The S box of major histocompatibility complex class II promoters is a key determinant for recruitment of the transcriptional co-activator CIITA

J Biol Chem. 2004 Sep 24;279(39):40529-35. doi: 10.1074/jbc.M406585200. Epub 2004 Jul 22.


Tightly regulated expression of major histocompatibility complex (MHC) class II genes is critical for the immune system. A conserved regulatory module consisting of four cis-acting elements, the W, X, X2 and Y boxes, controls transcription of MHC class II genes. The X, X2, and Y boxes are bound, respectively, by RFX, CREB, and NF-Y to form a MHC class II-specific enhanceosome complex. The latter constitutes a landing pad for recruitment of the transcriptional co-activator CIITA. In contrast to the well defined roles of the X, X2, and Y boxes, the role of the W region has remained controversial. In vitro binding studies have suggested that it might contain a second RFX-binding site. We demonstrate here by means of promoter pull-down assays that the most conserved subsequence within the W region, called the S box, is a critical determinant for tethering of CIITA to the enhanceosome complex. Binding of CIITA to the enhanceosome requires both integrity of the S box and a remarkably stringent spacing between the S and X boxes. Even a 1-2-base pair change in the native S-X distance is detrimental for CIITA recruitment and promoter function. In contrast to current models, binding of RFX to a putative duplicated binding site in the W box is thus not required for either CIITA recruitment or promoter activity. This paves the way for the identification of novel factors mediating the contribution of the S box to the activation of MHC class II promoters.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Binding Sites
  • Cell Line
  • Genes, MHC Class II*
  • Humans
  • Immunoblotting
  • Luciferases / metabolism
  • Major Histocompatibility Complex
  • Molecular Sequence Data
  • Mutation
  • Nuclear Proteins / genetics*
  • Promoter Regions, Genetic*
  • Protein Binding
  • Trans-Activators / genetics*
  • Transcription, Genetic*
  • Transcriptional Activation


  • MHC class II transactivator protein
  • Nuclear Proteins
  • Trans-Activators
  • Luciferases