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Identification of Myc-mediated death response pathways by microarray analysis
Qiang Yu1, Mei He, Norman H Lee
1Advanced Technology Center, Center for Cancer Research, NCI/National Institutes of Health, Gaithersburg, MD 20877, USA.
Abstract:
To understand the mechanisms of Myc-mediated apoptosis induced by DNA damage, we have characterized the death kinetics of three Rat-1 fibroblast cell lines that either overexpress Myc or lack Myc and their parental wild-type cells following exposure to the DNA-damaging agent VP-16, and we monitored the changes in gene expression using microarray. We have identified three groups of genes whose expressions are distinctly regulated during this process. One cluster (Cluster A) revealed a VP-16-dependent but Myc-independent induction of a set of genes that is not linked to the apoptotic response. Two other gene clusters, however, were associated with VP-16-induced apoptosis. Cluster B, which includes p53-responsive genes, was associated with the temporal onset of apoptosis but accounted for only the basal apoptosis. However, Cluster C, which includes c-jun, was highly regulated by Myc and appeared to be critical to mounting the maximal apoptotic response in Myc-expressing cells. Furthermore, the Myc level dropped sharply following VP-16 exposure, which varied inversely with the induction of Cluster C genes, suggesting Myc normally represses their transcription. Thus, we have proposed that removal of Myc-mediated repression of apoptotic signals, combined with Myc-associated acceleration of the p53 responsive pathway, results in complete and rapid cell death following DNA damage.
Insights
Myc
Area of Science:
- Cellular Biology
- Molecular Biology
- Genetics
Background:
- DNA damage can trigger programmed cell death (apoptosis).
- The role of Myc in DNA damage-induced apoptosis is complex and not fully understood.
- Understanding Myc's function is crucial for cancer research.
Purpose of the Study:
- To elucidate the mechanisms of Myc-mediated apoptosis following DNA damage.
- To identify genes regulated by Myc during the apoptotic process.
- To investigate the interplay between Myc, p53, and apoptosis.
Main Methods:
- Characterization of cell death kinetics in Rat-1 fibroblast cell lines with varying Myc levels (overexpressing, lacking, wild-type).
- Exposure of cells to the DNA-damaging agent VP-16.
- Gene expression profiling using microarray analysis to monitor changes.
Main Results:
- Identified three distinct gene expression clusters during VP-16 exposure.
- Cluster A genes were VP-16-dependent but Myc-independent and not linked to apoptosis.
- Cluster B (p53-responsive genes) correlated with basal apoptosis onset.
- Cluster C (including c-jun) was highly regulated by Myc and critical for maximal apoptosis.
- Myc levels decreased upon VP-16 exposure, inversely correlating with Cluster C gene induction, suggesting Myc repression.
Conclusions:
- Myc negatively regulates a subset of genes critical for maximal apoptosis.
- Myc accelerates the p53-responsive pathway, contributing to rapid cell death.
- Removal of Myc-mediated repression, coupled with accelerated p53 signaling, drives complete and rapid apoptosis after DNA damage.