Phosphorylation Sites on Tyr28 and the C-terminus of Rad9 are Required for Inhibition of Premature Chromosomal Condensation Across the Entire S Phase

ABSTRACT Infection of cells by many viruses affects the cell division cycle of the host cell to favor viral replication. We examined the ability of the paramyxovirus simian parainfluenza virus 5 (SV5) to affect cell cycle progression, and we found that SV5 slows the rate of proliferation of HeLa T4 cells. The SV5-infected cells had a delayed transition from G1 to S phase and prolonged progression through S phase, and some of the infected cells were arrested in G2 or M phase. The levels of p53 and p21CIP1were not increased in SV5-infected cells compared to mock-infected cells, suggesting that the changes in the cell cycle occur through a p53-independent mechanism. However, the phosphorylation of the retinoblastoma protein (pRB) was delayed and prolonged in SV5-infected cells. The changes in the cell cycle were also observed in cells expressing the SV5 V protein but not in the cells expressing the SV5 P protein or the V protein lacking its unique C terminus (VΔC). The unique C terminus of the V protein of SV5 was shown previously to interact with DDB1, which is the 127-kDa subunit of the multifunctional damage-specific DNA-binding protein (DDB) heterodimer. The coexpression of DDB1 with V can partially restore the changes in the cell cycle caused by expression of the V protein.

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Ykt6 membrane-to-cytosol cycling regulates exosomal Wnt secretion

10.1101/485565 ◽

2018 ◽

Cited By ~ 2

Author(s):

Karen Linnemannstöns ◽

Pradhipa Karuna M ◽

Leonie Witte ◽

Jeanette Clarissa Kittel ◽

Adi Danieli ◽

...

Keyword(s):

Plasma Membrane ◽

Wnt Signaling ◽

Signaling Pathways ◽

Long Range ◽

Protein Trafficking ◽

Secretory Pathway ◽

Multivesicular Bodies ◽

Phosphorylation Sites ◽

Wnt Proteins ◽

C Terminus

Protein trafficking in the secretory pathway, for example the secretion of Wnt proteins, requires tight regulation. These ligands activate Wnt signaling pathways and are crucially involved in development and disease. Wnt is transported to the plasma membrane by its cargo receptor Evi, where Wnt/Evi complexes are endocytosed and sorted onto exosomes for long-range secretion. However, the trafficking steps within the endosomal compartment are not fully understood. The promiscuous SNARE Ykt6 folds into an auto-inhibiting conformation in the cytosol, but a portion associates with membranes by its farnesylated and palmitoylated C-terminus. Here, we demonstrate that membrane detachment of Ykt6 is essential for exosomal Wnt secretion. We identified conserved phosphorylation sites within the SNARE domain of Ykt6, which block Ykt6 cycling from the membrane to the cytosol. In Drosophila, Ykt6-RNAi mediated block of Wg secretion is rescued by wildtype but not phosphomimicking Ykt6. The latter accumulates at membranes, while wildtype Ykt6 regulates Wnt trafficking between the plasma membrane and multivesicular bodies. Taken together, we show that a regulatory switch in Ykt6 fine-tunes sorting of Wnts in endosomes.

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Nuclear localization of vertebrate cyclin A correlates with its ability to form complexes with cdk catalytic subunits

Journal of Cell Science ◽

10.1242/jcs.106.2.535 ◽

1993 ◽

Vol 106 (2) ◽

pp. 535-544 ◽

Cited By ~ 4

Author(s):

G. Maridor ◽

P. Gallant ◽

R. Golsteyn ◽

E.A. Nigg

Keyword(s):

Nuclear Localization ◽

Immunofluorescence Microscopy ◽

Cyclin A ◽

S Phase ◽

Catalytic Subunits ◽

Kinase Activation ◽

Indirect Immunofluorescence Microscopy ◽

C Terminus ◽

Dependent Protein ◽

Cycle Regulation

Cyclins control the activities of cyclin-dependent protein kinases (cdks) and hence play a key role in cell cycle regulation. While B-type cyclins associate with p34cdc2 to trigger entry into mitosis, progression through S phase requires cyclin A, presumably in association with p33cdk2. Vertebrate A- and B-type cyclins display strikingly distinct subcellular localizations, but the mechanisms underlying these differential distributions are unknown. Here, we have begun to study the requirements for nuclear localization of cyclin A. We have isolated a cDNA coding for chicken cyclin A and constructed a series of deletion mutants. These were then transfected into HeLa cells, and the subcellular distribution of the mutant cyclin A proteins was determined by indirect immunofluorescence microscopy. In parallel, the cyclin A mutants were assayed for their ability to form complexes with cdk subunits. We found that deletion of more than 100 residues from the N terminus of cyclin A did not impair nuclear localization or cdk subunit binding and kinase activation. In contrast, removal of as few as 15 residues from the C terminus, or deletion of part of the internal cyclin box domain, abolished nuclear localization of cyclin A as well as its ability to bind to and activate cdk subunits. These results suggest that nuclear transport of cyclin A may depend on the formation of multiprotein complexes comprising cdk catalytic subunits.

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Cdc18p can block mitosis by two independent mechanisms

Journal of Cell Science ◽

10.1242/jcs.111.20.3101 ◽

1998 ◽

Vol 111 (20) ◽

pp. 3101-3108 ◽

Cited By ~ 2

Author(s):

E. Greenwood ◽

H. Nishitani ◽

P. Nurse

Keyword(s):

Dna Replication ◽

S Phase ◽

Checkpoint Control ◽

Replication Checkpoint ◽

Mitotic Kinase ◽

C Terminus ◽

N Terminus ◽

Dna Replication Checkpoint ◽

Checkpoint Genes

The DNA replication checkpoint is required to maintain the integrity of the genome, inhibiting mitosis until S phase has been successfully completed. The checkpoint preventing premature mitosis in Schizosaccharomyces pombe relies on phosphorylation of the tyrosine-15 residue on cdc2p to prevent its activation and hence mitosis. The cdc18 gene is essential for both generating the DNA replication checkpoint and the initiation of S phase, thus providing a key role for the overall control and coordination of the cell cycle. We show that the C terminus of the protein is capable of both initiating DNA replication and the checkpoint function of cdc18p. The C terminus of cdc18p acts upstream of the DNA replication checkpoint genes rad1, rad3, rad9, rad17, hus1 and cut5 and requires the wee1p/mik1p tyrosine kinases to block mitosis. The N terminus of cdc18p can also block mitosis but does so in the absence of the DNA replication checkpoint genes and the wee1p/mik1p kinases therefore acting downstream of these genes. Because the N terminus of cdc18p associates with cdc2p in vivo, we suggest that by binding the cdc2p/cdc13p mitotic kinase directly, it exerts an effect independently of the normal checkpoint control, probably in an unphysiological manner.

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Phosphorylation sites at the C-terminus of the platelet-derived growth factor receptor bind phospholipase C gamma 1.

Molecular Biology of the Cell ◽

10.1091/mbc.4.1.49 ◽

1993 ◽

Vol 4 (1) ◽

pp. 49-57 ◽

Cited By ~ 41

Author(s):

A Kashishian ◽

J A Cooper

Keyword(s):

Growth Factor ◽

Phospholipase C ◽

Tyrosine Phosphorylation ◽

Growth Factor Receptor ◽

Mitogen Activated Protein Kinase ◽

Platelet Derived Growth Factor ◽

Phosphorylation Sites ◽

C Terminus ◽

Mitogen Activated Protein ◽

Src Homology

We have identified two tyrosine phosphorylation sites, Tyr 1009 and Tyr 1021, in the C-terminal noncatalytic region of the human platelet-derived growth factor (PDGF) receptor beta subunit. Mutant receptors with phenylalanine substitutions at either or both of these tyrosines were expressed in dog epithelial cells. Mutation of Tyr 1021 markedly reduced the PDGF-stimulated binding of phospholipase C (PLC) gamma 1 but had no effect on binding of the GTPase activator protein of Ras or of phosphatidylinositol 3 kinase. Mutation of Tyr 1009 reduced binding of PLC gamma 1 less severely. Mutation of Tyr 1021, or both Tyr 1009 and Tyr 1021, also reduced the PDGF-dependent binding of a transiently expressed fusion protein containing the two Src-homology 2 domains from PLC gamma 1. Mutation of Tyr 1021, or both Tyr 1009 and Tyr 1021, greatly reduced PDGF-stimulated tyrosine phosphorylation of PLC gamma 1 but did not prevent the tyrosine phosphorylation of other cell proteins, including mitogen-activated protein kinase. We conclude that Tyr 1021, and possibly Tyr 1009, is a binding site for PLC gamma 1.

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Identification of Three Tyrosine Phosphorylation Sites in the p53 Binding Domain of Apoptosis-Stimulating p53 Protein 2 (ASPP2) That Are Differentially Phosphorylated in Response to Chemotherapy in Patient Derived AML Blasts

Blood ◽

10.1182/blood.v118.21.1396.1396 ◽

2011 ◽

Vol 118 (21) ◽

pp. 1396-1396

Author(s):

Kerstin M Kampa-Schittenhelm ◽

Charles D Lopez ◽

Marcus M Schittenhelm

Keyword(s):

Acute Leukemia ◽

Tyrosine Phosphorylation ◽

Ex Vivo ◽

Phosphorylation Sites ◽

Apoptosis Induction ◽

P53 Mutations ◽

Expression Levels ◽

C Terminus ◽

Response To Chemotherapy

Abstract Abstract 1396 Acute myeloid leukemias (AML) are difficult to treat, and risk-stratification for successful chemotherapy remains a major challenge. Inactivation of the p53 tumor suppressor pathway is a frequent event in many cancers that promotes tumorigenesis and resistance to chemotherapy. However, p53 mutations are rare in AML, and thus the p53-pathway must be inactivated by other mechanisms. ASPP2 is a haploinsufficient tumor suppressor that belongs to a family of p53-binding proteins that enhance apoptosis in part by stimulation of p53-transactivation of selected pro-apoptotic target genes. High ASPP2 expression levels in the absence of p53 mutations thereby argue for proper apoptosis induction capacity and thereby for better response rates. Indeed, low ASPP2 expression levels are correlated with aggressive courses of different tumors. As we have previously shown by qPCR (Kampa-Schittenhelm et al., ASH 2010) and confirm now by intracellular immunostaining in a larger patient cohort, ASPP2 expression levels vary widely in acute leukemias. In vitro silencing of ASPP2 transcription leads to abrogation of induction of apoptosis after application of chemotherapy, arguing for inferior in vivo response rates to therapy of patients lacking ASPP2 expression. Of note, the highest expression levels we have seen was in a patient with good prognosis core binding factor leukemia lacking an autoactivating KIT mutation. The p53 core domain must interact with the ASPP2 C-terminus to fully stimulate apoptotic function. To further investigate how regulation of the p53-ASPP2 interaction may play a role in apoptosis induction in AML, we identified several highly conserved and highly predicted tyrosine phosphorylation sites at the ASPP2 C-terminus. To study whether these sites modulate the p53-ASPP2 interaction and apoptotic function, we developed phospho-specific antibodies against the three highest-scoring phosphorylation sites and confirmed. tyrosine phosphorylation at Y1029, Y1046 and Y1114 in ex vivo blasts from AML patients. Intriguingly, based on the crystal structure of the p53-ASPP2 complex, phosphorylation of all three tyrosines is predicted to disrupt p53-ASPP2 binding. Tantalizingly, we found that these phosphorylation expression patterns changed after in vitro treatment of native blasts with chemotherapy: blasts treated with daunorubicin revealed an early change of tyrosine phosphorylation patterns. Using these new phospho-specific antibodies, we are continuing to analyze changes in phosphorylation patterns in primary AML blasts (with and without ex vivo chemotherapy) and are performing univariate and multivariate analysis to correlate with available clinical data. Preliminary data suggests that altered ASPP2 tyrosine phosphorylation in AML may play an important role in modulating response to chemotherapy-induced apoptosis in the absence of inactivating p53 mutations. Ongoing work is prospectively analyzing pY-ASPP2 in patients with acute leukemia during induction chemotherapy. These results aim to evaluate ASPP2 expression as an early-on prediction marker of therapy response in acute leukemia. Further, we aim to provide new and clinically relevant insight into p53 pathway inactivation in acute leukemia – which suggests a novel potential target for therapy to increase the effectiveness of chemotherapy in these patients. Disclosures: No relevant conflicts of interest to declare.

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Identification of novel ERK-mediated feedback phosphorylation sites at the C-terminus of B-Raf

Oncogene ◽

10.1038/sj.onc.1207185 ◽

2003 ◽

Vol 22 (55) ◽

pp. 8823-8834 ◽

Cited By ~ 73

Author(s):

Tilman Brummer ◽

Heike Naegele ◽

Michael Reth ◽

Yukiko Misawa

Keyword(s):

Phosphorylation Sites ◽

C Terminus

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Actopaxin is phosphorylated during mitosis and is a substrate for cyclin B1/cdc2 kinase

Biochemical Journal ◽

10.1042/bj3630233 ◽

2002 ◽

Vol 363 (2) ◽

pp. 233-242 ◽

Cited By ~ 10

Author(s):

Michael CURTIS ◽

Sotiris N. NIKOLOPOULOS ◽

Christopher E. TURNER

Keyword(s):

Cell Division ◽

Focal Adhesions ◽

Cyclin B1 ◽

Actin Binding ◽

Phosphorylation Sites ◽

Cdc2 Kinase ◽

C Terminus ◽

N Terminus ◽

Focal Adhesion Protein

Prior to cell division, normal adherent cells adopt a round morphology that is associated with a loss of actin stress fibres and disassembly of focal adhesions. In this study, we investigate the mitotic phosphorylation of the recently described paxillin and actin-binding focal-adhesion protein actopaxin [Nikolopoulos and Turner (2000) J. Cell Biol. 151, 1435–1448]. Actopaxin is comprised of an N-terminus containing six putative cdc2 phosphorylation sites and a C-terminus consisting of tandem calponin homology domains. Here we show that the N-terminus of actopaxin is phosphorylated by cyclin B1/cdc2 kinase in vitro and that this region of actopaxin precipitates cdc2 kinase activity from mitotic lysates. Actopaxin exhibits reduced electrophoretic mobility during mitosis that is dependent on phosphorylation within the first two consensus cdc2 phosphorylation sites. Finally, as cells progress from mitosis to G1 there is an adhesion-independent dephosphorylation of actopaxin, suggesting that actopaxin dephosphorylation precedes cell spreading and the reformation of focal adhesions. Taken together, these results suggest a role for cyclin B1/cdc2-dependent phosphorylation of actopaxin in regulating actin cytoskeleton reorganization during cell division.

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Casein Kinase 1γ Ensures Monopolar Growth Polarity under Incomplete DNA Replication Downstream of Cds1 and Calcineurin in Fission Yeast

Molecular and Cellular Biology ◽

10.1128/mcb.01465-14 ◽

2015 ◽

Vol 35 (9) ◽

pp. 1533-1542 ◽

Cited By ~ 6

Author(s):

Takayuki Koyano ◽

Manabu Konishi ◽

Sophie G. Martin ◽

Yoshikazu Ohya ◽

Dai Hirata ◽

...

Keyword(s):

Fission Yeast ◽

Cell Polarity ◽

Molecular Mechanisms ◽

Kinase Activity ◽

Developmental Stages ◽

Casein Kinase ◽

S Phase ◽

Cellular Functions ◽

C Terminus ◽

Polarity Transition

Cell polarity is essential for various cellular functions during both proliferative and developmental stages, and it displays dynamic alterations in response to intracellular and extracellular cues. However, the molecular mechanisms underlying spatiotemporal control of polarity transition are poorly understood. Here, we show that fission yeast Cki3 (a casein kinase 1γ homolog) is a critical regulator to ensure persistent monopolar growth during S phase. Unlike the wild type,cki3mutant cells undergo bipolar growth when S phase is blocked, a condition known to delay transition from monopolar to bipolar growth (termed NETO [newendtakeoff]). Consistent with this role, Cki3 kinase activity is substantially increased, and cells lose their viability in the absence of Cki3 upon an S-phase block. Cki3 acts downstream of the checkpoint kinase Cds1/Chk2 and calcineurin, and the latter physically interacts with Cki3. Autophosphorylation in the C terminus is inhibitory toward Cki3 kinase activity, and calcineurin is responsible for its dephosphorylation. Cki3 localizes to the plasma membrane, and this localization requires the palmitoyltransferase complex Erf2-Erf4. Membrane localization is needed not only for proper NETO timing but also for Cki3 kinase activity. We propose that Cki3 acts as a critical inhibitor of cell polarity transition under S-phase arrest.

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The C-terminus and Third Cytoplasmic Loop Cooperatively Activate Mouse Melanopsin Phototransduction

10.1101/2020.02.12.946129 ◽

2020 ◽

Author(s):

J.C. Valdez-Lopez ◽

S.T. Petr ◽

M.P. Donohue ◽

R.J. Bailey ◽

M. Gebreeziabher ◽

...

Keyword(s):

G Protein ◽

Visual Pigment ◽

Image Formation ◽

Phosphorylation Sites ◽

Tyrosine Residue ◽

Ionic Interaction ◽

Cytoplasmic Loop ◽

Light Responses ◽

C Terminus ◽

Activation Rate

ABSTRACTMelanopsin, an atypical vertebrate visual pigment, mediates non-image forming light responses including circadian photoentrainment and pupillary light reflexes, and contrast detection for image formation. Melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs), are characterized by sluggish activation and deactivation of their light responses. The molecular determinants of mouse melanopsin’s deactivation have been characterized (i.e. C-terminal phosphorylation and β-arrestin binding), but a detailed analysis of melanopsin’s activation is lacking. We propose that an extended 3rd cytoplasmic loop is adjacent to the proximal C-terminal region of mouse melanopsin in the inactive conformation which is stabilized by ionic interaction of these two regions. This model is supported by site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy of melanopsin, the results of which suggests a high degree of steric freedom at the 3rd cytoplasmic loop, which is increased upon C-terminus truncation, supporting the idea that these two regions are close in 3-dimensional space in wild-type melanopsin. To test for a functionally critical C-terminal conformation, calcium imaging of melanopsin mutants including a proximal C-terminus truncation (at residue 365) and proline mutation of this proximal region (H377P, L380P, Y382P) delayed melanopsin’s activation rate. Mutation of all potential phosphorylation sites, including a highly conserved tyrosine residue (Y382), into alanines also delayed the activation rate. A comparison of mouse melanopsin with armadillo melanopsin—which has substitutions of various potential phosphorylation sites and a substitution of the conserved tyrosine—indicates that substitution of these potential phosphorylation sites and the tyrosine residue result in dramatically slower activation kinetics, a finding that also supports the role of phosphorylation in signaling activation. We therefore propose that melanopsin’s C-terminus is proximal to intracellular loop 3 and C-terminal phosphorylation permits the ionic interaction between these two regions, thus forming a stable structural conformation that is critical for initiating G-protein signaling.STATEMENT OF SIGNIFICANCEMelanopsin is an important visual pigment in the mammalian retina that mediates non-image forming responses such as circadian photoentrainment and pupil constriction, and supports contrast detection for image formation. In this study, we detail two critical structural features of mouse melanopsin—its 3rd cytoplasmic loop and C-terminus—that are important in the activation of melanopsin’s light responses. Furthermore, we propose that these two regions directly participate in coupling mouse melanopsin to its G-protein. These findings contribute to further understanding of GPCR-G-protein coupling, and given recent findings suggesting flexibility of melanopsin signal transduction in the retina (possibly by coupling more than one G-protein type), these findings provide insight into the molecular basis of melanopsin function in the retina.

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