Conserved structure and promoter sequence similarity in the mouse and human genes encoding the zinc finger factor BERF-1/BFCOL1/ZBP-89.

We have characterized the genomic structure of the mouse Zfp148 gene encoding Beta-Enolase Repressor Factor-1 (BERF-1), a Kruppel-like zinc finger protein involved in the transcriptional regulation of several genes, which is also termed ZBP-89, BFCOL1. The cloned Zfp148 gene spans 110 kb of genomic DNA encompassing the 5'-end region, 9 exons, 8 introns, and the 3'-untranslated region. The promoter region displays the typical features of a housekeeping gene: a high G+C content and the absence of canonical TATA and CAAT boxes consistent with the multiple transcription initiation sites determined by primary extension analysis. Computer-assisted search in the human genome database allowed us to determine that the same genomic structure with identical intron-exon organization is conserved in the human homologue ZNF 148. Functional analysis of the 5'-flanking sequence of the mouse gene indicated that the region from nucleotide -205 to +144, relative to the major transcription start site, contains cis-regulatory elements that promote basal expression. Such sequences and the overall promoter architecture are highly conserved in the human gene. Furthermore, we show that the complex transcription pattern of the Zfp148 gene might be due to a combination of alternative splicing and differential polyadenylation sites utilization.

Negative regulation of beta enolase gene transcription in embryonic muscle is dependent upon a zinc finger factor that binds to the G-rich box within the muscle-specific enhancer.

We have previously identified a muscle-specific enhancer within the first intron of the human beta enolase gene. Present in this enhancer are an A/T-rich box that binds MEF-2 protein(s) and a G-rich box (AGTGGGGGAGGGGGCTGCG) that interacts with ubiquitously expressed factors. Both elements are required for tissue-specific expression of the gene in skeletal muscle cells. Here, we report the identification and characterization of a Kruppel-like zinc finger protein, termed beta enolase repressor factor 1, that binds in a sequence-specific manner to the G-rich box and functions as a repressor of the beta enolase gene transcription in transient transfection assays. Using fusion polypeptides of beta enolase repressor factor 1 and the yeast GAL4 DNA-binding domain, we have identified an amino-terminal region responsible for the transcriptional repression activity, whereas a carboxyl-terminal region was shown to contain a potential transcriptional activation domain. The expression of this protein decreases in developing skeletal muscles, correlating with lack of binding activity in nuclear extract from adult skeletal tissue, in which novel binding activities have been detected. These results suggest that in addition to the identified factor, which functionally acts as a negative regulator and is enriched in embryonic muscle, the G-rich box binds other factors, presumably exerting a positive control on transcription. The interplay between factors that repress or activate transcription may constitute a developmentally regulated mechanism that modulates beta enolase gene expression in skeletal muscle.

The gene encoding the transcriptional repressor BERF-1 maps to a region of conserved synteny on mouse chromosome 16 and human chromosome 3 and a related pseudogene maps to mouse chromosome 8.

We have recently identified and characterized a Kruppel-like zinc finger protein (BERF-1), that functions as a repressor of beta enolase gene transcription. By interspecific backcross analysis the gene encoding BERF-1 was localized 4.7 cM proximal to the Mtv6 locus on mouse chromosome 16, and an isolated pseudogene was localized to mouse chromosome 8, about 5.3 cM distal to the D8Mit4 marker. Nucleotide sequence identity and chomosome location indicate that the gene encoding BERF-1 is the mouse homologue (Zfp148) of ZNF148 localized to human chromosome 3q21, a common translocation site in acute myeloid leukemia patients.

Transcription of the human beta enolase gene (ENO-3) is regulated by an intronic muscle-specific enhancer that binds myocyte-specific enhancer factor 2 proteins and ubiquitous G-rich-box binding factors.

To provide evidence for the cis-regulatory DNA sequences and trans-acting factors involved in the complex pattern of tissue- and stage-specific expression of the beta enolase gene, constructs containing fragments of the gene fused to the chloramphenicol acetyltransferase gene were used in transient-transfection assays of C2C12 myogenic cells. Deletion analysis revealed the presence of four major regions: two negative regions in the 5'-flanking sequence, a basal promoter region which directs expression at low levels in proliferating and differentiated muscle cells, and a positive region within the first intron that confers cell-type-specific and differentiation-induced expression. This positive regulatory element is located in the 3'-proximal portion of the first intron (nucleotides +504 to +637) and acts as an enhancer irrespective of orientation and position from the homologous beta enolase promoter or the heterologous thymidine kinase promoter, conferring in both cases muscle-specific expression to the linked reporter gene. Deletion of a putative myocyte-specific enhancer factor 1 (MEF-1) binding site, containing a canonical E-box motif, had no effects on muscle-specific transcription, indicating that this site is not required for the activity of the enhancer. Gel mobility shift assays, competition analysis, DNase I footprinting, and mutagenesis studies indicated that this element interacts through an A/T-rich box with a MEF-2 protein(s) and through a G-rich box with a novel ubiquitous factor(s). Mutation of either the G-rich box or the A/T-rich box resulted in a significantly reduced activity of the enhancer in transient-transfection assays. These data indicate that MEF-2 and G-rich-box binding factors are each necessary for tissue-specific expression of the beta enolase gene in skeletal muscle cells.