Protein phosphatase 4 plays dual roles during cell proliferation

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Protein Phosphatase 4 (PP4) is essential for cell proliferation and survival.
• PP4 deletion causes developmental defects in various organisms.
• The effects of PP4 up-regulation on cellular processes were previously unknown.

Purpose of the Study:

• To investigate the impact of PP4 modulation on HepG2 cell proliferation, cell cycle, and morphology.
• To identify proteins interacting with PP4.
• To elucidate the regulatory mechanisms of PP4 in cell proliferation.

Main Methods:

• PP4 was down-regulated using siRNA or inhibited using a phosphatase-dead mutant (PP4RL).
• PP4 was up-regulated using adenoviruses.
• Functional proteomics identified interacting proteins, followed by rescue experiments.

Main Results:

• Both PP4 up-regulation and inhibition suppressed cell proliferation.
• PP4 up-regulation caused prometaphase/metaphase arrest with defects in chromosome alignment and spindle assembly.
• Scaffold Attachment Factor A (SAF-A) was identified as a novel PP4-interacting protein involved in the prometaphase/metaphase transition.

Conclusions:

• PP4 plays a dual role in cell proliferation, with both increased and decreased activity being detrimental.
• A novel regulatory mechanism involving the interaction between PP4 and SAF-A in the cell cycle was discovered.