Deoxyribonucleotide Biosynthesis in Green Algae. S Phase-Specific Thymidylate Kinase and Unspecific Nucleoside Diphosphate Kinase in Scenedesmus obliquus

1988 ◽  
Vol 43 (5-6) ◽  
pp. 377-385 ◽  
Author(s):  
Beate Klein ◽  
Hartmut Follmann
Keyword(s):  
Cell Cycle ◽  
Molecular Weight ◽  
Green Algae ◽  
De Novo ◽  
Scenedesmus Obliquus ◽  
Nucleoside Diphosphate Kinase ◽  
S Phase ◽  
Ndp Kinase ◽  
Thymidylate Kinase

NDP kinase and thymidylate kinase are essential for DNA precursor formation in that they phosphorylate the products of de novo deoxyribonucleotide biosynthesis, deoxyribonucleoside 5′-diphosphates and thymidine 5′-monophosphate to the corresponding triphosphates which then serve as DNA polymerase substrates. The two enzymes have been measured in synchronous cultures of the green algae, S. obliquus. Thymidylate kinase exhibits an activity peak at the 11 -12th hour of the 24-hour cell cycle, coinciding with DNA synthesis. Enzyme activity is markedly stimulated in presence of fluorodeoxyuridine in the culture medium. This behaviour of dTMP kinase is very similar to that of three other S phase-specific peak enzymes previously analyzed in synchronous algae, viz. ribonucleotide reductase, thymidylate synthase, and dihydrofolate reductase. In contrast, NDP kinase exhibits high and constant activity through the entire cell cycle. The two kinases have been isolated from cell-free extracts, and separated from each other by chromatography on Blue Sepharose. The peak enzyme, dTMP kinase, has been purified to near homogeneity and its catalytic properties are described; the molecular weight is 56,000. NDP kinase activity is separable into two enzyme fractions, both of molecular weight 100,000 (or higher), which are unspecific with respect to ribonucleotide and deoxyribonucleotide substrates. Characterization and purification of the whole series of deoxyribonucleotide-synthesizing enzymes from one organism provides a basis for in vitro experiments towards reconstitution of an S phase-specific DNA precursor/DNA replication multienzyme aggregate.

scholarly journals Uncoupled cell cycle without mitosis induced by a protein kinase inhibitor, K-252a.

1991 ◽  
Vol 115 (5) ◽  
pp. 1275-1282 ◽  
Author(s):  
T Usui ◽  
M Yoshida ◽  
K Abe ◽  
H Osada ◽  
K Isono ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Protein Kinase ◽  
Dna Synthesis ◽  
Kinase Activity ◽  
Kinase Inhibitor ◽  
De Novo ◽  
S Phase ◽  
Continuous Treatment ◽  
Protein Kinase Activity

The staurosporine analogues, K-252a and RK-286C, were found to cause DNA re-replication in rat diploid fibroblasts (3Y1) without an intervening mitosis, producing tetraploid cells. Analysis of cells synchronized in early S phase in the presence of K-252a revealed that initiation of the second S phase required a lag period of 8 h after completion of the previous S phase. Reinitiation of DNA synthesis was inhibited by cycloheximide, actinomycin D, and serum deprivation, but not by Colcemid, suggesting that a functional G1 phase dependent on de novo synthesis of protein and RNA is essential for entry into the next S phase. In a src-transformed 3Y1 cell line, as well as other cell lines, giant cells containing polyploid nuclei with DNA contents of 16C to 32C were produced by continuous treatment with K-252a, indicating that the agent induced several rounds of the incomplete cell cycle without mitosis. Although the effective concentration of K-252a did not cause significant inhibition of affinity-purified p34cdc2 protein kinase activity in vitro, in vivo the full activation of p34cdc2 kinase during the G2/M was blocked by K-252a. On the other hand, the cyclic fluctuation of partially activated p34cdc2 kinase activity peaking in S phase still continued. These results suggest that a putative protein kinase(s) sensitive to K-252a plays an important role in the mechanism for preventing over-replication after completion of previous DNA synthesis. They also suggest that a periodic activation of p34cdc2 is required for S phases in the cell cycle without mitosis.

In vitro evidence that LHRH stimulates the recruitment of prolactin mRNA-expressing cells during the postnatal period in the rat

1994 ◽  
Vol 12 (1) ◽  
pp. 107-118 ◽  
Author(s):  
A Van Bael ◽  
R Huygen ◽  
B Himpens ◽  
C Denef
Keyword(s):  
Cell Cycle ◽  
Cell Population ◽  
Blot Hybridization ◽  
Postnatal Period ◽  
S Phase ◽  
Female Rats ◽  
Mrna Levels ◽  
Dot Blot ◽  
Total Cell Population

ABSTRACT We have studied the effect of LHRH and neuropeptide Y (NPY) on prolactin (PRL) mRNA levels in pituitary reaggregate cell cultures from 14-day-old female rats, by means of in situ hybridization and Northern blot analysis. As estimated by computer-image analysis, addition of LHRH on day 5 in culture for 40 h resulted in a 37% increase in the total cytoplasmic areas of cells containing PRL mRNA, visualized using a digoxigenin-labelled PRL cRNA. The size of individual PRL-expressing cells was not influenced, nor was the content of PRL mRNA per cell. A similar effect of LHRH was found by dot blot hybridization of extracted RNA. PRL mRNA levels were not affected by NPY. LHRH induced a 29% increase in the number of PRL mRNA-expressing cells processing through the S phase of the cell cycle, visualized by the incorporation of [3H]thymidine ([3H]T) into DNA over 16 h. The fraction of [3H]T-labelled cells was 10–12% of the total cell population. NPY did not influence the number of [3H]T-positive cells expressing PRL mRNA, but completely blocked the effect of LHRH on the latter population. The present data suggest that LHRH, probably via a paracrine action of gonadotrophs, stimulates the recruitment of new lactotrophs, an action which is negatively modulated by NPY. Since the magnitude of this effect was the same in the total pituitary cell population as in cells processing through the S phase of the cell cycle and presumably mitosis, recruitment of lactotrophs seems to be based on differentiation of progenitor or immature cells into PRL-expressing cells, rather than on a mitogenic action on pre-existing lactotrophs alone.

Transcription of the histone H5 gene is not S-phase regulated

1986 ◽  
Vol 6 (2) ◽  
pp. 601-606
Author(s):  
S Dalton ◽  
J R Coleman ◽  
J R Wells
Keyword(s):  
Cell Cycle ◽  
Steady State ◽  
Northern Blotting ◽  
S Phase ◽  
Erythroid Cells ◽  
Dividing Cells ◽  
Steady State Levels ◽  
Avian Erythroblastosis Virus ◽  
Histone H5

Levels of the tissue-specific linker histone H5 are elevated in mature erythroid cells as compared with levels in dividing cells of the same lineage. We examined levels of H5 mRNA in relation to the cell cycle in early erythroid cells transformed by avian erythroblastosis virus to determine whether the gene for this unusual histone is S-phase regulated. Northern blotting analyses revealed that during the cell cycle steady-state levels of H5 mRNA remained relatively constant in contrast to levels of the major core and H1 mRNAs which increased approximately 15-fold during S phase. In vitro pulse-labeling experiments involving nuclei isolated from synchronized cells at various stages of the cell cycle revealed that transcription of the H5 gene was not initiated at any particular stage of the cell cycle but was constitutive. In contrast, transcription of the H2A gene(s) initiated in early S phase, was present throughout the DNA replicative phase, and was essentially absent in G1 and G2 phases.

scholarly journals Differences in cell cycle characteristics among patients with acute nonlymphocytic leukemia

Blood ◽  
1987 ◽  
Vol 69 (6) ◽  
pp. 1647-1653 ◽  
Author(s):  
A Raza ◽  
Y Maheshwari ◽  
HD Preisler
Keyword(s):  
Cell Cycle ◽  
Tritiated Thymidine ◽  
S Phase ◽  
Total Cell ◽  
Acute Nonlymphocytic Leukemia ◽  
Cell Cycle Time ◽  
Myeloid Leukemias ◽  
History Of

The proliferative characteristics of myeloid leukemias were defined in vivo after intravenous infusions of bromodeoxyuridine (BrdU) in 40 patients. The percentage of S-phase cells obtained from the biopsies (mean, 20%) were significantly higher (P = .00003) than those determined from the bone marrow (BM) aspirates (mean, 9%). The post- BrdU infusion BM aspirates from 40 patients were incubated with tritiated thymidine in vitro. These double-labeled slides were utilized to determine the duration of S-phase (Ts) in myeloblasts and their total cell cycle time (Tc). The Ts varied from four to 49 hours (mean, 19 hours; median, 17 hours). Similarly, there were wide variations in Tc of individual patients ranging from 16 to 292 hours (mean, 93 hours; median, 76 hours). There was no relationship between Tc and the percentage of S-phase cells, but there was a good correlation between Tc and Ts (r = .8). Patients with relapsed acute nonlymphocytic leukemia (ANLL) appeared to have a longer Ts and Tc than those studied at initial diagnosis. A subgroup of patients at either extreme of Tc were identified who demonstrated clinically documented resistance in response to multiple courses of chemotherapy. We conclude that Ts and Tc provide additional biologic information that may be valuable in understanding the variations observed in the natural history of ANLL.

scholarly journals Imaging the fate of histone Cse4 reveals de novo replacement in S phase and subsequent stable residence at centromeres

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Jan Wisniewski ◽  
Bassam Hajj ◽  
Jiji Chen ◽  
Gaku Mizuguchi ◽  
Hua Xiao ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Elevated Temperatures ◽  
De Novo ◽  
Histone H3 ◽  
S Phase ◽  
Nuclear Accumulation ◽  
Histone H3 Variant ◽  
Functionally Impaired ◽  
Cell Cycle Dynamics ◽  
Cell Lethality

The budding yeast centromere contains Cse4, a specialized histone H3 variant. Fluorescence pulse-chase analysis of an internally tagged Cse4 reveals that it is replaced with newly synthesized molecules in S phase, remaining stably associated with centromeres thereafter. In contrast, C-terminally-tagged Cse4 is functionally impaired, showing slow cell growth, cell lethality at elevated temperatures, and extra-centromeric nuclear accumulation. Recent studies using such strains gave conflicting findings regarding the centromeric abundance and cell cycle dynamics of Cse4. Our findings indicate that internally tagged Cse4 is a better reporter of the biology of this histone variant. Furthermore, the size of centromeric Cse4 clusters was precisely mapped with a new 3D-PALM method, revealing substantial compaction during anaphase. Cse4-specific chaperone Scm3 displays steady-state, stoichiometric co-localization with Cse4 at centromeres throughout the cell cycle, while undergoing exchange with a nuclear pool. These findings suggest that a stable Cse4 nucleosome is maintained by dynamic chaperone-in-residence Scm3.

Stage specificity in the mesenchyme requirement of rodent lung epithelium in vitro: a matter of growth control?

Development ◽  
1983 ◽  
Vol 74 (1) ◽  
pp. 183-206
Author(s):  
Kirstie A. Lawson
Keyword(s):  
Cell Cycle ◽  
Bronchial Epithelium ◽  
Branching Morphogenesis ◽  
S Phase ◽  
Growth Fraction ◽  
Early Event ◽  
Rat Lung ◽  
Lung Epithelium ◽  
Dividing Cells

Epithelia from lung rudiments in which secondary bronchial buds are already established (14th and 13th gestational day for rat and mouse respectively) are able to undergo branching morphogenesis and cytodifferentiation in submandibular mesenchyme in vitro, whereas lung epithelium from one day younger foetuses rarely gives a morphogenetic response to submandibular mesenchyme and usually differentiates into primary (non-budding) bronchial epithelium. The failure of 13-day rat lung epithelium to respond to submandibular mesenchyme can be prevented by peeling off the submandibular mesenchyme from the lung epithelium after 2½ days culture and replacing the same mesenchyme, or renewing it with fresh salivary mesenchyme ex vivo. Changes in the epithelial contour are visible by 10 h and buds form within 24 h; this is followed by branching morphogenesis in more than 66% of the samples. The number of cells in S-phase in the epithelium is doubled within 3 to 5 h after the operation and the number of mitotic cells (colchicine block) is increased during an 11 to 19 h period after the operation. Substituting stomach mesenchyme for submandibular mesenchyme after the operation failed to elicit morphogenesis or an increase in the number of S-phase cells in the epithelium. The proportion of epithelial cells in S-phase in unoperated recombinates does not differ from the proportion in the primary bronchial epithelium (non-budding) of homotypic lung recombinates, whereas the proportion of S-phase cells in operated recombinates approaches that found in the buds of homotypic lung recombinates. The distribution of S-phase cells in visibly responding recombinates 15 to 17 h after operation shows the same heterogeneity as in homotypic lung recombinates, newly formed buds having twice as many cells labelled with [3H]thymidine as the non-budding area. Cell cycle parameters of intact rat lung growing in vitro were estimated using the labelled mitoses method. Primary bronchial epithelium and bronchial buds both had a total cell cycle time of about 13 h and an S-phase of about 10 h. The growth fraction was 0·54 in the primary bronchus and 0·95 in the buds. It is suggested that, also in the recombinates, differences in the proportion of S-phase cells at any one time in morphogenetically active and inactive areas of the epithelium are due to differences in the growth fraction. It is concluded that an early event in the morphogenetic response of lung epithelium to submandibular mesenchyme after removing and restoring the mesenchyme is an increase in the size of the population of dividing cells and it is suggested that a high proportion of dividing cells in an epithelial population is a prerequisite for further interaction of epithelium and mesenchyme leading to branching morphogenesis.

scholarly journals Elacestrant (RAD1901) exhibits anti-tumor activity in multiple ER+ breast cancer models resistant to CDK4/6 inhibitors

2019 ◽  
Vol 21 (1) ◽  
Author(s):  
Hitisha K. Patel ◽  
Nianjun Tao ◽  
Kyung-Min Lee ◽  
Mariela Huerta ◽  
Heike Arlt ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Cell Cycle ◽  
Estrogen Receptor ◽  
De Novo ◽  
Single Agent ◽  
Metastatic Breast ◽  
Cancer Resistance ◽  
Treatment Paradigm ◽  
Anti Tumor Activity

Abstract Background Addition of CDK4/6 inhibitors (CDK4/6i) to endocrine therapy significantly increased progression-free survival, leading to their approval and incorporation into the metastatic breast cancer treatment paradigm. With these inhibitors being routinely used for patients with advanced estrogen receptor-positive (ER+) breast cancer, resistance to these agents and its impact on subsequent therapy needs to be understood. Considering the central role of ER in driving the growth of ER+ breast cancers, and thus endocrine agents being a mainstay in the treatment paradigm, the effects of prior CDK4/6i exposure on ER signaling and the relevance of ER-targeted therapy are important to investigate. The objective of this study was to evaluate the anti-tumor activity of elacestrant, a novel oral selective estrogen receptor degrader (SERD), in preclinical models of CDK4/6i resistance. Methods Elacestrant was evaluated as a single agent, and in combination with alpelisib or everolimus, in multiple in vitro models and patient-derived xenografts that represent acquired and “de novo” CDK4/6i resistance. Results Elacestrant demonstrated growth inhibition in cells resistant to all three approved CDK4/6i (palbociclib, abemaciclib, ribociclib) in both ESR1 wild-type and mutant backgrounds. Furthermore, we demonstrated that elacestrant, as a single agent and in combination, inhibited growth of patient-derived xenografts that have been derived from a patient previously treated with a CDK4/6i or exhibit de novo resistance to CDK4/6i. While the resistant lines demonstrate distinct alterations in cell cycle modulators, this did not affect elacestrant’s anti-tumor activity. In fact, we observe that elacestrant downregulates several key cell cycle players and halts cell cycle progression in vitro and in vivo. Conclusions We demonstrate that breast cancer tumor cells continue to rely on ER signaling to drive tumor growth despite exposure to CDK4/6i inhibitors. Importantly, elacestrant can inhibit this ER-dependent growth despite previously reported mechanisms of CDK4/6i resistance observed such as Rb loss, CDK6 overexpression, upregulated cyclinE1 and E2F1, among others. These data provide a scientific rationale for the evaluation of elacestrant in a post-CDK4/6i patient population. Additionally, elacestrant may also serve as an endocrine backbone for rational combinations to combat resistance.

Apoptosis in megaloblastic anemia occurs during DNA synthesis by a p53-independent, nucleoside-reversible mechanism

Blood ◽  
2000 ◽  
Vol 96 (9) ◽  
pp. 3249-3255 ◽  
Author(s):  
Mark J. Koury ◽  
James O. Price ◽  
Geoffrey G. Hicks
Keyword(s):  
Dna Synthesis ◽  
De Novo ◽  
Megaloblastic Anemia ◽  
Experimental Studies ◽  
Hematopoietic Cells ◽  
S Phase ◽  
De Novo Synthesis ◽  
Complete Reversal ◽  
Phase Accumulation

Abstract Deficiency of folate or vitamin B12 (cobalamin) causes megaloblastic anemia, a disease characterized by pancytopenia due to the excessive apoptosis of hematopoietic progenitor cells. Clinical and experimental studies of megaloblastic anemia have demonstrated an impairment of DNA synthesis and repair in hematopoietic cells that is manifested by an increased percentage of cells in the DNA synthesis phase (S phase) of the cell cycle, compared with normal hematopoietic cells. Both folate and cobalamin are required for normal de novo synthesis of thymidylate and purines. However, previous studies of impaired DNA synthesis and repair in megaloblastic anemia have concerned mainly the decreased intracellular levels of thymidylate and its effects on nucleotide pools and misincorporation of uracil into DNA. An in vitro model of folate-deficient erythropoiesis was used to study the relationship between the S-phase accumulation and apoptosis in megaloblastic anemia. The results indicate that folate-deficient erythroblasts accumulate in and undergo apoptosis in the S phase when compared with control erythroblasts. Both the S-phase accumulation and the apoptosis were induced by folate deficiency in erythroblasts fromp53 null mice. The complete reversal of the S-phase accumulation and apoptosis in folate-deficient erythroblasts required the exogenous provision of specific purines or purine nucleosides as well as thymidine. These results indicate that decreased de novo synthesis of purines plays as important a role as decreased de novo synthesis of thymidylate in the pathogenesis of megaloblastic anemia.

scholarly journals Identification of DHX9 as a cell cycle regulated nucleolar recruitment factor for CIZ1

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Urvi Thacker ◽  
Tekle Pauzaite ◽  
James Tollitt ◽  
Maria Twardowska ◽  
Charlotte Harrison ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Cell Cycle Progression ◽  
Zinc Finger Protein ◽  
S Phase ◽  
Cycle Progression ◽  
Inactive X Chromosome ◽  
Functional Characterisation ◽  
Interaction Partners

Abstract CIP1-interacting zinc finger protein 1 (CIZ1) is a nuclear matrix associated protein that facilitates a number of nuclear functions including initiation of DNA replication, epigenetic maintenance and associates with the inactive X-chromosome. Here, to gain more insight into the protein networks that underpin this diverse functionality, molecular panning and mass spectrometry are used to identify protein interaction partners of CIZ1, and CIZ1 replication domain (CIZ1-RD). STRING analysis of CIZ1 interaction partners identified 2 functional clusters: ribosomal subunits and nucleolar proteins including the DEAD box helicases, DHX9, DDX5 and DDX17. DHX9 shares common functions with CIZ1, including interaction with XIST long-non-coding RNA, epigenetic maintenance and regulation of DNA replication. Functional characterisation of the CIZ1-DHX9 complex showed that CIZ1-DHX9 interact in vitro and dynamically colocalise within the nucleolus from early to mid S-phase. CIZ1-DHX9 nucleolar colocalisation is dependent upon RNA polymerase I activity and is abolished by depletion of DHX9. In addition, depletion of DHX9 reduced cell cycle progression from G1 to S-phase in mouse fibroblasts. The data suggest that DHX9-CIZ1 are required for efficient cell cycle progression at the G1/S transition and that nucleolar recruitment is integral to their mechanism of action.

scholarly journals Functional Interactions between Herpesvirus Oncoprotein MEQ and Cell Cycle Regulator CDK2

1999 ◽  
Vol 73 (5) ◽  
pp. 4208-4219 ◽  
Author(s):  
Juinn-Lin Liu ◽  
Ying Ye ◽  
Zheng Qian ◽  
Yongyi Qian ◽  
Dennis J. Templeton ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Phosphorylation Site ◽  
Fibroblast Cell ◽  
S Phase ◽  
Morphological Transformation ◽  
Necrosis Factor Alpha ◽  
Coiled Bodies ◽  
Cdk Phosphorylation

ABSTRACT Marek’s disease virus, an avian alphaherpesvirus, has been used as an excellent model to study herpesvirus oncogenesis. One of its potential oncogenes, MEQ, has been demonstrated to transform a rodent fibroblast cell line, Rat-2, in vitro by inducing morphological transformation and anchorage- and serum-independent growth and by protecting cells from apoptosis induced by tumor necrosis factor alpha, C2-ceramide, UV irradiation, or serum deprivation. In this report, we show that there is a cell cycle-dependent colocalization of MEQ protein and cyclin-dependent kinase 2 (CDK2) in coiled bodies and the nucleolar periphery during the G1/S boundary and early S phase. To our knowledge, this is the first demonstration that CDK2 is found to localize to coiled bodies. Such an in vivo association and possibly subsequent phosphorylation may result in the cytoplasmic translocation of MEQ protein. Indeed, MEQ is expressed in both the nucleus and the cytoplasm during the G1/S boundary and early S phase. In addition, we were able to show in vitro phosphorylation of MEQ by CDKs. We have mapped the CDK phosphorylation site of MEQ to be serine 42, a residue in the proximity of the bZIP domain. An indirect-immunofluorescence study of the MEQ S42D mutant, in which the CDK phosphorylation site was mutated to a charged residue, reveals more prominent cytoplasmic localization. This lends further support to the notion that the translocation of MEQ is regulated by phosphorylation. Furthermore, phosphorylation of MEQ by CDKs drastically reduces the DNA binding activity of MEQ, which may in part account for the lack of retention of MEQ oncoprotein in the nucleus. Interestingly, the localization of CDK2 in coiled bodies and the nucleolar periphery is observed only in MEQ-transformed Rat-2 cells, implicating MEQ in modifying the subcellular localization of CDK2. Taken together, our data suggest that there is a novel reciprocal modulation between the herpesvirus oncoprotein MEQ and CDK2.

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