Purification and characterization of OTF-1, a transcription factor regulating cell cycle expression of a human histone H2b gene

Characterization of the 55-kb mouse histone gene cluster on chromosome 3

The histone gene cluster on mouse chromosome 3 has been isolated as a series of overlapping P1 clones, covering 110-120 kb, by probing with the histone H3-614 gene that had been mapped previously to mouse chromosome 3. There are genes for 10 core histone proteins present in a 55-kb cluster within this contig. There are three histone H3 genes, two of which are identical; four histone H2a genes, two of which are identical, one histone H4 gene; and two histone H2b genes. These histone H3 and H2a genes encode approximately 40% of the total H3 and H2a mRNA, whereas the histone H4 and histone H2b genes encode < 10% of the total H4 and H2b mRNA. There are no histone H1 genes present in this cluster. All of the histone H2a genes encode histone H2a.2 proteins (or variants of H2a.2), and account for all the H2a.2 genes in the mouse genome. All three histone H3 genes encode the histone H3.2 protein. A 21-kb region containing the adjacent H3-614 and H2a-614 genes has been duplicated and is present in an inverted repeat separated by 4.5 kb. The other two H2a genes are adjacent, with the 3' ends of their mRNAs separated by only 49 nucleotides in the DNA and the U7 snRNP binding sites separated by only 20 nucleotides. One of the histone H2b genes has lost the stem-loop sequence characteristic of the replication-dependent histone mRNAs and encodes only polyadenylated mRNAs.

Regulation of a physiological apoptosis: mouse mammary involution

Continuous milk production during lactation is dependent on a complex interplay of lactogenic hormones and the suckling stimulus exerted by the young. Involution can be initiated in the mouse mammary gland at any stage of lactation by removing the pups; involution then remains reversible for about 30 to 36 h. Involution in the mouse mammary gland is characterized by a massive loss of secretory epithelial cells from programmed cell death. The nuclear activation of protein kinase A and transcription factor activator protein 1 precede the irreversible phase of involution that is characterized by internucleosomal DNA fragmentation. Activation of activator protein 1 and fragmentation of chromosomal DNA can be prevented by lactogenic hormone treatment in explant cultures derived from mammary tissue at lactation. The elevation in activator protein 1 coincides with the epithelial expression of sulfated glycoprotein 2, a potential target gene of activator protein 1. Programmed cell death in the mammary gland is associated with the expression of the growth arrest gene, gas-1, and the integrin-associated protein gene, IAP, which codes for a putative Ca2+ channel that is dependent on integrin. Their potential roles during involution are discussed.

The E2F transcription factor activates a replication-dependent human H2A gene in early S phase of the cell cycle

Histone gene expression is restricted to the S phase of the cell cycle. Control is mediated by a complex network of sequence-specific DNA-binding factors and protein-protein interactions in response to cell cycle progression. To further investigate the regulatory functions that are associated at the transcriptional level, we analyzed the regulation of a replication-dependent human H2A.1-H2B.2 gene pair. We found that transcription factor E2F binds specifically to an E2F recognition motif in the H2A.1 promoter region. Activation of the H2A.1 promoter by E2F-1 was shown by use of luciferase reporter constructs of the intergenic promoter region. Overexpression of the human retinoblastoma suppressor gene product RB suppressed E2F-1 mediated transcriptional activation, indicating an E2F-dependent regulation of promoter activity during the G1-to-S-phase transition. Furthermore, the activity of the H2A.1 promoter was also downregulated by overexpression of the RB-related p107, a protein that has been detected in S-phase-specific protein complexes of cyclin A, E2F, and cdk2. In synchronized HeLa cells, expression of luciferase activity was induced at the beginning of DNA synthesis and was dependent on the presence of an E2F-binding site in the H2A.1 promoter. Together with the finding that E2F-binding motifs are highly conserved in H2A promoters of other species, our results suggest that E2F plays an important role in the coordinate regulation of S-phase-specific histone gene expression.

Oct-1 [corrected] and Oct-2 DNA-binding site specificity is regulated in vitro by different kinases

The transcription factors Oct-1 and Oct-2 bind differentially to three octamer binding sequences corresponding to the octamer binding site from the H2B promoter [ATGCTAATAA], a simple TAATGARAT motif, found in herpes simplex virus IE4/5 genes [GCGGTAATGAGAT], and a perfect consensus overlapping octamer/TAATGARAT motif [ATGCTAATGAGAT]. By comparing the effects of protein kinase A, protein kinase C and casein kinase 2 in vitro on the binding of Oct-1 and Oct-2 to the three motifs, we show that the actions of these kinases regulate Oct-1 and Oct-2 DNA binding independently of each other in a binding-site-specific manner. Inhibition of cellular phosphatases also regulate Oct-1 and Oct-2 DNA binding in a binding-site-specific manner. Both kinase and phosphatase activity are important for regulating the DNA binding activity of Oct-1 and Oct-2 because, in the presence of phosphatase inhibitors, protein kinase A attenuates the binding of both Oct-1 and Oct-2 to the octamer binding site but enhances binding when phosphatase inhibitors are omitted. Thus the DNA specificity of Oct-1 and Oct-2 can be regulated in vitro by the action of different kinases.

Cell cycle-regulated binding of nuclear proteins to elements within a mouse H3.2 histone gene

The histone gene family in mammals consists of 15-20 genes for each class of nucleosomal histone protein. These genes are classified as either replication-dependent or -independent in regard to their expression in the cell cycle. The expression of the replication-dependent histone genes increases dramatically as the cell prepares to enter S phase. Using mouse histone genes, we previously identified a coding region activating sequence (CRAS) involved in the upregulation of at least two (H2a and H3) and possibly all nucleosomal replication-dependent histone genes. Mutation of two seven-nucleotide elements, alpha and omega, within the H3 CRAS causes a decrease in expression in stably transfected Chinese hamster ovary cells comparable with the effect seen upon deletion of the entire CRAS. Further, nuclear proteins interact in a highly specific manner with nucleotides within these sequences. Mutation of these elements abolishes DNA/protein interactions in vitro. Here we report that the interactions of nuclear factors with these elements are differentially regulated in the cell cycle and that protein interactions with these elements are dependent on the phosphorylation/dephosphorylation state of the nuclear factors.

Structure of a cluster of mouse histone genes

The structure of a 25 kilobase region of mouse DNA containing 6 functional histone genes and an H2a pseudogene has been determined. The sequences and levels of expression of the H3 and H2b gene as well as the sequence of the H2a pseudogene have been determined.

Nuclear transcription factor Oct-1 binds to the 5'-upstream region of CYP1A1 and negatively regulates its expression

The cytochrome P450-dependent monooxygenases, which represent an extended superfamily, catalyze the biotransformation of many endogenous and exogenous substances. One of these hemoproteins, cytochrome P4501A1, is most closely associated with the bioactivation of polycyclic aromatic hydrocarbons such as benzo[a]pyrene, which may play a role in environmental carcinogenesis. A negative regulatory element (NRE) has been localized in the 5'-upstream region of the cytochrome P4501A1 gene (CYP1A1) at -843 to -746 base pairs from the site of transcription. The purpose of this research was to define any interactions of trans-acting proteins with this cis element. Rat liver nuclei were used as the source of trans-acting proteins and a biotinylated NRE-bearing fragment (-782 to -843 bp) from a plasmid which contained the CYP1A1 was prepared by the polymerase chain reaction technique. Gel mobility shift assays were used to demonstrate interactions between this NRE fragment and nuclear proteins. The specific binding to an octamer-containing motif in the 5'-upstream region of CYP1A1 was demonstrated; this was used as a step in the partial purification from rat liver of the transcription factor, Oct-1. Conventional chromatographic procedures and DNA recognition site affinity chromatography were also used. HepG2 human hepatoma cells were transfected with both pMCoLUC+ which contains the luciferase gene as a reporter gene driven by the CYP1A1 promoter (including the NRE), and an Oct-1 expression vector. Luciferase activity/mg protein in the doubly-transfected cells was significantly lower than in cells containing only pMCoLUC+. A nuclear transcription factor Oct-1 interacts with a portion of the NRE of the rat CYP1A1, suppressing the expression of this gene. These findings may help to explain the low level of basal expression of CYP1A1 in mammalian systems.

3'-Azido-3'-deoxythymidine inhibits erythroid-specific transcription factors in human erythroid K562 leukemia cells

The present study examines genetic mechanism(s) possibly involved in the observed 3'-azido-3'-deoxythymidine (AZT)-induced inhibition of globin gene transcription by evaluating the direct phenotypic erythroid effects of AZT on erythroid-specific transcription factors which regulate globin gene promoters. In vitro binding of GATA-1 or NFE-2 to its consensus sequence was decreased in the presence of AZT reaching a maximum inhibition as early as 24 h after AZT treatment. Nuclear extracts from butyric acid-induced K562 cells treated with an IC50 concentration of AZT exhibited a decrease in GATA-1 and NFE-2 binding by approximately 30% and 35%. In contrast, 2',3'-dideoxycytidine which inhibits cell growth without affecting hemoglobin synthesis, had no effect on binding of GATA-1 and NFE-2 factors. Northern blot analysis revealed a 25% decrease by AZT in GATA-1 mRNA steady-state levels at 24 h and this inhibitory effect was maintained until 72 h after drug addition. A similar decrease in NFE-2 mRNA steady-state levels was observed at 72 h after AZT treatment. This study suggests that AZT inhibition of erythroid differentiation is subsequent to a decrease of nuclear factors gene expression which affect their DNA binding.

The interferon-inducible p202 protein as a modulator of transcription: inhibition of NF-kappa B, c-Fos, and c-Jun activities

The antimicrobial, immunomodulatory, and cell growth-regulatory activities of the interferons are mediated by interferon-inducible proteins. One of these is p202, a nuclear protein that is encoded by the Ifi 202 gene from the interferon-activatable gene 200 cluster. Overexpression of p202 in transfected cells slows down cell proliferation. As shown earlier, p202 binds to the hypophosphorylated form of the retinoblastoma susceptibility protein. Here we report that p202 inhibits the activities of the NF-kappa B and the AP-1 enhancers both in transiently transfected cells and in transfected stable cell lines overexpressing p202. Furthermore, p202 binds the NF-kappa B p50 and p65 and the AP-1 c-Fos and c-Jun transcription factors in vitro and in vivo. NF-kappa B, c-Fos, and c-Jun participate in the transcription of various cellular and viral genes, and thus p202 can modulate the expression of these genes in response to interferons.

Displacement of sequence-specific transcription factors from mitotic chromatin

The general inhibition in transcriptional activity during mitosis abolishes the stress-inducible expression of the human hsp70 gene. Among the four transcription factors that bind to the human hsp70 promoter, the DNA-binding activities of three (C/EBP, GBP, and HSF1) were normal, while Sp1 showed reduced binding activity in mitotic cell extracts. In vivo footprinting and immunocytochemical analyses revealed that all of the sequence-specific transcription factors were displaced from promoter sequences as well as from bulk chromatin during mitosis. The correlation of transcription factor displacement with chromatin condensation suggests an involvement of chromatin structure in mitotic repression. However, retention of DNase I hypersensitivity suggests that the hsp70 promoter was not organized in a canonical nucleosome structure in mitotic chromatin. Displacement of transcription factors from mitotic chromosomes could present another window in the cell cycle for resetting transcriptional programs.

Involvement of a putative protein-tyrosine phosphatase and I kappa B-alpha serine phosphorylation in nuclear factor kappa B activation by tumor necrosis factor

Inhibitors of phosphotyrosyl protein phosphatases, pervanadate and phenylarsine oxide, abrogate tumor necrosis factor (TNF)-induced nuclear factor kappa B (NF-kappa B) nuclear translocation in transformed cell lines (U-937 and Jurkat) and primary fibroblasts (MRC-5 and REF). The inhibitors also abrogate NF-kappa B activation by the phosphoseryl/threonyl protein phosphatase inhibitor okadaic acid in U-937 cells. Inhibition of NF-kappa B activation is not due to a general inhibitory effect since neither pervanadate nor phenylarsine oxide treatment affected the constitutive DNA-binding activity of the transcription factors octamer-1 and cAMP response element-binding protein in U-937 cells, nor did these compounds inhibit the TNF-induced phosphorylation of proteins, viz. hsp-27, eukaryotic initiation factor 4e, and pp19, in MRC-5 fibroblasts. Overexpression of the protein-tyrosine phosphatase HPTP alpha resulted in a constitutive nuclear NF-kappa B-like DNA-binding activity in REF cells. Conversely, treatment of human protein-tyrosine phosphatase alpha-overexpressing cells with phenylarsine oxide led to a loss of the constitutive NF-kappa B activity. The presence of a tyrosine phosphorylation site on the inhibitor of NF-kappa B (I kappa B-alpha) suggested that it could be a target for TNF/okadaic acid-induced tyrosine dephosphorylation. However, no tyrosine phosphorylation was detected on I kappa B-alpha fron unstimulated cells, while TNF/okadaic acid-treated cells showed increased phosphorylation of I kappa B-alpha exclusively at serine residue(s). Treatment of cells with pervanadate inhibited TNF-induced I kappa B-alpha phosphorylation and degradation, whereas the serine protease inhibitors tosylphenylalanyl chloromethyl ketone and N alpha-p-tosyl-L-lysine chloromethyl ketone prevented TNF-induced I kappa B-alpha degradation and NF-kappa B nuclear translocation, but not the TNF-induced phosphorylation of I kappa B-alpha. The data suggest that TNF and okadaic acid induce the activation of a putative protein-tyrosine phosphatase(s), leading to I kappa B-alpha serine phosphorylation and degradation and NF-kappa B nuclear translocation.

Isolation and characterization of the androgen-dependent mouse cysteine-rich secretory protein-3 (CRISP-3) gene

The mRNA for cysteine-rich secretory protein-3 (CRISP-3) was originally identified in the mouse salivary gland as an androgen-dependent transcript, and is closely related to CRISP-1 and CRISP-2 which are abundantly expressed in the epididymis and testis respectively. Overlapping phage clones encompassing the entire length of the CRISP-3 gene were isolated from a lambda EMBL3 genomic library and analysed. DNA sequencing revealed that the gene consisted of eight exons ranging between 55 and 740 bp in size, and seven introns. All exon-intron junctions conformed to the GT/AG rule established for eukaryotic genes. The length of the introns was determined by PCR and was found to vary between 1.0 and 3.7 kb, indicating that the gene spans over 20 kb of the mouse genome. Primer extension allowed the mapping of the major transcription initiation site to an adenine located at the appropriate position downstream of a bona fide TATA box, in a region corresponding well to the eukaryotic consensus sequence. Over 800 bp of CRISP-3 promoter region were determined and two regions almost exactly matching the androgen-responsive element consensus RGWACANNNTGTWCY detected. In addition, sequences described in the Drosophila melanogaster Sgs-3 gene as being involved in its salivary gland-specific expression as well as two putative OTF- and GATA-binding elements were also found.

Stimulation of basal transcription from the mouse mammary tumor virus promoter by Oct proteins

The steroid hormone-inducible promoter of mouse mammary tumor virus (MMTV) contains three overlapping sequences related to the consensus octamer motif ATGCAAAT. Basal promoter activity in the absence of hormone induction from a template in which all three octamer elements were mutated was decreased by two-to threefold in in vitro transcription assays. Oct-1 protein purified from HeLa cell nuclear extracts, as well as recombinant Oct-1 expressed in bacteria, recognized MMTV octamer-related sequences, as shown by DNase I footprinting. Furthermore, rabbit polyclonal antiserum directed against recombinant Oct-1 completely inhibited the formation of specific complexes between MMTV octamer-related sequences and proteins present in nuclear extracts of HeLa cells, indicating that Oct-1 is the major protein in HeLa nuclear extracts that recognizes octamer-related sequences in the MMTV promoter. In addition, depletion of Oct-1 from the nuclear extract by using Oct-1-specific antiserum or a sequence-specific DNA affinity resin decreased in vitro transcription from the wild-type MMTV promoter to a level identical to that obtained from a promoter in which all three octamer-related sequences were mutated. Addition of purified HeLa Oct-1 or recombinant Oct-1 to the depleted extract selectively increased transcription from the wild-type relative to the mutated promoter, demonstrating that Oct-1 transcription factor stimulates basal transcription from the MMTV promoter. A similar effect was observed when purified recombinant Oct-2 was added to the Oct-1-depleted extract, suggesting that Oct-2 may play an important role in MMTV transcription in B cells.

The peri-kappa B site mediates human immunodeficiency virus type 2 enhancer activation in monocytes but not in T cells

Human immunodeficiency virus type 2 (HIV-2), like HIV-1, causes AIDS and is associated with AIDS cases primarily in West Africa. HIV-1 and HIV-2 display significant differences in nucleic acid sequence and in the natural history of clinical disease. Consistent with these differences, we have previously demonstrated that the enhancer/promoter region of HIV-2 functions quite differently from that of HIV-1. Whereas activation of the HIV-1 enhancer following T-cell stimulation is mediated largely through binding of the transcription factor NF-kappa B to two adjacent kappa B sites in the HIV-1 long terminal repeat, activation of the HIV-2 enhancer in monocytes and T cells is dependent on four cis-acting elements: a single kappa B site, two purine-rich binding sites, PuB1 and PuB2, and a pets site. We have now identified a novel cis-acting element within the HIV-2 enhancer, immediately upstream of the kappa B site, designated peri-kappa B. This site is conserved among isolates of HIV-2 and the closely related simian immunodeficiency virus, and transfection assays show this site to mediate HIV-2 enhancer activation following stimulation of monocytic but not T-cell lines. This is the first description of an HIV-2 enhancer element which displays such monocyte specificity, and no comparable enhancer element has been clearly defined for HIV-1. While a nuclear factor(s) from both peripheral blood monocytes and T cells binds the peri-kappa B site, electrophoretic mobility shift assays suggest that either a different protein binds to this site in monocytes versus T cells or that the protein recognizing this enhancer element undergoes differential modification in monocytes and T cells, thus supporting the transfection data. Further, while specific constitutive binding to the peri-kappa B site is seen in monocytes, stimulation with phorbol esters induces additional, specific binding. Understanding the monocyte-specific function of the peri-kappa B factor may ultimately provide insight into the different role monocytes and T cells play in HIV pathogenesis.

Alternative mRNA splicing and differential promoter utilization determine tissue-specific expression of the apolipoprotein B mRNA-editing protein (Apobec1) gene in mice. Structure and evolution of Apobec1 and related nucleoside/nucleotide deaminases

Apolipoprotein (apo) B mRNA editing consists of a C-->U conversion involving the first base of the codon CAA, encoding Gln 2153, to UAA, a stop codon. Editing occurs in the intestine only in most mammals, and in both the liver and intestine in a few mammalian species including mouse. We have cloned the cDNA for the mouse apoB mRNA editing protein, apobec1. Expression of mouse apobec1 cDNA in HepG2 cells results in the editing of the intracellular apoB mRNA. The cDNA predicts a 229-amino acid protein showing 92, 66, and 70% identity to the rat, rabbit, and human proteins, respectively. Based on the estimated values of divergence of apobec1 sequences in terms of the numbers of synonymous and non-synonymous suhstitutions per site, we found that apobec1 is a fairly rapidly evolving protein. Sequence comparison among mammalian apobec1 sequences has permitted the identification of seven conserved regions that may be functionally important for editing activity. We present a phylogenetic tree relating apobec1 sequences to double-stranded RNA adenosine deaminase and other nucleotide/nucleoside deaminases. Northern blot analysis indicates that apobec1 mRNA exists in two different sizes, a approximately 2.2-kilobase (kb) form in small intestine and a approximately 2.4-kb form in liver, spleen, kidney, lung, muscle, and heart. To study the molecular basis for the different sized apobec1 mRNAs, we cloned the apobec1 gene and characterized its exon-intron organization together with the sequences expressed in the hepatic and intestinal mRNA. The mouse apobec1 gene contains 8 exons and spans approximately 25 kb, and is located in chromosome 6. The major hepatic mRNA contains all 8 exons, whereas the major small intestinal mRNA misses the first 3 exons and its transcription is initiated in exon 4. The intestinal mRNA also contains at its 5' end a unique 102-nucleotide piece that is absent in the liver mRNA. We also identified two alternatively spliced hepatic apobec1 mRNAs with different acceptor sites in exon 4. Transient expression studies using promoter-reporter gene constructs in HeLa, Hepa, and Caco-2 cells indicate that the 5'-flanking sequences of the liver mRNA (i.e. upstream of exon 1) have predominantly hepatic promoter activity and the 5'-flanking sequences of the major small intestine mRNA (i.e. upstream of exon 4) have preferential intestinal promoter activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Sequence-specific DNA binding activities of nuclear matrix proteins of mammalian lens epithelial cells

This study examines matrix and nonmatrix nuclear proteins of the rabbit lens epithelial cells. The nuclear matrix proteins were isolated by modified Penman technique, which requires presence of detergents and nucleases, whereas nonmatrix nuclear proteins were obtained by high salt extraction. The data from these experiments revealed presence of DNA binding activities for SP-1 and OCT-1 proteins in both matrix and non-matrix compartments of rabbit lens epithelial cells. Comparison of the relative abundance of SP-1 and OCT-1 binding activities in nuclear matrix and nonmatrix fractions suggest the distribution between these two compartments is cell type specific and possibly related to the control of cell growth.

Cloning, sequencing and expression of two isoforms of the murine oct-1 transcription factor

Oct-1 is a ubiquitously expressed regulatory gene of the POU domain family. The Oct-1 protein binds to the octamer motif present in the control regions of a variety of genes such as the immunoglobulins, histone H2B and snRNAs. To learn about Oct-1 and its possible role in B-cell maturation, we have used oct-2 cDNA to screen a murine pre-B cell, cDNA library. Two cDNA clones were identical in their POU-homeo box DNA binding domain, but differed in their 3'-region. Whereas one clone (oct-1a) was very similar to its human oct-1 homologue, the other (oct-1b), contained an additional 72 bp sequence (designated E1) at the serine threonine rich coding region (position 1485 of the human oct-1), and a deletion of another 72 bp sequence (designated E2) downstream (position 1920). These changes preserve the protein reading frame. DNA blot analysis indicates that murine oct-1 is a single copy gene and that the two oct-1 isoforms oct-1 is expressed as a large approximately 10 kb transcript in all the cell are generated by alternative RNA splicing. RNA blots showed that oct-1 is expressed as a large approximately 10 kb transcript in all the cell lines tested. PCR analysis of the E1 and E2 72 bp regions, indicated the presence of a third isoform containing both E1 and E2 (Oct-1c). Oct-1a and Oct-1b were present in all cell types examined, but the level of expression was lower in liver and spleen as compared to testis, thymus and kidney. The ratio of Oct-1b to Oct-1a ranged between 0.2 to 0.5, for all tissues examined except for testis which expressed higher amounts of oct-1b and/or oct-1c. Our findings thus show that the pattern of expression of the oct-1 gene is more complex than hitherto thought.

Dynamic and differential Oct-1 expression during early Xenopus embryogenesis: persistence of Oct-1 protein following down-regulation of the RNA

As a first step towards the elucidation of the role of the transcription factor Oct-1 in development, we prepared a monoclonal antibody to study the spatio-temporal distribution of Oct-1 protein in vivo. Here we report differential expression of the Oct-1 gene in the Xenopus embryo both at the RNA and the protein level. Transcripts and protein are detected in ectodermal and mesodermal cell lineages, in which the expression exhibits a pattern of progressive spatial restriction in the course of development. The Oct-1 expression as reported here is not correlated with cell density or cell proliferation in the embryo. Our results suggest a role of Oct-1 in the specification and differentiation of neuronal and neural crest cells. In many other cells, the developmental decision to down regulate Oct-1 is delayed, probably due to a high stability of the protein.

Tissue-specific expression of the 230-kDa bullous pemphigoid antigen gene (BPAG1). Identification of a novel keratinocyte regulatory cis-element KRE3

The 230-kDa bullous pemphigoid antigen gene (BPAG1) is expressed exclusively in basal keratinocytes of epidermis. In this study, we have identified a novel cis-element, keratinocyte responsive element 3 (KRE3), at position -216 to -197 of the human BPAG1 gene. A promoter-CAT construct containing this element had approximately 50-fold higher expression than a similar construct devoid of this sequence when tested in transient transfections of cultured human keratinocytes. However, there was no effect on the low base-line level of expression in cultured skin fibroblasts. KRE3 contains a palindromic sequence 5'-CAAATATTTG-3', and mutations in this sequence significantly reduced the promoter activity. Gel mobility shift assays with an oligomer containing KRE3 sequence demonstrated binding activity with nuclear proteins isolated from keratinocytes. One of the DNA/protein complexes was clearly specific, since competition with > 12.5-fold excess of the unlabeled oligomer resulted in disappearance of this band. No specific binding activity was noted with nuclear proteins extracted from fibroblasts. Thus, KRE3 appears to serve as the binding site for keratinocyte-specific trans-activating factor(s), and KRE3 may thus confer the tissue-specific expression to the BPAG1 gene.

The cellular C1 factor of the herpes simplex virus enhancer complex is a family of polypeptides

The alpha/immediate early genes of herpes simplex virus are regulated by the specific assembly of a multiprotein enhancer complex containing the Oct-1 POU domain protein, the viral alpha-transinduction factor alpha TIF, (VP16, ICP25), and the C1 cellular factor. The C1 factor from mammalian cells is a heterogeneous but related set of polypeptides that interact directly with the alpha-transinduction factor to form a heteromeric protein complex. The isolation of cDNAs encoding the polypeptides of the C1 factor suggests that these proteins are proteolytic products of a novel precursor. The sequence of the amino termini of these polypeptide products indicate that the proteins are generated by site-specific cleavages within a reiterated 20-amino acid sequence. Although the C1 factor appears to be ubiquitously expressed, it is localized to subnuclear structures in specific cell types.

Functional characterization of the cis-regulatory elements of the rat ribophorin I gene

The ribophorin I gene encodes a rough endoplasmic reticulum (RER) specific membrane protein which is a subunit of the oligosaccharyltransferase. To establish the functional activity of its promoter region we have performed transient gene transcription experiments employing plasmid constructs that contain 5' flanking regions of the ribophorin I gene cloned upstream of the CAT reporter gene. Among the restriction fragments obtained from the 1.3-kilobase 5' flanking region, a proximal fragment (-42 to +24) containing two GC-rich elements was required for basic promoter activity, while a fragment (-364 to +24) encoding an additional GC-box and an octamer like motif at -233 conferred the maximal promoter activity. In order to investigate the functionality of an octomer-like sequence co-transfection experiments were performed with Oct-2 cDNA and the CAT reporter gene containing the ribophorin I fragment (-364 to +24). A 3-4-fold increase in the transcriptional activity was observed with this construct. In addition, gel shift experiments showed Oct-2 binding to this construct. These results indicate that Oct-2 is most likely involved in the regulation of the ribophorin I gene transcription. We suggest that the GC-rich elements are necessary for constitutive ribophorin I expression while octamer motif binding proteins function synergistically with the GC-rich element binding proteins to increase the expression of the ribophorin I gene during the proliferation of RER.

Involvement of the Ets family factor PU.1 in the activation of immunoglobulin promoters

The B cell-specific expression of immunoglobulin (Ig) genes is controlled by the concerted action of variable (V) region promoters and intronic or 3' enhancers, all of which are active in a lymphoid-specific manner. A crucial highly conserved element of the V region promoters is the octamer site -ATTTGCAT-, which can be bound by ubiquitous (Oct-1) as well as B cell-specific (Oct-2) factors. Another less conserved element found in many Ig promoters is pyrimidine-rich and has been shown to be functionally important, in particular for those Ig promoters that have only an imperfect octamer site. In this study we have analyzed the factors binding specifically to the pyrimidine-rich motif of the V kappa 19 promoter, a light chain gene promoter with an imperfect octamer site. Using nuclear extracts prepared from B cells, we detected two sets of specific complexes in electrophoretic mobility shift experiments. One complex appears to be ubiquitous but enriched in lymphoid cells and represents the binding of a potentially novel factor with an apparent molecular mass of approximately 50 kDa. The other complex was found only with extracts from pre-B or B cells as well as from a macrophage cell line and appears to be caused by the binding of PU.1, a factor of the Ets family. We show that on this Ig promoter Oct factors (Oct-1 or Oct-2) and PU.1 can bind concomitantly but without synergism. By transfection experiments in non-B cells we demonstrate that PU.1 is indeed able to activate this promoter in concert with Oct-2. Furthermore, we show that PU.1 can bind with varying affinities to the pyrimidine-rich elements of several other Ig promoters. These data suggest a more general role for PU.1 or other members of the Ets family in the activation of Ig promoters.

Down regulation of the octamer binding protein Oct-1 during growth arrest and differentiation of a neuronal cell line

The octamer binding transcription/DNA replication factor Oct-1 is present in virtually all cell types including proliferating cell lines of neuronal origin but is not detectable in mature non-dividing neurons. Cell cycle arrest in G0/G1 and morphological differentiation of a neuronal cell line is accompanied by a decline in the level of Oct-1 DNA binding, although the level of DNA binding by another octamer binding protein, Oct-2 is unaltered. This effect is paralled by a decline in the level of the Oct-1 mRNA in the non-dividing cells. The decrease in Oct-1 levels occurs only with the production of a mature, non-dividing neuronal phenotype and not when the cells are arrested in late G1 and do not undergo morphological differentiation. The potential role of Oct-1 and other octamer binding proteins in gene regulation in neuronal cells and in their differentiation is discussed.

Distamycin analogues with improved sequence-specific DNA binding activities

In the present study we have investigated the effect of unprecedented chemical modifications introduced in the distamycin molecule, with the aim of assessing their ability to interfere with sequence-specific DNA-protein interactions in vitro. By using an electrophoretic mobility shift assay, we have been able to identify novel distamycin analogues with improved displacing abilities on the binding of octamer nuclear factors to their target DNA sequence. While variations in the number of pyrrole rings and/or reversion of an internal amide bond result in distamycin-like compounds with identical or very similar properties, the reversion of the formamido into a carboxyamido group or its replacement with the charged formimidoyl moiety significantly improves the ability of the resulting novel distamycin derivatives to compete with OCT-1 (octamer 1 nuclear factor) for its target DNA sequence. Tissue-specific octamer-dependent in vitro transcription is similarly affected by these chemical modifications, suggesting that the ability of distamycins to bind octamer sequences has a direct influence on the functional state of octamer-containing promoters. These data represent an initial, successful attempt to rationalize the design of DNA binding drugs, using distamycins as a model.

Analysis of Oct2-isoform expression in lipopolysaccharide-stimulated B lymphocytes

Oct2-isoform expression in splenic B cells stimulated with lipopolysaccharide or lipopolysaccharide plus phorbol-di-butyrate was analysed by cDNA cloning. The frequency of Oct2-positive clones was 1/15,000 in both libraries. Two new isoforms were found that generate novel amino- or carboxy-terminal sequences. An isoform lacking exon 11 destroyed the carboxy-terminal leucin-zipper region and introduced a frame shift creating a novel, proline-rich carboxy terminus. A new exon containing a highly basic region (4c) was characterized, between exons 4 and 5. This exon was inserted between glutamine-rich regions 2 and 3, carboxy terminal of a tentative leucine-zipper structure. In addition, a new combination isoform containing Oct2a's amino terminal insert (exon 7a) and Oct2b's carboxy terminal insert (exon 13) was found that created a novel large isoform, Oct2ab. More frequent use of the classical Oct2a and Oct2b isoforms was observed in the lipopolysaccharide-stimulated B cells, while a preference for the Oct2ab and Oct2ba isoforms was observed in lipopolysaccharide plus phorbol-di-butyrate-treated cells.

Organization and expression of H1 histone and H1 replacement histone genes

The H1 family is the most divergent subgroup of the highly conserved class of histone proteins [Cole: Int J Pept Protein Res 30:433-449, 1987]. In several vertebrate species, the H1 complement comprises five or more subtypes, and tissue specific patterns of H1 histones have been described. The diversity of the H1 histone family raises questions about the functions of different H1 subtypes and about the differential control of expression of their genes. The expression of main type H1 genes is coordinated with DNA replication, whereas the regulation of synthesis of replacement H1 subtypes, such as H1 zero and H5, and the testis specific H1t appears to be more complex. The differential control of H1 gene expression is reflected in the chromosomal organization of the genes and in different promoter structures. This review concentrates on a comparison of the chromosomal organization of main type and replacement H1 histone genes and on the differential regulation of their expression. General structural and functional data, which apply to both H1 and core histone genes and which are covered by recent reviews, will not be discussed in detail.

Stably integrated mouse mammary tumor virus long terminal repeat DNA requires the octamer motifs for basal promoter activity

In the mouse mammary tumor virus promoter, a tandem of octamer motifs, recognized by ubiquitous and tissue-restricted Oct transcription factors, is located upstream of the TATA box and next to a binding site for the transcription factor nuclear factor I (NF-I). Their function was investigated with mutant long terminal repeats under different transfection conditions in mouse Ltk- cells and quantitative S1 nuclease mapping of the transcripts. In stable transfectants, which are most representative of the state of proviral DNA with respect to both number of integrated DNA templates and chromatin organization, a long terminal repeat mutant of both octamer sites showed an average 50-fold reduction of the basal transcription level, while the dexamethasone-stimulated level was unaffected. DNase I in vitro footprinting assays with L-cell nuclear protein extracts showed that the mutant DNA was unable to bind octamer factors but had a normal footprint in the NF-I site. I conclude that mouse mammary tumor virus employs the tandem octamer motifs of the viral promoter, recognized by the ubiquitous transcription factor Oct-1, for its basal transcriptional activity and the NF-I binding site, as previously shown, for glucocorticoid-stimulated transcription. A deletion mutant with only one octamer site showed a marked base-level reduction at high copy number but little reduction at low copies of integrated plasmids. The observed transcription levels may depend both on the relative ratio of transcription factors to DNA templates and on the relative affinity of binding sites, as determined by oligonucleotide competition footprinting.

Stably integrated mouse mammary tumor virus long terminal repeat DNA requires the octamer motifs for basal promoter activity

In the mouse mammary tumor virus promoter, a tandem of octamer motifs, recognized by ubiquitous and tissue-restricted Oct transcription factors, is located upstream of the TATA box and next to a binding site for the transcription factor nuclear factor I (NF-I). Their function was investigated with mutant long terminal repeats under different transfection conditions in mouse Ltk- cells and quantitative S1 nuclease mapping of the transcripts. In stable transfectants, which are most representative of the state of proviral DNA with respect to both number of integrated DNA templates and chromatin organization, a long terminal repeat mutant of both octamer sites showed an average 50-fold reduction of the basal transcription level, while the dexamethasone-stimulated level was unaffected. DNase I in vitro footprinting assays with L-cell nuclear protein extracts showed that the mutant DNA was unable to bind octamer factors but had a normal footprint in the NF-I site. I conclude that mouse mammary tumor virus employs the tandem octamer motifs of the viral promoter, recognized by the ubiquitous transcription factor Oct-1, for its basal transcriptional activity and the NF-I binding site, as previously shown, for glucocorticoid-stimulated transcription. A deletion mutant with only one octamer site showed a marked base-level reduction at high copy number but little reduction at low copies of integrated plasmids. The observed transcription levels may depend both on the relative ratio of transcription factors to DNA templates and on the relative affinity of binding sites, as determined by oligonucleotide competition footprinting.

Identification of the 5' regulatory elements of avian lipoprotein lipase gene: synergistic effect of multiple factors

The organization of cis-acting regulatory elements of the chicken lipoprotein lipase gene was investigated in 5.4 kb of 5' flanking sequences. Various lengths of 5' flanking sequence were linked to the bacterial chloramphenicol acyltransferase (CAT) gene and transfected into primary cultures of chicken adipocytes by DEAE-dextran transfection method. Negative elements are present between -1947 and -139 of the 5' flanking sequence. Removal of these sequences revealed the presence of positive elements located within 138 bp upstream of the major transcription start site. Sequence analysis showed that the region from the major transcription start site to -138 contains an inverted GC box (ACCACGCCCC), a CCAAT element and two direct repeats of the octamer motif, ATTTGCAT. DNase I footprinting assays using a probe extending from -175 to +191, identified three sites protected by nuclear factors. Site I (-126 to -123), a C-rich sequence, GCCC, was identified only on the coding strand. Site II covered the sequence from -95 to -68 and includes the GC box. Site III, from -53 to -26, contained two octamer repeats. Site I is the 5' portion of a 10 bp sequence (CCCTCCCCCC; -126/-116) which is perfectly conserved in the avian and the human promoter. Single or multiple copies of a 37 bp DNA fragment (-138/-102) containing the 10 bp conserved sequence were cloned into LPLCAT-51, upstream or downstream of the major transcription start site and in both orientations; transfection and CAT activity assays with these constructs indicate that the -138/-102 fragment has an enhancer like activity. Additional 5' and internal deletions of LPLCAT-138 suggest that the factors binding to the C-rich element, the GC box and the two octamer repeats have a synergistic effect on promoter activity.

Specific cleavage of transcription factors by the thiol protease, m-calpain

The intracellular nonlysosomal calcium-dependent cysteine protease, m-calpain, is shown to specifically cleave the bHLHzip transcription factor USF leaving the binding and dimerisation domains intact. The resultant protein is capable of efficient DNA binding but is no longer able to activate transcription. A surprisingly high proportion of other transcription factors tested, AP1 (c-Fos/c-Jun), Pit-1, Oct-1, CP1a and b, c-Myc, ATF/CREB, AP2 and AP3 but not Sp1, were similarly cleaved by m-calpain to produce specific partial digestion products. These properties make m-calpain a particularly useful protease for proteolytic studies of transcription factors and also raise the possibility that m-calpain may be involved in vivo in regulation of turnover or transcriptional activity of a number of transcription factors.

Transcriptional control of human papillomavirus (HPV) oncogene expression: composition of the HPV type 18 upstream regulatory region

The malignant transformation potential of high-risk human papillomaviruses (HPVs) is closely linked to the expression of the viral E6 and E7 genes. To elucidate the molecular mechanisms resulting in HPV oncogene expression, a systematic analysis of the cis-regulatory elements within the HPV type 18 (HPV18) upstream regulatory region (URR) which regulate the activity of the E6/E7 promoter was performed. As the functional behavior of a given cis-regulatory element can be strongly influenced by the overall composition of a transcriptional control region, individual elements were inactivated by site-directed mutagenesis in the physiological context of the complete HPV18 URR. Subsequently, the effects of these mutations on the activity of the E6/E7 promoter were assessed by transient transfection assays. We found that the transcriptional stimulation of the E6/E7 promoter largely depends on the integrity of cis-regulatory elements bound by AP1, SP1, and in certain epithelial cells, KRF-1. In contrast to previous reports by implying a key role for NF1 and Oct-1 recognition motifs in the stimulation of papillomavirus oncogene expression, the inactivation of these elements in the context of the HPV18 URR did not strongly affect the transcriptional activity of the E6/E7 promoter. Mutation of a promoter-proximal glucocorticoid response element completely abolished dexamethasone inducibility of the HPV18 E6/E7 promoter and resulted in an increase of its basal activity. Functional dissection of the HPV18 constitutive enhancer region indicates that its transcriptional activity is largely generated by functional synergism between a centrally located AP1 module and thus far undetected cis-active elements present in the 5' flank of the enhancer. Furthermore, comparative analyses using homologous and heterologous promoters show that the transcriptional activity of HPV18 enhancer elements is influenced by the nature of the test promoter in a cell-type-specific manner.

Differential regulation of the human H1 zero-histone-gene transcription in human tumor-cell lines

Cloning and sequence analysis of about 2 kb of the 5' flanking region of the human H1 zero histone gene reveals several potential regulatory elements upstream of the transcribed portion of this gene. Transfection studies using the chloramphenicol acetyl transferase (CAT) gene as a reporter gene with a series of promoter deletions revealed that the expression of the H1 zero gene may depend on a complex interplay of several transcription factors, including members of the retinoic acid and/or thyroid-hormone-receptor superfamily, at the 5' flanking region of the H1 zero gene. CAT assays demonstrate varied patterns of expression and regulation in different human tumor-cell lines. The leukemia cell line HL60 does not express H1 zero mRNA and shows no CAT activity. HeLa cells strongly express the CAT gene under the control of the H1 zero promoter. Under the same conditions, HepG2 cells also transcribe the CAT gene, although at a lower rate than HeLa cells. Using different promoter-deletion clones, the CAT activity differs in HepG2 and HeLa cells in the very distal promoter region. In both cell lines, the CAT activity decreases several fold when the region between nucleotides -450 and -600 upstream of the mRNA start site is deleted. It also decreases when just the proximal portion but not the distal promoter region is deleted. In summary, the regulatory patterns of these three cell lines differ, indicating a cell-type-specific regulation of the human H1 zero-histone-gene expression.

Presence of particular transcription regulatory elements in the 5'-intergenic region shared by the chicken H2A-III and H2B-V pair

The two chicken histone gene families, H2A and H2B, contain nine and eight members, respectively, within two major histone gene clusters. Six genes each from families H2A and H2B have been found to be closely associated in inverted directions as H2A/H2B gene pairs. Two previously sequenced H2A members (H2A-I and H2A-II) encode the same amino acid (aa) sequence (class I), whereas seven sequenced H2B genes encode three different variants (classes I, II and III). In this study, we first sequenced H2A-III, a member of the H2A family, which is located in inverted orientation and 350 bp upstream from H2B-V, encoding the class-III H2B protein. The protein encoded by H2A-III differs from the class-I H2A protein in a single aa (Ala70-->Pro; class II). As a step toward elucidation of the transcriptional regulation of the H2A and H2B families, we fused this 5'-intergenic region to the cat gene in inverted orientations to generate two chimeric plasmids, pH2A-III-350 and pH2B-V-350. Transient CAT assays using these constructs indicated that the promoter of H2B-V is more active than that of H2A-III. CAT assays with 5'-deletion mutants of H2A-III and H2B-V showed that they each possess particular transcriptional motifs which are located relatively close to, or apart from, their own coding regions. These findings, together with those reported previously on the H2A-V/H2B-II pair, suggest distinct manners of transcription regulation of different members of the chicken histone gene families, H2A and H2B.

Proteins interacting with an androgen-responsive unit in the C3(1) gene intron

The expression of the three genes encoding the components C1, C2 and C3 of prostatic binding protein (PBP) is under androgen control and restricted to the rat ventral prostate. The SstI-PvuII fragment of the first intron of the C3(1) gene displays two binding sites for ubiquitous transcription factors and one for a tissue-specific factor in a 80-bp region upstream of its androgen response element (ARE). The octamer transcription factor 1 (OTF-1) binds to the most distal element (site 1) while a member of the nuclear factor I (NF-I) family recognizes site 2. A third unidentified prostate-specific factor, which also occurs in castrated rats, interacts with the proximal element (site 3). In T-47D cells, both the OTF-1 and the NF-I-like factor can modulate the androgen response of the promoter in a reporter gene construct containing the C3(1) intronic fragment.

Molecular cloning of a diverged homeobox gene that is rapidly down-regulated during the G0/G1 transition in vascular smooth muscle cells

Adult vascular smooth muscle cells dedifferentiate and reenter the cell cycle in response to growth factor stimulation. Here we describe the molecular cloning from vascular smooth muscle, the structure, and the chromosomal location of a diverged homeobox gene, Gax, whose expression is largely confined to the cardiovascular tissues of the adult. In quiescent adult rat vascular smooth muscle cells, Gax mRNA levels are down-regulated as much as 15-fold within 2 h when these cells are induced to proliferate with platelet-derived growth factor (PDGF) or serum growth factors. This reduction in Gax mRNA is transient, with levels beginning to rise between 8 and 24 h after mitogen stimulation and returning to near normal by 24 to 48 h. The Gax down-regulation is dose dependent and can be correlated with the mitogen's ability to stimulate DNA synthesis. PDGF-AA, a weak mitogen for rat vascular smooth muscle cells, did not affect Gax transcript levels, while PDGF-AB and -BB, potent mitogens for these cells, were nearly as effective as fetal bovine serum. The removal of serum from growing cells induced Gax expression fivefold within 24 h. These data suggest that Gax is likely to have a regulatory function in the G0-to-G1 transition of the cell cycle in vascular smooth muscle cells.

Molecular cloning of a diverged homeobox gene that is rapidly down-regulated during the G0/G1 transition in vascular smooth muscle cells

Adult vascular smooth muscle cells dedifferentiate and reenter the cell cycle in response to growth factor stimulation. Here we describe the molecular cloning from vascular smooth muscle, the structure, and the chromosomal location of a diverged homeobox gene, Gax, whose expression is largely confined to the cardiovascular tissues of the adult. In quiescent adult rat vascular smooth muscle cells, Gax mRNA levels are down-regulated as much as 15-fold within 2 h when these cells are induced to proliferate with platelet-derived growth factor (PDGF) or serum growth factors. This reduction in Gax mRNA is transient, with levels beginning to rise between 8 and 24 h after mitogen stimulation and returning to near normal by 24 to 48 h. The Gax down-regulation is dose dependent and can be correlated with the mitogen's ability to stimulate DNA synthesis. PDGF-AA, a weak mitogen for rat vascular smooth muscle cells, did not affect Gax transcript levels, while PDGF-AB and -BB, potent mitogens for these cells, were nearly as effective as fetal bovine serum. The removal of serum from growing cells induced Gax expression fivefold within 24 h. These data suggest that Gax is likely to have a regulatory function in the G0-to-G1 transition of the cell cycle in vascular smooth muscle cells.

Convergent regulation of NF-IL6 and Oct-1 synthesis by interleukin-6 and retinoic acid signaling in embryonal carcinoma cells

The nuclear signaling by the pleiotropic cytokine interleukin-6 (IL-6) has been investigated in human embryonal carcinoma cells and T cells. We show that Oct-1, a ubiquitously expressed octamer-binding protein known to be regulated posttranslationally, can also be regulated at the levels of mRNA and protein synthesis by IL-6 and by retinoic acid (RA) in human embryonal carcinoma cells. NF-IL6, an IL-6-inducible transcription factor of the C/EBP family, can confer this regulation and is itself regulated by both signals. The abundance and the molar ratios of the three forms of NF-IL6, corresponding to peptides initiated in frame from different AUGs of the same NF-IL6 mRNA species, are regulated by IL-6 and by RA. These results suggest that the two signal transduction pathways overlap in human embryonal carcinoma cells and that Oct-1 may be downstream of NF-IL6 in the shared regulatory cascade. Enhanced Oct-1 synthesis correlates with one of the functions of Oct-1, i.e., stimulation of adenovirus DNA replication. This provides an example of a possible functional consequence of IL-6 and RA signaling that is mediated by NF-IL6 and Oct-1 regulation.

Skn-1a and Skn-1i: two functionally distinct Oct-2-related factors expressed in epidermis

Two forms of a member of the POU domain family of transcriptional regulators, highly related to Oct-2, are selectively expressed in terminally differentiating epidermis and hair follicles. One form, referred to as Skn-1i, contains an amino-terminal domain that inhibits DNA binding and can inhibit transactivation by Oct-1. A second form, Skn-1a, contains an alternative amino terminus and serves to activate cytokeratin 10 (K10) gene expression. The pattern of expression of the Skn-1a/i gene products and the effect of the alternative products on the expression of other genes suggest that these factors serve regulatory functions with respect to epidermal development.

Convergent regulation of NF-IL6 and Oct-1 synthesis by interleukin-6 and retinoic acid signaling in embryonal carcinoma cells

The nuclear signaling by the pleiotropic cytokine interleukin-6 (IL-6) has been investigated in human embryonal carcinoma cells and T cells. We show that Oct-1, a ubiquitously expressed octamer-binding protein known to be regulated posttranslationally, can also be regulated at the levels of mRNA and protein synthesis by IL-6 and by retinoic acid (RA) in human embryonal carcinoma cells. NF-IL6, an IL-6-inducible transcription factor of the C/EBP family, can confer this regulation and is itself regulated by both signals. The abundance and the molar ratios of the three forms of NF-IL6, corresponding to peptides initiated in frame from different AUGs of the same NF-IL6 mRNA species, are regulated by IL-6 and by RA. These results suggest that the two signal transduction pathways overlap in human embryonal carcinoma cells and that Oct-1 may be downstream of NF-IL6 in the shared regulatory cascade. Enhanced Oct-1 synthesis correlates with one of the functions of Oct-1, i.e., stimulation of adenovirus DNA replication. This provides an example of a possible functional consequence of IL-6 and RA signaling that is mediated by NF-IL6 and Oct-1 regulation.

The immunoglobulin heavy chain locus contains another B-cell-specific 3' enhancer close to the alpha constant region

The transcription of immunoglobulin genes is controlled by variable region promoters and by enhancers, both of which are lymphoid specific. Because immunoglobulin genes are subject to an extremely complex regulation, we anticipated that there might be additional control elements for these genes. We therefore sought additional enhancers and demonstrate here that there is indeed another weak transcriptional enhancer just 3' to the mouse alpha constant region. This novel immunoglobulin enhancer is lymphoid specific and at two positions can bind members of the Oct family of transcription factors.