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S-Phase progression mediates activation of a silenced gene in synthetic nuclei
A J Crowe1, J L Piechan, L Sang
1Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, Cincinnati, Ohio 45267-0524, USA.
Abstract:
Aberrant expression of developmentally silenced genes, characteristic of tumor cells and regenerating tissue, is highly correlated with increased cell proliferation. By modeling this process in vitro in synthetic nuclei, we find that DNA replication leads to deregulation of established developmental expression patterns. Chromatin assembly in the presence of adult mouse liver nuclear extract mediates developmental stage-specific silencing of the tumor marker gene alpha-fetoprotein (AFP). Replication of silenced AFP chromatin in synthetic nuclei depletes sequence-specific transcription repressors, thereby disrupting developmentally regulated repression. Hepatoma-derived factors can target partial derepression of AFP, but full transcription activation requires DNA replication. Thus, unscheduled entry into S phase directly mediates activation of a developmentally silenced gene by (i) depleting developmental stage-specific transcription repressors and (ii) facilitating binding of transactivators.
Insights
Tumor cells can reactivate silenced genes through DNA replication, which depletes repressors and activates gene expression. This process involves disrupting developmental silencing, impacting cell proliferation and tumor marker genes like alpha-fetoprotein (AFP).
Area of Science:
- Molecular Biology
- Developmental Biology
- Cancer Biology
Background:
- Aberrant gene expression, particularly of developmentally silenced genes, is a hallmark of cancer and regeneration.
- This aberrant expression correlates with increased cell proliferation, suggesting a link to cell cycle regulation.
Purpose of the Study:
- To investigate the role of DNA replication in the deregulation of developmentally silenced genes in vitro.
- To model the process of gene reactivation using synthetic nuclei and understand the mechanisms involved.
Main Methods:
- Utilized synthetic nuclei to model chromatin assembly and DNA replication in vitro.
- Employed adult mouse liver nuclear extract to study developmental stage-specific gene silencing.
- Investigated the impact of DNA replication on the expression of the tumor marker gene alpha-fetoprotein (AFP).
Main Results:
- DNA replication in synthetic nuclei led to the deregulation of established developmental expression patterns.
- Chromatin assembly with nuclear extract mediated developmental stage-specific silencing of AFP.
- Replication of silenced AFP chromatin depleted sequence-specific transcription repressors, disrupting repression.
- Hepatoma-derived factors induced partial AFP derepression, but full activation required DNA replication.
Conclusions:
- Unscheduled entry into S phase directly activates developmentally silenced genes.
- This activation occurs by depleting developmental stage-specific transcription repressors and facilitating transactivator binding.
- The findings provide insights into the mechanisms of oncogene activation during tumorigenesis and regeneration.