Cellular senescence, epigenetic switches and c-Myc

Area of Science:

• Cellular senescence
• Oncogene signaling
• Tumor suppression

Background:

• Normal human cells can enter replicative senescence as a tumor defense mechanism in response to hyperproliferative signaling from oncogenes.
• Proto-oncogene c-Myc plays a role in regulating cell proliferation and is often dysregulated in cancer.

Purpose of the Study:

• To investigate the mechanism by which human fibroblasts and endothelial cells enter senescence.
• To identify the molecular players involved in a telomere-independent senescence pathway triggered by reduced c-Myc expression or oxidative stress.

Main Methods:

• Genetically engineering human fibroblasts and endothelial cells to reduce proto-oncogene c-Myc expression.
• Analyzing the frequency of cellular senescence.
• Investigating the involvement of the polycomb group repressor Bmi-1 and the cyclin-dependent kinase inhibitor p16(INK4a) in the senescence pathway.

Main Results:

• Reduced c-Myc expression increased the frequency of senescence in human fibroblasts and endothelial cells.
• This senescence occurred via a telomere-independent mechanism.
• The regulatory circuit involved Bmi-1 and p16(INK4a) and was also triggered by mild oxidative stress.

Conclusions:

• A mechanism exists for monitoring hypoproliferative signaling, limiting the proliferation of physiologically compromised cells.
• This pathway, involving Bmi-1 and p16(INK4a), serves as a tumor defense mechanism.
• This mechanism may represent another instance of antagonistic pleiotropy contributing to organismal aging.