Climacostol, a compound produced by the ciliated protozoan Climacostomum virens, displayed cytotoxic properties in vitro. This study demonstrates that it has anti-tumour potential. Climacostol caused a reduction of viability/proliferation of B16-F10 mouse melanoma cells, a rapidly occurring DNA damage, and induced the intrinsic apoptotic pathway characterised by the dissipation of the mitochondrial membrane potential, the translocation of Bax to the mitochondria, the release of Cytochrome c from the mitochondria, and the activation of Caspase 9-dependent cleavage of Caspase 3. The apoptotic mechanism of climacostol was found to rely on the up-regulation of p53 and its targets Noxa and Puma. In vivo analysis of B16-F10 allografts revealed a persistent inhibition of tumour growth rate when melanomas were treated with intra-tumoural injections of climacostol. In addition, it significantly improved the survival of transplanted mice, decreased tumour weight, induced a remarkable reduction of viable cells inside the tumour, activated apoptosis and up-regulated the p53 signalling network. Importantly, climacostol toxicity was more selective against tumour than non-tumour cells. The anti-tumour properties of climacostol and the molecular events associated with its action indicate that it is a powerful agent that may be considered for the design of pro-apoptotic drugs for melanoma therapy.
The crystal structure of the pheromone Er-I from the unicellular eukaryotic organism Euplotes raikovi was determined at 1.6 A resolution and refined to a crystallographic R factor of 19.9%. In the tightly packed crystal, two extensive intermolecular helix-helix interactions arrange the Er-i molecules into layers. Since the putative receptor of the pheromone is a membrane-bound protein, whose extracellular C-terminal domain is identical in amino acid sequence to the soluble pheromone, the interactions found in the crystal may mimic the pheromone-receptor interactions as they occur on a cell surface. Based on this, we propose a model for the interaction between soluble pheromone molecules and their receptors. In this model, strong pheromone-receptor binding emerges as a consequence of the cooperative utilization of several weak interactions. The model offers an explanation for the results of binding studies and may also explain the adhesion between cells that occurs during mating.Pheromones from the ciliated protozoan Euplotes raikovi are proteins of 37-40 amino acids that function both as growth factors and as signaling molecules in cellular adhesion during mating (1-3). Over a dozen different cell types of E. raikovi have been identified based on their ability to form mating pairs (1). In the presence of only one cell type, the homologous secreted Er (Er-x = E. raikovi pheromone of type x) molecules stimulate growth of the cells by binding to cell-surface receptors in an autocrine fashion. In the presence of two different cell types or just one cell type to which heterologous pheromone has been added, Er molecules also stimulate cell adhesion between mating pair partners presumably by binding to the same cell-surface receptors (2, 3) in a paracrine manner. The putative receptors of the pheromones are membranebound proteins whose extracellular C-terminal domain is identical in amino acid sequence to the soluble pheromones (4). They arise by alternate splicing of the transcripts of the same gene that carries the information for the soluble pheromone (4).Different cell types can also be distinguished by the amino acid sequence of their pheromones. Sequences from nine different cell types have been determined (5-8), yielding seven unique sequences with pairwise sequence identities ranging from about 25% to 95%. Only seven residues are conserved among all sequences; these are the N-terminal aspartic acid and six cysteines that are involved in formation of three disulfide bridges (9).The NMR structures of three of the pheromones (Er-1, Er-2, and Er-10) have been determined and compared to each other (10-13). They revealed the three-helical bundle fold of the proteins and the orientations for about two-thirds of the side chains. The crystal structure reported here offers a detailed picture of the monomer and reveals two types of interactions between molecules that provide the basis for a model for receptor recognition, cell adhesion, and signaling. (14) is 1.53 A3/Da and the solvent content of the crystals is ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.