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1173152 
Journal Article 
Abstract 
Sequential phosphorylation by protein kinase CK2 regulates NRF2 activation and degradation: Potential role In arsenic-induced skin carcinogenesis 
Pi, J; Diwan, BA; Qu, W; Liu, J; Bai, Y; Fahl, W; Yamauchi, H; Collins, S; Waalkes, MP 
2006 
1 
Toxicological Sciences
ISSN: 1096-6080
EISSN: 1096-0929 
90 
1-S 
12 
English 
Arsenic is a well-documented human carcinogen that targets skin and may induce genetic damage through generation of reactive oxygen species (ROS). Nrf2 is a key transcription factor that regulates expression of genes whose products protect cells against ROS. We have explored here the role that phosphorylation plays in regulating Nrf2 activity and have explored the association between protein kinase CK2, Nrf2 activation and arsenic-induced skin carcinogenesis. Events relative to skin carcinogenesis were studied in a human keratinocyte cell line (HaCaT) undergoing malignant transformation as a result of chronic arsenic exposure. Nrf2 phosphorylation was detected in acute arsenic-treated cells using Nrf2 western blot both before and after in vitro phosphatases treatment. Gel-shift assay, Real-time RT-PCR and Western blot were employed to evaluate Nrf2 transcriptional activity in both its native and phosphorylated forms. Two phosphorylated forms of Nrf2 were identified after arsenic-induced oxidative stress. Additional study showed CK2 mediated, sequential phosphorylation of Nrf2 to first produce an active, phosphorylated form and then a hyper-phosphorylated form which was inactive and underwent degradation. Continuous exposure to arsenic (100 nM) for 28 weeks induced malignant transformation in HaCaT cells and concurrently upregulated CK2 expression and activity. Arsenic-transformed keratinocytes had more Nrf2 hyper-phosphorylation and exhibited a dysfunctional antioxidant response. These results provide compelling evidence for phosphorylation by CK2 as a critical controlling factor in Nrf2-mediated cellular antioxidant response. Chronic arsenic-induced CK2 upregulation is a potentially important event in skin carcinogenesis as it may increase the susceptibility to oxidative damage by altering Nrf2 phosphorylation and cellular antioxidant response. 
45th Annual Meeting of the Society of Toxicology 
San Diego, CA 
March 5-9, 2006