Identification of additional members of human G-protein-coupled receptor kinase multigene family

Human neutrophils express several distinct guanine nucleotide binding (G)-protein-coupled receptors that mediate their responsiveness to chemoattractants. Phosphorylation by receptor-specific and second messenger-activated protein kinases is a common mechanism for regulation of G-protein-coupled receptors. To explore the possibility that chemoattractant receptors are regulated by unique receptor kinases, we utilized PCR to identify receptor kinases in human neutrophils. Here, we report the isolation of three G-protein-coupled-receptor-kinase (GPRK)-like sequences termed GPRK5, GPRK6, and GPRK7 in addition to the beta-adrenergic receptor kinase (beta ARK) 1 and 2 isoforms (beta ARK1 and beta ARK2). Two, GPRK5 and GPRK6, showed high homology at the amino acid level to the recently identified receptor-kinase-like sequence localized close to the Huntington disease locus. GPRK7 is of interest in that it contains a DLG (Asp-Leu-Gly) amino acid motif of receptor kinases preceded by a DFD (Asp-Phe-Asp) motif. We isolated cDNAs corresponding to GPRK6; the complete sequence shows > 66% identity and 81% similarity at the amino acid level to the GPRK from the Huntington disease locus. The GPRK6 cDNA probe hybridizes to two mRNAs of 2.9 and 2.1 kb that were expressed in all the tested human tissues including HL-60 cells and neutrophils. Genomic Southern blot analysis and chromosome mapping showed that GPRK6 hybridizes to two closely related genes located on chromosomes 5 and 13 and are, therefore, distinct from the GPRK located near the Huntington disease locus on chromosome 4. The identification herein of three putative receptor kinases indicates that in addition to beta ARK and rhodopsin kinase subfamilies, there are other receptor-kinase subfamilies that regulate the broad spectrum of G-protein-coupled receptors.