Heme oxygenase-1 does not affect formation of stress granules

Heme oxygenase-1 (HO-1) is a cytoprotective enzyme responsible for heme degradation and is commonly upregulated during cellular stress. Stress granules (SGs), membraneless assemblies formed from untranslated messenger ribonucleoproteins, constitute an important component of the adaptive stress response. In this study, we examined whether HO-1 expression levels or its intracellular localization influence SG formation in murine induced pluripotent stem cells (miPSCs). Using immunofluorescence-based visualization of the canonical SG marker G3BP1, we found that neither HO-1 abundance nor its partitioning between cytosolic and nuclear compartments influenced SG induction in response to arsenite. These observations indicate that HO-1, despite being a key stress-responsive enzyme, is not directly involved in modulating SG assembly in iPS cells during oxidative challenges. In contrast, we observed that protein overexpression, irrespective of the identity of the introduced transgene, facilitates SG formation in response to MG-132 treatment. These results show that SG induction under proteotoxic stress conditions is sensitive to increased protein burden. Importantly, without appropriate controls, such effects could be misinterpreted as protein-specific regulation of SG formation. Therefore, experimental overexpression of proteins may act as a confounding factor in studies of SG formation in response to proteasome inhibition.