Competing docking interactions can bring about bistability in the MAPK cascade

Area of Science:

• Cellular signaling pathways
• Molecular biology
• Biochemistry

Background:

• Mitogen-activated protein kinases (MAPKs) regulate critical cell fate processes like proliferation, differentiation, and apoptosis.
• The Raf-Mek-Erk cascade often exhibits all-or-none responses, suggesting underlying bistable behavior.
• Existing models attribute bistability to enzyme depletion in Erk phosphorylation cycles.

Purpose of the Study:

• To identify and characterize novel regulatory mechanisms within the Raf-Mek-Erk signaling cascade.
• To investigate the role of sequestration effects in generating pathway bistability.
• To explore how this new mechanism synergizes with known mechanisms to influence signaling dynamics.

Main Methods:

• Experimental observation of sequestration effects in the Raf-Mek-Erk cascade.
• Mathematical modeling to demonstrate bistability arising from the proposed positive-feedback circuit.
• Integration of sequestration feedback with enzyme depletion models.

Main Results:

• A previously unrecognized positive-feedback mechanism involving Erk-mediated sequestration of Mek was identified.
• This sequestration inhibits cascade activation under weak stimulation but amplifies signaling upon phosphorylation.
• The positive feedback circuit generates bistability using experimentally measured parameters.
• Synergy between sequestration feedback and enzyme depletion significantly expands the bistable range.

Conclusions:

• Sequestration effects, driven by stable docking interactions and competition, can create potent feedback loops in protein kinase cascades.
• This sequestration-based feedback mechanism is a key contributor to the bistability of the Raf-Mek-Erk pathway.
• The combined effects of sequestration and enzyme depletion provide a more comprehensive explanation for the observed bistable behavior and its impact on cell fate decisions.