Depletion of membrane cholesterol causes ligand-independent activation of Fas and apoptosis.
ABSTRACT Fas is a member of the tumour necrosis factor receptor superfamily. Fas-mediated apoptosis is an essential mechanism protecting against skin cancer. Activation of Fas by specific ligand or agonistic antibodies leads to the formation of a membrane associated death-inducing signalling complex comprising aggregates of Fas, the Fas-associated death domain protein (FADD), and caspase-8. It has recently been suggested that activity of Fas is not only regulated by its cognate ligand but also by the association of this receptor with cholesterol-enriched lipid domains in the plasma membrane (lipid rafts). We report here that disruption of lipid rafts by cholesterol-depleting compounds (methyl-beta-cyclodextrin, filipin III, cholesterol oxidase, and mevastatin) leads to a spontaneous clustering of Fas in the non-raft compartment of the plasma membrane, formation of Fas-FADD complexes, activation of caspase-8, and apoptosis. We propose that in some cell types exclusion of Fas from lipid rafts leads to the spontaneous, ligand-independent activation of this death receptor, a mechanism that can potentially be utilized in anticancer therapy.
Article: Statins and cancer prevention.[show abstract] [hide abstract]
ABSTRACT: Randomized controlled trials for preventing cardiovascular disease indicated that statins had provocative and unexpected benefits for reducing colorectal cancer and melanoma. These findings have led to the intensive study of statins in cancer prevention, including recent, large population-based studies showing statin-associated reductions in overall, colorectal and prostate cancer. Understanding the complex cellular effects (for example, on angiogenesis and inflammation) and the underlying molecular mechanisms of statins (for example, 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) reductase-dependent processes that involve geranylgeranylation of Rho proteins, and HMG-CoA-independent processes that involve lymphocyte-function-associated antigen 1) will advance the development of molecularly targeted agents for preventing cancer. This understanding might also help the development of drugs for other ageing-related diseases with interrelated molecular pathways.Nature reviews. Cancer 01/2006; 5(12):930-42. · 37.54 Impact Factor
Article: Statin-triggered cell death in primary human lung mesenchymal cells involves p53-PUMA and release of Smac and Omi but not cytochrome c.[show abstract] [hide abstract]
ABSTRACT: Statins inhibit 3-hydroxy-3-methyl-glutarylcoenzyme CoA (HMG-CoA) reductase, the proximal enzyme for cholesterol biosynthesis. They exhibit pleiotropic effects and are linked to health benefits for diseases including cancer and lung disease. Understanding their mechanism of action could point to new therapies, thus we investigated the response of primary cultured human airway mesenchymal cells, which play an effector role in asthma and chronic obstructive lung disease (COPD), to simvastatin exposure. Simvastatin induced apoptosis involving caspase-9, -3 and -7, but not caspase-8 in airway smooth muscle cells and fibroblasts. HMG-CoA inhibition did not alter cellular cholesterol content but did abrogate de novo cholesterol synthesis. Pro-apoptotic effects were prevented by exogenous mevalonate, geranylgeranyl pyrophosphate and farnesyl pyrophosphate, downstream products of HMG-CoA. Simvastatin increased expression of Bax, oligomerization of Bax and Bak, and expression of BH3-only p53-dependent genes, PUMA and NOXA. Inhibition of p53 and silencing of p53 unregulated modulator of apoptosis (PUMA) expression partly counteracted simvastatin-induced cell death, suggesting a role for p53-independent mechanisms. Simvastatin did not induce mitochondrial release of cytochrome c, but did promote release of inhibitor of apoptosis (IAP) proteins, Smac and Omi. Simvastatin also inhibited mitochondrial fission with the loss of mitochondrial Drp1, an essential component of mitochondrial fission machinery. Thus, simvastatin activates novel apoptosis pathways in lung mesenchymal cells involving p53, IAP inhibitor release, and disruption of mitochondrial fission.Biochimica et Biophysica Acta 04/2010; 1803(4):452-67. · 4.66 Impact Factor
Article: CD47-dependent molecular mechanisms of blood outgrowth endothelial cell attachment on cholesterol-modified polyurethane.[show abstract] [hide abstract]
ABSTRACT: We previously showed that blood outgrowth endothelial cells (BOECs) had a high affinity for polyurethane (PU) covalently configured with cholesterol residues (PU-Chol). However, the molecular mechanisms responsible for this enhanced affinity were not determined. CD47, a multifunctional transmembrane glycoprotein involved in cellular attachment, can form a cholesterol-dependent complex with integrin alpha(v)beta(3) and heterotrimeric G proteins. We tested herein the hypothesis that CD47, and the other components of the multi-molecular complex, enhance the attachment of BOECs to PU-Chol. Immunoprecipitation studies, of human and ovine BOECs, demonstrated that CD47 associates with integrin alpha(v) and integrin beta(3) as well as G(alphai-2) protein. The three-fold increase in BOEC attachment to PU-Chol, compared to unmodified PU, was reversed with the addition of blocking antibodies specific for CD47 and integrin alpha(v) and integrin beta(3). Similar results were observed with the addition of methyl-beta-cyclodextrin (MbetaCD), a known disruptor of the CD47 complex as well as of the membrane cholesterol content, to seeded BOEC or PU-Chol films. Reducing CD47 expression, via lentivirus transduced shRNA, decreased BOEC binding to PU-Chol by 50% compared to control groups. These data are the first demonstration of a role for the CD47 cholesterol-dependent signaling complex in BOEC attachment onto synthetic surfaces.Biomaterials 09/2010; 31(25):6394-9. · 7.40 Impact Factor