AP-1-independent sensitization to oxidative stress-induced apoptosis by proteasome inhibitors

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Hydrogen peroxide (H2O2) triggers mesangial cell apoptosis through c-Jun N-terminal kinase (JNK)-activator protein-1 (AP-1) and extracellular signal-regulated kinase (ERK)-AP-1 signaling pathways.
• Subtoxic doses of proteasome inhibitors, including MG132 and lactacystin, were previously found to significantly potentiate H2O2-induced apoptosis in mesangial cells.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the enhanced apoptosis of mesangial cells induced by proteasome inhibitors in combination with H2O2.
• To specifically elucidate the role of the AP-1 signaling pathway in this potentiated apoptotic response.

Main Methods:

• Reporter assays were employed to assess AP-1 activation.
• Pharmacological inhibitors (retinoic acid, curcumin, PD98059) and dominant-negative mutants of JNK, c-Jun, and ERK were used to block specific signaling components.
• The effect of MG132 pretreatment on H2O2-induced AP-1 activation was examined.

Main Results:

• Reporter assays confirmed that MG132 activates AP-1.
• However, AP-1 inhibitors and pathway-specific suppressions (JNK-AP-1, ERK-AP-1) failed to attenuate the pro-apoptotic effect of MG132.
• MG132 pretreatment did not enhance H2O2-induced AP-1 activation, indicating the effect is not mediated by increased AP-1 signaling.

Conclusions:

• Proteasome inhibitors promote H2O2-induced mesangial cell apoptosis through a mechanism independent of the AP-1 signaling pathway.
• These findings reveal a novel pathway by which proteasome inhibitors contribute to apoptosis, distinct from their known effects on AP-1 activation.