The block to transcription elongation is promoter dependent in normal and Burkitt's lymphoma c-myc alleles.

Abstract

Aberrant c-myc expression patterns occur in human Burkitt's lymphoma cells, which consistently exhibit c-myc chromosomal translocations, mutations within and flanking the translocated allele, a loss of the block to transcription elongation in exon 1, and a promoter shift to use of the upstream P1 promoter. To define the mechanism responsible for the loss of transcription elongation blockage and resulting c-myc deregulation in Burkitt's lymphoma, we analyzed transcription patterns after transfer of normal and Burkitt's lymphoma c-myc alleles into murine cells and Xenopus oocyte germinal vesicles. We have determined that although the mutations within and surrounding several Burkitt's lymphoma c-myc alleles are not sufficient, in themselves, to abrogate the transcription elongation block, transcription initiation from the P2 promoter may be necessary to obtain the block to transcription elongation. To test directly the role of c-myc promoters in programming transcription elongation blockage, we analyzed transcription patterns from in vitro mutagenized c-myc genes containing deletions of either the P1 or P2 promoter. These data confirm that Pl-initiated c-myc transcripts do not terminate at discrete sites near the 3' end of exon 1, whereas P2-initiated transcripts either terminate or read through the transcription block signals. Therefore, overexpression and/or constitutive expression from the c-myc P1 promoter may contribute to increased readthrough transcription in Burkitt's lymphoma cells and, hence, to aberrant expression patterns or levels of c-myc steady-state transcripts. In addition, the ability of normal cells to modulate c-myc P2-initiated transcription to either read through or to block elongation provides a fine control mechanism over c-myc steady-state RNA levels.

The c-MYC allele that is translocated into the IgH locus undergoes constitutive hypermutation in a Burkitt's lymphoma line

“…There is no obvious correlation between the single nucleotide mutations detected in the c-MYC exon 1 and the major polymerase II pausing/ termination site described in this exon. Thus, the data do not lend any strong support to a connection between transcriptional pausing and antibody hypermutation although (I) the pause sites in the translocated c-MYC could di er from those in the germline allele (Spencer et al, 1990) and (II) two of the three insertion/duplication events that we observed in the Ramos c-MYC are within the homopolymeric dT stretch that constitutes the major exon 1 pause site.…”

Transcription elongation in the human c-myc gene is governed by overall transcription initiation levels in Xenopus oocytes.

“…The human c-myc gene is regulated by a block to transcription elongation during a number of in vivo processes such as differentiation of HL-60 cells and stimulation of quiescent cells by mitogens (2,29). In addition, the block to transcription elongation is lost in several tumor cells, such as HeLa and Burkitt's lymphoma cells, contributing to high or constitutive levels of c-myc mRNA in these cells (52,54).…”

“…This assay has been used to study transcription arrest from the human c-myc gene (3,33,54), the murine c-myc gene (45,59), the human and mouse adenosine deaminase genes (8,9,40), and the Xenopus oa-tubulin gene (34).…”

FUBP/KH domain proteins in transcription: Back to the future

“…9 The exon 1 mutation prevents the Pol II block and leads to constitutive Pol II read-through and elevated MYC. 8,[10][11][12] The complexity of the MYC promoter and regulation by post-initiation release of paused Pol II reflects the multitude of signaling inputs converging on MYC transcription. As early studies found a correlation between MYC promoter sensitivity to nuclease cleavage and expression levels, 9,10,13 analysis of nucleasesensitive elements was used as a means to understand integration of signaling inputs.…”