Vimentin-Ser82 as a memory phosphorylation site in astrocytes

Area of Science:

• Cell Biology
• Biochemistry
• Neuroscience

Background:

• Astrocytes play crucial roles in brain function.
• Vimentin, a type III intermediate filament, is dynamically regulated in astrocytes.
• Calcium signaling pathways influence astrocyte function and intermediate filament organization.

Purpose of the Study:

• To investigate the differential dephosphorylation of vimentin phosphorylation sites in astrocytes.
• To elucidate the role of protein phosphatase 1 catalytic subunit (PP1c) in vimentin dephosphorylation.
• To determine the functional consequences of sustained vimentin phosphorylation at Ser82.

Main Methods:

• In vitro dephosphorylation assays using purified PP1c.
• In vivo association studies of PP1c with vimentin filaments in astrocytes.
• Stimulation of astrocytes with PGF(2alpha) or ionomycin to induce vimentin phosphorylation.
• Analysis of vimentin filament structure following repetitive ionomycin treatment.

Main Results:

• Vimentin phosphorylation at Ser38 and Ser82 is induced by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in astrocytes.
• Phospho-Ser82 is dephosphorylated much slower than phospho-Ser38.
• PP1c efficiently dephosphorylates phospho-Ser38 but not phospho-Ser82 in vitro, despite binding to vimentin via a VxF motif.
• PP1c associates with vimentin filaments in vivo.
• Sustained Ser82 phosphorylation due to repetitive stimulation leads to vimentin filament disassembly.

Conclusions:

• Vimentin is a novel binding partner of PP1c in astrocytes.
• The VxF motif interaction hinders PP1c access to phospho-Ser82, prolonging its phosphorylation.
• Vimentin Ser82 phosphorylation may function as a memory site, impacting astrocyte cytoskeletal dynamics.