Protein phosphatase 2A (PP2A) holoenzymes regulate death-associated protein kinase (DAPK) in ceramide-induced anoikis

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Death-associated protein kinase (DAPK) is a tumor suppressor regulating cytoskeletal dynamics.
• DAPK activity is inhibited by autophosphorylation at Ser-308.
• A novel phosphatase dephosphorylates Ser-308, enhancing DAPK activity and degradation.

Purpose of the Study:

• Identify the phosphatase responsible for DAPK Ser-308 dephosphorylation.
• Investigate the role of this phosphatase in regulating DAPK activity and stability.
• Determine the functional significance of PP2A-mediated DAPK activation in cell adhesion and anoikis.

Main Methods:

• Co-immunoprecipitation to identify DAPK-interacting proteins.
• In vitro and in vivo phosphatase assays to assess DAPK phosphorylation.
• Western blotting and proteasome inhibition assays to evaluate DAPK degradation.
• Cell rounding and detachment assays in HEK293 cells.
• Analysis of ceramide-induced anoikis.

Main Results:

• Two holoenzyme forms of protein phosphatase 2A (PP2A), ABalphaC and ABdeltaC, were identified as DAPK-interacting proteins.
• PP2A holoenzymes dephosphorylate DAPK at Ser-308, enhancing its catalytic activity.
• PP2A activity promotes proteasome-mediated degradation of DAPK.
• Overexpression of wild-type DAPK, but not an inactive S308E mutant, induces cell rounding and detachment.
• PP2A-mediated DAPK activation is essential for ceramide-induced anoikis.

Conclusions:

• PP2A directly dephosphorylates and activates DAPK at Ser-308.
• PP2A regulates DAPK stability through proteasomal degradation.
• The PP2A-DAPK pathway is critical for controlling cell adhesion and anoikis.