GRK5-Mediated Exacerbation of Pathological Cardiac Hypertrophy Involves Facilitation of Nuclear NFAT Activity

Abstract

Rationale G protein-coupled receptor (GPCR) kinases (GRKs) acting in the cardiomyocyte regulate important signaling events that control cardiac function. Both GRK2 and GRK5, the predominant GRKs expressed in the heart, have been shown to be up-regulated in failing human myocardium. While the canonical role of GRKs is to desensitize GPCRs via phosphorylation, it has been demonstrated that GRK5, unlike GRK2, can reside in the nucleus of myocytes and exert GPCR-independent effects that promote maladaptive cardiac hypertrophy and heart failure (HF). Objective To explore novel mechanisms by which GRK5 acting in the nucleus of cardiomyocytes participates in pathological cardiac hypertrophy. Methods and Results In this study, we have found that GRK5-mediated pathological cardiac hypertrophy involves the activation of nuclear factor of activated T-cells (NFAT) as GRK5 causes enhancement of NFAT-mediated hypertrophic gene transcription. Transgenic mice with cardiomyocyte-specific GRK5 overexpression activate an NFAT-reporter in mice basally and after hypertrophic stimuli including transverse aortic constriction (TAC) and phenylephrine treatment. Complimentary to this, GRK5 null mice exhibit less NFAT transcriptional activity after TAC. Further, loss of NFATc3 expression in the heart protected GRK5 overexpressing transgenic mice from the exaggerated hypertrophy and early progression to HF seen after TAC. Molecular studies suggest that GRK5 acts in concert with NFAT to increase hypertrophic gene transcription in the nucleus via GRK5’s ability to bind DNA directly without a phosphorylation event. Conclusions GRK5, acting in a kinase-independent manner, is a facilitator of NFAT activity and part of a DNA binding complex responsible for pathological hypertrophic gene transcription.

Orphan Nuclear Receptor Nur77 Inhibits Cardiac Hypertrophic Response to Beta-Adrenergic Stimulation

“…To measure global cardiac function, echocardiography was performed with the VisualSonics VeVo 2100 imaging system in anesthetized animals (1.5% [vol/vol] isoflurane). The internal diameter of the left ventricle was measured in the short-axis view from M-mode recordings in end diastole and end systole as described previously (27).…”

Feedback regulation of G protein-coupled receptor signaling by GRKs and arrestins

“…Interestingly, additional reports argue that GRK5 can oppose NF-κB activity through mediating IκBα nuclear accumulation [84]. Furthermore, GRK5 augments nuclear factor of activated T cells (NFAT) transcriptional activity in an apparent kinase independent manner, potentially by some molecular scaffold activity [85]. …”

“Canonical and non-canonical actions of GRK5 in the heart”

“…However, recently we have shown a second novel action of GRK5 in the nucleus of myocytes. It was found that GRK5 interacts with the NFAT-pathway in the nucleus during pathological hypertrophy [55]. First, utilizing cardiac-specific NFAT luciferase reporter mice it was shown that GRK5 overexpression leads to an increase in NFAT activity while GRK5 KO mice exhibited less NFAT transcriptional activity [55].…”

“…It was found that GRK5 interacts with the NFAT-pathway in the nucleus during pathological hypertrophy [55]. First, utilizing cardiac-specific NFAT luciferase reporter mice it was shown that GRK5 overexpression leads to an increase in NFAT activity while GRK5 KO mice exhibited less NFAT transcriptional activity [55]. Interestingly, double transgenic mice with cardiac-specific GRK5 over-expression and deletion of NFATc3 were protected from the early progression to HF observed with increased cardiac GRK5 levels following TAC[55].…”