Transcription inhibition of the somatic-type phosphoglycerate kinase 1 gene in vitro by a testis-specific factor that recognizes a sequence similar to the binding site for Ets oncoproteins

An upstream activator sequence regulates the murine Pgk-1 promoter and binds multiple nuclear proteins

The murine Pgk-1 gene is driven by a strong promoter that is regulated by a 304 bp upstream activator sequence (UAS). The activity of the UAS is high in undifferentiated embryonal carcinoma cells but declines when these cells are induced to differentiate with retinoic acid. The effect of the UAS on promoter activity is particularly striking when the activity of the Pgk-1 promoter is assayed following its integration into the genome, suggesting that it may function by regulating chromatin structure in the region of the core promoter. Three sites on the UAS bind nuclear proteins. Two of these sites bind factors present in both embryonal carcinoma cells and their differentiated derivatives whereas one site binds factors present only in differentiated cells. There appears to be both cooperation and antagonism in the binding of proteins to different sites in the UAS, suggesting that the activity of the Pgk-1 promoter is determined by the constellation of proteins assembled upstream of its transcription start site.

Ectopic activation of the transcription promoter for the testis-specific mouse Pgk-2 gene on elimination of a cis-acting upstream DNA region

Transgenic mice carrying the coding sequence of beta-galactosidase, for which expression was driven by various upstream regions including the transcription promoter of the testis-specific mouse Pgk-2 gene, were generated. Expression of beta-galactosidase mRNA driven by the region between nucleotide positions -1404 and +61, with respect to the transcription initiation site numbered +1, was examined by reverse transcription-mediated polymerase chain reaction, blot hybridization and in situ hybridization, and compared with that of endogenous Pgk-2 mRNA. The results revealed that the 1.4kb DNA region is sufficient for determining the organ-specific, developmental stage-specific and spermatogenic stage-specific transcription of the mouse Pgk-2 gene. When the region between -684 and +61 was used to generate transgenic mice, beta-galactosidase mRNA was detectable not only in the testis, but also in other organs such as brain and lung. However, the timing and cell-type specificity of testicular expression of beta-galactosidase mRNA were retained in these mice. Because the region between -1404 and -685 repressed the Pgk-2 promoter in somatic cell-derived cell lines, it is suggested that the organ specificity of Pgk-2 transcription is achieved at least partly by negative regulation.

Regulation of Pdha-2 expression is mediated by proximal promoter sequences and CpG methylation

Spermatogenesis is a complex process requiring the coordinate expression of a number of testis-specific genes. One of these, Pdha-2, codes for the murine spermatogenesis-specific isoform of the E1a subunit of the pyruvate dehydrogenase complex. To begin to delineate the mechanisms regulating its expression in vivo, we have generated transgenic mice lines carrying Pdha-2 promoter deletion constructs. Here we report that transgenic mice harboring a construct containing only 187 bp of promoter and upstream sequences (core promoter) is sufficient for directing the testis-specific expression of a chloramphenicol acetyltransferase (CAT) reporter gene. Like the endogenous Pdha-2, the CAT gene is expressed in testis in a stage-specific manner. Our studies also show a correlation between CpG methylation within the core promoter and its capacity to regulate transcription. In NIH 3T3 cell lines stably transfected with the Pdha-2 core promoter-CAT construct, high levels of CAT reporter expression are observed, whereas the endogenous Pdha-2 gene is repressed. In these cells, the CpG dinucleotides residing within the transfected promoter are hypomethylated whereas those residing in the endogenous promoter are methylated. Furthermore, promoter activity can be abated by the in vitro methylation of its CpG dinucleotides. DNase I footprint analysis indicates that at least one site for the methylation-mediated repression may occur through the ATF/cyclic AMP response element binding element located within the core promoter. Mutations within this element reduces activity to approximately 50% of the wild-type promoter activity. These results suggest that tissue-specific gene expression may be modulated by other mechanisms in addition to specific transcription factor availability and cooperativity. We propose that methylation may be a mechanism by which repression of the testis-specific Pdha-2 gene is established in somatic tissue.

Analysis of the negative transcriptional regulatory element in the angiotensin-converting enzyme gene

We have characterized the sequence requirements and the protein binding properties of the previously identified transcriptional negative element present in the rabbit angiotensin-converting enzyme (ACE) gene. DNase footprinting experiments revealed that within the negative element (-715 to -610) several regions interact with proteins present in the nuclear extracts of ACE-expressing and -nonexpressing cell lines. Transfection analysis using the heterologous beta-actin promoter and mutated negative elements demonstrated that the SP1 site, the collagen-silencer-like sequence, and the inverted repeat elements are dispensable for their functioning. Deletion of the region between -692 to -668, however, completely eliminated the activity of the negative element, and mutation of the synapsin-silencer-like sequence present within this region vastly reduced it. This region (-692 to -668) by itself, when present in two copies, could effectively repress the activity of the beta-actin promoter. The same point mutations in the silencer element that destroyed its action on the beta-actin promoter greatly increased the transcriptional efficiency of the native ACE promoter. Electrophoretic mobility shift assay using the -692 to -668 ACE silencer sequence demonstrated the formation of a DNA/protein complex. UV cross-linking of the components of this complex revealed the presence of one prominent protein of approximately 21.5 kDa. This protein may be responsible for mediating the transcriptional-repressing activity of the ACE negative element. Homology between the ACE silencer and neuronal silencer consensus sequence, together with the promoter- and tissue-independent function of the the ACE silencer, suggests this element may bind a member of a large family of common negative regulatory transcription factors.

A 252 bp upstream region of the rat spermatocyte-specific hst70 gene is sufficient to promote expression of the hst70-CAT hybrid gene in testis and brain of transgenic mice

The rat hst70 gene belongs to a heat shock hsp70 multigene family and its expression has been detected so far solely in spermatocytes. To investigate the cis-elements responsible for testis-specific expression of the hst70 gene we produced several lines of transgenic mice carrying fragments of the 5'-flanking regions of the hst70 gene fused to the chloramphenicol acetyltransferase (CAT) reporter gene. Hybrid genes of series B were constructed such that, besides the 780 bp, 343 bp and 163 bp 5'-flanking region these plasmids contained no other sequences of the hst70 gene. In hybrid genes of series D the CAT gene was ligated to 343 bp and 252 bp 5'-flanking regions together with the 57 bp of the 5'-end nontranslated (leader) sequences of the hst70 gene. We found that in 780/B, 343/B, 343/D and 252/D adult mice the transgene was specifically and highly expressed in testes. In developing testes the high CAT activity appeared in transgenic mice aged 3 weeks and older. None of the three 163/B transgenic lines exhibited CAT activity in any tissue analyzed. In all CAT expressing lines a weak but significant CAT activity (up to 5% of that in testis) was detected also in the brain. RNase protection assay confirmed that the endogenous hst70 gene transcripts are present in testis as well as in brain of nontransgenic rats and mice. Our data show that the cis-regulatory sequences responsible for testis-specific and developmentally regulated expression of the hst70 gene are localized within the 252 bp region 5' to the gene and neither the 5'-end nor 3'-end nontranslated sequences of the gene are important for this specificity.

Pdha-2: a model for studying transcriptional regulation in early spermatocytes

Precise temporal and tissue-specific expression of genes during spermatocyte differentiation is crucial for the formation of functional spermatozoa. However, the mechanisms that regulate gene expression during spermatogenesis are poorly understood. One testis-specific gene, Pdha-2, is beginning to emerge as a potentially important model for the study of these events. This review focuses on our current understanding of the expression and regulation of Pdha-2 during spermatogenesis.

Murine PGK-1 promoter drives widespread but not uniform expression in transgenic mice

Pgk-1 is an X-linked gene encoding 3-phosphoglycerate kinase, an enzyme necessary in every cell for glycolysis. The regulatory sequences of the Pgk-1 gene were used to drive the E. coli lacZ reporter gene and 2 strains of transgenic animals created with this Pgk-lacZ transgene carried on autosomes. The levels of expression of Pgk-1 varied from one adult tissue to another and the transgene was similarly regulated. However, in situ staining of the beta-galactosidase encoded by the transgene indicated extensive cell-to-cell variability in its level of expression. A reproducible subset of cells stained darkly for the transgene product. Some of these beta-galactosidase positive cells were rapidly proliferating while others appeared to be metabolically very active, suggesting that the Pgk-1 promoter is regulated so as to be more active in cells requiring high levels of glycolysis. Although Pgk-1 is X-linked and subject to X chromosome inactivation, the transgenes were not inactivated in either female somatic or male germ cells. Thus, the Pgk-1 promoter drives transgene expression in all tissues but the levels of expression are not uniform in each cell.

Identification of negative-acting and protein-binding elements in the mouse alpha A-crystallin -1556/-1165 region

The mouse alpha A-crystallin-encoding gene (alpha A-cry) is expressed in a highly lens-preferred manner. To date, it has been shown that this lens-preferred expression is controlled by four proximal positive-acting transcriptional regulatory elements: DE1 (-111/-97), alpha A-CRYBP1 (-66/-57), PE1/TATA (-35/-19) and PE2 (+24/+43). The present study extends our knowledge of mouse alpha A-cry transcriptional regulatory elements to the far upstream region of that gene by demonstrating that the -1556 to -1165 region contains negative-acting sequence elements which function in transfected lens cells derived from mouse, rabbit and chicken. This is the first negative-acting regulatory region identified in mouse alpha A-cry. The -1556 to -1165 region contains sequences similar to repressor/silencer elements identified in other genes, including those highly expressed in the lens, such as the delta 1-crystallin (delta 1-cry) and vimentin (vim) genes. The -1480 to -1401 region specifically interacts with nuclear proteins isolated from the alpha TN4-1 mouse lens cell line. Contained within this protein-binding region and positioned at -1453 to -1444 is a sequence (RS1) similar to the chicken delta 1-cry intron 3 repressor, and which competes for the formation of -1480 to -1401 DNA-protein complexes. Our findings suggest that lens nuclear proteins bind to the mouse alpha A-cry RS1 region. We demonstrate that the chicken delta 1-cry intron repressor binds similar nuclear proteins in chicken embryonic lens cells and mouse alpha TN4-1 lens cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The silencer of mouse Pgk-2 consists of two discrete DNA elements that individually have no effect

Pgk-2 encodes a testis-specific phosphoglycerate kinase isozyme (PGK), and the expression of mouse Pgk-2 is activated during the spermatogenic pathway at the pachytene spermatocyte stage. We previously reported the identification of a silencer-like cis-acting element in a region between nucleotides (nt) -1404 and -685 of mouse Pgk-2, which could be responsible for the repression of Pgk-2 expression in somatic tissues and pre-meiotic testicular germ cells. In the present study, the silencer was precisely located within an 87-bp region between nt -882 and -796. This region contained two distinct sequences that individually bound factors present in nuclear extracts of mouse cultured cells and rat tissues. The two sequences, when aligned in tandem upstream from the Pgk-2 promoter, inhibited cat expression driven by the promoter in mouse erythroleukemia cells, whereas either sequence alone did not show any effect. The results indicate that the Pgk-2 silencer consists of two distinct DNA elements which do not individually influence promoter activity. Binding of distinct nuclear factors to each DNA element appeared to be required for the silencer action.

Identification of positive and negative transcriptional regulatory elements of the rabbit angiotensin-converting enzyme gene

The two tissue-specific mRNAs encoding the isozymes of rabbit angiotensin-converting enzyme (ACE) are generated from the same gene by alternative choice of two transcription initiation sites 5.7 kb apart. In the current study, we have characterized the regulatory sites controlling the transcription of the larger pulmonary isozyme mRNA. For this purpose, reporter genes driven by varying lengths of upstream region of the ACE gene were transfected into ACE-producing cells. Our results demonstrated that the transcription of this gene is primarily driven by positive elements within the first 274 bp DNA upstream of the transcription initiation site. The reporter gene driven by this region was expressed in two ACE-producing cells but not in two ACE-non-producing cells thereby establishing its tissue specificity. Our experiments also revealed the existence of a strong negative element located between -692 and -610 positions. This element suppressed the expression of the reporter gene in a dose-dependent and position and orientation-independent fashion thus suggesting that it is a true silencer element. It could also repress the expression of a reporter gene driven by the heterologous strong promoter of the beta-actin gene. The repressing effects of the negative element could be partially overcome by cotransfecting the isolated negative element along with the reporter gene containing the negative element. This result was possibly due to the functional removal of a limiting trans-acting factor which binds to this element. Electrophoretic mobility shift assays revealed that the negative element can form several complexes with proteins present in the nuclear extract of an ACE-producing cell line. At least part of the negative element is strongly conserved in the upstream regions of the human and mouse ACE genes.

A factor stimulating transcription of the testis-specific Pgk-2 gene recognizes a sequence similar to the binding site for a transcription inhibitor of the somatic-type Pgk-1 gene

The glycolytic enzyme phosphoglycerate kinase (PGK) consists of two isozymes, somatic-type PGK-1 and testis-specific PGK-2. The isozyme switch from PGK-1 to PGK-2 occurs during spermatogenesis at the mRNA level. The distal upstream region of the gene encoding mouse PGK-2 (Pgk-2) possesses a silencer-like negative cis element. In the present study, a positive cis element located in the proximal upstream region and factor(s) bound to it were analyzed in vitro. Cell-free transcription using nuclear extracts of rat organs demonstrated that the region between nucleotide positions -82 and -64, relative to the most distal transcription initiation site at +1, stimulates transcription in testis extracts. The cis element did not act on the promoter of the thymidine kinase gene, suggesting that it stimulates Pgk-2 transcription in a promoter-specific manner. The cis element bound a nuclear factor(s), which we designated TAP-1. Introducing various base substitutions within the cis element revealed that TAP-1-binding to the element requires the sequence 5'-GGAA-3', which is the binding motif for Ets oncoproteins. We previously reported that TIN-1, a transcription inhibitor of Pgk-1, binds to a sequence similar to the Ets-binding site. The addition of an oligo DNA containing the TIN-1-binding sequence of Pgk-1 prevented TAP-1 from binding to the Pgk-2 cis element, and vice versa. These results suggest that both TIN-1 and TAP-1, which are presumably involved in transcription regulation of the two Pgk genes, recognize DNA sequences related to the Ets-binding motif.

The Ets family of transcription factors

Interest in the Ets proteins has grown enormously over the last decade. The v-ets oncogene was originally discovered as part of a fusion protein expressed by a transforming retrovirus (avian E26), and later shown to be transduced from a cellular gene. About 30 related proteins have now been found in species ranging from flies to humans, that resemble the vEts protein in the so-called 'ets domain'. The ets domain has been shown to be a DNA-binding domain, that specifically interacts with sequences containing the common core trinucleotide GGA. Furthermore, it is involved in protein-protein interactions with co-factors that help determine its biological activity. Many of the Ets-related proteins have been shown to be transcription activators, like other nuclear oncoproteins and anti-oncoproteins (Jun, Fos, Myb, Myc, Rel, p53, etc.). However, Ets-like proteins may have other functions, such as in DNA replication and a general role in transcription activation. Ets proteins have been implicated in regulation of gene expression during a variety of biological processes, including growth control, transformation, T-cell activation, and developmental programs in many organisms. Signals regulating cell growth are transmitted from outside the cell to the nucleus by growth factors and their receptors. G-proteins, kinases and transcription factors. We will discuss how several Ets-related proteins fit into this scheme, and how their activity is regulated both post- and pre-translationally. Loss of normal control is often associated with conversion to an oncoprotein. vEts has been shown to have different properties from its progenitor, which might explain how it has become oncogenic. Oncogene-related products have been implicated in the control of various developmental processes. Evidence is accumulating for a role for Ets family members in Drosophila development, Xenopus oocyte maturation, lymphocyte differentiation, and viral infectious cycles. An ultimate hope in studying transformation by oncoproteins is to understand how cells become cancerous in humans, which would lead to more effective treatments. vEts induces erythroblastosis in chicken. Cellular Ets-family proteins can be activated by proviral insertion in mice and, most interestingly, by chromosome translocation in humans. We are at the beginning of understanding the multiple facets of regulation of Ets activity. Future work on the Ets family promises to provide important insights into both normal control of growth and differentiation, and deregulation in illness.

A positive regulator of the ribosomal protein gene, beta factor, belongs to the ETS oncoprotein family

The beta factor, which interacts with the rpL32 promoter, binds to the sequence 5'-GAGCCGGAAGTG and trans-activates this gene. Comparison of the DNA sequences bound by the beta factor with those bound by other known DNA-binding proteins revealed that the ETS proteins interact with similar DNA sequences. Consequently we have examined the relationship of the beta factor to the several ETS proteins so far reported. Antibody and oligonucleotide competition experiments, performed by using electrophoretic shift analysis, revealed that the beta factor contains ETS epitopes and that it is immunologically related to both of the GA-binding proteins (GABPs), implying that the beta factor may consist of two separate protein subunits.

A silencer-like cis element for the testis-specific phosphoglycerate-kinase-2-encoding gene

Phosphoglycerate kinase (PGK), a glycolytic enzyme, possesses two isozymes: somatic-type PGK-1 and testis-specific PGK-2, encoded by distinct genes. Tissue-specific expression of the two PGK-encoding genes (Pgk) seems to be transcriptionally controlled, since tissue distribution of the mRNAs coincides well with that of the proteins. In the present study, we determined the cis-acting DNA elements that regulate the transcription of mouse Pgk-2. A transient expression assay of DNAs having various portions of the Pgk-2 upstream region linked to the chloramphenicol acetyltransferase (CAT)-encoding gene (cat) was performed using mouse cell lines that exclusively express Pgk-1. A substantial increase in cat expression was observed when the region between nucleotides (nt) -1404 and -685, relative to the most distal transcription start point at nt +1, was lost. This cis-acting region appeared to function as a silencer, since it repressed cat expression independently of either orientation to or distance from the Pgk-2 promoter. Moreover, the cis element inhibited Pgk-2 transcription with no effect on Pgk-1 transcription in a cell-free system using nuclear extracts of rat liver. These results suggest that a silencer-like negative cis element is responsible, at least partly, for tissue-specific transcription of Pgk-2.