title: Mechanism of 17-beta-estradiol-induced Erk1/2 activation in breast cancer cells. A role for HER2 AND PKC-delta.
abstract: Activation of mitogen-activated protein kinase (Erk/MAPK) is a critical signal transduction event for estrogen (E(2))-mediated cell proliferation. Recent studies from our group and others have shown that persistent activation of Erk plays a major role in cell migration and tumor progression. The signaling mechanism(s) responsible for persistent Erk activation are not fully characterized, however. In this study, we have shown that E(2) induces a slow but persistent activation of Erk in MCF-7 breast carcinoma cells. The E(2)-induced Erk activation is dependent on new protein synthesis, suggesting that E(2)-induced growth factors play a major role in Erk activation. When MCF-7 cells were treated with E(2) in the presence of an anti-HER-2 monoclonal antibody (herceptin), 60-70% of E(2)-induced Erk activation is blocked. In addition, when untreated MCF-7 cells were exposed to conditioned medium from E(2)-treated cells, Erk activity was significantly enhanced. Furthermore Erk activity was blocked by an antibody against HER-2 or by heregulin (HRG) depletion from the conditioned medium through immunoprecipitation. In contrast, epidermal growth factor receptor (Ab528) antibody only blocked 10-20% of E(2)-induced Erk activation, suggesting that E(2)-induced Erk activation is predominantly mediated through the secretion of HRG and activation of HER-2 by an autoctine/paracrine mechanism. Inhibition of PKC-delta-mediated signaling by a dominant negative mutant or the relatively specific PKC-delta inhibitor rottlerin blocked most of the E(2)-induced Erk activation but had no effect on TGF alpha-induced Erk activation. By contrast inhibition of Ras, by inhibition of farnesyl transferase (Ftase-1) or dominant negative (N17)-Ras, significantly inhibited both E(2)- and TGF alpha-induced Erk activation. This evaluation of downstream signaling revealed that E(2)-induced Erk activation is mediated by a HRG/HER-2/PKC-delta/Ras pathway that could be crucial for E(2)-dependent growth-promoting effects in early stages of tumor progression.
authors.affiliation: Department of Pathology, Wayne State University, Detroit, Michigan 48201, USA.
authors.forename: Venkateshwar G
authors.initials: VG
authors.lastname: Keshamouni
authors.forename: Raymond R
authors.initials: RR
authors.lastname: Mattingly
authors.forename: Kaladhar B
authors.initials: KB
authors.lastname: Reddy
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000201:enzymology*; D002455:Cell Division; D003513:Cycloheximide / Q000494:pharmacology; D018076:DNA, Complementary / Q000378:metabolism; D018450:Disease Progression; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D005799:Genes, Dominant; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D020890:Neuregulin-1 / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology*; D051745:Protein Kinase C-delta; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D016211:Transforming Growth Factor alpha / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D003513:Cycloheximide; D018076:DNA, Complementary; D066246:ErbB Receptors; D004958:Estradiol; D007527:Isoenzymes; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020559:Monomeric GTP-Binding Proteins; D020890:Neuregulin-1; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D011500:Protein Synthesis Inhibitors; D018719:Erb-b2 Receptor Tyrosine Kinases; D016211:Transforming Growth Factor alpha; C497258:PRKCD protein, human