Apoptosis signaling triggered by the marine alkaloid ascididemin is routed via caspase-2 and JNK to mitochondria.

The marine alkaloid ascididemin (ASC) was shown to exert cytotoxicity even against multidrug-resistant cancer cells. Here, we address the signaling pathways utilized by ASC to trigger apoptosis in Jurkat leukemia T cells. We show that ASC (0.5-20 microM) induces a mitochondrial pathway that requires the activation of the initiator caspase-2 upstream of mitochondria. ASC-triggered apoptosis occurred independent of CD95, but required mitochondrial dysfunction. The activation of caspase-2 was shown to precede the processing of caspase-8, -9 and -3. The specific caspase-2 inhibitor zVDVADfmk abrogated ASC-induced DNA fragmentation almost completely. Overexpression of Bcl-x(L) blocked caspase-8 but not caspase-2 processing. Conversely, caspase-2 inhibition strongly reduced caspase-9 activation. As a possible link between caspase-2 and mitochondrial dysfunction, Bid was found to be cleaved by ASC. In addition, JNK was activated by ASC upstream of mitochondria via reactive oxygen species. The specific JNK inhibitor SP600125 partially inhibited caspase-2 and -9 processing as well as cytochrome c release and DNA fragmentation indicating that JNK contributes to, but is not necessary for ASC-mediated apoptosis. Thus, ASC triggers a pathway in which early activation of caspase-2 provides a possible link between its DNA-damaging activity and the induction of mitochondrial dysfunction. The activation of JNK contributes to this signaling upstream of mitochondria.

Cyclopentenone isoprostanes induced by reactive oxygen species trigger defense gene activation and phytoalexin accumulation in plants.

Lipid peroxidation may be initiated either by lipoxygenases or by reactive oxygen species (ROS). Enzymatic oxidation of alpha-linolenate can result in the biosynthesis of cyclic oxylipins of the jasmonate type while free-radical-catalyzed oxidation of alpha-linolenate may yield several classes of cyclic oxylipins termed phytoprostanes in vivo. Previously, we have shown that one of these classes, the E1-phytoprostanes (PPE1), occurs ubiquitously in plants. In this work, it is shown that PPE1 are converted to novel cyclopentenone A1- and B1-phytoprostanes (PPA1 and PPB1) in planta. Enhanced formation of PPE1, PPA1, and PPB1 is observed after peroxide stress in tobacco cell cultures as well as after infection of tomato plants with a necrotrophic fungus, Botrytis cinerea. PPA1 and PPB1 display powerful biologic activities including activation of mitogen-activated protein kinase (MAPK) and induction of glutathione-S-transferase (GST), defense genes, and phytoalexins. Data collected so far infer that enhanced phytoprostane formation is a general consequence of oxidative stress in plants. We propose that phytoprostanes are components of an oxidant-injury-sensing, archaic signaling system that serves to induce several plant defense mechanisms.

Polycephalin B and C: Unusual Tetramic Acids from Plasmodia of the Slime Mold Physarum polycephalum (Myxomycetes).

Illumination results in increased formation of metabolites 1 and 2 in the plasmodia of the slime mold Physarum polycephalum. This was determined from HPLC studies undertaken in the search for the photoactive substances involved in the "blue-light phenomenon". The isolation and structure elucidation of 1 and 2 is described.