beta 1 integrin antagonism on adherent, differentiated human neuroblastomacells triggers an apoptotic signaling pathway

Integrin receptors mediate several functions including prevention of matrix detachment-induced apoptosis (anoikis) of several adherent cell types. We report here that antagonists of beta1 integrins trigger an apoptotic signal ing pathway in adherent differentiated LAN-5 human neuroblastoma cells, a c ell line which represents a model system for the study of human neurons. Th e pathway is characterized by cytochrome c release into the cytoplasm, and activation of caspase-9 and caspase-3, 4-6 h after treatment; cleavage prod ucts of caspase-8 and caspase-2 were not detectable in the cells. Coordinat e inactivation of cell survival pathways, including cleavage of focal adhes ion kinase, decreased expression of protein kinase B, and reduced phosphory lation of the pro-apoptotic protein, Bad, also characterized the signaling pathway. These events occurred in adherent cells; DNA fragmentation and det achment followed as late events 18-24 h after addition of beta1 integrin an tagonists, zDEVD-fmk, an irreversible inhibitor of caspase-3-like enzymes, and cytochalasin D, an actin depolymerizing agent, blocked caspase-3 cleava ge and delayed cell death. In contrast to these results, undifferentiated, adherent and dividing LAN-5 cells did not die in response to beta1 integrin antagonists. These studies identify a distinct apoptotic pathway which is triggered by antagonists of beta1 integrins on differentiated adherent neur onal cells. (C) 2000 IBRO. Published by Elsevier Science Ltd. All rights re served.