G3BP2 is involved in isoproterenol-induced cardiac hypertrophy through activating the NF-κB signaling pathway

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Abstract

The RasGAP SH3 domain-binding proteins (G3BPs) are a family of RNA-binding proteins that can co-ordinate signal transduction and post-transcriptional gene regulation. G3BPs have been shown to be involved in mediating a great diversity of cellular processes such as cell survival, growth, proliferation and apoptosis. But the potential roles of G3BPs in the pathogenesis and progression of cardiovascular diseases remain to be clarified. In the present study, we provide the first evidence that suggests the participation of G3BP2 in cardiac hypertrophy. In cultured neonatal rat cardiomyocytes (NRCMs), treatment with isoproterenol (ISO, 0.1-100 μmol/L) significantly elevated the mRNA and protein levels of G3BP2. Similar results were observed in the hearts of rats subjected to 7D-injection of ISO, accompanied by obvious heart hypertrophy and elevated the expression of hypertrophy marker genes ANF, BNP and β-MHC in heart tissues. Overexpression of G3BP2 in NRCMs led to hypertrophic responses evidenced by increased cellular surface area and the expression of hypertrophy marker genes, whereas knockdown of G3BP2 significantly attenuated ISO-induced hypertrophy of NRCMs. We further showed that G3BP2 directly interacted with IκBα and promoted the aggregation of the NF-κB subunit p65 in the nucleus and increased NF-κB-dependent transcriptional activity. NF-κB inhibition with PDTC (50 μmol/L) or p65 knockdown significantly decreased the hypertrophic responses in NRCMs induced by ISO or G3BP2 overexpression. These results give new insight into the functions of G3BP2 and may help further elucidate the molecular mechanisms underlying cardiac hypertrophy.

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Both G3BP1 and G3BP2 contribute to stress granule formation.

Hideaki Matsuki, Masahiko Takahashi, Masaya Higuchi … (2013)

Upon exposure to various environmental stresses such as arsenite, hypoxia, and heat shock, cells inhibit their translation and apoptosis and then repair stress-induced alterations, such as DNA damage and the accumulation of misfolded proteins. These types of stresses induce the formation of cytoplasmic RNA granules called stress granules (SGs). SGs are storage sites for the many mRNAs released from disassembled polysomes under these stress conditions and are essential for the selective translation of stress-inducible genes. Ras-GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) is a component of SGs that initiates the assembly of SGs by forming a multimer. In this study, we examined the role of G3BP2, a close relative of G3BP1, in SG formation. Although single knockdown of either G3BP1 or G3BP2 in 293T cells partially reduced the number of SG-positive cells induced by arsenite, the knockdowns of both genes significantly reduced the number. G3BP2 formed a homo-multimer and a hetero-multimer with G3BP1. Moreover, like G3BP1, the overexpression of G3BP2 induced SGs even without stress stimuli. Collectively, these results suggest that both G3BP1 and G3BP2 play a role in the formation of SGs in various human cells and thereby recovery from these cellular stresses. © 2012 The Authors Genes to Cells © 2012 by the Molecular Biology Society of Japan and Wiley Publishing Asia Pty Ltd.

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Sirt1 acts in association with PPARα to protect the heart from hypertrophy, metabolic dysregulation, and inflammation.

Francesc Villarroya, Marta Giralt, Roser Iglesias … (2011)

A complex set of metabolic and inflammatory processes are involved in the development of cardiac hypertrophy. Accumulating evidence indicates an important role for Sirt1 in cardiac function, whereas peroxisome proliferator-activated receptor-α (PPARα) is a master controller of cardiac lipid metabolism and plays a protective role on cardiac hypertrophy. The objective of the present study was to explore the relationships between Sirt1 and PPARα in the control of hypertrophy, metabolism, and inflammation processes in the heart. Neonatal cardiomyocytes (NCMs) were used for studies in vitro. Both the activation of Sirt1 with resveratrol (RSV) and overexpression of Sirt1 inhibited phenylephrine (PE)-induced NCM hypertrophy and prevented PE-induced down-regulation of fatty acid oxidation genes. Sirt1 also inhibited the PE-induced increase in mRNA levels of the pro-inflammatory cytokine monocyte chemoattractant protein-1 in NCMs and blocked the enhanced nuclear factor-κB (NF-κB) activity associated with exposure to PE. Importantly, inhibition of PPARα suppressed the beneficial effects of Sirt1 on hypertrophy, fatty acid metabolism, and inflammation. Co-immunoprecipitation studies revealed that overexpression of Sirt1 enhanced PPARα binding to the p65 subunit of NF-κB and led to p65-deacetylation in NCMs. Moreover, Sirt1 overexpression led to the deacetylation of the PPARα co-activator PGC-1α. Consistent with these observations in vitro, isoproterenol-induced cardiac hypertrophy, metabolic dysregulation, and inflammation in vivo were prevented by RSV in wild-type mice but not in PPARα-null mice. Collectively, these findings reveal a major involvement of the Sirt1-PPARα interaction in the protective role of Sirt1 against cardiac hypertrophy.

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RasGAP-associated endoribonuclease G3Bp: selective RNA degradation and phosphorylation-dependent localization.

J Tazi, Imed E. Gallouzi, H Tourrière … (2001)

Mitogen activation of mRNA decay pathways likely involves specific endoribonucleases, such as G3BP, a phosphorylation-dependent endoribonuclease that associates with RasGAP in dividing but not quiescent cells. G3BP exclusively cleaves between cytosine and adenine (CA) after a specific interaction with RNA through the carboxyl-terminal RRM-type RNA binding motif. Accordingly, G3BP is tightly associated with a subset of poly(A)(+) mRNAs containing its high-affinity binding sequence, such as the c-myc mRNA in mouse embryonic fibroblasts. Interestingly, c-myc mRNA decay is delayed in RasGAP-deficient fibroblasts, which contain a defective isoform of G3BP that is not phosphorylated at serine 149. A G3BP mutant in which this serine is changed to alanine remains exclusively cytoplasmic, whereas a glutamate for serine substitution that mimics the charge of a phosphorylated serine is translocated to the nucleus. Thus, a growth factor-induced change in mRNA decay may be modulated by the nuclear localization of a site-specific endoribonuclease such as G3BP.