title: The Akt/Mcl-1 pathway plays a prominent role in mediating antiapoptotic signals downstream of the B-cell receptor in chronic lymphocytic leukemia B cells.
abstract: Sustained engagement of the B-cell receptor (BCR) increases apoptosis resistance in chronic lymphocytic leukemia (CLL) B cells, whereas transient stimulation usually has an opposite effect. The antiapoptotic BCR signal has been associated with prolonged activation of the PI3K/Akt and MEK/ERK pathways, which are key regulators of survival and proliferation in various cell types. To further define the relative contribution of the Akt and ERK kinases in regulating CLL B-cell survival, we introduced constitutively active mutants of Akt and MEK in primary CLL B cells and evaluated changes in the expression of relevant pro- and antiapoptotic proteins. Sustained activation of Akt resulted in increased leukemic cell viability and increased expression of the antiapoptotic proteins Mcl-1, Bcl-xL, and X-linked inhibitor of apoptosis protein (XIAP), thus largely recapitulating the effects of sustained BCR stimulation. Constitutively active MEK2 also up-regulated XIAP, but did not show a significant impact on leukemic cell survival. Down-regulation of Mcl-1 by siRNA treatment induced rapid and potent apoptosis in CLL B cells and blocked the antiapoptotic effect of sustained BCR stimulation, whereas down-regulation of Bcl-xL and XIAP did not affect leukemic cell viability. These data demonstrate that Akt and Mcl-1 are major components of a survival pathway that can be activated in CLL B cells by antigen stimulation.
authors.affiliation: International Centre for Genetic Engineering and Biotechnology Molecular Hematology Group, Campus A. Buzzati-Traverso, Rome, Italy.
authors.forename: Pablo G
authors.initials: PG
authors.lastname: Longo
authors.forename: Luca
authors.initials: L
authors.lastname: Laurenti
authors.forename: Stefania
authors.initials: S
authors.lastname: Gobessi
authors.forename: Simona
authors.initials: S
authors.lastname: Sica
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Leone
authors.forename: Dimitar G
authors.initials: DG
authors.lastname: Efremov
mesh_terms: D017209:Apoptosis; D001402:B-Lymphocytes / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism; D005260:Female; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D048370:MAP Kinase Kinase 2 / Q000235:genetics / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000235:genetics; D008297:Male; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D011947:Receptors, Antigen, B-Cell / Q000235:genetics / Q000378:metabolism*; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: C494811:BCL2L1 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D011947:Receptors, Antigen, B-Cell; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D051020:bcl-X Protein; C482128:MAP2K2 protein, human; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D048370:MAP Kinase Kinase 2