Disease relevance of RFX1

• RFX1, a transactivator of hepatitis B virus enhancer I, belongs to a novel family of homodimeric and heterodimeric DNA-binding proteins [1].
• Identification of an epigenetically silenced gene, RFX1, in human glioma cells using restriction landmark genomic scanning [2].
• Hybrid protein effectors between RFX1 and RFX5 and the activation domain of VP16 from the herpes simplex virus were co-expressed with plasmid targets, which contained the isolated X box, X box and selected flanking CUS, or the entire DRA promoter [3].
• In type III bare lymphocyte syndrome (BLS) patients, defects in the RFX protein complex result in a lack of MHC class II and reduced MHC class I cell surface expression [4].
• The Epstein-Barr virus promoter initiating B-cell transformation is activated by RFX proteins and the B-cell-specific activator protein BSAP/Pax5 [5].

High impact information on RFX1

• The study of RFX and CIITA has made major contributions to our comprehension of the molecular mechanisms controlling MHCII genes and has made this system into a textbook model for the regulation of gene expression [6].
• The finding that RFX5 is a subunit of the nuclear RFX-complex has confirmed that a deficiency in the binding of this complex is indeed the molecular basis for MHC-II deficiency in the majority of patients [7].
• Its interaction with RFX5 and RFXAP is essential for binding of the RFX complex to MHC-II promoters [8].
• RFX1, -2 and -3 regulate expression of other medically important gene products (for example, interleukin-5 receptor alpha chain, IL-5R alpha) [9].
• Regulatory factor X (RFX) proteins are transcriptional activators that recognize X-boxes (DNA of the sequence 5'-GTNRCC(0-3N)RGYAAC-3', where N is any nucleotide, R is a purine and Y is a pyrimidine) using a highly conserved 76-residue DNA-binding domain (DBD) [9].

Chemical compound and disease context of RFX1

• Treatment of glioma cells with a demethylating agent, 5-azacytidine, resulted in the expression of RFX1, indicating that the silencing of the RFX1 gene may be attributable to its methylation [2].

Biological context of RFX1

• Tissue- and lineage-specific transcriptional activation with the full-length RFX1 fusion plasmid on a reporter controlled by GAL4 binding sites was observed [10].
• Methylation at +7 on the coding strand increases RFX1 complex formation in gel shift assays [11].
• These results suggest that RFX1 and 3 are pivotal factors in down-regulation of the MAP1A 5' promoter in non-neuronal cells [12].
• In this report, we demonstrate that RFX1 forms homodimers as well as heterodimers with RFX2 spanning the collagen transcription start site [11].
• RFX1 is a transacting DNA-binding regulatory factor involved in the control of MHC class II gene expression [13].

Anatomical context of RFX1

• In other cell lines and tissues, RFX mRNA levels are variable, particularly for RFX2 and RFX3 [1].
• In addition, an RFX5 complex present in human fibroblasts interacts with the collagen RFX site, which is not sensitive to methylation [11].
• We also demonstrated that the isolated CpG island located in the seventh intron of the RFX1 gene had enhancer activity and was hypermethylated in all of the glioma tissues and cell lines analysed, but not in normal brains or lymphocytes [2].
• In addition, we show that treatment with retinoic acid induces both MIBP1 and RFX1 protein, as well as their DNA-binding activity, upon granulocytic differentiation of HL60 cells, with a gel mobility pattern identical to that of HeLa cells [14].
• RFX2 levels decrease but RFX1 levels increase in early spermatids where H1t gene transcription is downregulated [15].

Associations of RFX1 with chemical compounds

• RFX proteins share several novel features, including new DNA-binding and dimerization motifs and a peculiar dependence on methylated CpG dinucleotides at certain sites [1].
• The DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine, which inhibits DNA methylation, reduces RFX1/HDAC1 binding to the collagen transcription start site in chromatin immunoprecipitation assays [16].
• Induction of Myc-intron-binding polypeptides MIBP1 and RFX1 during retinoic acid-mediated differentiation of haemopoietic cells [14].
• Two of the protein-DNA complexes formed with liver extracts (C4 and C5) are due to the zinc finger proteins Sp1 and Sp3, respectively, whereas another complex (C6) is due to the transcription factor RFX1 [17].
• An activation domain containing a glutamine-rich region is found in the N-terminal half of RFX1, while a region with repressor activity overlaps the C-terminal dimerization domain [18].

Physical interactions of RFX1

• In vitro synthesized RFX4 protein bound to typical RFX binding sites in a sequence-dependent manner [19].
• The RFX family interacts at the collagen (COL1A2) start site and represses transcription [11].
• 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 [20].
• The trimeric RFX complex was also present in fibroblast cells with or without IFN-gamma treatment [21].
• However, other RFX family members have the same DNA-binding domain and they also may regulate H1t gene expression [15].

Enzymatic interactions of RFX1

• RFX1 represses the unmethylated COL1A1 less efficiently than COL1A2 [22].

Regulatory relationships of RFX1

• Our studies indicate that the regulatory factor for X-box (RFX) family proteins repress collagen alpha2(I) gene (COL1A2) expression (Xu, Y., Wang, L., Buttice, G., Sengupta, P. K., and Smith, B. D. (2003) J. Biol. Chem. 278, 49134-49144; Xu, Y., Wang, L., Buttice, G., Sengupta, P. K., and Smith, B. D. (2004) J. Biol. Chem. 279, 41319-41332) [16].

Other interactions of RFX1

• In contrast to other mammalian RFX members that form dimers, RFX4 is revealed to have no distinct transcriptional activation domains [19].
• The transcription start site of the collagen alpha2(1) gene (COL1A2) has a sequence-specific binding site for a DNA methylation-responsive binding protein called regulatory factor for X-box 1 (RFX1) (Sengupta, P. K., Erhlich, M., and Smith, B. D. (1999) J. Biol. Chem. 274, 36649-36655) [11].
• Cotransfection studies indicated that RFX1, which is expressed ubiquitously, down-regulated the MAP1A 5' promoter activity in non-neuronal cells [12].
• 3. These two regulatory genes are thus assigned to a region of high gene density and RFX1 is close to another DNA-binding factor, LYL1 [13].
• Finally, both RFX1 and RFX5 are acetylated in vivo [16].
• These results demonstrate that RFX1 mediates the immediate early response of the Id2 gene by serum stimulation and suggest that the function of RFX1 is regulated intramolecularly in its suppression in growth-arrested cells [23].

Analytical, diagnostic and therapeutic context of RFX1

• In situ hybridization with 3H-labeled RFX1 cDNA has allowed us to identify two distinct targets on the short arm of chromosome 19 (19p13.1 and 19p13.2-p13.3) [13].
• Functional analysis in cell culture demonstrated that a truncated version of RFX1 (*RFX1) lacking the repressor domain was able to activate transcription from B10.RRE [24].
• When the TRAX1 complex was incubated with antibodies against a known recombinant X-box-binding protein, RFX1, and tested in electrophoretic mobility shift assays, TRAX1 was neither shifted nor blocked by the antibody [25].
• To characterize this novel motif, we have performed a detailed dissection of the site-specific DNA binding activity of RFX1, a prototypical member of the RFX family [26].
• Analytical ultracentrifugation (AUC) has demonstrated that RFX is a heterotrimer [27].

References