Interactions between protein kinase CK2 and Pin1. Evidence for phosphorylation-dependent interactions

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Pin1 (peptidyl-prolyl isomerase) is crucial for cell cycle regulation through phosphorylation-dependent interactions.
• Protein kinase CK2 is a tetrameric enzyme with catalytic (CK2 alpha/alpha') and regulatory (CK2 beta) subunits.

Purpose of the Study:

• To investigate the interaction between Pin1 and protein kinase CK2.
• To elucidate the role of CK2 alpha phosphorylation in mediating this interaction.
• To explore Pin1's influence on CK2-mediated phosphorylation of topoisomerase II alpha.

Main Methods:

• Co-immunoprecipitation assays to detect Pin1-CK2 interactions.
• Site-directed mutagenesis to substitute CK2 alpha phosphorylation sites.
• Analysis of chimeric proteins to assess functional domains.
• In vitro kinase assays to measure phosphorylation inhibition.

Main Results:

• Pin1 interacts with CK2 complexes containing CK2 alpha, but not CK2 alpha'.
• Direct interaction occurs with the C-terminal domain of CK2 alpha, dependent on phosphorylation.
• Mutations at phosphorylation sites on CK2 alpha reduce Pin1 binding.
• Pin1 inhibits CK2-catalyzed phosphorylation of Thr-1342 on topoisomerase II alpha.
• Pin1 mutants (isomerase-deficient, WW domain-deficient) show impaired CK2 interaction and inhibition of topoisomerase II alpha phosphorylation.

Conclusions:

• Pin1 and CK2 alpha interact in a phosphorylation-dependent manner.
• Pin1 may regulate topoisomerase II alpha phosphorylation through CK2.
• This study reveals a novel mechanism for CK2 substrate specificity during mitosis.