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W Schaffner

Publications and source records attributed to W Schaffner.

At least 181 records · Page 10Linked to original sources
PubMed1990

A single DNA-binding transcription factor is sufficient for activation from a distant enhancer and/or from a promoter position.

Typical cell type-specific or inducible mammalian genes are under the control of one or more remote enhancers which transmit their effect to the promoter region located at the initiation site of transcription. Both enhancers and promoters are composed of multiple binding sites for transcription factors. To study the requirements for promoter and enhancer function, we have used a reporter gene that is completely dependent on a single DNA-binding transcription factor in vivo. This factor is a truncated, hormone-independent form of the glucocorticoid receptor which interacts strongly with a palindromic binding site. After transfection into HeLa cells, transcription of a reporter gene with one, two or four copies of the binding site upstream of the TATA box is enhanced less than 10, at least 100 and greater than 1000-fold respectively, in the presence of the receptor. Even when the TATA box is deleted, the four upstream binding sites confer receptor-dependent transcription, though from scattered initiation sites. When four copies of the palindromic binding site are placed downstream of the transcription unit, they form a very strong receptor-dependent enhancer. This enhancer can activate comparably well promoters containing binding sites for either glucocorticoid receptor, Sp1 factor, or octamer factor. Our data show that a single defined DNA-binding factor can mediate both promoter and enhancer activity, and that it can co-operate functionally both with itself and with seemingly unrelated transcription factors.

Animals↗
PubMed1990

Transcription factor Oct-2A contains functionally redundant activating domains and works selectively from a promoter but not from a remote enhancer position in non-lymphoid (HeLa) cells.

In non-lymphoid cells such as HeLa cells, ectopic expression of the lymphocyte-specific transcription factor Oct-2A can activate reporter genes whose promoters consist of a single octamer sequence (ATTTGCAT) upstream of a TATA box. While the factor is strongly active in a promoter position, it tails as an enhancer factor: an enhancer consisting of multiple copies of the octamer sequence placed downstream of the reporter gene is not active in HeLa cells, even at high concentration of Oct-2A. In B lymphoid cells, however, the same enhancer is highly active. This could mean that an additional factor is required for enhancer activation in B cells. Furthermore, we have tested the transcriptional activation potential of Oct-2A with a series of N-terminal and C-terminal deletions. We show that a glutamine-rich domain near the N-terminus is required for full activity. Otherwise, large segments of the N-terminal half or the entire C-terminal region are dispensable in our assay, as long as the deletions do not impinge on the conserved POU domain which is sufficient for DNA binding. While N-terminal and C-terminal regions can functionally compensate for each other, a combined deletion that only retains the POU domain is a strong down mutation. We also find that activity depends on the promoter structure of the reporter gene: the POU domain by itself shows some activity with a promoter where the octamer sequence is located very close to the TATA box, but no activity with another promoter construction where the octamer sequence is located further upstream. The two promoters also respond differently to the deletion of the glutamine-rich stretch important for transcriptional activation. From these experiments we consider it likely that the natural octamer factor variants can selectively activate the different naturally occurring octamer-containing promoters.

Amino Acid Sequence↗
PubMed1990

A transcriptional terminator between enhancer and promoter does not affect remote transcriptional control.

Enhancers stimulate transcription of RNA polymerase II-transcribed genes in an orientation-independent manner and over long distances. This stimulation is known to be associated with an increased polymerase density over the linked gene. However, many aspects of the exact mechanism of remote gene control remain to be elucidated. Based on some reports on RNA polymerase I transcription, we wanted to test whether RNA polymerase II enters at the enhancer and from there proceeds towards the promoter while synthesizing unstable transcripts ("scanning/readthrough transcription" model). For this, we have inserted a complete terminator region from the mouse beta-globinmaj gene between the SV40 enhancer and the rabbit beta-globin promoter. In contrast to what the model predicts, insertion of the terminator had no affect on remote enhancer action. Furthermore, we have determined the RNA polymerase density over the spacer DNA between enhancer and promoter, and over the reporter gene, by means of the so-called run-on transcription assay. We find very low transcription of the spacer, but high transcription of the globin reporter gene. Thus, our data are not consistent with a scanning/readthrough transcription mechanism where RNA polymerase II would move from the enhancer to the promoter while transcribing the intervening spacer DNA. These and other findings are compatible with a model where enhancer and promoter are brought into close proximity, perhaps with concomitant looping out of the intervening DNA.

Animals↗
PubMed1990

Effect of salmon calcitonin on the infiltration of T lymphocytes in a synovium-like membrane of a rat inflammatory model.

The effect of salmon calcitonin (SCT) on the number of T lymphocytes accumulating in air pouch lining membranes produced on the back of Wistar rats was studied. SCT was given from day 0 through day seven following the air cavitation by daily injections of 2.5-20 micrograms/kg directly into the air cavity. Compared with saline controls, treatment with SCT caused a clear reduction in percentage of T lymphocytes, T helper cells and T non-helper subset in the synovial-like air pouch lining as revealed by FITC-labeled monoclonal antibodies and quantified by flow cytophotometric measurements. This effect may be due to a reduction in local vascular permeability caused by SCT.

Air↗
PubMed1990

Transcriptional enhancers can act in trans.

Enhancers have been defined operationally as cis-regulatory sequences that can stimulate transcription of RNA polymerase-II-transcribed genes over large distances and even when located downstream of the gene. Recently, it has become evident that enhancers can also stimulate transcription in trans if they are brought into close proximity to the promoter/gene. These reports provide clues to the mechanism of remote enhancer action. In addition, the findings, together with genetic studies in Drosophila, strongly suggest that enhancer action in trans could underlie phenomena such as 'transvection', where one chromosome affects gene expression in the paired homolog.

Animals↗
PubMed1990

[Acinospesigenin: A New Triterpene from the Leaves of Phytolacca acinosa].

The investigation of the hydrolysed aqueous methanolic extract from the leaves of PHYTOLACCA ACINOSA Roxb. resulted in the isolation of phytolaccagenin ( 1) besides a new pentacyclic triterpenoid which was identified as 2beta,3beta-dihydroxy-23,30-dimethoxycarbonyl-28-carboxy-olean-12-ene = acinospesigenin ( 2).

English Abstract↗
PubMed1990

Novel dihydrofolate reductases isolated from epidemic strains of trimethoprim/sulfamethoxazole-resistant Shigella sonnei.

Two strains of trimethoprim-resistant Shigella sonnei bearing R plasmids pBH600 and pBH700 each elaborated a dihydrofolate reductase (DHFR) and were moderately resistant to trimethoprim (minimum inhibitory concentrations, 128 and 256 micrograms/ml, respectively). Neither plasmid hybridized to probes for DHFR types I, II, or III. The trimethoprim resistance genes from the R plasmids resided on a 1600-base pair (bp) PstI fragment of pBH600 and an 1800-bp PstI fragment of pBH700. Isoelectric focusing showed distinct isoelectric points for the enzymes coded for on pBH600 (5.3) and pBH700 (5.6-5.7). Trimethoprim-resistant S. sonnei from 10 locations in nine states were examined. Isolates from 8 locations hybridized only to a pBH700-derived probe and one isolate hybridized to a pBH600-derived probe. These two trimethoprim resistance genes appear novel. The gene on plasmid pBH700 codes for an enzyme that seems widespread among S. sonnei isolates in the USA.

Ampicillin Resistance↗
PubMed1990

Foodborne hepatitis A: evidence that microwaving reduces risk?

During July 1988, 68 persons in Chattanooga, Tennessee, developed serologically confirmed hepatitis A. Between 15 June and 3 July, 93% of case-patients ate at a specific restaurant compared with only 3% of the local community. An intravenous drug user who worked as a cook was identified as the source. A case-control study was done to identify the vehicle of transmission. Case-patients were more likely than controls to have eaten hamburger buns and pickles, the only foods routinely handled after cooking. Of the restaurant patrons included in the study, 12 microwaved their food before consumption; none developed clinical illness despite eating large amounts of food handled after cooking. Sandwiches that were not microwaved were significantly associated with illness (odds ratio = 9.6; P less than .02). This epidemiologic evidence suggests that microwaves inactivate hepatitis A virus in food.

Adolescent↗
PubMed1990

Octamer transcription factors and the cell type-specificity of immunoglobulin gene expression.

Antibodies are produced exclusively in B lymphocytes. The expression of the antibody-encoding genes, the immunoglobulin (Ig) genes, is also restricted to B cells. The octamer sequence ATGCAAAT is present in the promoter and the enhancer of Ig genes, and plays an important role in its tissue-specific expression. This sequence motif is a binding site for nuclear proteins, the so-called octamer transcription factors (Oct or OTF factors). The Oct-1 protein is present in all cell types analyzed so far, whereas Oct-2A and Oct-2B are found mainly in B lymphocytes. All three proteins show the same sequence specificity and binding affinity. It appears that the B cell-specific expression of Ig genes is mediated at least in part by cell type-specific Oct factors, and that there are both quantitative and qualitative differences between Oct-1 and Oct-2 factors. Recently, a number of other octamer factor variants were identified. Many of these may be created by alternative splicing of a primary transcript of one Oct factor gene and may serve a specific function in the fine tuning of gene expression.

Amino Acid Sequence↗
PubMed1990

Immunization of hospital personnel and other health care workers.

Hospital personnel and other health care workers are at increased risk of acquiring certain communicable diseases that can be prevented by immunization. These include hepatitis B, influenza, rubella, measles, and mumps, among others. The use of vaccines to protect health care workers as well as certain barriers to institutional immunization programs is discussed.

Hepatitis B Vaccines↗
PubMed1990

Mumps transmission in hospitals.

Although sporadic transmission of mumps within hospitals to patients and staff is well documented, outbreaks of mumps within hospitals have only rarely been reported. The widespread mumps outbreaks that occurred in Tennessee in 1986-1987 provided an opportunity to assess the extent of the problems caused by mumps in hospitals. Information was obtained from 146 (95%) of 154 infection control practitioners in the state. Infection control problems caused by mumps were reported from 17 (12%) of 146 hospitals. The 17 hospitals in which these incidents occurred were located in counties that accounted for 67% of the reported mumps cases statewide during this period. Although most cases of mumps in health care workers were community-acquired, six health care workers in three different hospitals developed mumps following nosocomial exposure. In two institutions, nine patients contracted mumps while hospitalized. Both were long-term-care facilities housing adolescents, who had substantial contact with a community where mumps outbreaks were ongoing. This study suggests that mumps poses a small but real risk to both patients and staff in hospitals, particularly in long-term-care facilities caring for adolescents and young adults. In communities where mumps activity is ongoing, hospitals should consider identifying potentially susceptible staff members at risk for infection and offering vaccine. Likewise, susceptible patients in long-term-care facilities should be immunized.

Cross Infection↗
PubMed1990

Strongyloides infections in transplant recipients.

Solid organ transplant recipients can experience serious disease and death from infection due to the parasitic roundworm Strongyloides stercoralis. This parasite lives in soil contaminated with human feces. Domestic dogs and cats may be another reservoir. Larvae can penetrate the skin, are carried hematogenously to the lungs, migrate up the bronchial tree, and then can be passed to the upper small intestine. Autoinfection occurs in the setting of immunosuppression when invasive larvae penetrate the gut wall and cause disseminated infection. Polymicrobial sepsis is sometimes seen due to enteric organisms adhering to the parasite. Transplant recipients are at highest risk during the first 3 months posttransplant. Many organ systems may be affected. Pulmonary symptoms include cough, wheezing, sputum production, dyspnea, hemoptysis, tachypneas, and pleuritic pain. Hyperinfection, an augmentation of the normal skin-lung-intestine life cycle, occurs in roughly two-thirds of infected transplant recipients, with dissemination in the remainder. Diagnosis is made primarily by examination of the stool or intestinal secretions for ova and parasites. Occasionally, parasites are noted in the sputum. New serologic tests show promise. The parasite may remain in the host for over 25 years before immunosuppression causes either dissemination or hyperinfection. Thiabendazole given for 3 to 7 days is the treatment of choice for organ transplant recipients. Repeat courses may be needed to eradicate infection.

Adult↗
PubMed1989

Two closely spaced promoters are equally activated by a remote enhancer: evidence against a scanning model for enhancer action.

To explain the activation of transcription by a remote enhancer, two models are most often considered, namely looping and scanning. A scanning model, also referred to as 'polymerase entry site' model predicts that for two adjacent promoters the one proximal to an enhancer would be preferentially activated. Preferential activation of the proximal promoter in a tandem promoter arrangement has been found before in several laboratories, including our own, but for technical reasons the data were inconclusive with regards to the enhancer mechanism. In the work presented here, we readdress the question of preferential promoter activation by an enhancer using a more clearly defined system. Two identical promoters were kept closeby in a divergent, or directly repeated orientation. The SV40 enhancer was placed at a great distance on one or the other side of the two promoters, to see whether the enhancer position influenced the relative efficiency of the two promoters in transfected cells. Our finding that the promoter usage is virtually unaffected by the enhancer position does not favor a scanning model, but is compatible with a looping model of enhancer action.

Animals↗
PubMed1989

An enhancer stimulates transcription in trans when attached to the promoter via a protein bridge.

Two principal models have been invoked to explain transcriptional stimulation of RNA polymerase II genes by enhancers/upstream promoter elements: in one, upstream regulatory sequences directly interact with proximal promoter elements via proteins bound to the DNA ("looping" model); in the other, RNA polymerase II (or a transcription factor) binds to distal sequences and then scans along the DNA until it reaches the promoter ("scanning" or "entry site" model). So far, it has been reported that enhancers or upstream promoter elements transmit their effect on a gene only via covalently closed DNA, i.e., in a cis configuration. The looping model predicts, however, that the effect can be transmitted also in certain trans configurations. Here we demonstrate that an enhancer from SV40 or cytomegalovirus can stimulate transcription in vitro even when noncovalently attached to the beta-globin promoter via the proteins streptavidin or avidin. These findings are consistent with the looping model rather than the scanning model. In addition, stimulation of transcription in trans, as shown by our experiments, may be found in nature in phenomena such as transvection, where one chromosome affects gene expression in the paired homolog.

Animals↗