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Biomedical subjects

A E Milner

Publications and source records attributed to A E Milner.

At least 19 recordsLinked to original sources
PubMed2004

Expression of the cellular FLICE-inhibitory protein (c-FLIP) protects Hodgkin's lymphoma cells from autonomous Fas-mediated death.

Hodgkin's lymphoma (HL) is characterized by the presence of malignant so-called Hodgkin's/Reed-Sternberg (HRS) cells, which display resistance to certain apoptotic stimuli, including a lack of sensitivity to Fas-mediated cell death. However, the mechanisms responsible for their resistance to apoptosis inducers have not been elucidated. Here we confirm that both HL-derived cell lines and the HRS cells of primary HL tissues express Fas ligand (FasL) along with the inhibitory c-FLIP protein. Down-regulation of cellular FLICE (FADD-like IL-1beta-converting enzyme)-inhibitory protein (c-FLIP) through the use of specific small inhibitory RNAs (siRNAs) leads to reduced viability of the L428 and L591 HL-derived cell lines. To determine whether endogenous FasL was responsible for the reduction in cell viability observed after down-regulation of c-FLIP, L428 and L591 cells were treated with c-FLIP-specific siRNAs with and without siRNAs directed to FasL. Treatment of these cells with both c-FLIP- and FasL-specific siRNAs in combination restored cell viability to near control levels. Our results provide a mechanism whereby HRS cells are protected from autonomous FasL-mediated cell death while preserving their ability to evade immunosurveillance. Targeting c-FLIP could provide a novel approach to the treatment of HL.

Apoptosis↗
PubMed2003

Mechanism of cell death induced by the novel enzyme-prodrug combination, nitroreductase/CB1954, and identification of synergism with 5-fluorouracil.

Virus-directed enzyme prodrug therapy (VDEPT) utilising the bacterial enzyme nitroreductase delivered by a replication-defective adenovirus vector to activate the prodrug CB1954 is a promising strategy currently undergoing clinical trials in patients with a range of cancers. An understanding of the mechanism of tumour cell death induced by activated CB1954 will facilitate this clinical development. Here, we report that activated CB1954 kills cells predominantly by caspase-dependent apoptosis. This may have important implications for the generation of immune-mediated bystander effects. Further, the use of a replication-defective adenovirus vector to deliver nitroreductase may negatively affect cellular apoptotic pathways stimulated by activated CB1954. Finally, examination of nitroreductase/CB1954 in combination with conventional chemotherapy reveals a synergistic interaction with 5-fluorouracil. These data will facilitate the further development and future clinical trial design of this novel therapy.

Adenoviridae↗
PubMed2002

Induction of apoptosis by chemotherapeutic drugs: the role of FADD in activation of caspase-8 and synergy with death receptor ligands in ovarian carcinoma cells.

Although ovarian tumours initially respond to chemotherapy, they gradually acquire drug resistance. The aims of this study were to identify how chemotherapeutic drugs with diverse cellular targets activate apoptotic pathways and to investigate the mechanism by which exposure to a combination of drugs plus death receptor ligands can increase tumour cell kill. The results show that drugs with distinct cellular targets differentially up-regulate TRAIL and TNF as well CD95L, but do not require interaction of these ligands with their receptor partners to induce cell death. Factors that were critical in drug-induced apoptosis were activation of caspases, with caspase-8 being activated by diverse drugs in a FADD-independent manner. Certain drugs also demonstrated some dependence on FADD in the induction of cell death. Caspase-9 was activated more selectively by chemotherapeutic agents. Combining ligation of death receptors with exposure to drugs increased tumour cell kill in both drug resistant cell lines and primary ovarian carcinoma cells, even though these cells were not sensitive to death receptor ligation alone. CD95L was more consistent at combining with drugs than TRAIL or TNF. Investigation of the mechanism by which a combination of drugs plus CD95 ligation can increase cell death showed that caspase-8 was activated in cells exposed to a combination of cisplatin and anti-CD95, but not in cells exposed to either agent alone.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Isolation of methicillin-resistant Staphylococcus aureus from non-sterile sites: evaluation of a new selective medium.

Methicillin-resistant Staphylococcus aureus (MRSA) are relatively common nosocomial isolates, causing problems for health-care professionals worldwide. Therefore, early detection of the organisms by the laboratory is essential. A new selective medium for MRSA is described, comprising a DNA-containing base and a combination of stains that permit direct visualisation of DNase activity around colonies. The medium is made partially selective by adding a number of antibiotics (aztreonam, polymyxin B, nystatin and oxacillin). When compared to other media used for the isolation of MRSA, it was found that the new medium allowed earlier detection of colonies and provided a good direct method of identification, reducing the need for time-consuming replating of colonies, and, therefore, the turnaround time for specimens entering the laboratory for MRSA screening.

Bacteriological Techniques↗
PubMed1999

The structure of the site on adenovirus early region 1A responsible for binding to TATA-binding protein determined by NMR spectroscopy.

Previous detailed mutational analysis has shown that the binding site on adenovirus (Ad) early region 1A (E1A) for TATA-binding protein (TBP) is located toward the N terminus of conserved region 3 (CR3). Here we demonstrate that synthetic peptides of between 15 and 22 amino acids, identical to amino acid sequences of CR3 present in the larger Ad5 E1A (13 S product) and in both the Ad12 E1A (13 and 12 S products) proteins that lie N-terminal to the zinc finger motif, can disrupt binding of E1A to TBP. These findings suggest that the peptides are biologically active in terms of interacting with TBP and must therefore comprise some, if not all, of the TBP binding site on E1A. The interaction between Ad12 E1A and TBP was confirmed by direct co-precipitation experiments. In 1H NMR studies of CR3 peptides, regular patterns of NOEs were observed from which their conformational preferences in aqueous solution were determined. Both Ad5 and Ad12 peptides were shown to contain regions of helical backbone structure in 50% trifluoroethanol. In each case, the type and intensities of NOE cross-peaks observed correlated best to alpha-helical turns. These helices are more extensive in larger peptides and extend from Glu141 to Val147 and from Arg144 to Pro152 in the full-length Ad5 and Ad12 13S E1A proteins, respectively. The structure of a 19-residue Ad5 CR3 peptide carrying the V147L mutation in the full-length protein that abolishes TBP binding was examined. No significant differences between the substituted and wild type peptides were observed, suggesting that this substitution in the intact protein may cause disruption of global rather than local structures.

Adenovirus E1A Proteins↗
PubMed1999

Adenovirus early region 1A protein binds to mammalian SUG1-a regulatory component of the proteasome.

Adenovirus early region 1A (Ad E1A) is a multifunctional protein which is essential for adenovirus-mediated transformation and oncogenesis. Whilst E1A is generally considered to exert its influence on recipient cells through regulation of transcription it also increases the level of cellular p53 by increasing the protein half-life. With this in view, we have investigated the relationship of Ad E1A to the proteasome, which is normally responsible for degradation of p53. Here we have shown that both Ad5 and Ad12 E1A 12S and 13S proteins can be co-immunoprecipitated with proteasomes and that the larger Ad12 E1A protein binds strongly to at least three components of the 26S but not 20S proteasome. One of these interacting species has been identified as mammalian SUGI, a proteasome regulatory component which also plays a role in the cell as a mediator of transcription. In vitro assays have demonstrated a direct interaction between Ad12 E1A 13S protein and mouse SUGI. Following infection of human cells with Ad5 wt and Ad5 mutants with lesions in the E1A gene it has been shown that human SUG1 can be co-immunoprecipitated with full-length E1A and with E1A carrying a deletion in conserved region 1 which is the region considered to be responsible for increased expression of p53. We have concluded therefore that Ad EIA binds strongly to SUGI but that this interaction is not responsible for inhibition of proteasome activity. This is consistent with the observation that purified Ad12 E1A inhibits the activity of the purified 20S but not 26S proteasomes. We have also demonstrated that SUGI can be co-immunoprecipitated with SV40 T and therefore we suggest that this may represent a common interaction of transforming proteins of DNA tumour viruses.

ATPases Associated with Diverse Cellular Activitie↗
PubMed1998

Structural determinants present in the C-terminal binding protein binding site of adenovirus early region 1A proteins.

The C-terminal binding protein (CtBP) has previously been shown to bind to a highly conserved six-amino acid motif very close to the C terminus of adenovirus early region 1A (Ad E1A) proteins. We have developed an enzyme-linked immunosorbent assay that has facilitated the screening of synthetic peptides identical or similar to the binding site on Ad E1A for their ability to bind CtBP and thus inhibit its interaction with Ad12 E1A. It has been shown that amino acids both C-terminal and N-terminal to the original proposed binding site contribute to the interaction of peptides with CtBP. Single amino acid substitutions across the binding site appreciably alter the Kd of the peptide for CtBP, indicative of a marked reduction in the affinity of the peptide for CtBP. The solution structures of synthetic peptides equivalent to the C termini of both Ad5 and Ad12 E1A and two substituted forms of these have been determined by proton NMR spectroscopy. Both the Ad12 and Ad5 peptides dissolved in trifluoroethanol/water mixtures were found to adopt regular secondary structural conformations seen as a series of beta-turns. An Ad12 peptide bearing a substitution that resulted in only very weak binding to CtBP (Ad12 L258G) was found to be random coil in solution. However, a second mutant (Ad12 V256K), which bound to CtBP rather more strongly (although not as well as the wild type), adopted a conformation similar to that of the wild type. We conclude that secondary structure (beta-turns) and an appropriate series of amino acid side chains are necessary for recognition by CtBP.

Adenovirus E1A Proteins↗
PubMed1998

Human cells arrest in S phase in response to adenovirus 12 E1A.

It has previously been shown that following viral infection, Ad5 E1A induces cell cycle progression of quiescent rodent cells, leading to DNA synthesis and mitosis. Here we have examined the effect of Ad12 E1A on the cell cycle characteristics of human cells. Human tumor (A549, KB, and HeLa) cells were infected with Ad12 d/620, a mutant virus which has a lesion in the E1B gene and essentially expresses only E1A. These infected cells progressed from being largely in G1 into S phase, where they arrested. Even up to 96 h postinfection (p.i.) the cells remained blocked in S phase. DNA synthesis did, however, proceed in Ad12 d/620-infected cells, giving rise to multiple copies of cellular DNA. Similar results were obtained when primary human skin fibroblasts were infected, although the polyploidy was less marked. The expression of cyclins A, B1, and E in the tumor cells increased appreciably in response to E1A. In contrast, there was a dramatic reduction in the levels of cyclin D1 and D3. Increases in cyclin D1 expression could be detected at very late times p.i. In those cell lines expressing low levels of cdc2 and cdk2 an appreciable increase in expression was seen soon after Ad12 E1A could be detected. The elevated levels of cyclins A, B1, and E were associated with increased protein kinase activity directed against histone H1. An increase in cyclin D1-associated kinase activity against Rb1 was also observed at late times. This deregulation of the cell cycle was not solely dependent on E1A inactivation of Rb, since similar effects were seen in Ad12 d/620-infected retinoblastoma (Y-79) cells, implicating p107 and p130 in E1A-mediated changes in cell cycle progression. We propose that the E1A-induced levels of cyclins A, B1, and E by Ad12 E1A in human cells may lead to an uncoupling of S phase from cell cycle progression.

Adenoviridae↗
PubMed1998

Regeneration of the binding properties of adenovirus 12 early region 1A proteins after preparation under denaturing conditions.

Adenovirus 12 early region 1A (Ad12 E1A) was expressed in Escherichia coli. Protein was purified in good yield in the presence of 8 M urea and then renatured by dialysis against dilute NH4HCO3 buffer. The affinity of this protein for pRb, C-terminal binding protein (CtBP), TATA binding protein (TBP), and SUG1 was similar to, or greater than, that of Ad12 E1A prepared by immunoaffinity chromatography under nondenaturing conditions. While the binding of the 266- and 235-amino-acid (aa) E1A components to TBP showed similar characteristics the larger E1A protein had a higher affinity for CtBP, pRb, and SUG1. Using nuclear magnetic resonance (NMR) spectroscopy it was shown that structural perturbations occurred in the 266-aa protein in the presence of Zn2+ consistent with binding--no such changes were seen for the 235-aa protein. Limited proteolysis of the 266- and 235-aa E1A proteins gave rise to comparable polypeptide products, suggesting overall similarities in structure. However, the different affinities of the 266- and 235-aa proteins for the partner proteins and the differences seen in the NMR spectra from the two proteins suggested structural differences.

Adenovirus E1A Proteins↗
PubMed1998

Homology between a human apoptosis specific protein and the product of APG5, a gene involved in autophagy in yeast.

Apoptosis specific proteins (ASP) are expressed in the cytoplasm of cultured mammalian cells of various lineages following induction of apoptosis. The cDNA encoding ASP has been cloned from a human expression library and has significant homology to the Saccharomyces cerevisiae APG5 gene which is essential for yeast autophagy. The ASP gene, known as hAPG5, can be transcribed to give mRNAs of 3.3 kbp, 2.5 kbp and 1.8 kbp which are present at comparable levels in viable and apoptotic cells, demonstrating that protein expression must be regulated at the translational level. These data indicate a possible relationship between apoptosis and autophagy and suggest evolutionary conservation in mammalian apoptosis of a degradative process present in yeast.

Animals↗
PubMed1997

Differential effects of BCL-2 on survival and proliferation of human B-lymphoma cells following gamma-irradiation.

Bcl-2 can inhibit apoptosis induced by a variety of stimuli, including radiation and its presence in tumour cells would be expected to indicate poor prognosis. Bcl-2-expressing tumours, however, are often low-grade and highly responsive to therapy. To investigate this apparent paradox, we analysed in vitro the responses of Burkitt lymphoma (BL) cells to gamma-irradiation in the presence and absence of Bcl-2. High-level expression of Bcl-2 was shown to promote BL cell survival following irradiation. However, a significant proportion of Bcl-2-rescued cells subsequently underwent apoptosis after an extended period in culture. In addition, in different BL lines, Bcl-2 was found either to promote or to inhibit long-term proliferative activity following gamma-irradiation. This differential regulation of proliferation correlated both with differential effects of Bcl-2 on the cell cycle and with differences in p53 status. Thus, by one week after irradiation, BL cells expressing only wild-type p53 (wt/wt) had arrested in G1, whereas those with a mutant allele (wt/mu) were arrested in all phases of the cell cycle. The proportion of Bcl-2-rescued cells that subsequently underwent apoptosis was reduced by ligation of CD40 at the time of irradiation in wt/wt BL cells, but not in wt/mu cells. CD40-ligation reduced both G1-arrest and apoptosis in parallel. These results indicate that, whilst Bcl-2 can delay apoptosis in BL cells following gamma-irradiation, the protein can also cause growth-arrest and thereby promote apoptosis. Long-term survival following Bcl-2-mediated rescue of gamma-irradiated cells may depend on p53 status and require additional death-repressing or growth-promoting signals.

CD40 Antigens↗
PubMed1996

Repression of apoptosis in human B-lymphoma cells by CD40-ligand and Bcl-2: relationship to the cell-cycle and role of the retinoblastoma protein.

Using a Burkitt lymphoma cell line to model human B-cell apoptosis in vitro, we observed that crosslinking, by antibody, of cell surface immunoglobulin induced G1 growth-arrest followed by apoptosis. By contrast, cells treated with the Ca(2+)-ionophore, ionomycin, generated apoptotic signals in G2/M as well as in G1. Both ionomycin and anti-immunoglobulin treatment induced rapid dephosphorylation of Rb prior to apoptosis. Apoptosis was repressed following exposure to CD40-ligand and was accompanied by hyperphosphorylation of Rb and cell-cycle progression but not Bcl-2 expression. Expression of Bcl-2 protein in stable bcl-2-transfectants, also resulted in repression of apoptosis and anti-immunoglobulin-treated cells no longer underwent growth-arrest. In Bcl-2-expressing cells in which apoptosis was repressed, Rb remained hyperphosphorylated, even during G1-arrest induced by ionomycin. TGF beta treatment of Bcl-2-expressing cells induced G1-arrest, de-phosphorylation of Rb and apoptosis. These results suggest that the functional activity of Bcl-2 in B-lymphoma cells is dependent upon, or leads to, sustained hyperphosphorylation of Rb and that Rb hyperphosphorylation can be uncoupled from cell-cycle progression.

Antibodies, Anti-Idiotypic↗
PubMed1996

Bcl-2 delays macrophage engulfment of human B cells induced to undergo apoptosis.

The capacity to be recognized and engulfed by phagocytes is an important characteristic of cells dying by apoptosis. Phagocytosis of apoptotic cells occurs rapidly in vivo, probably prior to plasma membrane breakdown. While the molecular mechanisms mediating phagocytosis of apoptotic cells are beginning to be defined, little is yet known of the relationship between the cell-death program itself and the surface changes on the dying cells that signal for engulfment. Here, we investigate to what extent the apoptosis repressor Bcl-2 can modulate the recognition and phagocytosis of human B cells exposed to triggers of apoptosis. Burkitt lymphoma (BL)-derived, Bcl-2- B cells were induced into apoptosis either by the Ca(2+)-ionophore ionomycin or by the inhibitor of protein synthesis cycloheximide. Apoptotic BL cells, but not viable BL cells, were recognized and phagocytosed by monocyte-derived macrophages. bcl-2-transfected BL populations showed a reduced capacity both to undergo apoptosis in response to these inducing agents and to interact with macrophages. Like their Bcl-2- counterparts, Bcl-2+ BL cells interacted with macrophages only after activation of their apoptotic program as assessed by changes in nuclear morphology. These results demonstrate not only that continued protein synthesis in B cells undergoing apoptosis is not essential for their recognition by macrophages, but also that macrophage recognition of apoptotic B cells cannot be uncoupled from the cell-death program that is controlled by Bcl-2. In this respect, the behavior of B cells contrasts markedly with that of neutrophils in which Bcl-2 has been reported to inhibit apoptosis without affecting phagocytic clearance.

Apoptosis↗
PubMed1995

Effects of interferon-alpha on human B cells: repression of apoptosis and prevention of cell growth are independent responses of Burkitt lymphoma lines.

We have previously shown that interferon-alpha (IFN-alpha) can repress apoptosis in Burkitt lymphoma (BL) cells. In this study, we have compared this protective response with a further, well-established effect of IFN-alpha on BL cells, that of growth arrest. Of a panel of BL lines comprising (i) EBV-positive and -negative lines that retain the phenotype of the parental tumour cells and (ii) the prototype IFN-alpha-growth-inhibited line, Daudi, only Daudi cells were found to undergo substantial growth inhibition in response to the cytokine. By contrast, all lines, with the notable exception of Daudi, were protected by IFN-alpha from high-rate apoptosis initiated by the Ca2+ ionophore ionomycin. Ionomycin failed to elicit an IFN-alpha-repressible apoptotic response in either wild-type Daudi cells or IFN-resistant sublines that were refractory to the growth-arresting effects of the cytokine. Analysis of c-myc protein levels confirmed previous observations that repression of apoptosis in IFN-alpha-rescuable BL cells was associated with an early inhibition of myc that was followed by a return to high-level expression. Significantly, ionomycin alone induced a comparable transient inhibition of myc protein in Daudi cells. In Daudi cells, but not in IFN-alpha-rescuable BL cells, renewed expression of myc observed after the early, transient down-regulation was followed by sustained down-regulation of the protein, which paralleled growth arrest. Our results indicate that long-term growth arrest and repression of apoptosis in BL are distinct cellular responses to IFN-alpha.

Apoptosis↗
PubMed1995

A novel protein expressed in mammalian cells undergoing apoptosis.

Human and rodent cells undergoing apoptosis were observed to express high levels of a novel 45,000 M(r) protein. The protein, which we have termed apoptosis specific protein (ASP), was found in Burkitt lymphoma (BL) cells and in adenovirus-transformed human and rat embryo cells induced into apoptosis by a variety of stimuli, including serum deprivation, exposure to the Ca2+ ionophore, ionomycin, treatment with inhibitors of macromolecular synthesis (cycloheximide and actinomycin D), and cold shock. In BL cells treated with apoptotic stimuli, expression of the oncoprotein Bcl-2 was found to both protect from apoptosis and prevent expression of ASP. ASP was not detected either in viable cells or in cells dying passively by necrosis. Laser scanning confocal microscopy showed high levels of ASP in the cytoplasm of cells displaying the chromatin condensation and fragmentation patterns typical of apoptosis. Retention of ASP was observed even when DNA was no longer detectable, and two-color immunofluorescence staining indicated that the protein primarily colocalized with, but was clearly distinct from, non-muscle actin. These findings, together with the observation that biochemical extraction of ASP was only possible under conditions which caused solubilization of the cytoskeleton, leads us to conclude that ASP forms part of, or at least strongly associates with, a modified cytoskeleton unique to cells undergoing apoptosis. While elucidation of its function will require further work, ASP constitutes a powerful marker for the diagnosis and quantitation of apoptosis in vivo and in vitro.

Animals↗
PubMed1994

Regulation of cell survival in Burkitt lymphoma: implications from studies of apoptosis following cold-shock treatment.

Burkitt lymphoma (BL) tumour-cell populations are known to display high rates both of proliferation and of apoptosis in vivo, but the mechanisms which determine whether a BL cell continues to cycle or engages its cell-death programme are not understood. Group-I BL-derived cell lines, which retain in vitro the proliferative and apoptotic capacities of the parental cells, selectively entered apoptosis when returned to 37 degrees C after a brief period at low temperature (1 degree C). The induction of apoptosis by cold treatment, as determined by morphological characteristics and DNA fragmentation, was readily detectable within the first 1 to 2 hr of re-incubation at 37 degrees C, reaching a maximum at 4 to 6 hours. Commitment to enter apoptosis occurred after as little as 20 to 30 min at 1 degree C. Significant cell death at 1 degree C occurred only during prolonged incubation in the cold and displayed the characteristics of necrosis. Both bcl-2-dependent and -independent survival pathways were found to provide protection from cold-induced apoptosis, but only if engaged before cold-shock treatment. These results indicate that continued cycling of group-I BL cells is dependent upon their capacity to inhibit or circumvent their normally constitutively active apoptotic programme, and are consistent with the notion that the synthesis of one or more critical "survival" proteins of short half-life is necessary to guarantee successful passage through the cell cycle. Notably, high levels of apoptosis were also inducible in group-I BL cells by inhibitors of RNA and protein synthesis.

Apoptosis↗