latrunculin-b and Neuroblastoma

Inhibition of integrins alphavbeta3 and alphavbeta5 in human brain microvascular endothelial cells (HBMECs) by the function-blocking peptide RGDfV induces loss of spreading on vitronectin, cell detachment, and apoptosis. We demonstrate that cell detachment is not required for apoptosis because plating on bovine serum albumin-blocked poly-L-lysine (allows attachment, but not integrin ligation and cell spreading) also induced apoptosis. Latrunculin B (LatB), which inhibits F-actin polymerization, induced transient loss of HBMEC spreading on vitronectin, but not their detachment, and induced apoptosis despite recovery of cell spreading. However, LatB did not cause apoptosis in 5 tumor cell lines. In HBMECs, both LatB and RGDfV induced transient Y412 and Y245 phosphorylation of endogenous c-Abl, a nonreceptor tyrosine kinase that reciprocally regulates F-actin. LatB also induced nuclear translocation of c-Abl in HBMECs. STI-571 (imatinib), a targeted therapy for BCR-ABL1(+) leukemias and inhibitor of c-Abl, platelet-derived growth factor receptor, and c-Kit, decreased endothelial apoptosis. LatB-induced HBMEC apoptosis, and its inhibition by STI-571 also occurred in a 3-dimensional collagen model, supporting physiologic relevance. Last, siRNA to c-Abl (but not nonspecific siRNA) also inhibited RGDfV- and LatB-induced apoptosis. Thus, endogenous c-Abl mediates endothelial apoptosis induced by inhibition of integrins alphavbeta3/alphavbeta5 or by LatB-induced disruption of F-actin.

Topics: Actin Cytoskeleton; Actins; Animals; Apoptosis; Bridged Bicyclo Compounds, Heterocyclic; Cattle; Cell Adhesion; Cell Line, Tumor; Cell Shape; Culture Media; Culture Media, Serum-Free; Endothelial Cells; Fetal Blood; Genes, abl; Glioblastoma; Humans; Integrin alphaVbeta3; Medulloblastoma; Membrane Potential, Mitochondrial; Neuroblastoma; Proto-Oncogene Proteins c-abl; Receptors, Vitronectin; RNA Interference; RNA, Small Interfering; Thiazolidines

Two toxins, latrunculins A and B, which contain a new class of 16- and 14-membered marine macrolides attached to the rare 2-thiazolidinone moiety, were purified recently from the Red Sea sponge Latrunculia magnifica. The effects of these toxins on cultured mouse neuroblastoma and fibroblast cells have been evaluated. In both types of cells, submicromolar toxin concentrations rapidly induce striking changes in cell morphology that are reversible upon removal of the toxin. Immunofluorescence studies with antibodies specific for cytoskeletal proteins reveal that the toxins cause major alterations in the organization of microfilaments without obvious effects on the organization of the microtubular system.

Topics: Actins; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Cytoskeleton; Fibroblasts; Marine Toxins; Microscopy, Fluorescence; Microtubules; Neuroblastoma; Thiazoles; Thiazolidines