Luteolin inhibits the nuclear factor-kB transcriptional activity in Rat-1 fibroblasts Sun-Hee Kim a , Kum-Joo Shin a , Dohan Kim a , Yun-Hee Kim a , Myoung Sook Han a , Taehoon G. Lee b , Euikyung Kim a , Sung Ho Ryu a , Pann-Ghill Suh a,* a Department of Life Science, Division of Molecular and Life Science and School of Environmental Science and Engineering, Pohang University of Science and Technology, San 31 Hyojadong, Nam-Gu, Pohang, Kyungbuk 790-784, South Korea b SIGMOL, Inc., Pohang University of Science and Technology, San 31 Hyojadong, Nam-Gu, Pohang, Kyungbuk 790-784, South Korea Received 31 January 2003; accepted 11 June 2003 Abstract Flavonoids are natural polyphenolic compounds that have anti-inflammatory, cytoprotective and anticarcinogenic effects. In this study, we investigated the effects of several flavonoids on nuclear factor-kappa B (NF-kB) activation by using luciferase reporter gene assay. Among the flavonoids examined, luteolin showed the most potent inhibition on lipopolysaccharide (LPS)-stimulated NF-kB transcrip- tional activity in Rat-1 fibroblasts. Luteolin did not inhibit either IkBa degradation or NF-kB nuclear translocation, DNA binding or phosphorylation by LPS. However, luteolin prevented LPS-stimulated interaction between the p65 subunit of NF-kB and the transcriptional coactivator CBP. In addition, a specific PKA inhibitor that blocked the phosphorylation of CREB and c-Jun by luteolin partially reversed the inhibitory effect of luteolin on NF-kBCBP complex formation and NF-kB transcriptional activity by LPS. These data imply that inhibition of NF-kB transcriptional activity by luteolin may occur through competition with transcription factors for coactivator that is available in limited amounts. Taken together, this study provides a molecular basis for the understanding of the anti- inflammatory effects of luteolin. # 2003 Elsevier Inc. All rights reserved. Keywords: Nuclear factor-kappa B; Luteolin; Coactivator; Lipopolysaccharide; Fibroblast; Anti-inflammation 1. Introduction Flavonoids are a group of about 4000 naturally occurring polyphenolic compounds that are ubiquitous in all vascular plants. They are classified into several subgroups including flavonols, flavones, isoflavones, and flavanones according to the presence of different substituents on the benzene rings and the degree of benzo-g-pirone ring saturation. Flavo- noids without a sugar molecule are able to pass through the cell membrane. Flavonoids, once absorbed, influence many biological functions including protein synthesis, cell pro- liferation and angiogenesis [1]. Luteolin is a 3 0 ,4 0 ,5,7-tetra- hydroxyflavone and usually occurs as glycosylated forms in celery, green pepper, perilla leaf and camomile tea [2]. It has been found to possess antimutagenic [3], antitumorigenic [4], antioxidant [5] and anti-inflammatory properties [6]. Several reports have suggested that the anti-inflammatory effects of luteolin are mediated through the inhibition of nitric oxide release [5], cytokine production, protein tyr- osine phosphorylation and NF-kB-mediated gene expres- sion [6]. However, the molecular mechanism is still unclear. Nuclear factor-kB is a ubiquitous transcription factor and has a highly Rel homology domain, which controls DNA binding, dimerization and interactions with inhibitory pro- teins, IkB. In unstimulated cells, the NF-kB complex, which associates with IkB, is localized in the cytoplasm. Upon stimulation by tumor necrosis factor (TNF), inter- leukin-1 (IL-1) or bacterial LPS, IkB is phosphorylated, ubiquitinated and degraded. The removal of IkB allows NF-kB translocation to the nucleus where it binds to Biochemical Pharmacology 66 (2003) 955–963 0006-2952/$ – see front matter # 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0006-2952(03)00465-9 * Corresponding author. Tel.: þ82-54-279-2293; fax: þ82-54-279-2199. E-mail address: pgs@postech.ac.Kr (P.-G. Suh). Abbreviations: NF-kB, nuclear factor-kappa B; IkB, inhibitor of NF-kB; CREB, cyclic AMP response element-binding protein; AP-1, activator protein-1; CBP, CREB-binding protein; LPS, lipopolysaccharide.