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R G Wolford

Publications and source records attributed to R G Wolford.

13 recordsLinked to original sources
PubMed1992

Transcription factor loading on the MMTV promoter: a bimodal mechanism for promoter activation.

The mouse mammary tumor virus (MMTV) promoter attains a phased array of six nucleosomes when introduced into rodent cells. This architecture excludes nuclear factor 1/CCAAT transcription factor (NF1/CTF) from the promoter before glucocorticoid treatment and hormone-dependent access of nucleolytic agents to promoter DNA. In contrast, when the promoter was transiently introduced into cells, NF1/CTF was bound constitutively and nucleolytic attack was hormone-independent. Thus, induction at this promoter was a bimodal process involving receptor-dependent remodeling of chromatin that allows NF1/CTF loading and direct receptor-mediated recruitment of additional transcription factors.

Animals↗
PubMed1991

Transcription factor access is mediated by accurately positioned nucleosomes on the mouse mammary tumor virus promoter.

A fragment of the mouse mammary tumor virus (MMTV) promoter was reconstituted from pure histones into a dinucleosome with uniquely positioned octamer cores. Core boundaries for the in vitro-assembled dinucleosome corresponded to the observed in vivo phasing pattern for long terminal repeat nucleosomes A and B. Nuclear factor 1 (NF1), a constituent of the MMTV transcription initiation complex, was excluded from the assembled dinucleosome, whereas the glucocorticoid receptor was able to bind. During transcription of MMTV in vivo, displacement of nucleosome B was necessary to permit assembly of the initiation complex. These results indicate that the nucleoprotein structure of the promoter can provide differential access to sequence-specific DNA-binding proteins and that active chromatin remodeling can occur during transcription activation.

Animals↗
PubMed1991

Proopiomelanocortin gene promoter elements required for constitutive and glucocorticoid-repressed transcription.

The POMC gene is expressed predominantly in the anterior pituitary. The high level of POMC transcription in this tissue is modulated by peptide hormones and repressed by glucocorticoids. In this present study we have investigated promoter elements required for the high basal transcription and glucocorticoid repression using transient transfection and in vitro transcription assays. We first determined that the region between -77 to -51 of the promoter, which has previously been shown to harbor a glucocorticoid receptor-binding site, is required for high basal expression both in vivo and in vitro. This promoter domain is also required for glucocorticoid repression of transcription in vivo. Two site-directed mutants within this area both decreased basal transcription, but were fully repressed by glucocorticoids, implying that the -77 to -51 region is a complex regulatory region harboring separable basal and glucocorticoid-repressible elements. Electrophoretic mobility shift and exonuclease III footprinting analysis revealed the existence of two factors that bind in this region. We also examined the effect of broad promoter deletions on basal expression and glucocorticoid repression. These experiments revealed that the region between -480 and -320 is also required for glucocorticoid repression. Taken together, the data suggest a model in which high basal transcription is generated by direct interaction of factors binding between -480 to -320 and -77 to -51. Glucocorticoid repression could occur by direct receptor disruption of these interactions.

Animals↗
PubMed1990

A novel transcriptional activator (PO-B) binds between the TATA box and cap site of the pro-opiomelanocortin gene.

We demonstrate that a factor (PO-B), detected in a number of mammalian cell lines, binds specifically between the TATA box and the transcription initiation site of the pituitary-specific pro-opiomelanocortin (POMC) gene. Methylation interference and DNAse 1 footprint analysis revealed that the binding site of this protein, -3 to -15, does not overlap the POMC TATA box or cap site. Mutation of the PO-B binding site significantly decreased the transcriptional activity of the POMC promoter after transient transfection into the ATt-20 mouse pituitary tumor cell line and also in in vitro transcription assays. In contrast, mutation of the TATA box produced no overall decrease in transcription in vivo but induced multiple heterogeneous start sites in vitro. A vector harboring the PO-B site alone was unable to direct transcription initiation. PO-B represents a new transcription factor that may be able to facilitate POMC gene expression by interacting with components of the transcription initiation complex.

Animals↗
PubMed1984

Modulation of enhancer activity by the hormone responsive regulatory element from mouse mammary tumor virus.

Addition of the transcriptional enhancers present in the U3 region of the Harvey murine sarcoma virus (HaMuSV) long terminal repeat (LTR) to recombinant chimeras in which the HaMuSV transforming gene (Ha-v-ras) is expressed from the mouse mammary tumor virus (MMTV) promoter increases the ability of the MMTV v-ras chimeras to transform mouse fibroblasts in culture 50- to 100-fold. Significant stimulation of transfection efficiency occurs only when glucocorticoids are present in the culture medium. Glucocorticoids also elevate the steady-state concentration of MMTV-initiated v-ras mRNA in cell lines isolated from these transfections, and MMTV-v-ras fusion transcripts are initiated at the normal MMTV cap site; potential cryptic initiation events associated with the enhancer could not be detected. The ability of the enhancer to increase the transcriptional activity of the MMTV promoter was also studied in acute transfection assays where expression of the chloramphenical acetyl transferase (CAT) gene is driven by the MMTV promoter. In this system the strong positive effect on MMTV transcription is again obtained only when the cells are hormone treated. These experiments indicate that the hormone-regulatory region is capable of modulating the function of an exogenously introduced enhancer element.

Acetyltransferases↗
PubMed1983

Glucocorticoid regulation of transcription at an amplified, episomal promoter.

The mouse mammary tumor virus long terminal repeat (MMTV LTR) has been introduced into cultured murine cells, using the 69% transforming fragment of bovine papilloma virus type 1 (BPV). Transformed cells contain up to 200 copies of the chimeric molecules per diploid genome. The restriction endonuclease map of the acquired recombinants, as well as the physical structure of the DNA, indicates that the LTR-BPV molecules present in these cells occur exclusively as unintegrated, extrachromosomal episome. When a 72-base pair direct repeat "enhancer" element (derived from the Harvey sarcoma retrovirus) was included in the MMTV LTR-BPV chimeric plasmids, DNA acquired through transfection, with a single exception, was integrated or rearranged or both. The transcriptional potential of the episomal MMTV promoter present in these cells was tested in two ways. First, steady-state levels of MMTV-initiated RNA were measured by quantitative S1 mapping. Second, the relative number of transcription complexes initiated in vivo was determined by using a subnuclear fraction highly enriched for MMTV-BPV minichromosomes in an in vitro transcription extension assay. Both approaches showed that the MMTV LTR present in the episomal state was capable of supporting glucocorticoid hormone-regulated transcription. We have therefore demonstrated the hormone response for the first time in a totally defined primary sequence environment. Significant differences both in the basal level of MMTV-initiated transcription and in the extent of glucocorticoid induction were observed in individual cell lines with similar episomal copy numbers. These phenotypic variations suggest that epigenetic structure is an important component of the mechanism of regulation.

Animals↗
PubMed1975

Expression of mouse mammary tumor viral polypeptides in milks and tissues.

A 14,000-dalton polypeptide (p14) from RIII murine mammary tumor virus (MMTV) has been isolated by column chromatography in 6 M GuHCl. Antiserum prepared in rabbits specifically precipitated 125I-labeled p14; in double antibody competition, radioimmunoassays performed with limiting amounts of antibody, both purified p14 and disrupted MMTV, competed specifically with labeled antigen. The expression of this MMTV type B virus antigen could be measured by competition radioimmunoassays in milks, mammary glands, tumors, and tissue culture cells. MMTV expression measured by p14 immunoassay correlated well with the spontaneous incidence of mammary adenocarcinomas in different murine strains but not with type C MuLV p30 antigen expression. Levels of MMTV gp52, the major type-B viral glycoprotein, corresponded to p14 levels, suggesting that their control is comparably regulated. Evidence that this low m.w. polypeptide is present in feral and inbred strains of widely differing geographic origin and in MMTV with apparently different biologic properties suggests surprising conservation of MMTV protein homology.

Animals↗
PubMed1973

5-Bromo-2'-deoxyuridine potentiation of transformation of rat-embryo cells induced in vitro by 3-methylcholanthrene: induction of rat leukemia virus gs antigen in transformed cells.

Low-passage rat-embryo cells were not transformed by 3-methylcholanthrene or by 5-bromo-2' deoxyuridine. However, prior treatment with bromodeoxyuridine, followed by treatment with methylcholanthrene, resulted in cell transformation about three subpassages after removal of the carcinogen. RNA-directed DNA polymerase activity could not be detected in either normal or transformed cells. However, gs-1 antigen specific for rat C-type RNA virus was detected in cultures derived from bromodeoxyuridine-treated cells. No gs-1 antigen for the C-type RNA virus was detected in cultures that had not been treated with bromodeoxyuridine during the 25 subpassages of these experiments.High-passage rat-embryo cells, derived from a different cell pool, were transformed by either methylcholanthrene or dimethylbenzanthracene without prior infection with an exogenous virus, and without prior treatment with bromodeoxyuridine, gs-1 antigen for C-type RNA virus was also detected in 4 of 4 randomly selected transformed cell lines; the gs-1 antigen was not detected in any of 4 nontransformed control cultures. Considering these and previously published findings, we conclude that the lowpassage cells cannot be transformed by methylcholanthrene because of powerful cellular controls over the endogenous virus. Bromodeoxyuridine triggers some expressions of the endogenous virus; thus, the bromodeoxyuridine-treated cells are more susceptible to the transforming effects of methylcholanthrene. High-passage rat cells do not maintain perfect control over expression of their endogenous virus; the cell cultures are susceptible to the transforming effects of chemical carcinogens.

Animals↗
PubMed1972

Elimination of Mycoplasma contaminants from virus stocks by treatment with nonionic detergents.

Five nonionic detergents (Tweens 20, 40, 60, and 80, and Triton WR-1339) were tested for their ability to inactivate four Mycoplasma species which are common contaminants of animal cell cultures. Tween 20 was found to be the most effective, in that a concentration of 2.5 mg/ml completely inactivated cultures of M. hominis, M. hyorhinis, and Acholeplasma laidlawii within 1 hr and a culture of M. orale within 3 hr. The other detergents exhibited various degree of activity against the different mycoplasmas, with Triton WR-1339 being the least effective. The virucidal activity of the detergents was determined for six viruses. All four Tween compounds were highly virucidal for herpes simplex virus. Tween 20 also exhibited virucidal effects against vesicular stomatitis virus, California encephalitis virus, and Newcastle disease virus, and Tween 80 was found to be active against California encephalitis and Newcastle disease viruses. Detergent treatment procedures were effective in two instances in eliminating mycoplasma contaminants from virus preparations while the preparations retained most of the viral infectivity. The limitations of this technique for routine use are discussed.

Animals↗