Sustained JNK activation in response to tumor necrosis factor is mediated by caspases in a cell type-specific manner

Area of Science:

• Cellular Biology
• Molecular Signaling
• Immunology

Background:

• Tumor necrosis factor (TNF) typically causes transient JNK pathway activation.
• In cells with inhibited NF-kappaB, TNF can induce a secondary, sustained JNK activation phase linked to cell death.
• The precise roles of JNK, caspases, and NF-kappaB in TNF-induced cell death require further elucidation.

Purpose of the Study:

• To investigate the relationship between cell death, caspase activity, JNK, and NF-kappaB signaling in response to TNF.
• To determine if sustained JNK activation is a prerequisite for TNF-induced cell death.
• To explore the pathways mediating transient versus sustained JNK activation by TNF.

Main Methods:

• Utilized four distinct cellular systems to study TNF signaling.
• Employed NF-kappaB inhibition strategies.
• Administered caspase inhibitors (Z-VAD-fmk) and antioxidants (butylated hydroxyanisole).
• Overexpressed antiapoptotic proteins (FLIP-L, Bcl2).
• Monitored JNK activation, caspase activity, and cell death induction.

Main Results:

• NF-kappaB inhibition consistently enhanced TNF-induced cell death and primed cells for sustained JNK activation.
• Caspase inhibitors and antiapoptotic proteins differentially affected transient and sustained JNK activation, suggesting distinct pathways.
• Inhibition of JNK signaling had minimal impact on TNF-induced cell death across cell types.
• Interference with TNF-induced cell death by Z-VAD-fmk and antioxidants did not strictly correlate with JNK inhibition.

Conclusions:

• Sustained JNK activation by TNF is not obligatory for TNF-induced cell death.
• The pathways leading to transient and sustained JNK activation by TNF are distinct and involve caspases and reactive oxygen species in a cell-type-specific manner.