Metarhizin A suppresses cell proliferation by inhibiting cytochrome c oxidase activity

Aims

Metarhizin A was originally isolated from Metarhizium flavoviride as a potent inhibitor of the growth of insect and mammalian cells. In this study, we aimed to understand the molecular targets of metarhizin A involved in its anti-proliferative activity against human cells.

Main methods

Cell cycle regulators and signaling molecules were examined by immunoblotting using specific antibodies. A mitochondria-enriched fraction was prepared from mouse liver, and mitochondrial activity was monitored using an oxygen electrode. Enzyme activity was measured using purified cytochrome c oxidase and permeabilized cells.

Key findings

Metarhizin A inhibits the growth of MCF-7 cells with an IC₅₀ value of ~ 0.2 μM and other cells in a similar manner; a cell cycle-dependent kinase inhibitor, p21, is selectively induced. Significant amounts of reactive oxygen species (ROS) are generated and ERK1/2 is activated in cells treated with metarhizin A. Metarhizin A completely suppresses oxygen consumption by mitochondria, and potently inhibits the activity of cytochrome c oxidase. It induces cell death when MCF-7 cells are cultured under limiting conditions.

Significance

Metarhizin A is a potent inhibitor of cytochrome c oxidase and activates the MAPK pathway through the generation of ROS, which induces growth arrest of cells, and, under some conditions, enhances cell death. The cytochrome c oxidase system is a possible molecular target of metarhizin A.     

Arabidopsis SOI33／AtENT8 Gene Encodes a Putative Equilibrative Nucleoside Transporter That Is Involved in Cytokinin Transport In Planta

The plant phytohormone cytokinin plays an important role in many facets of plant growth and development by regulating cell division and differentiation. Recent studies have shed significant light into the mechanisms of cytokinin metabolism and signaling. However, little is known about how the hormone is transported in planta, although it has been proposed that the hormone is presumably transported in nucleoside-conjugated forms. Here, we report the identification and characterization of cytokinin transporters in Arabidopsis. We previously reported that a gain-of-function mutation in the PGA22/AtlPT8 gene caused overproduction of cytokinins in planta. In an effort to screen for suppressor of pga22/atipt8 (soi) mutants, we identified a mutant soi33-1. Molecular and genetic analyses indicated that S0133 encodes a putative equilibrative nucleoside transporter (ENT), previously designated as AtENT8. Members of this small gene family are presumed to be involved in the transport of nucleosides in eukaryodc cells. Under conditions of nitrogen starvation, loss-of-function mutations in SOI33/AtENT8 or in a related gene AtENT3 cause a reduced sensitivity to the nucleoside-type cytokinins isopentenyladenine riboside (iPR) and transzeatin riboside (tZR), but display a normal response to the free base-type cytokinins isopentenyladenine (iP) and trans-zeatin (tZ). Conversely, overexpression of SOI33/AtENT8 renders transgenic plants hypersensitive to iPR but not to iP. An in planta measurement experiment indicated that uptake efficiency of^3Hlabeled iPR was reduced more than 40% in soi33 and atent3 mutants. However, a mutation in AtENT1 had no substantial effect on the cytokinin response and iPR uptake efficiency. Our results suggest that SOI33/AtENT8 and AtENT3 are involved in the transport of nucleoside-type cytokinins in Arabidopsis.     

A Haplotype of Two Novel Polymorphisms in δ-Sarcoglycan Gene Increases Risk of Dilated Cardiomyopathy in Mongoloid Population

The role of genetic abnormality of δ-sarcoglycan (δ-SG) gene in dilated (DCM) and hypertrophied (HCM) cardiomyopathy patients is still unfolding. In this study we first defined the promoter region and then searched for polymorphisms/mutations among the promoter, 5''-untranslated region, and the encoding exons in δ-SG gene in 104 Chinese patients with DCM, 145 with HCM, and 790 normal controls. Two novel polymorphisms were found, an 11 base-pair (bp) deletion (c._-100~-110; -) in the promoter region and a missense polymorphism of A848G resulting in p.Q283R in the highly conserved C-terminus. The prevalence of homozygous genotype -/- of c._-100~-110 was slightly higher in DCM (14.42%) and HCM patients (14.48%), as compared with normal controls (11.01%). The prevalence of genotype of 848A/G was significantly higher in DCM (6.73%; OR = 9.43; p = 0.0002), but not in HCM patients (1.38%; OR = 1.37; p = 0.62), as compared with controls (0.76%). Haplotype -_G consisting c._-100~-110 and A848G was associated with increased risk of DCM (OR = 17.27; 95%CI = 3.19–93.56; p = 0.001) but not associated with HCM (OR = 1.90; 95%CI = 0.38–9.55; p = 0.44). Co-occurrence of the genotypes -/- of c._-100~-110 and 848A/G was found in 5 patients with DCM (4.81%; OR = 39.85; p = 0.0001), none of HCM patients, and only 1 of the controls (0.13%). Both polymorphisms were also found in the Japanese population, but not in the Africans and Caucasians. C._-100~-110 resulted in a decrease of δ-SG promoter activity to 64±3% of the control level (p<0.01). Both co-immunoprecipitation and in vitro protein pull-down assays demonstrated that δ-SG-283R interacts normally to β- and γ-SG, but significantly decreased localization of β/δ/γ-SG on the plasma membrane. In conclusion, haplotype -_G composed of c._-100~-110 and A848G confers higher susceptibility to DCM in the Mongoloid population.     

Effects of alcoholic beverage treatment on spatial learning and fear memory in mice

Although chronic ethanol treatment is known to impair learning and memory, humans commonly consume a range of alcoholic beverages. However, the specific effects of some alcoholic beverages on behavioral performance are largely unknown. The present study compared the effects of a range of alcoholic beverages (plain ethanol solution, red wine, sake and whiskey; with a matched alcohol concentration of 10%) on learning and memory. 6-week-old C57BL6J mice were orally administered alcohol for 7 weeks. The results revealed that red wine treatment exhibited a trend toward improvement of spatial memory and advanced extinction of fear memory. Additionally, red wine treatment significantly increased mRNA levels of brain-derived neurotrophic factor (BDNF) and N-methyl-D-aspartate (NMDA) receptors in mice hippocampus. These results support previous reports that red wine has beneficial effects.     

Co-precipitation molecules hemopexin and transferrin may be key molecules for fibrillogenesis in TTR V30M amyloidogenesis

The disease model of familial amyloidotic polyneuropathy—7.2-hMet30 mice—manifests amyloid deposition that consists of a human amyloidogenic mutant transthyretin (TTR) (TTR V30M). Our previous study found amyloid deposits in 14 of 27 7.2-hMet30 mice at 21–24 months of age. In addition, non-fibrillar TTR deposits were found in amyloid-negative 7.2hMet30 mice. These results suggested that TTR amyloidogenesis required not only mutant TTR but also an additional factor (or factors) as an etiologic molecule. To determine the differences in serum proteome in amyloid-positive and amyloid-negative mice in the 7.2-hMet30 model, we used proteomic analyses and studied serum samples obtained from these mice. Hemopexin (HPX) and transferrin (Tf) were detected in the serum samples from amyloid-positive mice and were also found in amyloid deposits via immunohistochemistry, but serum samples from amyloid-negative mice did not contain HPX and Tf. These two proteins were also not detected in non-fibrillar TTR deposits. In addition, in silico analyses suggested that HPX and Tf facilitate destabilization of TTR secondary structures and misfolding of TTR. These results suggest that HPX and Tf may be associated with TTR amyloidogenesis after fibrillogenesis in vivo.     

Male origin determines satyrization potential of <Emphasis Type="Italic">Aedes aegypti</Emphasis> by invasive <Emphasis Type="Italic">Aedes albopictus</Emphasis>

Rapid displacements of resident Aedes aegypti by invasions of Aedes albopictus have been documented in the southeastern United States and Bermuda. Interspecific mating has been detected in nature between these species and proposed as a likely mechanism for these displacements by means of asymmetric reproductive interference, or satyrization. However, rapid displacements of A. aegypti have not been detected in most localities where these two invasive species are known to co-occur. Aedes albopictus invaded the United States and Brazil at approximately the same time, in the mid-1980s, but the origins of the invading strains are known to be different. Here we tested the hypothesis, in standardized cage environments, that A. albopictus males from Brazil are less capable of satyrizing A. aegypti females than A. albopictus males from the United States. Using strains of A. aegypti and A. albopictus from the United States of known susceptibility to and capacity for interspecific mating, we demonstrate that A. albopictus colonized from collections in the Brazilian cities of Rio de Janeiro and Manaus were relatively unsuccessful in inseminating virgin female A. aegypti from Key West Florida compared to A. albopictus from peninsular Florida. We suggest that the low satyrization potential of Brazilian A. albopictus males may contribute to the lack of documented competitive displacements of A. aegypti in that country.     

Impact of overgrazing on seed predation by rodents in the Thar desert,northwestern India

We compared the vegetation structure, rodent density and seed loss rate between protected and disturbed sites affected from grazing by cattle, goats and sheep, in the Thar desert of India. A perennial tussocky grassLasiurus sindicus Hent. was largely dominant in the protected site, whileL. sindicus was rare and replaced by undershrub speciesAerva pseudotomentosa Blatt. & Halb. andCrotalaria burbira Buch.-Ham. in the overgrazed site. In the grazed site, plant coverage was low, but the density of rodent burrows and the frequency of rodent captures were significantly high as compared to the protected site. Corresponding with the density of desert rodents, seed predation was significantly higher in the grazed site than in the protected site. These results suggest that overgrazing by large mammals has strong effects on plant succession by altering not only the species composition and abundance of plant community, but also the habitat suitability for seed-eating rodents.