Transcriptional remodeling effects of the nuclear receptor NR4A2 in adult rat ventricular myocytes

Sustained elevation of sympathetic activity is an important contributor to pathological cardiac hypertrophy, ventricular arrhythmias, and left ventricular contractile dysfunction in chronic heart failure. The orphan nuclear receptor NR4A2 is an immediate early response gene activated in the heart under beta-adrenergic stimulation. The goal of this study was to identify the transcriptional remodeling events induced by NR4A2 expression in cardiomyocytes, and their impact on the physiological response of those cells to sustained beta-adrenergic stimulation. Treatment of adult rat ventricular myocytes (ARVMs) with isoproterenol induced a rapid (< 4 hours) but transient (< 24 hours) increase in NR4A2 expression levels that was accompanied by increased nuclear localization of the transcription factor. Adenovirus-mediated overexpression of NR4A2 modulated the expression of genes linked to adrenoceptor signaling, calcium signaling, cell growth and proliferation, and counteracted the increase in protein synthesis rate and cell surface area mediated by chronic isoproterenol stimulation. In consistence with those findings, NR4A2 overexpression also blocked the phosphorylative activation of ERK1/2, Akt, and of their downstream effector in protein synthesis p70S6K. Prominent among the transcriptional changes induced by NR4A2 was the > 7-fold up-regulation of the dual-specificity phosphatases DUSP2 and DUSP14, two known inhibitors of ERK1/2. Pre-treatment of NR4A2-overexpressing cardiomyocytes with the DUSPs inhibitor BCI prevented the inhibition of ERK1/2 and p70S6K following isoproterenol stimulation. In conclusion, our results suggest that NR4A2 acts as a novel negative feedback regulator of the beta-adrenergic receptor-mediated growth response in cardiomyocytes, and this at least partly through DUSP-mediated inhibition of ERK1/2 signaling. Overall design: Isolated adult rat ventricular myocytes (ARVMs) were transduced at 50 m.o.i. with a recombinant adenovirus containing the full-length cDNA of human NR4A2 under the transcriptional control of the CMV promoter (Vector Biolabs Ad-h-NR4A2; Cat. No: ADV-217057). ARVMs transduced with a recombinant eGFP adenovirus (Vector Biolabs Ad-GFP; Cat. No. 1060) were used as the cell transduction control. At 48 hours post transduction, total RNA was etracted. A total of six independent experiments were performed using ARVMs isolated from different Sprague Dawley rats.

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Ashraf S, Hegazy YK, Harmancey R