Role of the transcription factor activator protein-2alpha in prostate carcinogenesis

Activator protein 2α (AP-2) is a transcription factor known to play a crucial role in the progression of malignant melanoma, colorectal carcinoma, and breast cancer. Several AP-2 target genes are known to be deregulated in prostate cancer, therefore, we hypothesize that loss AP-2 expression plays a causal role in prostate carcinogenesis. Immunofluorescent staining for AP-2 of 30 radical prostatectomy specimens demonstrated that while AP-2 was highly expressed in normal prostate epithelium, its expression was lost in most cases of high grade prostatic intraepithelial neoplasia (PIN), and all cases of prostate cancer studied. Additional analyses demonstrated that AP-2 was associated with normal luminal differentiation and it was not expressed in the basal cell layer. In cell lines, AP-2 was strongly expressed in immortalized normal prostate epithelial cells, whereas low expression was observed in the LNCaP, LNCaP-LN3, and PC3M-LN4 prostate cancer cell lines. Transfection of the highly tumorigenic and metastatic cell line PC3M-LN4 with the AP-2 gene significantly decreased tumor growth in the prostate of nude mice (p = 0.032) and inhibited metastases to the lymph nodes. Moreover, transfection of the low tumorigenic, low metastatic cell line LNCaP-LN3 with full length AP-2; resulted in complete inhibition of tumor incidence in the AP-2 transfectants (0/19) vs. neo control (10/16). A potential mechanism for this loss of tumorigenicity was the modulation of gene expression in prostate cancer cells that mimicked the normal phenotype. Analysis of differential expression between neo control- and AP-2-transfected cells in vitro and in tumors demonstrated low VEGF expression in AP-2 transfectants. We further demonstrated that AP-2 acted as a transcriptional repressor of the VEGF promoter by binding to a GC-rich region located between −88 and −66. This region contains an AP-2 consensus element overlapping two Sp1 consensus elements. We found that Sp3 and AP-2 bound to this region in a mutually exclusive manner to promote activation or repression. Increased VEGF expression has been observed in high grade PIN and in prostate cancer. Here we provide evidence that this early molecular change could be a result of loss of AP-2 expression in the prostatic epithelium. ^

Na 1 Nachlass Max Horkheimer, 103 - Korrespondenzen u.a. mit Maria Pattermann und Franz Neumann (p. III 11, 1-335)

1 Drucksache der Rechtsanwaltskanzlei Pacht, Tannenbaum & Ross, 1951; 2 Briefe zwischen der Pädagogischen Hauptstelle der Gewerkschaft Erziehung u. Wissenschaft und Max Horkheimer, 1954; 1 Brief vom Pädagogischen Verlag B. Schulz an Max Horkheimer, 1950; 3 Briefe zwischen dem Professor Erwin Walter Palm und Max Horkheimer, 1957-1958; 2 Briefe zwischen Helena Brans und Max Horkheimer, 1953; 2 Briefe vom Park-Hotel Frankfurt an Max Horkheimer,1957-1958; 1 Brief von Enno Patalas an Max Horkheimer, 1 Brief von Theodor W. Adorno an Enno Patalas, 1956; 2 Briefe zwischen Dieter Pätzold und Max Horkheimer, 1952; 8 Briefe zwischen Maria Pattermann und Max Horkheimer, 1952-1958; 2 Briefe zwischen F. Perrot und Max Horkheimer, 1953; 2 Briefe zwischen der Buchhandlung Werner Peter und Max Horkheimer, 1954; 3 Briefe zwischen Alfred Peters und Max Horkheimer, 1952-1953; 1 Zeugnis von dem Studenten Joachim Peter, 1953; 1 Brief von Max Horkheimer an F.H. Peterson, 1950; Briefwechsel zwischen dem Studenten Klaus Peuker und Max Horkheimer, 1951; 1 Brief des Chefredakteuren Karl Pfannkuch an Max Horkheimer, 1955; 1 Brief von Dr. Karl Pfauter an Max Horkheimer, 1952; Briefwechsel zwischen der Studentin Renate Pflaume und Max Horkheimer, 1952; Briefwechsel zwischen Joseph B. Phillips und Max Horkheimer, 1955; 1 Brief von Professor Josef Pieper an Max Horkheimer , 1951; 1 Brief von Ehrenfried Pihan an Max Horkheimer, 1953; 1 Brief von F. G. Pincus an Theodor W. Adorno, 1954; Briefwechsel zwischen dem Professor Koppel S. Pinson und Max Horkheimer, 1956; 2 Briefe zwischen dem Professor Kurt Pinthus und Max Horkheimer, 1953; 1 Brief an Dr. Knut Pipping von Max Horkheimer, 1950; 2 Briefe zwischen Erwin Piscator und Max Horkheimer, 1954; Briefwechsel zwischen der Max-Planck-Gesellschaft zur Förderung der Wissenschaften und Max Horkheimer, 1953-1955; Briefwechsel zwischen dem Professor Richard Plant und Max Horkheimer, 1953 und 2 Briefe zwischen Professor Richard Plant und Margarete Feretty-Füredi, 1953; Briefwechsel zwischen dem Professor Johann Plenge und Max Horkheimer, 1951-1952; Briefwechsel zwischen Barbara Pleyer und Max Horkheimer, 1954; 1 Brief von Erich Paul Pechmann an Max Horkheimer, 1952; Briefwechsel zwischen Dr. Gerhard Poetzsch und an Max Horkheimer, 1958; Briefwechsel zwischen dem Committee on Science & Freedom und Max Horkheimer, 1955-1956; 1 Brief an den Professor Rudolf Pohl von Max Horkheimer, 1953; 1 Brief von der Zeitschrift "Die politsche Meinung" an Max Horkheimer, 1956; 1 Brief von Max F. Pollack an Max Horkheimer, 1954; 1 Brief von dem Professor Wilhelm Polligkeit an Max Horkheimer, 1951; 1 Brief von dem Poli-Verlag an Max Horkheimer, 1950; Briefwechsel zwischen Alexej Poremsky und Max Horkheimer, 1955; 1 Brief von Rita Post an Max Horkheimer, 1952; 1 Brief von Max Potzin an Max Horkheimer, 1951; Briefwechsel zwischen dem Oberstudienrat Max Preitz und Max Horkheimer, 1955; 1 Brief von dem Professor Wolfgang Preiser an Max Horkheimer, 1952; 1 Gutachten und Beilagen von Dr. Karl A. Preuschen an Max Horkheimer, 1955; Briefwechsel und Beilagen zwischen dem Direktor des The Commonwealth Fund E. K. Wickman und Max Horkheimer, 1955; Briefwechsel zwischen Klaus H. Pringsheim und Max Horkheimer, 1952-1958; 1 Brief von Curt Freiherr von Preuschen an Max Horkheimer, 1953; Briefwechsel zwischen Rüdiger Proske und Max Horkheimer, 1951; Briefwechsel und Beilagen zwischen Dr. Harry Pross und Max Horkheimer, 1954; 1 Brief von dem Professor Franz Neumann an Max Horkheimer, 1954; 1 Brief an G. H. Graber von Max Horkheimer, 1953; Briefwechsel zwischen dem Quaker Service und Max Horkheimer, 1950; Briefwechsel zwischn Günther Quandt und Max Horkheimer, 1953 und 2 Todesanzeigen, 1955; 1 Brief an den Querido-Verlag von Max Horkheimer, 1951; Briefwechsel zwischen Emil Querinjean und Max Horkheimer, 1955; Briefwechsel zwischen John Raatjes und Max Horkheimer, 1956; Briefwechsel zwischen der Zeitschrift the humanist radical und Max Horkheimer, 1957; Briefwechsel zwischen Sitangghu Chatterji und Max Horkheimer, 1957; 1 Brief von der Radio Corporation of America an Max Horkheimer, 1953; 1 Brief und Beilagen vom Radiodiffusion et Télévision Francaises an Max Horkheimer, 1955; Briefwechsel zwischen dem Österreichischer Rundfunk Radio Wien und Max Horkheimer, 1956; 1 Brief von dem Professor Boris Rajewsky an Max Horkheimer, 1953; 1 Brief an Else Rang von Max Horkheimer, 1950; Briefwechsel zwischen Heinz Raspini und Max Horkheimer, 1956; 1 Drucksache zwischen Hanna Becker vom Rath und Max Horkheimer, 1953; 1 Telegramm von dem Professor Roland Rather an Max Horkheimer und 2 Briefe von Max Horkheimer an Roland Rather, 1957; Briefwechsel zwischen dem Professor L. J. Rather und Max Horkheimer, 1955; Briefwechsel zwischen Phillip Roth und Max Horkheimer, 1958; Briefwechsel zwischen Sibnarayan Ray und Max Horkheimer, 1956-1957; Briefwechsel mit Beilagen zwischen dem Rationalisierungs-Kuratorium der Deutschen Wirtschaft und Max Horkheimer, 1954; 1 Aktennotiz von dem Jornalisten Rasten der dänischen Zeitung Politiken, 1953; Briefwechsel zwischen Wolfgang M. Rauch und Max Horkheimer, 1956; 1 Anzeige der Ingeborg Rauter, 1953; 1 Brief von dem Hotel Reber au lac an Max Horkheimer, 1955; Briefwechsel zwischen Alice Reboly und Max Horkheimer, 1955; 3 Briefe an die Regensburger Zeitungen von Max Horkheimer, 1956; 1 Brief an den Professor Klaus Reich von Max Horkheimer, 1950; Briefwechsel zwischen dem Reinhardt, Ernst, Verlag und Max Horkheimer, 1953; 1 Brief von dem Apotheker Hermann Reitberger an Max Horkheimer, 1955; Briefwechsel zwischen Dr. Paul Reiwald und Max Horkheimer, 1950; 1 Brief von dem Journalist Godo Remszhardt an Max Horkheimer, 1954; Briefwechsel zwischen Dr. Irmgard Rexroth-Kern und Max Horkheimer, 1952; Briefwechsel zwischen Hans Rheinbay und Max Horkheimer, 1955; 1 Brief von der Universität Bonn an Max Horkheimer, 1953; 1 Brief an den Rheinischer Merkur von Max Horkheimer, 1951; 1 Brief an die Rheinische Post von Max Horkheimer, 1954; 1 Brief an Hans Richter von Max Horkheimer, 1954; Briefwechsel zwischen Dr. Hermann Riefstahl und Max Horkheimer, 1957; Briefwechsel zwischen dem Professor Svend Riemer und Max Horkheimer, 1957; Briefwechsel zwischen dem Ring-Verlag und Max Horkheimer, 1957; Briefwechsel zwischen Werner Rings und Max Horkheimer, 1954; Briefwechsel zwischen Martha Ritter-Raabe und Max Horkheimer, 1955; Briefwechsel zwischen Otto-Heinz Rocholl und Max Horkheimer, 1954; 1 Brief von Hilde Rodemann an Max Horkheimer, 1952; 1 Brief von Edouard Roditi an Max Horkheimer, 1951 und 1 Brief von Theodor W. Adorno an Edouard Roditi, 1951; Briefwechsel zwischen der Zeitschrift Studenten-Kurier und Max Horkheimer, 1955; 1 Brief von Karl Roeloffs an Max Horkheimer, 1953; Briefwechsel zwischen der Kunsthistorikerin Hanna Rhode und Max Horkheimer, 1950-1951; 1 Brief an Dr. Anna Ronge von Max Horkheimer, 1954; 2 Brief an Kathe Romney von Max Horkheimer, 1952-1955; Briefwechsel zwischen Dr. Paul Rompel und Max Horkheimer, 1952; 1 Brief an den Zahnartz Dr. Ingo Ropper von Max Horkheimer, 1953; Briefwechsel zwischen Ilse Wallis Ross und Max Horkheimer, 1955-1956; 1 Brief von dem Professor Hans W. Rosenhaupt an Max Horkheimer, 1952; 1 Brief von Rosenthal an Max Horkheimer, 1958; Briefwechsel zwischen dem Generalstaatsanwalt und Staatssekretär Erich Rosenthal-Pelldram und Max Horkheimer, 1952-1956; Briefwechsel zwischen Lessing J. Rosenwald und Max Horkheimer, 1950; Briefwechsel zwischen dem Lieutenant Dr. Alan O. Ross und Max Horkheimer, 1955; 4 Briefe und Beilagen von Günther Roth an Max Horkheimer, 1953-1957; Briefwechsel zwischen dem Professor Wolfram Eberhardt und Max Horkheimer, 1955; 1 Brief an den Professor M. A. Stewart von Theodor W. Adorno, 1955; Briefwechsel zwischen dem Professor Rheinhard Bendix und Max Horkheimer, 1955; Briefwechsel zwischen der Studentin Valentine Rothe und Max Horkheimer, 1957; 1 Brief von dem Student Rudolf Rothrock an Max Horkheimer, 1953; 1 Brief von Guy Roustang an Max Horkheimer, ohne Jahr; 1 Brief von Heinz Maria Ledig-Rowohlt an Max Horkheimer, 1950; Briefwechsel zwischen Ellen Roy und Max Horkheimer, 1956; Briefwechsel zwischen dem Professor Paul Royen und Max Horkheimer, 1954; Briefwechsel zwischen dem Staatsminister August Rucker und Max Horkheimer, 1955-1957 1 Brief an den Staatsminister August Rucker von Leopold von Wiese, 1955; 1 Bericht von Walter Rüegg, 1953 und 2 Briefe von Max Horkheimer an den Professor Walter Rüegg, 1955; 3 Briefe an den Professor Alexander Rüstow von Max Horkheimer, 1953-1958; Briefwechsel zwischen Käthe von Ruckteschell und Max Horkheimer, 1951-1954; Briefwechsel zwischen dem Student Gerhard Rudolph und Max Horkheimer, 1954; 1 Brief von der Ruf und Echo, Arbeitsgemeischaft an Max Horkheimer, 1952; 3 Briefe an den Professor Jay Rumney von Max Horkheimer, 1952-1954; Briefwechsel zwischen Clarence R. Rungee und Max Horkheimer, 1951-1952;

Na 1 Nachlass Max Horkheimer, 96 - Korrespondenzen u.a. mit Jürgen Habermas (p. III 6, 1-421)

5 Briefe mit Antwort an Inga Haag, 1951-1955; 1 Brief mit Antwort von Jürgen Habermas an Max Horkheimer, 1955; 1 Brief von Ministerialrat i. R. Theodor Häbich an Max Horkheimer, 1957; 2 Briefe mit Antwort von cand. phil. Walter Hähnle an Max Horkheimer, 1955, 1957; 1 Brief mit Antwort von Sekretärin Jutta Hagen an Max Horkheimer, 1956; 1 Dissertationsauszug von Volker Freiherr von Hagen, 1954; 1 Brief mit Antwort von Julia Hagenbucher an Max Horkheimer, 1951/1952; 1 Entwurf zu einem Gratulationsschreiben von Max Horkheimer an Professor Otto Hahn, ohne Jahr; 2 Drucksachen von Obermagistratsrat Julius Hahn, 1953, 1955; 1 Brief mit Antwort von Theodor W. Adorno, von Dr. Hans Hahn an Max Horkheimer, 1952; 1 Brief von Theodor W. Adorno an Dr. Hans Hahn, 1952; 1 Danksagung von Rabbi Hugo Hahn, 1955; 3 Briefe mit Antwort von Paul Hahn an Max Horkheimer, 1951-1958; 1 Brief von Max Horkheimer an die Gebrüder Haldy, 1952; 1 Brief mit Antwort und Beilage von Professor George W. F. Hallgarten an Max Horkheimer, 1950; 1 Rundschreiben von Arzt und Psychotherapeut Hans Hammer, 1957; 1 Brief von Max Horkheimer an Margarete Hampf-Solm, 1955; 1 Brief mit Antwort von Professor Eduardo Hamuy an Max Horkheimer, 1952; 1 Brief von der Stadtärztin Dr. med. Carola Hannappel an Max Horkheimer, 1951; 1 Brief von Hansenmeister an Max Horkheimer, 1951; 1 Brief mit Antwort und Beilage von der Buchhandlung Ludwig Häntzschel an Max Horkheimer, 1958; 1 Brief von Professor Frederick Harris Harbison an Max Horkheimer, 1952; 3 Briefe mit Antwort von Robert Harcourt an Max Horkheimer, 1958; 1 Brief von Karl Hardach an Max Horkheimer, 1957; 1 Brief mit Antwort von Emilie Harlacher an Max Horkheimer, 1952; 1 Drucksache mit Antwort von Oberkirchenrat Otto L. A. von Harling an Max Horkheimer, 1955; 1 Brief mit Antwort von Gertrud Harms an Max Horkheimer, 1955; 2 Brief mit Antwort von Professor Wolfgang Hartke an Max Horkheimer, 1954-1956; 2 Briefe mit antwort von Max Horkheimer an Senator Georg Hartmann, 1951, 1954; 3 briefe mit Antwort und Beilage von Ökonom Heinz Hartmann an Max Horkheimer, 1956-1958; 1 Brief mit Antwort von Professor Wilbert E. Moore an Max Horkheimer, 1957; 3 Briefe mit Antwort und Beilage von Dr. phil. Leo Hartmann an Max Horkheimer, 1957-1858; 1 Brief mit Antowort von Dr. phil. Eckardt Mesch an Max Horkheimer, 1957; 1 Brief mit Antwort von Luzie Hatch an Max Horkheimer, 1954; 1 Brief von Max Horkheimer an den Direktor H. W. Haupt, 1950; 1 Drucksache von Haus Schwalbach, 1951; 4 Briefe mit Antwort von Professor Gottfried und Ellen Hausmann an Max Horkheimer, 1951-1958; 6 Briefe mit Antwort von Eva Haussner an Max Horkheimer, 1957, 1958; 1 Brief mit Antwort von Professor Robert J. Havighurst an Max Horkheimer, 1951; 1 Brief mit Beilage von Herbert Hax an Max Horkheimer, 1955; 2 Briefe mit Antwort und Beilage von Jean Louis Hébarre an Max Horkheimer, 1950-1952; 1 Brief mit Antwort von dem Hebedienst für Elektrizität, Gas und Wasser an Max Horkheimer, 1951; 5 Briefe mit Antwort und Beilage von Professor Otto Heckmann an Max Horkheimer, 1952, 1954; 1 Brief von Melvin J. Lasky an August Heckscher, 1957; 3 Briefe mit Antwort von Marie Heep an Max Horkheimer, 1956-1858; 1 Brief von der Buchhandlung Thekla Heer an Max Horkheimer, 1953; 1 Brief mit Antwort von dem Verleger Jakob Hegner an Max Horkheimer, 1955; 1 Brief von Dr. phil. Rudolf M. Heilbrunn an Max Horkheimer, 1953; 1 Brief mit Antwort von Professor Eduard Heimann an Max Horkheimer, 1952; 1 Brief von Professor Eduard Heimann an Theodor W. Adorno, 1957; 1 Brief mit Antwort von stud. phil. Wolfgang Heinrich an Max Horkheimer, 1958; 1 Brief von Max Horkheimer an den Direktor Helmuth Heintzmann, 1955; 1 Aktennotiz von Professor Bernhard Heller, 1956; 1 Brief mit Antwort von Philipp A. Heller an Max Horkheimer, 1952; 1 Brief von Max Horkheimer an Assistent Winfried Hellmann, 1957; 2 Briefe mit Antwort von Professor Arthur Henkel an Max Horkheimer, 1953/1954; 1 Brief von Max Horkheiemr an Dorothy Henkel, 1952; 2 Briefe mit Antwort von Dr. jur. Werner Hennig an Max Horkheimer, 1951; 1 Brief von Max Horkheimer an Professor Wilhelm Hennis, 1957; 3 Briefe mit Antwort und Beilage von Professor Fritz Hepner an Max Horkheimer, 1953; 1 Brief von Max Horkheimer an den Hessischer Minister für Erziehung und Volksbildung, 1950; 1 Brief mit Antwort von Professor Henrietta Herbolsheimer an Max Horkheimer, 1957/1958; 2 Briefe mit Antwort von P. G. Herbst an Max Horkheimer, 1952; 1 Brief von Max Horkheimer an den Herder Verlag, 1953; 2 Briefe mit Antwort, Beilagen und Aktennotizen von Guenter R. Herz an Max Horkheimer, 1956-1957; 2 Briefe mit Antwort unv Beilagen von Professor Theodor W. Adorno, von Dr. phil. Günther Herzberg an Max Horkheimer, 1951-1953; 1 Brief von Professor Theodor W. Adrono an Dr. phil. Günther Herzberg, 1951; 1 Brief von Dr. phil. G. Herzfeld an Max Horkheimer, 1952; 1 Brief von dem Herzog-Film an Max Horkheimer, 1952; 1 Brief mit Antwort von Professor Theodor W. Adorno, von Professor Erich Herzog an Max Horkheimer, 1952; 1 Brief von Professor Theodor W. Adorno an Professor Erich Herzog, 1952; 1 Brief mit Antwort von dem Verlag Otto H. Hess an Max Horkheimer, 1954; 1 Brief von Professor Gerhard Hess an Max Horkheimer, 1953; 1 Drucksachevon dem Hessischer Arbeitsausschuss gegen Rekrutierung, 1952; 1 Brief mit Beilage von dem Hotel Hessischer Hof an Max Horkheimer, 1956; 1 Brief mit Antwort von dem Hessischer Landesverband für Erwachsenenbildung an Max Horkheimer, 1956; 2 Briefe mit Antwort und Beilage von Marc Heurgon an Max Horkheimer, 1958; 1 Brief mit Beilage von Ruth Heydebrand an Max Horkheimer, [1955]; 1 Brief mit Antwort von Professor Frederick W. J. Heuser an Max Horkheimer, 1954; 2 Briefe mit Antwort von Professor Joh Erich Heyde an Max Horkheimer, 1958; 1 Befürwortung von Wolf von Heydebrand an Max Horkheimer, 1954; 1 Brief mit Antwort von Professor Heinz Joachim Heydorn an Max Horkheimer, 1953; 1 Brief mit Antwort und Beilage von dem Arzt Otto Heymann an Max Horkheimer, 1955; 5 Briefe zwischen dem Devisenberater und Steuerhelfer Joseph Christ und Max Horkheimer, 1955, 1956, 1961; 1 Brief von dem Office of the United States High Commissioner for Germany an Max Horkheimer, 1953; 1 Lebenslauf von Elen B. Hill, ohne Jahr; 1 Brief von Kurt H. Wolff an Max Horkheimer, 1952; 1 Brief von Rolf Himmelreich an Max Horkheimer, 1956; 1 Brief mit Antwort von Dr. Rolf Hinder an Max Horkheimer, 1953; 1 Brief mit Antwort von Anton Hinsinger an Max Horkheimer, 1953; 1 Brief mit Antwort von dem Hippokrates-Verlag an Max Horkheimer, 1952; 1 Brief von Bernice L. Hirsch anMax Horkheimer, 1957; 4 Briefe und Beilagen zwischen dem Historiker und Soziologe Helmut Hirsch an Max Horkheimer, 1951-1954, 25.05.1951; 3 Briefe mit Antwort von Lux Hirsch an Max Horkheimer, 1958; 1 Brief mit Antwort von Trude Hirschberg an Max Horkheimer, 1951; 1 Brief mit Antwort von Ingineur Paul F. Hirschfelder an Max Horkheimer, 1952; 1 Brief von Johannes Hirzel an Max Horkheimer, 1955; 1 Brief mit Antwort von dem Historisches Seminar Köln an Max Horkheimer, 1956; 1 Brief mit Antwort und Beilage von Professor Wolfgang Hochheimer an Professor Theodor W. Adorno, 1952; 2 Briefe von Max Horkheimer an Professor Wolfgang Hochheimer, 1953, 1954; 2 Memoranden von der Deutschen Gesellschaft für Psychologie, 1953; 1 Brief mit Beilage von Stud. phil. Erna Hochleitner an Max Horkheimer, 1956; 1 Brief mit Antwort von Professor Helmut Coing an Max Horkheimer, 1957; 3 Briefe mit Antwort von der Hochschule für Sozialwissenschaften Wilhelmshaven an Max Horkheimer, 1957, 1958; 1 Brief von Max Horkheimer an die Hochschule für Wirtschafts- und Sozialwissenschaften Nürnberg, 1953; 2 Drucksachen von dem Hochschul-Dienst, 1952; 2 Drucksachen von der Hochschule für politische Wissenschaften München, 1952; 1 Brief mit Antwort von Dr. Wolfram Hodermann an Max Horkheimer, 1951; 4 Briefe zwischen Dr. phil. Walter Höllerer und Max Horkheimer, 1956; 1 Brief mit Antwort von Privatdozent Dr. phil. Walter Hoeres anMax Horkheimer, 1956; 2 Briefe mit Antwort von Stud. phil. Charlotte Hoffmann an Max Horkheimer, 1950; 3 Briefe mit Antwort und Beilage von Professor Walter Hoffmann an Max Horkheimer, 1950-1955; 1 Brief mit Antwort von Wolfhart E. V. Hoffmann an Max Horkheimer, 1953; 1 Brief von Max Horkheimer an Dr. Werner Hofmann, 1956; 1 Glückwunschtelegramm mit Antwort von Ernst und Karl Hohner, 1953; 1 Brief von Dozent Uvo Hölscher an Max Horkheimer, 1950; 2 Briefe mit Antwort von Professor Dr. med. K. Holldack an Max Horkheimer, 1957; 2 Briefe mit Antwort von Dipl. Landwirt Bernhard Hollenhorst an Max Horkheimer, 1956; 1 Brief von Hans Heinz Holz an Max Horkheimer, 1951; 2 Briefe mit Antwort und Beilage von Dr. phil. Rudolf Holzinger an Max Horkheimer, 1951, 1952; 1 Brief mit Antwort von Jakob Hommen an Max Horkheimer, 1953; 1 Brief von Adele Hoppe anMax Horkheimer, 1953; 1 Brief mit Antwort von Dr. jur. Anton Horn an Max Horkheimer, 1954; 1 Brief mit Antwort von Dr. phil. Emil Horn an Max Horkheimer, 1953; 1 Brief von der Landesabgeordneten Ruth Horn an H. Maidon, 1953; 1 Brief mit Antwort von Reg.-Direktor Dr. phil. Kurt Horstmann an Max Horkheimer, 1953; 1 Brief von dem Hotel Baur au Lac an H. Maidon, 1958; 2 Briefe mit 1 Antwort von dem Hotel Frankfurter Hof an Max Horkheimer, 1956, 1958; 1 Brief mit Antwort von dem Hotel Stafflenberg an H. Maidon, 1953; 1 Brief von dem Hotel Vier Jahreszeiten, München an Max Horkheimer, 1951; 1 Brief von Max Horkheimer an Jean J. Hubener, 1951; 2 Briefe mit Antwort und Beilage von Susanna Huber-Weisser an Max Horkheimer, 1956; 1 Todesanzeige von dem Sozialgerichtsdirektor Gustav Adolf Hünniger, 1955; 1 Brief von dem Oberstudiendirektor F. Huf an Max Horkheimer, 1952; 1 Brief mit Antwort von Professor H. D. Huggins an Max Horkheimer, 1954; 2 Briefe mit 1 Antwort und 1 Beilage von dem Humboldt-Verlag, Wien-Stuttgart an Max Horkheimer, 1951; 1 Brief von Helge Pross an stud. rer. pol. Kristian Hungar, 1957; 1 Brief von Helmut Hungerland an Max Horkheimer, 1950; 1 Brief mit Antwort von James R. Huntley an Max Horkheimer, 1954; 1 Brief von Professor Robert Maynard Hutchins an Max Horkheimer, 1957;

Involvement of histone H3 methylation in Tup1-Ssn6 repression

The Tup1-Ssn6 complex regulates the expression of diverse classes of genes in Saccharomyces cerevisiae including those regulated by mating type, DNA damage, glucose, and anaerobic stress. The complex is recruited to target genes by sequence-specific repressor proteins. Once recruited to particular promoters, it is not completely clear how it functions to block transcription. Repression probably occurs through interactions with both the basal transcriptional machinery and components of chromatin. Tup1 interactions with chromatin are strongly influenced by acetylation of histories H3 and H4. Tup1 binds to underacetylated histone tails and requires multiple histone deacetylases (HDACs) for its repressive functions. Like acetylation, histone methylation is involved in regulation of gene expression. The possible role of histone methylation in Tup1 repression is not known. Here we examined possible roles of histone methyltransferases in Tup1-Ssn6 functions. We found that like other genes, Tup1-Ssn6 target genes exhibit increases in the levels of histone H3 lysine 4 methylation upon activation. However, deletion of individual or multiple histone methyltransferases (HMTs) and other SET-domain containing genes has no apparent effect on Tup1-Ssn6 mediated repression of a number of well-defined targets. Interestingly, we discovered that Ssn6 interacts with Set2. Since deletion of SET2 does not affect Tup1-Ssn6 repression, Ssn6 may utilize Set2 in other contexts to regulate gene repression. In order examine if the two components of the Tup1-Ssn6 complex have independent functions in the cell, we identified genes differentially expressed in tup1Δ and ssn6Δ mutants using DNA microarrays. Our data indicate that ∼4% of genes in the cell are regulated by Ssn6 independently of Tup1. In addition, expression of genes regulated by Tup1-Ssn6 seems to be differently affected by deletion of Ssn6 and deletion of Tup1, which indicates that these components might have separate functions. Our data shed new light on the classical view of Tup1-Ssn6 functions, and indicate that Ssn6 might have repressive functions as well. ^

The p120-catenin/Kaiso signaling pathway

The canonical and non-canonical Wnt signaling pathways appear to interact with one another as a network in development, or when hyper-activated, in the progression of disease. A much studied key mediator of the canonical Wnt pathway, β-catenin, is characterized by a central armadillo-repeat domain that engages in multiple protein-protein interactions, such as those with cadherins functioning at cell-cell contact regions. In the nucleus, β-catenin forms a complex with the repressor TCF/LEF, promoting the activation of genes participating in processes such as proliferation, differentiation and stem cell survival. Somewhat similarly, the p120-catenin binds the distinct transcriptional repressor Kaiso, relieving Kaiso-mediated repression to promote gene activation. Here, employing Xenopus laevis, I report upon both downstream and upstream aspects of the p120-catenin/Kaiso pathway which was previously poorly understood. I first show that Kaiso, a BTB/POZ zinc-finger family member, directly represses canonical Wnt gene targets (Siamois, c-Fos, Cyclin-D1 and c-Myc) in conjunction with TCF. Depletion or dominant-negative inhibition of xKaiso results in Siamois de-repression, while xKaiso over-expression induces additional Siamois repression through recruitment of N-CoR co-repressor and chromatin modifications. Functional interdependencies are further corroborated by the capacity of Kaiso to suppress β-catenin-induced axis duplication. Thus, my work inter-relates the p120-catenin/Kaiso and β-catenin/TCF pathways at the level of specific gene promoters important in development and cancer progression. Regarding upstream aspects of the p120-catenin/Kaiso pathway, I collaboratively identified p120 in association with Frodo, a protein previously identified as a component of the canonical (β-catenin dependent) Wnt pathway. I determined that canonical Wnt signals result in Frodo-mediated stabilization of p120-catenin, resulting in the sequestration of Kaiso to the cytoplasm and thereby the activation (relief of repression) of gene targets. Developmental evidence supporting this view included findings that Frodo has the capacity to partially rescue Kaiso over-expression phenotypes in early Xenopus embryos. Taken together, my studies point to the convergence of p120-catenin/Kaiso and β-catenin/TCF signaling pathways at the level of gene transcription as well as at more upstream points during vertebrate development. ^

Tp53-dependent repression of cell cycle target genes: Global and mechanistic analysis

Most studies of p53 function have focused on genes transactivated by p53. It is less widely appreciated that p53 can repress target genes to affect a particular cellular response. There is evidence that repression is important for p53-induced apoptosis and cell cycle arrest. It is less clear if repression is important for other p53 functions. A comprehensive knowledge of the genes repressed by p53 and the cellular processes they affect is currently lacking. We used an expression profiling strategy to identify p53-responsive genes following adenoviral p53 gene transfer (Ad-p53) in PC3 prostate cancer cells. A total of 111 genes represented on the Affymetrix U133A microarray were repressed more than two fold (p ≤ 0.05) by p53. An objective assessment of array data quality was carried out using RT-PCR of 20 randomly selected genes. We estimate a confirmation rate of >95.5% for the complete data set. Functional over-representation analysis was used to identify cellular processes potentially affected by p53-mediated repression. Cell cycle regulatory genes exhibited significant enrichment (p ≤ 5E-28) within the repressed targets. Several of these genes are repressed in a p53-dependent manner following DNA damage, but preceding cell cycle arrest. These findings identify novel p53-repressed targets and indicate that p53-induced cell cycle arrest is a function of not only the transactivation of cell cycle inhibitors (e.g., p21), but also the repression of targets that act at each phase of the cell cycle. The mechanism of repression of this set of p53 targets was investigated. Most of the repressed genes identified here do not harbor consensus p53 DNA binding sites but do contain binding sites for E2F transcription factors. We demonstrate a role for E2F/RB repressor complexes in our system. Importantly, p53 is found at the promoter of CDC25A. CDC25A protein is rapidly degraded in response to DNA damage. Our group has demonstrated for the first time that CDC25A is also repressed at the transcript level by p53. This work has important implications for understanding the DNA damage cell cycle checkpoint response and the link between E2F/RB complexes and p53 in the repression of target genes. ^

Mechanisms of heterosynaptic modulation of transmission in Aplysia

Heterosynaptic plasticity has received considerable attention as a means to induce and maintain cell-wide, as opposed to synapse-specific, learning-related modifications. Modulatory neurotransmitters are thought to provide the attentional and motivational state for memory formation. However, the cellular and molecular mechanisms mediating the effects of most of these modulators on synaptic plasticity and learning remain unclear. A well established system for the study of heterosynaptic plasticity is the Aplysia sensorimotor synapse, which is subject regulation by at least two neuromodulators, serotonin (5-HT) and FMRFa. ^ 5-HT engages multiple second messenger cascades to induce short- and long-term facilitation (STF and LTF, respectively) of synaptic transmission. One mechanism proposed to be involved in STF is mobilization of synaptic vesicles from a storage pool to a releasable pool. To investigate this hypothesis, we examined the involvement of the protein synapsin, a central element in the regulation of the storage pool of vesicles in nerve terminals, in STF. 5-HT induced phosphorylation of synapsin and modified its subcellular distribution via PKA and p42/44 MAPK. Electrophysiological experiments and computer simulations suggested that synapsin can support heterosynaptic plasticity by regulating vesicle mobilization. ^ FMRFa induce short- and long-term synaptic depression in Aplysia . Long-term depression (LTD) correlates with morphological changes, the mechanisms of which remain elusive. LTD is also transcription- and translation-dependent, but little is known about the genes expressed and their regulation. We investigated the role of protein degradation via the ubiquitin-proteasome system and the regulation of one of its components, ubiquitin C-terminal hydrolase (ap-uch), in LTD. LTD was sensitive to inhibition of the proteasome and was associated with upregulation of ap-uch mRNA and protein. This upregulation appeared to be mediated by the transcription factor CREB2, which is generally regarded as a transcription repressor. These results suggest that proteasome-mediated protein degradation is engaged in LTD and that CREB2 may act as a transcription activator under certain conditions. ^ These and additional studies on the interaction of the 5-HT and FMRFa-activated pathways suggest that different neuromodulators, by activating several and sometimes overlapping signaling cascades, can exercise bidirectional control on synaptic gain and information processing.^

Hypoxia-induced transcriptional regulation through chromatin modifications and NC2 function

In response to tumor hypoxia, specific genes that promote angiogenesis, proliferation, and survival are induced. Globally, I find that hypoxia induces a mixed pattern of histone modifications that are typically associated with either transcriptional activation or repression. Furthermore, I find that selective activation of hypoxia-inducible genes occurs simultaneously with widespread repression of transcription. I analyzed histone modifications at the core promoters of hypoxia-repressed and -activated genes and find that distinct patterns of histone modifications correlate with transcriptional activity. Additionally, I discovered that trimethylated H3-K4, a modification generally associated with transcriptional activation, is induced at both hypoxia-activated and repressed genes, suggesting a novel pattern of histone modifications induced during hypoxia. ^ In order to determine the mechanism of hypoxia-induced widespread repression of transcription, I focused my studies on negative cofactor 2 (NC2). Previously, we found that hypoxia-induced repression of the alpha-fetoprotein (AFP) gene occurs during preinitiation complex (PIC) assembly, and I find that NC2, an inhibitor of PIC assembly, is induced during hypoxia. Moreover, I find that the beta subunit of NC2 is essential for hypoxia-mediated repression of AFP, as well as the widespread repression of transcription observed during hypoxia. Previous data in Drosophila and S. cerevisiae indicate that NC2 functions as either an activator or a repressor of transcription. The mechanism of NC2-mediated activation remains unclear; although, Drosophila NC2 function correlates with specific core promoter elements. I tested if NC2 activates transcription in mammalian cells using this core promoter-specific model as a guide. Utilizing site-specific mutagenesis, I find that NC2 function in mammalian cells is not dependent upon specific core promoter elements; however, I do find that mammalian NC2 does function in a gene-specific manner as either an activator or repressor of transcription during hypoxia. Furthermore, I find that binding of the alpha subunit of NC2 specifically correlates with NC2-mediated transcriptional activation. NC2α and NC2β are both required for NC2-mediated transcriptional activation; whereas, NC2β alone is required for hypoxia-induced transcriptional repression. Together, these data indicate that hypoxia mediates changes in gene expression through both chromatin modifications and NC2 function. ^

DNA methylation inhibits p53 mediated survivin repression in cancer cells

Survivin (BIRC5) is a member of the Inhibitor of Apoptosis (IAP) gene family and functions as a chromosomal passenger protein as well as a mediator of cell survival. Survivin is widely expressed during embryonic development then becomes transcriptionally silent in most highly differentiated adult tissues. It is also overexpressed in virtually every type of tumor. The survivin promoter contains a canonical CpG island that has been described as epigenetically regulated by DNA methylation. We observed that survivin is overexpressed in high grade, poorly differentiated endometrial tumors, and we hypothesized that DNA hypomethylation could explain this expression pattern. Surprisingly, methylation specific PCR and bisulfite pyrosequencing analysis showed that survivin was hypermethylated in endometrial tumors and that this hypermethylation correlated with increased survivin expression. We proposed that methylation could activate survivin expression by inhibit the binding of a transcriptional repressor. ^ The tumor suppressor protein p53 is a well documented transcriptional repressor of survivin and examination of the survivin promoter showed that the p53 binding site contains 3 CpG sites which often become methylated in endometrial tumors. To determine if methylation regulates survivin expression, we treated HCT116 cells with decitabine, a demethylation agent, and observed that survivin transcript and protein levels were significantly repressed following demethylation in a p53 dependent manner. Subsequent binding studies confirmed that DNA methylation inhibited the binding of p53 protein to its binding site in the survivin promoter. ^ We are the first to report this novel mechanism of epigenetic regulation of survivin. We also conducted microarray analysis which showed that many other cancer relevant genes may also be regulated in this manner. While demethylation agents are traditionally thought to inhibit cancer cell growth by reactivating tumor suppressors, our results indicate that an additional important mechanism is to decrease the expression of oncogenes. ^

The role of AKT-mediated phosphorylation in suppression of MAD1 and the development of new approach in protein complex detection

MAX dimerization protein 1 (MAD1) is a basic-helix-loop-helix transcription factors that recruits transcription repressor such as HDAC to suppress target genes transcription. It antagonizes to MYC because the promoter binding sites for MYC are usually also serve as the binding sites for MAD1 so they compete for it. However, the mechanism of the switch between MYC and MAD1 in turning on and off of genes' transcription is obscure. In this study, we demonstrated that AKT-mediated MAD1 phosphorylation inhibits MAD1 transcription repression function. The association between MAD1 and its target genes' promoter is reduced after been phosphorylated by AKT; therefore, consequently, allows MYC to occupy the binding site and activates transcription. Mutation of such phosphorylation site abrogates the inhibition from AKT. In addition, functional assays demonstrated that AKT suppressed MAD1-mediated transcription repression of its target genes hTERT and ODC. Cell cycle and cell growth were also been released from inhibition by MAD1 in the presents of AKT. Taken together, our study suggests that MAD1 is a novel substrate of AKT and AKT-mediated MAD1 phosphorylation inhibits MAD1function; therefore, activates MAD1 target genes expression. ^ Furthermore, analysis of protein-protein interaction is indispensable for current molecular biology research, but multiplex protein dynamics in cells is too complicated to be analyzed by using existing biochemical methods. To overcome the disadvantage, we have developed a single molecule level detection system with nanofluidic chip. Single molecule was analyzed based on their fluorescent profile and their profiles were plotted into 2 dimensional time co-incident photon burst diagram (2DTP). From this 2DTP, protein complexes were characterized. These results demonstrate that the nanochannel protein detection system is a promising tool for future molecular biology. ^

ARD1 stabilization of TSC2 suppresses tumorigenesis via the mTOR signaling pathway

Mammalian target of rapamycin (mTOR) plays an important role in regulating various cellular functions, and the tuberous sclerosis 1 (TSC1)/TSC2 complex serves as a major repressor of the mTOR pathway. Here we demonstrated that arrest-defective protein 1 (ARD1) physically interacts with, acetylates, and stabilizes TSC2, thereby reducing mTOR activity. The inhibition of mTOR by ARD1 suppresses cell proliferation and increases autophagy, which further impairs tumorigenicity. Correlation between the levels of ARD1 and TSC2 was found in multiple tumor types, suggesting the physiological importance of ARD1 in stabilizing TSC2. Moreover, evaluation of loss of heterozygosity (LOH) at Xq28 revealed allelic loss in 31% of tested breast cancer cell lines and tumor samples. Together, our findings suggest that ARD1 functions as a negative regulator of the mTOR pathway and that dysregulation of the ARD1/TSC2/mTOR axis may contribute to cancer development. To further explore the signaling pathway of ARD1, we provided evidence showing the phosphorylation of ARD1 by IKKβ, which mediated the destabilization of ARD1. Future work may be needed to study the biological effect of this post-translational modification. ^

Control of the master virulence regulatory gene atxA in Bacillus anthracis

Transcription of the Bacillus anthracis structural genes for the anthrax toxin proteins and biosynthetic operon for capsule are positively regulated by AtxA, a transcription regulator with unique properties. Consistent with the role of atxA in virulence factor expression, a B. anthracis atxA-null mutant is avirulent in a murine model for anthrax. In batch culture, multiple signals impact atxA transcript levels, and the timing and steady state level of atxA expression is critical for optimal toxin and capsule synthesis. Despite the apparent complex control of atxA transcription, only one trans-acting protein, the transition state regulator AbrB, has been demonstrated to directly interact with the atxA promoter. The AbrB-binding site has been described, but additional cis-acting control sequences have not been defined. Using transcriptional lacZ fusions, electrophoretic mobility shift assays, and Western blot analysis, the cis-acting elements and trans-acting factors involved in regulation of atxA in B. anthracis strains containing either both virulence plasmids, pXO1 and pXO2, or only one plasmid, pXO1, were studied. This work demonstrates that atxA transcription from the major start site P1 is dependent upon a consensus sequence for the housekeeping sigma factor SigA, and an A+T-rich upstream element (UP-element) for RNA polymerase (RNAP). In addition, the data show that a trans-acting protein(s) other than AbrB negatively impacts atxA transcription when it binds specifically to a 9-bp palindrome within atxA promoter sequences located downstream of P1. Mutation of the palindrome prevents binding of the trans-acting protein(s) and results in a corresponding increase in AtxA and anthrax toxin production in a strain- and culture-dependent manner. The identity of the trans-acting repressor protein(s) remains elusive; however, phenotypes associated with mutation of the repressor binding site have revealed that the trans-acting repressor protein(s) indirectly controls B. anthracis development. Mutation of the repressor binding site results in misregulation and overexpression of AtxA in conditions conducive for development, leading to a marked sporulation defect that is both atxA- and pXO2-61-dependent. pXO2-61 is homologous to the sensor domain of sporulation sensor histidine kinases and is proposed to titrate an activating signal away from the sporulation phosphorelay when overexpressed by AtxA. These results indicate that AtxA is not only a master virulence regulator, but also a modulator of proper B. anthracis development. Also demonstrated in this work is the impact of the developmental regulators AbrB, Spo0A, and SigH on atxA expression and anthrax toxin production in a genetically incomplete (pXO1+, pXO2-) and genetically complete (pXO1+, pXO2+) strain background. AtxA and anthrax toxin production resulting from deletion of the developmental regulators are strain-dependent suggesting that factors on pXO2 are involved in control of atxA. The only developmental deletion mutant that resulted in a prominent and consistent strain-independent increase in AtxA protein levels was an abrB-null mutant. As a result of increased AtxA levels, there is early and increased production of anthrax toxins in an abrB-null mutant. In addition, the abrB-null mutant exhibited an increase in virulence in a murine model for anthrax. In contrast, virulence of the atxA promoter mutant was unaffected in a murine model for anthrax despite the production of 5-fold more AtxA than the abrB-null mutant. These results imply that AtxA is not the only factor impacting pathogenesis in an abrB-null mutant. Overall, this work highlights the complex regulatory network that governs expression of atxA and provides an additional role for AtxA in B. anthracis development.

Potential REST Targets in Neural Stem Cells and Glioblastoma-Derived Stem Cells

Glioblastoma multiforme (GBM) tumors are the most common malignant primary brain tumors in adults. The current theory is that these tumors are caused by self-renewing glioblastoma-derived stem cells (GSCs). At the current time, the mechanisms that regulate self-renewal and other oncogenic properties of GSCs remain unknown. Recently, we found transcriptional repressor REST maintains self-renewal in neural stem cells (NSCs) and in GSCs. REST also regulates other oncogenic properties, such as apoptosis, invasion and proliferation. However, the mechanisms by which REST regulates these oncogenic properties are unknown. In an attempt to determine these mechanisms, we performed loss and gain-of-function experiments and genome-wide mRNA expression analysis in GSCs, and we were able to identify REST-regulated genes in GSCs. This was accomplished, after screening concordantly regulated genes in NSCs and GSCs, utilizing two RE1 databases, and setting two-fold expression as filters on the resulting genes. These results received further validation by qRT-PCR. Ingenuity Pathway Analysis (IPA) analysis further revealed the top REST target genes in GSCs were downstream targets of REST and/or involved in other cancers in other cell lines. IPA also revealed that many of the differentially-regulated genes identified in this study are involved in oncogenic properties seen in GBM, and which we believe are related to REST expression.

GENETIC INTERACTIONS OF FACTORS THAT REGULATE ALTERNATIVE RNA SPLICING IN THE MALE GERM LINE OF DROSOPHILA

Alternative RNA splicing is a critical process that contributes variety to protein functions, and further controls cell differentiation and normal development. Although it is known that most eukaryotic genes produce multiple transcripts in which splice site selection is regulated, how RNA binding proteins cooperate to activate and repress specific splice sites is still poorly understood. In addition how the regulation of alternative splicing affects germ cell development is also not well known. In this study, Drosophila Transformer 2 (Tra2) was used as a model to explore both the mechanism of its repressive function on its own pre-mRNA splicing, and the effect of the splicing regulation on spermatogenesis in testis. Half-pint (Hfp), a protein known as splicing activator, was identified in an S2 cell-based RNAi screen as a co-repressor that functions in combination with Tra2 in the splicing repression of the M1 intron. Its repressive splicing function is found to be sequence specific and is dependent on both the weak 3’ splice site and an intronic splicing silencer within the M1 intron. In addition we found that in vivo, two forms of Hfp are expressed in a cell type specific manner. These alternative forms differ at their amino terminus affecting the presence of a region with four RS dipeptides. Using assays in Drosophila S2 cells, we determined that the alternative N terminal domain is necessary in repression. This difference is probably due to differential localization of the two isoforms in the nucleus and cytoplasm. Our in vivo studies show that both Hfp and Tra2 are required for normal spermatogenesis and cooperate in repression of M1 splicing in spermatocytes. But interestingly, Tra2 and Hfp antagonize each other’s function in regulating germline specific alternative splicing of Taf1 (TBP associated factor 1). Genetic and cytological studies showed that mutants of Hfp and Taf1 both cause similar defects in meiosis and spermatogenesis. These results suggest Hfp regulates normal spermatogenesis partially through the regulation of taf1 splicing. These observations indicate that Hfp regulates tra2 and taf1 activity and play an important role in germ cell differentiation of male flies.

Regulation of the {\it neu\/} oncogene by the GTG element binding proteins

A previous study in our lab has shown that the transforming neu oncogene ($neu\sp\*$) was able to initiate signals that lead to repression of the neu promoter activity. Further deletion mapping of the neu promoter identified that the GTG element (GGTGGGGGGG), located between $-$243 and $-$234 relative to the translation initiation codon, mediates such a repression effect. I have characterized the four major protein complexes that interact with this GTG element. In situ UV-crosslinking indicated that each complex contains proteins of different molecular weights. The slowest migrating complex (S) contain Sp1 or Sp1-related proteins, as indicated by the data that both have similar molecular weights, similar properties in two affinity chromatographies, and both are antigenically related in gel shift analysis. Methylation protection and interference experiments demonstrated these complexes bind to overlapping regions of the GTG element. Mutations within the GTG element that either abrogate or enhance complex S binding conferred on the neu promoter with lower activity, indicating that positive factors other than Sp1 family proteins also contribute to neu promoter activity. A mutated version (mutant 4) of the GTG element, which binds mainly the fastest migrating complex that contains a very small protein of 26-kDa, can repress transcription when fused to a heterologous promoter. Further deletion and mutation studies suggested that this GTG mutant and its binding protein(s) may cooperate with some DNA element within a heterologous promoter to lock the basal transcription machinery; such a repressor might also repress neu transcription by interfering with the DNA binding of other transactivators. Our results suggest that both positive and negative trans-acting factors converge their binding sites on the GTG element and confer combinatorial control on the neu gene expression. ^