Regulation of endosome sorting by a specific PP2A isoform

Area of Science:

• Cell Biology
• Molecular Biology
• Protein Trafficking

Background:

• Regulated protein sorting in the trans-Golgi network (TGN)/endosomal system is crucial for protein function.
• The endoprotease furin is activated within the TGN/endosomal system.
• Furin's localization is regulated by phosphorylation by casein kinase II (CKII).

Purpose of the Study:

• To investigate the role of furin phosphorylation and dephosphorylation in its intracellular trafficking.
• To identify novel regulators of protein localization within the TGN/endosomal system.
• To elucidate the specific protein phosphatase 2A (PP2A) isoforms involved in furin routing.

Main Methods:

• Analysis of phosphorylated furin internalization from the cell surface.
• Investigation of the role of PACS-1 in furin trafficking.
• In vitro dephosphorylation assays using baculovirus-expressed PP2A subunits.
• In vivo studies using SV-40 small t antigen to assess PP2A activity.

Main Results:

• Phosphorylated furin internalized from the cell surface cycles between early endosomes and the plasma membrane, dependent on PACS-1.
• Dephosphorylation of furin in vitro requires heterotrimeric PP2A containing B family regulatory subunits.
• Specific PP2A isoforms are essential for routing furin from early endosomes to the TGN in vivo.

Conclusions:

• CKII and PP2A play critical roles in regulating furin localization through phosphorylation and dephosphorylation.
• PACS-1 mediates phosphorylation-dependent furin sorting.
• Signal transduction pathways involving CKII and PP2A acutely regulate the distribution of membrane proteins.