Real-time in vivo imaging of p16Ink4a reveals cross talk with p53
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Published on: May 14, 2016
Kimi Yamakoshi1, Akiko Takahashi, Fumiko Hirota
1The Cancer Institute, Japanese Foundation for Cancer Research, Koto-ku, Tokyo 135-8550, Japan.
Abstract:
Expression of the p16(Ink4a) tumor suppressor gene, a sensor of oncogenic stress, is up-regulated by a variety of potentially oncogenic stimuli in cultured primary cells. However, because p16(Ink4a) expression is also induced by tissue culture stress, physiological mechanisms regulating p16(Ink4a) expression remain unclear. To eliminate any potential problems arising from tissue culture-imposed stress, we used bioluminescence imaging for noninvasive and real-time analysis of p16(Ink4a) expression under various physiological conditions in living mice. In this study, we show that oncogenic insults such as ras activation provoke epigenetic derepression of p16(Ink4a) expression through reduction of DNMT1 (DNA methyl transferase 1) levels as a DNA damage response in vivo. This pathway is accelerated in the absence of p53, indicating that p53 normally holds the p16(Ink4a) response in check. These results unveil a backup tumor suppressor role for p16(Ink4a) in the event of p53 inactivation, expanding our understanding of how p16(Ink4a) expression is regulated in vivo.
Insights
Oncogenic stress up-regulates the p16(Ink4a) tumor suppressor gene. In vivo, ras activation triggers epigenetic changes reducing DNMT1 levels, leading to p16(Ink4a) expression, especially when p53 is absent.
Area of Science:
- Molecular Biology
- Cancer Biology
- Genetics
Background:
- The tumor suppressor gene p16(Ink4a) is upregulated by oncogenic stimuli in cell culture.
- Tissue culture stress complicates understanding of physiological regulation of p16(Ink4a).
- In vivo analysis is crucial to elucidate the true regulatory mechanisms of p16(Ink4a).
Purpose of the Study:
- To investigate the in vivo regulation of p16(Ink4a) expression under physiological conditions.
- To understand the role of epigenetic modifications and DNA damage response in p16(Ink4a) regulation.
- To explore the interplay between p53 and p16(Ink4a) in tumor suppression.
Main Methods:
- Utilized bioluminescence imaging for noninvasive, real-time monitoring of p16(Ink4a) expression in living mice.
- Induced oncogenic insults, such as ras activation, to study stress responses.
- Assessed changes in DNA methyl transferase 1 (DNMT1) levels and p53 status.
Main Results:
- Oncogenic insults, including ras activation, induce epigenetic derepression of p16(Ink4a) in vivo.
- This derepression occurs via a DNA damage response involving reduced DNMT1 levels.
- The pathway is accelerated in p53-deficient mice, indicating p53's inhibitory role.
Conclusions:
- p16(Ink4a) acts as a backup tumor suppressor, particularly important upon p53 inactivation.
- Epigenetic regulation involving DNMT1 reduction is a key mechanism for p16(Ink4a) induction by oncogenic stress in vivo.
- This study clarifies the physiological regulation of p16(Ink4a) beyond cell culture artifacts.
