Background: Inorganic sodium arsenite (iAs) is a ubiquitous environmental contaminant and is associated with an increased risk of skin hyperkeratosis and cancer.
Objectives: We investigated the molecular mechanisms underlying the regulation of the keratin 16 (K16) gene by iAs in the human keratinocyte cell line HaCaT.
Methods: We performed reverse transcriptase polymerase chain reaction, luciferase assays, Western blots, and electrophoretic mobility shift assays to determine the transcriptional regulation of the K16 gene by iAs. We used gene overexpression approaches to elucidate the nuclear factor erythroid-derived 2 related factor 2 (NRF2) involved in the K16 induction.
Results: iAs induced the mRNA and protein expression of K16. We also found that the expression of K16 was transcriptionally induced by iAs through activator protein-1-like sites and an antioxidant response element (ARE) in its gene promoter region. Treatment with iAs also enhanced the production and translocation of the NRF2 transcription factor, an ARE-binding protein, into the nucleus without modification of its mRNA expression. In addition, iAs elongated the half-life of the NRF2 protein. When overexpressed in HaCaT cells, NRF2 was also directly involved in not only the up-regulation of the detoxification gene thioredoxin but also K16 gene expression.
Conclusions: Our data clearly indicate that the K16 gene is a novel target of NRF2. Furthermore, our findings also suggest that NRF2 has opposing roles in the cell--in the activation of detoxification pathways and in promoting the development of skin disorders.
Keywords: antioxidant response element; arsenic; hyperkeratosis; keratin 16 (K16); keratinocytes; nuclear factor erythroid-derived 2 related factor 2 (NRF2); transcription.