Agonist-Induced Phosphorylation of the Angiotensin AT1a Receptor Is Localized to a Serine/Threonine-Rich Region of Its Cytoplasmic Tail

Publisher Website
Google Scholar
Abstract
The agonist-induced phosphorylation sites of the rat AT1aangiotensin receptor were analyzed using epitope-tagged mutant receptors expressed in Cos-7 cells. Angiotensin II-stimulated receptor phosphorylation was unaffected by truncation of the cytoplasmic tail of the receptor at Ser342 (Δ342) but was abolished by truncation at Ser325 (Δ325). Truncation at Ser335 (Δ335), or double-point mutations of Ser335 and Thr336 to alanine (ST-AA), reduced receptor phosphorylation by ∼50%, indicating that in addition to Ser335 and/or Thr336, amino acids within the Ser326-Thr332 segment are also phosphorylated. Agonist-induced phosphorylation of the ST-AA and Δ335 receptors was partially inhibited by staurosporine, suggesting that the single protein kinase C consensus site in the Ser326-Thr332 segment (Ser331) is phosphorylated. The impairment of receptor phosphorylation was broadly correlated with the attenuation of agonist-induced internalization rates (Δ325 < Δ335 < ST-AA < Δ342 < wild-type) and with the increasing rank order of magnitude of inositol phosphate production normalized to an equal number of receptors (Δ325 > Δ335 > ST-AA = Δ342 > wild-type). These results demonstrate that agonist-induced phosphorylation of the AT1a receptor is confined to an 11-amino-acid serine/threonine-rich segment of its carboxyl-terminal cytoplasmic tail and implicate this region in the mechanisms of receptor internalization and desensitization.

This publication has 41 references indexed in Scilit: