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Modification of Cysteine Residue in p65 Subunit of Nuclear Factor-B (NF-B) by Picroliv Suppresses NF-B–Regulated Gene Products and Potentiates Apoptosis

¹ Cytokine Research Laboratory, Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas and ² Sabinsa Corp., Piscataway, New Jersey

Requests for reprints: Bharat B. Aggarwal, Cytokine Research Laboratory, Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Unit 143, 1515 Holcombe Boulevard, Houston, TX 77030. Phone: 713-792-1817; Fax: 713-745-6339; E-mail: aggarwal{at}mdanderson.org.

Key Words: Picroliv • NF-B • TNF • Invasion • Angiogenesis

Picroliv, an iridoid glycoside derived from the plant Picrorhiza kurroa, is used traditionally to treat fever, asthma, hepatitis, and other inflammatory conditions. However, the exact mechanism of its therapeutic action is still unknown. Because nuclear factor-B (NF-B) activation plays a major role in inflammation and carcinogenesis, we postulated that picroliv must interfere with this pathway by inhibiting the activation of NF-B–mediated signal cascade. Electrophoretic mobility shift assay showed that pretreatment with picroliv abrogated tumor necrosis factor (TNF)–induced activation of NF-B. The glycoside also inhibited NF-B activated by carcinogenic and inflammatory agents, such as cigarette smoke condensate, phorbol 12-myristate 13-acetate, okadaic acid, hydrogen peroxide, lipopolysaccharide, and epidermal growth factor. When examined for the mechanism of action, we found that picroliv inhibited activation of IB kinase, leading to inhibition of phosphorylation and degradation of IB. It also inhibited phosphorylation and nuclear translocation of p65. Further studies revealed that picroliv directly inhibits the binding of p65 to DNA, which was reversed by the treatment with reducing agents, suggesting a role for a cysteine residue in interaction with picroliv. Mutation of Cys³⁸ in p65 to serine abolished this effect of picroliv. NF-B inhibition by picroliv leads to suppression of NF-B–regulated proteins, including those linked with cell survival (inhibitor of apoptosis protein 1, Bcl-2, Bcl-xL, survivin, and TNF receptor–associated factor 2), proliferation (cyclin D1 and cyclooxygenase-2), angiogenesis (vascular endothelial growth factor), and invasion (intercellular adhesion molecule-1 and matrix metalloproteinase-9). Suppression of these proteins enhanced apoptosis induced by TNF. Overall, our results show that picroliv inhibits the NF-B activation pathway, which may explain its anti-inflammatory and anticarcinogenic effects. [Cancer Res 2008;68(21):8861–70]

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