Signaling via Mitogen-Activated Protein Kinase Kinase (MEK1) Is Required for Golgi Fragmentation during Mitosis

Abstract

We have developed an assay using permeabilized cells to monitor fragmentation of the Golgi complex that occurs during mitosis. Golgi stacks, in permeabilized interphase normal rat kidney (NRK) cells, upon incubation with mitotic extracts undergo extensive fragmentation, and the fragmented Golgi membranes are dispersed throughout the cytoplasm. We find that the continued presence of p34cdc2, the mitosis initiation kinase, is not necessary for Golgi fragmentation. Instead, fragmentation depends on cytosolic mitogen-activated protein kinase kinase 1 (MEK1 or MAPKK1). However, the known cytoplasmic substrates for MEK1, ERK1, and ERK2 are not required for this process. Interestingly, we find a Golgi-associated ERK, which we propose as the likely target for MEK1 in Golgi fragmentation.

Mitogen-activated Protein Kinase Kinase 1-dependent Golgi Unlinking Occurs in G2Phase and Promotes the G2/M Cell Cycle Transition

“…In contrast to the dramatic dispersal of Golgi components induced by BFA, MEK1-induced Golgi breakdown in permeabilized cells seems to yield relatively large Golgi fragments (Acharya et al, 1998;Kano et al, 2000), suggesting that mitotic MEK1 signaling causes unlinking of Golgi cisternae. Recently, we found that linking of Golgi membranes into a ribbon structure depends on GM130/GRASP65 complexes (Puthenveedu et al, 2006).…”

“…As described above, MEK1 mediates mitotic Golgi disassembly in permeabilized cells (Acharya et al, 1998), but in intact cells it may not be required (Draviam et al, 2001). Alternatively, its role in vivo in Golgi disassembly may not have been adequately tested due to ERK-independent activities (Colanzi et al, 2000) or its upstream role in cell cycle progression (Roovers and Assoian, 2000).…”

“…Additionally, interfering with MEK1 signaling via expression of dominant-negative mutants, use of chemical inhibitors, or RNA interference (RNAi) significantly delays mitotic entry (Wright et al, 1999;Roberts et al, 2002;Liu et al, 2004), suggesting the existence of a novel mitotic target of MEKmediated signaling that promotes mitotic entry. Surprisingly, one apparent mitotic target of MEK1 is the mammalian Golgi apparatus (Acharya et al, 1998). The Golgi consists of a contiguous network of laterally linked ministacks positioned at the microtubule-organizing center.…”

“…Reassembly is initiated in daughter cells at about the time of cytokinesis. Mitotic Golgi disassembly can be induced in permeabilized cells by using mitotic cytosol, and, under these conditions, MEK1 and Raf1 are required components (Acharya et al, 1998;Kano et al, 2000;Colanzi et al, 2003b). Active MEK/ERK complexes are in fact present on the Golgi due to their association with Golgi-localized Sef (Torii et al, 2004a).…”

The Ras‐ERK pathway: Understanding site‐specific signaling provides hope of new anti‐tumor therapies

“…However, ERKs extranuclear component is just as important. It has been estimated that half of the ERKs content remains in the cytoplasm after stimulation [62] and processes such as the formation of cell-matrix contacts, [63] adhesion, [64] endosomal traffic, [65] Golgi fragmentation, [66] and anti-apoptotic signaling [67] are dependent on ERK extranuclear activity. It fact, nearly half of the $180 proteins thus far identified as ERKs substrates, are non-nuclear proteins.…”