title: AT1 receptor mutant lacking heterotrimeric G protein coupling activates the Src-Ras-ERK pathway without nuclear translocation of ERKs.
abstract: Angiotensin II (Ang II) type 1 receptors (AT1Rs) activate tyrosine kinases, including Src. Whether or not tyrosine kinase activation by AT1R occurs independently of heterotrimeric G protein coupling and, if so, the cellular function of such a mechanism are unknown. To address these questions, we used an AT1aR intracellular second loop mutant, which lacks heterotrimeric G protein coupling (AT1a-i2m). Surprisingly, Ang II-induced Src activation was preserved in AT1a-i2m, which was not attenuated by inhibiting protein kinase C and Ca(2+) or by inhibiting Galpha(i) or Galpha(q) in CHO-K1 cells. By contrast, Ang II-induced Src activation was abolished in a C-terminally truncated AT1a-(1--309), where Ang II-induced inositol phosphate response was preserved. Ang II activates ERKs via a Src-Ras-dependent mechanism in AT1a-i2m. ERKs activated by AT1a-i2m phosphorylate their cytoplasmic targets, including p90(RSK), but fail to translocate into the nucleus or to cause cell proliferation. Ang II-induced nuclear translocation of ERKs by wild type AT1aR was inhibited by overexpression of nuclear exportin Crm-1, while that by AT1a-i2m was restored by leptomycin B, an inhibitor of Crm-1. In summary, while Src and ERKs are activated by Ang II even without heterotrimeric G protein coupling, the carboxyl terminus of the AT1 receptor is required for activation of Src. Interestingly, ERKs activated by heterotrimeric G protein-independent mechanisms fail to phosphorylate nuclear targets due to lack of inhibition of Crm-1-induced nuclear export of ERKs. These results suggest that heterotrimeric G protein-dependent and -independent signaling mechanisms play distinct roles in Ang II-mediated cellular responses.
authors.affiliation: Cardiovascular Research Institute, Department of Cell Biology and Molecular Medicine, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103, USA.
authors.forename: Koichi
authors.initials: K
authors.lastname: Seta
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Nanamori
authors.forename: J Gregory
authors.initials: JG
authors.lastname: Modrall
authors.forename: Richard R
authors.initials: RR
authors.lastname: Neubig
authors.forename: Junichi
authors.initials: J
authors.lastname: Sadoshima
mesh_terms: D021581:Active Transport, Cell Nucleus; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D002455:Cell Division / Q000187:drug effects; D006224:Cricetinae; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D020962:Heterotrimeric GTP-Binding Proteins / Q000502:physiology*; D028884:Karyopherins / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin / Q000502:physiology*; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D014162:Transfection; D050807:ets-Domain Protein Elk-1; D018631:ras Proteins / Q000502:physiology*; D019061:src-Family Kinases / Q000502:physiology*; D000097606:Exportin 1 Protein
chemical_list: D000804:Angiotensin II; D004268:DNA-Binding Proteins; D020962:Heterotrimeric GTP-Binding Proteins; D028884:Karyopherins; D020928:Mitogen-Activated Protein Kinases; D011518:Proto-Oncogene Proteins; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D018631:ras Proteins; D019061:src-Family Kinases; D000097606:Exportin 1 Protein