Molecular mechanism of human Nrf2 activation and degradation: Role of sequential phosphorylation by protein kinase CK2

Laboratory of Comparative Carcinogenesis, NCI at NIEHS, NIH, Research Triangle Park, NC 27709, USA.
Free Radical Biology and Medicine (Impact Factor: 5.71). 07/2007; 42(12):1797-806. DOI: 10.1016/j.freeradbiomed.2007.03.001
Source: PubMed

ABSTRACT Nrf2 is a key transcription factor in the cellular response to oxidative stress. In this study we identify two phosphorylated forms of endogenous human Nrf2 after chemically induced oxidative stress and provide evidence that protein kinase CK2-mediated sequential phosphorylation plays potential roles in Nrf2 activation and degradation. Human Nrf2 has a predicted molecular mass of 66 kDa. However, immunoblots showed that two bands at 98 and 118 kDa, which are identified as phosphorylated forms, are increased in response to Nrf2 inducers. In addition, human Nrf2 was found to be a substrate for CK2 which mediated two steps of phosphorylation, resulting in two forms of Nrf2 migrating with differing M(r) at 98 kDa (Nrf2-98) and 118 kDa (Nrf2-118). Our results support a role in which calmodulin binding regulates CK2 activity, in that cold (25 degrees C) Ca(2+)-free media (cold/Ca(2+)-free) decreased both cellular calcium levels and CK2-calmodulin binding and induced Nrf2-118 formation, the latter of which was prevented by CK2-specific inhibitors. Gel shift assays showed that the Nrf2-118 generated under cold/Ca(2+)-free conditions does not bind to the antioxidant response element, indicating that Nrf2-98 has transcriptional activity. In contrast, Nrf2-118 is more susceptible to degradation. These results provide evidence for phosphorylation by CK2 as a critical controlling factor in Nrf2-mediated cellular antioxidant response.

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Available from: Jie Liu, Aug 19, 2015
    • "through cysteine thiol modification of Keap1 (Zhang and Hannink, 2003) or via phosphorylation of its serine/threonine residues by upstream kinases, such as protein kinase C (PKC) (Bloom and Jaiswal, 2003), extracellular signal-regulated kinase (ERK) (Yu et al., 2000), casein kinase-2 (Pi et al., 2007), cAMP-activated protein kinase-a (AMPKa) (Mo et al., 2013), and Akt (Martin et al., 2004). Thymoquinone (2-Isopropyl-5-methylbenzo-1,4-quinone; TQ) is an active constituent of black cumin (Nigella sativa), also known as black seed, which is widely consumed as a condiment and has long been used in Ayurvedic medicine. "
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    • "One of the best characterized include phosphorylation by PKC (Huang et al., 2000), which is necessary for liberating NRF2 from KEAP1 (Bloom and Jaiswal, 2003) and thus promoting transport to the nucleus. Protein kinase CK2 can also phosphorylate NRF2, which promotes transport of NRF2 into the nucleus (Pi et al., 2007). Similar activating effects on NRF2 translocation to the nucleus have been observed for phosphatidylinositide 3-kinases (PI3K) (Nakaso et al., 2003), c-Jun N-terminal kinase (JNK), extracellular regulated kinase (ERK) (Xu et al., 2006) and PERK (Cullinan et al., 2003). "
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    • "Moreover, Nrf2 can be a substrate for PERK that phosphorylates Nrf2 [23], and then enhances its nuclear translocation by disrupting Keap1 binding [23]. Furthermore, the phosphorylation of Nrf2 by CK2 is also a critical controlling factor in Nrf2 activity and degradation [31] "
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