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Biomedical subjects

C Brenner

Publications and source records attributed to C Brenner.

At least 37 records · Page 2Linked to original sources
PubMed2000

Bid acts on the permeability transition pore complex to induce apoptosis.

Similar to most if not all pro-apoptotic members of the Bcl-2 family, Bid (and its truncated product t-Bid) triggers cell death via mitochondrial membrane permeabilization (MMP). This effect can be monitored in intact cells, upon microinjection of recombinant Bid protein into the cytoplasm, as well as in purified mitochondria, upon addition of Bid protein. Here we show that Bid-induced MMP can be inhibited, both in cells and in the cell-free system, by three pharmacological inhibitors of the permeability transition pore complex (PTPC), namely cyclosporin A, N-methyl-4-Val-cyclosporin A, and bongkrekic acid (a ligand of the adenine nucleotide translocase, ANT, one of the PTPC components). Bid effects on synthetic membranes were studied either in proteoliposomes or in synthetic bilayers subjected to electrophysiological measurements. Full length Bid preferentially permeabilizes membranes and induces the formation of large conductance channels at neutral pH, when added to liposomes or bilayers containing both purified ANT and Bax, yet has no or little effect combined with ANT or Bax alone. t-Bid acts on membranes containing ANT alone with the same efficiency as on those containing both ANT and Bax. These results suggest that the proapoptotic effects of Bid are mediated, at least in part, by its functional interaction with ANT, one of the major components of PTPC.

Animals↗
PubMed2000

Apoptosis. Mitochondria--the death signal integrators.

Many of the intricate pathways of apoptosis that instruct a cell to kill itself involve the convergence of key proteins on the membranes of mitochondria. Such proteins induce the permeabilization of mitochondrial membranes and the release of caspase enzymes and nuclease activators that set in motion the final stages of programmed cell death. Now, as Brenner and Kroemer discuss in their Perspective, a proapoptotic transcription factor called TR3 has been found to move from its normal location in the nucleus to the mitochondria and to promote release of cytochrome c, a key event in apoptosis (Li et al.)

Animals↗
PubMed2000

A cultivated taste for yeast.

The availability of complete genomic sequences of Saccharomyces cerevisiae has catalyzed a cultural change in the practice of yeast biology, providing opportunities to develop high throughput techniques to define protein function, to define drug targets, and to discover and characterize drugs.

Animals↗
PubMed2000

Fhit-nucleotide specificity probed with novel fluorescent and fluorogenic substrates.

Fhit, a member of the histidine triad superfamily of nucleotide-binding proteins, binds and cleaves diadenosine polyphosphates and functions as a tumor suppressor in human epithelial cancers. Function of Fhit in tumor suppression does not require diadenosine polyphosphate cleavage but correlates with the ability to form substrate complexes. As diadenosine polyphosphates are at lower cellular concentrations than mononucleotides, we sought to quantify interactions between Fhit and competitive inhibitors with the use of diadenosine polyphosphate analogs containing fluorophores in place of one nucleoside. Appp-S-(7-diethylamino-4-methyl-3-(4-succinimidylphenyl)) coumarin (ApppAMC), Appp-S-(4-4-difluoro-5,7-dimethyl-4-bora-3a, 4a-diaza-s-indacine-3-yl) methylaminoacetyl (ApppBODIPY), and GpppBODIPY, synthesized in high yield, are effective Fhit substrates, producing AMP or GMP plus fluorophore diphosphates. GpppBODIPY cleavage is accompanied by a 5.4-fold increase in fluorescence because BODIPY fluorescence is quenched by stacking with guanine. Titration of unlabeled diadenosine polyphosphates, inorganic pyrophosphate, mononucleotides, and inorganic phosphate into fluorescent assays provided values of K(m) and K(I) as competitive inhibitors. The data indicate that Fhit discriminates between good substrates via k(cat) and against cellular competitors in equilibrium binding terms. Surprisingly, pyrophosphate competes better than purine mononucleotides.

Acid Anhydride Hydrolases↗
PubMed2000

Bcl-2 and Bax regulate the channel activity of the mitochondrial adenine nucleotide translocator.

Bcl-2 family protein including anti-apoptotic (Bcl-2) or pro-apoptotic (Bax) members can form ion channels when incorporated into synthetic lipid bilayers. This contrasts with the observation that Bcl-2 stabilizes the mitochondrial membrane barrier function and inhibits the permeability transition pore complex (PTPC). Here we provide experimental data which may explain this apparent paradox. Bax and adenine nucleotide translocator (ANT), the most abundant inner mitochondrial membrane protein, can interact in artificial lipid bilayers to yield an efficient composite channel whose electrophysiological properties differ quantitatively and qualitatively from the channels formed by Bax or ANT alone. The formation of this composite channel can be observed in conditions in which Bax protein alone has no detectable channel activity. Cooperative channel formation by Bax and ANT is stimulated by the ANT ligand atractyloside (Atr) but inhibited by ATP, indicating that it depends on the conformation of ANT. In contrast to the combination of Bax and ANT, ANT does not form active channels when incorporated into membranes with Bcl-2. Rather, ANT and Bcl-2 exhibit mutual inhibition of channel formation. Bcl-2 prevents channel formation by Atr-treated ANT and neutralizes the cooperation between Bax and ANT. Our data are compatible with a ménage à trois model of mitochondrial apoptosis regulation in which ANT, the likely pore forming protein within the PTPC, interacts with Bax or Bcl-2 which influence its pore forming potential in opposing manners.

Animals↗
PubMed2000

Oxidation of a critical thiol residue of the adenine nucleotide translocator enforces Bcl-2-independent permeability transition pore opening and apoptosis.

Mitochondrial membrane permeabilization is a critical event in the process leading to physiological or chemotherapy-induced apoptosis. This permeabilization event is at least in part under the control of the permeability transition pore complex (PTPC), which interacts with oncoproteins from the Bcl-2 family as well as with tumor suppressor proteins from the Bax family, which inhibit or facilitate membrane permeabilization, respectively. Here we show that thiol crosslinking agents including diazenedicarboxylic acid bis 5N, N-dimethylamide (diamide), dithiodipyridine (DTDP), or bis-maleimido-hexane (BMH) can act on the adenine nucleotide translocator (ANT), one of the proteins within the PTPC. ANT alone reconstituted into artificial lipid bilayers suffices to confer a membrane permeabilization response to thiol crosslinking agents. Diamide, DTDP, and BMH but not tert-butylhydroperoxide or arsenite cause the oxidation of a critical cysteine residue (Cys 56) of ANT. Thiol modification within ANT is observed in intact cells, isolated mitochondria, and purified ANT. Recombinant Bcl-2 fails to prevent thiol modification of ANT. Concomitantly, a series of different thiol crosslinking agents (diamide, DTDP, and BMH, phenylarsine oxide) but not tert-butylhydroperoxide or arsenite induce mitochondrial membrane permeabilization and cell death irrespective of the expression level of Bcl-2. These data indicate that thiol crosslinkers cause a covalent modification of ANT which, beyond any control by Bcl-2, leads to mitochondrial membrane permeabilization and cell death.

Animals↗
PubMed2000

Observations on some aspects of current psychoanalytic theories.

The competing theories in the psychoanalytic marketplace today should be judged on their merits, not on the basis of the authority of whoever first proposed them. What is valid in each theory should be included in any formulation of a psychoanalytic theory of mental development and functioning. Since psychoanalysis, as part of psychology, is a branch of natural science, pluralism in theory is to be avoided in psychoanalysis as in every branch of science. The psychoanalytic method is a valid one of studying a particular aspect of brain functioning. The method and the theories based upon it are as "organic" as is the case with any of the other neurosciences. Any valid psychoanalytic theory of mental functioning and development should include the following conclusions: (1) Unconscious mental processes are omnipresent and of great importance in mental functioning; (2) Thoughts are as causally related to one another as are other events in the universe; (3) Mental functioning is a developmental phenomenon with describable, sequential features; and (4) A major role in mental functioning and development is played by conflicts over the sexual and aggressive wishes that characterize mental life during the period from three to six years of age, and by the compromise formations that result from those conflicts. The last of these conclusions, though disputed by many, is abundantly supported by evidence that is not dependent on the use of the psychoanalytic method, as well as by evidence furnished by the use of the psychoanalytic method. There is also much evidence to support the assertion that any psychoanalytic theory that attributes language-dependent thoughts to a child whose brain is not yet mature enough to be capable of language is to be considered invalid, as are any observations made by the psychoanalytic method (= clinical observations) that are influenced by such an invalid theory. In psychoanalysis, as in every other branch of science, an observer--no matter how astute and how experienced--who subscribes to an invalid theory will be led astray by that theory, sooner or later, in one way or another.

Adult↗
PubMed2000

The PEA3 group of ETS-related transcription factors. Role in breast cancer metastasis.

The ets genes encode eukaryotic transcription factors that are involved in tumorigenesis and developmental processes. The signature of the Ets family is the ETS-domain, which binds to sites containing a central 5'-GGAA/T-3' motif. They can be sub-classified primarily because of the high amino acid conservation in their ETS-domains and, in addition, in the conservation of other domains generally characterized as transactivating. This is the case for the PEA3 group, which is currently made up of three members, PEA3/E1AF, ER81/ETV1 and ERM, which are more than 95% identical in the ETS-domain and more than 85% in the transactivation acidic domain. The members of the PEA3 group are activated through both the Ras-dependent and other kinase pathways, a function which emphasizes their involvement in several oncogenic mechanisms. The expression pattern of the three PEA3 group genes during mouse embryogenesis suggests that they are differentially regulated, probably to serve important functions such as tissue interaction. Although the target genes of these transcription factors are multiple, their most frequently studied role concerns their involvement in the metastatic process. In fact, PEA3 group members are over-expressed in metastatic human breast cancer cells and mouse mammary tumors, a feature which suggests a function of these transcription factors in mammary oncogenesis. Moreover, when they are ectopically over-expressed in non-metastatic breast cancer cells, these latter become metastatic with the activation of transcription of matrix metalloproteinases or adhesion molecules, such as ICAM-1.

Animals↗
PubMed2000

Permeabilization of the mitochondrial inner membrane during apoptosis: impact of the adenine nucleotide translocator.

Mitochondrial membrane permeabilization can be a rate limiting step of apoptotic as well as necrotic cell death. Permeabilization of the outer mitochondrial membrane (OM) and/or inner membrane (IM) is, at least in part, mediated by the permeability transition pore complex (PTPC). The PTPC is formed in the IM/OM contact site and contains the two most abundant IM and OM proteins, adenine nucleotide translocator (ANT, in the IM) and voltage-dependent anion channel (VDAC, in the OM), the matrix protein cyclophilin D, which can interact with ANT, as well as apoptosis-regulatory proteins from the Bax/Bcl-2 family. Here we discuss that ANT has two opposite functions. On the one hand, ANT is a vital, specific antiporter which accounts for the exchange of ATP and ADP on IM. On the other hand, ANT can form a non-specific pore, as this has been shown by electrophysiological characterization of purified ANT reconstituted into synthetic lipid bilayers or by measuring the permeabilization of proteoliposomes containing ANT. Pore formation by ANT is induced by a variety of different agents (e.g. Ca(2+), atractyloside, thiol oxidation, the pro-apoptotic HIV-1 protein Vpr, etc.) and is enhanced by Bax and inhibited by Bcl-2, as well as by ADP. In isolated mitochondria, pore formation by ANT leads to an increase in IM permeability to solutes up to 1500 Da, swelling of the mitochondrial matrix, and OM permeabilization, presumably due to physical rupture of OM. Although alternative mechanisms of mitochondrial membrane permeabilization may exist, ANT emerges as a major player in the regulation of cell death. Cell Death and Differentiation (2000) 7, 1146 - 1154

Animals↗
PubMed2000

The genetic revolution in artificial reproduction: a view of the future.

With the completion of the human genome project, micro-array technology offers the potential to open up a whole new vista in assisted reproduction. In the next 10-20 years we will be able to screen each human embryo for all numerical chromosomal abnormalities as well as many genetic diseases. Micro-array analysis may permit the screening of multiple alleles for monogenetic diseases and polygenic diseases, including diabetes, hypertension and schizophrenia. In the near future, it may be possible to assess an individual's genetic predisposition for cardiovascular disease, all types of cancer and infectious diseases. In the distant future, it may even be possible to screen for any genetic trait, e.g. stature, baldness, obesity, hair colour, skin colour or even IQ. Although it is still uncertain what molecular genetic tools may be available, we can be sure that some of these trends will have major consequences on the future of assisted reproduction and society at large.

Chromosome Aberrations↗
PubMed2000

Real-time PCR using molecular beacons for accurate detection of the Y chromosome in single human blastomeres.

We describe a highly accurate method for determining the sex of human embryos via real-time polymerase chain reaction (PCR) amplification of highly-conserved, moderately-repeated sequences within the TSPY genes on the Y chromosome and the U2 genes on chromosome 17. Individual male lymphocytes, female lymphocytes, and blastomeres from donated cleavage-stage embryos were lysed prior to PCR using an optimized buffer containing proteinase K. Molecular beacons, a new type of fluorescent probe, were used to detect and quantify accumulating amplicons during each cycle of PCR carried out in closed tubes. The present work is part of an ongoing study to construct and implement a new, convenient and reliable system of preimplantation genetic diagnosis (PGD).

Blastomeres↗