Centrosome-targeting region of CG-NAP causes centrosome amplification by recruiting cyclin E-cdk2 complex

Centrosome duplication occurs once per cell cycle and is thought to be triggered by cyclin E-cdk2. However, it is largely unknown how the duplication is regulated. Here, we found that the expression of the centrosome-targeting region of CG-NAP (centrosome and Golgi-localized PKN-associated protein), which we designate as CG-NAP/D, increased the number of centrosomes in Chinese hamster ovary (CHO)-K1 cells. The amplified centrosomes co-localized with centrosome markers gamma-tubulin, centrin-2 and kendrin as well as endogenous CG-NAP. When CG-NAP/D was dislocated from centrosomes by deleting the centrosome-targeting domain or by fusing with a membrane-targeting sequence, centrosome amplification was suppressed. CG-NAP/D interacted with exogenously expressed cyclin E, which co-localized at centrosomes. The immunoprecipitates of CG-NAP/D exhibited histone H1 kinase activity, suggesting the co-immunoprecipitation of active cyclin-cdk complexes. Furthermore, centrosome fractions prepared from cells expressing CG-NAP/D contained increased amount of cdk2 compared with those from control cells. Centrosome amplification by CG-NAP/D was suppressed by co-expression of a mutant cyclin E unable to interact with cdk2. These results suggest that CG-NAP/D causes centrosome amplification by anchoring excess amount of cyclin E-cdk2 to centrosomes and, possibly, CG-NAP participates in centrosome duplication by recruiting cyclin E-cdk2 to centrosomes in normal cell cycle.