Mouse mammary tumor virus proviruses in T-cell lymphomas lack a negative regulatory element in the long terminal repeat

Proviral copies of mouse mammary tumor virus (MMTV) are known to be amplified in certain T-cell lymphomas. Transcription of the amplffied MMTV proviruses was studied in detail in two T-cell lymphoma lines and showed the production of deletions and premature termination of env mRNAs and the premature termination of gag transcripts. EL-4 cells produce three env mRNAs, and sequence analysis of cDNAs of the two smaller transcripts revealed large deletions encompassing the 3' half of the env gene. The deletion in at least one of the altered transcripts appeared to be produced by a splicing mechanism. T-cell lymphoma line ML of DBA/2 mice also synthesizes two smaller env transcripts, both of which result from premature termination of transcription. Both lines transcribe high levels of gag mRNAs of about 0.8 kilobases in length, terminating at the end of the region encoding MMTV phosphoprotein pp2l. Restriction enzyme BamHI analysis of the amplified proviruses of EL-4 and ML cells as well as of additional non-mammary tumor cell types containing amplified MMTV proviruses suggested that the amplified proviruses were derived from exogenous viruses, or activated endogenous provirus MTV-1 in the case of DBA/2 strain tumor cells.

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Altered mouse mammary tumor virus transcript synthesis in T-cell lymphoma cells

Racevskis

1990

“…The constructs tested in the analysis shown in Fig. 4B remove sequences from the middle of the MMTV LTR, where regulatory elements that inhibit expression in certain nonmammary cells have been mapped (3,7,12,15,20,22,31). The ILCϩ⌬ClaI/StuI construct removes 224 bp from the MMTV promoter, from Ϫ862 to Ϫ638.…”

Section: Mmtv Sequences Enhance the Activity Of The Int-2 Promoter Inmentioning

confidence: 99%

Mouse Mammary Tumor Virus Sequences Responsible for Activating Cellular Oncogenes

Grimm¹,

Nordeen

1998

Integration of mouse mammary tumor virus (MMTV) near the int genes results in the inappropriate expression of these proto-oncogenes and initiates events that lead to the formation of mammary adenocarcinomas. In most cases, the MMTV provirus integrates in a transcriptional orientation opposite that of the int genes. We have used a novel, vector-based system designed to recapitulate the integration of MMTV upstream of the int-2 promoter. Compared to a cellular promoter or another retroviral promoter, the MMTV long terminal repeat (LTR) in this configuration is particularly efficacious at activating the int-2 promoter. The sequences responsible for enhancing the activity of the int-2 promoter map to two domains in the 5 end of the MMTV LTR. One domain is a previously defined element; the second is an element delineated by these studies that acts synergistically with the first. Both of these elements display mammary cell-specific activity. Thus, even though the MMTV promoter itself is weak without hormonal stimulation, viral integration can position the 5 LTR elements to efficiently activate transcription from cellular proto-oncogenes. Other functional elements in the LTR have little effect on the activation of the int-2 promoter. Even stimulation of the MMTV promoter with steroid hormones only modestly activates transcription from the int-2 promoter, suggesting that the 5 elements of the LTR are the predominant determinants of the tissue-and orientation-specific activation of cellular promoters by MMTV.

“…The hormone response element (HRE) has been localized to a region from about Ϫ200 to Ϫ80 with respect to the transcription initiation site (27,34,37,47), and it contains multiple binding sites for steroid hormone receptor proteins (14,44,49,50,60). MMTV transcription is also subject to modulation by a distal negative regulatory element (dNRE) located within the MMTV long terminal repeat (LTR) between Ϫ427 and Ϫ364, which selectively represses basal promoter activity in the absence of hormone induction (25,35,41,42). Repression by the dNRE is enhanced by a more promoter-proximal NRE that is located within the HRE between two adjacent receptor binding sites (33,35).…”

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confidence: 99%

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

Kim

Peterson

1995

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 twoto 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.