GRK5

GRK5 is a G protein-coupled receptor kinase that phosphorylates activated GPCRs and supports receptor desensitization, β-arrestin recruitment, and receptor signaling control^[1]. Mechanistically, GRK5 also enters the cardiomyocyte nucleus after selective hypertrophic Gq-coupled receptor activation through a Ca²⁺/calmodulin-dependent process^[2]. In the nucleus, GRK5 functions as an HDAC kinase and promotes maladaptive cardiac hypertrophy through transcriptional regulation^[3]. Disease-model evidence links GRK5 to pathological cardiac hypertrophy through facilitation of nuclear NFAT activity^[4]. In cardiac fibroblast models, GRK5 inhibition reduces fibroblast activation and attenuates cardiac fibrosis, supporting its use in heart-failure remodeling studies^[5]. Compared with related isoforms, GRK5 shows experimentally important selectivity distinctions because newly designed inhibitors achieved GRK5 IC₅₀ values of 10 nM and more than 100,000-fold selectivity over GRK2^[6]. For experimental applications, KR-39038 attenuated cardiac hypertrophy and improved cardiac function in heart-failure models, while CCG-215022 reduced rhabdomyosarcoma xenograft growth and self-renewal^[7][8].