Differential endoplasmic reticulum stress signaling pathways mediated by iNOS

Area of Science:

• Cellular Biology
• Molecular Biology
• Biochemistry

Background:

• Accumulated misfolded proteins in the endoplasmic reticulum (ER) trigger ER stress signaling pathways.
• ER stress is linked to the generation of reactive oxygen species (ROS), contributing to oxidative stress.
• Understanding the specific molecular mechanisms linking ER stress to ROS production is crucial.

Purpose of the Study:

• To identify the specific ER factors responsible for generating ROS during ER stress.
• To elucidate the role of inducible nitric oxide synthase (iNOS) in ER stress-induced oxidative stress.
• To differentiate between iNOS-dependent and -independent pathways of ROS generation.

Main Methods:

• Mouse NIH3T3 cells were treated with ER stress inducers: tunicamycin and thapsigargin.
• Oxidative stress levels were measured following inducer treatment.
• The effects of iNOS inhibitors (1400W, L-canavanine) and proteasome inhibitors (lactacystin, MG-132) on oxidative stress were evaluated.

Main Results:

• ER stress induced by thapsigargin led to increased ROS production, which was significantly reduced by iNOS inhibitors.
• This iNOS-dependent ROS generation was specific to ER stress caused by calcium (Ca2+) efflux, as tunicamycin treatment showed no such inhibition.
• Treatment with proteasome inhibitors increased UPR-induced oxidative stress, suggesting that clearing misfolded proteins mitigates oxidative stress.

Conclusions:

• Inducible nitric oxide synthase (iNOS) mediates a specific subpathway of ER stress-induced oxidative stress, particularly that resulting from Ca2+ efflux.
• ER stress signaling involves both iNOS-dependent and iNOS-independent pathways for ROS generation.
• Enhancing the clearance of misfolded proteins from the ER lumen may reduce ER stress-associated oxidative damage.