Abstract

The angiotensin AT₂ receptor is an atypical seven transmembrane domain receptor that is coupled to activation of tyrosine phosphatase and inhibition of MAP kinase, and does not undergo agonist-induced internalization. An investigation of the occurrence and nature of AT₂ receptor phosphorylation revealed that phorbol ester-induced activation of protein kinase C (PKC) in HA-AT₂ receptor-expressing COS-7 cells caused rapid and specific phosphorylation of a single residue (Ser³⁵⁴) located in the cytoplasmic tail of the receptor. Agonist activation of AT₂ receptors by angiotensin II (Ang II) also caused rapid PKC-dependent phosphorylation of Ser³⁵⁴ that was prevented by the AT₂antagonist, PD123177, and by inhibitors of PKC. In cells coexpressing AT₁ and AT₂ receptors, Ang II-induced phosphorylation of the AT₂ receptor was reduced by either PD123177 or the AT₁ receptor antagonist, DuP753, and was abolished by treatment with both antagonists or with PKC inhibitors. These findings indicate that the AT₂ receptor is rapidly phosphorylated via PKC during homologous activation by Ang II, and also undergoes heterologous PKC-dependent phosphorylation during activation of the AT₁ receptor. The latter process may regulate the counteracting effects of AT₂ receptors on growth responses to AT₁ receptor activation.