An iron-oxygen intermediate formed during the catalytic cycle of cysteine dioxygenase.

Cysteine dioxygenase is a key enzyme in the breakdown of cysteine, but its mechanism remains controversial. A combination of spectroscopic and computational studies provides the first evidence of a short-lived intermediate in the catalytic cycle. The intermediate decays within 20 ms and has absorption maxima at 500 and 640 nm.

Resveratrol and cancer: a review.

The various properties of the stilbene phytoalexin Resveratrol provide interesting new avenues of research in the field of chemoprevention and chemotherapy. A particular emphasis is given on xenobiotic-related carcinogenesis.

7-ketocholesterol is an endogenous modulator for the arylhydrocarbon receptor.

We have identified 7-ketocholesterol (7-KC) as an endogenous modulator that inhibits transactivation by the arylhydrocarbon receptor (AhR) through competitive binding against xenobiotic ligands. 7-KC binds AhR and displaces labeled dioxin (2,3,7,8-tetrachlorodibenzo(p)dioxin (TCDD)). IC(50) is 5 x 10(-7) m in vivo and 7 x 10(-6) m in vitro. These figures are consistent with its concentration in human blood plasma and tissues. Association with 7-KC prevents AhR binding to DNA. 7-KC blocks the TCDD-mediated transactivation of stably expressed reporter gene constructs in T47-D cells as well as the expression of the endogenous CYP 1A1 gene in HepG2 cells and in primary porcine aortic endothelial cells. Injection of 7-KC to rats blocks the induction of CYP 1A1 messenger RNA and protein in endothelial cells from myocardial blood vessels. The differential sensitivity of mammalian species to toxic effects of AhR ligands, especially dioxin (TCDD), correlates with the expression of 7-hydroxycholesterol dehydrogenase, which synthesizes 7-KC from 7-hydroxycholesterol. The documented involvement of AhR ligands in cardiovascular diseases through lipid peroxidation and endothelium dysfunction can now be examined in the context of displacement of this protective modulator.

Resveratrol has antagonist activity on the aryl hydrocarbon receptor: implications for prevention of dioxin toxicity.

Aryl hydrocarbon receptor (AhR) ligands such as dioxin and benzo[a]pyrene are environmental contaminants with many adverse health effects, including immunosuppression, carcinogenesis, and endothelial cell damage. We show here that a wine component, resveratrol (3,5,4'-trihydroxystilbene), is a competitive antagonist of dioxin and other AhR ligands. Resveratrol promotes AhR translocation to the nucleus and binding to DNA at dioxin-responsive elements but subsequent transactivation does not take place. Resveratrol inhibits the transactivation of several dioxin-inducible genes including cytochrome P-450 1A1 and interleukin-1beta, both ex vivo and in vivo. Resveratrol has adequate potency and nontoxicity to warrant clinical testing as a prophylactic agent against aryl hydrocarbon-induced pathology.

Specific binding of progesterone receptor to progesterone-responsive elements does not require prior dimerization.

Steroid-hormone receptors undergo, prior to binding to DNA, a hormone-dependent dimerization. It is generally accepted that this dimerization is indispensable for the high-affinity binding of hormone receptor to hormone-responsive elements. Using a progesterone-receptor mutant with the complete steroid-binding domain deleted (positions 663-930), with or without the epitope required for binding the monoclonal antibody Let 126, we have shown that this receptor species was unable to undergo dimerization in solution. However, this mutant retained a high affinity (60-70% of the affinity of the wild-type receptor) for the progesterone-responsive elements of the mouse-mammary-tumor-virus long-terminal-repeat promoter and for a consensus palindromic progesterone-responsive element, as measured by both DNase-I protection experiments and gel-shift experiments. This mutant also increased gene transcription. Thus, at least in the case of the progesterone receptor, prior dimerization is dispensable for receptor binding to regulatory DNA elements and for subsequent transcription activation.

Interaction of an intercalating antitumoral agent: 9-hydroxy-2-methyl ellipticinium (NMHE) with chromatin.

In this work we study the effects of an intercalating antitumoral agent: 9-hydroxy-2-methyl ellipticinium (NMHE) on the structure of chromatin, using micrococcal nuclease and DNase 1 as structural probes. The binding of the drug to chromatin, either in vitro or in the nuclei, induces two structural changes of chromatin: (a) an unfolding of the overall structure which results in an activation of the rate of degradation of chromatin by micrococcal nuclease and (b) a disorganisation of the core particle structure leading to the unwrapping of the DNA from the histone core. Moreover, by studying the interaction of MMHE with nuclei labeled in the active regions of the genome through a nick-translation reaction, it appears that the drug is overconcentrated in these regions and does not induce any new structural changes. The interaction of NMHE with DNase 1-sensitive regions of chromatin indicates that these regions are already "open" or relaxed and represent a preferential target for the drug.