title: γ-Secretase inhibitor I induces apoptosis in chronic lymphocytic leukemia cells by proteasome inhibition, endoplasmic reticulum stress increase and notch down-regulation.
abstract: γ-Secretase inhibitors (GSIs) have been proposed for combined therapies of malignancies with a dysregulated Notch signaling. GSI I (Z-Leu-Leu-Nle-CHO) induces apoptosis of some tumor cells by inhibiting proteasome and Notch activity. Alterations in these two cell survival regulators contribute to apoptosis resistance of chronic lymphocytic leukemia (CLL) cells. Here, we investigated the mechanisms whereby GSI I increases apoptosis of primary CLL cells. Time-course studies indicate that initial apoptotic events are inhibition of proteasome activity, concomitant with an increased endoplasmic reticulum (ER) stress apoptotic signaling, and a consistent Noxa protein up-regulation. These events precede, and some of them contribute to, mitochondrial alterations, which occur notwithstanding Mcl-1 accumulation induced by GSI I. In CLL cells, GSI I inhibits Notch1 and Notch2 activation only in the late apoptotic phases, suggesting that this event does not initiate CLL cell apoptosis. However, Notch inhibition may contribute to amplify GSI I-induced CLL cell apoptosis, given that Notch activation sustains the survival of these cells, as demonstrated by the evidence that both Notch1 and Notch2 down-regulation by small-interfering RNA accelerates spontaneous CLL cell apoptosis. Overall, our results show that GSI I triggers CLL cell apoptosis by inhibiting proteasome activity and enhancing ER stress, and amplifies it by blocking Notch activation. These findings suggest the potential relevance of simultaneously targeting these three important apoptosis regulators as a novel therapeutic strategy for CLL.
authors.affiliation: Department of Clinical and Experimental Medicine, General Pathology and Immunology Section, University of Perugia, Perugia, Italy. erosati@unipg.it
authors.forename: Emanuela
authors.initials: E
authors.lastname: Rosati
authors.forename: Rita
authors.initials: R
authors.lastname: Sabatini
authors.forename: Filomena
authors.initials: F
authors.lastname: De Falco
authors.forename: Beatrice
authors.initials: B
authors.lastname: Del Papa
authors.forename: Franca
authors.initials: F
authors.lastname: Falzetti
authors.forename: Mauro
authors.initials: M
authors.lastname: Di Ianni
authors.forename: Laura
authors.initials: L
authors.lastname: Cavalli
authors.forename: Katia
authors.initials: K
authors.lastname: Fettucciari
authors.forename: Andrea
authors.initials: A
authors.lastname: Bartoli
authors.forename: Isabella
authors.initials: I
authors.lastname: Screpanti
authors.forename: Pierfrancesco
authors.initials: P
authors.lastname: Marconi
mesh_terms: D053829:Amyloid Precursor Protein Secretases / Q000037:antagonists & inhibitors*; D017209:Apoptosis / Q000187:drug effects*; D015536:Down-Regulation; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D018384:Oxidative Stress; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051880:Receptors, Notch / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D004791:Enzyme Inhibitors; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D051880:Receptors, Notch; D048670:MAP Kinase Kinase 4; D053829:Amyloid Precursor Protein Secretases; D046988:Proteasome Endopeptidase Complex