The coactivator role of histone deacetylase 3 in IL-1-signaling involves deacetylation of p65 NF-κB.

Histone deacetylase (HDAC) 3, as a cofactor in co-repressor complexes containing silencing mediator for retinoid or thyroid-hormone receptors (SMRT) and nuclear receptor co-repressor (N-CoR), has been shown to repress gene transcription in a variety of contexts. Here, we reveal a novel role for HDAC3 as a positive regulator of IL-1-induced gene expression. Various experimental approaches involving RNAi-mediated knockdown, conditional gene deletion or small molecule inhibitors indicate a positive role of HDAC3 for transcription of the majority of IL-1-induced human or murine genes. This effect was independent from the gene regulatory effects mediated by the broad-spectrum HDAC inhibitor trichostatin A (TSA) and thus suggests IL-1-specific functions for HDAC3. The stimulatory function of HDAC3 for inflammatory gene expression involves a mechanism that uses binding to NF-κB p65 and its deacetylation at various lysines. NF-κB p65-deficient cells stably reconstituted to express acetylation mimicking forms of p65 (p65 K/Q) had largely lost their potential to stimulate IL-1-triggered gene expression, implying that the co-activating property of HDAC3 involves the removal of inhibitory NF-κB p65 acetylations at K122, 123, 314 and 315. These data describe a novel function for HDAC3 as a co-activator in inflammatory signaling pathways and help to explain the anti-inflammatory effects frequently observed for HDAC inhibitors in (pre)clinical use.

Calcium-dependent membrane association sensitizes soluble guanylyl cyclase to nitric oxide.

Nitric oxide (NO) is a ubiquitous, cell-permeable intercellular messenger. The current concept assumes that NO diffuses freely through the plasma membrane into the cytoplasm of a target cell, where it activates its cytosolic receptor enzyme, soluble guanylyl cyclase (sGC). Recent evidence, however, suggests that cellular membranes are not only the predominant site of calcium-dependent NO synthesis, but also the site of its distribution and binding. Here we extend this concept to NO signalling to show that active sGC is partially associated with the plasma membrane in a state of enhanced NO sensitivity. After cellular activation, sGC further translocates to the membrane fraction in human platelets and associates with the NO-synthase-containing caveolar fraction in rat lung endothelial cells, in a manner that is dependent on the concentration of intracellular calcium. Our data suggest that the entire NO signalling pathway is more spatially confined than previously assumed and that sGC dynamically translocates to the plasma membrane, where it is sensitized to NO.