Biochemistry Graduate Seminar
Monday, November 9, 2009
Lecture at 4:30 p.m. in Burt Hall 114
Coffee at 4:15 p.m. in Chalmers 168
Xiao Yao
Nitric oxide activation of Keap1/Nrf2 signaling in human colon carcinoma cells
NF-E2-related nuclear factor 2 (Nrf2) is the key transcriptional factor regulating the antioxidant response in mammalian cells. Kelch-like ECH-associated protein1 (Keap1) works as a substrate adaptor protein in the cytoplasm repressing Nrf2 signaling at basal condition. Upon oxidative stress, binding sites between Nrf2 and Keap1 dissociate causing Nrf2 translocation into the nucleus and subsequent activation of multiple antioxidant responsive genes. Our research interest lies in the phase after Nrf2 enters the nucleus. Experiments have been designed to elucidate the binding affinities of various antioxidant response elements (ARE) – reactive gene elements with Nrf2 in the presence of small Maf proteins. Later on, we plan to identify other possible binding partners in the nucleus by SPR capture and Mass Spectroscopy.
The paper presented today investigates how Keap1/Nrf2 signaling in the presence of nitric oxide induces apoptosis in human colon cancer HCT116 cells. Inflammation is an established risk factor for colon cancer in humans, and the excessive nitric oxide produced by inflammatory cells causing necrosis and apoptosis. Keap1/Nrf2 pathway mediates expression of detoxifying and antioxidant genes and protect against carcinogenesis and xenobiotic toxicity. The results showed that nitric oxide modulates Keap1 cysteines and may interfere with Nrf2 binding and induce Nrf2 accumulation in the nucleus. Nrf2, in the nucleus, forms a heterodimer with small Maf proteins and up-regulate HO-1, NQO1, and GCL genes. To sum up, Nrf2-Keap1 signaling pathway, activated by nitric oxide, contributes to the relative cytoprotection for HCT116 cells of nitric oxide toxicity. These findings shed light on protective mechanisms of how inflammatory cells respond to oxidative and nitrosative stresses caused by excessive nitric oxide.
References:
Li W, Kong A. Molecular mechanisms of Nrf2-mediated antioxidant response. Mol Carcinog 48: 91-104, 2009.
Li CQ, Kim MY, Godoy LC, Thiantanawat A, Trudel LJ, Wogan GN. Nitric oxide activation of Keap1/Nrf2 signaling in human colon carcinoma cells. Proc Natl Acad Sci 106(34): 14547-14551, 2009.