Molecular and Cellular Biology, May 2000, p. 3316-3329, Vol. 20, No. 9
Division of Hematology/Oncology,
Cedars-Sinai Research Institute/UCLA School of Medicine, Los
Angeles, California 900481;
Department of Medicine, Hematology/Oncology, University of
Münster, Münster, Germany2; and
Division of Biology, California Institute of Technology,
Pasadena, California 911253
Received 29 June 1999/Returned for modification 25 August
1999/Accepted 26 January 2000
Gene expression in mammalian organisms is regulated at multiple
levels, including DNA accessibility for transcription factors and
chromatin structure. Methylation of CpG dinucleotides is thought to be
involved in imprinting and in the pathogenesis of cancer. However, the
relevance of methylation for directing tissue-specific gene expression
is highly controversial. The cyclin A1 gene is expressed in very few
tissues, with high levels restricted to spermatogenesis and leukemic
blasts. Here, we show that methylation of the CpG island of the human
cyclin A1 promoter was correlated with nonexpression in cell lines, and
the methyl-CpG binding protein MeCP2 suppressed transcription from the
methylated cyclin A1 promoter. Repression could be relieved by
trichostatin A. Silencing of a cyclin A1 promoter-enhanced green
fluorescent protein (EGFP) transgene in stable transfected MG63
osteosarcoma cells was also closely associated with de novo promoter
methylation. Cyclin A1 could be strongly induced in nonexpressing cell
lines by trichostatin A but not by 5-aza-cytidine. The cyclin A1
promoter-EGFP construct directed tissue-specific expression in male
germ cells of transgenic mice. Expression in the testes of these mice
was independent of promoter methylation, and even strong promoter
methylation did not suppress promoter activity. MeCP2 expression was
notably absent in EGFP-expressing cells. Transcription from the
transgenic cyclin A1 promoter was repressed in most organs outside the
testis, even when the promoter was not methylated. These data show the
association of methylation with silencing of the cyclin A1 gene in
cancer cell lines. However, appropriate tissue-specific repression of the cyclin A1 promoter occurs independently of CpG methylation.
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Methylation of the Cyclin A1 Promoter Correlates
with Gene Silencing in Somatic Cell Lines, while Tissue-Specific
Expression of Cyclin A1 Is Methylation Independent
*
Corresponding author. Mailing address: Department of
Medicine, Hematology/Oncology, ICP-Laboratory, University of
Münster, Domagkstr. 3, 48129 Münster, Germany. Phone:
49-251-835-6229. Fax: 49-251-835-2673. E-mail:
muellerc{at}uni-muenster.de.
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