The role of a conserved region of the second intracellular loop in AT1 angiotensin receptor activation and signaling

Endocrinology. 2003 Jun;144(6):2220-8. doi: 10.1210/en.2002-0135.


The pleiotropic actions of angiotensin II are mediated by the primarily G(q) protein-coupled type 1 angiotensin (AT(1)) receptor. In this study a mutational analysis of the function of the conserved DRYXXV/IXXPL domain in the second intracellular loop of the rat AT(1A) receptor was performed in COS7 cells. Alanine substitution studies showed that single replacement of the highly conserved Asp(125) and Arg(126), but not Tyr(127), moderately impaired angiotensin II-induced inositol phosphate signaling. However, concomitant substitution of both Asp(125) and Arg(126) caused marked reduction of both inositol phosphate signaling and receptor internalization. Alanine scanning of the adjacent residues showed that substitution of Ile(130), His(132), and Pro(133) reduced agonist-induced inositol phosphate signal generation, whereas mutations of Met(134) also impaired receptor internalization. Expression of the D125A mutant AT(1A) receptor in COS7 cells endowed the receptor with moderate constitutive activity, as indicated by its enhanced basal Elk1 promoter activity and inositol phosphate response to partial agonists. Angiotensin II-induced stimulation of the Elk1 promoter showed parallel impairment with inositol phosphate signal generation in receptors containing mutations in this region of the AT(1A) receptor. These data confirm that Ca(2+) signal generation is required for the nuclear effects of angiotensin II-induced ERK activation. They are also consistent with the role of the conserved DRY sequence of the AT(1A) receptor in receptor activation, and of Asp(125) in constraining the receptor in its inactive conformation. Furthermore, in the cytoplasmic helical extension of the third helix, an apolar surface that includes Ile(130) and Met(134) appears to have a direct role in G protein coupling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • COS Cells
  • Conserved Sequence
  • DNA-Binding Proteins*
  • Endocytosis / physiology
  • GTP-Binding Proteins / metabolism
  • Inositol Phosphates / metabolism
  • Kinetics
  • MAP Kinase Signaling System / physiology*
  • Mitogen-Activated Protein Kinases / metabolism
  • Mutagenesis, Site-Directed
  • Protein Structure, Tertiary
  • Proto-Oncogene Proteins / metabolism
  • Rats
  • Receptor, Angiotensin, Type 1
  • Receptors, Angiotensin / chemistry
  • Receptors, Angiotensin / genetics*
  • Receptors, Angiotensin / metabolism*
  • Transcription Factors*
  • ets-Domain Protein Elk-1


  • DNA-Binding Proteins
  • Elk1 protein, rat
  • Inositol Phosphates
  • Proto-Oncogene Proteins
  • Receptor, Angiotensin, Type 1
  • Receptors, Angiotensin
  • Transcription Factors
  • ets-Domain Protein Elk-1
  • Mitogen-Activated Protein Kinases
  • GTP-Binding Proteins