Interferon beta-1a counteracts effects of activation on the expression of G-protein-coupled receptor kinases 2 and 3, beta-arrestin-1, and regulators of G-protein signalling 2 and 16 in human mononuclear leukocytes

Role of Regulators of G Protein Signaling Proteins in Bone Physiology and Pathophysiology

Regulators of G protein signaling (RGS) proteins enhance the intrinsic GTPase activity of α subunits of the heterotrimeric G protein complex of G protein-coupled receptors (GPCRs) and thereby inactivate signal transduction initiated by GPCRs. The RGS family consists of nearly 37 members with a conserved RGS homology domain which is critical for their GTPase accelerating activity. RGS proteins are expressed in most tissues, including heart, lung, brain, kidney, and bone and play essential roles in many physiological and pathological processes. In skeletal development and bone homeostasis as well as in many bone disorders, RGS proteins control the functions of various GPCRs, including the parathyroid hormone receptor type 1 and calcium-sensing receptor and also regulate various critical signaling pathways, such as Wnt and calcium oscillations. This chapter will discuss the current findings on the roles of RGS proteins in regulating signaling of key GPCRs in skeletal development and bone homeostasis. We also will examine the current updates of RGS proteins' regulation of calcium oscillations in bone physiology and highlight the roles of RGS proteins in selected bone pathological disorders. Despite the recent advances in bone and mineral research, RGS proteins remain understudied in the skeletal system. Further understanding of the roles of RGS proteins in bone should not only provide great insights into the molecular basis of various bone diseases but also generate great therapeutic drug targets for many bone diseases.

Role of regulator of G protein signaling proteins in bone

Regulators of G protein signaling (RGS) proteins are a family with more than 30 proteins that all contain an RGS domain. In the past decade, increasing evidence has indicated that RGS proteins play crucial roles in the regulation of G protein coupling receptors (GPCR), G proteins, and calcium signaling during cell proliferation, migration, and differentiation in a variety of tissues. In bone, those proteins modulate bone development and remodeling by influencing various signaling pathways such as GPCR-G protein signaling, Wnt, calcium oscillations and PTH. This review summarizes the recent advances in the understanding of the regulation of RGS gene expression, as well as the functions and mechanisms of RGS proteins, especially in regulating GPCR-G protein signaling, Wnt signaling, calcium oscillations signaling and PTH signaling during bone development and remodeling. This review also highlights the regulation of different RGS proteins in osteoblasts, chondrocytes and osteoclasts. The knowledge from the recent advances of RGS study summarized in the review would provide the insights into new therapies for bone diseases.

β-Arrestins in the immune system

β-Arrestins regulate G protein-coupled receptors through receptor desensitization while also acting as signaling scaffolds to facilitate numerous effector pathways. Recent studies have provided evidence that β-arrestins play a key role in inflammatory responses. Here, we summarize these advances on the roles of β-arrestins in immune regulation and inflammatory responses under physiological and pathological conditions, with an emphasis on translational implications of β-arrestins on human diseases.

R4 regulators of G protein signaling (RGS) identify an ancient MHC-linked synteny group

Regulators of G protein signaling (RGS) are key regulators of G protein signaling. RGS proteins of the R4 RGS group are composed of a mere RGS domain and are mainly involved in immune response modulation. In both human and mouse, most genes encoding the R4 RGS proteins are located in the same region of chromosome 1. We show here that the RGS1/RGS16 neighborhood constitutes a synteny group well conserved across tetrapods and closely linked to the MHC paralogon of chromosome 1. Genes located in the RGS1/RGS16 region have paralogs close to the MHC on chromosome 6 or close to the other MHC paralogons. In amphioxus, a cephalochordate, these genes possess orthologs that are located in the same scaffolds as a number of markers defining the proto-MHC in this species (Abi-Rached et al., Nat Genet 31:100-115, 2002). We therefore propose that the RGS1/RGS16 region provides useful markers to investigate the origins and the evolution of the MHC. In addition, we show that some genes of the region appear to have immune functions not only in human, but also in Xenopus.

A finer tuning of G-protein signaling through regulated control of RGS proteins

Regulators of G-protein signaling (RGS) proteins are GTPase-activating proteins (GAP) for various Gα subunits of heterotrimeric G proteins. Through this mechanism, RGS proteins regulate the magnitude and duration of G-protein-coupled receptor signaling and are often referred to as fine tuners of G-protein signaling. Increasing evidence suggests that RGS proteins themselves are regulated through multiple mechanisms, which may provide an even finer tuning of G-protein signaling and crosstalk between G-protein-coupled receptors and other signaling pathways. This review summarizes the current data on the control of RGS function through regulated expression, intracellular localization, and covalent modification of RGS proteins, as related to cell function and the pathogenesis of diseases.

β-Arrestin 1 modulates functions of autoimmune T cells from primary biliary cirrhosis patients

OBJECTIVES

Primary biliary cirrhosis (PBC) is an autoimmune disease, characterized by antimitochondrial antibodies and autoreactive T cells causing destruction of the primary bile ducts. The molecular mechanisms regulating the autoreactive T cells remain elusive. β-Arrestins (βarr) are multifunctional signaling molecules that are crucial to T cell survival. We hypothesized that βarr plays a critical regulatory function in the autoreactive T cells of PBC patients.

METHODS

Patients with hepatic biliary cirrhosis (n=60) were evaluated. Cytokine expression, T cell proliferation, and transcription factors were evaluated to assess regulatory functions in autoreactive T cells from the patient.

RESULTS

Our studies showed that expression of βarr1 was elevated significantly in T lymphocytes from patients with PBC. Moreover, the level of βarr1 mRNA positively correlated with Mayo risk score in PBC patients. Based on modulation of βarr in autoreactive T cell lines, overexpression of βarr1 increased T cell proliferation, augmented interferon production, downregulated activities of nuclear factor κB and AP-1, promoted acetylation of histone H4 in the promoter regions of CD40L, LIGHT, IL-17 and interferon-γ, while downregulating acetylation of histone H4 in the promoter regions of TRAIL, Apo2, and HDAC7A, thereby regulating expression of these genes.

CONCLUSIONS

Our findings suggest that βarr1 contributes to the pathogenesis of PBC, having significant implications for novel therapy strategy, further providing information for investigating the mechanisms of autoimmune disease.

Network analysis of transcriptional regulation in response to intramuscular interferon-β-1a multiple sclerosis treatment

Interferon-β (IFN-β) is one of the major drugs for multiple sclerosis (MS) treatment. The purpose of this study was to characterize the transcriptional effects induced by intramuscular IFN-β-1a therapy in patients with relapsing-remitting form of MS. By using Affymetrix DNA microarrays, we obtained genome-wide expression profiles of peripheral blood mononuclear cells of 24 MS patients within the first 4 weeks of IFN-β administration. We identified 121 genes that were significantly up- or downregulated compared with baseline, with stronger changed expression at 1 week after start of therapy. Eleven transcription factor-binding sites (TFBS) are overrepresented in the regulatory regions of these genes, including those of IFN regulatory factors and NF-κB. We then applied TFBS-integrating least angle regression, a novel integrative algorithm for deriving gene regulatory networks from gene expression data and TFBS information, to reconstruct the underlying network of molecular interactions. An NF-κB-centered sub-network of genes was highly expressed in patients with IFN-β-related side effects. Expression alterations were confirmed by real-time PCR and literature mining was applied to evaluate network inference accuracy.

Glucocorticoids regulate innate immunity in a model of multiple sclerosis: reciprocal interactions between the A1 adenosine receptor and beta-arrestin-1 in monocytoid cells

Desensitization of seven transmembrane receptors (7TMRs), which are modulated by the beta-arrestins, leads to altered G protein activation. The A1 adenosine receptor (A1AR) is an antiinflammatory 7TMR exhibiting reduced expression and activity in both multiple sclerosis (MS) and the murine MS model, experimental autoimmune encephalomyelitis (EAE) in monocytoid cells. Herein, we report that beta-arrestin-1 expression was increased in brains of MS patients relative to non-MS brains, whereas A1AR expression was concomitantly reduced. This inverse relationship between beta-arrestin-1 and A1AR was confirmed in cultured monocytoid cells as beta-arrestin-1 overexpression resulted in a down-regulation of A1AR together with the internalization of the surface receptor. Moreover, a physical interaction between beta-arrestin-1 and A1AR was demonstrated in monocytoid cells. Proinflammatory cytokines regulated the A1AR/beta-arrestin-1 interactions, while A1AR activation also modulated proinflammatory cytokines expression. During EAE, beta-arrestin-1 and A1AR expression in the spinal cord displayed a similar pattern compared to that observed in MS brains. EAE-induced neuroinflammation and neurobehavioral deficits were suppressed by glucocorticoid treatments, accompanied by concurrent reduced beta-arrestin-1 and enhanced A1AR expression. Thus, the interplay between beta-arrestin-1 and A1AR in the central nervous system during neuroinflammation represents a reciprocal regulatory mechanism through which neuroprotective therapeutic strategies for neuroinflammatory diseases might be further developed.

Paeoniflorin induced immune tolerance of mesenteric lymph node lymphocytes via enhancing beta 2-adrenergic receptor desensitization in rats with adjuvant arthritis

Paeoniflorin (Pae), a monoterpene glucoside, is one of the main bioactive components of total glucosides of paeony (TGP) extracted from the root of Paeonia lactiflora. TGP has anti-inflammatory and immunoregulatory effects. In this study, we investigated the effects of Pae on inflammatory and immune responses to the mesenteric lymph node (MLN) lymphocytes and the mechanisms by which Pae regulates beta 2-adrenergic receptor (beta 2-AR) signal transduction in adjuvant arthritis (AA) rats. The onset of secondary arthritis in rats appeared around day 14 after injection of Freund's complete adjuvant (FCA). Remarkable secondary inflammatory response and lymphocytes proliferation were observed in AA rats, along with the decrease of anti-inflammatory cytokines interleukin (IL)-4 and transforming growth factor-beta 1 (TGF-beta 1) of MLN lymphocytes, and the increase of pro-inflammatory cytokine IL-2. The administration of Pae (50, 100 mg kg(-1), days 17-24) significantly diminished the secondary hind paw swelling and arthritis scores, reversed the changes of cytokines as discussed above, and further decreased the lowered proliferation of MLN lymphocytes in AA rats. In vitro, Pae restored the previously increased level of cAMP of MLN lymphocytes at the concentrations of 12.5, 62.5 and 312.5 mg l(-1). Meanwhile, Pae increased protein expressions of beta 2-AR and GRK2, and decreased that of beta-arrestin 1, 2 of MLN lymphocytes in AA rats. These results suggested that Pae might induce the Th1 cells immune tolerance, which then shift to Th2, Th3 cells mediated activities to take effect the anti-inflammatory and immunoregulatory effects. The mechanisms of Pae on beta 2-AR desensitization and beta 2-AR-AC-cAMP transmembrane signal transduction of MLN lymphocytes play crucial roles in pathogenesis of this disease.

Microarray analysis identifies a set of CXCR3 and CCR2 ligand chemokines as early IFNbeta-responsive genes in peripheral blood lymphocytes in vitro: an implication for IFNbeta-related adverse effects in multiple sclerosis

Background

A substantial proportion of multiple sclerosis (MS) patients discontinue interferon-beta (IFNβ) treatment due to various adverse effects, most of which emerge at the early phase after initiation of the treatment and then diminish with time. At present, the molecular mechanism underlying IFNβ-related adverse effects remains largely unknown. The aim of this study is to identify a comprehensive list of early IFNβ-responsive genes (IRGs) in peripheral blood mononuclear cells (PBMC) that may play a key role in induction of adverse effects.

Methods

Total RNA of PBMC exposed to 50 ng/ml recombinant human IFNβ for 3 to 24 hours in vitro was processed for cDNA microarray analysis, followed by quantitative real-time RT-PCR analysis.

Results

Among 1,258 genes on the array, IFNβ elevated the expression of 107 and 87 genes, while it reduced the expression of 22 and 23 genes at 3 and 24 hours, respectively. Upregulated IRGs were categorized into conventional IFN-response markers, components of IFN-signaling pathways, chemokines, cytokines, growth factors, and their receptors, regulators of apoptosis, DNA damage, and cell cycle, heat shock proteins, and costimulatory and adhesion molecules. IFNβ markedly upregulated CXCR3 ligand chemokines (SCYB11, SCYB10 and SCYB9) chiefly active on effector T helper type 1 (Th1) T cells, and CCR2 ligand chemokines (SCYA8 and SCYA2) effective on monocytes, whereas it downregulated CXCR2 ligand chemokines (SCYB2, SCYB1 and IL8) primarily active on neutrophils.

Conclusion

IFNβ immediately induces a burst of gene expression of proinflammatory chemokines in vitro that have potential relevance to IFNβ-related early adverse effects in MS patients in vivo.

Dopamine fails to regulate activation of peripheral blood lymphocytes from multiple sclerosis patients: effects of IFN-beta

The neurotransmitter dopamine counteracts T cell functions through its specific receptor subtype D5R but favors T cell proliferation and adhesion when acting on D3R. We found diminished mRNA and protein levels of D5R, but not of D3R, in peripheral blood mononuclear cells (PBMCs) from untreated multiple sclerosis (MS) patients. Dopamine reduced T cell proliferation, secretion of interferon-gamma (IFN-gamma), and production of matrix metalloproteinase-9 (MMP-9) mRNA in PBMCs from controls but not from MS patients. By contrast, reduced levels of D3R and renewed dopamine-associated regulatory functions were found in PBMCs from IFN-beta treated MS patients. Failure of the dopaminergic system of lymphocytes may lessen the threshold of T cell activation and sustain the pathogenic cascade of MS.

Different mitogen-mediated Beta-adrenergic receptor modulation in murine T lymphocytes depending on the thyroid status

OBJECTIVE

The aim of this work was to analyze beta-adrenergic receptor (betaAR) regulation of T-lymphocyte proliferation in mice according to different thyroid hormone statuses.

METHODS

T cells from eu-, hypo- (by propylthiouracil treatment) and hyperthyroid (by thyroxine, T4 administration) mice were purified and specific radioligand binding assays were performed. The effects of the beta-agonist isoproterenol (ISO) on intracellular levels of cyclic AMP (cAMP) were determined. Mitogen-induced T-cell proliferation was measured by [(3)H]-thymidine incorporation. Finally, protein kinase C (PKC) activity in cytosol and membrane fractions were determined using radiolabelled enzymatic substrates.

RESULTS

Adecrease or a non-significant increase in betaAR number was found on T lymphocytes from hypo- and hyperthyroid mice compared to euthyroid controls. ISO stimulation of cAMP levels was lower in hypothyroid and higher in hyperthyroid T lymphocytes compared to controls. T-selective mitogen-induced proliferation was increased in T4-treated animals, but decreased in hypothyroid mice. During the peak of proliferation, downregulation of betaAR was observed in all animals. However, a higher or a lower decrease was observed in hyper- and hypothyroid T cells, respectively. In parallel, a higher translocation of PKC activity was observed in hyperthyroid cells, and a lower one was found in hypothyroid lymphocytes with respect to controls.

CONCLUSIONS

These results indicate that intracellular signals triggered by mitogen activation, namely PKC, would be related to differential betaAR downregulation in T lymphocytes depending on the thyroid hormone status, contributing to the distinct proliferative responses found in hypo- or hyperthyroidism compared to the euthyroid state.

Post-receptorial mechanisms underlie functional disregulation of beta2-adrenergic receptors in lymphocytes from Multiple Sclerosis patients

Increased density of beta2-adrenergic receptors has been demonstrated on peripheral blood mononuclear cells (PBMCs) from Multiple Sclerosis (MS) patients. In this study we found that isoproterenol reduces T-cell proliferation and IFNgamma secretion in PBMCs cultures from healthy controls and IFNbeta-treated but not untreated MS patients. Reduced expression levels of G protein coupled receptor kinase (GRK)2/3 (p < 0.05) and increased isoproterenol-induced cAMP accumulation (p < 0.0001) were found in PBMCs from all MS patients. Dibutyryl cAMP reduced the proliferation of PBMCs from all subgroups but in a slighter manner in untreated MS patients. We conclude that signalling through beta2-adrenergic receptors is chronically up-regulated but functionally uncoupled to immunoregulatory functions of lymphocytes from MS patients. Disregulation downstream the cAMP-associated signalling may underlie such a phenomenon.