Amplification of Fas-Mediated Apoptosis in Type II Cells via Microdomain Recruitment

Abstract

Fas triggers apoptosis via the caspase cascade when bound to its ligand FasL. In type I cells, Fas is concentrated into the plasma membrane lipid rafts, and these domains are required for the apoptotic signal to occur. In contrast, Fas is excluded from the microdomains in type II cells. We report that the coligation with Fas of the membrane receptor CD28 strongly increases Fas-induced apoptosis in type II T lymphocytes, whereas it has no effect in a type I cell line. The effect of CD28 is independent of its intracellular region and requires the recruitment of the microdomains. Indeed, upon CD28 costimulation, Fas is redistributed in the lipid rafts, and their disruption with a cholesterol chelator abrogates the effect of CD28. The microdomain-mediated cell death amplification does not alter death-induced signaling complex formation and is mediated by the enhancement of the mitochondrial apoptotic pathway. These findings indicate that the sensitivity to Fas-induced apoptosis of type II cells can be amplified in vivo by the recruitment of lipid rafts following interactions between nonapoptotic ligand/receptor pairs during cell-to-cell contacts.

ACKNOWLEDGMENTS

We thank J. Déchanet-Merville for insightful discussions. We thank M. E. Peter (Ben May institute for cancer research, Chicago, IL) for providing anti-c-FLIP (clone NF-6) and F. Belloc (laboratoire d'hématologie, Hôpital du Haut-Lévèque, CHU de Bordeaux) for the cell sorting experiments.

P.L. is supported by a grant from the Association pour la Recherche sur le Cancer. This work was supported by grants from the Association pour la Recherche sur le Cancer and from the Ligue Contre le Cancer des Landes, de la Charente, de la Dordogne, de la Gironde, des Pyrénées-Atlantiques.