Studies on the function of a centrosome and Golgi localized giant anchoring protein CG-NAP

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Protein kinases are the key components in the intracellular signal transduction. The signaling specificity of the protein kinases may be mediated by the targeting of them to the specific micro-organelles through the anchoring proteins. CG-NAP (centrosome and Golgi localized PKN-associated protein) is a coiled-coil protein identified as a binding protein for the regulatory domain of PKN that has a catalytic domain highly homologous to PKC in the carboxyl-terminal region and a unique regulatory domain in the amino-terminal region. In this study, we have analyzed the function of CG-NAP as an anchoring protein and obtained the results as follows.1. CG-NAP is a 450-kDa coiled-coil protein and is localized to centrosome throughout the cell cycle, the midbody at telophase, and the Golgi apparatus at interphase.2. In addition to PKN, CG-NAP associates with protein kinase A, PKCε, and protein phosphatases (PP1 and PP2A).3. CG-NAP anchors non/hypo-phosphrylated PKCε at Golgi/centrosome area during maturation, and serves as a scaffold for the phosphorylation reaction.4. CG-NAP provides sites for microtubule nucleation in the mammalian centrosome by anchoring γ-tubulin ring complex.5. The carboxyl-terminal region of CG-NAP is necessary for the localization to centrosome.