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MEK1 activation rescues Jurkat T cells from Fas-induced apoptosis
D J Wilson1, A Alessandrini, R C Budd
1Department of Medicine, The University of Vermont College of Medicine, Burlington, Vermont, 05405, USA.
Abstract:
Although the protease cascade initiated by Fas (CD95, Apo-1) is well characterized, there remains little known about how kinase pathways may impact on Fas-mediated apoptosis. We recently observed that in T lymphocytes Fas strongly induced activation of JNK (c-Jun N-terminal kinase) but not of second messengers leading to activation of ERK (extracellular regulated kinase). Additionally, Fas-mediated apoptosis was significantly inhibited with PMA, a potent activator of the ERK signaling pathway. This suggested a model whereby activation of the ERK pathway might attenuate Fas-mediated apoptosis. This was confirmed in the current study by showing that activation of MEK1, the upstream regulator of ERK, reduces Fas-mediated apoptosis, whereas inhibition of MEK1 augments apoptosis by Fas. Furthermore, Fas-mediated apoptosis of Jurkat T cells is not affected by constitutively active or dominant negative variants that modulate the JNK pathway. These results demonstrate that Fas-induced JNK activation is not required for apoptosis by Jurkat T cells, but rather is more likely secondary to cell stress during the early phases of apoptosis. This is supported by the ability of the caspase blocker zVAD to inhibit both apoptosis and JNK activation by Fas.
Insights
The extracellular signal-regulated kinase (ERK) pathway inhibits Fas-mediated apoptosis in T lymphocytes. Conversely, blocking ERK activation enhances apoptosis, revealing a novel regulatory mechanism in programmed cell death.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- The Fas receptor triggers apoptosis via a protease cascade.
- The role of kinase pathways, particularly ERK and JNK, in Fas-mediated apoptosis is not fully understood.
Purpose of the Study:
- To investigate the impact of kinase signaling pathways on Fas-mediated apoptosis in T lymphocytes.
- To elucidate the specific roles of the Extracellular signal-regulated Kinase (ERK) and c-Jun N-terminal Kinase (JNK) pathways in this process.
Main Methods:
- T lymphocytes were treated to induce Fas-mediated apoptosis.
- Activation of ERK and JNK pathways was assessed.
- Pharmacological inhibitors and genetic modulators (constitutively active/dominant-negative variants) of MEK1 (ERK upstream regulator) and JNK were employed.
- Caspase activity was blocked using zVAD to assess JNK's role.
Main Results:
- Fas activation strongly induced JNK but not ERK signaling in T lymphocytes.
- PMA, an ERK activator, significantly inhibited Fas-mediated apoptosis.
- MEK1 activation reduced Fas-mediated apoptosis, while MEK1 inhibition enhanced it.
- Modulation of the JNK pathway did not affect Fas-mediated apoptosis in Jurkat T cells.
- zVAD, a caspase blocker, inhibited both Fas-induced apoptosis and JNK activation.
Conclusions:
- The ERK signaling pathway attenuates Fas-mediated apoptosis.
- Fas-induced JNK activation is not essential for apoptosis but is likely a secondary event to cell stress.
- ERK pathway activation represents a potential therapeutic target for modulating Fas-mediated apoptosis.