Modification of the cysteine residues in IκBα kinase and NF-κB (p65) by xanthohumol leads to suppression of NF-κB–regulated gene products and potentiation of apoptosis in leukemia cells

Xanthohumol (XN), a prenylated chalcone isolated from hop plant, exhibits anti-inflammatory, antiproliferative, and antiangiogenic properties through an undefined mechanism. Whether examined by intracellular esterase activity, phosphatidylserine externalization, DNA strand breaks, or caspase activation, we found that XN potentiated tumor necrosis factor–induced apoptosis in leukemia and myeloma cells. This enhancement of apoptosis correlated with down-regulation of nuclear factor-κB (NF-κB) survivin, bcl-xL, XIAP, cIAP1, cIAP2, cylin D1, and c-myc. XN down-regulated both constitutive and inducible NF-κB activation, inhibition of phosphorylation and degradation of IκBα, suppression of p65 nuclear translocation, and NF-κB–dependent reporter gene transcription. XN directly inhibited tumor necrosis factor-induced IκBα kinase (IKK) activation and a reducing agent abolished this inhibition, indicating the role of cysteine residue. XN had no effect on the IKK activity when cysteine residue 179 of IKK was mutated to alanine. XN also directly inhibited binding of p65 to DNA, a reducing agent reversed this effect, and mutation of cysteine residue 38 to serine of p65 abolished this effect. Thus, our results show that modification of cysteine residues of IKK and p65 by XN leads to inhibition of the NF-κB activation pathway, suppression of antiapoptotic gene products, and potentiation of apoptosis in leukemia cells

DNA Sequence and Expression Variation of Hop (Humulus lupulus) Valerophenone Synthase (VPS), a Key Gene in Bitter Acid Biosynthesis

† Background The hop plant (Humulus lupulus) is a source of many secondary metabolites, with bitter acids essential in the beer brewing industry and others having potential applications for human health. This study investigated variation in DNA sequence and gene expression of valerophenone synthase (VPS), a key gene in the bitter acid bio-synthesis pathway of hop. † Methods Sequence variation was studied in 12 varieties, and expression was analysed in four of the 12 varieties in a series across the development of the hop cone. † Results Nine single nucleotide polymorphisms (SNPs) were detected in VPS, seven of which were synonymous. The two non-synonymous polymorphisms did not appear to be related to typical bitter acid profiles of the varieties studied. However, real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analysis of VPS expression during hop cone development showed a clear link with the bitter acid content. The highest levels of VPS expression were observed in two triploid varieties, ‘Symphony’ and ‘Ember’, which typically have high bitter acid levels. †Conclusions In all hop varieties studied, VPS expression was lowest in the leaves and an increase in expression was consistently observed during the early stages of cone development