title: The third cytoplasmic loop of the angiotensin II type 1 receptor exerts differential effects on extracellular signal-regulated kinase (ERK1/ERK2) and apoptosis via Ras- and Rap1-dependent pathways.
abstract: The third cytoplasmic loop of the angiotensin (Ang) II type 1 receptor (AT(1)) is important for receptor coupling to G proteins and activation of downstream events. Therefore, we determined whether specific AT(1) sequences were required for kinase activation and inhibition of apoptosis by transfecting wild-type (AT1Rwt) and mutated AT(1) into 293 cells. Ang II stimulated a 19.4-fold increase in extracellular signal-regulated kinase (ERK1/ERK2) activity in 293 cells transfected with AT1Rwt. However, in 293 cells that expressed a receptor in which amino acids 221 and 222 were deleted (AT1R[Del221/222]), Ang II-mediated ERK1/ERK2 activation was inhibited by >85%. In contrast, c-Jun NH(2)-terminal protein kinase (JNK) activation was similar in AT1Rwt- and AT1R(Del221/222)-transfected cells. Activation of ERK1/ERK2 by AT1Rwt was independent of Ca(2+), whereas the low level of ERK1/ERK2 activation by AT1R(Del221/222) was completely Ca(2+) dependent. Activation of ERK1/ERK2 in AT1Rwt required Ras, whereas AT1R(Del221/222) required Rap1. These results demonstrate the presence of 2 different pathways for ERK1/ERK2 activation by Ang II, which differ in their requirements for Ca(2+) and small G proteins (Ras versus Rap1). Furthermore, Ang II prevented serum deprivation-induced apoptosis in cells transfected with AT1Rwt but not AT1R(Del221/222). AKT was only phosphorylated by Ang II in AT1Rwt-transfected cells. Overexpression of constitutively active AKT significantly reduced serum deprivation-induced apoptosis in cells transfected with AT1R(Del221/222). This study shows for the first time a direct link between kinase activation and inhibition of apoptosis dependent on amino acids 221 and 222 in the third cytoplasmic loop of the AT(1).
authors.affiliation: Center for Cardiovascular Research, University of Rochester, Rochester, NY 14642, USA.
authors.forename: J
authors.initials: J
authors.lastname: Haendeler
authors.forename: M
authors.initials: M
authors.lastname: Ishida
authors.forename: L
authors.initials: L
authors.lastname: Hunyady
authors.forename: B C
authors.initials: BC
authors.lastname: Berk
mesh_terms: D002118:Calcium / Q000502:physiology; D016923:Cell Death; D002460:Cell Line; D004789:Enzyme Activation; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion; D015398:Signal Transduction; D014162:Transfection; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
chemical_list: D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin; D011994:Recombinant Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020827:rap1 GTP-Binding Proteins; D018631:ras Proteins; D002118:Calcium