Polo-like kinase is required for the fragmentation of pericentriolar Golgistacks during mitosis

The pericentriolar stacks of Golgi cisternae undergo extensive reorganizati on during mitosis in mammalian cells. GM130 and GRASP65 (Golgi reassembly s tacking protein of 65 kDa) are Golgi-associated proteins that are targets o f mitotic kinases, and they have also been implicated in the reorganization of the Golgi structure during cell division. Previous studies have reporte d that mitogen-activated protein kinase kinase-1 (MEK1} and Cdc2 protein ki nases are involved in these dynamic changes in the Golgi structure. More re cently, the mitotic polo-like kinase (Plk} has been shown to interact with and phosphorylate GRASP65. Here, we provide evidence that Plk is involved i n the mitosis-specific fragmentation of the Golgi apparatus. The addition o f kinase-defective Plk or immunodepletion of Plk disrupts the fragmentation process. Furthermore, Golgi fragmentation is inhibited by the addition of either full-length or truncated GRASP65. These findings suggest that phosph arylation of GRASP65 by Plk may be a critical event in the reorganization o f the Golgi structure during mitosis.