Inhibition of the Raf-MEK1/2-ERK1/2 signaling pathway, Bcl-xL down-regulation, and chemosensitization of non-Hodgkin's lymphoma B cells by Rituximab.
Rituximab (Rituxan, IDEC-C2B8) has been shown to sensitize non-Hodgkin's lymphoma (NHL) cell lines to chemotherapeutic drug-induced apoptosis. Rituximab treatment of Bcl-2-deficient Ramos cells and Bcl-2-expressing Daudi cells selectively decreases Bcl-(xL) expression and sensitizes the cells to paclitaxel-induced apoptosis. This study delineates the signaling pathway involved in rituximab-mediated Bcl-(xL) down-regulation in Ramos and Daudi NHL B cells. We hypothesized that rituximab may interfere with the extracellular signal-regulated kinase (ERK) 1/2 pathway, leading to decreased Bcl-(xL) expression. Rituximab (20 microg/mL) inhibited the kinase activity of mitogen-activated protein kinase kinase (MEK) 1/2 and reduced the phosphorylation of the components of the ERK1/2 pathway (Raf-1, MEK1/2, and ERK1/2) and decreased activator protein-1 DNA binding activity and Bcl-(xL) gene expression. These events occurred with similar kinetics and were observed 3 to 6 hours after rituximab treatment. Rituximab-mediated effects were corroborated by using specific inhibitors of the ERK1/2 pathway, which also reduced Bcl-(xL) levels and sensitized the NHL B cells to paclitaxel-induced apoptosis. Previous findings implicated a negative regulatory role of the Raf-1 kinase inhibitor protein (RKIP) on the ERK1/2 pathway. Rituximab treatment of NHL B cells significantly up-regulated RKIP expression, thus interrupting the ERK1/2 signaling pathway through the physical association between Raf-1 and RKIP, which was concomitant with Bcl-(xL) down-regulation. These novel findings reveal a signaling pathway triggered by rituximab, whereby rituximab-mediated up-regulation of RKIP adversely regulates the activity of the ERK1/2 pathway, Bcl-(xL) expression, and subsequent chemosensitization of drug-refractory NHL B cells. The significance of these findings is discussed.
Department of Microbiology, Immunology, and Molecular Genetics, Rhode Island Hospital and Brown University Medical School, Providence, Rhode Island, USA.
Ali R
AR
Jazirehi
Mario I
MI
Vega
Devasis
D
Chatterjee
Lee
L
Goodglick
Benjamin
B
Bonavida
D000595:Amino Acid Sequence; D000727:Androgen-Binding Protein / Q000096:biosynthesis / Q000235:genetics; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000494:pharmacology*; D058846:Antibodies, Monoclonal, Murine-Derived; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001402:B-Lymphocytes / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D004357:Drug Synergism; D006801:Humans; D008228:Lymphoma, Non-Hodgkin / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008969:Molecular Sequence Data; D017239:Paclitaxel / Q000008:administration & dosage / Q000494:pharmacology; D049488:Phosphatidylethanolamine Binding Protein; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000069283:Rituximab; D015854:Up-Regulation / Q000187:drug effects; D051020:bcl-X Protein
D000727:Androgen-Binding Protein; D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; C494811:BCL2L1 protein, human; C511482:PEBP1 protein, human; D049488:Phosphatidylethanolamine Binding Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D000069283:Rituximab; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D017239:Paclitaxel