Cardiotonic Steroids Stabilize Regulator of G Protein Signaling 2 Protein Levels

Sjögren, Benita; Parra, Sergio; Heath, Lauren; Atkins, Kevin B.; Xie, Zie Jian; Neubig, Richard R.

doi:10.1124/mol.112.079293

Cited by 25 publications

(49 citation statements)

References 60 publications

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“…Strategies to target regulation of RGS protein expression have focused on post-translational mechanisms that control protein stability (Sjögren et al, 2012;Raveh et al, 2014). In contrast, our data suggest predominantly transcriptional regulation of Rgs10 expression.…”

Section: Discussioncontrasting

confidence: 55%

“…Given the ability of RGS10 to regulate inflammatory signaling, understanding the mechanisms that control RGS10 levels in microglia may reveal new therapeutic strategies to address neuroinflammatory disease. The most commonly described mechanism for regulation of RGS protein abundance involves critical post-translational mechanisms that control protein stability (Sjögren et al, 2012;Raveh et al, 2014). However, our studies in ovarian cancer cells suggest that Rgs10 is transcriptionally regulated by DNA and histonetargeted epigenetic mechanisms (Ali et al, 2013;Cacan et al, 2014).…”

Section: Introductioncontrasting

confidence: 43%

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Regulator of G Protein Signaling 10 (Rgs10) Expression Is Transcriptionally Silenced in Activated Microglia by Histone Deacetylase Activity

et al. 2016

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RGS10 has emerged as a key regulator of proinflammatory cytokine production in microglia, functioning as an important neuroprotective factor. Although RGS10 is normally expressed in microglia at high levels, expression is silenced in vitro following activation of TLR4 receptor. Given the ability of RGS10 to regulate inflammatory signaling, dynamic regulation of RGS10 levels in microglia may be an important mechanism to tune inflammatory responses. The goals of the current study were to confirm that RGS10 is suppressed in an in vivo inflammatory model of microglial activation and to determine the mechanism for activation-dependent silencing of Rgs10 expression in microglia. We demonstrate that endogenous RGS10 is present in spinal cord microglia, and RGS10 protein levels are suppressed in the spinal cord in a nerve injury-induced neuropathic pain mouse model. We show that the histone deacetylase (HDAC) enzyme inhibitor trichostatin A blocks the ability of lipopolysaccharide (LPS) to suppress Rgs10 transcription in BV-2 and primary microglia, demonstrating that HDAC enzymes are required for LPS silencing of Rgs10. Furthermore, we used chromatin immunoprecipitation to demonstrate that H3 histones at the Rgs10 proximal promoter are deacetylated in BV-2 microglia following LPS activation, and HDAC1 association at the Rgs10 promoter is enhanced following LPS stimulation. Finally, we have shown that sphingosine 1-phosphate, an endogenous microglial signaling mediator that inhibits HDAC activity, enhances basal Rgs10 expression in BV-2 microglia, suggesting that Rgs10 expression is dynamically regulated in microglia in response to multiple signals.

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Section: Discussioncontrasting

confidence: 55%

Section: Introductioncontrasting

confidence: 43%

Regulator of G Protein Signaling 10 (Rgs10) Expression Is Transcriptionally Silenced in Activated Microglia by Histone Deacetylase Activity

et al. 2016

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“…Low RGS2 protein levels are associated with hypertension and other cardiovascular pathologies (Heximer et al, 2003;Takimoto et al, 2009;Tsang et al, 2010) and could also be involved in the progression of prostate and breast cancer (Cao et al, 2006;Lyu et al, 2015). In our initial screen, we identified digoxin and other cardiotonic steroids as selective stabilizers of RGS2 protein levels (Sjögren et al, 2012). In subsequent work, we demonstrated that digoxin is protective in a murine model of cardiac injury, an effect that was lost in RGS2 À/À mice (Sjögren et al, 2016b).…”

Section: Advances In Rgs Protein Drug Discovery -From Biochemical Actmentioning

confidence: 99%

“…Several RGS proteins are downregulated during pathological insults so finding ways to increase their expression, and thereby function, is an attractive alternative strategy to achieve this goal. This encouraged us to develop a cell based enzyme complementation assay to screen for small molecule stabilizers of RGS2 (Sjögren et al, 2012;Raveh et al, 2014). As discussed above, RGS2 is one of several RGS proteins that is rapidly degraded through the ubiquitin-proteasomal pathway.…”

Section: Advances In Rgs Protein Drug Discovery -From Biochemical Actmentioning

confidence: 99%

The evolution of regulators of G protein signalling proteins as drug targets – 20 years in the making: IUPHAR Review 21

Sjögren

2017

British J Pharmacology

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Regulators of G protein signalling (RGS) proteins are celebrating the 20th anniversary of their discovery. The unveiling of this new family of negative regulators of G protein signalling in the mid-1990s solved a persistent conundrum in the G protein signalling field, in which the rate of deactivation of signalling cascades in vivo could not be replicated in exogenous systems. Since then, there has been tremendous advancement in the knowledge of RGS protein structure, function, regulation and their role as novel drug targets. RGS proteins play an important modulatory role through their GTPase-activating protein (GAP) activity at active, GTP-bound Gα subunits of heterotrimeric G proteins. They also possess many non-canonical functions not related to G protein signalling. Here, an update on the status of RGS proteins as drug targets is provided, highlighting advances that have led to the inclusion of RGS proteins in the IUPHAR/BPS Guide to PHARMACOLOGY database of drug targets.Abbreviations DEP, Disheveled Egl-10 Pleckstrin; GAP, GTPase-activating protein; GGL, G protein γ-like; PPI, protein-protein interaction; RGS, regulator of G protein signalling; R7BP, R7 binding protein; R9AP, RGS9 associated protein IntroductionG protein-mediated signalling pathways have played a pivotal role in drug discovery and development for many decades. The large family of GPCRs or their downstream effectors are the target of 40% of clinically used drugs and thus represent a multi-billion-dollar industry (Wise et al., 2002). Interestingly, of the more than 300 non-olfactory GPCRs known, only a fraction of them are targeted by drugs. Thus, there is a large untapped area of drug development still available. Moreover, many GPCR drugs are associated with low efficacy and/or side effects. More targeted therapies are therefore required, and as we learn more about the structure and function of GPCRs and their regulators, these goals will be achievable.All biological signals are tightly regulated and for every on-switch there is usually an off-switch. GPCRs are activated by ligands, transmitting signalling information to Gα subunits of heterotrimeric G proteins by enhancing the exchange of GDP for GTP in the Gα nucleotide binding site, which results in the dissociation of Gα from Gβγ dimers and activation of both G protein components. Deactivation of G proteins does not occur by simple reversal of nucleotide exchange, but rather by an independently regulated GTPase activity, hydrolyzing GTP to GDP. Although Gα proteins possess an intrinsic ability to hydrolyze GTP, this process is very slow and cannot account for the transient nature of intracellular signalling cascades in vivo. Hence, additional kinetic mechanisms are required for the physiological timing of signals. One of the most critical of these kinetic mechanisms is mediated through regulator of G protein signalling (RGS) proteins, which have received increasing interest as novel drug targets in the past two decades. As a result, RGS proteins have now been added as the most recent ad...

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“…Finally, RGS2 expression was also found to be increased in patients with Bartter's/Gitelman's syndrome, a disorder characterized by low blood pressure (Calò et al, 2004). RGS2 protein levels are highly regulated by proteasomal degradation (Bodenstein et al, 2007;Sjögren et al, 2012). This rapid degradation of RGS2 and other RGS proteins by proteasomal mechanisms provides a useful control point at which to pharmacologically modulate RGS levels and function .…”

Section: Introductionmentioning

confidence: 99%

Digoxin-Mediated Upregulation of RGS2 Protein Protects against Cardiac Injury

Sjögren

Parra

Atkins

et al. 2016

Journal of Pharmacology and Experimental Therapeutics

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Regulator of G protein signaling (RGS) proteins have emerged as novel drug targets since their discovery almost two decades ago. RGS2 has received particular interest in cardiovascular research due to its role in regulating G q signaling in the heart and vascular smooth muscle. RGS22/2 mice are hypertensive, prone to heart failure, and display accelerated kidney fibrosis. RGS2 is rapidly degraded through the proteasome, and human mutations leading to accelerated RGS2 protein degradation correlate with hypertension. Hence, stabilizing RGS2 protein expression could be a novel route in treating cardiovascular disease. We previously identified cardiotonic steroids, including digoxin, as selective stabilizers of RGS2 protein in vitro. In the current study we investigated the functional effects of digoxin-mediated RGS2 protein stabilization in vivo. Using freshly isolated myocytes from wild-type and RGS22/2 mice treated with vehicle or low-dose digoxin (2 mg/kg/day for 7 days) we demonstrated that agonist-induced cAMP levels and cardiomyocyte contractility was inhibited by digoxin in wild-type but not in RGS2 2/2 mice. This inhibition was accompanied by an increase in RGS2 protein levels in cardiomyocytes as well as in whole heart tissue. Furthermore, digoxin had protective effects in a model of cardiac injury in wild-type mice and this protection was lost in RGS2 2/2 mice. Digoxin is the oldest known therapy for heart failure; however, beyond its activity at the Na 1 /K 1 -ATPase, the exact mechanism of action is not known. The current study adds a novel mechanism, whereby through stabilizing RGS2 protein levels digoxin could exert its protective effects in the failing heart.

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Cardiotonic Steroids Stabilize Regulator of G Protein Signaling 2 Protein Levels

Cited by 25 publications

References 60 publications

Regulator of G Protein Signaling 10 (Rgs10) Expression Is Transcriptionally Silenced in Activated Microglia by Histone Deacetylase Activity

Regulator of G Protein Signaling 10 (Rgs10) Expression Is Transcriptionally Silenced in Activated Microglia by Histone Deacetylase Activity

The evolution of regulators of G protein signalling proteins as drug targets – 20 years in the making: IUPHAR Review 21

Digoxin-Mediated Upregulation of RGS2 Protein Protects against Cardiac Injury

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