Proliferating cell nuclear antigen (PCNA) is a 36 kD nuclear protein associated with the cell cycle. A monoclonal antibody, PC10, that recognizes a fixation and processing resistant epitope has been used to investigate its tissue distribution. Nuclear PCNA immunoreactivity is found in the proliferative compartment of normal tissues. PCNA immunoreactivity is induced in lectin stimulated peripheral blood mononuclear cells in parallel with bromodeoxyuridine incorporation and the number of cells with PCNA immunoreactivity is reduced by induction of differentiation in HL60 cells. In non-Hodgkin's lymphomas a linear relation between Ki67 and PCNA staining was demonstrated. These data suggest that in normal tissues and lymphoid neoplasms, PCNA immunolocalization can be used as an index of cell proliferation. However, in some forms of neoplasia, including breast and gastric cancer and in vitro cell lines, the simple relation between PCNA expression and cell proliferation is lost. In some breast and pancreatic tumours there is apparent deregulation of PCNA with increased expression in tissues adjacent to the tumours. The over-expression in some tumours and in adjacent morphologically normal tissue may represent autocrine or paracrine growth factor influence on PCNA gene expression.
Understanding the mechanisms of long-term potentiation (LTP) should provide insights into the molecular basis of learning and memory in vertebrates. Ionotropic glutamate receptors play a central role in LTP; AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptors and NMDA (N-methyl-D-aspartate) receptors mediate synaptic responses that are enhanced in LTP and, in addition, NMDA receptors are necessary for the induction of LTP in most pathways. There is also circumstantial evidence that metabotropic glutamate receptors (mGluRs) may be involved in LTP because the specific mGluR agonist aminocyclopentane dicarboxylate can augment tetanus-induced LTP2 and, under certain circumstances, can itself induce a slow-onset potentiation. But the absence of any effective mGluR antagonist has prevented the determination of whether mGluRs are involved in the induction of tetanus-induced LTP. We report here that (RS)-alpha-methyl-4-carboxyphenylglycine is a specific mGluR antagonist in the hippocampus and have used this compound to examine the nature of the involvement of mGluRs in LTP. We show that synaptic activation of mGluRs is necessary for the induction of both NMDA receptor-dependent and NMDA receptor-independent forms of LTP in the hippocampus.
Poly (ADP-ribose) polymerase (PARP) inhibitors and platinum-based chemotherapies have been found to be particularly effective in tumors that harbor deleterious germline or somatic mutations in the BRCA1 or BRCA2 genes, the products of which contribute to the conservative homologous recombination repair of DNA double-strand breaks. Nonetheless, several setbacks in clinical trial settings have highlighted some of the issues surrounding the investigation of PARP inhibitors, especially the identification of patients who stand to benefit from such drugs. One potential approach to finding this patient subpopulation is to examine the tumor DNA for evidence of a homologous recombination defect. However, although the genomes of many breast and ovarian cancers are replete with aberrations, the presence of numerous factors able to shape the genomic landscape means that only some of the observed DNA abnormalities are the outcome of a cancer cell’s inability to faithfully repair DNA double-strand breaks. Consequently, recently developed methods for comprehensively capturing the diverse ways in which homologous recombination deficiencies may arise beyond BRCA1/2 mutation have used DNA microarray and sequencing data to account for potentially confounding features in the genome. Scores capturing telomeric allelic imbalance, loss of heterozygosity (LOH) and large scale transition score, as well as the total number of coding mutations are measures that summarize the total burden of certain forms of genomic abnormality. By contrast, other studies have comprehensively catalogued different types of mutational pattern and their relative contributions to a given tumor sample. Although at least one study to explore the use of the LOH scar in a prospective clinical trial of a PARP inhibitor in ovarian cancer is under way, limitations that result in a relatively low positive predictive value for these biomarkers remain. Tumors whose genome has undergone one or more events that restore high-fidelity homologous recombination are likely to be misclassified as double-strand break repair-deficient and thereby sensitive to PARP inhibitors and DNA damaging chemotherapies as a result of prior repair deficiency and its genomic scarring. Therefore, we propose that integration of a genomic scar-based biomarker with a marker of resistance in a high genomic scarring burden context may improve the performance of any companion diagnostic for PARP inhibitors.
1 The depressant actions on evoked electrical activity and the excitant amino acid antagonist properties of a range of w-phosphonic x-carboxylic amino acids have been investigated in the isolated spinal cord preparations of the frog or immature rat. 2 When tested on dorsal root-evoked ventral root potentials, members of the homologous series from 2-amino-5-phosphonovaleric acid to 2-amino-8-phosphonooctanoic acid showed depressant actions which correlated with the ability of the substances to antagonize selectively motoneuronal depolarizations induced by N-methyl-D-aspartate. of this substance had a relatively weak and non-selective antagonist action on depolarizations induced by N-methyl-D-aspartate, quisqualate and kainate and a similarly weak depressant effect when tested on evoked electrical activity. The (+)-form was more potent than the (-)-form in depressing electrically evoked activity but did not antagonize responses to amino acid excitants. At concentrations higher than those required to depress electrically evoked activity, the (+)-form produced depolarization. This action was blocked by 2-amino-5-phosphonovalerate.
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