Murine NFX.1: isolation and characterization of its messenger RNA, mapping of its chromosomal location and assessment of its developmental expression.
Arlotta P
et al.
Immunology 2002 Jun;106(2)173-181
Arlotta P, Miyazaki D, Copeland NG, Gilbert DJ, Jenkins NA, Ono SJ.
Immunology 2002 Jun;106(2)173-181
Abstract: We have previously isolated (by expression cloning) a human cDNA, termed NFX.1, encoding a nucleic acid-binding protein that interacts with the conserved X1 box cis-element first discovered in class II major histocompatibility complex (MHC) genes. Functional studies involving expression of NFX.1 and assessment of expression from class II reporter constructs and endogenous class II MHC genes indicated that the factor could repress transcription of class II MHC genes. Subsequent studies have extended the biological significance of the factor, indicating that it plays an important role in neuronal development. Indeed, the reiterated RING finger motifs in the central domain of the polypeptide strongly suggest that NF-XI is a probable E3 ubiquitin protein ligase, indicating that the protein may have multiple activities. Here we report the cloning of the mouse homologue of the human NfX.1 cDNA: m-Nfx.1. Comparison of the deduced primary sequence of mouse and human NFX.1 proteins shows very high homology and confirms that m-NFX.1 contains the conserved cysteine-rich DNA-binding motif first described in human NFX.1 (95% homology). Expression of MHC class II genes is substantially reduced following expression of m-NFX.1, which confirms that we have isolated the functional murine homologue of human NfX.1 cDNA. Further evidence comes from the mapping of m-Nfx.1 gene to the proximal region of mouse chromosome 4, a region syntenic to the location of human Nfx.1 (short arm of chromosome 9). Expression profiling shows that m-NFX.1 is expressed ubiquitously in both adult tissues and during development, supporting the hypothesis that it may have yet-undescribed roles in distinct biological processes.
A novel cysteine-rich sequence-specific DNA-binding protein interacts with the conserved X-box motif of the human major histocompatibility complex class II genes via a repeated Cys-His domain and functions as a transcriptional repressor.
Song Z
et al.
J Exp Med 1994 Nov;180(5)1763-1774
Song Z, Krishna S, Thanos D, Strominger JL, Ono SJ.
J Exp Med 1994 Nov;180(5)1763-1774
Abstract: The class II major histocompatibility complex (MHC) molecules function in the presentation of processed peptides to helper T cells. As most mammalian cells can endocytose and process foreign antigen, the critical determinant of an antigen-presenting cell is its ability to express class II MHC molecules. Expression of these molecules is usually restricted to cells of the immune system and dysregulated expression is hypothesized to contribute to the pathogenesis of a severe combined immunodeficiency syndrome and certain autoimmune diseases. Human complementary DNA clones encoding a newly identified, cysteine-rich transcription factor, NF-X1, which binds to the conserved X-box motif of class II MHC genes, were obtained, and the primary amino acid sequence deduced. The major open reading frame encodes a polypeptide of 1,104 amino acids with a symmetrical organization. A central cysteine-rich portion encodes the DNA-binding domain, and is subdivided into seven repeated motifs. This motif is similar to but distinct from the LIM domain and the RING finger family, and is reminiscent of known metal-binding regions. The unique arrangement of cysteines indicates that the consensus sequence CX3CXL-XCGX1-5HXCX3CHXGXC represents a novel cysteine-rich motif. Two lines of evidence indicate that the polypeptide encodes a potent and biologically relevant repressor of HLA-DRA transcription: (a) overexpression of NF-X1 from a retroviral construct strongly decreases transcription from the HLA-DRA promoter; and (b) the NF-X1 transcript is markedly induced late after induction with interferon gamma (IFN-gamma), coinciding with postinduction attenuation of HLA-DRA transcription. The NF-X1 protein may therefore play an important role in regulating the duration of an inflammatory response by limiting the period in which class II MHC molecules are induced by IFN-gamma.
Congenital immunodeficiencies associated with absence of HLA class II antigens on lymphocytes result from distinct mutations in trans-acting factors.
Hume CR
et al.
Hum Immunol 1989 Dec;26(4)288-309
Hume CR, Lee JS.
Hum Immunol 1989 Dec;26(4)288-309
Abstract: Coordinate regulation of HLA class II gene expression during development and coinduction of class II genes by soluble factors suggests that common trans-acting factor(s) control expression of these genes. In B-lymphoblastoid cell lines derived from two independent class II-deficient bare lymphocyte syndrome patients, we observed a drastic decrease in transcription rates of the class II genes. When these cell lines are fused, class II genes are reexpressed, indicating that immunodeficiencies in bare lymphocyte syndrome patients are the result of two distinct mutations. Further studies show that genes governing the expression of class II antigens fall into at least three complementation groups; two of these were previously unidentified in mutant cell lines generated in vitro. In addition, we report the identification of two discrete complexes, NFX1.1 and NFX1.2, that bind to the DRA X consensus element. Though the mutation in at least one mutant line generated in vitro (RJ2.2.5) affects products functioning via interaction with the X box, clear alterations in either NFX1.1 or NFX1.2 are not found in any of the mutant cell lines.
