Requirement for the CD95 receptor-ligand pathway in c-Myc-induced apoptosis

Proteomic changes associated with degeneration of myelin-forming cells in the central nervous system of c-myc transgenic mice

Myelin is necessary for the conduction of high frequency and high velocity nerve impulses in the central nervous system of mammals, and severe neurological disturbances develop as a result of myelin loss. In this report, we have characterized changes in the brain proteomic profile of transgenic mice that develop a c-myc-induced degenerative disorder of myelin. Marked differences were seen in the accumulation of cytoskeletal proteins associated with the pathological condition fibrous gliosis in the optic nerves of affected animals, including upregulation of glial fibrillary acid protein and vimentin. In addition, the expression of several major myelin proteins, including five isoforms of myelin basic protein, four isoforms of cyclic nucleotide 3'-phosphodiesterase, and myelin-associated glycoprotein, was markedly reduced in the brains of c-myc transgenic mice as revealed by immunocytochemistry and by two-dimensional immunoblots. A number of novel proteomic disease marker candidates were revealed, which displayed pronounced changes in their expression profile. Sequence determination of these proteins and molecular cloning of their mRNAs will provide an opportunity to further evaluate their roles in the disease process.

Mutation analysis of CD95 (APO-1/Fas) in childhood B-lineage acute lymphoblastic leukaemia

The CD95 system plays an important role in lymphocyte homeostasis, has been implicated in the development of lymphoid malignancies, exerts a tumour suppressor function, and contributes to drug-induced cytotoxicity. We hypothesized that mutations of CD95 may occur in childhood B-lineage acute lymphoblastic leukaemia (ALL), a disease known for its constitutive resistance towards CD95-mediated apoptosis. We investigated 32 primary B-lineage ALL of childhood and five B-lineage ALL cell lines. All primary leukaemias expressed CD9 5 and bcl-2 to a variable degree. Most of the leukaemias were resistant towards CD95-mediated apoptosis. However, using SSCP analysis, no mutations in the coding and proximal promoter region could be detected. We conclude that the resistance towards CD95-mediated apoptosis observed in most de novo B-lineage ALL is not caused by mutations of the CD95 death receptor.

Duplication of the DR3 gene on human chromosome 1p36 and its deletion in human neuroblastoma

The human DR3 gene, whose product is also known as Wsl-1/APO-3/TRAMP/LARD, encodes a tumor necrosis factor-related receptor that is expressed primarily on the surface of thymocytes and lymphocytes. DR3 is capable of inducing both NF-kappa B activation and apoptosis when overexpressed in mammalian cells, although its ligand has not yet been identified. We report here that the DR3 gene locus is tandemly duplicated on human chromosome band 1p36.2-p36.3 and that these genes are hemizygously deleted and/or translocated to another chromosome in neuroblastoma (NB) cell lines with amplified MYCN. Duplication of at least a portion of the DR3 gene, including the extracellular and transmembrane regions but not the cytoplasmic domain, was demonstrated by both fluorescence in situ hybridization and genomic Southern blotting. In most NB cell lines, both the DR3 and the DR3L sequences are simultaneously deleted and/or translocated to another chromosome. Finally, DR3/ Wsl-1 protein expression is quite variable among these NB cell lines, with very low or undetectable levels in 7 of 17 NB cell lines.

Control of cell proliferation by Myc

Myc proteins are key regulators of mammalian cell proliferation. They are transcription factors that activate genes as part of a heterodimeric complex with the protein Max. This review summarizes recent progress in understanding how Myc stimulates cell proliferation and how this might contribute to cellular transformation and tumorigenesis.

The activation of p38 and apoptosis by the inhibition of Erk is antagonized by the phosphoinositide 3-kinase/Akt pathway

Considerable attention has recently been focused on the role played by different kinase cascades in the control of apoptosis. The triggering of stress-activated kinases concomitant with the inhibition of the extracellular signal-regulated kinase (ERK) pathway has been observed in a number of cell systems undergoing programmed cell death. In addition, the activation of the phosphoinositide 3-kinase (PI 3-kinase)-Akt signaling cascade has been shown to protect from apoptosis. Here we have explored the potential role played by the inhibition of ERK in the activation of the stress kinases as well as the possible cross-talk with the PI 3-kinase pathway in HeLa cells. We show that the simple inhibition of ERK basal activity is sufficient to trigger apoptosis and p38 activation with no changes in Jun N-terminal kinase/stress-activated protein kinase. This is a process dependent on the caspases and is completely abrogated by serum. The incubation with wortmannin or the transfection of dominant negative mutants of p85 or Akt block the inhibitory function of serum, suggesting the involvement of the PI 3-kinase-Akt system. Consistent with this, expression of active mutants of PI 3-kinase and Akt inhibits p38 activation and apoptosis. We also show here that the inhibition of ERK triggers the caspase system, which is abolished by serum in a wortmannin-dependent manner. Collectively, these results demonstrate a link between ERK and the p38 apoptotic pathway that is modulated by the survival PI 3-kinase-Akt module, acting upstream the caspase system.

Hydrogen Peroxide Induces Up-Regulation of Fas in Human Endothelial Cells

Hydrogen peroxide (H2O2), an oxidant generated by inflammatory cells, is an important mediator of injury of endothelial cells (ECs). Here we show that H2O2 induces up-regulation of the expression of Fas, a death signal, in human ECs in culture. Flow cytometric analysis with a mAb against human Fas showed that incubation for 24 h with H2O2 induced a dose-dependent increase in the level of Fas in ECs. Coincubation with catalase, which rapidly degrades H2O2, inhibited H2O2-induced up-regulation of Fas. H2O2 also induced a dose-dependent increase in Fas mRNA level. A significant increase in Fas mRNA levels was observed from 6 h after stimulation with H2O2. Vanadate, a protein phosphatase inhibitor, significantly enhanced Fas mRNA and protein levels in H2O2-treated ECs. On the other hand, genistein, a tyrosine kinase inhibitor, inhibited H2O2-induced Fas mRNA expression. Furthermore, a flow cytometric method with propidium iodide staining and electron microscopic analysis showed that incubation with an agonistic Ab against Fas (anti-Fas IgM) induced apoptosis in H2O2-treated cells. These findings suggest that H2O2 induces up-regulation of Fas in ECs and that activation of protein tyrosine kinase may be involved in the mechanism of H2O2-induced Fas expression. Therefore, Fas-mediated apoptosis may have a pathologic role in H2O2-induced EC injury and thereby provide a new therapeutic target.

FADD: essential for embryo development and signaling from some, but not all, inducers of apoptosis

FADD (also known as Mort-1) is a signal transducer downstream of cell death receptor CD95 (also called Fas). CD95, tumor necrosis factor receptor type 1 (TNFR-1), and death receptor 3 (DR3) did not induce apoptosis in FADD-deficient embryonic fibroblasts, whereas DR4, oncogenes E1A and c-myc, and chemotherapeutic agent adriamycin did. Mice with a deletion in the FADD gene did not survive beyond day 11.5 of embryogenesis; these mice showed signs of cardiac failure and abdominal hemorrhage. Chimeric embryos showing a high contribution of FADD null mutant cells to the heart reproduce the phenotype of FADD-deficient mutants. Thus, not only death receptors, but also receptors that couple to developmental programs, may use FADD for signaling.

DNA damaging agents induce expression of Fas ligand and subsequent apoptosis in T lymphocytes via the activation of NF-kappa B and AP-1

Apoptosis induced by DNA damage and other stresses can proceed via expression of Fas ligand (FasL) and ligation of its receptor, Fas (CD95). We report that activation of the two transcription factors NF-kappa B and AP-1 is crucially involved in FasL expression induced by etoposide, teniposide, and UV irradiation. A nondegradable mutant of I kappa B blocked both FasL expression and apoptosis induced by DNA damage but not Fas ligation. These stimuli also induced the stress-activated kinase pathway (SAPK/JNK), which was required for the maximal induction of apoptosis. A 1.2 kb FasL promoter responded to DNA damage, as well as coexpression with p65 Rel or Fos/Jun. Mutations in the relevant NF-kappa B and AP-1 binding sites eliminated these responses. Thus, activation of NF-kappa B and AP-1 contributes to stress-induced apoptosis via the expression of FasL.