Homologous and heterologous phosphorylation of the AT(2) angiotensin receptor by protein kinase C

The angiotensin AT(2) receptor is an atypical seven transmembrane domain re ceptor that is coupled to activation of tyrosine phosphatase and inhibition of MAP kinase, and does not undergo agonist-induced internalization. An in vestigation of the occurrence and nature of AT(2) receptor phosphorylation revealed that phorbol ester-induced activation of protein kinase C (PKC) in HA-AT(2) receptor-expressing COS-7 cells caused rapid and specific phospho rylation of a single residue (Ser(354))located in the cytoplasmic tail of t he receptor. Agonist activation of AT(2) receptors by angiotensin II (Ang I I) also caused rapid PKC-dependent phosphorylation of Ser(354) that was pre vented by the AT(2) antagonist, PD123177, and by inhibitors of PKC. In cell s coexpressing AT(1) and AT(2) receptors, Ang II-induced phosphorylation of the AT(2) receptor was reduced by either PD123177 or the AT(1) receptor an tagonist, DuP753, and was abolished by treatment with both antagonists or w ith PKC inhibitors. These findings indicate that the AT(2) receptor is rapi dly phosphorylated via PKC during homologous activation by Ang II, and also undergoes heterologous PKC-dependent phosphorylation during activation of the AT(1) receptor. The latter process may regulate the counteracting effec ts of AT(2) receptors on growth responses to AT(1) receptor activation.