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Blood, 1 November 2007, Vol. 110, No. 9, pp. 3374-3383. Prepublished online as a Blood First Edition Paper on August 9, 2007; DOI 10.1182/blood-2007-02-071258.
NEOPLASIA The oncoprotein NPM-ALK of anaplastic large-cell lymphoma induces JUNB transcription via ERK1/2 and JunB translation via mTOR signaling1 Klinische Abteilung für Hämatologie, Universitätsklinik für Innere Medizin, Medizinische, Universität Graz, Graz, Austria; 2 Institut für Pathologie, Medizinische Universität Graz, Graz, Austria; 3 Mount Sinai School of Medicine, New York, NY; 4 Institut für Pharmakologie, Universität Wien, Wien, Austria; 5 Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSMZ), Braunschweig, Germany; 6 Institut für Molekulare Biowissenschaften, Karl-Franzens Universität Graz, Graz, Austria; 7 Department of Dermatology, Brigham and Women's Hospital, Boston, MA; 8 Roger Williams Medical Center, Providence, RI; 9 Institut für Pathologie, Medizinische Universität Wien, Wien, Austria; 10 Boltzmann Institute for Cancer Research, Vienna, Austria Anaplastic large cell lymphomas (ALCLs) are highly proliferating tumors that commonly express the AP-1 transcription factor JunB. ALK fusions occur in approximately 50% of ALCLs, and among these, 80% have the t(2;5) translocation with NPM-ALK expression. We report greater activity of JunB in NPM-ALK–positive than in NPM-ALK–negative ALCLs. Specific knockdown of JUNB mRNA using small interfering RNA and small hairpin RNA in NPM-ALK–expressing cells decreases cellular proliferation as evidenced by a reduced cell count in the G2/M phase of the cell cycle. Expression of NPM-ALK results in ERK1/2 activation and transcriptional up-regulation of JUNB. Both NPM-ALK–positive and –negative ALCL tumors demonstrate active ERK1/2 signaling. In contrast to NPM-ALK–negative ALCL, the mTOR pathway is active in NPM-ALK–positive lymphomas. Pharmacological inhibition of mTOR in NPM-ALK–positive cells down-regulates JunB protein levels by shifting JUNB mRNA translation from large polysomes to monosomes and ribonucleic particles (RNPs), and decreases cellular proliferation. Thus, JunB is a critical target of mTOR and is translationally regulated in NPM-ALK–positive lymphomas. This is the first study demonstrating translational control of AP-1 transcription factors in human neoplasia. In conjunction with NPM-ALK, JunB enhances cell cycle progression and may therefore represent a therapeutic target.
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