Comparative analysis of the intracellular localization of c-Myc, c-Fos, and replicative proteins during cell cycle progression

In eukaryotic cells, nucleus-cytoplasm exchanges play an important role in genomic regulation. We have analyzed the localization of four nuclear antigens in different growth conditions: two replicative proteins, DNA polymerase alpha and proliferating cell nuclear antigen (PCNA), and two oncogenic regulatory proteins, c-Myc and c-Fos. A kinetic study of subcellular localization of these proteins has been done. In cultures in which cells were sparse, these proteins were detected in the nucleus. When proliferation was stopped by the high density of culture cells or by serum starvation, these proteins left the nucleus for the cytoplasm with different kinetics. DNA polymerase alpha is the first protein to leave the nucleus, with the PCNA protein, c-Fos, and c-Myc leaving the nucleus later. In contrast, during serum stimulation c-Fos and c-Myc relocalize into the nucleus before the replicative proteins. We also noticed that in sparse cell cultures, 10% of the cells exhibit a perinuclear staining for the DNA polymerase alpha, PCNA, and c-Myc proteins but not for c-Fos. This peculiar staining was also observed as an initial step to nuclear localization after serum stimulation and in vivo in Xenopus embryos when the G1 phase is reintroduced in the embryonic cell cycle at the mid-blastula stage. We suggest that such staining could reflect specific structures involved in the initiation of the S phase.

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Involvement of proliferating cell nuclear antigen (cyclin) in DNA replication in living cells

Molecular and Cellular Biology ◽

10.1128/mcb.9.1.57-66.1989 ◽

1989 ◽

Vol 9 (1) ◽

pp. 57-66

Author(s):

M Zuber ◽

E M Tan ◽

M Ryoji

Keyword(s):

Dna Polymerase ◽

Proliferating Cell Nuclear Antigen ◽

Living Cells ◽

Nuclear Antigen ◽

Plasmid Replication ◽

Dna Polymerase Delta ◽

Dna Polymerase Alpha ◽

Proliferating Cell

Proliferating cell nuclear antigen (PCNA) (also called cyclin) is known to stimulate the activity of DNA polymerase delta but not the other DNA polymerases in vitro. We injected a human autoimmune antibody against PCNA into unfertilized eggs of Xenopus laevis and examined the effects of this antibody on the replication of injected plasmid DNA as well as egg chromosomes. The anti-PCNA antibody inhibited plasmid replication by up to 67%, demonstrating that PCNA is involved in plasmid replication in living cells. This result further implies that DNA polymerase delta is necessary for plasmid replication in vivo. Anti-PCNA antibody alone did not block plasmid replication completely, but the residual replication was abolished by coinjection of a monoclonal antibody against DNA polymerase alpha. Anti-DNA polymerase alpha alone inhibited plasmid replication by 63%. Thus, DNA polymerase alpha is also required for plasmid replication in this system. In similar studies on the replication of egg chromosomes, the inhibition by anti-PCNA antibody was only 30%, while anti-DNA polymerase alpha antibody blocked 73% of replication. We concluded that the replication machineries of chromosomes and plasmid differ in their relative content of DNA polymerase delta. In addition, we obtained evidence through the use of phenylbutyl deoxyguanosine, an inhibitor of DNA polymerase alpha, that the structure of DNA polymerase alpha holoenzyme for chromosome replication is significantly different from that for plasmid replication.

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Fibroblast proliferation during myocardial development in rats is regulated by IGF-1 receptors

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1995.269.3.h943 ◽

1995 ◽

Vol 269 (3) ◽

pp. H943-H951 ◽

Cited By ~ 3

Author(s):

K. Reiss ◽

W. Cheng ◽

J. Kajstura ◽

E. H. Sonnenblick ◽

L. G. Meggs ◽

...

Keyword(s):

Dna Replication ◽

Dna Polymerase ◽

Proliferating Cell Nuclear Antigen ◽

Cardiac Fibroblasts ◽

Nuclear Antigen ◽

Dna Polymerase Alpha ◽

Myocardial Development ◽

Left And Right ◽

Proliferating Cell

To determine whether the growth of cardiac fibroblasts during development is modulated by the insulin-like growth factor (IGF)-1 receptor (IGF-1R), the expression of IGF-1, IGF-2, and IGF-1R was determined in fibroblasts from fetal and postnatal hearts. The expression of proliferating cell nuclear antigen (PCNA) and DNA polymerase-alpha was also evaluated in combination with the estimation of DNA replication. In comparison with fetal hearts, at postnatal day 21, fibroblast expression of IGF-1R mRNA, IGF-2, PCNA, and DNA polymerase-alpha was reduced by 77, 70, 80, and 86%, respectively. Moreover, IGF-1R protein decreased by 48% at 21 days. Bromodeoxyuridine labeling decreased by 88 and 89% in the left and right ventricle, respectively, at this time. Two different antisense oligodeoxynucleotides to IGF-1R reduced DNA replication by 60 and 44% in fibroblasts in culture. In addition, this intervention markedly attenuated the growth response of fibroblasts to IGF-1 or serum. In conclusion, the IGF-1R system appears to play a major role in the regulation of fibroblast growth in the heart in vivo.

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Involvement of proliferating cell nuclear antigen (cyclin) in DNA replication in living cells.

Molecular and Cellular Biology ◽

10.1128/mcb.9.1.57 ◽

1989 ◽

Vol 9 (1) ◽

pp. 57-66 ◽

Cited By ~ 73

Author(s):

M Zuber ◽

E M Tan ◽

M Ryoji

Keyword(s):

Dna Polymerase ◽

Proliferating Cell Nuclear Antigen ◽

Living Cells ◽

Nuclear Antigen ◽

Plasmid Replication ◽

Dna Polymerase Delta ◽

Dna Polymerase Alpha ◽

Proliferating Cell

Proliferating cell nuclear antigen (PCNA) (also called cyclin) is known to stimulate the activity of DNA polymerase delta but not the other DNA polymerases in vitro. We injected a human autoimmune antibody against PCNA into unfertilized eggs of Xenopus laevis and examined the effects of this antibody on the replication of injected plasmid DNA as well as egg chromosomes. The anti-PCNA antibody inhibited plasmid replication by up to 67%, demonstrating that PCNA is involved in plasmid replication in living cells. This result further implies that DNA polymerase delta is necessary for plasmid replication in vivo. Anti-PCNA antibody alone did not block plasmid replication completely, but the residual replication was abolished by coinjection of a monoclonal antibody against DNA polymerase alpha. Anti-DNA polymerase alpha alone inhibited plasmid replication by 63%. Thus, DNA polymerase alpha is also required for plasmid replication in this system. In similar studies on the replication of egg chromosomes, the inhibition by anti-PCNA antibody was only 30%, while anti-DNA polymerase alpha antibody blocked 73% of replication. We concluded that the replication machineries of chromosomes and plasmid differ in their relative content of DNA polymerase delta. In addition, we obtained evidence through the use of phenylbutyl deoxyguanosine, an inhibitor of DNA polymerase alpha, that the structure of DNA polymerase alpha holoenzyme for chromosome replication is significantly different from that for plasmid replication.

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Regulation of Raf-1-dependent signaling during early Xenopus development.

Molecular and Cellular Biology ◽

10.1128/mcb.15.12.6686 ◽

1995 ◽

Vol 15 (12) ◽

pp. 6686-6693 ◽

Cited By ~ 21

Author(s):

A M MacNicol ◽

A J Muslin ◽

E L Howard ◽

A Kikuchi ◽

M C MacNicol ◽

...

Keyword(s):

Cell Cycle ◽

Cell Cycle Progression ◽

Mapk Pathway ◽

Mapk Signaling ◽

Embryonic Cell ◽

Cycle Progression ◽

Mapk Activity ◽

Cytostatic Factor ◽

Differentiation And Proliferation

The Raf-1 gene product is activated in response to cellular stimulation by a variety of growth factors and hormones. Raf-1 activity has been implicated in both cellular differentiation and proliferation. We have examined the regulation of the Raf-1/MEK/MAP kinase (MAPK) pathway during embryonic development in the frog Xenopus laevis. We report that Raf-1, MEK, and MAPK activities are turned off following fertilization and remain undetectable up until blastula stages (stage 8), some 4 h later. Tight regulation of the Raf-1/MEK/MAPK pathway following fertilization is crucial for embryonic cell cycle progression. Inappropriate reactivation of MAPK activity by microinjection of oncogenic Raf-1 RNA results in metaphase cell cycle arrest and, consequently, embryonic lethality. Our findings demonstrate an absolute requirement, in vivo, for inactivation of the MAPK signaling pathway to allow normal cell cycle progression during the period of synchronous cell divisions which occur following fertilization. Further, we show that cytostatic factor effects are mediated through MEK and MAPK.

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Evidence that POB1, a Saccharomyces cerevisiae protein that binds to DNA polymerase alpha, acts in DNA metabolism in vivo

Molecular and Cellular Biology ◽

10.1128/mcb.12.12.5724-5735.1992 ◽

1992 ◽

Vol 12 (12) ◽

pp. 5724-5735

Author(s):

J Miles ◽

T Formosa

Keyword(s):

Saccharomyces Cerevisiae ◽

Dna Replication ◽

Dna Polymerase ◽

Yeast Cells ◽

Chromosome Loss ◽

Dna Metabolism ◽

Checkpoint Gene ◽

Dna Polymerase Alpha ◽

In Cells

Potential DNA replication accessory factors from the yeast Saccharomyces cerevisiae have previously been identified by their ability to bind to DNA polymerase alpha protein affinity matrices (J. Miles and T. Formosa, Proc. Natl. Acad. Sci. USA 89:1276-1280, 1992). We have now used genetic methods to characterize the gene encoding one of these DNA polymerase alpha-binding proteins (POB1) to determine whether it plays a role in DNA replication in vivo. We find that yeast cells lacking POB1 are viable but display a constellation of phenotypes indicating defective DNA metabolism. Populations of cells lacking POB1 accumulate abnormally high numbers of enlarged large-budded cells with a single nucleus at the neck of the bud. The average DNA content in a population of cells lacking POB1 is shifted toward the G2 value. These two phenotypes indicate that while the bulk of DNA replication is completed without POB1, mitosis is delayed. Deleting POB1 also causes elevated levels of both chromosome loss and genetic recombination, enhances the temperature sensitivity of cells with mutant DNA polymerase alpha genes, causes increased sensitivity to UV radiation in cells lacking a functional RAD9 checkpoint gene, and causes an increased probability of death in cells carrying a mutation in the MEC1 checkpoint gene. The sequence of the POB1 gene indicates that it is identical to the CTF4 (CHL15) gene identified previously in screens for mutations that diminish the fidelity of chromosome transmission. These phenotypes are consistent with defective DNA metabolism in cells lacking POB1 and strongly suggest that this DNA polymerase alpha-binding protein plays a role in accurately duplicating the genome in vivo.

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Gene expression of human DNA polymerase alpha during cell proliferation and the cell cycle

Molecular and Cellular Biology ◽

10.1128/mcb.8.11.5016-5025.1988 ◽

1988 ◽

Vol 8 (11) ◽

pp. 5016-5025

Author(s):

A F Wahl ◽

A M Geis ◽

B H Spain ◽

S W Wong ◽

D Korn ◽

...

Keyword(s):

Gene Expression ◽

Cell Cycle ◽

Cell Proliferation ◽

Steady State ◽

Dna Polymerase ◽

Transformed Cells ◽

Mrna Levels ◽

Dna Polymerase Alpha ◽

Human Dna ◽

Alpha Gene

We studied the expression of the human DNA polymerase alpha gene during cell proliferation, during cell progression through the cell cycle, and in transformed cells compared with normal cells. During the activation of quiescent cells (G0 phase) to proliferate (G1/S phases), the steady-state mRNA levels, rate of synthesis of nascent polymerase protein, and enzymatic activity in vitro exhibited a substantial and concordant increase prior to the peak of in vivo DNA synthesis. In transformed cells, the respective values were amplified greater than 10-fold. In actively growing cells separated into discrete stages of the cell cycle by counterflow elutriation or by mitotic shakeoff, levels of steady-state transcripts, translation rates, and enzymatic activities of polymerase alpha were constitutively and concordantly expressed at all stages of the cell cycle, with only a moderate elevation prior to the S phase and a slight decline in the G2 phase. These findings support the conclusion that the regulation of human DNA polymerase alpha gene expression is at the transcriptional level and strongly suggest that the regulatory mechanisms that are operative during the entrance of a cell into the mitotic cycle are fundamentally different from those that modulate polymerase alpha expression in continuously cycling cells.

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Cell cycle progression and cell division are sensitive to hypoxia in Drosophila melanogaster embryos

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.2001.280.5.r1555 ◽

2001 ◽

Vol 280 (5) ◽

pp. R1555-R1563 ◽

Cited By ~ 25

Author(s):

Robert M. Douglas ◽

Tian Xu ◽

Gabriel G. Haddad

Keyword(s):

Cell Cycle ◽

Drosophila Melanogaster ◽

Mammalian Cells ◽

Fluorescent Protein ◽

Immunoblot Analysis ◽

Embryonic Cell ◽

Cell Cycle Checkpoints ◽

Cycle Phase ◽

Embryonic Cells

We and others recently demonstrated that Drosophila melanogaster embryos arrest development and embryonic cells cease dividing when they are deprived of O2. To further characterize the behavior of these embryos in response to O2 deprivation and to define the O2-sensitive checkpoints in the cell cycle, embryos undergoing nuclear cycles 3–13 were subjected to O2deprivation and examined by confocal microscopy under control, hypoxic, and reoxygenation conditions. In vivo, real-time analysis of embryos carrying green fluorescent protein-kinesin demonstrated that cells arrest at two major points of the cell cycle, either at the interphase (before DNA duplication) or at metaphase, depending on the cell cycle phase at which O2 deprivation was induced. Immunoblot analysis of embryos whose cell divisions are synchronized by inducible String (cdc25 homolog) demonstrated that cyclin B was degraded during low O2 conditions in interphase-arrested embryos but not in those arrested in metaphase. Embryos resumed cell cycle activity within ∼20 min of reoxygenation, with very little apparent change in cell cycle kinetics. We conclude that there are specific points during the embryonic cell cycle that are sensitive to the O2 level in D. melanogaster. Given the fact that O2deprivation also influences the growth and development of other species, we suggest that similar hypoxia-sensitive cell cycle checkpoints may also exist in mammalian cells.

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