Ostreocin-D, discovered in the past decade, is a marine toxin produced by dinoflagellates. It shares structure with
palytoxin, a toxic compound responsible for the seafood intoxication named clupeotoxism. At the cellular level, the action sites and pharmacological effects for
ostreocin-D are still almost unknown. Previously, we demonstrated that these toxins change the filamentous actin cytoskeleton, which is essential for multiple cellular functions. However, nothing has yet been reported about what happens with the unpolymerized actin pool. Here (i) the effects induced by
ostreocin-D on unpolymerized actin, (ii) the Ca2+ role in such a process, and (iii) the cytotoxic activity of
ostreocin-D on the human
neuroblastoma BE(2)-M17 cell line are shown for the first time. Fluorescently labeled
DNase I was used for staining of monomeric actin prior to detection with both
laser-scanning cytometry and confocal microscopy techniques. Cellular viability was tested through a microplate metabolic activity assay.
Ostreocin-D elicited a rearrangement of monomeric actin toward the nuclear region. This event was not accompanied by changes in its content. In addition, the presence or absence of external Ca2+ did not change these results. This toxin was also found to cause a decrease in the viability of
neuroblastoma cells, which was inhibited by the specific blocker of Na+/K+-
ATPase,
ouabain. All these responses were comparable to those obtained with
palytoxin under identical conditions. The data suggest that
ostreocin-D modulates the unassembled actin pool, activating signal transduction pathways not related to Ca2+ influx in the same way as
palytoxin.