Regulation of miRNA-21 by reactive oxygen species-activated ERK/NF-κB in arsenite-induced cell transformation

► Chronic exposure to arsenite induces the transformation of HELF cells. ► Arsenite improves miR-21 expression by reactive oxygen species activation of the ERK/NF-κB pathway. ► NF-κB regulates miR-21 expression by binding directly to the promoter of miR-21. ► MiR-21 has a feedback effect in regulating ERK activation via Spry1. ► MiR-21 affects the malignancy potential of arsenite-transformed HELF cells.