On the effects of cycloheximide on cell motility and polarisation in Dictyostelium discoideum

Enhanced dissolution and bioavailability of revaprazan using self-nanoemulsifying drug delivery system

A self-nanoemulsifying drug delivery system (SNEDDS) was developed to enhance the dissolution and oral bioavailability (BA) of revaprazan (RVP). Various SNEDDSs containing 200 mg of RVP were formulated using Capmul MCM, Tween 80, and Brij L4, and they were characterized according to their size, polydispersity index, and dissolution behavior. Dissolution rates of all SNEDDS formulations significantly (p <0.05) improved with the formation of nanoemulsion with monodispersity. Formulation D resulted in RVP dissolution exceeding 70% at 2 h. Compared to raw RVP, SNEDDS exhibited a 4.8- to 7.4-fold improved effective permeability coefficient (P_eff) throughout the intestine in the in situ single pass intestinal permeability study and a 5.1-fold increased oral BA in the in vivo oral absorption assessment in rats. To evaluate the degree of lymphatic uptake, cycloheximide (CYC), a chylomicron flowing blocker, was pretreated prior to the experiment. This pretreatment barely affected the absorption of raw RVP; however, it greatly influenced the absorption of SNEDDS, resulting in an approximately 40% reduction in both the P_eff value and oral BA representing lymphatic transport. Thus, we suggest that the SNEDDS formulation is a good candidate for improving oral absorption of RVP through enhanced lymphatic uptake.

B cells rapidly target antigen and surface-derived MHCII into peripheral degradative compartments

In order to mount high-affinity antibody responses, B cells internalise specific antigens and process them into peptides loaded onto MHCII for presentation to T helper cells (T_H cells). While the biochemical principles of antigen processing and MHCII loading have been well dissected, how the endosomal vesicle system is wired to enable these specific functions remains much less studied. Here, we performed a systematic microscopy-based analysis of antigen trafficking in B cells to reveal its route to the MHCII peptide-loading compartment (MIIC). Surprisingly, we detected fast targeting of internalised antigen into peripheral acidic compartments that possessed the hallmarks of the MIIC and also showed degradative capacity. In these vesicles, internalised antigen converged rapidly with membrane-derived MHCII and partially overlapped with cathepsin-S and H2-M, both required for peptide loading. These early compartments appeared heterogenous and atypical as they contained a mixture of both early and late endosomal markers, indicating a specialized endosomal route. Together, our data suggest that, in addition to in the previously reported perinuclear late endosomal MIICs, antigen processing and peptide loading could have already started in these specialized early peripheral acidic vesicles (eMIIC) to support fast peptide-MHCII presentation.

Self-microemulsifying drug delivery system for improving the bioavailability of huperzine A by lymphatic uptake

Huperzine A (Hup-A) is a poorly water-soluble drug with low oral bioavailability. A self-microemulsifying drug delivery system (SMEDDS) was used to enhance the oral bioavailability and lymphatic uptake and transport of Hup-A. A single-pass intestinal perfusion (SPIP) technique and a chylomicron flow-blocking approach were used to study its intestinal absorption, mesenteric lymph node distribution and intestinal lymphatic uptake. The value of the area under the plasma concentration–time curve (AUC) of Hup-A SMEDDS was significantly higher than that of a Hup-A suspension (P<0.01). The absorption rate constant (K_a) and the apparent permeability coefficient (P_app) for Hup-A in different parts of the intestine suggested a passive transport mechanism, and the values of K_a and P_app of Hup-A SMEDDS in the ileum were much higher than those in other intestinal segments. The determination of Hup-A concentration in mesenteric lymph nodes can be used to explain the intestinal lymphatic absorption of Hup-A SMEDDS. For Hup-A SMEDDS, the values of AUC and maximum plasma concentration (C_max) of the blocking model were significantly lower than those of the control model (P<0.05). The proportion of lymphatic transport of Hup-A SMEDDS and Hup-A suspension were about 40% and 5%, respectively, suggesting that SMEDDS can significantly improve the intestinal lymphatic uptake and transport of Hup-A.

Changes in specific protein degradation rates in Arabidopsis thaliana reveal multiple roles of Lon1 in mitochondrial protein homeostasis

Mitochondrial Lon1 loss impairs oxidative phosphorylation complexes and TCA enzymes and causes accumulation of specific mitochondrial proteins. Analysis of over 400 mitochondrial protein degradation rates using ¹⁵ N labelling showed that 205 were significantly different between wild type (WT) and lon1-1. Those proteins included ribosomal proteins, electron transport chain subunits and TCA enzymes. For respiratory complexes I and V, decreased protein abundance correlated with higher degradation rate of subunits in total mitochondrial extracts. After blue native separation, however, the assembled complexes had slow degradation, while smaller subcomplexes displayed rapid degradation in lon1-1. In insoluble fractions, a number of TCA enzymes were more abundant but the proteins degraded slowly in lon1-1. In soluble protein fractions, TCA enzymes were less abundant but degraded more rapidly. These observations are consistent with the reported roles of Lon1 as a chaperone aiding the proper folding of newly synthesized/imported proteins to stabilise them and as a protease to degrade mitochondrial protein aggregates. HSP70, prohibitin and enzymes of photorespiration accumulated in lon1-1 and degraded slowly in all fractions, indicating an important role of Lon1 in their clearance from the proteome.

Cycloheximide Inhibits Actin Cytoskeletal Dynamics by Suppressing Signaling via RhoA

Genome-wide screening of the yeast Saccharomyces cerevisiae knockout collection was used to characterize chemical-genetic interactions of cycloheximide (CHX). The results showed that while the act1Δ mutant was the only deletion mutant in the heterozygous essential gene deletion collection that showed hypersensitivity to sub-inhibitory concentrations of CHX, deletion of nonessential genes that work in concert with either cytoplasmic or nuclear actin in the homozygous deletion collection also highly sensitized yeast to CHX. Fluorescence microscopy analysis revealed that CHX disrupts filamentous actin structures and fluid phase endocytosis in the yeast cell. It also showed that CHX disrupts transforming growth factor-β1 (TGF-β1)-induced actin reorganization and polygonal architecture of microfilaments in mammalian cells. This inhibitory effect is mediated, at least in part, through the actin dynamics signaling pathway via suppression of activation of the small GTPase RhoA. J. Cell. Biochem. 117: 2886-2898, 2016. © 2016 Wiley Periodicals, Inc.

Calcitonin gene-related peptide regulation of glial cell-line derived neurotrophic factor in differentiated rat myotubes

Glial cell-line derived neurotrophic factor (GDNF) is the most potent trophic factor for motoneuron survival and neuromuscular junction formation. GDNF is upregulated in injured or denervated skeletal muscle and returns to normal levels following reinnervation. However, the mechanism by which GDNF is regulated in denervated muscle is not well understood. The nerve-derived neurotransmitter calcitonin gene-related peptide (CGRP) is upregulated following neuromuscular injury and is subsequently released from motoneurons at the neuromuscular junction. CGRP also promotes nerve regeneration, but the mechanism is not well understood. The current study investigates whether this increase in CGRP regulates GDNF, thus playing a key role in promoting regeneration of injured nerves. This study demonstrates that CGRP increases GDNF secretion without affecting its transcription or translation. Rat L6 myoblasts were differentiated into myotubes and subsequently treated with CGRP. GDNF mRNA expression levels were quantified by quantitative real-time reverse transcription-polymerase chain reaction, and secreted GDNF was quantified in the conditioned medium by ELISA. CGRP treatment increased secreted GDNF protein without altering GDNF mRNA levels. The translational inhibitor cycloheximide did not affect CGRP-induced GDNF secreted protein levels, whereas the secretional inhibitor brefeldin A blocked the CGRP-induced increase in GDNF. This study highlights the importance of injury-induced upregulation of CGRP by exposing its ability to increase GDNF levels and demonstrates a secretional mechanism for regulation of this key regeneration-promoting neurotrophic factor.

Intestinal absorption and intestinal lymphatic transport of sirolimus from self-microemulsifying drug delivery systems assessed using the single-pass intestinal perfusion (SPIP) technique and a chylomicron flow blocking approach: linear correlation with oral bioavailabilities in rats

This work aims to investigate the impact of different amount of oil or surfactant included in self-microemulsifying drug delivery systems on the intestinal lymphatic transport of sirolimus using the single-pass intestinal perfusion (SPIP) technique and a chylomicron flow blocking approach. Male Sprague-Dawley rats were pretreated intraperitoneally with 3.0mg/kg cycloheximide or saline. One hour later, single-pass intestinal perfusion experiments in jejunum and ileum and in vivo bioavailability studies were carried out to calculate the effective permeability coefficient and pharmacokinetic parameters, respectively. Drug absorption from oil-free formulation was mostly via the portal blood. In contrast, for the SMEDDS formulations containing ≥25% MCT, the lymphatic transport of sirolimus was a major contributor to oral bioavailability. The formulation including more content of oil presented higher lymphatic transport of drug and further exhibited the increased oral bioavailability. Besides, distal ileum presented much more lymphatic transport of drug compared to proximal jejunum. Furthermore, even though the smaller droplet size of resultant microemulsions and more surfactant content also can positively influence the intestinal absorption of drug, their influences on the drug intestinal lymphatic transport were relatively weaker than that of more oil content. In addition, there was a high linear correlation between the AUC values and the mean of P(eff) values in jejunum and ileum.

Understanding streaming in Dictyostelium discoideum: theory versus experiments

Recent experimental work involving Dictyostelium discoideum seems to contradict several theoretical models. Experiments suggest that localization of the release of the chemoattractant cyclic adenosine monophosphate to the uropod of the cell is important for stream formation during aggregation. Yet several mathematical models are able to reproduce streaming as the cells aggregate without taking into account localization of the chemoattractant. A careful analysis of the experiments and the theory suggests the two major features of the system which are important to stream formation are random cell motion and chemotaxis to regions of higher cell density. Random cell motion acts to reduce streaming, whereas chemotaxis to regions of higher cell density reinforces streaming. With this understanding, the experimental results can be explained in a manner consistent with the theoretical results. In all the experiments, alterations in the two main factors of random motion and chemotaxis to regions of higher cell density, not the localization of the release of the chemoattractant, can explain the results as they relate to streaming. Additionally, a comparison of results from a mathematical model that simulates cells which localize the chemoattractant and cells which do not shows little difference in the streaming patterns.

Breast tumor developed in a pregnant rat after treatment with the teratogen Cycloheximide

AIM

To describe histochemically and immunohistochemically a breast tumor presented in a pregnant rat given Cycloheximide to examine its teratogenic and embryotoxic effect on the embryos.

METHODS

Cycloheximide was injected in pregnant Wistar rats at a dose of 3 mg/kg.b.w. on both 10th and 11th gestational days. In one of the rats, a large breast tumor developed rapidly. Histochemical staining with Hematoxylin-Eosin and Masson Trichrome and immunohistochemical identification with mouse monoclonal antibodies: a) Estrogen Receptor A and b) Estrogen Receptor B was performed.

RESULTS

Analysis with A-receptor and B-receptor showed that the breast tumor which was developed after treatment with Cycloheximide was malignant. Positive immunohistochemical reaction was evident especially with A-receptor indicating the malignancy of the tumor.

CONCLUSIONS

Cycloheximide is a known toxic and teratogenic agent and potentially a carcinogenic drug. Thus it should be used with extreme caution as a pesticide.

Computational modelling suggests dynamic interactions between Ca2+, IP3 and G protein-coupled modules are key to robust Dictyostelium aggregation

Under conditions of starvation, Dictyostelium cells begin a programme of development during which they aggregate to form a multicellular structure by chemotaxis, guided by propagating waves of cyclic AMP that are relayed robustly from cell to cell. In this paper, we develop and analyse a new model for the intracellular and extracellular cAMP dependent processes that regulate Dictyostelium migration. The model allows, for the first time, a quantitative analysis of the dynamic interactions between calcium, IP(3) and G protein-dependent modules that are shown to be key to the generation of robust cAMP oscillations in Dictyostelium cells. The model provides a mechanistic explanation for the transient increase in cytosolic free Ca(2+) concentration seen in recent experiments with the application of the calmodulin inhibitor calmidazolium (R24571) to Dictyostelium cells, and also allows elucidation of the effects of varying both the conductivity of stretch-activated channels and the concentration of external phosphodiesterase on the oscillatory regime of an individual cell. A rigorous analysis of the robustness of the new model shows that interactions between the different modules significantly reduce the sensitivity of the resulting cAMP oscillations to variations in the kinetics of different Dictyostelium cells, an essential requirement for the generation of the spatially and temporally synchronised chemoattractant cAMP waves that guide Dictyostelium aggregation.

Collective cell migration requires vesicular trafficking for chemoattractant delivery at the trailing edge

Chemoattractant signaling induces the polarization and directed movement of cells secondary to the activation of multiple effector pathways. In addition, chemotactic signals can be amplified and relayed to proximal cells via the synthesis and secretion of additional chemoattractant. The mechanisms underlying such remarkable features remain ill defined. We show that the asymmetrical distribution of adenylyl cyclase (ACA) at the back of Dictyostelium discoideum cells, an essential determinant of their ability to migrate in a head-to-tail fashion, requires vesicular trafficking. This trafficking results in a local accumulation of ACA-containing intracellular vesicles and involves intact actin, microtubule networks, and de novo protein synthesis. We also show that migrating cells leave behind ACA-containing vesicles, likely secreted as multivesicular bodies and presumably involved in the formation of head-to-tail arrays of migrating cells. We propose that similar compartmentalization and shedding mechanisms exist in mammalian cells during embryogenesis, wound healing, neuron growth, and metastasis.

Phosphatidylinositol 3-kinase activity and asymmetrical accumulation of F-actin are necessary for establishment of cell polarity in the early development of monospores from the marine red alga Porphyra yezoensis

The polarized distribution of F-actin is important in providing the driving force for directional migration in mammalian leukocytes and Dictyostelium cells, in which compartmentation of phosphatidylinositol 3-kinase (PI3K) and phosphatidylinositol phosphatase is critical for the establishment of cell polarity. Since monospores from the red alga Porphyra yezoensis are a real example of migrating plant cells, the involvement of the cytoskeleton and PI3K was investigated during their early development. Our results indicate that the asymmetrical localization of F-actin at the leading edge is fixed by the establishment of the anterior-posterior axis in migrating monospores, which is PI3K-dependent and protein synthesis-independent. After migration, monospores adhere to the substratum and then become upright, developing into multicellular thalli via the establishment of the apical-basal axis. In this process, F-actin usually accumulates at the bottom of the basal cell and development after migration requires new protein synthesis. These findings suggest that the establishment of anterior-posterior and apical-basal axes are differentially regulated during the early development of monospores. Our results also indicate that PI3K-dependent F-actin asymmetry is evolutionally conserved in relation to the establishment of cell polarity in migrating eukaryotic cells.

Mechanisms of Gradient Detection: A Comparison of Axon Pathfinding with Eukaryotic Cell Migration

The detection of gradients of chemotactic cues is a common task for migrating cells and outgrowing axons. Eukaryotic gradient detection employs a spatial mechanism, meaning that the external gradient has to be translated into an intracellular signaling gradient, which affects cell polarization and directional movement. The sensitivity of gradient detection is governed by signal amplification and adaptation mechanisms. Comparison of the major signal transduction pathways underlying gradient detection in three exemplary chemotaxing cell types, Dictyostelium, neutrophils, and fibroblasts and in neuronal growth cones, reveals conserved mechanisms such as localized PI3 kinase/PIP3 signaling and a common output, the regulation of the cytoskeleton by Rho GTPases. Local protein translation plays a role in directional movement of both fibroblasts and neuronal growth cones. Ca(2+) signaling is prominently involved in growth cone gradient detection. The diversity of signaling between different cell types and its functional implications make sense in the biological context.