Extract of Ginkgo biloba induces phase 2 genes through Keap1-Nrf2-ARE signaling pathway.
The standard extract of Ginkgo biloba (EGb) has been demonstrated to possess remarkable antioxidant activity in both cell lines and animals. However, the molecular mechanism underlying this effect is not fully understood. Phase 2 enzymes play important roles in the antioxidant system by reducing electrophiles and reactive oxygen species (ROS). We demonstrated that EGb induced typical phase 2 genes: glutamate cysteine ligase catalytic subunit (GCLC) and glutathione-S-transferase subunit-P1 (GST-P1), by real-time PCR. To investigate the molecular mechanism of this induction, we used quinone oxidoreductase 1 (NQO1) -- Antioxidant response element (ARE) reporter assay and found that EGb activated the activity of the wild type but not the one with ARE mutated. It indicated that EGb induced these genes through ARE, a cis-acting motif located in the promoter region of nearly all phase 2 genes. Since nuclear factor erythroid 2-related factor 2 (Nrf2) binds ARE to enhance the expression of phase 2 genes, we detected the Nrf2 content in nucleus and found an accumulation of Nrf2 stimulated by EGb. In a further test of Kelch-like ECH-associated protein 1 (Keap1), the repression protein of Nrf2 in the cytosol under resting condition, we found that Keap1 content was inhibited by EGb and then more Nrf2 would be released to translocate into nucleus. Thus, EGb was testified for the first time to induce the phase 2 genes through the Keap1-Nrf2-ARE signaling pathway, which is (or part of) the antioxidant mechanism of EGb.
Liu
Xiao-Ping
XP
Institute of Clinical Pharmacology, Key Laboratory of Anti-inflammatory and Immunopharmacology in Anhui, Anhui Medical University, Meishan Road 81, Hefei Anhui 230032, PR China.
Goldring
Christopher E P
CE
Copple
Ian M
IM
Wang
Hai-Yi
HY
Wei
Wei
W
Kitteringham
Neil R
NR
Park
B Kevin
BK
D000975:Antioxidants / Q000494:pharmacology*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction; D005786:Gene Expression Regulation / Q000187:drug effects*; D020441:Ginkgo biloba / Q000737:chemistry*; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000096:biosynthesis* / Q000235:genetics; D010936:Plant Extracts / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction
D000975:Antioxidants; D047908:Intracellular Signaling Peptides and Proteins; C431364:KEAP1 protein, human; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D010936:Plant Extracts; D012333:RNA, Messenger; D010088:Oxidoreductases