Enzymes from the histone deacetylase (HDAC) family are highly regulated by different mechanisms. However, only very limited knowledge exists about the regulation of HDAC8, an established target in multiple types of cancer. A previous dedicated study of HDAC class I enzymes identified no redox-sensitive cysteinyl thiol in HDAC8. This is in contrast to the observation that HDAC8 preparations show different enzyme activities depending on the addition of reducing agents. In the light of the importance of HDAC8 in tumorigenesis a possible regulation by redox signaling was investigated using biochemical and biophysical methods combined with site directed mutagenesis. The occurrence of a characteristic disulfide bond under oxidizing conditions is associated with a complete but reversible loss of enzyme activity. Cysteines 102 and 153 are the integral components of the redox-switch. A possible regulation of HDAC8 by redox signal transduction is suggested by the observed relationship between inhibition of reactive oxygen species generating NOX and concomitant increased HDAC8 activity in neuroblastoma tumor cells. The slow kinetics for direct oxidation of HDAC8 by hydrogen peroxide suggests that transmitters of oxidative equivalents are required to transfer the H2O2 signal to HDAC8.

Human histoned eacetylase 8i saw ell-recognized target forT-cell lymphomaa nd particularly childhoodn euroblastoma. PD-404,182 was shown to be as elective covalent inhibitor of HDAC8t hat formsm ixed disulfides with several cysteine residues and is also able to transform thiol groups to thiocyanates. Moreover,H DAC8 was shown to be regulated by ar edox switch based on the reversible formation of a disulfideb ond between cysteines Cys 102 andC ys 153 .T his study on the distinct effects of PD-404,182 on HDAC8 reveals that this compound induces the dose-dependent formationo fi ntramolecular disulfide bridges. Therefore,t he inhibition mechanism of HDAC8b yP D-404,182 involves both, covalentmodification of thiols as well as ligand mediated disulfide formation. Moreover,t his study provides ad eep moleculari nsighti ntot he regulation mechanismo fH DAC8i nvolvings everal cysteines with graduated capability to form reversible disulfide bridges.

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Photochemical reactions typically proceed via multiple reaction pathways, yielding a variety of isomers and products. Enhancing the selectivity is challenging. Now, the potential of supramolecular control for oxidative photocyclization of a tetraarylethylene, containing a stereogenic -C=C- bond, is demonstrated. In solution, this photochemical reaction produces three constitutional isomers (substituted phenanthrenes), with slow kinetics. When the reactant is assembled into a crystalline framework, only one product forms with accelerated kinetics. Key to this selectivity enhancement is the integration into a surface grown metal-organic framework (SURMOF); the dramatic gain in selectivity is ascribed to the hindrance of the rotational freedom of the -C=C- double bond. The structure of the MOF is key; the corresponding reaction in the solid does not result in such a high increase in selectivity. A striking change of luminescence properties after photocyclization is observed.