TGFbeta acts as a tumor suppressor in normal epithelial cells and early-stage tumors and becomes an oncogenic factor in advanced tumors. The molecular mechanisms involved in the malignant function of TGFbeta are not fully elucidated. We demonstrate that high TGFbeta-Smad activity is present in aggressive, highly proliferative gliomas and confers poor prognosis in patients with glioma. We discern the mechanisms and molecular determinants of the TGFbeta oncogenic response with a transcriptomic approach and by analyzing primary cultured patient-derived gliomas and human glioma biopsies. The TGFbeta-Smad pathway promotes proliferation through the induction of PDGF-B in gliomas with an unmethylated PDGF-B gene. The epigenetic regulation of the PDGF-B gene dictates whether TGFbeta acts as an oncogenic factor inducing PDGF-B and proliferation in human glioma.

Glycosphingolipids, including gangliosides, are emerging as signaling intermediates of extracellular stimuli. Because mitochondria play a key role in the orchestration of death signals, we assessed the interaction of GD3 ganglioside (GD3) with mitochondria and the subsequent cascade of events that culminate in cell death. In vitro studies with isolated mitochondria from rat liver demonstrate that GD3 elicited a burst of peroxide production within 15-30 min, which preceded the opening of the mitochondrial permeability transition, followed by cytochrome c (cyt c) release. These effects were mimicked by lactosylceramide and N-acetyl-sphingosine but not by sphinganine or sphingosine and were prevented by cyclosporin A and butylated hydroxytoluene (BHT). Reconstitution of mitochondria pre-exposed to GD3 with cytosol from rat liver in a cell-free system resulted in the proteolytic processing of procaspase 3 and subsequent caspase 3 activation. Intact hepatocytes or U937 cells selectively depleted of glutathione in mitochondria by 3-hydroxyl-4-pentenoate (HP) with the sparing of cytosol reduced glutathione (GSH) were sensitized to GD3, manifested as an apoptotic death. Inhibition of caspase 3 prevented the apoptotic phenotype of HP-treated cells caused by GD3 without affecting cell survival; in contrast, BHT fully protected HP-treated cells to GD3 treatment. Treatment of cells with tumor necrosis factor increased the level of GD3, whereas blockers of mitochondrial respiration at complex I and II protected sensitized cells to GD3 treatment. Thus, the effect of GD3 as a lipid death effector is determined by its interaction with mitochondria leading to oxidant-dependent caspase activation. Mitochondrial glutathione plays a key role in controlling cell survival through modulation of the oxidative stress induced by glycosphingolipids.

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Mitochondrial glutathione (GSH) plays a key role against tumor necrosis factor ␣ (TNF)-induced apoptosis because its depletion is known to sensitize hepatocytes to TNF. The present study examined the role of tauroursodeoxycholic acid (TUDCA) administration to chronic ethanol-fed rats on mitochondrial GSH levels and kinetics, mitochondrial membrane physical properties, TNF-induced peroxide formation, and subsequent hepatocyte survival. TUDCA selectively increased the levels of GSH in mitochondria without an effect on cytosolic GSH. This outcome was accompanied by improved initial rate of GSH transport examined at low (1 mmol/L) and high (10 mmol/L) GSH concentrations both in intact mitochondria and mitoplasts prepared from ethanol-fed livers. Assessment of membrane fluidity revealed an increased order parameter in mitochondria and mitoplasts from ethanol-fed rats compared with pair-fed controls, which was prevented by TUDCA administration. Compared with hepatocytes from pair-fed rats, TNF stimulated peroxide generation in hepatocytes from ethanol-fed rats, preceding TNF-induced cell death. Administration of TUDCA to ethanol-fed rats prevented TNF-induced peroxide formation and cell death, an effect that was reversed on depletion of the recovered mitochondrial GSH levels by (R,S)-3-hydroxy-4-pentenoate before TNF treatment. The protective effect of TUDCA against TNF was not because of activation of phosphatidylinositol 3-kinase, discarding a role for a survivaldependent pathway. Thus, these findings reveal a novel role of TUDCA in protecting hepatocytes in long-term ethanolfed rats through modulation of mitochondrial membrane fluidity and subsequent normalization of mitochondrial GSH levels. (HEPATOLOGY 2001;34:964-971.)Mitochondria have attracted considerable attention because of the role they play in controlling cell survival and because mitochondrial dysfunction is recognized to contribute to the development of a number of pathologic conditions. 1,2 The generation of a varied repertoire of proapoptotic intermediates converge at the mitochondria where they stimulate the release of factors that collaborate in the activation of the molecular machinery of cell death. 3,4 Conversely, Bcl-2 and other related antiapoptotic family members confer protection against apoptosis induced by tumor necrosis factor (TNF) and members of the TNF family by preventing the release of mitochondrial proapoptotic factors. 5,6 Although the identification of the signalling intermediates responsible for the mitochondrial recruitment to the apoptotic pathway are not fully characterized, increasing evidence supports the participation of oxidative stress caused by overgeneration of reactive oxygen species from mitochondria in the TNF-induced cytotoxic action. [7][8][9][10] In line with this, it has been shown that prolonged cellular glutathione (GSH) depletion accentuates, whereas antioxidants attenuate, TNF-induced hepatocyte cell death. 9,11 Furthermore, the selective mitochondrial GSH limitation has been shown to enhance mitochondrial dys...