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Figure 4: Mild and severe oxidative stress have different effects on nuclear transport factors. The effects of mild (2 mM DEM) and severe oxidative stress (10 mM H2O2) on the subcellular distribution of importin-α1, Ran, and HuR were analyzed in HeLa cells. Proteins were located by indirect immunofluorescence [39, 69, 79]. DEM treatment accumulated importin-α1 in nuclei but did not drastically affect the distribution of Ran. By contrast, severe oxidative stress induced by H2O2 caused a pronounced nuclear accumulation of importin-α1 and collapsed the nucleocytoplasmic Ran gradient. Both treatments relocated HuR to the cytoplasm. However, DEM triggered the assembly of HuR-containing SGs, which were rare or absent upon incubation with H2O2.