CTCF functions as a critical regulator of cell-cycle arrest and death after ligation of the B cell receptor on immature B cells.
The WEHI 231 B cell lymphoma is used as a model of self-tolerance by clonal deletion because B cell receptor (BCR) ligation results in apoptosis. Two critical events precede cell death: an early rise and fall in expression of MYC and cell-cycle arrest associated with enhanced expression of p21, p27, and p53. CTCF is a transcription factor identified as a repressor of MYC recently shown to cause cell growth inhibition. The present studies demonstrate that BCR ligation of WEHI 231 as well as of normal immature B cells greatly increased expression of CTCF in association with down-regulation of MYC followed by growth arrest and cell death. Conditional expression of CTCF in WEHI 231 mimicked BCR ligation with activated cells showing repressed expression of MYC, enhanced expression of p27, p21, p53, and p19(ARF), and inhibition of cell growth and induction of apoptosis. In keeping with a central role for CTCF in control of B cell death, conditional expression of a CTCF antisense construct in WEHI 231 resulted in inhibition of p27, p21, p53, and p19(ARF) in association with enhanced expression of MYC. Activation of the endogenous CTCF locus by BCR ligation was also mimicked by three other routes to apoptotic death in WEHI 231: inhibition of the phosphoinositide 3-kinase or mTORFRAP signaling cascades and treatment with transforming growth factor (TGF)-beta. Rapid activation of CTCF by BCR ligation or treatment with TGF-beta was suppressed by ligation of CD40. These results demonstrate that CTCF is a common determinant to different pathways of death signaling in immature B cells.
Qi
Chen-Feng
CF
Laboratory of Immunopathology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Martensson
Annica
A
Mattioli
Michela
M
Dalla-Favera
Riccardo
R
Lobanenkov
Victor V
VV
Morse
Herbert C
HC
D017209:Apoptosis; D001402:B-Lymphocytes / Q000502:physiology*; D000076246:CCCTC-Binding Factor; D002453:Cell Cycle; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000502:physiology; D004268:DNA-Binding Proteins / Q000502:physiology*; D006801:Humans; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D012097:Repressor Proteins; D014157:Transcription Factors / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000502:physiology; D014407:Tumor Cells, Cultured; D025803:Tumor Suppressor Protein p14ARF / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000502:physiology
D000076246:CCCTC-Binding Factor; C493956:CDKN1A protein, human; C000619697:CTCF protein, human; C417743:Cdkn2a protein, mouse; C000619698:Ctcf protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D016271:Proto-Oncogene Proteins c-myc; D011947:Receptors, Antigen, B-Cell; D012097:Repressor Proteins; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53