IL-4 and TNF-alpha-mediated proliferation of the human megakaryocytic line M-O7E is regulated by induced autocrine production of GM-CSF

Granulocyte macrophage-colony stimulating factor and interleukin-3 increase expression of type II tumour necrosis factor receptor, increasing susceptibility to tumour necrosis factor-induced apoptosis. Control of leukaemia cell life/death switching

Tumour necrosis factor (TNF) induces apoptosis in a range of cell types via its two receptors, TNFR1 and TNFR2. Here, we demonstrate that proliferation and TNFR2 expression was increased in human leukaemic TF-1 cells by granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin-3 (IL-3), with TNFR1 expression unaffected. Consequently, they switch from a proliferative to a TNF-induced apoptotic phenotype. Raised TNFR2 expression and susceptibility to TNF-induced apoptosis was not a general effect of proliferation as IL-1beta and IFN-gamma both proliferated TF-1 cells with no effect on TNFR expression or apoptosis. Although raised TNFR2 expression correlated with the apoptotic phenotype, stimulation of apoptosis in GM-CSF-pretreated cells was mediated by TNFR1, with stimulation of TNFR2 alone insufficient to initiate cell death. However, TNFR2 did play a role in apoptotic and proliferative responses as they were blocked by the presence of an antagonistic TNFR2 antibody. Additionally, coincubation with cycloheximide blocked the mitotic effects of GM-CSF or IL-3, allowing only the apoptotic responses of TNF to persist. TNF life/death was also observed in K562, but not MOLT-4 and HL-60 human leukaemic cell types. These findings show a cooperative role of TNFR2 in the TNF life/death switching phenomenon.

Involution of thymus and lymphoid depletion in mice expressing the hTNF transgene

Tumour necrosis factor (TNF) is involved in the pathogenesis of several diseases. In mice, human TNF signals only through p55, one of two murine TNF receptors. We here report a study of growth, viability and morphological alterations in transgenic mice expressing a low constitutive and tissue-restricted level of human TNF in vivo. The transgene was expressed solely in T cells. The transgenic mice showed a marked failure to thrive and a rapid cellular depletion in spleen and thymus. Slight fibrosis was seen in most tissues investigated, in addition to immature adipose tissue and irregular lymphocytic areas. Serum levels of hTNF were only slightly increased in the transgenic mice, enough, however, to cause an inflammatory reaction. All the symptoms were abrogated by an inhibitory hTNF antibody, demonstrating the essential role of hTNF in this phenotype. Transgenic mice constitute a multidimensional system allowing observation of disease processes over time in all tissues. The effects of hTNF were seen first and foremost in the lymphoid organs of the transgenic mice, verifying their cells as major targets at low levels of hTNF expression in the T-cell compartments. Chronic, low levels of TNF expression cause profound disturbances in lymphoid tissue development resulting in cachexia and premature death.

Tumor necrosis factor-alpha-induced proliferation requires synthesis of granulocyte-macrophage colony-stimulating factor

OBJECTIVE

Tumor necrosis factor- alpha (TNF-alpha) induces a variety of cellular responses, some of them being at least seemingly contradictory. Thus, we set out to find differences in the modes of proliferative and apoptotic responses to TNF- alpha.

MATERIALS AND METHODS

We screened a panel of acute myeloid leukemia-derived cell lines for TNF- alpha-responsiveness. In two lines (OCI-AML-1, OCI-AML-11), TNF- alpha acted as an apoptotic agent; in others (HU-3, M-07e, TF-1), it had the opposite effect, preventing apoptosis and inducing proliferation. Direct and indirect signaling mechanisms, including NF-kappaB activation and cytokine synthesis, were analyzed.

RESULTS

All cell lines tested expressed TNF- alpha receptors I and II and responded to TNF- alpha by upregulation of intercellular adhesion molecule-1. In contrast to granulocyte-macrophage colony-stimulating factor (GM-CSF), TNF- alpha did not activate the MAP kinase and p70S6 kinase pathways. Nevertheless, inhibitors of these pathways clearly reduced the TNF-alpha-induced cell growth, indicating that TNF- alpha-proliferative cells produced a growth factor that induced proliferation upon stimulation of the above pathways. Anti-GM-CSF antibodies inhibited the TNF-alpha-induced growth, suggesting the presence of an autocrine loop for cell proliferation mediated by GM-CSF. Supporting this notion, TNF-alpha-induced upregulation of GM-CSF mRNA levels and protein secretion in the TNF-alpha-proliferative, but not in the TNF-alpha-apoptotic cell lines.

CONCLUSION

These data identify GM-CSF synthesis as an early and essential step in TNF- alpha-induced proliferation. We show for the first time that TNF-alpha-treated cell lines producing no or only minimal amounts of GM-CSF demonstrate an apoptotic phenotype, while cell lines with high GM-CSF expression rates can escape from growth arrest or even apoptosis. In this context, we discuss arguments pointing at NF-kappaB as regulator of GM-CSF synthesis and thus indirectly as regulator for the escape of TNF-alpha-induced apoptosis.

Activation of p38 mitogen-activated protein kinase is required for tumor necrosis factor-alpha -supported proliferation of leukemia and lymphoma cell lines

To elucidate mechanisms of tumor necrosis factor alpha (TNF-alpha)-induced proliferation of a number of human leukemia and lymphoma cell lines, we examined the role of p38 mitogen-activated protein kinase (MAPK) in TNF-alpha signaling in Mo7e and Hut-78 cells. TNF-alpha-dependent p38 MAPK activation was detected in both Mo7e and Hut-78 cells and was blocked by the p38 MAPK inhibitor, SB203580. Ablation of p38 MAPK activity by SB203580 abrogated TNF-alpha-induced Mo7e cell proliferation and TNF-alpha-dependent autocrine growth of Hut-78. As we have shown previously that activation of the nuclear factor kappaB (NF-kappaB) is also required for TNF-alpha-induced Mo7e cell proliferation, the involvement of p38 MAPK in NF-kappaB activation was assessed. SB203580 did not affect TNF-alpha-signaled nuclear translocation and DNA-binding activity of NF-kappaB, and inhibition of NF-kappaB function did not affect TNF-alpha-induced p38 MAPK activation, indicating that these events are not dependent on each other. However, SB203580 depressed the expression of NF-kappaB-dependent genes, as monitored by a kappaB-driven reporter gene. Our findings demonstrate that activation of both p38 MAPK and NF-kappaB plays a critical role in TNF-alpha-mediated survival and proliferation of human leukemia and lymphoma cells, and p38 MAPK acts at least in part by facilitating the transcriptional activation function of NF-kappaB.

TNF-α-Induced Growth Suppression of CD34+ Myeloid Leukemic Cell Lines Signals Through TNF Receptor Type I and Is Associated with NF-κB Activation

Conflicting results have been reported regarding the effect of TNF-α on the growth of human primitive hemopoietic cells. In this study, we have examined the effect of TNF-α on the proliferation of several CD34+/CD38+ (KG-1, TF-1) and CD34+/CD38− (KG-1a, TF-1a) myeloid leukemic progenitor cell lines. Our data show that TNF-α markedly inhibits the growth of these cells in both liquid and soft agar cultures. Addition of GM-CSF or IL-3 does not prevent TNF-α-induced growth inhibition. Flow cytometry analyses of propidium iodide-stained cells demonstrated cell death of all four cell lines, as judged by the presence of cells with hypodiploid DNA content after exposure of cells to TNF-α for 4 days. Annexin V assays detected apoptosis in TF-1, but not in TF-1a, KG-1, and KG-1a cells in terms of translocation of phosphatidylserine shortly after TNF-α treatment. Neutralizing anti-TNF receptor type I (TNFR-I; p55) Ab almost completely reversed TNF-α-induced growth inhibition in both liquid and soft agar cultures, whereas anti-TNFR-II (p75) Ab had only a marginal effect. TNF-α rapidly induced marked activation of nuclear transcription factor NF-κB in all 4 cell lines. The majority of this effect was abolished by the type I receptor Ab, whereas the type II receptor neutralizing Ab had no effect. Our data also show that TNF-α is incapable of inducing activation of the mitogen-activated protein kinase pathway in these leukemic cell lines.

Tumor necrosis factor-alpha-induced proliferation of human Mo7e leukemic cells occurs via activation of nuclear factor kappaB transcription factor

Tumor necrosis factor-alpha (TNF-alpha) stimulates proliferation of Mo7e, CMK, HU-3, and M-MOK human leukemic cell lines. We report here the signal transduction pathway involved in TNF-alpha-induced Mo7e cell proliferation. Mo7e cells spontaneously die in the absence of growth factors, but treating the cells with interleukin (IL)-3, IL-6, thrombopoietin, granulocyte/macrophage colony-stimulating factor, or TNF-alpha promotes their survival and proliferation. Although most of these factors activate MAP kinase and Jun NH2-terminal kinase/signal transducer and activators of transcription signaling pathways, TNF-alpha fails to activate either pathway. When Mo7e cells were treated with TNF-alpha, nuclear factor kappaB (NF-kappaB) was activated transiently. The activated NF-kappaB consisted of heterodimers of p65 and p50 subunits. The degradation of IkappaBalpha coincided with activation of NF-kappaB in TNF-alpha-treated cells. To investigate the role of activated NF-kappaB in TNF-alpha-induced Mo7e proliferation, a cell-permeable peptide (SN50) carrying the nuclear localization sequence of p50 NF-kappaB was used to block nuclear translocation of activated NF-kappaB. Pretreating Mo7e cells with SN50 blocked TNF-alpha-induced nuclear translocation of NF-kappaB and inhibited TNF-alpha-induced Mo7e cell survival and proliferation. A mutant SN50 peptide did not affect TNF-alpha-induced Mo7e cell growth. SN50 had no effects on IL-3- or granulocyte/macrophage colony-stimulating factor-induced Mo7e cell proliferation. The results indicate that activation of NF-kappaB is involved in TNF-alpha-induced Mo7e cell survival and proliferation.