title: Human epidermal growth factor receptor-1 expression renders Chinese hamster ovary cells sensitive to alternative aldosterone signaling.
abstract: The epidermal growth factor (EGF) regulates cell proliferation, differentiation, and ion transport using ERK1/2 as a downstream effector. Furthermore, the EGF receptor (EGFR) is involved in signaling by G-protein-coupled receptors, growth hormone, and cytokines via transactivation. It has been suggested that steroids interact with peptide hormones. Previously, we have shown that aldosterone modulates EGF responses in Madin-Darby canine kidney cells (Gekle, M., Freudinger, R., Mildenberger, S., and Silbernagl, S. (2002) Am. J. Physiol. 282, F669-F679). Here, we tested the hypothesis that human EGFR-1 can confer alternative aldosterone responsiveness with respect to ERK1/2 phosphorylation to Chinese hamster ovary cells, which do not express EGFR. Wild-type Chinese hamster ovary cells did not respond to EGF or aldosterone. After transfection of human EGFR-1, the cells responded to EGF, but not to aldosterone. However, when submaximal concentrations of EGF were used, nanomolar concentrations of aldosterone potentiated the action of EGF within minutes, resulting in a leftward shift of the EGF dose-response curve. This was not the case in mock-transfected cells. The EGFR kinase inhibitor tyrphostin AG1478 or the MEK1/2 inhibitor U0126 completely prevented the effect. Furthermore, aldosterone enhanced Tyr phosphorylation of c-Src and EGFR, and an inhibitor of cytosolic tyrosine kinases (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyriociaine) prevented the action of aldosterone. Our data show that aldosterone uses the EGF-EGFR-MEK1/2-ERK1/2 signaling cascade to elicit its alternative effects. In the presence of EGF, aldosterone leads to EGFR transactivation via cytosolic tyrosine kinases of the Src family.
authors.affiliation: Physiologisches Institut and the Institut für Medizinische Strahlenkunde und Zellforschung, Universität Würzburg, 97070 Würzburg, Germany.
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Krug
authors.forename: Claudia
authors.initials: C
authors.lastname: Schuster
authors.forename: Birgit
authors.initials: B
authors.lastname: Gassner
authors.forename: Ruth
authors.initials: R
authors.lastname: Freudinger
authors.forename: Sigrid
authors.initials: S
authors.lastname: Mildenberger
authors.forename: Jakob
authors.initials: J
authors.lastname: Troppmair
authors.forename: Michael
authors.initials: M
authors.lastname: Gekle
mesh_terms: D000450:Aldosterone / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004285:Dogs; D004797:Enzyme-Linked Immunosorbent Assay; D066246:ErbB Receptors / Q000235:genetics / Q000502:physiology*; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D000450:Aldosterone; D066246:ErbB Receptors; D016392:Proto-Oncogene Proteins pp60(c-src); D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases