Specific complex formation between the type II bare lymphocyte syndrome-associated transactivators CIITA and RFX5

Abstract

Two of the genes defective in the five complementation groups identified in the class II-negative bare lymphocyte syndrome or corresponding laboratory mutants have been cloned. One gene encodes a protein, RFX5, that is a member of the RFX family of DNA binding proteins. The other, CIITA, encodes a large protein with a defined acidic transcriptional activation domain; this protein does not interact with DNA. Expression plasmids encoding regions of RFX5 fused to the GAL4 DNA binding domain activated transcription from a reporter construct containing GAL4 sites in a cotransfection assay in the Raji human B cell line. However, these plasmids produced transcriptional activity in HeLa cells only in conjunction with interferon ␥ stimulation, a condition in which expression of both CIITA and class II major histocompatibility complex surface proteins are induced. Furthermore, these plasmids were not active in RJ2.2.5, an in vitro mutagenized derivative of Raji in which both copies of CIITA are defective. Transcriptional activation by the RFX5 fusion protein could be restored in RJ2.2.5 by cotransfection with a CIITA expression plasmid. Finally, a direct interaction between RFX5 and CIITA was detected with the yeast two-hybrid and far-Western blot assays. Thus, RFX5 can activate transcription only in cooperation with CIITA. RFX5 and CIITA associate to form a complex capable of activating transcription from class II major histocompatibility complex promoters. In this complex, promoter specificity is determined by the DNA binding domain of RFX5 and the general transcription apparatus is recruited by the acidic activation domain of CIITA.

Inactivation of class II transactivator by DNA methylation and histone deacetylation associated with absence of HLA-DR induction by interferon-γ in haematopoietic tumour cells

“…Expression of MHC class II molecules is also regulated by class II transactivator (CIITA) (Mach, 1999), which does not bind to DNA but acts as a coactivator, interacting with DNA-binding transcription factors such as regulatory factor X (RFX) family, NF-Y and CREB (Scholl et al, 1997;Zhu et al, 2000). Transcription of CIITA is regulated by CIITA promoters (CIITA-P) I -IV, each of which directs the expression of a unique first exon (MuhlethalerMottet et al, 1997): CIITA-PI is active primarily in dendritic cells and murine macrophages (Waldburger et al, 2001); CIITA-PII has been identified only in human cells, and its function remains unknown; CIITA-PIII is primarily responsible for directing constitutive expression of CIITA in B cells, and can drive CIITA expression after IFN-g stimulation in endothelial cells, fibroblasts or melanocytes (Piskurich et al, 1998;Deffrennes et al, 2001), and CIITA-PIV is a major regulator of IFN-g-inducible expression of CIITA (Muhlethaler-Mottet et al, 1997).…”

pRB is required for interferon-γ-induction of the MHC class II Aβ gene

“…Reconstitution of the RB-de®cient H2009 human SCLC line with wild type RB restores IFN-g-responsiveness at the DRb locus, but not at the DRa locus, indicating the existence of a speci®c factor required for induction of DRa (Lu et al, 1996). Indeed, several transcription factors have been shown to speci®cally modulate one or a subset of cII genes (Borras et al, 1995;Scholl et al, 1996). However, other than the current study on RB, no genetic experiments have been carried out to determine if these factors are essential for normal cII-regulation.…”

ZXDC, a novel zinc finger protein that binds CIITA and activates MHC gene transcription

“…A transcriptional co-factor, known as the class II trans-activator (CIITA), is also required for transcription of MHC class II genes (Steimle et al, 1993). CIITA does not bind DNA, but rather is recruited to MHC class II promoters by interacting with the CREB protein and subunits of the RFX and NFY complexes (DeSandro et al, 2000;Hake et al, 2000;Scholl et al, 1997;Zhu et al, 2000). In addition, the role of the W box in recruiting CIITA to MHC class II promoters is critical, though the factor(s) that binds this element have not been identified (Brown et al, 1998;Muhlethaler-Mottet et al, 2004).…”