HIGH EXPRESSION OF BETA-ADRENERGIC-RECEPTOR KINASE IN HUMAN PERIPHERAL-BLOOD LEUKOCYTES - ISOPROTERENOL AND PLATELET-ACTIVATING-FACTOR CAN INDUCE KINASE TRANSLOCATION

Receptor phosphorylation is a key step in the process of desensitizati on of the beta-adrenergic and other related receptors. A selective kin ase (called beta-adrenergic receptor kinase, beta-ARK) has been identi fied which phosphorylates the agonist-occupied form of the receptor. R ecently the bovine beta-ARK cDNA has been cloned and the highest level s of specific mRNA were found in highly innervated tissues. It was pro posed that beta-ARK may be primarily active on synaptic receptors. In the present study, the cDNA of human beta-ARK was cloned and sequenced . The sequence was very similar to that of the bovine-beta-ARK (the ov erall amino acid homology was 98%). Very high levels of beta-ARK mRNA and kinase activity were found in peripheral blood leukocytes and in s everal myeloid and lymphoid leukemia cell lines. Since agonist-induced beta-ARK translocation is considered the first step involved in beta- ARK-mediated homologous desensitization, we screened a number of G-pro tein-coupled receptor agonists for their ability to induce beta-ARK tr anslocation. In human mononuclear leukocytes, beta-AR agonist isoprote renol and platelet-activating factor were able to induce translocation of beta-ARK from cytosol to membrane. After 20 min of exposure to iso proterenol (10-mu-M), the cytosolic-beta-ARK activity decreased to 61% of control, while membrane-associated beta-ARK activity increased to 170%. 20-min exposure to platelet-activating factor (1-mu-M) reduced t he cytosolic-beta-ARK activity to 42% of control with concomitant incr ease in membrane-beta-ARK activity to 214% of control. The high levels of beta-ARK expression in human peripheral blood leukocytes together with the ability of isoproterenol and platelet-activating factor to in duce beta-ARK translocation, suggest a role for beta-ARK in modulating some receptor-mediated immune functions.