TNFα-Induced IEC-6 Cell Apoptosis Requires Activation of ICE Caspases whereas Complete Inhibition of the Caspase Cascade Leads to Necrotic Cell Death

doi:10.1006/bbrc.1999.0734

Biochemical and Biophysical Research Communications

Volume 260, Issue 1, 24 June 1999, Pages 159-166

https://doi.org/10.1006/bbrc.1999.0734 Get rights and content

Abstract

Tumor necrosis factor (TNF)α is considered to play a key pathogenetic role in inflammatory bowel diseases. In this study we analyzed the mechanisms by which TNFα induces intestinal epithelial cell apoptosis. TNFα alone, and more potently in combination with IFNγ, induced a high degree of IEC-6 cell apoptosis. This effect was more than 100-fold stronger if both of the TNF-R were stimulated, compared to stimulation of the p55-TNF-R alone, indicating an important apoptosis enhancing effect of the p75-TNF-R. TNFα-induced apoptosis required activation of ICE caspases and was completely abolished by its inhibitor, zVAD-fmk. Specific inhibition of caspase-3 with zDEVD-fmk did not alter the effect of TNFα. Western blot analyses confirmed that caspase-3 was not activated in response to TNFα. In the presence of complete inhibition of the caspase cascade with zVAD-fmk (≥50 μM), TNFα induced cell necrosis rather than apoptosis. Our data reveal that TNFα can trigger enterocyte cell death via apoptosis or necrosis, depending upon the activation or blockade of specific caspases.

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Microglial activation/proliferation and reactive astrogliosis are commonly observed and have been considered to be closely relevant pathological processes during spinal cord injury (SCI). However, the molecular mechanisms underlying this microglial–astroglial interaction are still poorly understood. We showed recently that the continuous injection of the cell cycle inhibitor olomoucine not only markedly suppressed microglial proliferation and associated release of pro-inflammatory cytokines, but also attenuated astroglial scar formation and the lesion cavity and mitigated the functional deficits in rat SCI animal model. In this study, we asked whether microglial activation/proliferation plays an initial role and also necessary in maintaining astrogliosis in SCI model. Our results showed that traumatic induced microglial activation/proliferation precedes astrogliosis, and the up-regulated GFAP expression at both mRNA and protein levels was temporally posterior to the microglial activation. Furthermore, when the cell cycle inhibitor olomoucine was administered only once 1 h post-SCI that should selectively suppress microglial proliferation, the subsequent SCI induced increase in GFAP expression at 1, 2 and 4 weeks was significantly attenuated, suggesting that microglial activation/proliferation played an important role for the later onset astrogliosis after SCI. Consistent with the results that microglial proliferation always precedes astroglial proliferation and there is at present no evidence of other astroglial precursors, which as always does not mean that they will not be uncovered by further searching, and in view of the fact that microglial-derived pro-inflammatory cytokines promote astrogliosis as we reported recently, these findings together suggest that by release of cytokines and other soluble products, the early onset microglial activation/proliferation can significantly influence the subsequent development of reactive astrogliosis and glial scar formation in SCI animal model.
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Regular ArticleTNFα-Induced IEC-6 Cell Apoptosis Requires Activation of ICE Caspases whereas Complete Inhibition of the Caspase Cascade Leads to Necrotic Cell Death

Abstract

Lancet

Gastro. Clin. N. Amer.

Gastroenterology

Immunol. Today

Biochem. Biophys. Res. Commun.

Cell

Cell

Cell

Cell

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

Regular Article
TNFα-Induced IEC-6 Cell Apoptosis Requires Activation of ICE Caspases whereas Complete Inhibition of the Caspase Cascade Leads to Necrotic Cell Death