Abstract 121: GRK5-NT Regulates the Activity of Calcium-Calmodulin-Dependent Transcription Factors
We have demonstrated that the amino terminal domain (GRK5-NT), which includes the RH domain and the region of binding to calmodulin, is able to regulate cardiac hypertrophy through inhibition of NFκB. Several studies indicate that mechanical stress and neuro-hormonal activation (Angiotensin, phenylephrine, endothelin) increase the levels of intracellular calcium, therefore activating calcineurin, a serine/threonine phosphatase that dephosphorylates nuclear factor of activated T cells (NFAT). Aim of this study is to evaluate the possibility that GRK5-NT regulates calcium-calmodulin dependent transcription factors. To this aim, we infected cardiomyoblasts in culture with an adenovirus encoding for GRK5-NT (AdGRK5-NT) or treated with a synthetic protein (TAT-RH), which reproduce the only RH domain of GRK5. Hypertrophic responses were induced by chronic stimulation of α1adrenergic receptors with phenylephrine (PE 10-7M,24h) and the levels of GATA4 and NFAT3 were assessed by western blot. PE induces activation and nuclear translocation of GATA4 and NFAT3 (NFAT:+38±3%;GATA4:+46±3% vs control), the treatment with AdGRK5-NT, but TAT-RH, reduces this effect (NFAT:-68±5%;GATA4:-56±2% vs PE). These data suggest that GRK5-NT using the NT domain regulates the activation of calcium-calmodulin dependent transcription factors through a mechanism of competition for binding to calmodulin. To confirm these data, we evaluated the effect of GRK5-NT in vivo in spontaneously hypertensive and hypertrophic rats (SHR). The overexpression of GRK5-NT in the heart was induced by intracardiac injection of 1010pfu/ml of AdGRK5-NT. The treatment inhibits nuclear translocation of NFAT3 and GATA4 (NFAT:-55±1%;GATA4:-34±3% vs PE) and is associated with a reduction in their DNA binding activity, as assessed by EMSA (NFAT:-47±1.5%;GATA4:-33±1% vs EP). In conclusion, our data indicate that GRK5-NT is able to regulate cardiac hypertrophy in two ways: inhibition of NFκB through binding and stabilization of IκB nuclear and inhibition activity of calcium- calmodulin dependent transcription factors, possibly by competing with calmodulin binding.
- © 2012 by American Heart Association, Inc.