title: Rituximab (chimeric anti-CD20) sensitizes B-NHL cell lines to Fas-induced apoptosis.
abstract: Rituximab (chimeric anti-CD20 monoclonal antibodies) is currently being used in the treatment of B non-Hodgkin's lymphoma (NHL). We have recently reported that rituximab triggers and modifies various intracellular signaling pathways in NHL B-cell lines, resulting in reverting the chemoresistant phenotype to a sensitive phenotype. This study investigated whether rituximab also modifies intracellular signaling pathways resulting in the sensitization of NHL cells to Fas-induced apoptosis. Treatment of the Fas-resistant NHL cell lines (2F7, Ramos and Raji) with rituximab sensitized the cells to CH-11 (FasL agonist mAb)-induced apoptosis and synergy was achieved. Fas expression was upregulated by rituximab as early as 6 h post-treatment as determined by flow cytometry, reverse transcriptase-polymerase chain reaction and Western blot. Rituximab inhibited both the expression and activity of the transcription repressor Yin-Yang 1 (YY1) that negatively regulates Fas transcription. Inhibition of YY1 resulted in the upregulation of Fas expression and sensitization of the tumor cells to CH-11-induced apoptosis. The downregulation of YY1 expression was the result of rituximab-induced inhibition of both the p38 mitogen-activated protein kinase (MAPK) signaling pathway and constitutive nuclear factor kappa of B cells (NF-kappaB) activity. The involvement of NF-kappaB and YY1 in the regulation of Fas expression was corroborated by the use of Ramos cells with a dominant-active inhibitor of NF-kappaB (Ramos IkappaB-estrogen receptor (ER) mutant) and by silencing YY1 with YY1 siRNA, respectively. Further, the role of rituximab-mediated inhibition of the p38 MAPK/NF-kappaB/YY1 pathway in the regulation of Fas and sensitization to CH-11-induced apoptosis was validated by the use of specific chemical inhibitors of this pathway and which mimicked rituximab-mediated effects. These findings provide a novel mechanism of rituximab-mediated activity by sensitizing NHL cells to Fas-induced apoptosis.
authors.affiliation: Department of Microbiology, Immunology and Molecular Genetics, University of California, 10833 Le Conte Avenue, A2-060 CHS, Los Angeles, CA 90095, USA.
authors.forename: Mario I
authors.initials: MI
authors.lastname: Vega
authors.forename: Sara
authors.initials: S
authors.lastname: Huerta-Yepez
authors.forename: Ali R
authors.initials: AR
authors.lastname: Jazirehi
authors.forename: Hermes
authors.initials: H
authors.lastname: Garban
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bonavida
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20 / Q000276:immunology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002051:Burkitt Lymphoma / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D016483:Lymphoma, AIDS-Related; D016393:Lymphoma, B-Cell / Q000473:pathology*; D016328:NF-kappa B / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D000069283:Rituximab; D014158:Transcription, Genetic / Q000187:drug effects; D019014:fas Receptor / Q000276:immunology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D007093:Imidazoles; D016328:NF-kappa B; D011725:Pyridines; D019014:fas Receptor; D000069283:Rituximab; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580