Truncated ALK derived from chromosomal translocation t(2;5)(p23;q35) binds to the SH3 domain of p85-PI3K.

The chromosomal translocation t(2;5)(p23;q35) is associated with "Anaplastic large cell lymphomas" (ALCL), a Non Hodgkin Lymphoma occurring in childhood. The fusion of the tyrosine kinase gene-ALK (anaplastic lymphoma kinase) on chromosome 2p23 to the NPM (nucleophosmin/B23) gene on chromosome 5q35 results in a 80 kDa chimeric protein, which activates the "survival" kinase PI3K. However, the binding mechanism between truncated ALK and PI3K is poorly understood. Therefore, we attempted to elucidate the molecular interaction between ALK and the regulatory p85 subunit of PI3K. Here we provide evidence that the truncated ALK homodimer binds to the SH3 domain of p85. This finding may be useful for the development of a new target-specific intervention.

FAS (CD95) mutations are rare in gastric MALT lymphoma but occur more frequently in primary gastric diffuse large B-cell lymphoma.

A loss of FAS (CD95) function has been proposed to constitute an important step in early mucosa-associated lymphoid tissue (MALT) lymphoma development and FAS mutations have been recognized in malignant lymphomas, in particular at extranodal sites. Since primary gastric lymphomas frequently exhibit resistance to FAS-mediated apoptosis, we investigated whether FAS is mutated in 18 gastric MALT lymphomas and 28 diffuse large B-cell lymphomas (DLBCL). We detected seven mutations in five lymphomas, one MALT lymphoma and four DLBCL; two DLBCL had two mutations. The MALT lymphoma exhibited a point mutation in the splice donor region of intron 3. Three DLBCL had missense mutations in exon 2, which encodes a signal peptide and a portion of the extracellular FAS ligand-binding domain. One DLBCL carried a point mutation in the splice donor region of intron 8, which would result in exon skipping. Two DLBCL harbored a missense mutation in exon 9, which encodes the intracellular death domain. The two death domain mutations inhibited FAS ligand-induced apoptosis in a dominant-negative mode, when transiently expressed in human T47D breast carcinoma and Jurkat T cells. A signal peptide and an extracellular domain mutation, however, failed to inhibit apoptosis in these transfection assays. They are likely to reduce apoptosis in lymphoma cells solely by a loss of function. In summary, our data show that FAS mutations are rare in primary gastric MALT lymphomas (5.6%) but occur in a subset of primary gastric DLBCL (14.3%) and suggest that these mutations contribute to the pathogenesis of gastric lymphomas by rendering lymphocytes resistant to apoptosis.

Transferrin ensures survival of ovarian carcinoma cells when apoptosis is induced by TNFalpha, FasL, TRAIL, or Myc.

The activation of Myc induces apoptosis of human ovarian adenocarcinoma N.1 cells when serum factors are limited. However, the downstream mechanism that is triggered by Myc is unknown. Myc-activation and treatment with the proapoptotic ligands TNFalpha, FasL, and TRAIL induced H-ferritin expression under serum-deprived conditions. H-ferritin chelates intracellular iron and also intracellular iron sequestration by deferoxamine-induced apoptosis of N.1 cells. Supplementation of serum-free medium with holo-transferrin blocked apoptosis of N.1 cells that was induced by Myc-activation or by treatment with TNFalpha, FasL, and TRAIL, whereas apotransferrin did not prevent apoptosis. This suggests that intracellular iron depletion was a trigger for apoptosis and that transferrin-bound iron rescued N.1 cells. Furthermore, apoptosis of primary human ovarian carcinoma cells, which was induced by TNFalpha, FasL, and TRAIL, was also inhibited by holo-transferrin. The data suggest that Myc-activation, FasL, TNFalpha, and TRAIL disturbed cellular iron homeostasis, which triggered apoptosis of ovarian carcinoma cells and that transferrin iron ensured survival by re-establishing this homeostasis.

The evolution of cell death programs as prerequisites of multicellularity.

One of the hallmarks of multicellularity is that the individual cellular fate is sacrificed for the benefit of a higher order of life-the organism. The accidental death of cells in a multicellular organism results in swelling and membrane-rupture and inevitably spills cell contents into the surrounding tissue with deleterious effects for the organism. To avoid this form of necrotic death the cells of metazoans have developed complex self-destruction mechanisms, collectively called programmed cell death, which see to an orderly removal of superfluous cells. Since evolution never invents new genes but plays variations on old themes by DNA mutations, it is not surprising, that some of the genes involved in metazoan death pathways apparently have evolved from homologues in unicellular organisms, where they originally had different functions. Interestingly some unicellular protozoans have developed a primitive form of non-necrotic cell death themselves, which could mean that the idea of an altruistic death for the benefit of genetically identical cells predated the invention of multicellularity. The cell death pathways of protozoans, however, show no homology to those in metazoans, where several death pathways seem to have evolved in parallel. Mitochondria stands at the beginning of several death pathways and also determines, whether a cell has sufficient energy to complete a death program. However, the endosymbiotic bacterial ancestors of mitochondria are unlikely to have contributed to the recent mitochondrial death machinery and therefore, these components may derive from mutated eukaryotic precursors and might have invaded the respective mitochondrial compartments. Although there is no direct evidence, it seems that the prokaryotic-eukaryotic symbiosis created the space necessary for sophisticated death mechanisms on command, which in their distinct forms are major factors for the evolution of multicellular organisms.

Potential mechanisms of benzamide riboside mediated cell death.

Benzamide riboside (BR) after anabolism to an analogue of NAD, was shown to inhibit the activity of NAD-dependent enzymes such as inosine 5'-monophosphate dehydrogenase (IMPDH), the rate limiting enzyme in de novo guanylate biosynthesis, and malate dehydrogenase which is involved in the citric cycle and respiratory chain. BR exhibits strong anti-carcinogenic effects due to growth retardation and due to induction of apoptosis and necrosis. Apoptosis is ascribed to the inhibition of IMPDH because cell death can be blocked by restoring intracellular guanylate metabolism by the addition of guanosine. It is shown here, however, that also survival-relevant genes such as cdc25A, akt, bcl-2 and transferrin receptor become repressed by BR, whereas the expression level of the apoptosis enforcing gene c-myc persists. Even though BR-mediated growth retardation still allows BR to induce apoptosis, rapamycin-mediated cell cycle block and cell contact inhibition prevent cell death, it strongly suggests that BR induces a type of c-Myc-dependent apoptosis. At high concentrations BR induces DNA double strand breaks by yet to be determined mechanisms that occur hours before necrosis can be detected. This is accompanied by a dramatic decrease of intracellular ATP. The artificial restoration of ATP by addition of adenosine or sufficient provision of an energy source such as glucose prevents BR-promoted necrosis and favors apoptosis. This observation may be of clinical relevance.