241 human active and 13 inactive phosphatases in total;
194 phosphatases have substrate data;
336 protein substrates;
83 non-protein substrates;
1215 dephosphorylation interactions;
299 KEGG pathways;
876 Reactome pathways;
last scientific update: 11 Mar, 2019
last maintenance update: 01 Sep, 2023
Nucleus Chromosome, centromere,kinetochore Cytoplasm, cytoskeleton, microtubule organizingcenter, centrosome Cytoplasm,cytoskeleton, spindle MidbodyNote=localization at the centrosome starts at the G1/S transition(PubMed:24018379) During early stages of mitosis, thephosphorylated form is detected on centrosomes and kinetochoresLocalizes to the outer kinetochore Presence of SGO1 andinteraction with the phosphorylated form of BUB1 is required forthe kinetochore localization Localizes onto the central spindleby phosphorylating and docking at midzone proteins KIF20A/MKLP2and PRC1 Colocalizes with FRY to separating centrosomes andspindle poles from prophase to metaphase in mitosis, but not inother stages of the cell cycle Localization to the centrosome isrequired for S phase progression (PubMed:24018379) Colocalizeswith HSF1 at the spindle poles during prometaphase(PubMed:18794143)
Function (UniProt annotation)
Serine/threonine-protein kinase that performs severalimportant functions throughout M phase of the cell cycle,including the regulation of centrosome maturation and spindleassembly, the removal of cohesins from chromosome arms, theinactivation of anaphase-promoting complex/cyclosome (APC/C)inhibitors, and the regulation of mitotic exit and cytokinesisPolo-like kinase proteins acts by binding and phosphorylatingproteins are that already phosphorylated on a specific motifrecognized by the POLO box domains Phosphorylates BORA,BUB1B/BUBR1, CCNB1, CDC25C, CEP55, ECT2, ERCC6L, FBXO5/EMI1,FOXM1, KIF20A/MKLP2, CENPU, NEDD1, NINL, NPM1, NUDC, PKMYT1/MYT1,KIZ, PPP1R12A/MYPT1, PRC1, RACGAP1/CYK4, SGO1, STAG2/SA2, TEX14,TOPORS, p73/TP73, TPT1, WEE1 and HNRNPU Plays a key role incentrosome functions and the assembly of bipolar spindles byphosphorylating KIZ, NEDD1 and NINL NEDD1 phosphorylationpromotes subsequent targeting of the gamma-tubulin ring complex(gTuRC) to the centrosome, an important step for spindleformation Phosphorylation of NINL component of the centrosomeleads to NINL dissociation from other centrosomal proteinsInvolved in mitosis exit and cytokinesis by phosphorylating CEP55,ECT2, KIF20A/MKLP2, CENPU, PRC1 and RACGAP1 Recruited at thecentral spindle by phosphorylating and docking PRC1 andKIF20A/MKLP2; creates its own docking sites on PRC1 andKIF20A/MKLP2 by mediating phosphorylation of sites subsequentlyrecognized by the POLO box domains Phosphorylates RACGAP1,thereby creating a docking site for the Rho GTP exchange factorECT2 that is essential for the cleavage furrow formation Promotesthe central spindle recruitment of ECT2 Plays a central role inG2/M transition of mitotic cell cycle by phosphorylating CCNB1,CDC25C, FOXM1, CENPU, PKMYT1/MYT1, PPP1R12A/MYPT1 and WEE1 Partof a regulatory circuit that promotes the activation of CDK1 byphosphorylating the positive regulator CDC25C and inhibiting thenegative regulators WEE1 and PKMYT1/MYT1 Also acts by mediatingphosphorylation of cyclin-B1 (CCNB1) on centrosomes in prophasePhosphorylates FOXM1, a key mitotic transcription regulator,leading to enhance FOXM1 transcriptional activity Involved inkinetochore functions and sister chromatid cohesion byphosphorylating BUB1B/BUBR1, FBXO5/EMI1 and STAG2/SA2 PLK1 ishigh on non-attached kinetochores suggesting a role of PLK1 inkinetochore attachment or in spindle assembly checkpoint (SAC)regulation Required for kinetochore localization of BUB1BRegulates the dissociation of cohesin from chromosomes byphosphorylating cohesin subunits such as STAG2/SA2 PhosphorylatesSGO1: required for spindle pole localization of isoform 3 of SGO1and plays a role in regulating its centriole cohesion functionMediates phosphorylation of FBXO5/EMI1, a negative regulator ofthe APC/C complex during prophase, leading to FBXO5/EMI1ubiquitination and degradation by the proteasome Acts as anegative regulator of p53 family members: phosphorylates TOPORS,leading to inhibit the sumoylation of p53/TP53 and simultaneouslyenhance the ubiquitination and subsequent degradation of p53/TP53Phosphorylates the transactivation domain of the transcriptionfactor p73/TP73, leading to inhibit p73/TP73-mediatedtranscriptional activation and pro-apoptotic functionsPhosphorylates BORA, and thereby promotes the degradation of BORAContributes to the regulation of AURKA function Also required forrecovery after DNA damage checkpoint and entry into mitosisPhosphorylates MISP, leading to stabilization of cortical andastral microtubule attachments required for proper spindlepositioning (PubMed:8991084, PubMed:11202906, PubMed:12207013,PubMed:12447691, PubMed:12524548, PubMed:12738781,PubMed:12852856, PubMed:12939256, PubMed:14532005,PubMed:14734534, PubMed:15070733, PubMed:15148369,PubMed:15469984, PubMed:16198290, PubMed:16247472,PubMed:16980960, PubMed:17081991, PubMed:17351640,PubMed:17376779, PubMed:17617734, PubMed:18174154,PubMed:18331714, PubMed:18418051, PubMed:18477460,PubMed:18521620, PubMed:18615013, PubMed:19160488,PubMed:19351716, PubMed:19468300, PubMed:19468302,PubMed:19473992, PubMed:19509060, PubMed:19597481,PubMed:23455478, PubMed:23509069) Together with MEIKIN, acts as aregulator of kinetochore function during meiosis I: required bothfor mono-orientation of kinetochores on sister chromosomes andprotection of centromeric cohesin from separase-mediated cleavage(By similarity) Phosphorylates CEP68 and is required for itsdegradation (PubMed:25503564) Regulates nuclear envelopebreakdown during prophase by phosphorylating DCTN1 resulting inits localization in the nuclear envelope (PubMed:20679239)Phosphorylates the heat shock transcription factor HSF1, promotingHSF1 nuclear translocation upon heat shock (PubMed:15661742)Phosphorylates HSF1 also in the early mitotic period; thisphosphorylation regulates HSF1 localization to the spindle pole,the recruitment of the SCF(BTRC) ubiquitin ligase complexinduicing HSF1 degradation, and hence mitotic progression(PubMed:18794143) Regulates mitotic progression byphosphorylating RIOK2 (PubMed:21880710)
The forkhead box O (FOXO) family of transcription factors regulates the expression of genes in cellular physiological events including apoptosis, cell-cycle control, glucose metabolism, oxidative stress resistance, and longevity. A central regulatory mechanism of FOXO proteins is phosphorylation by the serine-threonine kinase Akt/protein kinase B (Akt/PKB), downstream of phosphatidylinositol 3-kinase (PI3K), in response to insulin or several growth factors. Phosphorylation at three conserved residues results in the export of FOXO proteins from the nucleus to the cytoplasm, thereby decreasing expression of FOXO target genes. In contrast, the stress-activated c-Jun N-terminal kinase (JNK) and the energy sensing AMP-activated protein kinase (AMPK), upon oxidative and nutrient stress stimuli phosphorylate and activate FoxOs. Aside from PKB, JNK and AMPK, FOXOs are regulated by multiple players through several post-translational modifications, including phosphorylation, but also acetylation, methylation and ubiquitylation.
Mitotic cell cycle progression is accomplished through a reproducible sequence of events, DNA replication (S phase) and mitosis (M phase) separated temporally by gaps known as G1 and G2 phases. Cyclin-dependent kinases (CDKs) are key regulatory enzymes, each consisting of a catalytic CDK subunit and an activating cyclin subunit. CDKs regulate the cell's progression through the phases of the cell cycle by modulating the activity of key substrates. Downstream targets of CDKs include transcription factor E2F and its regulator Rb. Precise activation and inactivation of CDKs at specific points in the cell cycle are required for orderly cell division. Cyclin-CDK inhibitors (CKIs), such as p16Ink4a, p15Ink4b, p27Kip1, and p21Cip1, are involved in the negative regulation of CDK activities, thus providing a pathway through which the cell cycle is negatively regulated.Eukaryotic cells respond to DNA damage by activating signaling pathways that promote cell cycle arrest and DNA repair. In response to DNA damage, the checkpoint kinase ATM phosphorylates and activates Chk2, which in turn directly phosphorylates and activates p53 tumor suppressor protein. p53 and its transcriptional targets play an important role in both G1 and G2 checkpoints. ATR-Chk1-mediated protein degradation of Cdc25A protein phosphatase is also a mechanism conferring intra-S-phase checkpoint activation.
During meiosis, a single round of DNA replication is followed by two rounds of chromosome segregation, called meiosis I and meiosis II. At meiosis I, homologous chromosomes recombine and then segregate to opposite poles, while the sister chromatids segregate from each other at meoisis II. In vertebrates, immature oocytes are arrested at the PI (prophase of meiosis I). The resumption of meiosis is stimulated by progesterone, which carries the oocyte through two consecutive M-phases (MI and MII) to a second arrest at MII. The key activity driving meiotic progression is the MPF (maturation-promoting factor), a heterodimer of CDC2 (cell division cycle 2 kinase) and cyclin B. In PI-arrested oocytes, MPF is initially inactive and is activated by the dual-specificity CDC25C phosphatase as the result of new synthesis of Mos induced by progesterone. MPF activation mediates the transition from the PI arrest to MI. The subsequent decrease in MPF levels, required to exit from MI into interkinesis, is induced by a negative feedback loop, where CDC2 brings about the activation of the APC (anaphase-promoting complex), which mediates destruction of cyclin B. Re-activation of MPF for MII requires re-accumulation of high levels of cyclin B as well as the inactivation of the APC by newly synthesized Emi2 and other components of the CSF (cytostatic factor), such as cyclin E or high levels of Mos. CSF antagonizes the ubiquitin ligase activity of the APC, preventing cyclin B destruction and meiotic exit until fertilization occurs. Fertilization triggers a transient increase in cytosolic free Ca2+, which leads to CSF inactivation and cyclin B destruction through the APC. Then eggs are released from MII into the first embryonic cell cycle.
Xenopus oocytes are naturally arrested at G2 of meiosis I. Exposure to either insulin/IGF-1 or the steroid hormone progesterone breaks this arrest and induces resumption of the two meiotic division cycles and maturation of the oocyte into a mature, fertilizable egg. This process is termed oocyte maturation. The transition is accompanied by an increase in maturation promoting factor (MPF or Cdc2/cyclin B) which precedes germinal vesicle breakdown (GVBD). Most reports point towards the Mos-MEK1-ERK2 pathway [where ERK is an extracellular signal-related protein kinase, MEK is a MAPK/ERK kinase and Mos is a p42(MAPK) activator] and the polo-like kinase/CDC25 pathway as responsible for the activation of MPF in meiosis, most likely triggered by a decrease in cAMP.
The signal from unattached kinetochores is amplified through a Mad2 inhibitory signal that is propagated by the binding of Mad1 to the kinetochore, the association of Mad2 with Mad1, the conversion of Mad2 conformation to an inhibitory form through its association with Mad1 and finally the release of the inhibitory form of Mad2 from the kinetochore
At mitotic entry, Plk1 phosphorylates and activates Cdc25C phosphatase, whereas it phosphorylates and down-regulates Wee1A (Watanabe et al. 2004). Plk1 also phosphorylates and inhibits Myt1 activity (Sagata 2005). Cyclin B1-bound Cdc2, which is the target of Cdc25C, Wee1A, and Myt1, functions in a feedback loop and phosphorylates the latter components (Cdc25C, Wee1A, Myt1). The Cdc2- dependent phosphorylation provides docking sites for the polo-box domain of Plk1, thus promoting the Plk1-dependent regulation of these components and, as a result, activation of Cdc2-Cyclin B1.
PLK1 phosphorylates and activates the transcription factor FOXM1 which stimulates the expression of a number of genes needed for G2/M transition, including PLK1, thereby creating a positive feedback loop (Laoukili et al. 2005, Fu et al. 2008, Sadasivam et al. 2012, Chen et al. 2013)
The pericentriolar stacks of Golgi cisternae undergo extensive fragmentation and reorganization in mitosis. In mammalian cells, Golgi apparatus consists of stacked cisternae that are connected by tubules to form a ribbon-like structure in the perinuclear region, in vicinity of the centrosome. Reorganization of the Golgi apparatus during cell division allows both daughter cells to inherit this organelle, and may play additional roles in the organization of the mitotic spindle. First changes in the structure of the Golgi apparatus likely start in G2 and are subtle, involving unlinking of the Golgi ribbon into separate stacks. These changes are required for the entry of mammalian cells into mitosis (Sutterlin et al. 2002). This initial unlinking of the Golgi ribbon depends on GRASP proteins and on CTBP1 (BARS) protein, which induces the cleavage of the tubular membranes connecting the stacks (Hidalgo Carcedo et al. 2004, Colanzi et al. 2007), but the exact mechanism is not known. Activation of MEK1/2 also contributes to unlinking of the Golgi ribbon in G2 (Feinstein and Linstedt 2007). From prophase to metaphase, Golgi cisternae undergo extensive fragmentation that is a consequence of unstacking of Golgi cisternae and cessation of transport through Golgi. At least three mitotic kinases, CDK1, PLK1 and MEK1, regulate these changes. CDK1 in complex with cyclin B phosphorylates GOLGA2 (GM130) and GORASP1 (GRASP65), constituents of a cis-Golgi membrane complex (Lowe et al. 1998, Preisinger et al. 2005). Phosphorylation of GOLGA2 prevents binding of USO1 (p115), a protein localizing to the membrane of ER (endoplasmic reticulum) to Golgi transport vesicles and cis-Golgi, thereby impairing fusion of these vesicles with cis-Golgi cisternae and stopping ER to Golgi transport (Lowe et al. 1998, Seeman et al. 2000, Moyer et al. 2001). Phosphorylation of GORASP1 by CDK1 enables further phosphorylation of GORASP1 by PLK1 (Sutterlin et al. 2001, Preisinger et al. 2005). Phosphorylation of GORASP1 by CDK1 and PLK1 impairs stacking of Golgi cisternae by interfering with formation of GORASP1 trans-oligomers that would normally link the Golgi cisternae together (Wang et al. 2003, Wang et al. 2005, Sengupta and Linstedt 2010). In the median Golgi, GORASP2 (GRASP55), a protein that forms a complex with BLFZ1 (Golgin-45) and RAB2A GTPase and contributes to cisternae stacking and Golgi trafficking (Short et al. 2001), is also phosphorylated in mitosis. Phosphorylation of GORASP2 by MEK1/2-activated MAPK1 (ERK2) and/or MAPK3-3 (ERK1b in human, Erk1c in rat) contributes to Golgi unlinking in G2 and fragmentation of Golgi cisternae in mitotic prophase (Acharya et al. 1998, Jesch et al. 2001, Colanzi et al. 2003, Shaul and Seger 2006, Duran et al. 2008, Feinstein and Linstedt 2007, Feinstein and Linstedt 2008, Xiang and Wang 2010)
From late mitosis through G1 phase APC/C:Cdh1 insures the continued degradation of the mitotic proteins and during mitotic exit and G1 its substrates include Cdc20, Plk1, Aurora A, Cdc6 and Geminin (see Castro et al., 2005). Rape et al. have recently demonstrated that the order in which APC/C targeted proteins are degraded is determined by the processivity of multiubiquitination of these substrates. Processive substrates acquire a polyubiquitin chain upon binding to the APC/C once and are degraded. Distributive substrates bind, dissociate and reassociate with the APC/C multiple times before acquiring an ubiquitin chain of sufficient length to insure degradation. In addition, distributive substrates that dissociate from the APC/C with short ubiquitin chains are targeted for deubiquitination (Rape et al., 2006)
Phosphorylation of APC subunits is required for Cdc20 mediated activation by of the APC/C at the metaphase anaphase transition (Kramer et al., 2000). While the kinases responsible for phosphorylation in vivo have not been determined with certainty, both Plk1 and Cyclin B:Cdc2 have been implicated in this process
In mitotic prophase, the action of the condensin II complex enables initial chromosome condensation.The condensin II complex subunit NCAPD3 binds monomethylated histone H4 (H4K20me1), thereby associating with chromatin (Liu et al. 2010). Binding of the condensin II complex to chromatin is partially controlled by the presence of RB1 (Longworth et al. 2008). Two mechanisms contribute to the accumulation of H4K20me1 at mitotic entry. First, the activity of SETD8 histone methyltransferase peaks at G2/M transition (Nishioka et al. 2002, Rice et al. 2002, Wu et al. 2010). Second, the complex of CDK1 and cyclin B1 (CDK1:CCNB1) phosphorylates PHF8 histone demethylase at the start of mitosis, removing it from chromatin (Liu et al. 2010).Condensin II complex needs to be phosphorylated by the CDK1:CCNB1 complex, and then phosphorylated by PLK1, in order to efficiently condense prophase chromosomes (Abe et al. 2011)
While sister chromatids resolve in prometaphase, separating along chromosomal arms, the cohesion of sister centromeres persists until anaphase. At the anaphase onset, the anaphase promoting complex/cyclosome (APC/C) ubiquitinates PTTG1 (securin), targeting it for degradation (Hagting et al. 2002). PTTG1 acts as an inhibitor of ESPL1 (known as separin i.e. separase). Hence, PTTG1 removal initiated by APC/C, enables ESPL1 to become catalytically active (Zou et al. 1999, Waizenegger et al. 2002). ESPL1 undergoes autoleavage (Waizenegger et al. 2002) and also cleaves RAD21 subunit of centromeric cohesin (Hauf et al. 2001). RAD21 cleavage promotes dissociation of cohesin complexes from sister centromeres, leading to separation of sister chromatids. Subsequent movement of sister chromatids to opposite poles of the mitotic spindle segregates replicated chromosomes to two daughter cells (Waizenegger et al. 2000, Hauf et al. 2001, Waizenegger et al. 2002)
The resolution of sister chromatids in mitotic prometaphase involves removal of cohesin complexes from chromosomal arms, with preservation of cohesion at centromeres (Losada et al. 1998, Hauf et al. 2001, Hauf et al. 2005). CDK1-mediated phosphorylation of cohesin-bound CDCA5 (Sororin) at threonine T159 provides a docking site for PLK1, enabling PLK1-mediated phosphorylation of cohesin subunits STAG2 (SA2) and RAD21 (Hauf et al. 2005, Dreier et al. 2011, Zhang et al. 2011). Further phosphorylation of CDCA5 by CDK1 results in dissociation of CDCA5 from cohesin complex, which restores the activity of WAPAL in removing STAG2-phosphorylated cohesin from chromosomal arms (Hauf et al. 2005, Gandhi et al. 2006, Kueng et al. 2006, Shintomi and Hirano 2006, Nishiyama et al. 2010, Zhang et al. 2011). At centromeres, kinetochore proteins shugoshins (SGOL1 and SGOL2) enable PP2A-B56 (also a kinetochore constituent) to dephosphorylate the STAG2 subunit of centromeric cohesin. Dephosphorylation of STAG2 enables maintenance of centromeric cohesion, thus preventing separation of sister chromatids until anaphase (Salic et al. 2004, Kitajima et al. 2004, Kitajima et al. 2005, Kitajima et al. 2006)
The kinase activity of PLK1 is required for cell cycle progression as PLK1 phosphorylates and regulates a number of cellular proteins during mitosis. Centrosomic AURKA (Aurora A kinase), catalytically activated through AJUBA facilitated autophosphorylation on threonine residue T288 at G2/M transition (Hirota et al. 2003), activates PLK1 on centrosomes by phosphorylating threonine residue T210 of PLK1, critical for PLK1 activity (Jang et al. 2002), in the presence of BORA (Macurek et al. 2008, Seki et al. 2008). Once activated, PLK1 phosphorylates BORA and targets it for ubiquitination mediated degradation by SCF-beta-TrCP ubiquitin ligases. Degradation of BORA is thought to allow PLK1 to interact with other substrates (Seki, Coppinger, Du et al. 2008, Seki et al. 2008).The interaction of PLK1 with OPTN (optineurin) provides a negative-feedback mechanism for regulation of PLK1 activity. Phosphorylated PLK1 binds and phosphorylates OPTN associated with the Golgi membrane GTPase RAB8, promoting dissociation of OPTN from Golgi and translocation of OPTN to the nucleus. Phosphorylated OPTN facilitates the mitotic phosphorylation of the myosin phosphatase subunit PPP1R12A (MYPT1) and myosin phosphatase activation (Kachaner et al. 2012). The myosin phosphatase complex dephosphorylates threonine residue T210 of PLK1 and inactivates PLK1 (Yamashiro et al. 2008)
NEK6 and NEK7 are activated during mitosis by another NIMA family kinase, NEK9 (Belham et al. 2003, Richards et al. 2009), which is activated by CDK1- and PLK1-mediated phosphorylation (Roig et al. 2002, Bertran et al. 2011)
During interphase, Nlp interacts with gamma-tubulin ring complexes (gamma-TuRC), and is thought to contribute to the organization of interphase microtubules (Casenghi et al.,2003). Plk1 is activated at the onset of mitosis and phosphorylates Nlp triggering its displacement from the centrosome (Casenghi et al.,2003). Removal of Nlp appears to contribute to the establishment of a mitotic scaffold with enhanced microtubule nucleation activity
The mitotic spindle becomes established once centrosomes have\r migrated to opposite poles and the nuclear envelope has broken down. During this stage, interphase centrosomes mature into mitotic centrosomes\r recruiting additional gamma TuRC complexes and acquiring mitosis-associated centrosomal proteins including NuMA, Plk1 and CDK11p58 (reviewed in Schatten 2008; Raynaud-Messina and Merdes 2007)
In addition to recruiting proteins and complexes necessary for increased microtubule nucleation, centrosomal maturation involves the loss of proteins involved in interphase microtubule organization and centrosome cohesion (Casenghi et al., 2003; Mayor et al., 2002)
The NuMA protein, which functions as a nuclear matrix protein in interphase (Merdes and Cleveland 1998), redistributes to the cytoplasm following nuclear envelope breakdown where it plays an essential role in formation and maintenance of the spindle poles (Gaglio, et al., 1995; Gaglio, et al., 1996; Merdes et al, 1996). The mitotic activation of NuMA involves Ran-GTP-dependent dissociation from importin (Nachury et al, 2001, Wiese et al, 2001). NuMA is transported to the mitotic poles where it forms an insoluble crescent around centrosomes tethering microtubules into the bipolar configuration of the mitotic apparatus (Merdes et al., 2000; Kisurina-Evgenieva et al, 2004). Although NuMA is not a bona fide constituent of the mitotic centrosome but rather a protein associated with microtubules at the spindle pole, specific splice variants of NuMA have been identified that associate with the centrosome during interphase (Tang et al, 1994)
Cilium biogenesis is initiated by the docking of basal bodies, a centriole-derived organelle, to the plasma membrane (reviewed in Reiter et al, 2012). The centriole consists of a multiprotein core surrounded by a ring of nine microtubule triplets; the mother centriole additionally has 'distal' and 'subdistal appendages' that are critical for ciliogenesis (reviewed in Kim and Dynlacht, 2013; Firat-Karalar and Stearns, 2014; Bettencourt-Dias et al, 2011). Basal bodies initiate and anchor the extension of the axonemal microtubules and also associate with secretory vesicles which are thought to provide membrane components for the extension of the ciliary membrane (Sorokin, 1962; Sorokin, 1968; Bachmann-Gagescu et al, 2011; Tanos et al, 2013; reviewed in Ishikawa et al, 2011; Reiter et al, 2012). Basal bodies are attached to the plasma membrane through a proteinaceous network of transition fibers that form part of the 'transition zone' at the ciliary base. The transition zone acts as a selective barrier or ciliary pore, excluding vesicles and limiting the diffusion of proteins and lipids from the cytosol or plasma membrane (Deane et al, 2001; Craige et al, 2010; Garcia-Gonzalo et al, 2011; Ye et al, 2014; Joo et al, 2013; reviewed in Nachury et al, 2010; Hsiao et al, 2012; Reiter et al, 2012). In addition to the transition fibres, the transition zone also consists of the ciliary necklace (a row of protein particles at the ciliary membrane at the base of the cilium) and the Y-links (that connect the axonemal microtubules to the membrane at the ciliary necklace) (Williams et al, 2011; reviewed in Hsiao et al, 2012; Reiter et al, 2012)
Formins are a family of proteins with 15 members in mammals, organized into 8 subfamilies. Formins are involved in the regulation of actin cytoskeleton. Many but not all formin family members are activated by RHO GTPases. Formins that serve as effectors of RHO GTPases belong to different formin subfamilies but they all share a structural similarity to Drosophila protein diaphanous and are hence named diaphanous-related formins (DRFs).
DRFs activated by RHO GTPases contain a GTPase binding domain (GBD) at their N-terminus, followed by formin homology domains 3, 1, and 2 (FH3, FH1, FH2) and a diaphanous autoregulatory domain (DAD) at the C-terminus. Most DRFs contain a dimerization domain (DD) and a coiled-coil region (CC) in between FH3 and FH1 domains (reviewed by Kuhn and Geyer 2014). RHO GTPase-activated DRFs are autoinhibited through the interaction between FH3 and DAD which is disrupted upon binding to an active RHO GTPase (Li and Higgs 2003, Lammers et al. 2005, Nezami et al. 2006). Since formins dimerize, it is not clear whether the FH3-DAD interaction is intra- or intermolecular. FH2 domain is responsible for binding to the F-actin and contributes to the formation of head-to-tail formin dimers (Xu et al. 2004). The proline-rich FH1 domain interacts with the actin-binding proteins profilins, thereby facilitating actin recruitment to formins and accelerating actin polymerization (Romero et al. 2004, Kovar et al. 2006).
Different formins are activated by different RHO GTPases in different cell contexts. FMNL1 (formin-like protein 1) is activated by binding to the RAC1:GTP and is involved in the formation of lamellipodia in macrophages (Yayoshi-Yamamoto et al. 2000) and is involved in the regulation of the Golgi complex structure (Colon-Franco et al. 2011). Activation of FMNL1 by CDC42:GTP contributes to the formation of the phagocytic cup (Seth et al. 2006). Activation of FMNL2 (formin-like protein 2) and FMNL3 (formin-like protein 3) by RHOC:GTP is involved in cancer cell motility and invasiveness (Kitzing et al. 2010, Vega et al. 2011). DIAPH1, activated by RHOA:GTP, promotes elongation of actin filaments and activation of SRF-mediated transcription which is inhibited by unpolymerized actin (Miralles et al. 2003). RHOF-mediated activation of DIAPH1 is implicated in formation of stress fibers (Fan et al. 2010). Activation of DIAPH1 and DIAPH3 by RHOB:GTP leads to actin coat formation around endosomes and regulates endosome motility and trafficking (Fernandez-Borja et al. 2005, Wallar et al. 2007). Endosome trafficking is also regulated by DIAPH2 transcription isoform 3 (DIAPH2-3) which, upon activation by RHOD:GTP, recruits SRC kinase to endosomes (Tominaga et al. 2000, Gasman et al. 2003). DIAPH2 transcription isoform 2 (DIAPH2-2) is involved in mitosis where, upon being activated by CDC42:GTP, it facilitates the capture of astral microtubules by kinetochores (Yasuda et al. 2004, Cheng et al. 2011). DIAPH2 is implicated in ovarian maintenance and premature ovarian failure (Bione et al. 1998). DAAM1, activated by RHOA:GTP, is involved in linking WNT signaling to cytoskeleton reorganization (Habas et al. 2001)
The dissolution of the nuclear membrane marks the beginning of the prometaphase. Kinetochores are created when proteins attach to the centromeres. Microtubules then attach at the kinetochores, and the chromosomes begin to move to the metaphase plate
In this final phase of mitosis, new membranes are formed around two sets of chromatids and two daughter cells are formed. The chromosomes and the spindle fibers disperse, and the fiber ring around the center of the cell, composed of actin, contracts, pinching the cell into two daughter cells
Cell cycle progression is regulated by cyclin-dependent protein kinases at both the G1/S and the G2/M transitions. The G2/M transition is regulated through the phosphorylation of nuclear lamins and histones (reviewed in Sefton, 2001).The two B-type cyclins localize to different regions within the cell and are thought to have specific roles as CDK1-activating subunits (see Bellanger et al., 2007). Cyclin B1 is primarily cytoplasmic during interphase and translocates into the nucleus at the onset of mitosis (Jackman et al., 1995; Hagting et al., 1999). Cyclin B2 colocalizes with the Golgi apparatus and contributes to its fragmentation during mitosis (Jackman et al., 1995; Draviam et al., 2001)
GTSE1 (B99) was identified as a microtubule-associated protein product of the mouse B99 gene, which exhibits both a cell cycle regulated expression, with highest levels in G2, and DNA damage triggered expression under direct control of TP53 (p53) (Utrera et al. 1998, Collavin et al. 2000). Human GTSE1, similar to the mouse counterpart, binds to microtubules, shows cell cycle regulated expression with a peak in G2 and plays a role in G2 checkpoint recovery after DNA damage but is not transcriptionally regulated by TP53 (Monte et al. 2003, Monte et al. 2004, Scolz et al. 2012).
In G1 cells, GTSE1 is found at the microtubule lattice, likely due to direct binding to tubulin. An evolutionarily conserved interaction between GTSE1 and MAPRE1 (EB1), a microtubule plus end protein, promotes GTSE1 localization to the growing tip of the microtubules, which contributes to cell migration and is likely involved in cancer cell invasiveness. Highly invasive breast cancer cell lines exhibit high GTSE1 levels in G1, while GTSE1 levels in G1 are normally low. At the beginning of mitotic prometaphase, GTSE1 is phosphorylated by mitotic kinase(s), possibly CDK1, in proximity to the MAPRE1-binding region, causing GTSE1 dissociation from the plus end microtubule ends (Scolz et al. 2012).
During G2 checkpoint recovery (cell cycle re-entry after DNA damage induced G2 arrest), GTSE1 relocates to the nucleus where it binds TP53 and, in an MDM2-dependent manner, promotes TP53 cytoplasmic translocation and proteasome mediated degradation (Monte et al. 2003, Monte et al. 2004). Relocation of GTSE1 to the nucleus in G2 phase depends on PLK1-mediated phosphorylation of GTSE1 (Liu et al. 2010).
GTSE1-facilitated down-regulation of TP53 in G2 allows cells to avoid TP53 mediated apoptosis upon DNA damage and to re-enter cell cycle (Monte et al. 2003). While TP53 down-regulation mediated by GTSE1 in G2 correlates with decreased expression of TP53 target genes involved in apoptosis and cell cycle arrest, GTSE1 can also increase the half-life of the TP53 target p21 (CDKN1A). GTSE1-mediated stabilization of CDKN1A involves interaction of GTSE1 with CDKN1A and its chaperone complex, consisting of HSP90 and FKBPL (WISp39), and may be involved in resistance to paclitaxel treatment (Bublik et al. 2010)
TPX2 binds to aurora kinase A (AURKA) at centrosomes and promotes its activation by facilitating AURKA active conformation and autophosphorylation of the AURKA threonine residue T288 (Bayliss et al. 2003, Xu et al. 2011, Giubettini et al. 2011, Dodson and Bayliss 2012)