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Down-regulation of genes encoding DNA replication proteins during cell cycle exit
1Department of Pathology, Stanford University School of Medicine, California 94305.
Cell Growth & Differentiation : the Molecular Biology Journal of the American Association for Cancer Research
|May 1, 1994
Summary
Gene expression of DNA polymerase alpha-DNA primase increases when cells enter the cell cycle but decreases during terminal differentiation. This regulation occurs at the transcription initiation level.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- DNA replication is crucial for cell division and is tightly regulated.
- DNA polymerase alpha-DNA primase is a key enzyme complex for chromosomal replication.
- Understanding the regulation of replication genes during cell cycle transitions is essential.
Purpose of the Study:
- To investigate the regulation of DNA polymerase alpha-DNA primase gene expression during various cell growth events.
- To determine how gene expression changes during cell cycle entry, quiescence, and terminal differentiation.
- To elucidate the mechanisms underlying gene expression changes in differentiating cells.
Main Methods:
- Studied gene expression of DNA polymerase alpha-DNA primase in human and mouse cell lines.
- Utilized cell culture techniques to induce quiescence (contact inhibition, serum starvation) and terminal differentiation (HL-60, MEL cells).
- Employed a novel method to isolate pure populations of differentiating cells for analysis.
- Analyzed gene expression at both mRNA and protein levels, and investigated transcription rates.
Main Results:
- DNA polymerase alpha-DNA primase gene expression is upregulated upon cell cycle entry from quiescence.
- Gene expression is reduced in cells temporarily quiescent due to contact inhibition or serum starvation.
- In actively cycling cells, these genes are expressed throughout the cell cycle.
- Terminal differentiation of HL-60 and MEL cells leads to down-regulation of DNA polymerase alpha gene expression.
- DNA primase subunits (p49, p58) mRNA levels decrease in differentiated MEL cells.
- In differentiated HL-60 cells, DNA polymerase alpha expression declines at both transcript and protein levels.
- Down-regulation in HL-60 cells is partly due to decreased transcription initiation, not elongation block.
Conclusions:
- DNA polymerase alpha-DNA primase gene expression is dynamically regulated during cell cycle progression and differentiation.
- Terminal differentiation involves a specific down-regulation of key DNA replication machinery.
- Regulation of DNA polymerase alpha expression during differentiation involves transcriptional control, specifically initiation.
- These findings provide insights into the molecular mechanisms governing cell cycle exit and differentiation.