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.


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.


CONCLUSIONS
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.
Quentmeier
H
H
DSMZ-German Collection of Microorganisms and Cell Cultures, Department of Human and Animal Cell Cultures, Braunschweig, Germany. hqu@dsmz.de
Dirks
W G
WG
Fleckenstein
D
D
Zaborski
M
M
Drexler
H G
HG
D017209:Apoptosis / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D016207:Cytokines / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000096:biosynthesis* / Q000494:pharmacology*; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D018799:Intercellular Adhesion Molecule-1 / Q000187:drug effects / Q000502:physiology; D007951:Leukemia, Myeloid / Q000378:metabolism; D022423:Myeloid Cells / Q000187:drug effects; D016328:NF-kappa B / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology* / Q000502:physiology; D015854:Up-Regulation
D016207:Cytokines; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007166:Immunosuppressive Agents; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D018799:Intercellular Adhesion Molecule-1; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus