Rituximab (chimeric anti-CD20) sensitizes B-NHL cell lines to Fas-induced apoptosis

Oncogene. 2005 Dec 8;24(55):8114-27. doi: 10.1038/sj.onc.1208954.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Monoclonal / pharmacology*
  • Antibodies, Monoclonal, Murine-Derived
  • Antigens, CD20 / immunology
  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects*
  • Burkitt Lymphoma / pathology
  • Cell Line, Tumor
  • Cell Survival / drug effects
  • Enzyme Inhibitors / pharmacology
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Imidazoles / pharmacology
  • Lymphoma, AIDS-Related
  • Lymphoma, B-Cell / pathology*
  • NF-kappa B / pharmacology
  • Pyridines / pharmacology
  • Rituximab
  • Transcription, Genetic / drug effects
  • fas Receptor / immunology*
  • p38 Mitogen-Activated Protein Kinases / metabolism


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Murine-Derived
  • Antigens, CD20
  • Antineoplastic Agents
  • Enzyme Inhibitors
  • Imidazoles
  • NF-kappa B
  • Pyridines
  • fas Receptor
  • Rituximab
  • p38 Mitogen-Activated Protein Kinases
  • SB 203580