ABSTRACT
Apo2 ligand or tumour necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) is one of the several members of the tumour necrosis factor (TNF) gene superfamily that induce apoptosis through engagement of death receptors (DRs). Apo2L/TRAIL interacts with an unusually complex receptor system of two DRs and three decoys. This protein has garnered intense interest as a potential candidate for cancer therapy because as a trimer it selectively induces apoptosis in many transformed cells but not in normal cells. While much of the early characterisation of Apo2L/TRAIL and its receptors relied on overexpression studies, recent work using untransfected cells has clarified how endogenous proteins transmit apoptotic signals from this ligand. In this review, we focus on the apoptotic signalling pathways stimulated by Apo2L/TRAIL and summarise what is known about its physiological role.
Subject(s)
Apoptosis/physiology , Eukaryotic Cells/metabolism , Membrane Glycoproteins/metabolism , Receptors, Tumor Necrosis Factor/metabolism , Signal Transduction/physiology , Tumor Necrosis Factor-alpha/metabolism , Animals , Apoptosis Regulatory Proteins , Humans , Phylogeny , Protein Structure, Tertiary/physiology , Proto-Oncogene Proteins c-bcl-2/metabolism , TNF-Related Apoptosis-Inducing LigandABSTRACT
Faithful segregation of sister chromatids during cell division requires properly regulated cohesion between the sister centromeres. The sister chromatids are attached along their lengths, but particularly tightly in the centromeric regions. Therefore specific cohesion proteins may be needed at the centromere. Here we show that Drosophila MEI-S332 protein localizes to mitotic metaphase centromeres. Both overexpression and mutation of MEI-S332 increase the number of apoptotic cells. In mei-S332 mutants the ratio of metaphase to anaphase figures is lower than wild type, but it is higher if MEI-S332 is overexpressed. In chromosomal squashes centromeric attachments appear weaker in mei-S332 mutants than wild type and tighter when MEI-S332 is overexpressed. These results are consistent with MEI-S332 contributing to centromeric sister-chromatid cohesion in a dose-dependent manner. MEI-S332 is the first member identified of a predicted class of centromeric proteins that maintain centromeric cohesion.
Subject(s)
Cell Cycle Proteins , Chromatids/genetics , Drosophila Proteins , Drosophila/genetics , Insect Proteins/genetics , Insect Proteins/metabolism , Mitosis/physiology , Animals , Animals, Genetically Modified , Centromere/genetics , Centromere/metabolism , Drosophila/embryology , Drosophila/growth & development , Embryo, Nonmammalian , Female , Fetal Death/genetics , Gene Expression Regulation, Developmental , Larva , Male , Metaphase/geneticsABSTRACT
A theoretical model for the cytoplasmic membrane topology of the Rhodobacter capsulatus PucC protein was derived and tested experimentally with pucC'::pho'A gene fusions. The alkaline phosphatase (AP) activities of selected fusions were assayed, and the resultant pattern of high and low activity was compared with that of the theoretical model. High AP activity correlated well with fusion joints located in regions predicted to be periplasmic, and most fusions in predicted cytoplasmic loops yield approximately 1/20th as much activity. Replacement of pho'A with lac'Z in nine of the fusions confirmed the topology, as beta-galactosidase activities were generally reciprocal to the corresponding AP activity. On the basis of the theoretical analysis and the information provided by the activities of fusions, a model for PucC topology in which there are 12 membrane-spanning segments and both the N and C termini are located in the cytoplasm is proposed. Translationally out-of-frame pucC::phoA fusions were expressed in an R. capsulatus delta pucC strain. None of the fusions missing only one or two of the proposed C-terminal transmembrane segments restored the wild-type phenotype, suggesting that the C terminus of PucC is important for function.
Subject(s)
Bacterial Proteins , Light-Harvesting Protein Complexes , Photosynthetic Reaction Center Complex Proteins/chemistry , Photosynthetic Reaction Center Complex Proteins/metabolism , Photosystem II Protein Complex , Protein Structure, Secondary , Rhodobacter capsulatus/metabolism , Sequence Deletion , Alkaline Phosphatase/biosynthesis , Alkaline Phosphatase/metabolism , Amino Acid Sequence , Cell Membrane/metabolism , Genes, Bacterial , Models, Structural , Molecular Sequence Data , Plasmids , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/metabolism , Rhodobacter capsulatus/genetics , Spectrophotometry , beta-Galactosidase/metabolismABSTRACT
Gene deletions of the puc operon of Rhodobacter capsulatus showed that the pucC and pucE genes, but not pucD, were required for formation of wild-type levels of the LHII complex. Deletion of pucC or pucE also impaired photosynthetic growth. The effects of pucC deletion were suppressed by secondary mutations that mapped outside the puc operon. Fusion of a lac'Z gene to pucE' showed that most of pucE transcription originated from upstream of pucB. RNA blot analysis revealed a 2.4 kb transcript that hybridized to probes specific for the pucBA, pucC and pucDE regions, indicating that some puc operon messages extend from just before the pucB gene to just after the pucE gene.
