Avicins, natural anticancer saponins, permeabilize mitochondrial membranes

Avicins are a class of natural saponins with selective pro-apoptotic activity in cancer cells. In this work, we studied the influence of avicins on metabolic state of rat liver mitochondria. Avicin-treated mitochondria underwent a significant decrease in oxygen consumption rate that was completely restored by addition of exogenous cytochrome c. On the other hand, avicins increased the rotenone-insensitive oxidation of external NADH in the presence of exogenous cytochrome c, long before high amplitude swelling of mitochondria was observed. The increase in external NADH oxidation was cyclosporin A-insensitive. Avicin G significantly accelerated hydroperoxide-induced oxidation of mitochondrial endogenous NAD(P)H, the drop of the inner membrane potential and the high amplitude swelling of mitochondria. The obtained data might explain selective induction of apoptosis in tumor cells by avicins. Based on other studies showing that tumor cells generate hydroperoxides with a very high rate, avicins could provide a new strategy of anticancer therapy by sensitizing cells with high levels of reactive oxygen species to apoptosis.     

RNA binding is more critical to the suppression of silencing function of Cucumber mosaic virus 2b protein than nuclear localization

Previously, we found that silencing suppression by the 2b protein and six mutants correlated both with their ability to bind to double-stranded (ds) small RNAs (sRNAs) in vitro and with their nuclear/nucleolar localization. To further discern the contribution to suppression activity of sRNA binding and of nuclear localization, we have characterized the kinetics of in vitro binding to a ds sRNA, a single-stranded (ss) sRNA, and a micro RNA (miRNA) of the native 2b protein and eight mutant variants. We have also added a nuclear export signal (NES) to the 2b protein and assessed how it affected subcellular distribution and suppressor activity. We found that in solution native protein bound ds siRNA, miRNA, and ss sRNA with high affinity, at protein:RNA molar ratios ~2:1. Of the four mutants that retained suppressor activity, three showed sRNA binding profiles similar to those of the native protein, whereas the remaining one bound ss sRNA at a 2:1 molar ratio, but both ds sRNAs with 1.5-2 times slightly lower affinity. Three of the four mutants lacking suppressor activity failed to bind to any sRNA, whereas the remaining one bound them at far higher ratios. NES-tagged 2b protein became cytoplasmic, but suppression activity in patch assays remained unaffected. These results support binding to sRNAs at molar ratios at or near 2:1 as critical to the suppressor activity of the 2b protein. They also show that cytoplasmically localized 2b protein retained suppressor activity, and that a sustained nuclear localization was not required for this function.     

A novel checkpoint in the Bcl-2-regulated apoptotic pathway revealed by murine cytomegalovirus infection of dendritic cells

Infection with murine cytomegalovirus (MCMV) has contributed to understanding many aspects of human infection and, additionally, has provided important insight to understanding complex cellular responses. Dendritic cells (DCs) are a major target for MCMV infection. Here, we analyze the effects of MCMV infection on DC viability, and show that infected DCs become resistant to apoptosis induced by growth factor deprivation. The precise contribution of changes in the expression of Bcl-2 family proteins has been assessed and a new checkpoint in the apoptotic pathway identified. Despite their resistance to apoptosis, MCMV-infected DCs showed Bax to be tightly associated with mitochondria and, together with Bak, forming high molecular weight oligomers, changes normally associated with apoptotic cell death. Exposure of a constitutively occluded Bax NH2-terminal epitope was blocked after infection. These results suggest that MCMV has evolved a novel strategy for inhibiting apoptosis and provide evidence that apoptosis can be regulated after translocation, integration, and oligomerization of Bax at the mitochondrial membrane.     

豆科根瘤内气体交换和气体扩散模型研究

近年来的研究表明根瘤皮层内存在着可调节的气体扩散屏障,它是由根瘤皮层内的一层细胞及填充在胞间隙的水层构成的,而根瘤是通过改变填充该层胞间隙的水层厚度来调节对气体扩散的阻力。本文概述了关于模拟豆科根瘤内气体交换和气体扩散的数学模型研究,阐明调节根瘤内含类菌体细胞维持低氧分压的有关问题。模型研究使我们获得了对共生固氮根瘤内极为复杂的微生态环境的初步认识,有待于通过改进试验和借助其他理论进一步探索根瘤气体交换和气体扩散的本质。     

Early steps in cold sensing by plant cells: the role of actin cytoskeleton and membrane fluidity

Many plants acquire freezing tolerance through cold acclimatization (CA), a prolonged exposure to low but non-freezing temperatures at the onset of winter. CA is associated with gene expression that requires transient calcium influx into the cytosol. Alfalfa (Medicago sativa) cells treated with agents blocking this influx are unable to cold-acclimatize. Conversely, chemical agents causing increased calcium influx induce cold acclimatization-specific (cas) gene expression in alfalfa at 25 degrees C. How low temperature triggers calcium influx is, however, unknown. We report here that induction of a CA-specific gene (cas30), calcium influx and freezing tolerance at 4 degrees C are all prevented by cell membrane fluidization, but, conversely, are induced at 25 degrees C by membrane rigidification. cas30 expression and calcium influx at 4 degrees C are also prevented by jasplakinolide (JK), an actin microfilament stabilizer, but induced at 25 degrees C by the actin microfilament destabilizer cytochalasin D (CD). JK blocked the membrane rigidifier-induced, but not the calcium channel agonist-induced cas30 expression at 25 degrees C. These findings indicate that cytoskeleton re-organization is an integral component in low-temperature signal transduction in alfalfa cell suspension cultures, serving as a link between membrane rigidification and calcium influx in CA.     

The role of Ca2+/Calcineurin/NFAT signalling pathway in osteoblastogenesis

The bone remodelling process is closely related to bone health. Osteoblasts and osteoclasts participate in the bone remodelling process under the regulation of various factors inside and outside. Excessive activation of osteoclasts or lack of function of osteoblasts will cause occurrence and development of multiple bone‐related diseases. Ca²⁺/Calcineurin/NFAT signalling pathway regulates the growth and development of many types of cells, such as cardiomyocyte differentiation, angiogenesis, chondrogenesis, myogenesis, bone development and regeneration, etc. Some evidences indicate that this signalling pathway plays an extremely important role in bone formation and bone pathophysiologic changes. This review discusses the role of Ca²⁺/Calcineurin/NFAT signalling pathway in the process of osteogenic differentiation, as well as the influence of regulating each component in this signalling pathway on the differentiation and function of osteoblasts, whereby the relationship between Ca²⁺/Calcineurin/NFAT signalling pathway and osteoblastogenesis could be deeper understood.     

Catalytic residues and substrate specificity of scytalidoglutamic peptidase, the first member of the eqolisin in family (G1) of peptidases

Scytalidoglutamic peptidase (SGP) is the first-discovered member of the eqolisin family of peptidases with a unique structure and a presumed novel catalytic dyad (E136 and Q53) [Fujinaga et al., PNAS 101 (2004) 3364-3369]. Mutants of SGP, E136A, Q53A, and Q53E lost both the autoprocessing and enzymatic activities of the wild-type enzyme. Coupled with the results from the structural analysis of SGP, Glu136 and Gln53 were identified as the catalytic residues. The substrate specificity of SGP is unique, particularly, in the preference at the P3 (basic amino acid), P1' (small a.a.), and P3' (basic a.a.) positions. Superior substrates and inhibitors have been synthesized for kinetic studies based on the results reported here. kcat, Km, and kcat/Km of SGP for D-Dap(MeNHBz)-GFKFF*ALRK(Dnp)-D-R-D-R were 34.8 s-1, 0.065 microM, and 535 microM-1 s-1, respectively. Ki of Ac-FKF-(3S,4S)-phenylstatinyl-LR-NH2 for SGP was 1.2x10(-10) M. Taken together, we can conclude that SGP has not only structural and catalytic novelties but also a unique subsite structure.     

Factores de riesgo asociados a fallecimiento por la variante ómicron de COVID-19: análisis retrospectivo con personas mayores de Canarias

Background and aimsSince the beginning of the COVID-19 pandemic, the elderly population has had the highest rates of complications and mortality. This study aimed to determine the influence of different risk factors on deaths due to the Omicron variant in the Canary Islands.Materials and methodsA retrospective observational study of 16,998 cases of COVID-19 over 40 years of age was conducted in the Canary Islands between August 1, 2022, and January 31, 2023. We extracted sociodemographic data (age and sex) and clinical data (death, vaccination history, hospital admission, previous diseases, and treatments).ResultsAmong the deaths, there was a higher proportion of males aged over 70 years, with diabetes, cardiovascular, renal, respiratory, and systemic diseases, and nursing home residents. Significant differences were observed in the number of doses of the vaccine. The multiple regression model showed that male sex (OR [95% CI] = 1.92 [1.42–2.58]), age (70–79 years, 9.11 [4.27–19.43]; 80–89 years, 21.72 [10.40–45.36]; 90–99 years, 66.24 [31.03–141.38]; 100 years or older, 69.22 [12.97–369.33]), being unvaccinated (6.96, [4.01–12.08]), or having the last dose administered at least 12 months before the diagnosis (2.38, [1.48–3.81]) were significantly associated with mortality.ConclusionsMultiple factors may increase the risk of mortality due to COVID-19 in the elderly population. In our study, we found that only three predictors can effectively explain the variability: older age, male sex, and not being vaccinated or last vaccination date prior to one year.     

ATP1B3 Protein Modulates the Restriction of HIV-1 Production and Nuclear Factor κ Light Chain Enhancer of Activated B Cells (NF-κB) Activation by BST-2

Here, we identify ATP1B3 and fibrillin-1 as novel BST-2-binding proteins. ATP1B3 depletion in HeLa cells (BST-2-positive cells), but not 293T cells (BST-2-negative cells), induced the restriction of HIV-1 production in a BST-2-dependent manner. In contrast, fibrillin-1 knockdown reduced HIV-1 production in 293T and HeLa cells in a BST-2-independent manner. Moreover, NF-κB activation was enhanced by siATP1B3 treatment in HIV-1- and HIV-1ΔVpu-infected HeLa cells. In addition, ATP1B3 silencing induced high level BST-2 expression on the surface of HeLa cells. These results indicate that ATP1B3 is a co-factor that accelerates BST-2 degradation and reduces BST-2-mediated restriction of HIV-1 production and NF-κB activation.