Protein kinase B phosphorylates AHNAK and regulates its subcellular localization

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• AHNAK is a large phosphoprotein found ubiquitously in the body.
• Its cellular location differs between cell types: nuclear in non-epithelial cells and cytoplasmic/membrane-associated in epithelial cells.
• AHNAK was initially identified in neuroblastoma cells.

Purpose of the Study:

• To investigate the factors controlling AHNAK's extranuclear localization in epithelial cells.
• To determine if protein kinase B (PKB) phosphorylates AHNAK.
• To elucidate the mechanism linking cell-cell contact, PKB, and AHNAK localization.

Main Methods:

• Investigated AHNAK localization in epithelial cells with and without cell-cell contacts.
• Performed in vitro and in vivo phosphorylation assays using AHNAK and PKB.
• Analyzed the role of a specific serine residue (Serine 5535) in AHNAK phosphorylation by PKB.
• Studied the function of a nuclear export signal (NES) in AHNAK localization.

Main Results:

• Extranuclear localization of AHNAK in epithelial cells is dependent on cell-cell contact formation.
• AHNAK is confirmed as a direct phosphorylation substrate of PKB, both in vitro and in vivo.
• Phosphorylation of Serine 5535 by PKB is crucial for mediating nuclear exclusion of AHNAK.
• This phosphorylation event is a key factor in AHNAK's extranuclear localization.

Conclusions:

• AHNAK localization is regulated by cell-cell contacts and PKB-mediated phosphorylation.
• PKB plays a significant role in controlling AHNAK's extranuclear positioning.
• The function of AHNAK, while currently unknown, is likely influenced by its PKB-regulated localization.