A subset of RAB proteins modulates PP2A phosphatase activity

Area of Science:

• Molecular biology
• Biochemistry
• Cell biology

Background:

• Protein phosphatase 2A (PP2A) is a crucial serine-threonine phosphatase in mammalian cells, regulating vital physiological processes.
• PP2A's activity and substrate specificity are modulated by regulatory B subunits.
• Deregulation of PP2A is frequently linked to cancer development.

Purpose of the Study:

• To investigate novel molecular mechanisms controlling the tumor suppressor activity of PP2A.
• To identify new proteins interacting with PP2A using interactomics.
• To elucidate the role of RAB proteins in PP2A regulation.

Main Methods:

• Mass spectrometry-based interactomics to identify PP2A binding partners.
• In vitro and in vivo assays to confirm protein interactions.
• Biochemical assays to assess PP2A catalytic activity and binding competition.

Main Results:

• Identification of multiple RAB proteins interacting with the PP2A scaffold subunit (PPP2R1A), but not the catalytic subunit (PPP2CA).
• Demonstration that RAB9 competes with PPP2CA for binding to PPP2R1A.
• Evidence of these interactions occurring in specific subcellular compartments both in vitro and in vivo.

Conclusions:

• A novel mechanism for PP2A regulation involving competitive binding of RAB proteins to the scaffold subunit has been characterized.
• This interaction modulates PP2A catalytic activity, offering insights into its compromised function in cancers.
• The findings highlight the importance of RAB proteins in PP2A-mediated tumor suppression.