c-fos mediated stimulation of an AP-1 DNA binding activity in undifferentiated teratocarcinoma cell lines

Undifferentiated F9 and PCC4 embryonal carcinoma (EC) cells contain low levels of AP-1 DNA binding activity. Upon differentiation induced by retinoic acid and cyclic AMP or in differentiated cell lines, AP-1 DNA binding activity can be readily detected. Minute amounts of 3T6 cells extracts, that by themselves were unable to show any binding to an AP-1 site, stimulate AP-1 DNA binding activity when added to the EC cell extracts, suggesting that components of the 3T6 extracts stimulate this DNA binding activity in F9 and PCC4 cell extracts. This enhancement of DNA binding activity requires the presence in the donor fraction (3T6 cells) of a thermostable protein(s) that possesses neither protein kinase nor phosphatase activities. The proteins responsible for stimulation in 3T6 extracts can be separated from the ones responsible for AP-1 binding by chromatography. 3T6 c-fos immunodepleted fractions are unable to activate AP-1 DNA binding activity in EC cell extracts, while c-jun depleted fractions activate normally. Moreover, in vitro translated c-fos, but not c-jun proteins, are able to stimulate binding in EC extracts. These data suggest an important role for c-fos protein in activation of a specific DNA binding transcriptional factor during cellular differentiation and provide a convenient in vitro assay for c-fos function.

Modification of an adenovirus major late promoter-binding factor during poliovirus infection

To further characterize the mechanism involved in poliovirus-induced inhibition of HeLa cells mRNA synthesis, in vitro formation of DNA-protein complexes between nuclear upstream stimulatory transcription factor (USF) and the adenovirus type 2 major late promoter upstream promoter element (UPE; located between -45 and -65 base pairs) was studied. Using the gel shift assay, we found differences between the UPE-protein complex formed with partially purified nuclear extracts from poliovirus-infected HeLa cells and that obtained in the presence of mock-infected extracts. Formation of the modified UPE-USF complex coincided with virus-induced inhibition of host cell RNA synthesis in vivo and with a less efficient in vitro transcriptional activity of the nuclear extracts from infected cells. Furthermore, using a cross-linking protocol, we found that the host 46-kilodalton UPE-binding USF factor was severely diminished and that a virus-induced or -modified 50-kilodalton polypeptide appeared to be specifically bound to the UPE template.

Factors involved in specific transcription by mammalian RNA polymerase II. Role of factors IID and MLTF in transcription from the adenovirus major late and IVa2 promoters

The role of the adenovirus major late upstream transcription factor (MLTF) in transcription from the adenovirus major late and the IVa2 promoters was studied. The transcription initiation site of the IVa2 promoter is located 210 nucleotides upstream from the CAP site of the major late promoter. Transcription from these two promoters occurs on different DNA strands. Thus, this divergent transcription suggests that the same factor could simultaneously regulate the expression of two different genes. This was investigated utilizing a reconstituted transcription system in vitro. The addition of MLTF to reaction mixtures containing the purified general transcription factors and the major late promoter resulted in a 10-12-fold stimulation of transcription. This stimulation was because of an increase of the stability of the preinitiation complex. MLTF allowed DNA template molecules to undergo multiple rounds of transcription. MLTF also stimulated transcription from the adenovirus-encoded IVa2 promoter. Surprisingly, reconstitution experiments indicated that transcription from the IVa2 promoter which does not have a TATA sequence required all the previously described general transcription factors, including TFIID, the TATA binding protein. The requirement for TFIID was demonstrated by reconstitution experiments as well as by oligonucleotide competition experiments. The implications of this observation are discussed.

Promoter specificity and modulation of RNA polymerase II transcription

RNA polymerase II is a multisubunit enzyme involved in the transcription of protein encoding genes. Recently acquired knowledge of the transcription process and of the RNA polymerase molecule as well as the isolation of subunit clones have led to a better understanding of the enzyme's functional regulation. Specific transcription initiation occurs at promoter regions located upstream of the gene and requires a minimum of five basic factors in addition to the enzyme. Furthermore, proteins that bind to specific DNA elements within the promoter also regulate transcriptional activity. Additional factors are required for the elongation and, possibly, termination of transcription. Two elongation factors, SII and TFIIF, interact directly with the RNA polymerase II molecule. Functional domains of RNA polymerase II have been determined by analysis of genomic clones for the two largest subunits of the enzyme. For example, the 240-kDa largest subunit contains a highly phosphorylated carboxyl-terminal heptapeptide domain repeated 26-52 times that is absolutely required for transcription in vivo. Analysis of the polymerase molecule and its interaction with basic gene-specific transcription factors will aid in our studies of the control of gene expression.

Stimulation of erythropoietin gene transcription during hypoxia and cobalt exposure

Erythropoietin, a plasma glycoprotein produced primarily by the kidney, is a growth and differentiation factor for erythroid progenitor cells. Production of renal erythropoietin is regulated by modulation of mRNA levels in response to changes in tissue oxygenation. Exposure to cobalt, a nonphysiologic stimulus for erythropoietin production, also acts by inducing mRNA accumulation. To determine whether variations in erythropoietin mRNA levels result from enhanced transcription of the erythropoietin gene, in vitro transcription reactions were performed using isolated rat kidney cell nuclei. Quantitation of specific nuclear RNAs labeled during in vitro transcription revealed active erythropoietin gene transcription in kidney nuclei from anemic-hypoxic and cobalt-treated animals while erythropoietin transcriptional activity was undetectable in normal kidney nuclei. Time course studies showed that stimulation of transcription begins between two and four hours following cobalt treatment and parallels the kinetics of mRNA and plasma erythropoietin accumulation. These results indicate that tissue hypoxia and cobalt exposure specifically enhance erythropoietin gene expression. This increase in erythropoietin production is regulated at least in part at the level of gene transcription.

Purified human factor activates heat shock promoter in a HeLa cell-free transcription system

Heat shock protein (hsp) genes are typically silent and are activated by various stresses including heat. As a first step toward understanding this activation event, a human factor, referred to here as human heat shock transcription factor (human HTF), has been purified approximately 14,000-fold from extracts of heat-treated HeLa cells by means of sequence-specific DNA affinity chromatography. The most highly purified fraction of human HTF binds specifically to the known regulatory sequence element (HSE) of hsp genes as shown by footprinting experiments. Purified human HTF has an apparent molecular mass of 83 kDa. Human HTF is specifically required for activation of an hsp gene promoter in a reconstituted in vitro transcription system from human cells. Activation is dependent on the presence of the HSEs in the transcription template.

Transcription elongation factor SII interacts with a domain of the large subunit of human RNA polymerase II

Genomic sequences for the large subunit of human RNA polymerase II corresponding to a part of the fifth exon were inserted into an expression vector at the carboxy-terminal end of the beta-galactosidase gene. The in-frame construct produced a 125-kilodalton fusion protein, containing approximately 10 kilodaltons of the large subunit of RNA polymerase II and 116 kilodaltons of beta-galactosidase. The purified bacterially produced fusion protein inhibited specific transcription from the adenovirus type 2 major late promoter, while beta-galactosidase had no effect. This effect of the fusion protein was during RNA elongation, not at the level of initiation, resembling the faithfully initiated but incomplete transcripts produced with purified factors in the absence of SII. Similarly, monoclonal antibody 2-7B, which reacts with the RNA polymerase II region represented in the fusion protein, inhibited specific transcription at the level of elongation in a whole-cell extract. Both monoclonal antibody 2-7B and the fusion protein, although unable to inhibit purified RNA polymerase II in a nonspecific transcription assay, selectively blocked the stimulation elicited by transcription elongation factor SII on the activity of the purified enzyme in vitro. This suggests that the fusion protein traps the SII in nonstimulatory interactions and that antibody 2-7B inhibits SII binding to RNA polymerase II. Thus, this suggests that an SII-binding contact required for specific RNA elongation resides within the fifth exon region of the largest RNA polymerase II subunit.

A rapid purification method for calf thymus casein kinase II

We report here the rapid purification to homogeneity of a cyclic nucleotide-independent protein kinase sensitive to 5'6-dichloro-1-beta-D-ribofuranozylbenzimidazole (DRB), identical to the previously described casein kinase II, from lyophilized calf thymus by chromatography on phosphocellulose and Mono-Q FPLC columns.

Genetic profile of the transcriptional signals from the adenovirus major late promoter

Identical functional profiles were obtained for in vivo and in vitro transcription assays of more than 30 site-directed point mutants within the adenovirus major late promoter. The functional limits of the functional regions encompassing upstream promoter element are defined (-51 to -61), as well as a region around the transcription start site (-1 to +1), flanked by regions insensitive to sequence alterations.

Erythropoietin-beta-D-galactosidase. The generation, purification and use of a fusion protein

A human erythropoietin (Epo) cDNA fragment encoding the complete erythropoietin peptide sequence was fused to the 3'-end of the lacZ gene in the polylinker region of the high expression vector, pUR 278. Escherichia coli bacteria were transformed with the recombinant plasmid harboring the hybrid Epo-beta-D-galactosidase gene. After induction with isopropyl-thiogalactoside large amounts of the fusion protein, Epo-beta-D-galactosidase were synthesized in the transformed bacteria. The fusion protein was partially purified and shown to exhibit intact galactosidase enzymatic activity. Although no biological activity of the Epo counterpart of the fusion protein was detected both in an in vivo and in an in vitro bioassay, the fusion protein served as an effective antigen for the production of anti-erythropoietin antibodies. Antifusion protein antibodies raised in rabbits were shown to react with the intact human Epo molecule from erythropoietin producing culture supernatants. The affinity of these anti-fusion protein antibodies was sufficiently high to permit the development of a sensitive radioimmunoassay for human Epo. This fusion protein approach is a relatively straightforward and rapid method of generating antibodies with specificity for any protein encoded by a cloned eukaryotic gene.

Purine triphosphate beta-gamma bond hydrolysis requirements for RNA polymerase II transcription initiation and elongation

RNA polymerase II-specific transcription requires, in addition to auxiliary protein factors, the hydrolysis of the beta-gamma phosphate bond of ATP. The nonhydrolyzable analog of ATP, imidoadenosine triphosphate does not suffice for specific in vitro transcription (Bunick, D., Zandomeni, R., Ackerman, S., and Weinmann, R. (1982) Cell 29, 877-886), although it can be incorporated into RNA. The experiments presented here suggest two energy-dependent steps in RNA polymerase II transcription. One of these steps is required at, or close to, the point of initiation, as determined by 5' end primer extension analysis. In vitro transcription occurs efficiently in vitro when imidoadenosine triphosphate is supplemented with dATP to fulfill the energy requirement. In the presence both of imidoadenosine triphosphate and imidoguanosine triphosphate, the concentration of dATP required for transcription initiation is dramatically increased. This suggests that ATP and GTP are co-substrates in transcription initiation, supporting the role of protein kinase II in this process (Zandomeni, R., Zandomeni, M. C., Shugar, D., and Weinmann, R. (1986) J. Biol. Chem. 261, 3414-3419). The concentration of dATP required for maximal initiation is inadequate for the production of full-length transcripts, suggesting a second energy-dependent step in the RNA elongation process. Since the elongation step is unaffected by the presence of imidoguanosine triphosphate, GTP beta-gamma phosphate bond hydrolysis appears to be required only for initiation.

The phosphorylation of nucleoplasmin by casein kinase-2 is resistant to heparin inhibition

Highly purified preparations of casein kinase-2 from the nuclei of Xenopus laevis oocytes and from calf thymus can phosphorylate in vitro purified nucleoplasmin from X. laevis oocytes and eggs. The phosphorylation of nucleoplasmin by both kinase preparations is quite insensitive to heparin in contrast with casein phosphorylation which is completely abolished by heparin concentrations above 10 micrograms/ml. However, the phosphorylation of nucleoplasmin and casein are inhibited in a very similar fashion by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), a well characterized specific inhibitor of casein kinase-2. Similarly, nucleoplasmin phosphorylation by the oocyte enzyme can be stimulated several-fold by spermine, another characteristic of this enzyme. These findings indicate that the phosphorylation of nucleoplasmin by purified casein kinase-2, while showing typical response to DRB and spermine, exhibits anomalous behavior in its resistance to heparin inhibition. It is possible that the large clusters of acidic amino acids in nucleoplasmin permit this substrate to interact with the enzyme more efficiently than other protein substrates. Heparin is generally considered a potent and specific inhibitor of casein kinase-2. This study, however, questions the validity of utilizing heparin inhibition as a criterion for casein kinase-2 involvement.

Independent regulation of tumor necrosis factor and lymphotoxin production by human peripheral blood lymphocytes

We present evidence that human peripheral blood lymphocytes, free of contaminating monocytes, rapidly produce high levels of tumor necrosis factor (TNF) when stimulated with phorbol diester and calcium ionophore, and lower but significant levels of TNF when stimulated with mitogens. These two types of inducers act preferentially on T cells, both CD4+ and CD8+. NK cells produce TNF only when stimulated with phorbol diester and calcium ionophore, and they do so at a much lower level than T cells. The procedures used in the purification of lymphocytes and the differential ability to respond to various inducers allow us to exclude that monocytes or basophils contaminating the lymphocyte preparation participate in the production of TNF. In particular, LPS, a potent inducer of TNF production from monocytes, is unable to induce significant levels of TNF in the lymphocyte preparations. The TNF produced by lymphocytes has antigenic, physicochemical, and biochemical characteristics identical to those of the TNF produced by myeloid cell lines or monocytes upon stimulation with LPS. LT is also produced by lymphocyte preparations. Production of TNF and LT proteins in response to the different inducers is paralleled by accumulation of cytoplasmic TNF and LT mRNA. Both at mRNA and at protein levels, stimulation of T lymphocytes with phorbol diester and calcium ionophore preferentially induces TNF, whereas mitogen stimulation preferentially induces LT. Our data suggest that the TNF and LT genes, two closely linked genes encoding two partially homologous proteins with almost identical biological functions, are independently regulated in lymphocytes.

Purification and functional characterization of transcription factor SII from calf thymus. Role in RNA polymerase II elongation

SII was purified from calf thymus tissue to apparent homogeneity by a rapid procedure. The 38-kDa protein stimulated RNA synthesis by purified calf thymus RNA polymerase II 4-fold. The calf thymus SII had similar chromatographic properties and molecular size and cross-reacted immunologically with antibodies to mouse SII (Sekimizu, K., Nakanishi, Y., Mizuno, D., and Natori, S. (1979) Biochemistry 18, 1582-1588). We have substituted the purified calf thymus SII for the partially purified HeLa transcription factor IIS fraction in a HeLa (human) transcription system reconstituted with purified factors and RNA polymerase II. The purified protein stimulated specific transcription from the adenovirus 2 major late promoter by increasing the efficiency of the elongation reaction.

The gene encoding the large subunit of human RNA polymerase II is located on the short arm of chromosome 17

We have used chromosomal in situ hybridization and Southern blot analysis of DNA from somatic cell hybrids to determine the chromosomal localization of the subgenomic DNA fragment that encodes part of the large subunit of human RNA polymerase II. The results of our analysis demonstrate localization of the human RNA polymerase II large subunit gene to the short arm of chromosome 17.

Protein factor(s) binding independently to two different regions of the adenovirus 2 major late promoter

The protein factor(s) in a fraction from the HeLa cell nuclear extract required for specific in vitro transcription can specifically bind to adenovirus 2 major late promoter (Ad 2 MLP) DNA. We demonstrate by in vitro footprinting assay that there are two asymmetric protected regions covering the TATA box and the nucleotides upstream from the TATA box. In the coding strand, the DNAse I protected regions span from nucleotides -10 to -50 and from -52 to -68. In the noncoding strand, the protected regions span from nucleotides -10 to -32 and from -45 to -65. Using different Ad 2 MLP point mutants in this assay, we show that the transcriptional down mutants of the TATA box (AC-30 and AC-28) abolish the binding of protein factor(s) to the TATA box but do not affect binding in the upstream region. The new upstream transcriptional down mutant (TA-56) abolishes the binding of protein factor(s) in the upstream region but does not affect binding to the TATA box. The mutants which do not affect transcription efficiency (GA-51 and CG-61) do not modify the binding to either the TATA box or the upstream region. Methylation protection experiments show that the guanosines at -58 and -60 in the coding strand and at -57 (probably also -55) in the noncoding strand are in close contact with protein factor(s). The results indicate that the TATA box and its upstream region of Ad 2 MLP are independently bound by at least two different factors in vitro.

The cap structure of simian hemorrhagic fever virion RNA

The molecular weight of simian hemorrhagic fever virus RNA is 4.19 +/- 0.53 X 10(6) as determined by electron microscopy. Its base composition is 19.5 +/- 0.3 A, 33.3 +/- 0.3 U, 26.7 +/- 0.9 G, and 19.7 +/- 0.3 C per 100 nucleotides. The RNA of simian hemorrhagic fever virus contains a single type I cap per molecule, in the form m7G(5')ppp(5')Am.

Casein kinase type II is involved in the inhibition by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole of specific RNA polymerase II transcription

We have described a HeLa protein kinase whose activity is inhibited by the nucleotide analogue 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) at concentrations similar to those required to inhibit in vivo and in vitro specific transcription (Zandomeni, R., and Weinmann, R. (1984) J. Biol. Chem. 259, 14804-14822). We have now detected an analogous DRB-sensitive kinase from calf thymus and purified it to homogeneity. Based on the subunit composition of the enzyme and other common biochemical and chromatographic properties, we identified it as casein kinase II. The extent of DRB inhibition of the purified calf thymus enzyme is indistinguishable from that observed for inhibition of in vitro transcription with the HeLa cell extract. The DRB bromo- derivative, 5,6-dibromo-1-beta-D-ribofuranosylbenzimidazole is a more potent inhibitor of in vivo transcription and inhibits purified casein kinase II activity and specific in vitro transcription at 6-10 times lower concentrations than DRB. Moreover, addition of an excess of the purified calf thymus casein kinase II enzyme to a HeLa in vitro transcription reaction inhibited by DRB partially overcomes this inhibition. Thus, we conclude that casein kinase II is involved directly or indirectly in the inhibition by DRB of specific RNA polymerase II-mediated transcription. This demonstrates the participation of a protein kinase in a eukaryotic RNA polymerase II-specific transcription system.

The gene encoding the large subunit of human RNA polymerase II

As a first step to approach the structural and functional analysis of DNA-dependent RNA polymerase II (EC 2.7.7.8), we have isolated genomic sequences for the large subunit of the human enzyme. The sequences homologous to Drosophila RNA polymerase II large subunit sequences are present in the genome as single copy genes, when assayed at high stringency. The polypeptide information is encoded in a mRNA of 7.35 kilobases, as determined by Northern blot analysis. In vitro translation reveals a polypeptide of 220 kDa, similar in electrophoretic mobility to the largest subunit of the enzyme. A fusion-polypeptide synthesized in bacteria contains a region that cross-reacts with anti-RNA polymerase II antiserum. Antiserum directed against the purified fusion protein reacts with the large subunit of RNA polymerase II, whether in the intact IIA (220 kDa) or in the degraded IIB (180 kDa) forms. Moreover, the antifusion protein antibody inhibits not only the purified calf thymus RNA polymerase II activity but also specific RNA polymerase II transcription in a HeLa cell extract. Thus, the DNA fragment isolated contains structural and functional domains of the human RNA polymerase II large subunit.

Actin mRNAs in HeLa cells. Stabilization after adenovirus infection

We have carried out a comparative analysis of the expression of the actin genes in HeLa and adenovirus-infected HeLa cells. The rate of actin gene transcription was examined in these cells by pulse-labeling of the newly synthesized RNA and/or by in vitro transcription in nuclei isolated from uninfected or infected HeLa cells. In addition, accumulation of actin-specific heterogeneous nuclear RNA, and rate of appearance of the actin mRNAs in the cytoplasm were examined by dot and Northern blot analysis. The rate of actin gene transcription remained constant after infection of HeLa cells with adenovirus serotype 2, while the level of the actin precursor in the nuclei was slightly reduced. In the infected cells, newly synthesized actin mRNA enters the cytoplasm at a very reduced rate. The deficiency of transport does not affect the steady-state level of the messages in the cytoplasm. The half-life of cytoplasmic actin mRNAs was analyzed by traditional pulse-chase experiments and by a novel procedure using 5-6-diCl-1-beta-d-ribofuranosylbenzimidazole, which does not rely on labeled RNA. Both procedures gave identical results. Uninfected HeLa cells have actin mRNAs with relatively short half-lives, from less than six to 12 hours. In contrast, the half-lives of the actin-specific mRNAs, in the cytoplasm of adenovirus-infected cells, is greater than 14 to 24 hours. These observations suggest that, although the rate of transport of actin mRNAs to the cytoplasm is reduced upon infection with adenovirus, increased half-lives result in accumulation of actin mRNAs to normal levels in the cytoplasm.