CLONING, EXPRESSION, AND CHROMOSOMAL LOCALIZATION OF BETA-ADRENERGIC-RECEPTOR KINASE-2 - A NEW MEMBER OF THE RECEPTOR KINASE FAMILY

The beta-adrenergic receptor kinase (beta-ARK) specifically phosphorylates the agonist-occupied form of the beta-adrenergic and related G protein-coupled receptors. Structural features of this enzyme have been elucidated recently by the isolation of a cDNA that encodes bovine-beta-ARK. Utilizing a catalytic domain fragment of the beta-ARK cDNA to screen a bovine brain cDNA library we have isolated a clone encoding a beta-ARK-related enzyme which we have termed beta-ARK2. Overall, this enzyme has 85% amino acid identity with beta-ARK, with the protein kinase catalytic domain having 95% identity. The ability of beta-ARK2 to phosphorylate various substrates was studied after expression in COS 7 cells. Although beta-ARK2 is essentially equiactive with beta-ARK in phosphorylating an acid-rich synthetic model peptide it was only approximately 50% as active when the substrate was the agonist-occupied beta-2-adrenergic receptor and only approximately 20% as active toward light-bleached rhodopsin. As with beta-ARK, phosphorylation of the receptor substrates by beta-ARK2 was completely stimulus dependent. RNA blot analysis with selected bovine tissues reveals an mRNA of 8 kilobases with a distribution similar to that of beta-ARK. More detailed RNA analysis using a ribonuclease protection assay in various rat tissues suggests that the beta-ARK2 message is present at much lower levels (typically 10-20%) than the beta-ARK message. In the rat the beta-ARK2 mRNA is localized predominantly in neuronal tissues although low levels are also observed in various peripheral tissues. The beta-ARK2 gene has been localized to a region of mouse chromosome 5 whereas the beta-ARK gene is localized on mouse chromosome 19. These data suggest the existence of a ''family'' of receptor kinases which may serve broadly to regulate receptor function.