A quantitative model of the effect of unreplicated DNA on cell cycle progression in frog egg extracts

A critical goal in cell biology is to develop a systems-level perspective of eukaryotic cell cycle controls. Among these controls, a complex signaling network (called ‘checkpoints’) arrests progression through the cell cycle when there is a threat to genomic integrity such as unreplicated or damaged DNA. Understanding the regulatory principles of cell cycle checkpoints is important because loss of checkpoint regulation may be a requisite step on the roadway to cancer. Mathematical modeling has proved to be a useful guide to cell cycle regulation by revealing the importance of bistability, hysteresis and time lags in governing cell cycle transitions and checkpoint mechanisms. In this report, we propose a mathematical model of the frog egg cell cycle including effects of unreplicated DNA on progression into mitosis. By a stepwise approach utilizing parameter estimation tools, we build a model that is grounded in fundamental behaviors of the cell cycle engine (hysteresis and time lags), includes new elements in the signaling network (Myt1 and Chk1 kinases), and fits a large and diverse body of data from the experimental literature. The model provides a validated framework upon which to build additional aspects of the cell cycle checkpoint signaling network, including those control signals in the mammalian cell cycle that are commonly mutated in cancer.     

Baicalin suppresses the cell cycle progression and proliferation of prostate cancer cells through the CDK6/FOXM1 axis

Molecular and Cellular Biochemistry - Population data have consistently demonstrated a correlation between circulating branched-chain amino acids (BCAA) and insulin resistance. Most recently valine...     

The effect of iron and/or zinc diet supplementation and termination of this practice on the antioxidant status of the reproductive tissues and sperm viability in rats

AimsThe aim of this study was to investigate the effect of iron or/and zinc supplementation and termination of this treatment on the antioxidant defence of the male reproductive system and sperm viability in rats.MethodsThe study consisted of 3 stages: I) 4-week adaptation to the diets (C-control or D-iron deficient); II) 4-week iron and/or zinc supplementation (10-times more than in the C diet of iron: CSFe, DSFe; zinc: CSZn, DSZn; or iron and zinc: CSFeZn, DSFeZn; and III) 2-week post-supplementation period (the same diets as during stage I). Parameters of antioxidant status (total antioxidant capacity and SOD, GPx, and CAT activiy), oxidative damage (lipid and protein peroxidation), and sperm viability were measured.ResultsSimultaneous iron and zinc supplementation compared to iron supplementation (CSFeZn vs CSFe) increased SOD activity in the testes and decreased the level of malondialdehyde in the epididymis after stage II, and increased the percentage of live sperm after stage III. After discontinuation of the iron and zinc supplementation and a return to the control diet, the following was observed a decrease of SOD activity in the testes and GPx activity in the epididymis, and a increase malondialdehyde concentration in prostates. After stage III, in DSFeZn vs DSFe rats, an increase of SOD and CAT activity in the epididymis was found.ConclusionZinc supplementation simultaneous with iron may protect the male reproductive system against oxidative damage induced by high doses of iron and may have a beneficial effect on sperm viability. The effect of this supplementation was observed even two weeks after the termination of the intervention.     

Long noncoding RNA FOXD2-AS1 promotes glioma cell cycle progression and proliferation through the FOXD2-AS1/miR-31/CDK1 pathway

Long noncoding RNAs (lncRNAs) are vital mediators involved in cancer progression. Previous studies confirmed that FOXD2 adjacent opposite strand RNA 1 (FOXD2-AS1) is upregulated in tumor diseases. The potential influence of FOXD2-AS1 in glioma progression, however, remains unknown. In this paper, FOXD2-AS1 was found to be upregulated in glioma tissues. Its level was linked with glioma stage. Moreover, glioma patients expressing high level of FOXD2-AS1 suffered worse prognosis. Biological functions of FOXD2-AS1 in glioma cells were analyzed through integrative bioinformatics and TCGA RNA sequencing data analysis. Pathway enrichment analysis uncovered that FOXD2-AS1 was mainly linked with cell cycle regulation in both low-grade glioma and glioblastoma. Further experiments demonstrated that silence of FOXD2-AS1 inhibited proliferation, arrested cell cycle and downregulated cyclin-dependent kinase 1 (CDK1) in human glioma cells. Dual-luciferase reporter assay confirmed that FOXD2-AS1 upregulated CDK1 by sponging miR-31. Rescue assays were performed and confirmed the regulatory loop FOXD2-AS1/miR-31/CDK1 in glioma. Collectively, our results indicated that the FOXD2-AS1/miR-31/CDK1 axis influenced glioma progression, providing a potential new target for glioma patients.     

Effects of resveratrol on the G(0)-G(1) transition and cell cycle progression of mitogenically stimulated human lymphocytes

Resveratrol (RSV) has been suggested to have cancer preventive properties, on the basis that it suppresses proliferation and induces apoptosis in various tumor cells. Here we test its cytostatic effects on peripheral blood human lymphocytes. RSV (up to 50 microM) had no detectable effects on resting lymphocytes. With the mitogen phytohemagglutin (PHA), however, RSV elicited concentration- and time-dependent responses in lymphocytes. RSV (>/=50 microM) prevented cell entry into the cell cycle, resulting in 99% suppression at 100 microM. The arrested lymphocytes following 24h treatment with 50 microM RSV had minimal RNA content, the feature characteristic of G(0) cells, and were blocked at the stage past the induction of cyclins D2 and D3 and prior to induction of cyclin E. Prolonged treatment (72h) of PHA-stimulated lymphocytes with 100 microM RSV showed a pronounced decrease in the expression of pRb, cyclins E and B, and reduction in p34cdc2 and PCNA. The activation-induced apoptosis was also reduced in the presence of >/=50 microM RSV. These data suggest that studies designed to test RSV efficacy as a chemopreventive agent should include evaluation of its immunomodulatory effect revealed by suppression of lymphocyte stimulation as well as its effect on apoptosis of stimulated lymphocytes.     

DNA synthesis and the cell cycle in cultures of normal and mutant (mdg/mdg) embryonic mouse muscle cells.

The relationship between cell fusion, DNA synthesis and the cell cycle in cultured embryonic normal and dysgenic ($\text{mdg}\text{mdg}$) mouse muscle cells has been determined by autoradiography. The experimental evidence shows that the homozygous mutant myotubes form by a process of cell fusion and that nuclei within the myotubes do not synthesize DNA or undergo mitotic or amitotic division. The duration of the total cell cycle and its component phases was statistically the same in 2-day normal and mutant ($\text{mdg}\text{mdg}$) myogenic cultures with the approximate values: T, 21.5 hr; G₁, 10.5 hr; S, 7.5 hr; and G₂, 2.5 hr. In both kinds of cultures, labeled nuclei appeared in myotubes 15–16 hr after mononucleated cells were exposed to [³H]thymidine, and the rate of incorporation of labeled nuclei into multinucleated muscle cells was comparable in control and dysgenic cultures. Thus, homozygous $\text{mdg}\text{mdg}$ muscle cells in culture are similar to control cells with respect to their mechanism of myotube formation and the coordinate regulation of DNA synthesis and the cell cycle during myogenesis.     

Enhancement of cancer chemotherapy by simultaneously altering cell cycle progression and DNA-damage defenses through global modification of the serine/threonine phospho-proteome

Despite improvements in the therapeutic efficacy of rationally designed cancer treatment regimens, most cancers remain incurable once spread beyond their sites of origin. Failure to achieve sustained control or eradication of cancers arises in large part because a sub-population of quiescent “cancer stem cells” is insensitive to drugs targeting cell growth and replication and because defense mechanisms critical to survival of the normal cell also protect the cancer cell from cytotoxic injury. Global alteration of signal transduction by inhibition of serine/threonine dephosphorylation has recently been shown to markedly potentiate cancer cell killing by the DNA-methylating drug, temozolomide. Inhibition of the multifunctional protein phosphatase 2A appears to drive quiescent cancer cells into cycle and simultaneously inhibits cycle arrest, permitting cancer cell entry into mitosis despite the presence of chemotherapy induced DNA-damage. Absence of toxicity in animal models suggests that multi-site mutations in pathways regulating cell cycle in cancer cells make them more vulnerable than normal cells to large changes in the balance of phosphorylation-regulated signaling. Global modulation of the serine-threonine phospho-proteome may be a general method for enhancing the effectiveness of cytotoxic cancer therapy.     

Ivermectin inhibits the growth of glioma cells by inducing cell cycle arrest and apoptosis in vitro and in vivo

Glioma, the most predominant primary malignant brain tumor, remains uncured due to the absence of effective treatments. Hence, it is imperative to develop successful therapeutic agents. This study aimed to explore the antitumor effects and mechanisms of ivermectin (IVM) in glioma cells in vitro and in vivo. The effects of IVM on cell viability, cell cycle arrest, apoptosis rate, and morphological characteristics were determined respectively by MTT assay/colony formation assay, flow cytometry, and transmission electron microscope. In addition, the expression levels of cycle-related and apoptosis-associated proteins were individually examined by Western blot analysis. Moreover, cell proliferation and apoptosis analyses were carried out by TUNEL, Ki-67, cleaved caspase-3, and cleaved caspase-9 immunostaining assay. Our results demonstrated that IVM has a potential dosage-dependent inhibition effect on the apoptosis rate of glioma cells. Meanwhile, the results also revealed that IVM induced apoptosis by increasing caspase-3 and caspase-9 activity, upregulating the expressions of p53 and Bax, downregulating Bcl-2, activating cleaved caspase-3 and cleaved caspase-9, and blocking cell cycle in G0/G1 phase by downregulating levels of CDK2, CDK4, CDK6, cyclin D1, and cyclin E. These findings suggest that IVM has an inhibition effect on the proliferation of glioma cells by triggering cell cycle arrest and inducing cell apoptosis in vitro and in vivo, and probably represents promising agent for treating glioma.     

DACH1 regulates cell cycle progression of myeloid cells through the control of cyclin D, Cdk 4/6 and p21Cip1

The cell-fate determination factor Dachshund, a component of the Retinal Determination Gene Network (RDGN), has a role in breast tumor proliferation through the repression of cyclin D1 and several key regulators of embryonic stem cell function, such as Nanog and Sox2. However, little is known about the role of DACH1 in a myeloid lineage as a cell cycle regulator. Here, we identified the differential expression levels of extensive cell cycle regulators controlled by DACH1 in myeloid progenitor cells. The forced expression of DACH1 induced p27(Kip1) and repressed p21(Cip1), which is a pivotal characteristic of the myeloid progenitor. Furthermore, DACH1 significantly increased the expression of cyclin D1, D3, F, and Cdk 1, 4, and 6 in myeloid progenitor cells. The knockdown of DACH1 blocked the cell cycle progression of HL-60 promyeloblastic cells through the decrease of cyclin D1, D3, F, and Cdk 1, 4, and 6 and increase in p21(Cip1), which in turn decreased the phosphorylation of the Rb protein. The expression of Sox2, Oct4, and Klf4 was significantly up-regulated by the forced expression of DACH1 in mouse myeloid progenitor cells.     

Smad7 induces G0/G1 cell cycle arrest in mesenchymal cells by inhibiting the expression of G1 cyclins

The major Smad pathways serve in regulating the expression of genes downstream of TGFbeta signals. In this study, we examined the effects of sustained Smad7 expression in cultured cells. Interestingly, Smad7 caused various mesenchymal cells, including NIH3T3 fibroblast and ST2 bone-marrow stromal cells, to undergo a marked morphological alteration into a flattened cell shape, but kept them alive for as long as 60 days. Furthermore, Smad7 arrested the proliferation of the cells even before they reached confluence. These cells became quiescent in G0/G1 phase and accumulated a hypophosphorylated form of retinoblastoma. The cytostatic effect of Smad7 was closely associated with a preceding decrease in the levels of G1 cyclins, such as cyclin D1 and cyclin E. Accordingly, ectopic cyclin E was able to overcome the Smad7-induced arrest of proliferation. These results indicate that Smad7 functions upstream of G1 cyclins and suggest a novel role for Smad7 as an antiproliferative factor. In contrast to the growth of mesenchymal cells, that of epithelial cells was little susceptible to Smad7. The present findings raise the possibility that a link between Smad7 and the G1 to S phase transition may also contribute to the cell cycle control by certain Smad7-inducing stimuli in a cell-type-dependent fashion.     

Inactivation of Cdk1/Cyclin B in metaphase-arrested mouse FT210 cells induces exit from mitosis without chromosome segregation or cytokinesis and allows passage through another cell cycle

It is well known that inactivation of Cdk1/Cyclin B is required for cells to exit mitosis. The work reported here tests the hypothesis that Cdk1/Cyclin B inactivation is not only necessary but also sufficient to induce mitotic exit and reestablishment of the interphase state. This hypothesis predicts that inactivation of Cdk1 in metaphase-arrested cells will induce the M to G1-phase transition. It is shown that when mouse FT210 cells (in which Cdk1 is temperature-sensitive) are arrested in metaphase and then shifted to their non-permissive temperature, they rapidly exit mitosis as evidenced by reassembly of interphase nuclei, decondensation of chromosomes, and dephosphorylation of histones H1 and H3. The resulting interphase cells are functionally normal as judged by their ability to progress through another cell cycle. However, they have double the normal number of chromosomes because they previously bypassed anaphase, chromosome segregation, and cytokinesis. These results, taken together with other observations in the literature, strongly suggest that in mammalian cells, inactivation of Cdk1/cyclin B is the trigger for mitotic exit and reestablishment of the interphase state.     

Regulation of cell cycle and productivity in NS0 cells by the over-expression of p21CIP1.

We have constructed NS0 myeloma cell lines that inducibly express the p21CIP1 cyclin dependent kinase inhibitor, using the Lacswitch system. Ectopic p21(CIP1) protein expression was rapidly induced within 12 h of addition of IPTG, causing G1-phase arrest and almost complete inhibition of cell proliferation. The production of a chimeric IgG4 antibody, expressed constitutively from an independent promoter, was found to be significantly increased by more than 4-fold in p21CIP1-arrested cells. This study demonstrates for the first time the successful construction of anchorage-independent and proliferation-controlled NS0 cell lines with enhanced secreted chimeric antibody production independent of the inducible promoter activity used to achieve cytostasis.