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PubMed2002

Menin's interaction with glial fibrillary acidic protein and vimentin suggests a role for the intermediate filament network in regulating menin activity.

Recently the multiple endocrine neoplasia type 1 (MEN1) tumor suppressor gene was cloned. Its protein product, called menin, has been shown to associate with the AP1 transcription factor JunD and to repress JunD-mediated transcription. However, little is known concerning the regulation of menin. Here we report that menin interacts with the type III intermediate filament (IF) proteins glial fibrillary acidic protein (GFAP) and vimentin. Menin's interaction with these IF proteins was characterized and confirmed both in vitro and in vivo using GST pull-down analysis, co-immunoprecipitation experiments, and immunofluorescence studies. Deletion mutants of GFAP or vimentin involving the head domains of the molecules abolish the interaction with menin. Endogenous menin is colocalized with GFAP and vimentin in glioma cells as determined by confocal microscopy. Furthermore, a tailless GFAP deletion mutant, which disrupts the IF network, results in menin/GFAP/vimentin-containing aggregates. Triple immunofluorescence labeling studies with antibodies against menin, BrdU, and GFAP show that menin and GFAP colocalize in glioma cells at the S-G2 phase of the cell cycle, as measured by BrdU incorporation. Our data suggest that the intermediate filament network interacts with and may serve as a cytoplasmic sequestering network for menin at the S and early G2 phase of the cell cycle.

Gene Library↗

PubMed1978

[Synthesis of nucleic acids and proteins in synchronized Ehrlich tumour cells].

The activation of RNA synthesis in Ehrlich tumour cells occurs during the transition: G1 leads to S simultaneously with the onset of DNA replication and is intermittent. A high rate of synthesis is maintained at a constant level for some period of time and is decreased only by the end of the mitotic cycle. Actinomycin D (0.05 mkg/ml) inhibits the label incorporation into RNA in the S- and G2 phases, but has no inhibiting effect at earlier stages. These findings and the data from polyacrylamide gel electrophoresis suggest that all types of rRNA and tRNA are synthesized in the course of the S- and G2 phases. The rate of protein synthesis is correlated with that of protein synthesis in tumour cells at all stages of the cycle. Electrophoresis in polyacrylamide gel shows that the spectra of nuclear proteins and Ehrlich tumour cell cytoplasm are not significantly changed throughout the mitotic cycle. The amount of histones in the nuclei is increased simultaneously with the increase in the level of DNA, so that the histone/DNA ratio remains constant throughout the cycle and is equal to 0,96 +/- 0,03.

Animals↗

PubMed1977

Effect of interferon on growth and division cycle of Friend erythroleukemic murine cells in vitro.

The administration of appropriate doses of interferon to cultures of Friend leukemia cells causes a pronounced inhibition of cell growth. Several lines of evidence indicate that this effect is due to interferon itself, rather than to unknown contaminants of interferon preparations. Autoradiograph analysis of growth parameters of Friend leukemia cells during treatment with interferon demonstrates that the rate of entry into the S phase, the percent decline of unlabeled mitoses, and the mitotic indexes are significantly lower in interferon-treated cell cultures than in control untreated cultures when tritiated thymidine was added 12 h after the administration of interferon. These data indicate that fractions of interferon-treated cell population are delayed in both G1 and in G2 phases of the cell cycle. This was confirmed by exact measurements of the length of the various phases of the cycle. The interferon-induced inhibition of growth of Friend leukemia cells is reversible after removal of the compound. Autoradiograph data obtained from control cultures and from cultures previously treated with interferon that had been washed free of interferon and reseeded in interferon-free medium, demonstrate that during the first 12 h after removal of interferon, a large majority of the cells previously treated with interferon had a deranged flow into the S phase, a high number of unlabeled mitoses, and a low mitotic index. These data provide further evidence for the above-mentioned prolongations of G1 and G2 phases of the cell cycle. All growth parameters tested reverted to normal values within 12 h after washing out interferon.

Animals↗

PubMed1998

Apoptosis may be either suppressed or enhanced with strategic combinations of antineoplastic drugs or anti-IgM.

A variety of drugs have been used to treat B-lymphocyte neoplasms, including both cell cycle-specific (CCS) and non-cell-cycle-specific drugs. Although the therapy for such cancers is complex and can include both types of drugs, the efficacy of these drugs in inducing cell death remains unclear. In this paper we have concentrated on specific CCS drugs and have examined their ability to induce programmed cell death (apoptosis) in Burkitt's lymphoma cell lines derived from patients. The CCS drugs chosen were hydroxyurea and aphidicolin (active in late G1, early S phase), the topoisomerase poisons camptothecin and etoposide (S, early G2 phase) and vincristine and Taxol (late G2, M phase). These choices allow comparison of two drugs with differing modes of action for each of the various phases of the cell cycle. Our results indicate that the variation in apoptosis between drugs that act at the same phase of the cell cycle is negligible. Both S/G2 and G2/M blockers are very potent at inducing apoptosis whereas G1/S blockers are ineffective in the induction of apoptosis. In addition, marked kinetic variations in the rate of apoptosis induction were observed, etoposide and camptothecin being more rapid in their action than the other agents. The order of effectiveness in inducing apoptosis on a kinetic basis was S/G2 agents >> G2/M agents >> G1/S agents. In this study we have also found that growth inhibition was induced by all the CCS agents chosen and by anti-IgM in various Burkitt's lymphoma lines. Furthermore c-myc was down-regulated under similar conditions. Since apoptosis was only selectively induced by some of the CCS agents, it implies c-myc expression is associated with growth regulation and c-myc down-regulation is an insufficient condition for the induction of apoptosis. In addition, cotreatments using the CCS and other agents revealed the following: Cotreatment using two CCS drugs which act at the same stage in the cell cycle showed either no change or only additivity to the effects seen with either agent alone. However, cotreatment with CCS drugs showed that an inhibitory effect is found between G1/S and G2/M drugs or S/G2 and G2/M drugs. No effect was found between G1/S and S/G2 drugs. Anti-IgM, which by itself was capable of inducing apoptosis, was observed to augment apoptosis induced by very low concentrations of G2/M-acting drugs but it has little effect on G1/S or the S/G2 drugs. The inhibitory effect of anti-CD40 or TNF-alpha on anti-IgM-induced apoptosis did not carry over to an effect on apoptosis induction by the CCS agents. Thus specific combinations of agents may lead to either enhancement, inhibition, or no interactive effect on apoptosis.

Antibodies, Anti-Idiotypic↗

PubMed2006

Misregulated chromosome condensation in MCPH1 primary microcephaly is mediated by condensin II.

Autosomal recessive primary microcephaly (MCPH) is a neurodevelopmental disorder characterized by marked reduction in brain size and mental retardation. Mutations in the gene MCPH1, encoding microcephalin, cause MCPH and a unique cellular phenotype with premature chromosome condensation in early G2 phase and delayed decondensation post mitosis. Here, we show that in MCPH1 patient cells, siRNA-mediated depletions of condensin II subunits lead to a pronounced reduction of cells with the condensation defects in both G1 and G2 phases of the cell cycle. Similar results are obtained when microcephalin and condensin II are simultaneously depleted in HeLa cells. In contrast, depletions of condensin I subunits do not reverse the cellular phenotype. Consistently, condensin I stays in the cytoplasm in the prophase-like cells of MCPH1 patients. Our results offer a molecular explanation for the aberrant chromosome condensation in MCPH1-deficiency and provide additional evidence that condensin I and II are regulated by distinct pathways.

Adenosine Triphosphatases↗

PubMed1992

The contribution of DNA and chromosome repair deficiencies to the radiosensitivity of ataxia-telangiectasia.

Cells derived from individuals with ataxia-telangiectasia (AT) are more sensitive to ionizing radiation and radiomimetic drugs, as evidenced by decreased survival and increased chromosome aberrations at mitosis when compared with normal cell lines. Our previous studies showed that, despite similar initial levels of DNA double-strand breaks (DSBs), AT cells express higher initial chromosome damage than do normal cells as demonstrated by the technique of premature chromosome condensation. However, this finding accounted for only a portion of the increased sensitivity (T. K. Pandita and W. N. Hittelman, Radiat. Res. 130, 94-103, 1992). The purpose of the study reported here was to examine the contribution of DNA and chromosome repair to the radiosensitivity of AT cells. Exponentially growing AT and normal lymphoblastoid cells were fractionated into cell cycle phase-enriched populations by centrifugal elutriation, and their DNA and chromosome repair characteristics were evaluated by DNA neutral filter elution (for DNA DSBs) and by premature chromosome condensation, respectively. AT cells exhibited a reduced fast-repair component in both G1- and G2-phase cells, as observed at the level of both DNA DSBs and the chromosome; however, S-phase cells showed nearly normal DNA DSB repair. The findings that AT cells exhibit an increased level of chromosome damage and a deficiency in the fast component (but not the slow component) of repair suggest that chromatin organization might play a major role in the observed sensitivity of AT cells. When survival was plotted as a function of the residual amount of chromosome damage in G1- and G2- phase cells after 90 min of repair, the curves for normal and AT cells approached each other but did not overlap. These results suggest that, although higher initial levels of chromosome damage and reduced chromosome repair capability can explain much of the radiosensitivity of AT cells, other differences in AT cells must also contribute to their sensitivity phenotype.

Ataxia Telangiectasia↗

PubMed1989

Bromodeoxyuridine amplifies free-radical-mediated DNA damage.

Elevated oxygen concentrations and paraquat, a superoxide-generating compound, induce an arrest of cells in the G2 phase of the cell cycle, which can be enhanced by adding bromodeoxyuridine (BrdU) to the culture medium. Experiments with the lipophilic peroxide cumene hydroperoxide and the free-radical scavenger vitamin E demonstrate that the BrdU-dependent G2 arrest is not mediated by lipid peroxidation. The BrdU-dependency of arrest in the G2 phase can be used as a sensitive cell biological assay to detect DNA damage elicited by oxygen free radicals.

Bromodeoxyuridine↗

PubMed1993

9-Nitro-camptothecin delays growth of U-937 leukemia tumors in nude mice and is cytotoxic or cytostatic for human myelomonocytic leukemia lines in vitro.

The camptothecin derivatives 9-nitro-camptothecin (9NC) and 9-amino-camptothecin (9AC) inhibit similarly growth of HL-60, KG-1, and U-937 cells in vitro, whereas growth of THP-1 cells is inhibited by 9AC, but not by 9NC. Growth inhibition is accompanied by enlargement of cells which contain one (HL-60, THP-1) or more (KG-1, U-937) nuclei. Flow cytometry studies showed that 9NC-treated HL-60 and U-937 cells accumulate in the S and G2 phases of the cell cycle; then they die by apoptosis, with the HL-60 cells being more sensitive than U-937 cells to 9NC. In contrast, 9NC-treated KG-1 and THP-1 cells accumulate in S and G2 phases, but resist death by apoptosis. Of the cell lines tested, only U-937 cells xenografted in nude mice generated subcutaneous myeloid tumors, which exhibited a delayed growth in the presence of 9NC. Further, 9NC-treated advanced U-937 tumors regressed temporarily, indicating that U-937 cells consist of 9NC-sensitive and 9NC-resistant populations.

Animals↗

PubMed1978

The structure of nucleolar chromatin in Physarum polycephalum.

The nucleolar DNA of Physarum polycephalum has been differentially labelled with 3H-thymidine and the structure of the nucleolar chromatin investigated by digestion with micrococcal nuclease. Nucleolar chromatin which had been labelled in G2 phase of the cell cycle and then digested before mitosis had an identical DNA repeat length to main band DNA (165 +/- 5 base pairs) but there was a definite indication that the rate of digestion was faster for nucleolar DNA than for main band DNA. Nucleolar chromatin which had been labelled in G2 and the label chased through mitosis into G2 phase of the next cycle showed an identical DNA repeat length to main band DNA and was also digested at the same rate. We conclude that nucleolar chromatin, at least 25 per cent of which is maximally transcriptionally active in G2, has a nucleosome-like structure.

Cell Cycle↗

PubMed2004

Telomere shortening triggers senescence of human cells through a pathway involving ATM, p53, and p21(CIP1), but not p16(INK4a).

Cellular senescence can be triggered by telomere shortening as well as a variety of stresses and signaling imbalances. We used multiparameter single-cell detection methods to investigate upstream signaling pathways and ensuing cell cycle checkpoint responses in human fibroblasts. Telomeric foci containing multiple DNA damage response factors were assembled in a subset of senescent cells and signaled through ATM to p53, upregulating p21 and causing G1 phase arrest. Inhibition of ATM expression or activity resulted in cell cycle reentry, indicating that stable arrest requires continuous signaling. ATR kinase appears to play a minor role in normal cells but in the absence of ATM elicited a delayed G2 phase arrest. These pathways do not affect expression of p16, which was upregulated in a telomere- and DNA damage-independent manner in a subset of cells. Distinct senescence programs can thus progress in parallel, resulting in mosaic cultures as well as individual cells responding to multiple signals.

Ataxia Telangiectasia Mutated Proteins↗

PubMed1988

Transforming growth factor-beta-induced growth inhibition and cellular hypertrophy in cultured vascular smooth muscle cells.

We have explored the hypothesis that hypertrophy of vascular smooth muscle cells may be regulated, in part, by growth inhibitory factors that alter the pattern of the growth response to serum mitogens by characterizing the effects of the potent growth inhibitor, transforming growth factor-beta (TGF-beta), on both hyperplastic and hypertrophic growth of cultured rat aortic smooth muscle cells. TGF-beta inhibited serum-induced proliferation of rat aortic smooth muscle cells (ED50 = 2 pM); this is consistent with previously reported observations in bovine aortic smooth muscle cells (Assoian et al. 1982. J. Biol. Chem. 258:7155-7160). Growth inhibition was due in part to a greater than twofold increase in the cell cycle transit time in cells that continued to proliferate in the presence of TGF-beta. TGF-beta concurrently induced cellular hypertrophy as assessed by flow cytometric analysis of cellular protein content (47% increase) and forward angle light scatter (32-50% increase), an index of cell size. In addition to being time and concentration dependent, this hypertrophy was reversible. Simultaneous flow cytometric evaluation of forward angle light scatter and cellular DNA content demonstrated that TGF-beta-induced hypertrophy was not dependent on withdrawal of cells from the cell cycle nor was it dependent on growth arrest of cells at a particular point in the cell cycle in that both cycling cells in the G2 phase of the cell cycle and those in G1 were hypertrophied with respect to the corresponding cells in vehicle-treated controls. Chronic treatment with TGF-beta (100 pM, 9 d) was associated with accumulation of cells in the G2 phase of the cell cycle in the virtual absence of cells in S phase, whereas subsequent removal of TGF-beta from these cultures was associated with the appearance of a significant fraction of cycling cells with greater than 4c DNA content, consistent with development of tetraploidy. Results of these studies support a role for TGF-beta in the control of smooth muscle cell growth and suggest that at least one mechanism whereby hypertrophy and hyperploidy may occur in this, as well as other cell types, is by alterations in the response to serum mitogens by potent growth inhibitors such as TGF-beta.

Animals↗

PubMed1983

Proliferative activity of bone marrow cells in primary dysmyelopoietic (preleukemic) syndromes.

The proliferative activity of bone marrow cells was studied in 24 patients with primary dysmyelopoiesis by means of flow cytometry and 3H-TdR autoradiography. Abnormal DNA content was found in two cases with aneuploid karyotypes. DNA content typical of a diploid population was observed in all patients with normal karyotype and in three patients with chromosomal aberrations. The fraction of bone marrow cells in S- and G2-phase was higher in primary acquired sideroblastic anemia and refractory anemia (without excess of blasts) than in refractory anemia with excess of blasts and chronic myelomonocytic leukemia. Regardless to the diagnosis, the patients with low fraction of cells in S- and G2-phase had short survival time and showed high rate of evolution into acute nonlymphoblastic leukemia. The labeling (LI) and mitotic (MI) indexes of both erythroblasts and granulocytic cells were decreased in nearly all patients. The lowest values of LI and MI of the granulocytic compartment were found in the patients who subsequently developed acute leukemia. These data suggest that cytokinetic analysis allows investigators to achieve useful information on the stage of disease in the dysmyelopoietic syndromes.

Adult↗

PubMed1985

Variations in antigen expression during the cell cycle of a human B-lymphoblastoid cell line.

Expression of six surface markers during the cell cycle of a human B-lymphoblastoid cell line has been examined. Cultures were synchronised by a double thymidine block, then monitored through a complete cell cycle following release. Surface marker expression was studied by manual immunofluorescence and flow cytometry. Surface topography of the cells during the cycle was examined by scanning electron microscopy. Some variation in the expression of all markers was observed during the cell cycle. Four antigens (surface membrane immunoglobulin, common ALL antigen, an immature cell marker identified by monoclonal antibody 11D1, and an ubiquitous leucocyte antigen identified by monoclonal antibody 6B1) showed maximal expression in S and/or G2 phase and minimal expression during mitosis. These results could be due to changes in cell size. However, the individual patterns of expression of these four antigens during the phases of the cell cycle implied that changes in antigen density also occurred, at least in some cases. In contrast, expression of HLA-A, B, C and Ia antigens did not parallel cell size and was lowest during the S and G2 phases, increasing to a peak in early G1 phase.

Antigens, Neoplasm↗

PubMed1994

[Cell cycle arrest induced by epidermal growth factor on human squamous cell carcinoma cell lines].

Although human squamous cell carcinoma (SCC) cell lines frequently contain an elevated number of epidermal growth factor (EGF) receptor accompanied with amplification of EGF receptor/c-erbB gene, it is well known that EGF inhibits the growth of these cells in culture at doses that stimulate the growth of epidermal keratinocytes and dermal fibroblasts. To study this growth inhibitory effect of EGF on the SCC cell lines, 3H-thymidine incorporation into DNA and cell cycle distribution were analyzed. In HSC-1 and NA cells, which contain the highest number of EGF receptor among these SCC cell lines, the inhibition of 3H-thymidine incorporation was apparent 2 to 4 hours after treatment with 100 ng/ml of EGF and reached more than 95% inhibition after 24 hours. Two-color cell cycle analysis using fluorescein isothiocyanate (FITC)-conjugated anti-Bromodeoxyuridine (BrdU) antibody and propidium iodide revealed that this inhibitory effect was due to cell cycle arrest not only in G1 but also in G2 phase. This effect was well correlated to the sensitivity to the growth inhibitory effect of EGF among the 4 SCC cell lines. These observations suggest that the SCC cells contain altered machineries which regulate the normal cell growth in both G1 and G2 phases, and the EGF affects these machineries via overexpressed its receptor.

Carcinoma, Squamous Cell↗

PubMed1997

Deficient DNA repair in chronic ulcerative colitis.

Carcinoma of the colon is a serious complication of chronic ulcerative colitis (CUC), a disease of unknown etiology. Peripheral blood lymphocytes from nine patients with CUC showed deficient repair of radiation-induced DNA damage compared with a group of healthy controls. DNA repair was measured indirectly by quantifying chromatid breaks after irradiation of cells with X-rays or ultraviolet during G2 phase of the cell cycle. Such breaks represent unrepaired DNA strand breaks that may arise directly from the damaging agent or indirectly during repair processes. Two types of deficiency were revealed. One was an abnormally high frequency of chromatid breaks after G2-phase X-irradiation. These may reflect deficient strand-break repair. The second deficiency was manifest as a low frequency of breaks not increased by addition of the DNA repair inhibitor araC. This low frequency apparently results from negligible incision activity. Deficient DNA repair in CUC may thus be a requisite predisposing factor for genomic instability and the potential development of colon carcinoma.

Adult↗

PubMed1990

Effects of etoposide (VP-16) on the survival and progression of cultured HeLa S3 cells through the cell cycle.

The survival of cultured HeLa S3 cells and their progression through the cell cycle after exposure to Etoposide (VP-16) were studied. The dose survival curve of exponentially growing cells was of a biphasic nature; the curve had an exponential slope starting from a small shoulder, and finally attained a plateau against increasing concentrations of the drug. Throughout the cell cycle, VP-16 exerted its main killing activity on cells in the late S and G2 phases, whereas cells in the G1 phase were resistant to the drug. By using a low concentration of VP-16, which allowed 85% of the treated cells to survive, it was found that the inhibition of the cell progression by the drug was greatest in the late S and G2 phases.

Cell Cycle↗

PubMed2002

Growth arrest in G1 protects against oxygen-induced DNA damage and cell death.

Although oxygen is required for normal aerobic respiration, hyperoxia (95% O(2)/5% CO(2)) damages DNA, inhibits proliferation in G1, S and G2 phases of the cell cycle, and induces necrosis. The current study examines whether growth arrest in G1 protects pulmonary epithelial cells from oxidative DNA damage and cell death. Mv1Lu pulmonary adenocarcinoma cells were chosen for studies because hyperoxia inhibits their proliferation in S and G2 phase, while they can be induced to arrest in G1 by altering culture conditions. Hyperoxia inhibited proliferation, increased intracellular redox, and rapidly reduced clonogenic survival. In contrast, Mv1Lu cells treated with transforming growth factor (TGF)-beta1, deprived of serum or grown to confluency, arrested and remained predominantly in G1 even during exposure. Growth arrest in G1 significantly enhanced clonogenic survival by 10-50-fold. Enhanced survival was not due to reduction in the intracellular redox-state of the cells, but instead was associated with reduced DNA strand breaks and p53 expression. Our findings suggest that the protective effects of G1 is mediated not simply by a reduction in intracellular ROS, but rather through an enhanced ability to limit or rapidly recognize and repair damaged DNA.

Adenocarcinoma↗

PubMed1981

Responses of synchronized HeLa cells to the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate as evaluated by flow cytometry.

A flow cytometric study was carried out on the effects of tumor-promoting 12-O-tetradecanoylphorbol-13-acetate (TPA; 10(-8) M) on HeLa cells synchronized by amethopterin for DNA synthesis. Cells treated with TPA at the time of release from the amethopterin block showed a delayed passage through S phase and partially through G2 in their immediate life span as measured 24 hr after release. This late G2 delay was not observed when TPA was added to cells during late S or G2 phase. In this case, however, a direct inhibition of cells in G2 became evident as observed about 15 hr after release from block. None of these effects was caused by the nonpromoting 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate (10(-6) M). These data support observations obtained with asynchronous cultures. The TPA effects resemble those reported after X-irradiation of cell cultures.

Cell Cycle↗