A novel role of the NRF2 transcription factor in the regulation of arsenite-mediated keratin 16 gene expression in human keratinocytes.
BACKGROUND
Inorganic sodium arsenite (iAs) is a ubiquitous environmental contaminant and is associated with an increased risk of skin hyperkeratosis and cancer.


OBJECTIVE
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.
Endo
Hitoshi
H
Department of Health Science, Asahikawa Medical College, Midorigaoka, Asahikawa, Hokkaido, Japan.
Sugioka
Yoshihiko
Y
Nakagi
Yoshihiko
Y
Saijo
Yasuaki
Y
Yoshida
Takahiko
T
D018053:Arsenites / Q000633:toxicity*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression; D006801:Humans; D053536:Keratin-16 / Q000096:biosynthesis* / Q000235:genetics; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D017670:Sodium Compounds / Q000633:toxicity*; D015533:Transcriptional Activation
D018053:Arsenites; C507431:KRT16 protein, human; D053536:Keratin-16; D051267:NF-E2-Related Factor 2; D012333:RNA, Messenger; D017670:Sodium Compounds; C017947:sodium arsenite