Regulation of Stress Granule Formation by Inflammation, Vascular Injury, and Atherosclerosis

Objective: Stress granules (SGs) are dynamic cytoplasmic aggregates containing mRNA, RNA-binding proteins, and translation factors that form in response to cellular stress. SGs have been shown to contribute to the pathogenesis of several human diseases, but their role in vascular diseases is unknown. This study shows that SGs accumulate in vascular smooth muscle cells (VSMCs) and macrophages during atherosclerosis. Approach and Results: Immunohistochemical analysis of atherosclerotic plaques from LDLR − /− mice revealed an increase in the stress granule-specific markers Ras-G3BP1 (GTPase-activating protein SH3 domain-binding protein) and PABP (poly-A-binding protein) in intimal macrophages and smooth muscle cells that correlated with disease progression. In vitro, PABP+ and G3BP1+ SGs were rapidly induced in VSMC and bone marrow–derived macrophages in response to atherosclerotic stimuli, including oxidized low-density lipoprotein and mediators of mitochondrial or oxidative stress. We observed an increase in eIF2α (eukaryotic translation initiation factor 2-alpha) phosphorylation, a requisite for stress granule formation, in cells exposed to these stimuli. Interestingly, SG formation, PABP expression, and eIF2α phosphorylation in VSMCs is reversed by treatment with the anti-inflammatory cytokine interleukin-19. Microtubule inhibitors reduced stress granule accumulation in VSMC, suggesting cytoskeletal regulation of stress granule formation. SG formation in VSMCs was also observed in other vascular disease pathologies, including vascular restenosis. Reduction of SG component G3BP1 by siRNA significantly altered expression profiles of inflammatory, apoptotic, and proliferative genes. Conclusions: These results indicate that SG formation is a common feature of the vascular response to injury and disease, and that modification of inflammation reduces stress granule formation in VSMC.

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FXR1 Is an IL-19-Responsive RNA-Binding Protein that Destabilizes Pro-inflammatory Transcripts in Vascular Smooth Muscle Cells

Cell Reports ◽

10.1016/j.celrep.2018.07.002 ◽

2018 ◽

Vol 24 (5) ◽

pp. 1176-1189 ◽

Cited By ~ 12

Author(s):

Allison B. Herman ◽

Christine N. Vrakas ◽

Mitali Ray ◽

Sheri E. Kelemen ◽

Michael J. Sweredoski ◽

...

Keyword(s):

Smooth Muscle ◽

Vascular Smooth Muscle ◽

Smooth Muscle Cells ◽

Vascular Smooth Muscle Cells ◽

Rna Binding ◽

Binding Protein ◽

Rna Binding Protein ◽

Muscle Cells

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EGF receptor transactivation is obligatory for protein synthesis stimulation by G protein-coupled receptors

AJP Cell Physiology ◽

10.1152/ajpcell.00261.2001 ◽

2002 ◽

Vol 283 (2) ◽

pp. C446-C455 ◽

Cited By ~ 51

Author(s):

Laure Voisin ◽

Sylvain Foisy ◽

Edith Giasson ◽

Chantal Lambert ◽

Pierre Moreau ◽

...

Keyword(s):

Protein Synthesis ◽

Smooth Muscle ◽

Smooth Muscle Cells ◽

G Protein ◽

Muscle Cells ◽

G Protein Coupled Receptors ◽

Translation Initiation Factor ◽

Initiation Factor ◽

Egfr Transactivation ◽

G Protein Coupled

The epidermal growth factor receptor (EGFR) was recently identified as a signal transducer of G protein-coupled receptors (GPCRs). In this study, we have examined the contribution of EGFR transactivation to the growth-promoting effect of GPCRs on vascular smooth muscle cells. Activation of the Gq-coupled ANG II receptor or Gi-coupled lysophosphatidic acid receptor resulted in increased tyrosine phosphorylation and activation of EGFR. Specific inhibition of EGFR kinase activity by tyrphostin AG-1478 or expression of a dominant-negative EGFR mutant abolished this response. Importantly, inhibition of EGFR function strongly attenuated the global stimulation of protein synthesis by GPCR agonists in vitro in cultured aortic smooth muscle cells and in vivo in the rat aorta and in small resistance arteries. The growth inhibition was associated with a marked reduction of extracellular signal-regulated kinase and phosphoinositide 3-kinase pathway activity and the resulting suppression of eukaryotic translation initiation factor 4E and 4E binding protein 1 phosphorylation. Our results demonstrate that EGFR transactivation is a physiologically relevant action of GPCRs linked to translational control and protein synthesis.

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Enhanced Proliferation of Cultured Human Vascular Smooth Muscle Cells Linked to Increased Function of RNA-binding Protein HuR

Journal of Biological Chemistry ◽

10.1074/jbc.m501106200 ◽

2005 ◽

Vol 280 (24) ◽

pp. 22819-22826 ◽

Cited By ~ 46

Author(s):

Rudolf Pullmann ◽

Magdalena Juhaszova ◽

Isabel López de Silanes ◽

Tomoko Kawai ◽

Krystyna Mazan-Mamczarz ◽

...

Keyword(s):

Smooth Muscle ◽

Vascular Smooth Muscle ◽

Smooth Muscle Cells ◽

Vascular Smooth Muscle Cells ◽

Rna Binding ◽

Binding Protein ◽

Rna Binding Protein ◽

Muscle Cells

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RNA-binding protein HuR regulates RGS4 mRNA stability in rabbit colonic smooth muscle cells

AJP Cell Physiology ◽

10.1152/ajpcell.00093.2010 ◽

2010 ◽

Vol 299 (6) ◽

pp. C1418-C1429 ◽

Cited By ~ 12

Author(s):

Fang Li ◽

Danielle Y. Hu ◽

Shu Liu ◽

Sunila Mahavadi ◽

William Yen ◽

...

Keyword(s):

Smooth Muscle ◽

Smooth Muscle Cells ◽

G Protein ◽

Mrna Stability ◽

Rna Binding ◽

Binding Protein ◽

Rna Binding Protein ◽

Muscle Cells ◽

G Protein Signaling ◽

Protein Signaling

Regulator of G protein signaling 4 (RGS4) regulates the strength and duration of G protein signaling and plays an important role in smooth muscle contraction, cardiac development, and psychiatric disorders. Little is known about the posttranscriptional regulation of RGS4 expression. We cloned the full-length cDNA of rabbit RGS4, which contains a long 3′-untranslated region (UTR) with several AU-rich elements (AREs). We determined whether RGS4 mRNA stability is mediated by the RNA-binding protein human antigen R (HuR) and contributes to IL-1β-induced upregulation of RGS4 expression. We show that IL-1β treatment in colonic smooth muscle cells doubled the half-life of RGS4 mRNA. Addition of RGS4 3′-UTR to the downstream of Renilla luciferase reporter induced dramatic reduction in the enzyme activity and mRNA expression of luciferase, which was attenuated by the site-directed mutation of the two 3′-most ARE sites. IL-1β increased luciferase mRNA stability in a UTR-dependent manner. Knockdown of HuR significantly aggravated UTR-mediated instability of luciferase and inhibited IL-1β-induced upregulation of RGS4 mRNA. In addition, IL-1β increased cytosolic translocation and RGS4 mRNA binding of HuR. These findings suggest that 3′-most ARE sites within RGS4 3′-UTR are essential for the instability of RGS4 mRNA and IL-1β promotes the stability of RGS4 mRNA through HuR.

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The Leader Protein of Theiler's Virus Prevents the Activation of PKR

Journal of Virology ◽

10.1128/jvi.01010-19 ◽

2019 ◽

Vol 93 (19) ◽

Cited By ~ 4

Author(s):

Fabian Borghese ◽

Frédéric Sorgeloos ◽

Teresa Cesaro ◽

Thomas Michiels

Keyword(s):

Stress Granule ◽

Translation Initiation Factor ◽

Initiation Factor ◽

Wild Type Virus ◽

Granule Formation ◽

Double Stranded Rna ◽

Eif2α Phosphorylation ◽

Leader Protein ◽

Infected Cells ◽

L Proteins

ABSTRACT Leader (L) proteins encoded by cardioviruses are multifunctional proteins that contribute to innate immunity evasion. L proteins of Theiler’s murine encephalomyelitis virus (TMEV), Saffold virus (SAFV), and encephalomyocarditis virus (EMCV) were reported to inhibit stress granule assembly in infected cells. Here, we show that TMEV L can act at two levels in the stress granule formation pathway: on the one hand, it can inhibit sodium arsenite-induced stress granule assembly without preventing eIF2α phosphorylation and, thus, acts downstream of eIF2α; on the other hand, it can inhibit eucaryotic translation initiation factor 2 alpha kinase 2 (PKR) activation and the consequent PKR-mediated eIF2α phosphorylation. Interestingly, coimmunostaining experiments revealed that PKR colocalizes with viral double-stranded RNA (dsRNA) in cells infected with L-mutant viruses but not in cells infected with the wild-type virus. Furthermore, PKR coprecipitated with dsRNA from cells infected with L-mutant viruses significantly more than from cells infected with the wild-type virus. These data strongly suggest that L blocks PKR activation by preventing the interaction between PKR and viral dsRNA. In infected cells, L also rendered PKR refractory to subsequent activation by poly(I·C). However, no interaction was observed between L and either dsRNA or PKR. Taken together, our results suggest that, unlike other viral proteins, L indirectly acts on PKR to negatively regulate its responsiveness to dsRNA. IMPORTANCE The leader (L) protein encoded by cardioviruses is a very short multifunctional protein that contributes to evasion of the host innate immune response. This protein notably prevents the formation of stress granules in infected cells. Using Theiler’s virus as a model, we show that L proteins can act at two levels in the stress response pathway leading to stress granule formation, the most striking one being the inhibition of eucaryotic translation initiation factor 2 alpha kinase 2 (PKR) activation. Interestingly, the leader protein appears to inhibit PKR via a novel mechanism by rendering this kinase unable to detect double-stranded RNA, its typical activator. Unlike other viral proteins, such as influenza virus NS1, the leader protein appears to interact with neither PKR nor double-stranded RNA, suggesting that it acts indirectly to trigger the inhibition of the kinase.

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