Integration of G-protein coupled receptor signaling pathways for activation of a transcription factor (EGR-3)

Activation of p38 mitogen-activated protein kinase by norepinephrine in T-lineage cells

The catecholamine norepinephrine (NE) stimulates T lymphocytes through a beta-adrenergic receptor (βAR)/adenylyl cyclase (AC)/cyclic AMP (cAMP)/protein kinase A (PKA) pathway, leading to altered cell responsiveness and apoptosis. p38 Mitogen-activated protein kinase (MAPK), a major intracellular signalling mediator for cellular and environmental stressors, is involved in the production of immune modulators and in the regulation of T-cell development, survival and death. In these studies we investigated the relationship among NE signalling, p38 MAPK activity and T-cell death. We showed that NE stimulation of BALB/c mouse thymocytes and S49 thymoma cells selectively increases the dual phosphorylation and activity of p38α MAPK. p38 MAPK activation involves the βAR, Gs protein, AC, cAMP and PKA, as determined through the use of a βAR antagonist, activators of AC and cAMP, and S49 clonal mutants deficient in Gs and PKA. Dual phosphorylation of p38 MAPK is also dependent on its own catalytic activity. Inhibition of p38 MAPK activity revealed its involvement in cAMP-mediated activating transcription factor-2 (ATF-2) phosphorylation, Fas ligand messenger RNA (mRNA) up-regulation, and cell death. These results identify a mechanism through which NE stimulation of the βAR/Gs/PKA pathway activates p38 MAPK, which can be potentiated by autophosphorylation, and leads to changes in T-cell dynamics, in part through the regulation of Fas ligand mRNA expression.

Neurocognitive deficits in major depression and a new theory of ADHD: a model of impaired antagonism of cholinergic-mediated prepotent behaviours in monoamine depleted individuals

The study builds on the propositions introduced in a companion paper on the neuropharmacology of cognition and its relation to key findings in psychiatry. Cognitive inhibition is often invoked to explain performance in psychiatric illness. Yet it remains only a general conceptual model of executive dysfunction. Premotor theory proposes both neuroanatomical and neuropharmacological equivalents of conscious and unconscious processes. The interaction between monoaminergic and cholinergic neurotransmission is stated to have an inverse effect on these two fundamental psychological processes. If one conceives of cognitive inhibition as a failure to voluntarily suppress unconscious prepotent responses, then a deficit in monoaminergic antagonism of cholinergic facilitated prepotent responses accounts for the observed behavioural phenotypes. The plasticity of behaviour is further hypothesized to have an equivalent in intracellular signalling leading to plastic changes in neural networks. Apart from inhibition of prepotent responses it permits the formulation of new behavioural phenotypes. At the receptor level Gi-Gq/11 transduction coupling is proposed to mediate this effect. A hypofunctioning monoaminergic system is thought to underlie the clinical pictures of major depression and ADHD. The neurocognitive deficits of depression include memory loss, poor concentration and rumination. ADHD is characterized by inattention, impulsivity and hyperactivity. Both these syndromes effectively respond to raising serotonin and dopamine levels, respectively. The core symptoms can usefully be attributed to an imbalance between the neuromodulatory effects of monoamines and ACh. Taking the model of monoaminergic-muscarinic receptor interactions presented previously and extended here, a new hypothesis is proposed for the core symptoms of ADHD. Accordingly, impulsivity and hyperactivity result from impaired dopaminergic inhibition and remodelling of muscarinic mediated prepotent responses. The model also predicts memory impairment in major depression by proposing that low serotonin levels in the neocortex is linked to focal hippocampal dysfunction. Hippocampal theta is proposed to trigger phasic monoaminergic activation involved in encoding of cortical traces and plasticity of propotent networks. It proposes a hypothesis for the enhancement of mood and behaviour induced by antidepressants is partly a response to plasticity of neural networks, that is, remodelling of cholinergic-mediated negative habitual behaviours.

The CXCR4 antagonist AMD3100 releases a subset of G-CSF-primed peripheral blood progenitor cells with specific gene expression characteristics

OBJECTIVE

AMD3100 is a new CXCR4 antagonist that induces a rapid release of hematopoietic progenitors from the bone marrow to the peripheral blood. We conducted a clinical study where patients with multiple myeloma and non-Hodgkin's lymphoma were treated with AMD3100 (A) to increase the number of peripheral blood progenitor cells (PBPCs) when given a mobilization regimen of granulocyte colony-stimulating factor (G-CSF, G). Because experimental data suggest that A+G-mobilized PBPCs are functionally different from G-mobilized PBPCs, we were interested in an intraindividual comparison of the gene expression profile of CD34+ cells in the two different settings.

METHODS

To this end peripheral blood CD34+ cells of three patients (three G, three A+G samples) were isolated by immunomagnetic followed by flow cytometric sorting to a purity of >99%. Total RNA was purified. Differentially expressed genes were analyzed by using the Affymetrix GeneChip Human Genome U133 Plus2.0 and the software package Micro Array Solutions 1.3 (SAS Institute Inc.).

RESULTS

We found a pattern of unanimously higher (81 genes, log2 ratio > 0.5; p < 0.0001) or lower (29 genes, log2 ratio < -0.4; p < 0.0001) expressed genes in the A+G-mobilized vs G-mobilized CD34+ PBPCs. Significant changes of four selected genes noted in the microarray analysis were validated by quantitative real-time polymerase chain reaction. Genes were grouped according to gene function. Only increased expression was found in the categories antiapoptosis (e.g., MPO, HSPA1B), cell cycle (e.g., MS4A3, RRM2), replication/DNA repair (e.g., MPO, HSPA1B), cell motility (e.g., TNFSF4, HMMR), and oxygen transport. Decreased expression occurred in the proapoptosis gene group (e.g., MDA5, BCL10). CXCR4 receptor gene expression itself was significantly 1.5-fold higher in the A+G vs G group.

CONCLUSION

We conclude that A+G-mobilized CD34+ PBPCs express significantly higher amounts of genes that potentially promote superior engraftment after myeloablative therapy than G-mobilized CD34+ PBPCs.

Phosphatidylinositol 3-Kinase in the G Protein-Coupled Receptor–Induced Chemokinesis and Chemotaxis of MDA-MB-468 Breast Carcinoma Cells: A Comparison with Leukocytes

The polarization of tumor cells and leukocytes into a front end and a rear end is a crucial prerequisite for their autonomous, directed movement. Phosphatidylinositol 3-kinase (PI3K) is assumed to play an important role in this polarization process, whereas the results obtained with different cell types and different migration assays widely vary. Thus, we conducted a comparative study on the role of the PI3K in the locomotor activity and directionality of the migration of tumor cells on the example of MDA-MB-468 breast carcinoma cells in comparison with CTLs and neutrophil granulocytes. We used our well-established, collagen-based, three-dimensional migration assay for the investigation of the chemokinesis and chemotaxis of these cells. Our results show that the role of the PI3K in the regulation of migratory activity is distinct between the investigated cell types: the migration of CTLs and MDA-MB-468 cells was impaired by the inhibition of the PI3K with wortmannin, whereas neutrophil granulocytes were only slightly affected. However, neither cell type was impaired in the ability to respond chemotactically to gradients of ligands to G protein-coupled receptors. Thus, the PI3K contributes to the regulation of migratory activity but not to the directionality of migration of MDA-MB-468 breast carcinoma cells. As a further conclusion with regard to cancer treatment, the PI3K is not a suitable target for the inhibition of metastasis formation, because the migration of leukocytes is also affected, which leads to a dysfunction of the immune defense.

Multiplexing Fluo-4 NW and a GeneBLAzer® Transcriptional Assay for High-Throughput Screening of G-Protein-Coupled Receptors

Activation of G-protein-coupled receptors (GPCRs) leads to a cascade of signaling events, including calcium mobilization and downstream transcriptional activation of various proteins. Two commonly used methods of high-throughput screening for GPCRs include calcium-sensitive dyes, such as Fluo-4 NW, and reporter gene assays, such as beta-lactamase. To determine whether the advantages of each assay format could be combined by multiplexing, Jurkat and CHO-K1 cell lines over-expressing the M1 muscarinic receptor and beta-lactamase under control of an NFAT response element were tested in a multiplexed format. The Jurkat cell line was further screened with a subset of the LOPAC1280 library. The multiplexing assay was compatible with both the CHO-K1 and Jurkat cell lines. For the screen, there was 100% correlation of on-target hits in the multiplexed format, and several false positives with each assay format were identified. Therefore, not only can the assays be multiplexed, but by multiplexing, the false positives associated with each assay format also could be easily identified. In addition to enhanced reliability, this method saves time and money because only half the amount of compounds, cells, and consumables are needed to screen a cell line in a multiplexed mode versus separate screening by both methods.