Regulation of Nuclear Factor κB (NF-κB) in the Nucleus of Cardiomyocytes by G Protein-coupled Receptor Kinase 5 (GRK5)

Background: NF-B activation and GRK5 up-regulation have been shown to be associated with heart disease. Results: GRK5 induces NF-B signaling pathway both in cardiomyocytes and in mouse hearts. Conclusion: GRK5 triggers the binding of NF-B (p50/p65) to DNA in the nucleus and promotes gene transcription including hypertrophic gene. Significance: GRK5 up-regulation may lead to a significant increase in expression and activation of NF-B seen in heart disease. G protein-coupled receptor kinase 5 GRK5 plays a key role in regulating cardiac signaling and its expression is increased in heart failure. GRK5 activity in the nucleus of myocytes has been shown to be detrimental in the setting of pressure-overload hypertrophy. The ubiquitous nuclear transcription factor B (NF-B) is involved in the regulation of numerous genes in various tissues, and activation of NF-B has been shown to be associated with heart disease. Herein, we investigated whether GRK5 can specifically regulate the NF-B signaling pathway in myocytes. We found that overexpression of GRK5 increased the levels of NF-B -p50 and p65 in vitro and in vivo, whereas loss of GRK5 resulted in lower cardiac NF-B levels. Furthermore, increased GRK5 expression induced the phosphorylation status of p65, increased the activity of a NF-B reporter, and increased NF-B DNA binding activity in cultured neonatal rat ventricular myocytes. Importantly, siRNA against GRK5 presented with the opposite results in neonatal rat ventricular myocytes as p65 and p50 were decreased, and there was a loss of NF-B DNA binding activity. The influence of GRK5 on NF-B expression and activity was dependent on its nuclear localization as overexpression of a mutant GRK5 that cannot enter the nucleus was devoid of NF-B activation or DNA binding. Our study demonstrates that a novel pathological consequence of GRK5 up-regulation in the injured and failing heart is the induction of NF-B expression and activity.