The GRK2 Promoter Is Regulated by Early-Growth Response Transcription Factor EGR-1

Abstract

The G-protein-coupled receptor kinase 2 (GRK2) plays a major role in cardiovascular diseases, and its expression is increased in heart failure. However, only little is known about factors being involved in up-regulation of GRK2 expression through transcriptional regulation of its promoter. Since the transcription factor early-growth response 1 (EGR-1) is also up-regulated in patients with heart failure, we tested the hypothesis that EGR-1 regulates GRK2 transcription. Stimulation of immortalized rat cardiomyocytes (H9c2) with phorbol 12-myristate 13-acetate (PMA) resulted in up-regulation of Egr-1 and subsequently of Grk2 mRNA expression, with maximum Grk2 expression (p = 0.008) 5 hr after PMA stimulation and being abolished by actinomycin D, indicating a transcriptional mechanism. To identify naturally occurring variants affecting promoter transcriptional activity, we identified a novel G(-43)A polymorphism (rs182084609), which surrounded a putative EGR-1-binding site. While the minor A allele frequency was rare (0.02), this variant was used to explore regulation by EGR-1 and promoter construct with altered alleles at nt-43 were subjected of reporter assays in human embryonic kidney cells (Hek293). Here, EGR-1 over-expression resulted in a more than twofold increase in GRK2 promoter activity but only in the presence of the G-allele (p = 0.04). In electrophoretic mobility shift assays, EGR-1 over-expression resulted in a specific binding of transcription factors only to the G oligonucleotide. Finally, EGR-1 over-expression resulted in increased GRK2 mRNA expression (p = 0.03). We identified EGR-1 as a regulator of GRK2 transcription. Suppression of GRK2 expression by inhibition of EGR-1 binding to GRK2 might be a promising approach to mitigate adrenergic desensitization.