Dimethylsulfoxide gold-thallium complexes. Effects of the metal-metal interactions in the luminescence

The heteropolynuclear complexes [AuTl(C₆X₅)₂]_n (X = F, Cl) react with dimethylsulfoxide (DMSO) in different molar ratios leading to products of stoichiometry [Tl₂{Au(C₆F₅)₂}₂{μ-DMSO}₃]_n (1), and [Tl₂{Au(C₆Cl₅)₂}₂{μ-DMSO}₂]_n (2). These complexes have been structurally characterized and can be viewed as extended linear chains built with Tl-Au-Tl units in which the thallium atoms are bridged by the oxygen atoms of DMSO ligands. Additional [Au(C₆X₅)₂]⁻ fragments interact with one or two thallium centres, respectively, giving rise to two different types of metal-metal interactions in each molecule. Both of them show a strong luminescence in solid state and complex 2 also in solution. The thallium-thallium interaction in this complex is considered to be the responsible of its luminescence, which remains in solution.     

Intracellular redox equilibrium is essential for the constitutive expression of AP-1 dependent genes in resting cells: studies on TGF-β1 regulation

The mechanisms involved in the continuous expression of constitutive genes are unclear. We hypothesize that steady state intracellular reactive oxygen species (ROS), which their levels are tightly maintained, could be regulating the expression of these constitutive genes in resting cells. We analyzed the regulation of an important constitutive gene, TGF-β1, after decreasing intracellular ROS concentration in human mesangial cells. Decreased intracellular hydrogen peroxide by catalase addition reduced TGF-β1 protein, mRNA expression and promoter activity. Furthermore, catalase decreased the basal activity of Activated Protein-1 (AP-1) that regulates TGF-β1 promoter activity. This effect disappeared when AP-1 binding site was removed. Similar results were observed with another protein containing AP-1 binding sites in its promoter, such as eNOS, but it was not the case in other constitutive genes without any AP-1 binding site, as COX1 or PKG1. The pharmacological inhibition of the different ROS synthesis sources by blocking NADPH oxidase, the mitochondrial respiratory chain or xanthine oxidase, or the use of human fibroblasts with genetically deficient mitochondrial activity, induced a similar, significant reduction of steady state ROS concentration as the one observed with catalase. Moreover, there was decreased TGF-β1 expression in all the cases excepting the xanthine oxidase blockade. These findings suggest a novel role for the steady state intracellular ROS concentration, where the compartmentalized, different systems involved in the intracellular ROS production, could be essential for the expression of constitutive AP1-dependent genes, as TGF-β1.