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M Chaisson

Publications and source records attributed to M Chaisson.

5 recordsLinked to original sources
PubMed2000

Disruption of redox homeostasis in tumor necrosis factor-induced apoptosis in a murine hepatocyte cell line.

Tumor necrosis factor (TNF) is a mediator of the acute phase response in the liver and can initiate proliferation and cause cell death in hepatocytes. We investigated the mechanisms by which TNF causes apoptosis in hepatocytes focusing on the role of oxidative stress, antioxidant defenses, and mitochondrial damage. The studies were conducted in cultured AML12 cells, a line of differentiated murine hepatocytes. As is the case for hepatocytes in vivo, AML12 cells were not sensitive to cell death by TNF alone, but died by apoptosis when exposed to TNF and a small dose of actinomycin D (Act D). Morphological signs of apoptosis were not detected until 6 hours after the treatment and by 18 hours approximately 50% of the cells had died. Exposure of the cells to TNF+Act D did not block NFkappaB nuclear translocation, DNA binding, or its overall transactivation capacity. Induction of apoptosis was characterized by oxidative stress indicated by the loss of NAD(P)H and glutathione followed by mitochondrial damage that included loss of mitochondrial membrane potential, inner membrane structural damage, and mitochondrial condensation. These changes coincided with cytochrome C release and the activation of caspases-8, -9, and -3. TNF-induced apoptosis was dependent on glutathione levels. In cells with decreased levels of glutathione, TNF by itself in the absence of transcriptional blocking acted as an apoptotic agent. Conversely, the antioxidant alpha-lipoic acid, that protected against the loss of glutathione in cells exposed to TNF+Act D completely prevented mitochondrial damage, caspase activation, cytochrome C release, and apoptosis. The results demonstrate that apoptosis induced by TNF+Act D in AML12 cells involves oxidative injury and mitochondrial damage. As injury was regulated to a larger extent by the glutathione content of the cells, we suggest that the combination of TNF+Act D causes apoptosis because Act D blocks the transcription of genes required for antioxidant defenses.

Amino Acid Chloromethyl Ketones↗
PubMed1999

Tumor necrosis factor induces DNA replication in hepatic cells through nuclear factor kappaB activation.

Tumor necrosis factor (TNF) signaling through TNF receptor 1 (TNFR1) with downstream participation of nuclear factor kappaB (NFkappaB), interleukin 6 (IL-6), and signal transducers and activators of transcription 3 (STAT3) is required for initiation of liver regeneration. It is not known whether the proliferative effect of TNF on hepatocytes is direct or requires the participation of Kupffer cells, the liver resident macrophages. Moreover, it has not been determined whether NFkappaB activation is an essential step in TNF-induced proliferation. To answer these questions, we conducted studies in LE6 cells, a rat liver epithelial cell line with hepatocyte progenitor capacity. We report that TNF induces DNA replication in growth-arrested LE6 cells and that its effect involves the activation of NFkappaB and STAT3 and an increase in c-myc and IL-6 mRNAs. All of these effects, which mimic the events that initiate liver regeneration in vivo, are blocked if NFKB activation is inhibited by expression of a dominant-inhibitor IkappaBalpha mutant (deltaN-IkappaBalpha). Although NFkappaB blockage by deltaN-IkappaBalpha causes caspase activation and massive death of cells stimulated by TNF, inhibition of NFkappaB and STAT3 binding by the serine protease inhibitor N-tosyl-L-phenylalanine chloromethyl ketone results in G0-G1 cell cycle arrest without death. We conclude that NFkappaB is an essential component of the TNF proliferative pathway and that TNF-induced changes in IL-6 mRNA, STAT3, and c-myc mRNA are dependent on NFkappaB activation. Blockage of NFkappaB inhibits TNF-induced proliferation but does not necessarily cause cell death.

Animals↗