mTOR inhibition acts as an unexpected checkpoint in p53-mediated tumor suppression

Area of Science:

• Molecular Biology
• Oncology
• Genetics

Background:

• The tumor suppressor protein p53 plays a critical role in preventing cancer.
• p53's tumor suppressive functions, including cell cycle arrest, senescence, apoptosis, and ferroptosis, are regulated by post-translational modifications like acetylation.
• Acetylation-defective p53 mutants (p53-4KR) exhibit impaired tumor suppression but paradoxically fail to develop early-onset tumors.

Purpose of the Study:

• To investigate the role of p53 acetylation in tumor suppression and embryonic development.
• To identify novel p53 acetylation sites and their functional consequences.
• To elucidate the relationship between p53, mTOR signaling, and tumor formation.

Main Methods:

• Generation and analysis of acetylation-defective p53 mutant mice (p53-4KR and p53-5KR).
• Investigation of embryonic lethality rescue in Mdm2-deficient mice with different p53 backgrounds.
• Assessment of mTOR signaling pathway activity in p53 mutant cells.
• Evaluation of tumor formation in response to mTOR inhibitor treatment.

Main Results:

• Acetylation-defective p53-4KR mice were tumor-prone but did not develop early-onset tumors.
• A novel p53 acetylation site (K136) was identified, and mutations at all five sites (p53-5KR) further diminished tumor suppression.
• p53-4KR, but not p53-5KR, could rescue embryonic lethality in Mdm2-deficient mice.
• p53-4KR retained mTOR suppression activity, which was lost in p53-5KR.
• mTOR inhibition suppressed early-onset tumor formation in p53-null and p53-4KR mice.

Conclusions:

• p53 acetylation is crucial for its tumor suppressive functions and embryonic development.
• p53-mediated mTOR regulation is vital for both embryonic development and tumor suppression, independent of canonical p53 pathways.
• Targeting mTOR signaling may offer therapeutic strategies for p53-related cancers.