article accepted in Molecular Biology of the Cell (MBoC)
PKD controls mitotic Golgi complex fragmentation through a Raf-MEK1 pathway
Christine Kienzle, Stephan A. Eisler, Julien Villeneuve§, Tilman Brummer#, Monilola A.
Olayioye*, Angelika Hausser*
Institute of Cell Biology and Immunology, University of Stuttgart, Allmandring 31, 70569 Stuttgart, Germany, phone ++497116856-6995, fax ++497116856-7484
#Centre for Biological Systems Analysis (ZBSA) and BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University Freiburg, Habsburgerstraße 49, 79104 Freiburg, Germany, phone ++49761203-97179, fax ++49761 203-8456
§ Centre for Genomic Regulation (CRG), C/ Dr. Aiguader 88, 08003 Barcelona, Spain, phone ++34 93 316 0099, fax ++34 93 3969 983
*corresponding authors (firstname.lastname@example.org; email@example.com)
Prior to entering mitosis, the stacks of the Golgi cisternae are separated from each other and inhibiting this process delays entry of mammalian cells into mitosis. Protein kinase D (PKD) is known to be involved in Golgi to cell surface transport by controlling the biogenesis of specific transport carriers. Here we show that depletion of PKD1 and PKD2 proteins from HeLa cells by siRNA leads to the accumulation of cells in the G2 phase of the cell cycle and prevents cells from entering mitosis. We further provide evidence that inhibition of PKD blocks mitotic Raf-1 and MEK activation, and, as a consequence, mitotic Golgi fragmentation, which could be rescued by expression of active MEK1. Finally, Golgi FRAP analyses demonstrated that PKD is crucial for the cleavage of the non-compact zones of Golgi membranes in G2 phase. Our findings suggest that PKD controls interstack Golgi connections in a Raf-1-MEK1 dependent manner, a process required for entry of the cells into mitosis.