Mixed-species bird flocks re-assemble interspecific associations across an elevational gradient.

Understanding how non-trophic social systems respond to environmental gradients is still a challenge in animal ecology, particularly in comparing changes in species composition to changes in interspecific interactions. Here, we combined long-term monitoring of mixed-species bird flocks, data on participating species' evolutionary history and traits, to test how elevation affected community assemblages and interspecific interactions in flock social networks. Elevation primarily affected flocks through reassembling interspecific associations rather than modifying community assemblages. Specifically, flock networks at higher elevations (compared to low elevations) had stronger interspecific associations (larger average weighted degree), network connectivity (enhanced network density) and fewer subnetworks. A phylogenetic and functional perspective revealed that associations between similar species weakened, whereas connections between dissimilar and/or random species were unchanged or strengthened with elevation. Likewise, network assortativity for the traits of vertical stratum and breeding period declined with elevation. The overall pattern is a change from modular networks in the lowlands, where species join flocks with other species that have matching traits, to a more open, random system at high elevations. Collectively, this rewiring of interspecific networks across elevational gradients imparts network stability and resiliency and makes mixed-species flocks less sensitive to local extinctions caused by harsh environments.

Biomonitoring chromium III or VI soluble pollution by moss chlorophyll fluorescence.

We systematically compared the impacts of four Cr salts (chromic chloride, chromic nitrate, potassium chromate and potassium bichromate) on physiological parameters and chlorophyll fluorescence in indigenous moss Taxiphyllum taxirameum. Among the four Cr salts, K2Cr2O7 treatment resulted in the most significant decrease in photosynthetic efficiency and antioxidant enzymes, increase in reactive oxygen species (ROS), and obvious cell death. Different form the higher plants, although hexavalent Cr(VI) salt treatments resulted in higher accumulation levels of Cr and were more toxic than Cr(III) salts, Cr(III) also induced significant changes in moss physiological parameters and chlorophyll fluorescence. Our results showed that Cr(III) and Cr(VI) could be monitored distinguishably according to the non-photochemical quenching (NPQ) fluorescence of sporadic purple and sporadic lavender images respectively. Then, the valence states and concentrations of Cr contaminations could be evaluated according to the image of maximum efficiency of PSII photochemistry (Fv/Fm) and the quantum yield of PSII electron transport (ΦPSII). Therefore, this study provides new ideas of moss's sensibility to Cr(III) and a new method to monitor Chromium contaminations rapidly and non-invasively in water.

Comparison of phosphorylation and assembly of photosystem complexes and redox homeostasis in two wheat cultivars with different drought resistance.

Reversible phosphorylation of proteins and the assembly of thylakoid complexes are the important protective mechanism against environmental stresses in plants. This research was aimed to investigate the different responses of the antioxidant defense system and photosystem II (PSII) to osmotic stress between drought-resistant and drought-susceptible wheat cultivars. Results showed that the decrease in PSII photochemistry and six enzyme activities was observed in drought-susceptible wheat compared with drought-resistant wheat under osmotic stress. In addition, a lower accumulation of reactive oxygen species (ROS) and cell death were found in the resistant wheat compared with the susceptible wheat under osmotic stress. Western blot analysis revealed that osmotic stress led to a remarkable decline in the steady state level of D1 protein in drought-susceptible wheat. However, the CP29 protein was strongly phosphorylated in drought-resistant wheat compared with the susceptible wheat under osmotic stress. Our results also showed that drought-resistant wheat presented higher phosphorylated levels of the light-harvesting complex II (LHCII), D1, and D2 proteins and a more rapid dephosphorylated rate than drought-susceptible wheat under osmotic stress. Furthermore, the PSII-LHCII supercomplexes and LHCII trimers were more rapidly disassembled in drought-susceptible wheat than the drought-resistant wheat under osmotic stress. These findings provide that reversible phosphorylation of thylakoid membrane proteins and assembly of thylakoid membrane complexes play important roles in plant adaptation to environmental stresses.

AKT/TSC2/p70S6K signaling pathway is involved in quinocetone-induced death-promoting autophagy in HepG2 cells.

Quinocetone (QCT, 3-methyl-2-quinoxalin benzenevinylketo-1, 4-dioxide) is widely used as a veterinary drug and animal feed additive in China. Although it promotes growth and improves feed efficiency, QCT's in vitro and in vivo toxicities remain uncertain. This study was conducted to explore the mechanism of QCT-induced autophagy in HepG2 cells. By the results obtained from monodansylcadaverine (MDC) staining, ultrastructural observation by transmission electron microscopy (TEM), as well as Western blotting analysis for LC3, p62, and Beclin-1, it was demonstrated that QCT induced autophagy in HepG2 cells. Furthermore, PI3K/AKT inhibitor significantly enhanced QCT-induced autophagy, while TSC2 knockdown attenuated this process. In addition, inhibition of autophagy by pharmacological approach remarkably increased the viability of QCT-treated cells detected by MTT assay, suggesting that QCT-triggered autophagy may play as a promotion mechanism for cell death. Meanwhile, apoptosis was markedly downregulated after autophagy blockage, and evaluated by flow cytometry and Western blotting analysis for caspase-3 cleavage. Consequently, these results suggested that QCT-induced autophagy was mediated by AKT/TSC2/p70S6K signaling pathway, and inhibition of autophagy promoted QCT-treated cell survival by attenuating apoptosis.

Thapsigargin induces apoptosis when autophagy is inhibited in HepG2 cells and both processes are regulated by ROS-dependent pathway.

Thapsigargin (TG), is widely used to induce endoplasmic reticular stress. Treated with TG for a long time, cells suffer the unfolded protein response (UPR) to elude apoptosis, but may activate autophagy. However, the switch between autophagy and apoptosis is unclear. To clarify the key signal for selection of these two protective responses, we studied the correlation of autophagy and apoptosis in HepG2 cells exposed to TG with time. TG induced apoptosis in HepG2 cells was evidenced by typical cell morphological changes and the activation of caspase-12, caspase-9 and caspase-3. Meanwhile, cytochrome c was released following with the dissipation of mitochondrial membrane potential (MMP), and the ratio of Bax/Bcl-2 was increased. TG-induced autophagy was confirmed by the accumulation of MDC, GFP-LC3 staining autophagic vacuoles, and the improved expression of LC3 II and Beclin-1. Additionally, inhibited autophagy via chloroquine (CQ) markedly enhanced the apoptosis induced by TG, which was linked to the Bcl-2 family. Furthermore, TG induced the generation of reactive oxygen species (ROS), and the ROS scavenger effectively suppressed TG-induced apoptosis and autophagy. All these results proved that restraint of autophagy may enhance TG-induced apoptosis through increasing the Bax/Bcl-2 ratio and both processes were regulated by ROS.

Reactive oxygen species-dependent JNK downregulated olaquindox-induced autophagy in HepG2 cells.

Autophagy plays an important role in response to intracellular and extracellular stress to sustain cell survival. However, dysregulated or excessive autophagy may lead to cell death, known as "type II programmed cell death," and it is closely associated with apoptosis. In our previous study, we proposed that olaquindox induced apoptosis of HepG2 cells through a caspase-9 dependent mitochondrial pathway. In this study, we investigated autophagy induced by olaquindox and explored the crosstalk between apoptosis and autophagy in olaquindox-treated HepG2 cells. Olaquindox-induced autophagy was demonstrated by the accumulation of monodansylcadervarine, as well as elevated expression of autophagy-related MAP-LC3 and Beclin 1 proteins. The autophagy inhibitor 3-methyladenine significantly increased the apoptotic rate induced by olaquindox, which was correlated with increased ratio of Bax/Bcl-2. The further studies showed that olaquindox increased the levels of reactive oxygen species (ROS), and antioxidant N-acetyl-L-cysteine (NAC) effectively blocked the accumulation of ROS but failed to block autophagy. Moreover, olaquindox induced the activation of c-Jun N-terminal protein kinase (JNK), and JNK inhibitor SP600125 failed to block autophagy. Instead, olaquindox-induced autophagy was enhanced by NAC or SP600125. Meanwhile, JNK activation was remarkably blocked by NAC, indicating that ROS may be the upstream signaling molecules of JNK activation and involved in the negative regulation of olaquindox-induced autophagy. These results suggest that olaquindox induces autophagy in HepG2 cells and that olaquindox-induced apoptosis can be enhanced by 3-methyladenine. Olaquindox-induced autophagy in HepG2 cells is upregulated by Beclin 1 but downregulated by ROS-dependent JNK.

Furazolidone induces apoptosis through activating reactive oxygen species-dependent mitochondrial signaling pathway and suppressing PI3K/Akt signaling pathway in HepG2 cells.

Furazolidone (FZD), a synthetic nitrofuran with a broad spectrum of antimicrobial activities, has been shown to be genotoxic and potentially carcinogenic in several types of cells. However, the proper molecular mechanisms of FZD toxicity remain unclear. This study was aimed to explore the effect of FZD on apoptosis in HepG2 cells and uncover signaling pathway underlying the cytotoxicity of FZD. The results showed that FZD induced apoptosis in HepG2 cells in a dose-dependent manner characterized by nuclei morphology changes, cell membrane phosphatidylserine translocation, poly (ADP-ribose) polymerase (PARP) cleavage and a cascade activation of caspase-9 and -3. FZD could enhance reactive oxygen species (ROS) generation, up-regulate Bax/Bcl-2 ratio, disrupt mitochondrial membrane potential (MMP) and subsequently cause cytochrome c release. Both ROS scavenger (N-acetyl cysteine, NAC) and caspase inhibitors suppressed FZD-induced apoptosis. Furthermore, NAC attenuated FZD-induced ROS generation and mitochondrial dysfunction. Meanwhile, FZD treatment inhibited both the activation and expression of Akt, and PI3K/Akt inhibitor LY294002 promoted FZD-induced apoptosis. On the contrary, PI3K/Akt activator insulin-like growth factor-1 (IGF-1) attenuated lethality of FZD in HepG2 cells. In conclusion, it is first demonstrated that FZD-induced apoptosis in HepG2 cells might be mediated through ROS-dependent mitochondrial signaling pathway and involves PI3K/Akt signaling.

TNFR1/TNF-α and mitochondria interrelated signaling pathway mediates quinocetone-induced apoptosis in HepG2 cells.

Quinocetone, a new quinoxaline 1, 4-dioxide derivative, has been widely used as an animal feed additive in China. This study was conducted to explore the molecular mechanisms of apoptosis induced by quinocetone in HepG2 cells. MTT assay revealed that the viability of HepG2 cells was significantly inhibited by quinocetone in a dose- and time-dependent manner. Quinocetone-induced apoptosis in HepG2 cells was characterized by cell and nuclei morphology change, cell membrane phosphatidylserine translocation, DNA fragmentation, cleavage of poly (ADP-ribose) polymerase (PARP) and a cascade activation of caspase-8, caspase-9 and caspase-3. Simultaneously, quinocetone induced HepG2 cell cycle arrest, which was supported by overexpression of p21. Cytochrome c release was caused by the mitochondrial membrane potential dissipation, a process related to quinocetone-induced Bid cleavage and elevated Bax/Bcl-2 ratio. Moreover, quinocetone treatment caused the up-regulation of TNF-α and TNFR1 in HepG2 cells. Both soluble TNFR1 receptors and caspase inhibitors suppressed quinocetone-induced apoptosis. In addition, the protein levels of p53, p-p38 and p-JNK were increased in quinocetone-treated cells. Taken together, quinocetone induced apoptosis in HepG2 cells via activation of caspase, interaction of TNF-α and TNFR1 and modulation of the protein levels of Bid, Bax and Bcl-2, involving the participation of p53, p38 and JNK.

Olaquindox-induced apoptosis is suppressed through p38 MAPK and ROS-mediated JNK pathways in HepG2 cells.

We investigated mitogen-activated protein kinase (MAPK) pathways as well as reactive oxygen species (ROS) in olaquindox-induced apoptosis. Exposure of HepG2 cells to olaquindox resulted in the phosphorylation of p38 MAPK and c-Jun N-terminal kinases (JNK). To confirm the role of p38 MAPK and JNK, HepG2 cells were pretreated with MAPKs-specific inhibitors prior to olaquindox treatment. Olaquindox-induced apoptosis was significantly potentiated by the JNK inhibitor (SP600125) or the p38 MAPK inhibitor (SB203580). Furthermore, we observed that olaquindox treatment led to ROS generation and that olaquindox-induced apoptosis and ROS generation were both significantly reduced by the antioxidants, superoxide dismutase and catalase. In addition, the levels of phosphorylation of JNK, but not p38 MAPK, were significantly suppressed after pretreatment of the antioxidants, while inhibition of the activations of JNK or p38 MAPK had no effect on ROS generation. This result suggested that ROS may be the upstream mediator for the activation of JNK. Conclusively, our results suggested that apoptosis in response to olaquindox treatment in HepG2 cells might be suppressed through p38 MAPK and ROS-JNK pathways.

Opposite effects of JNK and p38 MAPK signaling pathways on furazolidone-stimulated S phase cell cycle arrest of human hepatoblastoma cell line.

Furazolidone (FZD), a synthetic nitrofuran with a broad spectrum of antimicrobial actions, is known to induce genotoxicity and potential carcinogenicity in several types of cells, but little is known about its p38 mitogen-activation protein kinase (p38 MAPK) and c-Jun N-terminal protein kinase (JNK) pathways in human hepatoblastoma cell line (HepG2). Given the previously described essential roles of p38 MAPK and JNK pathways in HepG2 cells, we undertook the present study to investigate the roles of p38 MAPK and JNK pathways in cell cycle arrest of HepG2 cells stimulated with FZD. Here we reported that FZD could obviously induce S phase cell cycle arrest, suppress cell growth, increase the activity of phosphorylated p38 (p-p38), and decrease the activity of phosphorylated JNK (p-JNK) in HepG2 cells. Simultaneously, inhibition of p38 MAPK pathway could significantly reduce FZD-stimulated S phase cell cycle arrest, active cell growth, decrease the activity of p-p38, and increase the activity of p-JNK. To the opposite, inhibition of JNK pathway could significantly increase FZD-stimulated S phase cell cycle arrest, suppress cell growth, decrease the activity of p-JNK, and increase the activity of p-p38. These results demonstrate that JNK and p38 MAPK pathways have opposite roles in FZD-stimulated S phase cell cycle arrest of HepG2 cells. FZD induces S phase cell cycle arrest and suppresses cell proliferation of HepG2 cells via activating the pathway from p38 to p-p38 and inhibiting the pathway from JNK to p-JNK.

Involvement of the p38 MAPK signaling pathway in S-phase cell-cycle arrest induced by Furazolidone in human hepatoma G2 cells.

Given the previously described essential role for the p38 mitogen-activation protein kinase (p38 MAPK) signaling pathway in human hepatoma G2 cells (HepG2), we undertook the present study to investigate the role of the p38 MAPK signaling pathway in cell-cycle arrest induced by Furazolidone (FZD). The aim of this study was to determine the effects of FZD on HepG2 cells by activating and inhibiting the p38 MAPK signaling pathway. The cell cycle and proliferation of HepG2 cells treated with FZD were detected by flow cytometry and MTT assay in the presence or absence of p38 MAPK inhibitors (SB203580), respectively. Cyclin D1, cyclin D3 and CDK6 were detected by quantitative real-time PCR and western blot analysis. Our data showed that p38 MAPK became phosphorylated after stimulation with FZD. Activation of p38 MAPK could arise S-phase cell-cycle arrest and suppress cell proliferation. Simultaneously, inhibition of the p38 MAPK signaling pathway significantly prevented S-phase cell-cycle arrest, increased the percentage of cell viability and decreased the expression of cyclin D1, cyclin D3 and CDK6. These results demonstrated that FZD arose S-phase cell-cycle arrest via activating the p38 MAPK signaling pathway in HepG2 cells. Cyclin D1, cyclin D3 and CDK6 are target genes functioning at the downstream of p38 MAPK in HepG2 cells induced by FZD.

c-Myc influences olaquindox-induced apoptosis in human hepatoma G2 cells.

Olaquindox, a synthetic antimicrobial compound, was banned as feed additives in the U.S. and the EU. In China, the use of olaquindox is banned in poultry and aquaculture feed, restricted in livestock feed for growth promotion. Olaquindox's safety is the object of increasing attention. The present study was undertaken to investigate whether and how olaquindox elevates expression of c-Myc, which influences olaquindox-induced apoptosis in HepG2 cells. For a better understanding of c-Myc's role in susceptibility of human hepatoma G2 cells to olaquindox-induced apoptosis, two vectors (the pSilencer-cmyc(Si-cmyc) and the control vector) were transfected to HepG2 cells. The cells were pretreated with Si-cmyc, which expressed only 35-65% c-Myc protein levels compared to those of the parental cells and the control cells. We examined effects of olaquindox on reactive oxygen species (ROS) production in these c-Myc low-expressing cells, and on apoptosis. Our data revealed that ROS production induced by olaquindox treatment was partially blocked by Si-cmyc transfection and partly inhibited olaquindox-induced apoptosis through decreased ROS generation. Further data showed that olaquindox induced decreased ROS by Si-cmyc transfection through decreased cytochrome c release to cytosol, which inhibited apoptosis of the cells. These results suggest that c-Myc might be important during olaquindox-induced apoptosis in human hepatoma G2 cells.