title: Angiotensin II stimulates ERK via two pathways in epithelial cells: protein kinase C suppresses a G-protein coupled receptor-EGF receptor transactivation pathway.
abstract: In GN4 rat liver epithelial cells, angiotensin II (Ang II) produces intracellular calcium and protein kinase C (PKC) signals and stimulates ERK and JNK activity. JNK activation appears to be mediated by a calcium-dependent tyrosine kinase (CADTK). To define the ERK pathway, we established GN4 cells expressing an inhibitory Ras(N17). Induction of Ras(N17) blocked EGF- but not Ang II- or phorbol ester (TPA)-dependent ERK activation. In control cells, Ang II and TPA produced minimal increases in Ras-GTP level and Raf kinase activity. PKC depletion by chronic TPA exposure abolished TPA-dependent ERK activation but failed to diminish the effect of Ang II. In PKC-depleted cells, Ang II increased Ras-GTP level and activated Raf and ERK in a Ras-dependent manner. In PKC depleted cells, Ang II stimulated Shc and Cbl tyrosine phosphorylation, suggesting that without PKC, Ang II activates another tyrosine kinase. PKC-depletion did not alter Ang II-dependent tyrosine phosphorylation or activity of p125(FAK), CADTK, Fyn or Src, but PKC depletion or incubation with GF109203X resulted in Ang II-dependent EGF receptor tyrosine phosphorylation. In PKC-depleted cells, EGF receptor-specific tyrosine kinase inhibitors blocked Ang II-dependent EGF receptor and Cbl tyrosine phosphorylation, and ERK activation. In summary, Ang II can activate ERK via two pathways; the latent EGF receptor, Ras-dependent pathway is equipotent to the Ras-independent pathway, but is masked by PKC action. The prominence of this G-protein coupled receptor to EGF receptor pathway may vary between cell types depending upon modifiers such as PKC.
authors.affiliation: Lineberger Comprehension Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: X
authors.initials: X
authors.lastname: Li
authors.forename: J W
authors.initials: JW
authors.lastname: Lee
authors.forename: L M
authors.initials: LM
authors.lastname: Graves
authors.forename: H S
authors.initials: HS
authors.lastname: Earp
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011799:Quinazolines / Q000494:pharmacology; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology
chemical_list: D004791:Enzyme Inhibitors; D011799:Quinazolines; D011994:Recombinant Proteins; D000804:Angiotensin II; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate; C088860:4-((3-bromophenyl)amino)-6,7-dimethoxyquinazoline