c-MYC-Induced AP4 Attenuates DREAM-Mediated Repression by p53
Markus Kaller1, Wenjing Shi1, Heiko Hermeking1,2,3
1Experimental and Molecular Pathology, Institute of Pathology, Ludwig-Maximilians-University München, D-80337 Munich, Germany.
Background:
The deregulated expression of the c-MYC oncogene activates p53, which is presumably mediated by ARF/INK4, as well as replication-stress-induced DNA damage. Here, we aimed to determine whether the c-MYC-inducible AP4 transcription factor plays a role in this context using a genetic approach.
Methods:
We used a CRISPR/Cas9 approach to generate AP4- and/or p53-deficient derivatives of MCF-7 breast cancer cells harboring an ectopic, inducible c-MYC allele. Cell proliferation, senescence, DNA damage, and comprehensive RNA expression profiles were determined after activation of c-MYC. In addition, we analyzed the expression data from primary breast cancer samples.
Results:
Loss of AP4 resulted in elevated levels of both spontaneous and c-MYC-induced DNA damage, senescence, and diminished cell proliferation. Deletion of p53 in AP4-deficient cells reverted senescence and proliferation defects without affecting DNA damage levels. RNA-Seq analyses showed that loss of AP4 enhanced repression of DREAM and E2F target genes after p53 activation by c-MYC. Depletion of p21 or the DREAM complex component LIN37 abrogated this effect. These p53-dependent effects were conserved on the level of clinical and gene expression associations found in primary breast cancer tumors.
Conclusions:
Our results establish AP4 as a pivotal factor at the crossroads of c-MYC, E2F, and p53 target gene regulation.
Insights
The transcription factor AP4 is crucial for regulating genes involved in cell cycle control and DNA damage response. Its absence exacerbates c-MYC-induced DNA damage and senescence, highlighting its role in cancer pathways.
Area of Science:
- Molecular Biology
- Cancer Genetics
- Cellular Regulation
Background:
- The oncogene c-MYC deregulates p53 activation and induces DNA damage.
- The role of the AP4 transcription factor in this process was previously unclear.
Purpose of the Study:
- To investigate the role of the c-MYC-inducible AP4 transcription factor in regulating p53, DNA damage, and cell proliferation.
- To determine the genetic interactions between AP4 and p53 in breast cancer cells.
Main Methods:
- CRISPR/Cas9 was used to create AP4- and/or p53-deficient MCF-7 breast cancer cells with inducible c-MYC.
- Assessed cell proliferation, senescence, DNA damage, and RNA expression profiles after c-MYC activation.
- Analyzed gene expression data from primary breast cancer samples.
Main Results:
- Loss of AP4 increased spontaneous and c-MYC-induced DNA damage, senescence, and reduced proliferation.
- p53 deletion in AP4-deficient cells restored senescence and proliferation but not DNA damage.
- AP4 deficiency enhanced repression of DREAM and E2F target genes, a p53-dependent effect observed in breast tumors.
Conclusions:
- AP4 acts as a key regulator connecting c-MYC, E2F, and p53 target gene expression.
- This finding has implications for understanding breast cancer development and therapeutic strategies.
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