scholarly journals cdc25 is a nuclear protein expressed constitutively throughout the cell cycle in nontransformed mammalian cells.

1992 ◽  
Vol 118 (4) ◽  
pp. 785-794 ◽  
Author(s):  
F Girard ◽  
U Strausfeld ◽  
J C Cavadore ◽  
P Russell ◽  
A Fernandez ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Tyrosine Phosphatase ◽  
Specific Protein ◽  
Cyclin B ◽  
Early Prophase ◽  
Cdc25 Phosphatase ◽  
Nuclear Envelope Breakdown ◽  
Cellular Compartments ◽  
Cdc25 Protein

A family of proteins homologous to the cdc25 gene product of the fission yeast bear specific protein tyrosine phosphatase activity involved in the activation of the p34cdc2-cyclin B kinase. Using affinity-purified antibodies raised against a synthetic peptide corresponding to the catalytic site of the cdc25 phosphatase, we show that cdc25 protein is constitutively expressed throughout the cell cycle of nontransformed mammalian fibroblasts and does not undergo major changes in protein level. By indirect immunofluorescence, cdc25 protein is found essentially localized in the nucleus throughout interphase and during early prophase. Just before the complete nuclear envelope breakdown at the prophase-prometaphase boundary, cdc25 proteins are redistributed throughout the cytoplasm. During metaphase and anaphase, cdc25 staining remains distributed throughout the cell and excludes the condensed chromosomes. The nuclear locale reappears during telophase. In light of the recent data describing the cytoplasmic localization of cyclin B protein (Pines, J., and T. Hunter. 1991. J. Cell Biol. 115:1-17), the data presented here suggest that separation in two distinct cellular compartments of the cdc25 phosphatase and its substrate p34cdc2-cyclin B may be of importance in the regulation of the cdc2 kinase activity.

Subcellular localisation of human wee1 kinase is regulated during the cell cycle

1995 ◽  
Vol 108 (6) ◽  
pp. 2425-2432
Author(s):  
V. Baldin ◽  
B. Ducommun
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Tyrosine Phosphatase ◽  
Cyclin B ◽  
Microtubule Assembly ◽  
Subcellular Localisation ◽  
Temporal Regulation ◽  
Wee1 Kinase ◽  
Cdc2 Activity ◽  
Intracellular Localisation

Wee1 kinase-dependent phosphorylation of cdc2 maintains the cdc2/cyclin B complex in an inert form until it is activated by the cdc25 tyrosine phosphatase at the end of G2. As described for cdc25, cell cycle-linked changes in the intracellular localisation of wee1 may constitute an important aspect of the temporal regulation of cdc2 activity. Here we report that the subcellular distribution of human wee1 changes during the cell cycle in HeLa and IMR90 cells. During interphase, wee1 is found almost exclusively in the nucleus. When the cell enters mitosis, wee1 is relocalised into the cytoplasm. During cell division, wee1 becomes restricted to the mitotic equator and by the end of mitosis it is found exclusively in association with midbody bridges, a phenomenon that is dependent on microtubule assembly. The relocalisations of wee1 and its association with subcellular structures may play key regulatory roles at different stages of the cell cycle and during mitosis.

Sperm nuclear envelope: breakdown of intrinsic envelope and de novo formation in hamster oocytes or eggs

Zygote ◽  
1997 ◽  
Vol 5 (1) ◽  
pp. 35-46 ◽  
Author(s):  
Noriko Usui ◽  
Atsuo Ogura ◽  
Yasuyuki Kimura ◽  
Ryuzo Yanagimachi
Keyword(s):  
Cell Cycle ◽  
Nuclear Envelope ◽  
De Novo ◽  
Germinal Vesicle ◽  
Mature Oocyte ◽  
Sperm Nucleus ◽  
Sperm Chromatin ◽  
Early Prophase ◽  
Nuclear Envelope Breakdown ◽  
M Phase

SummaryDuring fertilisation of a fully mature oocyte, the sperm intrinsic nuclear envelope (SINE) disappears soon after sperm-oocyte fusion. A new nuclear envelope appears around the decondensed sperm chromatin when the oocyte reaches telophase II. Whether the SINE persists or rapidly disappears after sperm entery into immature oocytes or fertilised eggs has been controversial. Nuclear envelopes have been demonstrated around the sperm chromatin, which cannot be decondensed within the ooplasm of these oocytes or eggs, but whether these envelopes are persisting SINEs or newly formed envelopes has been apoint of dispute. To resolve this issue, the fate of the germinal vesicle stage(GV oocytes) or fertilised eggs at the pronuclear stage(PN eggs). The SINEs disappeared quikly within these oocytes or eggs, like those within maturing or mature oocytes, suggesting that the envelops around the sperm chromatin must be newly formed after SINE breakdown. To obtain further evidence, a detergent-treated, SINE-free sperm nucleus was injected into a PN egg. A new envelope appeared around the still-condensed or partially decondensed sperm chromatin within 3h after injection. Thus, disassembly of the SINE within ooplasm, unlike that of nuclear envelopes of other cells at prophase, is independent of the cell cycle stage of the oocyte or egg, whereas the ability of the ooplasm to assemble the new envelope is restricted to certain periods of the cycle. i.e. early prophase and telophase during meiosis and interphase, periods when active M-phase Promoting factor (MPF) is absent from the ooplasm.

scholarly journals Entry into Mitosis in Vertebrate Somatic Cells Is Guarded by a Chromosome Damage Checkpoint That Reverses the Cell Cycle When Triggered during Early but Not Late Prophase

1998 ◽  
Vol 142 (4) ◽  
pp. 1013-1022 ◽  
Author(s):  
Conly L. Rieder ◽  
Richard W. Cole
Keyword(s):  
Cell Cycle ◽  
Somatic Cells ◽  
Early Prophase ◽  
Checkpoint Control ◽  
Late Prophase ◽  
Cytoplasmic Microtubule ◽  
Nuclear Envelope Breakdown ◽  
Prophase Nucleus ◽  
Nuclear Events ◽  
A Cell

When vertebrate somatic cells are selectively irradiated in the nucleus during late prophase (<30 min before nuclear envelope breakdown) they progress normally through mitosis even if they contain broken chromosomes. However, if early prophase nuclei are similarly irradiated, chromosome condensation is reversed and the cells return to interphase. Thus, the G2 checkpoint that prevents entry into mitosis in response to nuclear damage ceases to function in late prophase. If one nucleus in a cell containing two early prophase nuclei is selectively irradiated, both return to interphase, and prophase cells that have been induced to returned to interphase retain a normal cytoplasmic microtubule complex. Thus, damage to an early prophase nucleus is converted into a signal that not only reverses the nuclear events of prophase, but this signal also enters the cytoplasm where it inhibits e.g., centrosome maturation and the formation of asters. Immunofluorescent analyses reveal that the irradiation-induced reversion of prophase is correlated with the dephosphorylation of histone H1, histone H3, and the MPM2 epitopes. Together, these data reveal that a checkpoint control exists in early but not late prophase in vertebrate cells that, when triggered, reverses the cell cycle by apparently downregulating existing cyclin-dependent kinase (CDK1) activity.

scholarly journals Periodic changes in phosphorylation of the Xenopus cdc25 phosphatase regulate its activity.

1992 ◽  
Vol 3 (8) ◽  
pp. 927-939 ◽  
Author(s):  
T Izumi ◽  
D H Walker ◽  
J L Maller
Keyword(s):  
Tyrosine Phosphatase ◽  
Mitotic Cell ◽  
Cdc25 Phosphatase ◽  
Mobility Shift ◽  
Cdc2 Kinase ◽  
Kinase Activation ◽  
Cell Cycles ◽  
M Phase ◽  
Egg Extracts ◽  
Cdc25 Protein

The cdc25 tyrosine phosphatase is known to activate cdc2 kinase in the G2/M transition by dephosphorylation of tyrosine 15. To determine how entry into M-phase in eukaryotic cells is controlled, we have investigated the regulation of the cdc25 protein in Xenopus eggs and oocytes. Two closely related Xenopus cdc25 genes have been cloned and sequenced and specific antibodies generated. The cdc25 phosphatase activity oscillates in both meiotic and mitotic cell cycles, being low in interphase and high in M-phase. Increased activity of cdc25 at M-phase is accompanied by increased phosphorylation that retards electrophoretic mobility in gels from 76 to 92 kDa. Treatment of cdc25 with either phosphatase 1 or phosphatase 2A removes phosphate from cdc25, reverses the mobility shift, and decreases its ability to activate cdc2 kinase. Furthermore, the addition of okadaic acid to egg extracts arrested in S-phase by aphidicolin causes phosphorylation and activation of the cdc25 protein before cyclin B/cdc2 kinase activation. These results demonstrate that the activity of the cdc25 phosphatase at the G2/M transition is directly regulated through changes in its phosphorylation state.

Repurposing of Alexidine Dihydrochloride as an Apoptosis Initiator and Cell Cycle Inhibitor in Human Pancreatic Cancer

2020 ◽  
Vol 20 (16) ◽  
pp. 1956-1965
Author(s):  
Ezgi Kasikci ◽  
Esra Aydemir ◽  
Bekir M. Yogurtcu ◽  
Fikrettin Sahin ◽  
Omer F. Bayrak
Keyword(s):  
Cell Cycle ◽  
Pancreatic Cancer ◽  
Cell Lines ◽  
Tyrosine Phosphatase ◽  
Annexin V ◽  
Specific Protein ◽  
Human Pancreatic Cancer ◽  
Western World ◽  
Potential Candidate ◽  
Orally Bioavailable

Background: Highly aggressive and resistant to chemotherapy, pancreatic cancers are the fourth leading cause of cancer-related deaths in the western world. The absence of effective chemotherapeutics is leading researchers to develop novel drugs or repurpose existing chemicals. Alexidine Dihydrochloride (AD), an orally bioavailable bis-biguanide compound, is an apoptosis stimulating reagent. It induces mitochondrial damage by inhibiting a mitochondrial-specific protein tyrosine phosphatase, PTPMT1. The aim of this study was to test AD as a novel compound to induce apoptosis in a human pancreatic adenocarcinoma cell lines, Panc-1, MIA PaCa-2, AsPC-1, and Psn-1. Methods: After the IC50 value of the AD was determined by cytotoxicity assay, apoptosis was observed by a variety of methods, including the detection of early apoptosis marker Annexin V and the proteomic profile screening by apoptosis array. Multicaspase and mitochondrial depolarization were measured, and changes in the cell cycle were analyzed. Results: AD is found to initiate apoptosis by activating the intrinsic pathway and inhibit the cell cycle in pancreatic cancer cell lines. Conclusions: In conclusion, considering its anti-cancer properties and bioavailability, Alexidine dihydrochloride can be considered as a potential candidate against pancreatic adenocarcinomas.

scholarly journals Cell cycle control by Xenopus p28Kix1, a developmentally regulated inhibitor of cyclin-dependent kinases.

1996 ◽  
Vol 7 (3) ◽  
pp. 457-469 ◽  
Author(s):  
W Shou ◽  
W G Dunphy
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Cell Cycle Progression ◽  
Cyclin E ◽  
Cell Cycle Control ◽  
Cyclin A ◽  
Cyclin B ◽  
Nuclear Antigen ◽  
Cdk Inhibitors ◽  
Egg Extracts

We have isolated Xenopus p28Kix1, a member of the p21CIP1/p27KIP1/p57KIP2 family of cyclin-dependent kinase (Cdk) inhibitors. Members of this family negatively regulate cell cycle progression in mammalian cells by inhibiting the activities of Cdks. p28 shows significant sequence homology with p21, p27, and p57 in its N-terminal region, where the Cdk inhibition domain is known to reside. In contrast, the C-terminal domain of p28 is distinct from that of p21, p27, and p57. In co-immunoprecipitation experiments, p28 was found to be associated with Cdk2, cyclin E, and cyclin A, but not the Cdc2/cyclin B complex in Xenopus egg extracts. Xenopus p28 associates with the proliferating cell nuclear antigen, but with a substantially lower affinity than human p21. In kinase assays with recombinant Cdks, p28 inhibits pre-activated Cdk2/cyclin E and Cdk2/cyclin A, but not Cdc2/cyclin B. However, at high concentrations, p28 does prevent the activation of Cdc2/cyclin B by the Cdk-activating kinase. Consistent with the role of p28 as a Cdk inhibitor, recombinant p28 elicits an inhibition of both DNA replication and mitosis upon addition to egg extracts, indicating that it can regulate multiple cell cycle transitions. The level of p28 protein shows a dramatic developmental profile: it is low in Xenopus oocytes, eggs, and embryos up to stage 11, but increases approximately 100-fold between stages 12 and 13, and remains high thereafter. The induction of p28 expression temporally coincides with late gastrulation. Thus, although p28 may play only a limited role during the early embryonic cleavages, it may function later in development to establish a somatic type of cell cycle. Taken together, our results indicate that Xenopus p28 is a new member of the p21/p27/p57 class of Cdk inhibitors, and that it may play a role in developmental processes.

Nuclear envelope breakdown in mammalian cells involves stepwise lamina disassembly and microtubule-drive deformation of the nuclear membrane

1997 ◽  
Vol 110 (17) ◽  
pp. 2129-2140 ◽  
Author(s):  
S.D. Georgatos ◽  
A. Pyrpasopoulou ◽  
P.A. Theodoropoulos
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Mitotic Spindle ◽  
Mammalian Cells ◽  
Nuclear Lamina ◽  
Early Prophase ◽  
Nuclear Surface ◽  
Late Prophase ◽  
Lamin B ◽  
Nuclear Envelope Breakdown

We have studied nuclear envelope disassembly in mammalian cells by morphological methods. The first signs of nuclear lamina depolymerization become evident in early prophase as A-type lamins start dissociating from the nuclear lamina and diffuse into the nucleoplasm. While B-type lamins are still associated with the inner nuclear membrane, two symmetrical indentations develop on antidiametric sites of the nuclear envelope. These indentations accommodate the sister centrosomes and associated astral microtubules. At mid- to late prophase, elongating microtubules apparently push on the nuclear surface and eventually penetrate the nucleus. At this point the nuclear envelope becomes freely permeable to large ligands, as indicated by experiments with digitonin-treated cells and by the massive release of solubilized A-type lamins into the cytoplasm. At the prophase/prometaphase transition, the B-type lamina is fragmented, but ‘islands’ of lamin B polymer can still be discerned on the tips of congressing chromosomes. Finally, at metaphase, the lamin B polymer breaks down into small pieces, which tend to concentrate in the area of the mitotic spindle. Nuclear envelope breakdown is not prevented when the microtubules are depolymerized by nocodazole; however, the mode of nuclear lamina fragmentation in the absence of microtubules is markedly different from the normal one and involves multiple raffles and gaps, which develop rapidly along the entire surface of the nuclear envelope. These data suggest that nuclear envelope disassembly is a stepwise process in which the microtubules play an important part.

scholarly journals A novel transcriptional cascade is involved in Fzr-mediated endoreplication

2020 ◽  
Vol 48 (8) ◽  
pp. 4214-4229
Author(s):  
Wenliang Qian ◽  
Zheng Li ◽  
Wei Song ◽  
Tujing Zhao ◽  
Weina Wang ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Chromosome Segregation ◽  
Mammalian Cells ◽  
Cyclin B ◽  
Signaling Cascade ◽  
Genome Replication ◽  
Anaphase Promoting Complex ◽  
Related Protein ◽  
Histone H2b ◽  
Subsequent Degradation

Abstract Endoreplication, known as endocycle, is a variant of the cell cycle that differs from mitosis and occurs in specific tissues of different organisms. Endoreplicating cells generally undergo multiple rounds of genome replication without chromosome segregation. Previous studies demonstrated that Drosophila fizzy-related protein (Fzr) and its mammalian homolog Cdh1 function as key regulators of endoreplication entrance by activating the anaphase-promoting complex/cyclosome to initiate the ubiquitination and subsequent degradation of cell cycle factors such as Cyclin B (CycB). However, the molecular mechanism underlying Fzr-mediated endoreplication is not completely understood. In this study, we demonstrated that the transcription factor Myc acts downstream of Fzr during endoreplication in Drosophila salivary gland. Mechanistically, Fzr interacts with chromatin-associated histone H2B to enhance H2B ubiquitination in the Myc promoter and promotes Myc transcription. In addition to negatively regulating CycB transcription, the Fzr-ubiquitinated H2B (H2Bub)-Myc signaling cascade also positively regulates the transcription of the MCM6 gene that is involved in DNA replication by directly binding to specific motifs within their promoters. We further found that the Fzr-H2Bub-Myc signaling cascade regulating endoreplication progression is conserved between insects and mammalian cells. Altogether, our work uncovers a novel transcriptional cascade that is involved in Fzr-mediated endoreplication.

scholarly journals The COP9 signalosome: at the interface between signal transduction and ubiquitin-dependent proteolysis

2002 ◽  
Vol 115 (3) ◽  
pp. 467-473 ◽  
Author(s):  
Dawadschargal Bech-Otschir ◽  
Michael Seeger ◽  
Wolfgang Dubiel
Keyword(s):  
Cell Cycle ◽  
Signal Transduction ◽  
Transcription Factors ◽  
Protein Interactions ◽  
Mammalian Cells ◽  
Specific Protein ◽  
26S Proteasome ◽  
Cop9 Signalosome ◽  
Protein Protein Interactions ◽  
Ubiquitin System

Recently the COP9 signalosome (CSN) has become a focus of interest for many researchers, because of its function at the interface between signal transduction and ubiquitin-dependent proteolysis. It is required for the proper progression of the cell cycle in Schizosaccharomyces pombe and is essential for development in plants and Drosophila. However, its function in mammalian cells remains obscure. Although the CSN shares structural similarities with the 26S proteasome lid complex (LID), its functions seem to be different from that of the LID. A variety of CSN-specific protein-protein interactions have been described in mammalian cells. However,it is currently unclear how many reflect true functions of the complex. Two activities associated with the CSN have been identified so far: a protein kinase and a deneddylase. The CSN-associated kinase phosphorylates transcription factors, which determines their stability towards the ubiquitin system. The associated deneddylase regulates the activity of specific SCF E3 ubiquitin ligases. The CSN thus appears to be a platform connecting signalling with proteolysis.

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