Vol. 58, Issue 5, 1156-1161, November 2000

ACCELERATED COMMUNICATION
Homologous and Heterologous Phosphorylation of the AT₂ Angiotensin Receptor by Protein Kinase C

Jesus A. Olivares-Reyes, Suman Jayadev, László Hunyady, Kevin J. Catt, and Roger D. Smith

Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland (J.A.O.-R., S.J., K.J.C., R.D.S.); and Department of Physiology, Semmelweis University of Medicine, Budapest, Hungary (L.H.)

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 AT₂ antagonist, 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.