Interferon-gamma induced cell death: Regulation and contributions of nitric oxide, cJun N-terminal kinase, reactive oxygen species and peroxynitrite.

Interferon-gamma (Ifnγ), a known immunomodulatory cytokine, regulates cell proliferation and survival. In this study, the mechanisms leading to the selective susceptibility of some tumor cells to Ifnγ were deciphered. Seven different mouse tumor cell lines tested demonstrated upregulation of MHC class I to variable extents with Ifnγ; however, only the cell lines, H6 hepatoma and L929 fibrosarcoma, that produce higher amounts of nitric oxide (NO) and reactive oxygen species (ROS) are sensitive to Ifnγ-induced cell death. NO inhibitors greatly reduce Ifnγ-induced ROS; however, ROS inhibitors did not affect the levels of Ifnγ-induced NO, demonstrating that NO regulates ROS. Consequently, NO inhibitors are more effective, compared to ROS inhibitors, in reducing Ifnγ-induced cell death. Further analysis revealed that Ifnγ induces peroxynitrite and 3-nitrotyrosine amounts and a peroxynitrite scavenger, FeTPPS, reduces cell death. Ifnγ treatment induces the phosphorylation of c-jun N-terminal kinase (Jnk) in H6 and L929 but not CT26, a colon carcinoma cell line, which is resistant to Ifnγ-mediated death. Jnk activation downstream to NO leads to induction of ROS, peroxynitrite and cell death in response to Ifnγ. Importantly, three cell lines tested, i.e. CT26, EL4 and Neuro2a, that are resistant to cell death with Ifnγ alone become sensitive to the combination of Ifnγ and NO donor or ROS inducer in a peroxynitrite-dependent manner. Overall, this study delineates the key roles of NO as the initiator and Jnk, ROS, and peroxynitrite as the effectors during Ifnγ-mediated cell death. The implications of these findings in the Ifnγ-mediated treatment of malignancies are discussed.

c-Jun NH2 -terminal kinase is a critical node in the death of CD4+ CD8+ thymocytes during Salmonella enterica serovar Typhimurium infection.

Thymic atrophy, due to the depletion of CD4(+) CD8(+) thymocytes, is observed during infections with numerous pathogens. Several mechanisms, such as glucocorticoids and inflammatory cytokines, are known to be involved in this process; however, the roles of intracellular signaling molecules have not been investigated. In this study, the functional role of c-Jun NH2 -terminal kinase (JNK) during infection-induced thymic atrophy was addressed. The levels of phosphorylated JNK in immature CD4(+) CD8(+) thymocytes from C57BL/6 (Nramp-deficient) and 129/SvJ (Nramp-sufficient) mice were increased upon oral infection of mice with Salmonella enterica serovar Typhimurium (S. typhimurium). Furthermore, inhibition of JNK signaling, but not ERK or p38 MAPK, prevented the in vitro death of infected thymocytes. Importantly, the in vivo inhibition of JNK signaling with SP600125 protected C57BL/6 CD4(+) CD8(+) thymocytes from depletion via multiple mechanisms as follows: lower intracellular ROS, inflammatory cytokines, Bax and caspase 3 activity, increase in Bcl-xL amounts, and prevention of the loss in mitochondrial membrane potential. Notably, thymic architecture was preserved in infected mice treated with SP600125. Overall, this study identifies a novel role for JNK as a crucial regulator of the death of CD4(+) CD8(+) thymocytes during S. typhimurium infection.

Regulation of chemokines, CCL3 and CCL4, by interferon γ and nitric oxide synthase 2 in mouse macrophages and during Salmonella enterica serovar typhimurium infection.

BACKGROUND: Interferon γ (IFN-γ) increases the expression of multiple genes and responses; however, the mechanisms by which IFN-γ downmodulates cellular responses is not well understood. In this study, the repression of CCL3 and CCL4 by IFN-γ and nitric oxide synthase 2 (NOS2) in macrophages and upon Salmonella typhimurium infection of mice was investigated. METHODS: Small molecule regulators and adherent peritoneal exudates cells (A-PECs) from Nos2(-/-)mice were used to identify the contribution of signaling molecules during IFN-γ-mediated in vitro regulation of CCL3, CCL4, and CXCL10. In addition, infection of bone marrow-derived macrophages (BMDMs) and mice (C57BL/6, Ifn-γ(-/), and Nos2(-/-)) with S. typhimurium were used to gain an understanding of the in vivo regulation of these chemokines. RESULTS: IFN-γ repressed CCL3 and CCL4 in a signal transducer and activator of transcription 1 (STAT1)-NOS2-p38 mitogen activated protein kinase (p38MAPK)-activating transcription factor 3 (ATF3) dependent pathway in A-PECs. Also, during intracellular replication of S. typhimurium in BMDMs, IFN-γ and NOS2 repressed CCL3 and CCL4 production. The physiological roles of these observations were revealed during oral infection of mice with S. typhimurium, wherein endogenous IFN-γ and NOS2 enhanced serum amounts of tumor necrosis factor α and CXCL10 but repressed CCL3 and CCL4. CONCLUSIONS: This study sheds novel mechanistic insight on the regulation of CCL3 and CCL4 in mouse macrophages and during S. typhimurium oral infection.

Interferon-γ- and glucocorticoid-mediated pathways synergize to enhance death of CD4(+) CD8(+) thymocytes during Salmonella enterica serovar Typhimurium infection.

Thymic atrophy is known to occur during infections; however, there is limited understanding of its causes and of the cross-talk between different pathways. This study investigates mechanisms involved in thymic atrophy during a model of oral infection by Salmonella enterica serovar Typhimurium (S. typhimurium). Significant death of CD4(+) CD8(+) thymocytes, but not of single-positive thymocytes or peripheral lymphocytes, is observed at later stages during infection with live, but not heat-killed, bacteria. The death of CD4(+) CD8(+) thymocytes is Fas-independent as shown by infection studies with lpr mice. However, apoptosis occurs with lowering of mitochondrial potential and higher caspase-3 activity. The amounts of cortisol, a glucocorticoid, and interferon-γ (IFN-γ), an inflammatory cytokine, increase upon infection. To investigate the functional roles of these molecules, studies were performed using Ifnγ(-/-) mice together with RU486, a glucocorticoid receptor antagonist. Treatment of C57BL/6 mice with RU486 does not affect colony-forming units (CFU), amounts of IFN-γ and mouse survival; however, there is partial rescue in thymocyte death. Upon infection, Ifnγ(-/-) mice display higher CFU and lower survival but more surviving thymocytes are recovered. However, there is no difference in cortisol amounts in C57BL/6 and Ifnγ(-/-) mice. Importantly, the number of CD4(+) CD8(+) thymocytes is significantly higher in Ifnγ(-/-) mice treated with RU486 along with lower caspase-3 activity and mitochondrial damage. Hence, endogenous glucocorticoid and IFN-γ-mediated pathways are parallel but synergize in an additive manner to induce death of CD4(+) CD8(+) thymocytes during S. typhimurium infection. The implications of this study for host responses during infection are discussed.

Interferon-gamma and nitric oxide synthase 2 mediate the aggregation of resident adherent peritoneal exudate cells: implications for the host response to pathogens.

Interferon-gamma (Ifnγ), a key macrophage activating cytokine, plays pleiotropic roles in host immunity. In this study, the ability of Ifnγ to induce the aggregation of resident mouse adherent peritoneal exudate cells (APECs), consisting primarily of macrophages, was investigated. Cell-cell interactions involve adhesion molecules and, upon addition of Ifnγ, CD11b re-localizes preferentially to the sites of interaction on APECs. A functional role of CD11b in enhancing aggregation is demonstrated using Reopro, a blocking reagent, and siRNA to Cd11b. Studies with NG-methyl-L-arginine (LNMA), an inhibitor of Nitric oxide synthase (Nos), NO donors, e.g., S-nitroso-N-acetyl-DL-penicillamine (SNAP) or Diethylenetriamine/nitric oxide adduct (DETA/NO), and Nos2-/- mice identified Nitric oxide (NO) induced by Ifnγ as a key regulator of aggregation of APECs. Further studies with Nos2-/- APECs revealed that some Ifnγ responses are independent of NO: induction of MHC class II and CD80. On the other hand, Nos2 derived NO is important for other functions: motility, phagocytosis, morphology and aggregation. Studies with cytoskeleton depolymerizing agents revealed that Ifnγ and NO mediate the cortical stabilization of Actin and Tubulin which contribute to aggregation of APECs. The biological relevance of aggregation of APECs was delineated using infection experiments with Salmonella Typhimurium (S. Typhimurium). APECs from orally infected, but not uninfected, mice produce high amounts of NO and aggregate upon ex vivo culture in a Nos2-dependent manner. Importantly, aggregated APECs induced by Ifnγ contain fewer intracellular S. Typhimurium compared to their single counterparts post infection. Further experiments with LNMA or Reopro revealed that both NO and CD11b are important for aggregation; in addition, NO is bactericidal. Overall, this study elucidates novel roles for Ifnγ and Nos2 in regulating Actin, Tubulin, CD11b, motility and morphology during the aggregation response of APECs. The implications of aggregation or "group behavior" of APECs are discussed in the context of host resistance to infectious organisms.