A mitochondrial pool of sphingomyelin is involved in TNFα-induced Bax translocation to mitochondria

Abstract

We recently showed that targeting bSMase (bacterial sphingomyelinase) specifically to mitochondria caused accumulation of ceramide in mitochondria, and induced cytochrome c release and cell death [Birbes, El Bawab, Hannun and Obeid (2001) FASEB J., 15, 2669-2679]. In the present study, we investigated the role of this mitochondrial pool of ceramide in response to a receptor-mediated event, namely TNFalpha (tumour necrosis factor alpha), and the involvement of this mitochondrial pool of ceramide in Bax translocation to mitochondria, an event that precedes cytochrome c release. Treatment of MCF7 cells with TNFalpha caused an increase in ceramide levels in the mitochondrial fraction which accompanied Bax translocation to mitochondria. Targeting bSMase to mitochondria specifically resulted in Bax translocation to mitochondria, suggesting that the mitochondrial ceramide pool is involved in Bax translocation. Moreover, in a reconstituted cell-free system, treatment of isolated mitochondria with bSMase enhanced Bax association with mitochondrial membranes. Collectively, these results suggest that the generation of ceramide in mitochondria in response to TNFalpha is sufficient to induce Bax translocation to mitochondria and subsequent cytochrome c release and cell death.

Lipid microdomains contribute to apoptosis-associated modifications of mitochondria in T cells

“…2 The DC of isolated mitochondria was quantified by cytofluorimetric analysis after mitochondria staining with 1 mM tetramethylrhodamine-methyl-ester-perchlorate (TMRM; Molecular Probes), a potential sensitive probe: low levels of TMRM incorporation (revealed by a decrease of red fluorescence) indicated a low DC. As a positive control, 300 mM Ca 2 þ was employed.…”

“…1 In addition, the presence of a metabolic pathway of sphingolipids, including several enzyme activities of sphingolipid metabolism, has been described in mitochondria. 2 The cell expression pattern of gangliosides depends on the cell type. In human lymphocytic cells monosialoganglioside GM3 is the main constituent 3 and disialoganglioside GD3 is also well expressed.…”

Recent advances in the immunobiology of ceramide

“…Antisense bax was found to inhibit cytochrome c release, poly (ADPribose) (PARP) cleavage and cell death in HL-60 cells; furthermore, ceramide induced mitochondrial translocation of Bax, and increased the ratio of Bax to Bcl-xl (Kim et al, 2001). Recent studies suggest that TNF-alpha-mediated mitochondrial generation of ceramide is involved in translocation of Bax to mitochondria and subsequent release of cytochrome c and cell death (Birbes et al, 2005). Moreover, ultraviolet light-induced acid sphingomyelinase activation is involved in conformational change of Bax at the mitochondrial membrane and subsequent release of cytochrome c (Kashkar et al, 2005).…”

Effets du PACAP et du C2- céramide sur la motilité des neurones en grain du cervelet : Rien ne sert de courir, il faut partir à point

“…IRS 2 est ensuite phosphorylé sur des résidus tyrosines par l'activité tyrosine kinase du récepteur et recrute alors des effecteurs intracellulaires. Un de ces effecteurs, la phosphatidylinositol-3-kinase, est également impliqué dans les effets hypothalamiques de l'insuline [6]. Toutefois, les étapes ultérieures restent inconnues.…”

“…Comparativement aux facteurs neurotrophiques, peu d'études ont été consacrées à l'action de molécules inductrices de la mort cellulaire programmée, un processus pourtant indispensable au développement harmonieux du système nerveux [5]. Les céramides constituent une classe de messagers intracellulaires produits soit par synthèse de novo, soit à partir de l'hydrolyse des sphingolipides sous l'effet de sphingomyélinases activées par des cytokines pro-inflammatoires telles que le TNFα ou FasL [6]. Il a été montré que les céramides peuvent induire des effets pro-apoptotiques au cours du neurodéveloppement suggérant une interaction avec le neuropeptide PACAP lors de la corticogenèse du cervelet [7,8].…”