p63 uses a switch-like mechanism to set the threshold for induction of apoptosis

Area of Science:

• Cellular Biology
• Molecular Biology
• Genetics

Background:

• The p53 homolog TAp63α is essential for maintaining genome integrity in oocytes.
• TAp63α activation, critical for apoptosis induction after DNA damage, involves multistep phosphorylation by casein kinase 1 (CK1).
• This phosphorylation cascade transitions TAp63α from an inactive dimer to an active tetramer.

Purpose of the Study:

• To investigate the kinetics and structural mechanisms underlying TAp63α activation by CK1.
• To elucidate the biphasic phosphorylation behavior of TAp63α.
• To understand how phosphorylation site availability influences the rate of subsequent phosphorylation events.

Main Methods:

• Measurement of TAp63α activation kinetics in ovarian tissue.
• In vitro kinetic analysis of single-site phosphorylation using peptides and full-length TAp63α.
• X-ray crystallography to determine the structure of CK1 in complex with phosphorylated TAp63α peptides.

Main Results:

• TAp63α phosphorylation by CK1 exhibits biphasic kinetics: the initial two phosphorylations are rapid, while the third, critical for activation, is slow.
• Structural analysis revealed an unusual substrate interaction where a phosphorylated site inhibits subsequent CK1 activity on the same substrate.
• This auto-inhibitory mechanism explains the slow kinetics of the final activating phosphorylation step.

Conclusions:

• The study uncovers a novel auto-inhibitory mechanism in TAp63α phosphorylation by CK1.
• This mechanism dictates the slow kinetics of TAp63α activation, highlighting its importance in regulating apoptosis.
• Understanding this process provides insights into genome integrity maintenance in oocytes.