Osmotic stress sensitizes naturally resistant cells to TNF-α-induced apoptosis

Abstract

Most cells are naturally resistant to TNF-a-induced cell death and become sensitized when NF-kB transactivation is blocked or in the presence of protein synthesis inhibitors that prevent the expression of anti-apoptotic genes. In this report we analyzed the role of osmotic stress on TNF-a-induced cell death. We found that it sensitizes the naturally resistant HeLa cells to TNF-a-induced apoptosis, with the involvement of an increase in the activity of several kinases, the inhibition of Bcl-2 expression, and a late increase on NF-kB activation. Cell death occurs regardless of the enhanced NF-kB activity, whose inhibition produces an increase in apoptosis. The inhibition of p38 kinase, also involved in NF-kB activation, significantly increases the effect of osmotic stress on TNF-a-induced cell death.

The p160 nuclear receptor co-activator RAC3 exerts an anti-apoptotic role through a cytoplasmatic action

“…These observations are in accordance with a predominance of an anti-apoptotic route through the increase in the NF-kB activity and the action of this kinase over this transcription factor (Franco et al, 2002). Although ERK activation is primarily associated with cell survival (Cobb et al, 1991;Kultz and Burg, 1998), we found reduced activity of this kinase in cells overexpressing RAC3.…”

“…Overexpression of RAC3 co-activator inhibits caspase-9 activation It has been previously reported that peroxides induce cell death by activating the apoptotic mitochondrial pathway with the subsequent activation of caspase-9 (Franco et al, 2002;Katoh et al, 2004). We therefore analysed the effect of co-activator overexpression on H 2 O 2 -induced caspase-9 activation in HEK293 cells.…”

“…Taken together, all these results indicate that overexpression of RAC3 in HEK293 cells To determine the role of these signal transduction pathways on the protective action of RAC3, we performed experiments on surviving cells by using the specific inhibitors of each kinase and NF-kB activation pathway. In these experiments, cells overexpressing or not overexpressing the co-activator were preincubated with the p38 inhibitor SB202190, the inositol-AKT inhibitors wortmannin or LY294002 and the NF-kB inhibitor sulfasalazine (Franco et al, 2002) before the addition of H 2 O 2 . As shown in Figure 5a, all the inhibitors significantly reduce the RAC3-protective effect, suggesting that all these pathways are required for an optimal anti-apoptotic action of the co-activator.…”

“…In addition to its pivotal role in immune response and inflammation, NF-kB regulates the expression of genes that control the cell cycle and cell viability (Beg and Baltimore, 1996;Guttridge et al, 1999;Hinz et al, 1999). Although several pro-apoptotic signals such as the cytokine tumor necrosis factor-a (TNF-a), osmotic and oxidative stress could activate NF-kB, most evidence supports an anti-apoptotic role for this transcription factor (Franco et al, 2002).…”

“…There is also considerable evidence indicating the participation of mitogen-activated protein kinases (MAPKs) in the control of cell cycle and survival (Kultz and Burg, 1998;Ono and Han, 2000;Franco et al, 2002), and it is well known that stress and peroxides activate several of these kinases (Ono and Han, 2000). Their role in apoptosis is controversial.…”