CDK8 and CDK19: positive regulators of signal-induced transcription and negative regulators of Mediator complex proteins

We have conducted a detailed transcriptomic, proteomic and phosphoproteomic analysis of CDK8 and its paralog CDK19, alternative enzymatic components of the kinase module associated with transcriptional Mediator complex and implicated in development and diseases. This analysis was performed using genetic modifications of CDK8 and CDK19, selective CDK8/19 small molecule kinase inhibitors and a potent CDK8/19 PROTAC degrader. CDK8/19 inhibition in cells exposed to serum or to agonists of NFκB or protein kinase C (PKC) reduced the induction of signal-responsive genes, indicating a pleiotropic role of Mediator kinases in signal-induced transcriptional reprogramming. CDK8/19 inhibition under basal conditions initially downregulated a small group of genes, most of which were inducible by serum or PKC stimulation. Prolonged CDK8/19 inhibition or mutagenesis upregulated a larger gene set, along with a post-transcriptional increase in the proteins comprising the core Mediator complex and its kinase module. Regulation of both RNA and protein expression required CDK8/19 kinase activities but both enzymes protected their binding partner cyclin C from proteolytic degradation in a kinase-independent manner. Analysis of isogenic cell populations expressing CDK8, CDK19 or their kinase-inactive mutants revealed that CDK8 and CDK19 have the same qualitative effects on protein phosphorylation and gene expression at the RNA and protein levels, whereas differential effects of CDK8 versus CDK19 knockouts were attributable to quantitative differences in their expression and activity rather than different functions.

Time-delayed feedback control of coherence resonance near subcritical Hopf bifurcation: theory versus experiment

Using the model of a generalized Van der Pol oscillator in the regime of subcritical Hopf bifurcation, we investigate the influence of time delay on noise-induced oscillations. It is shown that for appropriate choices of time delay, either suppression or enhancement of coherence resonance can be achieved. Analytical calculations are combined with numerical simulations and experiments on an electronic circuit.

Synchronization of multi-frequency noise-induced oscillations

Using a model system of FitzHugh-Nagumo type in the excitable regime, the similarity between synchronization of self-sustained and noise-induced oscillations is studied for the case of more than one main frequency in the spectrum. It is shown that this excitable system undergoes the same frequency lockings as a self-sustained quasiperiodic oscillator. The presence of noise-induced both stable and unstable limit cycles and tori, as well as their tangential bifurcations, are discussed. As the FitzHugh-Nagumo oscillator represents one of the basic neural models, the obtained results are of high importance for neuroscience.

Translocation of p21rac2 from cytosol to plasma membrane is neither necessary nor sufficient for neutrophil NADPH oxidase activity

Activation of the membrane-associated NADPH oxidase of neutrophils requires several cytosolic factors including p47phox, p67phox and p21rac2. We compared NADPH oxidase activity with the membrane translocation of p47phox, p67phox, and p21rac2. In a cell-free system, GTP gamma S stimulated translocation of p47phox and p67phox to the plasma membrane only in the presence of arachidonate, and this translocation correlated with NADPH oxidase activity of the reisolated plasma membranes (R = 0.94 and 0.97, respectively). In contrast, GTP gamma S-stimulated p21rac2 translocation with or without arachidonate, and the extent of translocation did not correlate with oxidase activity (R = 0.17). Neutrophil cytoplasts were used to relate membrane translocation of p47phox, p67phox and p21rac2 to membrane oxidase activity in response to the inflammatory agonists. Whereas N-formyl-methionyl-leucyl-phenylalanine stimulated equimolar, transient membrane translocation of p47phox and p67phox which kinetically paralleled NADPH oxidase activity, relatively little p21rac2 translocated (moles of p47phox/p21rac2 = 16.6). Moreover, although phorbol 12-myristate 13-acetate stimulated both the stable translocation of p47phox and p67phox and sustained NADPH oxidase activity, it did not stimulate p21rac2 translocation. From these data we conclude that membrane translocation of p21rac2 does not regulate NADPH oxidase activity stoichiometrically.

Activation-dependent carboxyl methylation of neutrophil G-protein gamma subunit

The gamma subunits of heterotrimeric guanine nucleotide-binding regulatory (G) proteins (G gamma) are post-translationally processed at their C termini by prenylation, proteolysis, and carboxyl methylation. Whereas prenylation of G gamma is required for membrane association of G proteins, the role of carboxyl methylation is unknown. Here we show that human neutrophils express G gamma 2 but not G gamma 3 or G gamma 7 and that carboxyl methylation of G gamma 2 is associated with signal transduction. In a reconstituted cell-free system, neutrophil G gamma 2 was labeled by the methyl donor S-[methyl-3H]adenosyl-L-methionine. Carboxyl methylation was confirmed by alkaline hydrolysis and quantitation of volatile [3H]methanol. Neutrophil G gamma 2 methylation was stimulated by activation of G protein with guanosine 5'-[beta, gamma-thio]triphosphate. We estimate that after 1 hr of G-protein activation at least 6% of the total pool of G gamma 2 was carboxyl-methylated. The inflammatory agonist fMet-Leu-Phe stimulated guanosine 5'-[beta,gamma-thio]triphosphate-dependent carboxyl methylation. Methylation of G gamma 2 was inhibited by the carboxyl methyltransferase inhibitor N-acetyl-S-trans,trans-farnesylcysteine at concentrations that affected signal transduction in neutrophils. These results demonstrate that activation of neutrophil Gi is associated with alpha-carboxyl methyl esterification of G gamma 2 and suggest that carboxyl methylation of G gamma may play a role in signal transduction.