A cholesterol-regulated PP2A/HePTP complex with dual specificity ERK1/2 phosphatase activity

Area of Science:

• Cellular biology
• Biochemistry
• Molecular biology

Background:

• Extracellular signal-regulated kinases (ERK) are crucial signaling proteins.
• ERK activity is regulated by phosphorylation and dephosphorylation.
• Membrane cholesterol levels are known to influence cellular signaling pathways.

Purpose of the Study:

• To investigate the mechanism by which membrane cholesterol affects ERK activity.
• To identify and characterize the phosphatase responsible for dephosphorylating pERK1/2.
• To elucidate the role of cholesterol in regulating this phosphatase activity.

Main Methods:

• Isolation and characterization of a high molecular weight phosphatase complex.
• Biochemical assays to determine phosphatase activity and substrate specificity.
• Cholesterol depletion experiments in human fibroblasts.
• Analysis of protein complex assembly and disassembly.

Main Results:

• A ~440 kDa, cholesterol-regulated phosphatase complex was isolated.
• This complex dephosphorylates both phosphotyrosine and phosphothreonine residues of pERK1/2.
• The dual specificity arises from the combined action of PP2A and HePTP phosphatases.
• Acute cholesterol depletion disrupts the complex, leading to loss of phosphatase activity and increased pERK1/2 levels.
• Increased pERK1/2 was observed in caveolae/raft domains and cytosol.

Conclusions:

• A novel cholesterol-regulated dual-specificity phosphatase (HePTP/PP2A complex) controls ERK1/2 activity.
• Cholesterol is essential for maintaining the integrity and activity of this phosphatase complex.
• This finding provides a molecular basis for cholesterol's effect on ERK signaling.
• Suggests a potential role for ERK in regulating cholesterol transport.