Previous Article | Next Article ![]()
Mol. Cell. Biol., Oct 1997, 5813-5822, Vol 17, No. 10
SA Patel, DM Graunke and RO Pieper
Tumor-associated aberrant silencing of CpG island-containing genes has been
correlated with increased cytosine methylation, a "closed" chromatin
structure, and exclusion of transcription factor binding in the CpG
island/promoter regions of affected genes. Given the lack of understanding
of what constitutes a closed chromatin structure in CpG islands, however,
it has been difficult to assess the relationship among cytosine
methylation, chromatin structure, and inappropriate gene silencing. In this
study, nuclease accessibility analysis was used to more clearly define the
chromatin structure in the CpG island of the human O6-methylguanine DNA
methyltransferase (MGMT) gene. Chromatin structure was then related to in
vivo DNA-protein interactions and cytosine methylation status of the MGMT
CpG island in human glioma cells varying in MGMT expression. The results of
these studies indicated that the "open" chromatin structure associated with
the MGMT CpG island in MGMT+ cells consisted of an approximately 250-bp
transcription factor-binding, nuclease-accessible, nucleosome-free region
of DNA, whose formation was associated with at least four flanking,
precisely positioned nucleosome-like structures. In MGMT- cells, this
precise nucleosomal array was lost and was replaced by randomly positioned
nucleosomes (i.e., the closed chromatin structure), regardless of whether
methylation of the CpG island was spread over the entire island or limited
to regions outside the transcription factor binding region. These results
suggest that CpG islands facilitate the expression of housekeeping genes by
facilitating nucleosomal positioning and that the conditions that alter the
formation of this array (such as perhaps methylation) may indirectly affect
CpG island- containing gene expression.
Copyright © 1997, American Society for Microbiology
Aberrant silencing of the CpG island-containing human O6-methylguanine DNA methyltransferase gene is associated with the loss of nucleosome- like positioning
Program in Molecular Biology and Division of Hematology/Oncology, Loyola University Chicago, Maywood, Illinois 60153, USA.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»