Ebselen inhibits NO-induced apoptosis of differentiated PC12 cells via inhibition of ASK1-p38 MAPK-p53 and JNK signaling and activation of p44/42 MAPK and Bcl-2

Ebselen, a selenium-containing heterocyclic compound, prevents ischemia-induced cell death. However, the molecular mechanism through which ebselen exerts its cytoprotective effect remains to be elucidated. Using sodium nitroprusside (SNP) as a nitric oxide (NO) donor, we show here that ebselen potently inhibits NO-induced apoptosis of differentiated PC12 cells. This was associated with inhibition of NO-induced phosphatidyl Serine exposure, cytochrome c release, and caspase-3 activation by ebselen. Analysis of key apoptotic regulators during NO-induced apoptosis of differentiated PC12 cells showed that ebselen blocks the activation of the apoptosis signaling-regulating kinase 1 (ASK1), and inhibits phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-jun N-terminal protein kinase (JNK). Moreover, ebselen inhibits NO-induced p53 phosphorylation at Ser15 and c-Jun phosphorylation at Ser63 and Ser73. It appears that inhibition of p38 MAPK and p53 phosphorylation by ebselen occurs via a thiol-redox-dependent mechanism. Interestingly, ebselen also activates p44/42 MAPK, and inhibits the downregulation of the antiapoptotic protein Bcl-2 in SNP-treated PC12 cells. Together, these findings suggest that ebselen protects neuronal cells from NO cytotoxicity by reciprocally regulating the apoptotic and antiapoptotic signaling cascades.     

Experimental test of biotic resistance to an invasive herbivore provided by potential plant mutualists

Understanding the influence of resident species on the success of invaders is a core objective in the study and management of biological invasions. We asked whether facultative food-for-protection mutualism between resident, nectar-feeding ants and extrafloral nectar-bearing plants confers biotic resistance to invasion by a specialist herbivore. Our research focused on the South American cactus-feeding moth Cactoblastis cactorum Berg (Lepidopetra: Pyralidae) in the panhandle region of Florida. This species has been widely and intentionally redistributed as a biological control agent against weedy cacti (Opuntia spp.) but arrived unintentionally in the southeast US, where it attacks native, non-target cacti and is considered a noxious invader. The acquired host-plants of C. cactorum in Florida secrete extrafloral nectar, especially on young, vegetative structures, and this attracts ants. We conducted ant-exclusion experiments over 2 years (2008 and 2009) at two sites using potted plants of two vulnerable host species (O. stricta and O. ficus-indica) to evaluate the influence of cactus-visiting ants (total of eight species) at multiple points in the moth life cycle (oviposition, egg survival, and larval survival). We found that the presence of ants often increased the mortality of lab-reared C. cactorum eggsticks (stacks of cohered eggs) and larvae that we introduced onto plants in the field, although these effects were variable across sites, years, host-plant species, ant species, and/or between old and young plant structures. In contrast to these “staged” encounters, we found that ants had little influence on the survival of cactus moths that occurred naturally at our field sites, or on moth damage and plant growth. In total, our experimental results suggest that the influence of cactus-visiting ants on C. cactorum invasion dynamics is weak and highly variable.     

Cdk5 mediates vimentin Ser56 phosphorylation during GTP-induced secretion by neutrophils

Secretion by neutrophils contributes to acute inflammation following injury or infection. Vimentin has been shown to be important for secretion by neutrophils but little is known about its dynamics during secretion, which is regulated by cyclin-dependent kinase 5 (Cdk5). In this study, we sought to examine the vimentin dynamics and its potential regulation by Cdk5 during neutrophil secretion. We show that vimentin is a Cdk5 substrate that is specifically phosphorylated at Ser56. In response to neutrophil stimulation with GTP, vimentin Ser56 was phosphorylated and colocalized with Cdk5 in the cytoplasmic compartment. Vimentin pSer56 and Cdk5 colocalization was consistent with coimmunoprecipitation from stimulated cells. Vimentin Ser56 phosphorylation occurred immediately after stimulation, and a remarkable increase in phosphorylation was noted later in the secretory process. Decreased GTP-induced vimentin Ser56 phosphorylation and secretion resulted from inhibition of Cdk5 activity by roscovitine or olomoucine or by depletion of Cdk5 by siRNA, suggesting that GTP-induced Cdk5-mediated vimentin Ser56 phosphorylation may be related to GTP-induced Cdk5-mediated secretion by neutrophils. Indeed, inhibition of vimentin Ser56 phosphorylation led to a corresponding inhibition of GTP-induced secretion, indicating a link between these two events. While fMLP also induced vimentin Ser56 phosphorylation, such phosphorylation was unaffected by roscovitine, which nonetheless, inhibited secretion, suggesting that Cdk5 regulates fMLP-induced secretion via a mechanism independent of Cdk5-mediated vimentin Ser56 phosphorylation. These findings demonstrate the distinct involvement of Cdk5 in GTP- and fMLP-induced secretion by neutrophils, and support the notion that specific targeting of Cdk5 may serve to inhibit the neutrophil secretory process.