Sustained high expression of NRF2 inhibits cell apoptosis in arsenite-transformed human keratinocytes

Our previous study identified that nuclear factor-erythroid-2 p45-related factor 2 (NRF2) was activated in arsenite-induced tumorigenesis. However, the underlying mechanisms of NRF2 mediating apoptosis in arsenic-induced skin carcinogenesis remain unknown. This study explored the dynamic changes in apoptosis rate and the expression of apoptosis proteins in immortalized human keratinocytes (HaCaT) malignant transformation caused by 1.0 μM NaAsO₂ at passages 0, 1, 7, 14, 21, 28, and 35. The result showed that the apoptosis rate decreased. The apoptosis-related proteins cleaved-caspase-3/caspase-3 ratio decreased in the later stages (passages 21, 28, and 35). Moreover, the expression of intrinsic ER stress pathway-related CHOP, ATF4, ATF6, and the intrinsic mitochondrial pathway-related Bax protein decreased in the later stages, while Bcl-2 and Mcl-1 increased, and NRF2 protein levels also increased. The apoptosis rate increased by silencing NRF2 expression in arsenite-transformed HaCaT (T-HaCaT) cells. Meanwhile, the expression of pro-apoptotic proteins (cleaved-caspase-3/caspase-3, CHOP, Bax) and ATF4, ATF6 increased. On the contrary, antiapoptotic protein levels (Bcl-2 and Mcl-1) decreased. The ability of colony formation and migration of T-HaCaT cells decreased. In conclusion, arsenite activated NRF2 in the later stages, decreasing apoptosis characterized by inhibiting endoplasmic reticulum stress-depended and mitochondria-depended apoptosis pathway, and further promoting NaAsO₂-induced HaCaT cellular malignant transformation.