New B-lymphocyte-specific enhancer-binding protein

Misregulation effect of a novel allelic variant in the Z promoter region found in cis with the CYP21A2 p.P482S mutation: implications for 21-hydroxylase deficiency

The aim of the current study was to search for the presence of genetic variants in the CYP21A2 Z promoter regulatory region in patients with congenital adrenal hyperplasia due to 21-hydroxylase deficiency. Screening of the 10 most frequent pseudogene-derived mutations was followed by direct sequencing of the entire coding sequence, the proximal promoter, and a distal regulatory region in DNA samples from patients with at least one non-determined allele. We report three non-classical patients that presented a novel genetic variant-g.15626A>G-within the Z promoter regulatory region. In all the patients, the novel variant was found in cis with the mild, less frequent, p.P482S mutation located in the exon 10 of the CYP21A2 gene. The putative pathogenic implication of the novel variant was assessed by in silico analyses and in vitro assays. Topological analyses showed differences in the curvature and bendability of the DNA region bearing the novel variant. By performing functional studies, a significantly decreased activity of a reporter gene placed downstream from the regulatory region was found by the G transition. Our results may suggest that the activity of an allele bearing the p.P482S mutation may be influenced by the misregulated CYP21A2 transcriptional activity exerted by the Z promoter A>G variation.

Modular usage of the HLA-DRA promoter in extra-hematopoietic and hematopoietic cell types of transgenic mice

Class II MHC genes (for example, the human HLA-DRA gene) are expressed at the cell surface in many professional and nonprofessional antigen-presenting cells in a variety of anatomical locations. Here, we report about 13 mouse transgenic lines (11 of which have not been previously described) generated with four distinct sets of DRA transgenes carrying progressive, informative 5' and 3' deletions. DRA expression was assessed in B lymphocytes, dendritic cells, macrophages, and extra-hematopoietic cells (particularly kidney epithelial cells). A compact transcriptional unit was identified that efficiently directs DRA expression [both constitutive and interferon (IFN)-gamma induced] in extra-hematopoietic tissues and dendritic cells. It extends from position -266 upstream of the transcription initiation site to position +119 downstream of the last DRA exon. The same fragment, however, did not efficiently direct IFN-gamma-induced DRA expression in macrophages, that required additional 5' sequences. Thus, IFN-gamma uses distinct promoter segments and mechanisms to up-regulate class II in different cell lineages. In contrast to previous results in transgenic mice expressing murine class II transgenes, we were unable to generate reproducible patterns of HLA-DRA expression in B cells.

The proline-rich homeodomain protein recruits members of the Groucho/Transducin-like enhancer of split protein family to co-repress transcription in hematopoietic cells

The proline-rich homeodomain protein (PRH/Hex) is important in the control of cell proliferation and differentiation and in the regulation of multiple processes in embryonic development. We have shown previously that PRH contains two domains that can independently bring about transcriptional repression. The PRH homeodomain represses transcription by binding to TATA box sequences, whereas the proline-rich N-terminal domain of PRH can repress transcription when attached to a heterologous DNA-binding domain. The Groucho/transducin-like enhancer of split (TLE) family of proteins are transcriptional co-repressors that interact with a number of DNA-bound transcription factors and play multiple roles in development. Here we demonstrate that the proline-rich N-terminal domain of PRH binds to TLE1 in vitro and in yeast two-hybrid assays. We show that PRH and TLE proteins are co-expressed in hematopoietic cells and interact in co-immunoprecipitation assays. We demonstrate that TLE1 increases repression by PRH in transient transfection assays and that titration of endogenous TLE proteins by co-expression of Grg5, a natural trans-dominant negative protein, alleviates transcriptional repression by PRH. Finally, we show that a mutation in the PRH N-terminal domain that blocks the PRH-TLE1 interaction in vitro eliminates co-repression. We discuss these results in terms of the roles of PRH and TLE in cell differentiation and development.

Transcriptional regulatory elements of the human gene for cytochrome P450c21 (steroid 21-hydroxylase) lie within intron 35 of the linked C4B gene

The CYP21 gene, which encodes P450c21, the adrenal steroid 21-hydroxylase needed for glucocorticoid synthesis, lies in the major histocompatibility locus only 2.3 kilobase pairs (kb) downstream from the C4 gene. A 300-base pair (bp) proximal promoter and two upstream regions within C4 are needed for expression of mouse CYP21; the human gene also has a proximal promoter, but upstream elements have not been studied. To search for upstream regulatory elements in human CYP21B, we examined up to 9 kb of 5'-flanking DNA by transient transfection into human adrenal NCI-H295A cells. The 300-bp proximal promoter had substantial activity, but constructs retaining the DNA between -4.6 and -5.6 kb had increased activity, indicating the presence of distal elements. This region does not correspond to the mouse upstream regions, lying further upstream within intron 35 of C4B, which encompasses the previously described "Z promoter." DNase I footprinting located two elements, F1 and F2, lying -186 to -195 bp and -142 to -151 bp upstream from the Z cap site (-4862 to -4871 and -4818 to -4827 bp upstream of the CYP21B cap site). Each element formed a specific DNA-protein complex and conferred orientation-independent expression to a heterologous promoter. Mutations abolished formation of the DNA-protein complexes but only partially decreased expression. We identified a third site, F3, lying at -33 to -42 bp from Z. Competitive gel mobility supershift assays and co-transfection studies with SF-1 produced in vitro indicate F2 and F3 bind SF-1; BLAST searches and Southwestern blotting suggest that NF-W2 may bind F1. These results indicate that the Z promoter is a component of the CYP21 promoter needed to drive its adrenal-specific expression and that CYP21 transcription elements within C4 have kept these two genes linked during evolution.

Cellular transcription factors regulate human papillomavirus type 16 gene expression by binding to a subset of the DNA sequences recognized by the viral E2 protein

Human papillomavirus type 16 (HPV-16) is a DNA tumour virus that has been implicated in the development of cervical cancer. The HPV-16 E2 protein binds to four sites that are present upstream of the viral P97 promoter and regulates transcription of the E6 and E7 oncogenes. Here, it is shown that cellular transcription factors bind to two of these E2 sites. One cellular E2 site-binding factor, which is here named CEF-1, binds tightly to E2 site 1. CEF-2, an unrelated cellular E2 site-binding factor, binds tightly to E2 site 3. Transient transfection studies performed in the absence of the E2 protein showed that mutations that blocked the binding of CEF-1 to E2 site 1 or CEF-2 to E2 site 3 significantly reduced P97 promoter activity. Further characterization of CEF-1 indicated that this factor has not previously been identified and that CEF-1 and E2 competed for binding at E2 site 1.

Structure and evolution of the promoter regions of the DQA genes

HLA-DQ antigens are unique among the class II antigens in that their alpha chains are highly polymorphic. In the present study, we characterized the general structure of the promoter regions of the DQA genes derived from different DR haplotypes and defined their nucleotide sequence polymorphisms. The promoter of each DQA1 allele contains three sequence motifs which are not present in non-DQA related class II genes: one identical to a tumor necrosis factor (TNF alpha) response element, one similar to an NF kappa B binding element, and one similar to a W motif. All DQA alleles lack TATA and CCAAT boxes in the proximal promoter region but carry other sequence elements characteristic of MHC class II genes, including S, X, X2, and Y boxes, and a pyrimidine-rich tract upstream of the X box. Nucleotide sequence polymorphisms among the various DQA1 alleles were noted within the promoter region, with some of the differences mapping within, or close to, regulatory elements that are important for the expression of MHC class II genes. All DQA1 alleles carry an unrearranged, full length, Alu-Sx related repeat immediately upstream of the proximal promoter region. This repeat was not present in the DQA2 (DXA) genes analyzed, confirming that DQ locus duplication probably occurred before integration of the Alu repeat into the primordial DQA1 locus, some 31-43 million years (myr) ago. The DQA2 promoter region is highly conserved between DR4 and DR3 haplotypes, with the degree of conservation exceeding that expected from the neutral mutation rate.

Identification of a highly conserved region at the 5' flank of the phospholamban gene

Phospholamban is a protein that regulates the activity of the sarcoplasmic reticulum Ca(2+)-ATPase. The rat phospholamban gene contains a single intron of 6.5 kilobases which interrupts the 5' untranslated region. Primer extension and nuclease mapping analysis identified a major transcription initiation site 87 nucleotides upstream of the first exon/intron junction. A highly conserved region was identified at the 5' flank of the phospholamban gene. This region contained a TATA motif at position -52 which bound nuclear extract, and a consensus CAAT motif at position -76. This highly conserved region may be important in the regulation of basal transcriptional activity.

A pre-B- and B cell-specific DNA-binding protein, EBB-1, which binds to the promoter of the VpreB1 gene

The VpreB1 protein is thought to be expressed on the surface of pre-B cells in association with lambda 5 and mu heavy chain, and to play an important role on B cell differentiation. The expression of VpreB1 and lambda 5 is pre-B cell specific, and regulated at the initiation of transcription. We have identified at least two sequence-specific DNA-binding proteins which bind to the region -191 to -74 of the promoter of the mouse VpreB1 gene. These DNA-binding proteins also bind to the promoter of the mouse lambda 5 gene. One of the two DNA-binding proteins, called EBB-1, is restricted to pre-B and B cells, but not detected in plasma cells, T cells and cells of other lineages. Transient transfection analysis of reporter constructs revealed that the binding sites of these proteins play a significant role in the activity of the promoter, especially the binding site of EBB-1. Taken together these results suggest that EBB-1 might be one of the crucial factors which regulates a series of intracellular events in B cell differentiation.

An HLA-DR alpha promoter DNA-binding protein is expressed ubiquitously and maps to human chromosomes 22 and 5

The class II major histocompatibility complex antigens are a family of integral membrane proteins whose expression is tissue-specific and developmentally regulated. Three consensus sequences, X1, X2, and Y, separated by an interspace element, is found upstream from all class II genes. Deletion of each of these sequences eliminates expression of class II genes in vitro or in transgenic mice. Here we further characterize the expression of a cDNA encoding a DNA binding protein (human X-box binding protein, hXBP-1) which, like the proteins in whole nuclear extract, recognizes both the X2 promoter element of the human DR alpha and DP beta and mouse A alpha genes. The hXBP-1 cDNA hybridizes to human RNA species of approximately 2.2 kilobases (kb) and 1.6 kb, which are expressed in class II negative as well as class II positive cells. hXBP-1 transcripts are present in several class II deficient mutant B cell lines, although in one such line, 6.1.6, levels were somewhat reduced. Chromosome mapping studies demonstrate that hXBP-1 arises from a small gene family, two of whose members map to human chromosomes 5 and 22. Taken together, these data suggest a high degree of complexity in the transcriptional control of the class II gene family.

Fine-tuning of MHC class II gene expression in defined microenvironments

Strict control of major histocompatibility complex class II gene expression is essential for proper functioning of the immune system. Recent transgenic mouse studies have revealed an intricate fine-tuning of class II gene transcription in microenvironments such as the germinal centers and thymic cortex and medulla.