CK2 and GSK3 phosphorylation on S29 controls wild-type ATXN3 nuclear uptake

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• The protein ATXN3 (ATXN3Q6) plays a role in various cellular processes.
• Understanding the regulation of ATXN3 subcellular localization is crucial for comprehending its function.

Purpose of the Study:

• To investigate the role of phosphorylation at serine 29 (S29) in the nuclear uptake of murine ATXN3 (ATXN3Q6).
• To identify the kinases responsible for S29 phosphorylation and their impact on ATXN3 subcellular sorting.

Main Methods:

• In vitro phosphorylation assays using purified ATXN3Q6.
• Mass spectrometry (MS) analysis in transfected COS-7 cells to confirm S29 phosphorylation.
• Site-directed mutagenesis of S29 to alanine and aspartic acid.
• Treatment with casein kinase 2 (CK2) and glycogen synthase kinase 3 (GSK3) inhibitors.

Main Results:

• Phosphorylation of S29, a conserved residue in the Josephin domain, promotes ATXN3Q6 nuclear uptake.
• Both CK2 and GSK3 kinases phosphorylate S29 in ATXN3Q6.
• Mutating S29 to alanine reduced nuclear uptake, while a phospho-mimic mutation restored it.
• Inhibiting CK2 and GSK3 prevented S29 phosphorylation and reduced nuclear uptake.

Conclusions:

• Serine 29 phosphorylation within the Josephin domain is a key regulator of ATXN3 nuclear uptake.
• CK2 and GSK3 are the primary kinases involved in mediating S29 phosphorylation and ATXN3 subcellular sorting.
• This study elucidates a novel mechanism for ATXN3 regulation and localization.