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Mol Biol Cell. Nov 2008; 19(11): 4852–4862.
PMCID: PMC2575180
Phosphatase Inhibitor-2 Balances Protein Phosphatase 1 and Aurora B Kinase for Chromosome Segregation and Cytokinesis in Human Retinal Epithelial Cells
Weiping Wang,* P. Todd Stukenberg, and David L. Brautigancorresponding author*
*Center for Cell Signaling,
Departments of Microbiology and
Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908
Yixian Zheng, Monitoring Editor
corresponding authorCorresponding author.
Address correspondence to: David L. Brautigan (db8g/at/virginia.edu)
Received May 6, 2008; Accepted August 8, 2008.
Abstract
Mitosis in Saccharomyces cerevisiae depends on IPL1 kinase, which genetically interacts with GLC8. The metazoan homologue of GLC8 is inhibitor-2 (I-2), but its function is not understood. We found endogenous and ectopic I-2 localized to the spindle, midzone, and midbody of mitotic human epithelial ARPE-19 cells. Knockdown of I-2 by RNA interference produced multinucleated cells, with supernumerary centrosomes, multipolar spindles and lagging chromosomes during anaphase. These defects did not involve changes in levels of protein phosphatase-1 (PP1), and the multinuclear phenotype was rescued by overexpression of I-2. Appearance of multiple nuclei and supernumerary centrosomes required progression through the cell cycle and I-2 knockdown cells failed cytokinesis, as observed by time-lapse microscopy. Inhibition of Aurora B by hesperadin produced multinucleated cells and reduced H3S10 phosphorylation. I-2 knockdown enhanced this latter effect. Partial knockdown of PP1Cα prevented multiple nuclei caused by either knockdown of I-2 or treatment with hesperadin. Expression of enhanced green fluorescent protein-I-2 or hemagglutinin-I-2 made cells resistant to hesperadin. We propose that I-2 acts to enhance Aurora B by inhibiting specific PP1 holoenzymes that dephosphorylate Aurora B substrates necessary for chromosome segregation and cytokinesis. Conserved together throughout eukaryotic evolution, I-2, PP1 and Aurora B function interdependently during mitosis.
Articles from Molecular Biology of the Cell are provided here courtesy of
American Society for Cell Biology