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

Garofalo, Tina; Giammarioli, Anna Maria; Misasi, Roberta; Tinari, Antonella; Manganelli, Valeria; Gambardella, Lucrezia; Pavan, Antonio; Malorni, Walter; Sorice, Maurizio

doi:10.1038/sj.cdd.4401672

Cited by 108 publications

(165 citation statements)

References 54 publications

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“…Blots are representative of at least four independent experiments lymphoblastoid cells, with the cholesterol chelator methylb-cyclodextrin (Mbc, 500 mg/ml) was reported to lead to cholesterol depletion and to inhibit tBid-induced Cytochrome c release, leading the authors to propose that cholesterol-rich MOM microdomains might be essential for MOM permeabilization. 30 Unpublished results from our group show that at this concentration Mbc prevents tBid-induced MOM permeabilization, but does not modify the cholesterol content of HeLa mitochondria, suggesting that the effect of Mbc on MOM permeabilization might not be due to cholesterol depletion.…”

Section: Discussionmentioning

confidence: 71%

“…Some mitochondrial proteins were recently reported to remain insoluble under similar conditions, suggesting that analogous lipid rafts might be present in mitochondrial membranes. 30 If such microdomains exist in the MOMs, our results suggest that membrane order might locally impede Bax oligomerization. However, treatment of mitochondria isolated from human The mitochondrial pellets were further treated with an alkaline solution of sodium carbonate, ultracentrifuged, and the pellets were analyzed by immunoblotting to look at the insertion of Bax and tBid in the membranes.…”

Section: Discussionmentioning

confidence: 82%

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Bax activation and stress-induced apoptosis delayed by the accumulation of cholesterol in mitochondrial membranes

2007

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Activation of Bax or Bak is essential for the completion of many apoptotic programmes. Under cytotoxic conditions, these proteins undergo a series of conformational rearrangements that end up with their oligomerization. We found that unlike inactive monomeric Bax, active oligomerized Bax is partially resistant to trypsin digestion, providing a convenient read out to monitor Bax activation. Using this assay, we studied how the lipid composition of membranes affects tBid-induced Bax activation in vitro with pure liposomes. We report that Bax activation is inhibited by cholesterol and by decreases in membrane fluidity. This observation was further tested in vivo using the drug U18666A, which we found increases mitochondrial cholesterol levels. When incubated with tBid, mitochondria isolated from U18666A-treated cells showed a delay in the release of Smac/Diablo and Cytochrome c, as well as in Bax oligomerization. Moreover, pre-incubation with U18666A partially protected cells from stressinduced apoptosis. As many tumours display high mitochondrial cholesterol content, inefficient Bax oligomerization might contribute to their resistance to apoptosis-inducing agents. Among the stimuli that lead to apoptosis, a series of stress conditions trigger the permeabilization of the mitochondrial outer membrane (MOM) and the release of pro-apoptotic factors that will activate caspases in the cytosol. This so-called intrinsic apoptotic pathway is tightly regulated by proteins of the Bcl-2 family, among which the pro-apoptotic members Bax and Bak are essential. They seem to be the central players whose activation results in MOM permeabilization.Under resting conditions, whereas Bak essentially resides in the MOMs, Bax is found in loose association with membranes (mainly the MOMs) or as a soluble protein in the cytosol. Following many cytotoxic signals, Bax and Bak undergo a series of conformational rearrangements. 1 Bax translocates to mitochondria and inserts into the MOMs in a form that cannot be detached by alkali treatment. Bax and Bak then uncover N-terminal epitopes and oligomerize. Oligomerization, shown by size exclusion chromatography, 2 crosslinking experiments 3,4 and native gel electrophoresis, 5 appears as the critical step resulting in MOM permeabilization. However, despite many efforts, it remains unclear how each of these conformational rearrangements is regulated, and how Bax/Bak oligomerization leads to the release of mitochondrial apoptogenic factors. Both processes are undoubtedly regulated by other members of the Bcl-2 family, 6,7 but the participation of many unrelated proteins was also proposed. 8 While a BH3-only protein appears to be sufficient for Bax to oligomerize in synthetic liposomes, 9,10 additional proteins could be required for its activation in isolated mitochondria. 11 These might directly interact with Bax, and/or modify the membrane properties to allow its oligomerization. Interaction with mitochondrial lipids is indeed an important parameter to consider as the final conformational rearrange...

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Section: Discussionmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 82%

Bax activation and stress-induced apoptosis delayed by the accumulation of cholesterol in mitochondrial membranes

2007

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“…Purified T cells were incubated with human anti-ER␣ antibodies purified from SLE patient sera or IVIG for 1 hour at 4°C, and TEM was performed as previously described (30). Sections were observed with a Philips 208 electron microscope at 80 kV.…”

Section: Methodsmentioning

confidence: 99%

Autoantibodies to estrogen receptor α interfere with T lymphocyte homeostasis and are associated with disease activity in systemic lupus erythematosus

Colasanti¹,

Maselli²,

Conti³

et al. 2012

Arthritis & Rheumatism

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Objective. Estrogens influence many physiologic processes and are also implicated in the development or progression of numerous diseases, including autoimmune disorders. Aberrations of lymphocyte homeostasis that lead to the production of multiple pathogenic autoantibodies, including autoantibodies specific to estrogen receptor (ER), have been detected in the peripheral blood of patients with systemic lupus erythematosus (SLE). This study was undertaken to assess the presence of both anti-ER␣ and anti-ER␤ antibodies in sera from patients with SLE, to analyze the effect of these antibodies on peripheral blood T lymphocyte homeostasis, and to evaluate their role as determinants of disease pathogenesis and progression.Methods. Anti-ER antibody serum immunoreactivity was analyzed by enzyme-linked immunosorbent assay in samples from 86 patients with SLE and 95 healthy donors. Phenotypic and functional analyses were performed by flow cytometry and Western blotting.Results. Anti-ER␣ antibodies were present in 45% of the patients with SLE, whereas anti-ER␤ antibodies were undetectable. In healthy donors, anti-ER␣ antibodies induced cell activation and consequent apoptotic cell death in resting lymphocytes as well as proliferation of anti-CD3-stimulated T lymphocytes. A significant association between anti-ER␣ antibody values and clinical parameters, i.e., the SLE Disease Activity Index and arthritis, was found.Conclusion. Our data suggest that anti-ER␣ autoantibodies interfere with T lymphocyte homeostasis and are significantly associated with lupus disease activity.The involvement of estrogens, which influence many physiologic processes, has been shown in the development or progression of several autoimmune disorders (1-4). There is evidence that 17␤-estradiol directly modulates the development and function of immune cells, although the mechanism by which this might occur is not well understood (5,6). The primary mechanism of 17␤-estradiol activity is mediated by transcription activity of the intracellular estrogen receptors (ERs), ER␣ and ER␤, to produce genomic effects (7). A variety of cellular responses to physiologic concentrations of 17␤-estradiol occur rapidly, within seconds to a few minutes. These rapid estrogen-mediated effects (referred to as nongenomic) are triggered through the activation of membrane-associated ER and are independent of transcription pathways and protein synthesis.

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“…For instance, this applies to avicins, betulinic acid, CD437, resveratrol, and the bile acid glycochenodeoxycholic acid. These agents might perturb the lipid composition of mitochondrial membranes and induce lipid rafts, which in turn may favor MOMP (Garofalo et al, 2005). Avicins can form channels in synthetic membranes (Li et al, 2005).…”

Section: Chemotherapy and Mitochondriamentioning

confidence: 99%

Mitochondria as therapeutic targets for cancer chemotherapy

et al. 2006

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Mitochondria are vital for cellular bioenergetics and play a central role in determining the point-of-no-return of the apoptotic process. As a consequence, mitochondria exert a dual function in carcinogenesis. Cancer-associated changes in cellular metabolism (the Warburg effect) influence mitochondrial function, and the invalidation of apoptosis is linked to an inhibition of mitochondrial outer membrane permeabilization (MOMP). On theoretical grounds, it is tempting to develop specific therapeutic interventions that target the mitochondrial Achilles' heel, rendering cancer cells metabolically unviable or subverting endogenous MOMP inhibitors. A variety of experimental therapeutic agents can directly target mitochondria, causing apoptosis induction. This applies to a heterogeneous collection of chemically unrelated compounds including positively charged a-helical peptides, agents designed to mimic the Bcl-2 homology domain 3 of Bcl-2-like proteins, ampholytic cations, metals and steroid-like compounds. Such MOMP inducers or facilitators can induce apoptosis by themselves (monotherapy) or facilitate apoptosis induction in combination therapies, bypassing chemoresistance against DNA-damaging agents. In addition, it is possible to design molecules that neutralize inhibitor of apoptosis proteins (IAPs) or heat shock protein 70 (HSP70). Such IAP or HSP70 inhibitors can mimic the action of mitochondrion-derived mediators (Smac/DIABLO, that is, second mitochondria-derived activator of caspases/direct inhibitor of apoptosis-binding protein with a low isoelectric point, in the case of IAPs; AIF, that is apoptosis-inducing factor, in the case of HSP70) and exert potent chemosensitizing effects.

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

Cited by 108 publications

References 54 publications

Bax activation and stress-induced apoptosis delayed by the accumulation of cholesterol in mitochondrial membranes

Bax activation and stress-induced apoptosis delayed by the accumulation of cholesterol in mitochondrial membranes

Autoantibodies to estrogen receptor α interfere with T lymphocyte homeostasis and are associated with disease activity in systemic lupus erythematosus

Mitochondria as therapeutic targets for cancer chemotherapy

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