-suppurative meningoencephalomyelitis, but the etiology was not determined. Almost twenty years later, the disorder now known as staggering disease (SD), was further characterized both clinically and pathologically. The same histopathological picture was seen as in the previous study, with inflammatory nodules, neuronal degeneration and perivascular cuffs mainly consisting of lymphocytes. The most severe inflammatory changes were seen in the grey matter of the brain stem, basal ganglia and hippocampus. Clinically the same major neurological signs were seen. Although the cats were examined for several known infectious agents causing central nervous system (CNS) disturbances, no etiological cause of SD was determined.     

A non-conservative polymorphism in the IL-6 signal transducer (IL6ST)/gp130 is associated with myocardial infarction in a hypertensive population

Inflammation is a key component in the development of atherosclerosis, and myocardial infarction (MI); therefore we investigated the association between an interleukin-6 signal transducer (IL6ST)/gp130 polymorphism, gp130 function and risk of MI. Structural modeling suggested that a non-conservative single nucleotide polymorphism in the gp130, Gly148Arg, can change the stability and functional properties of the molecule. In vitro studies were done with BAF/3 cells lacking endogenous gp130. Cells stably transfected with the gp130 148Arg variant proliferated less and showed slightly lower STAT-3 phosphorylation in response to gp130 stimulation as compared to cells transfected with gp130 148Gly. In a prospectively followed hypertensive cohort we identified 167 patients who suffered a MI during the study and compared them to matched controls (mean age 57 years, 73% males, n=482). Carriers of the 148Arg variant (f(Arg)=0.12) of the gp130 receptor had decreased odds ratio for MI in univariate analysis (0.56, 95% CI 0.34-0.91, p=0.02). In conclusion, a genetically determined structural variant of the IL-6 receptor subunit gp130 is, independently of other known risk factors, associated with decreased risk of MI. The variant is also associated with decreased IL-6 responsiveness and could lead to a configuration change in the gp130 receptor.     

Arg-vasopressin increases proliferation of human osteoblast-like cells and decreases production of interleukin-6 and macrophage colony-stimulating factor

Patients with arginine-vasopressin (AVP) deficiency have been reported to have a decreased bone mass. The mechanism behind this is not known. In this study, the effects of AVP on primary human osteoblast-like (hOB) cells and SaOS-2 cells were investigated. Cell proliferation was measured by [3H]thymidine incorporation or a commercially available kit (EZ4U), and protein synthesis by [3H]proline incorporation. In addition, the production of interleukin-6 (IL-6) and macrophage colony-stimulating factor (M-CSF) in hOB cells was determined. AVP at 10-100 pmol/l increased cell proliferation in hOB and SaOS-2 cells (p < 0.05). Protein synthesis increased in SaOS-2 cells incubated with 10-100 pmol/l AVP (p < 0.01). When hOB and SaOS-2 cells were incubated with AVP together with a vasopressin receptor-1 (V1)-antagonist ([beta-Mercapto-beta,beta-cyclopenta-methylenepropionyl1,O-Me-Tyr2,Arg8]-vasopressin) or a protein kinase C (PKC)-inhibitor (chelerythrine) the increase in cell proliferation in response to AVP was abolished. The production of IL-6 and M-CSF was decreased in hOB-cells incubated with 10 pmol/l AVP (p < 0.01). In addition, by RT-PCR, we found evidence for expression of mRNA for the vasopressin 1a (V1a)-receptor in hOB cells. In conclusion, AVP stimulated proliferation of hOB- and SaOS-2 cells. We suggest that the effect was mediated through the V1-receptor. Additionally, AVP decreased production of IL-6 and M-CSF from the hOB cells. Moreover, the V1a-receptor seems to be expressed in hOB cells.     

Population heterogeneity in microbial bioprocesses: origin,analysis, mechanisms,and future perspectives

Bioprocess and Biosystems Engineering - Population heterogeneity is omnipresent in all bioprocesses even in homogenous environments. Its origin, however, is only so well understood that potential...     

How pollinator-mediated mating varies with population size in plants

In most higher plants sexual interactions are mediated by animal pollinators that affect the number and differential reproductive success of mates. The number and sex of breeding individuals in populations are central factors in evolutionary theory, but the quantitative effect of plant population size on pollinator-mediated mating is understudied. We investigated variation in pollen removal (male function) and fruit set (female function) among flowering populations of different size of two bumblebee-and one butterfly-pollinated, rewardless, pollen-limited, hermaphroditic orchid species in Sweden. As the amount of pollen removed from plants by insects (either absolute or proportional) increased, so did the number of pollinations, whereas the proportions of plants with different pollinator-designated functional sex (male, female, hermaphrodite) depended primarily on the ratio between the amount of fruit set and pollen removed within populations. A larger population size was found to have several effects: (1) the total numbers of pollinia removed and fruits set increased; (2) the proportion of pollen removed from plants decreased; (3) the proportion of flowers pollinated decreased in the butterfly-but was not affected in the bumblebee-pollinated species; (4) the ratio between fruits set and pollinia removed increased linearly in the bumblebee-pollinated species but reached a maximum at c. 80 individuals in the butterfly-pollinated species; (5) the numbers of pollinator-designated pure male and hermaphrodite individuals increased; and (6) the variance in pollinium removal, but not fruit set, increased among individuals. These findings empirically verify the basic importance of population size for the mating structure of outcrossing plants, and indicate that selection for female sexual traits is reinforced when population size is smaller while selection for male sexual traits is reinforced when population size is larger.     

Ebsulfur Is a Benzisothiazolone Cytocidal Inhibitor Targeting the Trypanothione Reductase of Trypanosoma brucei

Trypanosoma brucei is the causing agent of African trypanosomiasis. These parasites possess a unique thiol redox system required for DNA synthesis and defense against oxidative stress. It includes trypanothione and trypanothione reductase (TryR) instead of the thioredoxin and glutaredoxin systems of mammalian hosts. Here, we show that the benzisothiazolone compound ebsulfur (EbS), a sulfur analogue of ebselen, is a potent inhibitor of T. brucei growth with a favorable selectivity index over mammalian cells. EbS inhibited the TryR activity and decreased non-protein thiol levels in cultured parasites. The inhibition of TryR by EbS was irreversible and NADPH-dependent. EbS formed a complex with TryR and caused oxidation and inactivation of the enzyme. EbS was more toxic for T. brucei than for Trypanosoma cruzi, probably due to lower levels of TryR and trypanothione in T. brucei. Furthermore, inhibition of TryR produced high intracellular reactive oxygen species. Hydrogen peroxide, known to be constitutively high in T. brucei, enhanced the EbS inhibition of TryR. The elevation of reactive oxygen species production in parasites caused by EbS induced a programmed cell death. Soluble EbS analogues were synthesized and cured T. brucei brucei infection in mice when used together with nifurtimox. Altogether, EbS and EbS analogues disrupt the trypanothione system, hampering the defense against oxidative stress. Thus, EbS is a promising lead for development of drugs against African trypanosomiasis.