en
Scientific article
English

Purified X2 binding protein (X2BP) cooperatively binds the class II MHC X box region in the presence of purified RFX, the X box factor deficient in the bare lymphocyte syndrome

Published inThe Journal of immunology, vol. 155, no. 9, p. 4313-4321
Publication date1995
Abstract

The conserved X2 box sequence of MHC class II promoters is homologous to TRE/CRE elements, and is required for B cell expression and IFN-gamma induction of MHC class II genes. The X2 binding protein (X2BP) was initially identified as a DNA-binding activity that specifically interacts with the conserved X2 box sequence in both the MHC HLA-DRA and HLA-DRB promoters. To begin to demonstrate that X2BP is the X2 box factor responsible for class II expression in B cells, we have purified X2BP to homogeneity from B cell nuclear extracts using DNA-affinity chromatography. X-box DNA-affinity purification indicates that X2BP is most likely composed of two polypeptides of 120 kDa and 46 kDa. The 120-kDa protein was specifically cross-linked to an X-box probe by exposure to UV irradiation. The 46-kDa subunit of X2BP cross-reacted with anti-rat CREB polyclonal Abs but not to anti-human CREB Abs in Western analysis and supershift assays, indicating that it may be a novel member of the ATF/CREB family. Purified X2BP interacted with purified RFX, a factor that binds to the adjacent X1 box and is absent in some cell lines that are mutant for MHC class II transcription. This interaction increases the DNA-binding half-life of RFX from 5 to at least 60 min, suggesting that X2BP functions in class II MHC gene expression by forming a stable complex with RFX.

Keywords
  • Base Sequence
  • Cross Reactions
  • DNA-Binding Proteins/genetics/ isolation & purification
  • Genes, MHC Class II
  • Half-Life
  • Heparin
  • Humans
  • Lymphoma, B-Cell
  • Molecular Sequence Data
  • Molecular Weight
  • Nuclear Proteins/genetics/ isolation & purification
  • Peptides/chemistry/isolation & purification
  • Protein Binding
  • Transcription Factors/genetics/ isolation & purification
  • Tumor Cells, Cultured
Citation (ISO format)
MORENO, C. S. et al. Purified X2 binding protein (X2BP) cooperatively binds the class II MHC X box region in the presence of purified RFX, the X box factor deficient in the bare lymphocyte syndrome. In: The Journal of immunology, 1995, vol. 155, n° 9, p. 4313–4321.
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ISSN of the journal0022-1767
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