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Molecular and Cellular Biology, November 1998, p. 6281-6292, Vol. 18, No. 11
Fred Hutchinson Cancer Research
Center,1 and
Department of Pathology and
Radiation Oncology, University of Washington School of
Medicine,3 Seattle, Washington, and
Department of Biological Sciences, University of Warwick,
Coventry, United Kingdom2
Received 7 April 1998/Returned for modification 8 June
1998/Accepted 6 August 1998
In chromosome translocations characteristic of Burkitt lymphomas
(BL) and murine plasmacytomas, c-myc genes become
juxtaposed to immunoglobulin heavy-chain (IgH) sequences, resulting in
aberrant c-myc transcription. Translocated
c-myc alleles that retain the first exon exhibit increased
transcription from the normally minor c-myc
promoter, P1, and increased transcriptional elongation through inherent
pause sites proximal to the major c-myc promoter, P2. We
recently demonstrated that a cassette derived from four DNase I-hypersensitive sites (HS1234) in the 3'C
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Copyright © 1998, American Society for Microbiology. All rights reserved.
The Immunoglobulin Heavy Chain Locus Control Region Increases
Histone Acetylation along Linked c-myc Genes
region of the IgH locus
functions as an enhancer-locus control region (LCR) and directs a
similar pattern of deregulated expression of linked c-myc
genes in BL and plasmacytoma cell lines. Here, we report that the
HS1234 enhancer-LCR mediates a widespread increase in histone
acetylation along linked c-myc genes in Raji BL cells. Significantly, the increase in acetylation was not restricted to
nucleosomes within the promoter region but also was apparent upstream
and downstream of the transcription start sites as well as along vector
sequences. Histone hyperacetylation of control c-myc genes,
which was induced by the deacetylase inhibitor trichostatin A, mimics
the effect of the HS1234 enhancer on expression from the
c-myc P2 promoter, but not that from the P1 promoter. These results suggest that the HS1234 enhancer stimulates
transcription of c-myc by a combination of mechanisms.
Whereas HS1234 activates expression from the P2 promoter through a
mechanism that includes increased histone acetylation, a general
increase in histone acetylation is not sufficient to explain the
HS1234-mediated activation of transcription from P1.
*
Corresponding author. Mailing address: Fred Hutchinson
Cancer Research Center, 1100 Fairview Ave. N., Seattle, WA 98109. Phone: (206) 667-4496. Fax: (206) 667-5894. E-mail:
markg{at}fred.fhcrc.org.
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