Dephosphorylation of Iqg1 by Cdc14 Regulates Cytokinesis in Budding Yeast
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Missouri University of Science and Technology Scholars' Mine Biological Sciences Faculty Research & Creative Works Biological Sciences 01 Jan 2015 Dephosphorylation of Iqg1 by Cdc14 Regulates Cytokinesis in Budding Yeast Daniel P. Miller Hana Kenton Hall Ryan Chaparian Madison Mara et. al. For a complete list of authors, see https://scholarsmine.mst.edu/biosci_facwork/97 Follow this and additional works at: https://scholarsmine.mst.edu/biosci_facwork Part of the Biology Commons Recommended Citation D. P. Miller et al., "Dephosphorylation of Iqg1 by Cdc14 Regulates Cytokinesis in Budding Yeast," Molecular Biology of the Cell, vol. 26, no. 16, pp. 2913-2926, American Society for Cell Biology, Jan 2015. The definitive version is available at https://doi.org/10.1091/mbc.E14-12-1637 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License. This Article - Journal is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in Biological Sciences Faculty Research & Creative Works by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. M BoC | ARTICLE Dephosphorylation of Iqg1 by Cdc14 regulates cytokinesis in budding yeast Daniel P. Millera, Hana Hallb, Ryan Chaparianb, Madison Maraa, Alison Muellera, Mark C. Hallb, and Katie B. Shannona aDepartment of Biological Sciences, Missouri University of Science and Technology, Rolla, MO 65401; bDepartment of Biochemistry, Purdue Center for Cancer Research, Purdue University, West Lafayette, IN 47907 ABSTRACT Cytokinesis separates cells by contraction of a ring composed of filamentous Monitoring Editor actin (F-actin) and type II myosin. Iqg1, an IQGAP family member, is an essential protein in Daniel J. Lew Saccharomyces cerevisiae required for assembly and contraction of the actomyosin ring. Lo- Duke University calization of F-actin to the ring occurs only after anaphase and is mediated by the calponin Received: Dec 22, 2014 homology domain (CHD) of Iqg1, but the regulatory mechanisms that temporally restrict ac- Revised: Jun 8, 2015 tin ring assembly are not well defined. We tested the hypothesis that dephosphorylation of Accepted: Jun 9, 2015 four perfect cyclin-dependent kinase (Cdk) sites flanking the CHD promotes actin ring forma- tion, using site-specific alanine mutants. Cells expressing the nonphosphorylatableiqg1-4A allele formed actin rings before anaphase and exhibited defects in myosin contraction and cytokinesis. The Cdc14 phosphatase is required for normal cytokinesis and acts on specific Cdk phosphorylation sites. Overexpression of Cdc14 resulted in premature actin ring assem- bly, whereas inhibition of Cdc14 function prevented actin ring formation. Cdc14 associated with Iqg1, dependent on several CHD-flanking Cdk sites, and efficiently dephosphorylated these sites in vitro. Of importance, the iqg1-4A mutant rescued the inability of cdc14-1 cells to form actin rings. Our data support a model in which dephosphorylation of Cdk sites around the Iqg1 CHD by Cdc14 is both necessary and sufficient to promote actin ring formation. Temporal control of actin ring assembly by Cdk and Cdc14 may help to ensure that cytokine- sis onset occurs after nuclear division is complete. INTRODUCTION Cytokinesis, the final step in cell division, divides the cytoplasm and Pollard, 1992; Fishkind and Wang, 1995). The actomyosin ring between two daughter cells. Precise temporal control is necessary is a transient structure that is precisely positioned to bisect the to coordinate cytokinesis and mitosis so that proper chromosome elongating anaphase spindle, ensuring proper chromosome segre- segregation can be completed. Cytokinetic failure results in tetra- gation (Pollard, 2010). In yeast, actomyosin ring contraction must ploid cells, and there is evidence that tetraploidy is an intermediate be coordinated with septation, the process of adding new cell wall state leading to chromosomal instability, aneuploidy, and tumori- material between the dividing cells (Bi, 2001). genesis (Ganem et al., 2007; Storchova and Kuffer, 2008). In animal In budding yeast, both actomyosin ring assembly and contrac- and fungal cells, cytokinesis is achieved by a ring composed of fila- tion are cell cycle regulated. The type II myosin heavy chain, Myo1, mentous actin (F-actin) and nonmuscle type II myosin (Satterwhite forms a ring at the bud neck in G1 (Bi et al., 1998; Lippincott and Li, 1998b). Localization of F-actin and contraction of the ring occur af- ter anaphase and require the essential protein Iqg1/Cyk1 (Epp and This article was published online ahead of print in MBoC in Press (http://www Chant, 1997; Lippincott and Li, 1998b; Lippincott et al., 2001). Iqg1 .molbiolcell.org/cgi/doi/10.1091/mbc.E14-12-1637) on June 17, 2015. is a 173-kDa scaffolding protein homologous to mammalian Address correspondence to: Katie B. Shannon ([email protected]). IQGAPs. IQGAP family members are essential for actin-based pro- Abbreviations used: Cdk, cyclin-dependent kinase; CHD, calponin homology domain; FEAR, fourteen early anaphase release; MEN, mitotic exit network. cesses such as phagocytosis, cell adhesion, migration, and cytokine- © 2015 Miller et al. This article is distributed by The American Society for Cell Bi- sis (Shannon, 2012; White et al., 2012). Iqg1 shares with other ology under license from the author(s). Two months after publication it is available IQGAPs multiple functional domains: an N-terminal calponin homol- to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0). ogy domain (CHD), IQ repeats, a GTPase-related domain (GRD), “ASCB®,” “The American Society for Cell Biology®,” and “Molecular Biology of and a Ras-GAP C-terminus (RGCt; Epp and Chant, 1997; Lippincott the Cell®” are registered trademarks of The American Society for Cell Biology. and Li, 1998a; Shannon, 2012). Iqg1 is recruited to the bud neck by Supplemental Material can be found at: Volume 26 August 15, 2015 http://www.molbiolcell.org/content/suppl/2015/06/14/mbc.E14-12-1637v1.DC1.html 2913 the myosin regulatory light chain, Mlc1, via interactions with the IQ primarily to promote proper spindle function and chromosome seg- domains (Boyne et al., 2000; Shannon and Li, 2000). Iqg1 recruit- regation. After chromosome segregation is completed, the MEN ment to the ring is restricted to mitosis even though Mlc1 localizes triggers widespread release of Cdc14 to the cytoplasm (Queralt and to the bud neck earlier in the cell cycle (Boyne et al., 2000; Shannon Uhlmann, 2008; Uhlmann et al., 2011). Although many Cdc14 target and Li, 2000). Iqg1 binds F-actin via the CHD and recruits F-actin to proteins required for mitotic exit and other mitotic events are well the bud neck during anaphase/telophase of mitosis, which com- characterized, a direct role for Cdc14 in regulating actomyosin ring pletes actomyosin ring assembly (Shannon and Li, 1999). The C- assembly has not previously been described. terminus of Iqg1, containing both the GRD and RGCt domains, in- In the yeast Candida albicans, the Igq1 homologue is phosphor- teracts with the GTPase Tem1 and is required for contraction of the ylated in vitro by the cyclin-dependent kinase Cdk1. Mutation of 15 actomyosin ring (Shannon and Li, 1999). Tem1 is part of the mitotic minimal Cdk1 consensus sites (S/T-P) in Iqg1 flanking the CHD re- exit network (MEN), and temperature-sensitive alleles of Tem1 and sulted in premature assembly and delayed disassembly of the acto- other MEN proteins cause mitotic arrest in late anaphase before myosin ring, resulting in cytokinesis defects (Li et al., 2008). Budding cytokinesis (Jaspersen et al., 1998; McCollum and Gould, 2001). yeast Iqg1 is phosphorylated in vivo by Cdk1 (Holt et al., 2009), and The MEN, a signaling cascade that leads to the full release and a recent report demonstrated that loss of various combinations of activity of the phosphatase Cdc14, regulates mitotic exit, cytokine- N-terminal Cdk1 sites caused premature recruitment of Iqg1 and sis, and septation in budding yeast (Bardin and Amon, 2001; Meit- actin filaments to the contractile ring (Naylor and Morgan, 2014). inger et al., 2012). The MEN brings about exit from mitosis by inac- Although there are 20 minimal consensus Cdk sites (S/T-P) in bud- tivating the mitotic cyclin-dependent kinase 1 (Cdk1). Cdk1, or ding yeast Iqg1, only 4 match the strict Cdk consensus motif S/T-P- Cdc28-Clb2 in budding yeast, is inactivated during anaphase via x-R/K, and these are all adjacent to the CHD near the Iqg1 N-termi- two partially redundant methods: inhibition of its kinase activity by nus. Recently, Cdc14 was shown to possess specificity for the Sic1 and degradation of the mitotic cyclin Clb2 by the APCCdh1 com- phosphoserine subset of the perfect Cdk consensus sites, and 3 of plex (Jaspersen et al., 1998; Visintin et al., 1998). Both Sic1 and the CHD-flanking Cdk consensus sites also match the consensus for Cdh1 become active once dephosphorylated by the MEN compo- dephosphorylation by Cdc14 (Bremmer et al., 2012; Eissler et al., nent Cdc14, leading to inhibition of Cdk1 activity (Visintin et al., 2014). We hypothesized that dephosphorylation of these Cdk sites 1998). When Cdk1 activity drops, MEN proteins Cdc15, Dbf2-Mob1, by Cdc14 is important for controlling Iqg1 function in cytokinesis. In Dbf20-Mob1, and Cdc14 all accumulate to the bud neck by an un- this study we present genetic, cell biological, and biochemical evi- known mechanism, where they are positioned to regulate cytokine- dence supporting this hypothesis and demonstrate that dephos- sis and septation (Bembenek et al., 2005; Meitinger et al., 2012). phorylation of Iqg1 by Cdc14 is required for normal assembly of Although Cdk1 must be inactivated in order for actomyosin ring Iqg1 and F-actin in the contractile ring, providing insight into the assembly and contraction to occur, the MEN has a role in promoting mechanism of temporal regulation of cytokinesis.