Centrosomal Anchoring of the Protein Kinase CK1δ Mediated by Attachment to the Large, Coiled-coil Scaffolding Protein CG-NAP/AKAP450

Protein kinase CK1 (formerly termed casein kinase I) is ubiquitous in eukaryotic cells and comprises a family of as many as 14 isoforms (including splice variants) in mammalian cells. Mammalian CK1δ and CK1ε, which are highly related to each other, are enriched at the centrosomes in interphase cells and at the spindle during mitosis. In the present study we have isolated, using the yeast two-hybrid system, a 182 amino acid residue fragment of the centrosomal and golgi N-kinase anchoring protein (CG-NAP, also known as AKAP450), which specifically interacts with CK1δ and CK1ε, but not with other CK1 isoforms. The 182 amino acid residue CG-NAP fragment, or full length CG-NAP, co-immunoprecipitates with CK1δ and CK1ε from mammalian cells. Consistent with this association, endogenous CG-NAP/AKAP450 and CK1δ co-localize in cells. Moreover, when expressed in the presence of CK1δ the 182 amino acid residue CG-NAP fragment adopts the same sub-cellular localization as CK1δ. Strikingly, attachment of the CG-NAP fragment to the plasma membrane is sufficient to re-localize a significant level of CK1δ to the membrane. These findings support a model in which sub-cellular localization of CK1δ/ε molecules at the centrosome is mediated, at least in part, through the action of CG-NAP/AKAP450 and provide a potential mechanism by which the contribution to cell cycle progression by CK1δ/ε may be regulated.