Angiotensin II-induced Association of Phospholipase Cγ1 with the G-protein-coupled AT1 Receptor

Abstract

An early event in signaling by the G-protein-coupled angiotensin II (Ang II) AT 1 receptor in vascular smooth muscle cells is the tyrosine phosphorylation and activation of phospholipase C␥1 (PLC␥1). In the present study, we show that stimulation of this event by Ang II in vascular smooth muscle cells is accompanied by binding of PLC␥1 to the AT 1 receptor in an Ang II-and tyrosine phophorylation-dependent manner. The PLC␥1-AT 1 receptor interaction appears to depend on phosphorylation of tyrosine 319 in a YIPP motif in the C-terminal intracellular domain of the AT 1 receptor and binding of the phosphorylated receptor by the most C-terminal of two Src homology 2 domains in PLC␥1. PLC␥1 thus binds to the same site in the receptor previously identified for binding by the SHP-2 phosphotyrosine phosphatase⅐JAK2 tyrosine kinase complex. A single site in the C-terminal tail of the AT 1 receptor can, therefore, be bound in a ligand-dependent manner by two different downstream effector proteins. These data demonstrate that G-protein-coupled receptors can physically associate with intracellular proteins other than G proteins, creating membrane-delimited signal transduction complexes similar to those observed for classic growth factor receptors.Growth factor receptors belong to a family of receptors that contain an extracellular ligand binding domain, a single transmembrane portion, and a large intracellular tyrosine kinase catalytic domain. Ligand-induced receptor autophosphorylation promotes the interaction of the intracellular domains of the receptors with a number of downstream effector proteins or enzymes. Typically, these proteins contain one or more domains known as Src homology 2 (SH2) 1 domains. Among these SH2 domain-containing proteins are phosphoinositide-specific phospholipase C␥ (PLC␥), the 85-kDa subunit of phosphatidylinositol 3-kinase, GTPase-activating proteins, growth factor receptor binding protein 2, the phosphotyrosine phosphatase SHP-2, and members of the nonreceptor Src family of tyrosine kinases (1, 2). Autophosphorylation of growth factor receptors occurs on defined tyrosine residues. These phosphorylated residues function to initiate cellular signaling cascades by acting as high affinity binding sites for the SH2 domains of various effector proteins. The selectivity of the receptor-effector interaction is determined, not only by the phosphorylated tyrosine residue in the receptor but also by the three amino acids Cterminal to the phosphorylated tyrosine and by the structure of the SH2 domain of the interacting protein. For example, one of the identified sites for binding of the SH2 domains of PLC␥1 to the platelet-derived growth factor ␣ and ␤ receptors is a YIPP motif present in the receptors at residues 1018 -1021 and 1021-1024, respectively. Phosphorylation of tyrosines 1018 and 1021 in these motifs promotes binding of PLC␥1 to the platelet-derived growth factor receptor and tyrosine phosphorylation and activation of the enzyme (3, 4).Another family of cell surface receptors are the G-protein...

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