Tumor Necrosis Factor-α Mediates Both Apoptotic Cell Death and Cell Proliferation in a Human Hematopoietic Cell Line Dependent on Mitotic Activity and Receptor Subtype Expression

Abstract

The TF-1 human erythroleukemic cell line exhibits opposing physiological responses toward tumor necrosis factor-␣ (TNF) treatment, dependent upon the mitotic state of the cells. Mitotically active cells in log growth respond to TNF by rapidly undergoing apoptosis whereas TNF exposure stimulates cellular proliferation in mitotically quiescent cells. The concentrationdependent TNF-induced apoptosis was monitored by cellular metabolic activity and confirmed by both DNA epifluorescence and DNA fragmentation. Moreover, these responses could be detected by measuring extracellular acidification activity, enabling rapid prediction (within ϳ 1.5 h of TNF treatment) of the fate of the cell in response to TNF. Growth factor resupplementation of quiescent cells, resulting in reactivation of cell cycling, altered TNF action from a proliferative stimulus to an apoptotic signal. Expression levels of the type II TNF receptor subtype (p75TNFR) were found to correlate with sensitivity to TNF-induced apoptosis. Pretreatment of log growth TF-1 cells with a neutralizing antip75TNFR monoclonal antibody inhibited TNF-induced apoptosis by greater than 80%. Studies utilizing TNF receptor subtype-specific TNF mutants and neutralizing antisera implicated p75TNFR in TNF-dependent apoptotic signaling. These data show a bifunctional physiological role for TNF in TF-1 cells that is dependent on mitotic activity and controlled by the p75TNFR.Cells have the capability of responding to a multitude of signals that it encounters in its extracellular environment. One such signal with widespread pleiotropic actions is the cytokine tumor necrosis factor-␣ (TNF) 1 (1). TNF has been shown to modulate proliferation, differentiation, and apoptotic or necrotic cell death in a number of different cell types (2-4). These disparate responses to TNF are mediated by TNF binding to specific cell surface receptors. Two distinct TNF receptors, type I (p55TNFR) and type II (p75TNFR) (M r 55,000 -60,000 and 70,000 -80,000 in human cells, respectively), have been identified (5, 6), although it remains unclear which of the many responses reported for TNF can be attributed to a specific receptor subtype (4). Moreover, the precise signal transduction pathways for each of these receptor subtypes have yet to be fully delineated. One action of TNF, the induction of apoptosis, is characterized by a discrete set of cellular events regulated by gene expression (7,8). The physiological events accompanying apoptosis include condensation of the chromatin, degradation of DNA through the activation of endogenous nucleases, and dissolution of the cell into small membrane-bound apoptotic vesicles (9, 10). In vivo, these vesicles are phagocytosed by macrophages or other phagocytic cells. Cell death by apoptosis is essential in many physiological processes, including embryonic development of the nervous system (11), oncogenic pathology (12), and clonal selection of hematopoietic cells (13).Conversely, TNF has also been shown to stimulate cellular proliferation in a variety of systems...

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

“…8 Here, we show that GM-CSF and IL-3 pretreatment can switch TF-1 cells from a TNF proliferative-to a TNF apoptotic phenotype. When GM-CSF or IL-3 was added to TF-1 cells, a large increase in total cell number was observed (Figure 1a).…”

“…These latter cytokines had little or no effect on the expression of either TNF receptor, whereas GM-CSF and IL-3 both increased the expression of TNFR2, but not TNFR1, as has also been previously demonstrated. 8,27 It is therefore possible that the increased levels of TNFR2 may be responsible for the increased susceptibility to apoptosis.…”

“…The relative surface expression of these two TNF receptors can affect the cellular responses to TNF stimulation and this can be altered by the growth state or metabolic activity of the cell. 5,8 A variety of agents have been tested with regard to their ability to alter the level of TNFRs, and subsequently alter the effects of TNF. [9][10][11][12] Apoptosis (programmed cell death) plays an important role in the homeostasis and development of all tissues within an organism.…”

“…26,27 Previous studies using these cytokines, before and during chemotherapy to recruit leukaemia cells into cell cycle, and thus make them more susceptible to chemotherapy, have revealed no benefit. 28 However, with the findings that certain conditions can increase the expression of TNFR2, 8 this may represent a possible mechanism with which to increase susceptibility to TNF-induced apoptosis, while avoiding some of the deleterious side effects of TNF. In this study, we investigated the effects of cytokines on the levels of TNFR expression and the effect these cytokines have on the relative susceptibility of TF-1 cells to TNF-induced apoptosis.…”

Lack of TNFR2 expression by CD4+ T cells exacerbates experimental colitis

“…TNFR2 signaling has also been shown to stimulate proliferation, particularly in lymphocytes [13,14]. Although TNFR2 does not contain a DD in its intracellular domain, this receptor can mediate pro-apoptotic effects [15][16][17]. Hence, the complexity of TNF-mediated functions may in part be attributed to the presence of two different TNFR with different expression patterns and signaling pathways.…”