SummaryAnucleate cells can be induced to undergo programmed cell death (PCD), indicating the existence of a cytoplasmic PCD pathway that functions independently from the nucleus. Cytoplasmic structures including mitochondria have been shown to participate in the control of apoptotic nuclear disintegration. Before cells exhibit common signs of nuclear apoptosis (chromatin condensation and endonuclease-mediated DNA fragmentation), they undergo a reduction of the mitochondrial transmembrane potential (A~m) that may be due to the opening of mitochondrial permeability transition (PT) pores. Here, we present direct evidence indicating that mitochondrial PT constitutes a critical early event of the apoptotic process. In a cell-free system combining purified mitochondria and nuclei, mitochondria undergoing PT suffice to induce chromatin condensation and DNA fragmentation. Induction of PT by pharmacological agents augments the apoptosis-inducing potential of mitochondria. In contrast, prevention of PT by pharmacological agents impedes nuclear apoptosis, both in vitro and in vivo. Mitochondria from hepatocytes or lymphoid cells undergoing apoptosis, but not those from normal cells, induce the disintegration of isolated Hela nuclei. A specific ligand of the mitochondrial adenine nucleotide translocator (ANT), bongkrekic acid, inhibits PT and reduces apoptosis induction by mitochondria in a cell-free system. Moreover, it inhibits the induction of apoptosis in intact cells. Several pieces of evidence suggest that the proto-oncogene product Bcl-2 inhibits apoptosis by preventing mitochondrial PT. First, to inhibit nuclear apoptosis, Bcl-2 must be localized in mitochondrial but not in nuclear membranes. Second, transfection-enforced hyperexpression of Bcl-2 directly abolishes the induction of mitochondrial PT in response to a protonophore, a pro-oxidant, as well as to the ANT ligand atractyloside, correlating with its apoptosis-inhibitory effect. In conclusion, mitochondrial PT appears to be a critical step of the apoptotic cascade. Since it has been shown that anucleate cells (cytoblasts) can be induced to undergo programmed cell death (PCD) 1 (1-3), it has become clear that a cytoplasmic PCD pathway must function independently from the nucleus. Both mitochondria (4) and specific ced-3-1ike proteases 1Abbreviations used in this paper:

Cancer development and chemo-resistance are often due to impaired functioning of the p53 tumor suppressor through genetic mutation or sequestration by other proteins. In glioblastoma multiforme (GBM), p53 availability is frequently reduced because it binds to the Murine Double Minute-2 (MDM2) oncoprotein, which accumulates at high concentrations in tumor cells. The use of MDM2 inhibitors that interfere with the binding of p53 and MDM2 has become a valid approach to inhibit cell growth in a number of cancers; however little is known about the efficacy of these inhibitors in GBM. We report that a new small-molecule inhibitor of MDM2 with a spirooxoindolepyrrolidine core structure, named ISA27, effectively reactivated p53 function and inhibited human GBM cell growth in vitro by inducing cell cycle arrest and apoptosis. In immunoincompetent BALB/c nude mice bearing a human GBM xenograft, the administration of ISA27 in vivo activated p53, inhibited cell proliferation and induced apoptosis in tumor tissue. Significantly, ISA27 was non-toxic in an in vitro normal human cell model and an in vivo mouse model. ISA27 administration in combination with temozolomide (TMZ) produced a synergistic inhibitory effect on GBM cell viability in vitro, suggesting the possibility of lowering the dose of TMZ used in the treatment of GBM. In conclusion, our data show that ISA27 releases the powerful antitumor capacities of p53 in GBM cells. The use of this MDM2 inhibitor could become a novel therapy for the treatment of GBM patients.

In this work, the naturally occurring antimicrobial peptides temporin A (TA) and L (TL) are studied by spectroscopic (CD and NMR) techniques and molecular dynamics simulation. We analyzed the interactions of TA and TL with sodium dodecyl sulfate (SDS) and dodecylphosphocholine (DPC) micelles, which mimic bacterial and mammalian membranes, respectively. In SDS, the peptides prefer a location at the micelle-water interface; in DPC, they prefer a location perpendicular to the micelle surface, with the N-terminus imbedded in the hydrophobic core. TL shows higher propensity, with respect to TA, in forming alpha-helical structures in both membrane mimetic systems and the highest propensity to penetrate the micelles. Hence, we have proposed a different molecular mechanism underlying the antimicrobial and hemolytic activities of the two peptides. We also designed new analogues of TA and TL and found interesting differences in their efficacy against microbial species and human erythrocytes.

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