title: MEK ablation in MCF-7 cells blocks DNA synthesis induced by serum, but not by estradiol or growth factors.
abstract: The role of mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) signaling in estrogen receptor positive (ER(+)) MCF-7 breast carcinoma cells is not well understood. We depleted MEK by cotransfection of MEK1 and MEK2 siRNA duplexes in a MCF-7 derived line (MCF-7/ lacZ, ML-20) and determined its effect on serum, 17beta-estradiol (E(2)), and growth factor induced DNA synthesis. MEK knockdown did not decrease fetal bovine serum-induced DNA synthesis in ML-20 cells although it did inhibit DNA synthesis induced by estrogen-stripped calf serum (CCS) suggesting that MEK activation plays an important role in growth signaling induced by serum components other than estrogen. Consistent with this notion, MEK knockdown only modestly decreased DNA synthesis induced by E(2)-supplemented CCS medium in ML-20 cells. Similarly, MEK knockdown only caused moderate decreases in DNA synthesis induced by fibroblast growth factor-1 (FGF-1) or heregulin-beta1 (HRGbeta1) in this media. Also, there were only minimal effects of MEK knockdown in cells treated with growth factor-supplemented serum-free medium. Although MEK depletion inhibited ERK1/2 phosphorylation induced by CCS in these cells, that induced by growth factor supplemented CCS media was relatively unaffected. Similarly, ERK1/2 phosphorylation induced by growth factor-supplemented serum-free media was also relatively unaffected by MEK depletion. These results suggest that pathways regulating DNA synthesis induced by serum in MCF-7 cells are significantly more dependent on constitutive MEK levels than that induced by E(2) or growth factors.
authors.affiliation: Biochemistry and Molecular Biology Department, Drug Discovery Division, Southern Research Institute, Birmingham, AL 35255, USA.
authors.forename: Norman R
authors.initials: NR
authors.lastname: Estes
authors.forename: Jaideep V
authors.initials: JV
authors.lastname: Thottassery
authors.forename: Louise
authors.initials: L
authors.lastname: Westbrook
authors.forename: Francis G
authors.initials: FG
authors.lastname: Kern
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D001973:Bromodeoxyuridine / Q000378:metabolism; D016895:Culture Media, Serum-Free; D004273:DNA, Neoplasm / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D004958:Estradiol / Q000494:pharmacology*; D016220:Fibroblast Growth Factor 1 / Q000037:antagonists & inhibitors / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000494:pharmacology; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology*; D048369:MAP Kinase Kinase 1 / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D020890:Neuregulin-1 / Q000037:antagonists & inhibitors / Q000494:pharmacology; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000235:genetics; D044967:Serum; D014162:Transfection
chemical_list: D016895:Culture Media, Serum-Free; D004273:DNA, Neoplasm; D036341:Intercellular Signaling Peptides and Proteins; D020890:Neuregulin-1; D019384:Nucleic Acid Synthesis Inhibitors; D034741:RNA, Small Interfering; D016220:Fibroblast Growth Factor 1; C087230:heregulin beta1; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; C482128:MAP2K2 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020930:MAP Kinase Kinase Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D001973:Bromodeoxyuridine