Moloney Murine Sarcoma Virus Enhancer Research Articles

Sodium butyrate selectively induces transcription of promoters adjacent to the MoMSV viral enhancer

The long terminal repeat region of the Moloney murine sarcoma virus (MoMSV) was cloned upstream from the Chinese hamster ovary adenine phosphoribosyltransferase (APRT)-encoding gene ( APRT) in order to enhance synthesis of the APRT protein. The replacement of the native promoter with the viral enhancer-promoter increased the enzymatic activity of APRT two- to threefold. Addition of sodium butyrate (NaBu) to the cell growth medium induced APRT activity tento 20-fold above wild-type levels in both transient and stable transfectants. The introduction of the APRT native promoter between the MoMSV enhancer-promoter and structural gene reduced the magnitude of the NaBu response. The bacterial cat gene was also stimulated by NaBu when linked to the viral enhancer-promoter. No NaBu response was found in constructs lacking the MoMSV enhancer region. Northern analysis and nuclear run-on experiments indicated that NaBu enhanced transcription of APRT mRNA in both transiently and stably transfected cells, but not in cells inhibited by cycloheximide. Thus, a butyrate-response element ( BRE) is associated with the MoMSV enhancer and the action of the MoMSV BRE is promoter-dependent.

Expression and Characterization of Recombinant Human Protein S in Heterologous Cells - Studies of the Interaction of Amino Acid Residues Leu-608 to Glu-612 with Human C4b-Binding Protein

Mouse C127 epithelioid cells were genetically engineered to produce biologically active gamma-carboxylated human protein S. A full length human protein S cDNA was cloned into a bovine papilloma virus (BPV) based shuttle vector under the transcriptional control of the Moloney murine sarcoma virus enhancer and the mouse metallothionein promoter. Stable expression was obtained in transfected C127 cells. Expression of gamma-carboxylated protein S was dependent on the presence of vitamin K in the culture medium. Protein sequence analysis showed that recombinant and plasma protein S have the same amino terminal sequence. Analysis of specific post-translationally modified amino acids shows that recombinant protein S is fully gamma-carboxylated and fully beta-hydroxylated. Immunoblotting analysis using polyclonal and monoclonal antibodies shows that recombinant protein S has a slightly higher molecular weight than plasma protein S. After N-Glycanase treatment, identical molecular weights are observed for recombinant and plasma protein S, indicating that the difference is caused by differences in the N-linked carbohydrate side chains. Recombinant protein S also demonstrates normal cofactor activity for activated protein C in a clotting assay. Binding studies with the complement component, C4b-binding protein (C4BP), shows that recombinant protein S binds to C4BP with the same apparent affinity as plasma protein S. Two variant molecules are also tested for their binding to C4BP. The first variant has a replacement of amino acid residue leu-608 by val and was designated B variant. The second variant has three alterations, at positions 609, 611 and 612 where the acidic amino acid residues asp, asp and glu were replaced by asn, asn and gln, respectively and this variant was designated C variant.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoid responsiveness of the transcriptional enhancer of Moloney Murine Sarcoma Virus

The long terminal repeat of Moloney Murine Sarcoma Virus (MoMSV) contains an imperfect direct repeat that serves as a strong transcriptional enhancer. The strength of the MoMSV enhancer is strongly dependent on the presence of glucocorticoid hormone. Mapping studies in combination with DNAase I foot-printing experiments define the presence of glucocorticoid regulatory elements at the promoter-proximal ends of each enhancer repeat. These elements behave like inducible enhancers: their regulatory activity is independent of position and orientation when they are linked in cis to a heterologous promoter. These data demonstrate the modular nature of the MoMSV enhancer and identify the glucocorticoid receptor as one of the trans-acting factors that interact with the MoMSV enhancer and mediate its transcriptional activity.

Two Different Factors Act Separately or Together To Specify Functionally Distinct Activities at a Single Transcriptional Enhancer

The expression of genes fused downstream of the Moloney murine sarcoma virus (MoMSV) long terminal repeat is stimulated by glucocorticoids. We mapped the glucocorticoid response element that conferred this hormonal regulation and found that it is a hormone-dependent transcriptional enhancer, designated Sg; it resides within DNA fragments that also carry a previously described enhancer element (B. Levinson, G. Khoury, G. Vande Woude, and P. Gruss, Nature [London] 295:568-572, 1982), here termed Sa, whose activity is independent of the hormone. Nuclease footprinting revealed that purified glucocorticoid receptor bound at multiple discrete sites within and at the borders of the tandemly repeated sequence motif that defines Sa. The Sa and Sg activities stimulated the apparent efficiency of cognate or heterologous promoter utilization, individually providing modest enhancement and in concert yielding higher levels of activity. A deletion mutant lacking most of the tandem repeat but retaining a single receptor footprint sequence lost Sa activity but still conferred Sg activity. The two enhancer components could also be distinguished physiologically: both were operative within cultured rat fibroblasts, but only Sg activity was detectable in rat exocrine pancreas cells. Therefore, the sequence determinants of Sa and Sg activity may be interdigitated, and when both components are active, the receptor and a putative Sa factor can apparently bind and act simultaneously. We concluded that MoMSV enhancer activity is effected by at least two distinct binding factors, suggesting that combinatorial regulation of promoter function can be mediated even from a single genetic element.

Two different factors act separately or together to specify functionally distinct activities at a single transcriptional enhancer.

The expression of genes fused downstream of the Moloney murine sarcoma virus (MoMSV) long terminal repeat is stimulated by glucocorticoids. We mapped the glucocorticoid response element that conferred this hormonal regulation and found that it is a hormone-dependent transcriptional enhancer, designated Sg; it resides within DNA fragments that also carry a previously described enhancer element (B. Levinson, G. Khoury, G. Vande Woude, and P. Gruss, Nature [London] 295:568-572, 1982), here termed Sa, whose activity is independent of the hormone. Nuclease footprinting revealed that purified glucocorticoid receptor bound at multiple discrete sites within and at the borders of the tandemly repeated sequence motif that defines Sa. The Sa and Sg activities stimulated the apparent efficiency of cognate or heterologous promoter utilization, individually providing modest enhancement and in concert yielding higher levels of activity. A deletion mutant lacking most of the tandem repeat but retaining a single receptor footprint sequence lost Sa activity but still conferred Sg activity. The two enhancer components could also be distinguished physiologically: both were operative within cultured rat fibroblasts, but only Sg activity was detectable in rat exocrine pancreas cells. Therefore, the sequence determinants of Sa and Sg activity may be interdigitated, and when both components are active, the receptor and a putative Sa factor can apparently bind and act simultaneously. We concluded that MoMSV enhancer activity is effected by at least two distinct binding factors, suggesting that combinatorial regulation of promoter function can be mediated even from a single genetic element.

Delineation of transcriptional control signals within the Moloney murine sarcoma virus long terminal repeat.

We identified three distinct elements within the Moloney murine sarcoma virus long terminal repeat that control transcription. The phenotypes of unidirectional deletion mutants of the long terminal repeat were assayed in microinjected frog oocytes and in transfected mouse fibroblasts. Steady-state levels of RNA bearing the same 5' terminus as the authentic Moloney murine sarcoma viral transcripts were measured by primer extension in assays that included a pseudo-wild-type internal reference. Mutant phenotypes define the boundaries of three functional elements. A region between 21 and 31 base pairs upstream from the mRNA cap site contains AT-rich sequences that function to establish the transcription start site. A second control element, termed the distal signal, lies between 31 and 84 base pairs upstream of the mRNA cap site. A CAT box consensus sequence is located at the 5' boundary of the distal signal. Additional components of the distal signal include a hexanucleotide sequence that is repeated four times. The distal signal augments transcription efficiency in oocytes but contributes only weakly to long terminal repeat-mediated expression in mouse fibroblasts. A third transcriptional control element lies between 156 and 364 base pairs upstream of the mRNA cap site. This element includes the 75-base-pair repeats previously identified as the Moloney murine sarcoma virus enhancer. In contrast to the distal signal, the Moloney murine sarcoma virus enhancer is crucial for significant expression in mouse fibroblasts but does not contribute to transcriptional expression in frog oocytes.

Delineation of transcriptional control signals within the Moloney murine sarcoma virus long terminal repeat.

We identified three distinct elements within the Moloney murine sarcoma virus long terminal repeat that control transcription. The phenotypes of unidirectional deletion mutants of the long terminal repeat were assayed in microinjected frog oocytes and in transfected mouse fibroblasts. Steady-state levels of RNA bearing the same 5' terminus as the authentic Moloney murine sarcoma viral transcripts were measured by primer extension in assays that included a pseudo-wild-type internal reference. Mutant phenotypes define the boundaries of three functional elements. A region between 21 and 31 base pairs upstream from the mRNA cap site contains AT-rich sequences that function to establish the transcription start site. A second control element, termed the distal signal, lies between 31 and 84 base pairs upstream of the mRNA cap site. A CAT box consensus sequence is located at the 5' boundary of the distal signal. Additional components of the distal signal include a hexanucleotide sequence that is repeated four times. The distal signal augments transcription efficiency in oocytes but contributes only weakly to long terminal repeat-mediated expression in mouse fibroblasts. A third transcriptional control element lies between 156 and 364 base pairs upstream of the mRNA cap site. This element includes the 75-base-pair repeats previously identified as the Moloney murine sarcoma virus enhancer. In contrast to the distal signal, the Moloney murine sarcoma virus enhancer is crucial for significant expression in mouse fibroblasts but does not contribute to transcriptional expression in frog oocytes.

Alternate utilization of two regulatory domains within the Moloney murine sarcoma virus long terminal repeat.

The Moloney murine sarcoma virus long terminal repeat (LTR) harbors two distinct positive activators of transcription, namely, a distal signal and an enhancer. In this report we demonstrate that infection by herpes simplex virus (HSV) can markedly affect the utilization of these two Moloney murine sarcoma virus transcription signals. We investigated the HSV-mediated trans-acting effects with two goals in mind: first, to gain insight into LTR function, and second, to probe the mechanisms used by HSV to establish its own transcription cascade. In mock-infected cells, LTR-mediated expression was heavily dependent on the Moloney murine sarcoma virus enhancer but was effectively distal signal independent. HSV infection mobilized the use of the LTR distal signal and concomitantly alleviated enhancer dependence. Indeed, enhancer function may actually be inhibited by HSV trans-acting factors. These results suggest that the two positive control signals of the Moloney murine sarcoma virus LTR facilitate transcriptional activation by two different pathways. We further observed that the identity of the structural gene driven by the LRT, as well as the state of integration of a transfected template, can exert a substantial effect on the response of a template to HSV infection. According to these findings, we propose a tentative model to account for the initial temporal shift of the HSV transcriptional cascade.

Alternate utilization of two regulatory domains within the Moloney murine sarcoma virus long terminal repeat.

The Moloney murine sarcoma virus long terminal repeat (LTR) harbors two distinct positive activators of transcription, namely, a distal signal and an enhancer. In this report we demonstrate that infection by herpes simplex virus (HSV) can markedly affect the utilization of these two Moloney murine sarcoma virus transcription signals. We investigated the HSV-mediated trans-acting effects with two goals in mind: first, to gain insight into LTR function, and second, to probe the mechanisms used by HSV to establish its own transcription cascade. In mock-infected cells, LTR-mediated expression was heavily dependent on the Moloney murine sarcoma virus enhancer but was effectively distal signal independent. HSV infection mobilized the use of the LTR distal signal and concomitantly alleviated enhancer dependence. Indeed, enhancer function may actually be inhibited by HSV trans-acting factors. These results suggest that the two positive control signals of the Moloney murine sarcoma virus LTR facilitate transcriptional activation by two different pathways. We further observed that the identity of the structural gene driven by the LRT, as well as the state of integration of a transfected template, can exert a substantial effect on the response of a template to HSV infection. According to these findings, we propose a tentative model to account for the initial temporal shift of the HSV transcriptional cascade.

Mutational analyses of the Moloney murine sarcoma virus enhancer.

Retroviral enhancers seem to play an integral role in determining tissue tropism. In an attempt to define the sequences essential for Moloney murine sarcoma virus (Mo-MSV) enhancer activity, we have undertaken deletion and insertion mutational analyses of the 72-bp repeats. We demonstrate that, in contrast to simian virus 40 (SV40), the proximal 19 bp of the 72-bp unit of Mo-MSV are not essential for enhancer function in mouse fibroblasts. Our analysis further localizes the 5' boundary of the Mo-MSV enhancer to a 5'-CAGGAT-3' region.

Efficient transcription of a protein-coding gene from the RNA polymerase I promoter in transfected cells.

The activity of the mouse ribosomal promoter was examined after fusion to the gene coding for chloramphenicol acetyltransferase (CAT) and transfection into mouse cells. Very little CAT enzyme but high levels of CAT-specific RNA correctly initiated at the ribosomal DNA start site were synthesized. The amount of specific transcripts was neither influenced by long stretches of upstream spacer sequences nor by the insertion of the Moloney murine sarcoma virus enhancer. The deletion mutant pMr delta-39, which has been shown to be fully active in vitro, exhibited a 90% decrease in template activity in vivo. A mutant in which 22 base pairs of ribosomal DNA (between positions -35 and -14) were substituted by foreign DNA sequences proved transcriptionally inactive. The fusion genes were only transcribed in mouse cells, indicating that species-specific transcription factors are involved in ribosomal promoter recognition.

Characterization of enhancer elements in the long terminal repeat of Moloney murine sarcoma virus.

A series of recombinant molecules were constructed which direct the expression of the easily assayed gene chloramphenicol acetyltransferase. We have used these recombinants to show that the 73/72-base-pair tandem repeat unit from the Moloney murine sarcoma virus long terminal repeat shares a number of properties with the prototypic enhancer element, the simian virus 40 72-base-pair repeat. Specifically, the Moloney murine sarcoma virus sequence significantly enhances the level of gene expression at both 5' and 3' locations and in either orientation relative to the test gene. It is able to enhance gene activity both from its own promoter and from a heterologous (simian virus 40) promoter. The 73/72-base-pair subunits of the Moloney murine sarcoma virus enhancer differ in sequence by four nucleotides and also in the strength of their enhancer function. The promoter distal A repeat is at least three times as active as the promoter proximal B repeat in enhancing chloramphenicol acetyltransferase expression. Results of these studies also show that the enhancer sequence alone is unable to induce gene activity but requires other promoter elements, including a proximal GC-rich sequence and the Goldberg-Hogness box.

A functional component of the sea urchin H2A gene modulator contains an extended sequence homology to a viral enhancer.

The DNA sequences imparting a maximal rate of sea urchin H2A gene transcription in the frog oocyte nucleus were narrowed down by deletion mapping to a DNA segment -165 to -111, far-upstream of the H2A mRNA cap site. C to T base changes in this area create strong down mutations, hence the primary structure of this DNA sequence is of paramount importance to the H2A gene expression. Sequence comparisons suggest that the -165 to -111 region may contain two essential sequence blocks. Most strikingly, the -135 area contains a 14 out of 17 basepair homology to the Moloney murine sarcoma virus enhancer and to topologically related 5' LTR-sequences of the simian sarcoma virus and the murine Friend spleen focus forming virus.