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J Biol Chem. 2004 Jun 4;279(23):24108-15. Epub 2004 Mar 31.

Oligomerization of wild type and nonfunctional mutant angiotensin II type I receptors inhibits galphaq protein signaling but not ERK activation.

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1
Laboratory of Molecular Cardiology, the Heart Centre and Copenhagen Heart Arrhythmia Research Centre, Copenhagen University Hospital Section 9312 and the Faculty of Health, University of Copenhagen, 20 Juliane Mariesvej, Copenhagen DK-2100, Denmark.

Abstract

The 7-transmembrane or G protein-coupled receptors relay signals from hormones and sensory stimuli to multiple signaling systems at the intracellular face of the plasma membrane including heterotrimeric G proteins, ERK1/2, and arrestins. It is an emerging concept that 7-transmembrane receptors form oligomers; however, it is not well understood which roles oligomerization plays in receptor activation of different signaling systems. To begin to address this question, we used the angiotensin II type 1 (AT(1)) receptor, a key regulator of blood pressure and fluid homeostasis that in specific context has been described to activate ERKs without activating G proteins. By using bioluminescence resonance energy transfer, we demonstrate that AT(1) receptors exist as oligomers in transfected COS-7 cells. AT(1) oligomerization was both constitutive and receptor-specific as neither agonist, antagonist, nor co-expression with three other receptors affected the bioluminescence resonance energy transfer 2 signal. Furthermore, the oligomerization occurs early in biosynthesis before surface expression, because we could control AT(1) receptor export from the endoplasmic reticulum or Golgi by using regulated secretion/aggregation technology (RPD trade mark ). Co-expression studies of wild type AT(1) and AT(1) receptor mutants, defective in either ligand binding or G protein and ERK activation, yielded an interesting result. The mutant receptors specifically exerted a dominant negative effect on Galpha(q) activation, whereas ERK activation was preserved. These data suggest that distinctly active conformations of AT(1) oligomers can couple to each of these signaling systems and imply that oligomerization plays an active role in supporting these distinctly active conformations of AT(1) receptors.

PMID:
15056658
DOI:
10.1074/jbc.M400092200
[Indexed for MEDLINE]
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