A blast without power - cell death induced by the tuberculosis-necrotizing toxin fails to elicit adequate immune responses.

In this study, we deploy a doxycycline-dependent suicide switch integrated in a tumor challenge model. With this experimental setup, we characterized the immunological consequences of cells dying by four distinct cell death stimuli in vivo. We observed that apoptotic cell death induced by expression of the truncated form of BH3 interacting-domain death agonist (tBid) and a constitutively active form of caspase 3 (revC3), respectively, showed higher immunogenicity than cell death induced by expression of the tuberculosis-necrotizing toxin (TNT). Our data indicate that the early release of ATP induces the silent clearance of dying cells, whereas the simultaneous presence of 'find me' signals and danger-associated molecular patterns (DAMPs) promotes inflammatory reactions and increased immunogenicity. This proposed model is supported by findings showing that the production and release of high concentrations of IL-27 by bone-marrow-derived macrophages (BMDM) is limited to BMDM exposed to those forms of death that simultaneously released ATP and the DAMPs heat-shock protein 90 (HSP90) and high-mobility group box-1 protein (HMGB1). These results demonstrate that the tissue microenvironment generated by dying cells may determine the subsequent immune response.

Changes in signaling pathways of cell proliferation and apoptosis during NK/Ly lymphoma aging.

Expression of specific proteins involved in regulation of cell proliferation and apoptosis was studied at the initial (7-8 days after tumor inoculation), median (13-14 days), and terminal (20-21 days) stages of murine NK/Ly lymphoma development. Western-blot analysis using antibodies to MEK-ERK signaling pathway, E2F-1/2 and c-Myc, pSTAT1, pSTAT3, pSTAT5, anti-apoptotic Bcl-XL and pro-apoptotic p53 and Rb proteins, as well as active cleaved forms of caspases-3, -6, -7, was carried out to investigate the growth and survival status of NK/Ly cells. There was a marked increase in the expression of E2F-1/2 transcription factors, MAPK signaling cascade and c-Myc, which suggests intensive proliferation of lymphoma cells at terminal stage of tumor development. However, cytomorphological investigation and electrophoretic study of DNA fragmentation have shown degeneration of NK/Ly lymphoma cells and increase in their death. No expression of p53 protein or cleaved forms of caspases-3, -6, -7 was found, which suggests a caspase-independent type of apoptosis in these cells. Ascitic fluid collected at a terminal stage of NK/Ly lymphoma development was significantly weaker in supporting tumor cell growth than ascitic fluid collected at the initial stage of tumor development. It is suggested that uncontrolled cell proliferation at terminal stage of the NK/Ly lymphoma development causes nutrient deprivation and deficiency of specific growth factors in the ascitic fluid, due to overexpression of MEK-ERK, E2F and c-Myc, thereby leading to the induction of apoptosis.