title: Mitogen-activated protein kinase kinase 1-dependent Golgi unlinking occurs in G2 phase and promotes the G2/M cell cycle transition.
abstract: Two controversies have emerged regarding the signaling pathways that regulate Golgi disassembly at the G(2)/M cell cycle transition. The first controversy concerns the role of mitogen-activated protein kinase activator mitogen-activated protein kinase kinase (MEK)1, and the second controversy concerns the participation of Golgi structure in a novel cell cycle "checkpoint." A potential simultaneous resolution is suggested by the hypothesis that MEK1 triggers Golgi unlinking in late G(2) to control G(2)/M kinetics. Here, we show that inhibition of MEK1 by RNA interference or by using the MEK1/2-specific inhibitor U0126 delayed the passage of synchronized HeLa cells into M phase. The MEK1 requirement for normal mitotic entry was abrogated if Golgi proteins were dispersed before M phase by treatment of cells with brefeldin A or if GRASP65, which links Golgi stacks into a ribbon network, was depleted. Imaging revealed that unlinking of the Golgi apparatus begins before M phase, is independent of cyclin-dependent kinase 1 activation, and requires MEK signaling. Furthermore, expression of the GRASP family member GRASP55 after alanine substitution of its MEK1-dependent mitotic phosphorylation sites inhibited both late G(2) Golgi unlinking and the G(2)/M transition. Thus, MEK1 plays an in vivo role in Golgi reorganization, which regulates cell cycle progression.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
authors.forename: Timothy N
authors.initials: TN
authors.lastname: Feinstein
authors.forename: Adam D
authors.initials: AD
authors.lastname: Linstedt
mesh_terms: D002455:Cell Division / Q000235:genetics; D016195:G2 Phase / Q000235:genetics; D006056:Golgi Apparatus / Q000201:enzymology*; D000077614:Golgi Matrix Proteins; D006367:HeLa Cells; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism; D008938:Mitosis / Q000235:genetics; D010766:Phosphorylation; D034622:RNA Interference
chemical_list: C122048:GORASP2 protein, human; D000077614:Golgi Matrix Proteins; D008565:Membrane Proteins; D048369:MAP Kinase Kinase 1