Cell Cycle Traversal Research Articles

MicroRNA-204-5p-Mediated Regulation of SIRT1 Contributes to the Delay of Epithelial Cell Cycle Traversal in Diabetic Corneas.

We investigated how the microRNA (miRNA) modifies the expression of silent mating type information regulation 2 homolog 1 (SIRT1) in diabetic corneas. The bioinformatic assay was used to predict which miRNAs might regulate the expression of SIRT1. A lipid transfection protocol was used to upregulate or knockdown the miRNA expression in TKE2 cells. Adenovirus-expressing short interfering RNA was used to knockdown the expression of SIRT1 in TKE2 cells and Ins2(Akita/+) mice were used to evaluate how miRNA promotes diabetic corneal epithelial wound healing. Cell cycle status was determined by flow cytometry assay and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to analyze the cell viability. Nine miRNAs were selected for quantitative PCR (qPCR) detection after bioinformatics analysis. The miR-204-5p merited further investigation, because it was increased almost 5-fold in diabetic corneal epithelia compared to nondiabetic control corneal epithelia. Using luciferase activity assay, we identified SIRT1 was a direct target of miR-204-5p. The results of flow cytometry and MTT assay demonstrated that downregulation of miR-204-5p increased TKE2 cell growth and restored cell cycle progression in high glucose (HG) conditions by the regulation of Cyclin D1 and p16. Furthermore, we showed downregulation of miR-204-5p promoted HG attenuation of corneal epithelial wound healing via upregulation of SIRT1 in Ins2(Akita/+) mice. Our data provide firm evidence of a role for miR-204-5p in the direct regulation of SIRT1 in diabetic corneas and identified the miR-204-5p-mediated regulation of SIRT1 contributes to the delay of epithelial cell cycle traversal in diabetic keratopathy. : Chinese Abstract.

Thiamine and benfotiamine prevent increased apoptosis in endothelial cells and pericytes cultured in high glucose.

High glucose induces pathological alterations in small and large vessels, possibly through increased formation of AGE, activation of aldose reductase and protein kinase C, and increased flux through the hexosamine pathway. We showed previously that thiamine and benfotiamine correct delayed replication and increase lactate production in endothelial cells subjected to high glucose. We now aim at verifying the effects of thiamine and benfotiamine on cell cycle, apoptosis, and expression of adhesion molecules in endothelial cells and pericytes, under high ambient glucose. Human umbilical vein endothelial cells and bovine retinal pericytes were cultured in normal (5.6 mmol/L) or high (28 mmol/L) glucose, with or without thiamine or benfotiamine, 50 or 100 micro mol/L. Apoptosis was determined by two separate ELISA methods, measuring DNA fragmentation and caspase-3 activity, respectively. Cell cycle and integrin subunits alpha3, alpha5, and beta1 concentration were measured by flow cytometry. Apoptosis was increased in high glucose after 3 days of culture, both in endothelium and pericytes. Thiamine and benfotiamine reversed such effects. Neither cell cycle traversal nor integrin concentrations were modified in these experimental conditions. Thiamine and benfotiamine correct increased apoptosis due to high glucose in cultured vascular cells. Further elucidations of the mechanisms through which they work could help set the basis for clinical use of this vitamin in the prevention and/or treatment of diabetic microangiopathy.

P21Waf1/Cip1 and the prevention of oxidative stress.

pulmonary dysfunction resulting from acute oxygen toxicity is due at least in part to the death of lung epithelial cells. Pulmonary epithelial cells are essential to the maintenance of the alveolar-capillary barrier, and compromise may lead to leakage of fluid and proteins in the airways and alveoli

Human bronchial smooth muscle cell lines show a hypertrophic phenotype typical of severe asthma.

We developed clonal cell lines of human bronchial smooth muscle origin by retroviral transduction of temperature-sensitive simian virus 40 large tumor (T) antigen. These cells show increased growth potential at 33 degrees C, but on shift to the nonpermissive temperature (39 degrees C), they show diminished or arrested growth. In addition to the expected reduction in the level of large T antigen, cells shifted to 39 degrees C show increased expression of the cyclin-dependent kinase inhibitor p21(Waf1/Cip1), characteristic of cells arrested in G1 of the cell cycle. Shifted cells undergo a process of cell hypertrophy, as demonstrated by increased time of flight and forward scatter, as well as increased expression of the contractile proteins alpha-smooth muscle actin, myosin light chain kinase, and SM22. Changes in contractile protein expression were regulated primarily in a posttranscriptional manner. Phosphatidylinositol 3-kinase activity was increased in shifted cells, and chemical inhibition of phosphatidylinositol 3-kinase attenuated alpha-actin and myosin light-chain kinase expression. We have developed clonal cell lines of human bronchial smooth muscle origin that may be useful for the study of airway smooth muscle biology. Furthermore, we demonstrate that arrest of airway smooth muscle cell cycle traversal can induce cellular hypertrophy, which parallels changes observed in the airways of patients with severe asthma.

A study of capillary pericyte viability on extracellular matrix produced by endothelial cells in high glucose.

Thickening of the basement membrane and selective loss of pericytes occur early in diabetic retinopathy. As we showed previously that pericyte adhesion is impaired on extracellular matrix produced by endothelial cells in high hexose concentrations, we aimed to verify if altered adhesion could influence pericyte viability and replication. Conditioned extracellular matrices were obtained by growing human umbilical vein endothelial cells in media containing 28 mmol/l D-glucose, with or without the inhibitors of protein glycation thiamine or aminoguanidine, and D-galactose or L-glucose up to 28 mmol/l. Having removed the endothelium, bovine retinal pericytes were grown on these matrices and, in separate experiments, on laminin, fibronectin or type IV collagen. Pericyte viability and replication were measured by cell counts and DNA synthesis after 7 days, cell cycle traversal after 2 days and apoptosis after 18 h, 2 days and 7 days. Pericyte counts and DNA synthesis were reduced on matrices produced in high D-glucose and D-galactose, whilst matrix obtained in L-glucose reduced DNA synthesis but not counts. Both thiamine and aminoguanidine corrected reduced pericyte viability when added to high D-glucose. Cell cycle and apoptosis were not affected by growing pericytes on different conditioned matrices. Laminin, fibronectin and type IV collagen did not modify pericyte replication. Reduced pericyte counts could depend on impaired initial adhesion to the extracellular matrix produced by endothelium in high hexose concentrations, rather than impaired replication or viability. Altered cell-matrix interactions might facilitate pericyte dropout in diabetic retinopathy, independently of the effects of high glucose on pericyte replication.

Protection against chemotherapy-induced cytotoxicity by cyclin-dependent kinase inhibitors (CKI) in CKI-responsive cells compared with CKI-unresponsive cells

Inactivation of the retinoblastoma (Rb) protein caused by gene mutation, association with oncoproteins from small DNA viruses, mutational inactivation of p16(Ink4a), or overexpression of cyclin D is a common feature of many human cancer cells and is causally associated with the aberrant proliferation control of cancer cells; whereas normal cells maintain an integrated cell cycle machinery and are subject to cell cycle checkpoint control by cyclin-dependent kinase (CDK) inhibitors (CKIs). To determine whether this difference can be translated into a therapeutic advantage to protect normal cells from adverse cytotoxicity caused by chemotherapy, we established cell model systems for ecdysone-inducible expression of p16(Ink4a), p21(Waf1), and p27(Kip1) in one CKI-responsive cell line (A431 human vulvar epidermoid carcinoma cells with functional Rb) and one CKI-unresponsive cell line (SiHa human cervical cancer cells with nonfunctional Rb). Expression of p16(Ink4a), p21(Waf1), or p27(Kip1) in both SiHa and A431 cells strongly inhibited CDK2 activity, indicating functional expression of the CDK inhibitors in both cell lines. However, only in A431 cells did expression of p16(Ink4a), p21(Waf1), or p27(Kip1) cause Rb dephosphorylation, arrest cell cycle traversal, and potently inhibit cell proliferation. Induction of p16(Ink4a), p21(Waf1), or p27(Kip1) in SiHa cells failed to cause Rb dephosphorylation or to arrest cell cycle traversal, and such induction only minimally inhibited cell proliferation. We then compared the chemosensitivity of clones derived from these two cell lines when the CKIs were and were not induced. Induction of p16(Ink4a), p21(Waf1), or p27(Kip1) conferred strong resistance to paclitaxel- or cisplatin-mediated cytotoxicity on the CKI-responsive A431 cells but not on the CKI-unresponsive SiHa cells. Our results support a novel chemotherapy strategy for treating patients with Rb pathway-impaired cancers by concurrent administration of chemotherapy with CKIs as chemoprotective agents for normal cells.

Invited review: the circle of life: cell cycle regulation in airway smooth muscle.

Severe asthma is characterized by increased airway smooth muscle (ASM) mass, due predominantly to ASM hyperplasia. Diverse stimuli, which include growth factors, plasma- or inflammatory cell-derived mediators, contractile agonists, cytokines, and extracellular matrix proteins, induce ASM proliferation. Mitogens act via receptor tyrosine kinase, G protein-coupled receptors, or cytokine receptors, to activate p21ras and stimulate two parallel signaling pathways in ASM cells, namely, the extracellular signal-regulated kinase (ERK) or the phosphatidylinositol 3-kinase (PI3K) pathways. ERK and PI3K regulate cell cycle protein expression and thus modulate cell cycle traversal. ERK activation and downstream effectors of PI3K, such as Rac1 and Cdc42, stimulate expression of cyclin D1, a key regulator of G(1) progression in the mammalian cell cycle. In addition, PI3K activates 70-kDa ribosomal S6 kinase, an enzyme that also regulates the translation of many cell cycle proteins, including the elongation factor E2F. The present review examines the mitogens and critical signal transduction pathways that stimulate ASM cell proliferation. Further study in this area may reveal new therapeutic targets to abrogate ASM hyperplasia in diseases such as asthma and chronic obstructive pulmonary disease.

P38 MAP kinase negatively regulates cyclin D1 expression in airway smooth muscle cells.

We have demonstrated that platelet-derived growth factor (PDGF) stimulates p38 mitogen-activated protein (MAP) kinase activation in bovine tracheal myocytes, suggesting that p38 is involved in growth regulation. We therefore examined whether p38 regulates expression of cyclin D1, a G(1) cyclin required for cell cycle traversal. The chemical p38 inhibitors SB-202190 and SB-203580 each increased basal and PDGF-induced cyclin D1 promoter activity and protein abundance. Overexpression of a dominant negative allele of MAP kinase kinase-3 (MKK3), an upstream activator of p38alpha, had similar effects. Conversely, active MKK3 and MKK6, both of which increase p38alpha activity, each decreased transcription from the cyclin D1 promoter. Together, these data demonstrate that p38 negatively regulates cyclin D1 expression. We tested whether p38 regulates cyclin D1 expression via inhibition of extracellular signal-regulated kinase (ERK) activation. Chemical inhibitors of p38 induced modest ERK phosphorylation and activation. However, dominant negative MKK3 was insufficient to activate ERK, and active MKK3 and MKK6 did not attenuate platelet-derived growth factor-mediated ERK activation. These data are consistent with the notion that p38alpha negatively regulates cyclin D1 expression via an ERK-independent pathway.

Regulation of cyclin D(1) expression and DNA synthesis by phosphatidylinositol 3-kinase in airway smooth muscle cells.

We have shown in bovine tracheal myocytes that extracellular signal-regulated kinase (ERK) and Rac1 function as upstream activators of transcription from the cyclin D(1) promoter. We now examine the role of phosphatidylinositol (PI) 3-kinase in this process. PI 3-kinase activity was increased by platelet-derived growth factor (PDGF) and attenuated by the PI 3-kinase inhibitors wortmannin and LY294002. These inhibitors also decreased cyclin D(1) promoter activity, protein abundance, and DNA synthesis. Overexpression of the active catalytic subunit of PI 3-kinase (p110(PI) (3-K)CAAX) was sufficient to activate the cyclin D(1) promoter. Wortmannin and LY294002 failed to attenuate PDGF-induced ERK activation, and overexpression of p110(PI) (3-K)CAAX was insufficient to activate ERK. p110(PI) (3-K)CAAX-induced cyclin D(1) promoter activity was not blocked by PD98059, an inhibitor of mitogen-activated protein kinase/ERK kinase. We next examined whether PI 3-kinase and the 21-kD guanidine triphosphatase Rac1 regulate cyclin D(1) promoter activity by similar mechanisms. p110(PI) (3-K)CAAX-induced cyclin D(1) promoter activity was decreased by two inhibitors of Rac1-mediated signaling, catalase and diphenylene iodonium. Further, PDGF, PI 3-kinase, and Rac1 each activated the cyclin D(1) promoter at the cyclic adenosine monophosphate response element binding protein (CREB)/activating transcription factor (ATF)-2 binding site, as evidenced by expression of a CREB/ATF-2 reporter plasmid. Finally, PI 3-kinase and Rac1-induced CREB/ATF-2 transactivation were each inhibited by catalase. Together, these data suggest that in airway smooth muscle (ASM) cells, PI 3-kinase regulates transcription from the cyclin D(1) promoter and DNA synthesis in an ERK-independent manner. Further, PI 3-kinase and Rac1 regulate ASM cell cycle traversal via a common cis-regulatory element in the cyclin D(1) promoter.

Cloning and characterization of a novel RNA involved in cellular growth regulation.

During the course of antisense oligodeoxynucleotide (oligo) inhibition experiments investigating the role of insulin-like growth factor I (IGF-I) in the WI-38 cell cycle, we found that a sense-strand oligo (S oligo), used as a control, inhibited DNA synthesis 90 to 95%. S1 nuclease protection assays demonstrated that this S oligo formed intracellular duplexes with WI-38 RNA, and Northern (RNA) hybridization analyses demonstrated specific hybridization of this 32P-labeled S oligo to 1.8-, 2.3-, and 3.2-kb RNAs. We have cloned and sequenced a 2,251-bp cDNA, designated BB1, corresponding to the 2.3-kb RNA. Decoding of the BB1 cDNA sequence reveals several open reading frames arranged in a motif similar to that seen in proteins subject to translational control mechanisms. Homology searches of nucleic acid and protein data bases reveal no significant homology of BB1 with known sequences other than a 234-bp region in the BB1 5' untranslated region that shared 97% homology with a region in the 3' untranslated region of the human cdc42 mRNA. S1 nuclease protection analyses performed with IGF-I gene fragments and computer homology searches demonstrated that the BB1 RNA does not derive from transcription from the opposite strand of the IGF-I gene. Northern hybridization analyses of RNA extracted from serum-starved HeLa S3 cells demonstrated that steady-state BB1 RNA levels increased upon serum growth stimulation, with steady-state levels peaking 4 h after release from the block induced by serum starvation. Antisense oligo inhibition experiments using specific BB1 antisense oligos targeted to the putative open reading frames of the BB1 RNA reduce DNA synthesis of HeLa S3 cells to 15% of control levels, indicating that the BB1 RNA is essential for cell cycle traversal and, as such, encodes a growth-reguLating gene product.

Cell Cycle Traverse in NHIK-3025 Carcinoma of the Uterine Cervix after Low-Dose-Rate Irradiation

Theoretically, fractionation schemes could be tailored to the individual pattern of radiation-induced synchronization of cells in the radiosensitive G2 phase, leading to more effective radiotherapy. Using a human cervical carcinoma xenografted to nude mice, the effects of low-dose-rate irradiation on the cell cycle distribution were studied. Flow cytometric analysis demonstrated that cells accumulated in G2 + M phase 35 h after a total dose of 10 Gy of 137Cs irradiation. This accumulation time corresponded closely to the cell cycle time (Tc) (31 h) of this tumor, as determined by autoradiography. Further experiments are planned to determine the potential of fractionation schemes adjusted to the Tc-related accumulation in G2 in improving the effectiveness of radiotherapy.

High glucose prolongs cell-cycle traversal of cultured human endothelial cells.

There is evidence suggesting that the diabetic state adversely affects replication of certain cell populations. We document that exposure to high ambient glucose (20 mM) induces delay in various phases of the cell cycle of human endothelial cells in primary culture. Cells in S phase were labeled with bromodeoxyuridine (an analogue of thymidine), and the cell-cycle position of the labeled cohort was analyzed by flow cytometry at successive time points. The movement of cells exposed to high glucose for 7-8 days was retarded both in S and G2 phases so that the increase in bromodeoxyuridine-positive cells over 24 h was 1.6-fold, versus 2.0-fold in control cultures. In experiments in which mitotic arrest with vinblastine was used to investigate the movement of cells out of G1 phase without interference from reentering cells, depletion of the G1 compartment was significantly inhibited in cultures grown in high glucose. The effects of chronic high glucose on cell cycle occurred while total protein synthesis was not diminished. Acute exposure to high glucose had no effect on cell-cycle traversal or cell generation time. Cell-cycle abnormalities observed in this study may relate to the DNA damage we have previously observed in endothelial cells exposed to high glucose and, if occurring in vivo, could be of pathogenetic importance for the vascular lesions and teratogenicity of diabetes.

High glucose prolongs cell-cycle traversal of cultured human endothelial cells

High glucose prolongs cell-cycle traversal of cultured human endothelial cells

Cell cycle regulation of ribonucleoside diphosphate reductase activity in permeable mouse L cells and in extracts.

Ribonucleoside diphosphate reductase (EC1.17.4.1) was previously characterized in exponentially growing mouse L cells selectively permeabilized to small molecules by treatment with dextran sulfate (Kucera and Paulus, 1982b). This characterization has now been extended to cells in specific phases of the cell cycle and in transition between cell cycle phases, with activity studied both in situ (permeabilized cells) and in cell extracts. Cells at various stages in the cell cycle were obtained by unit-gravity sedimentation employing a commercially available reorienting chamber device, by G1 arrest induced by isoleucine limitation, and by metaphase arrest induced by Colcemid. G1 cells from both cycling and noncycling populations had negligible levels of ribonucleotide reductase activity as measured by CDP reduction both in situ and in extracts. When G1 arrested cells were allowed to progress to S phase, ribonucleotide reductase activity increased in parallel with [3H]thymidine incorporation into DNA. Ribonucleotide reductase activity in extracts increased at a somewhat greater rate than in situ activity. S phase ribonucleotide reductase activity measured in situ resembled the previously characterized activity in exponentially growing cells with respect to an absolute dependence on ATP or its analogs as positive allosteric effector, sensitivity to the negative allosteric effector dATP, and low susceptibility to stimulation by NADPH, dithiothreitol, and FeCl3. Disruption of permeabilized cells caused reductase activity to become highly dependent on the presence of both dithiothreitol and FeCl3. As synchronized cultures progressed from S into G2/M phase, no significant change in ribonucleotide reductase activity was seen. On the other hand, when cells that had been arrested in metaphase by Colcemid were allowed to resume cell cycle traversal by removing the drug, in situ ribonucleotide reductase activity decreased by 75% within 2.5 h. This decrease seemed to be a late mitotic event, since it was not correlated with the percentage of cells entering G1 phase. The cause of a subsequent slight increase of in situ ribonucleotide reductase activity is not clear. Parallel measurements of ribonucleotide reductase activity in cell extracts indicated also an initial decline accompanied by increasing dependence on added dithiols and FeCl3, followed by complete activity loss. Our results suggest a cell cycle pattern of ribonucleotide reductase activity that involves negligible levels in G1 phase, a progressive increase of activity upon entry into S phase paralleling overall DNA synthesis, continued retention of significant ribonucleotide reductase activity well into the metaphase period of mitosis, and a very rapid decline in activity during the later phases of mitosis. The periods of increase and decrease of ribonucleotide reductase activity were accompanied by modulation of the properties of the enzyme as indicated by differential changes in enzyme activity measured in situ and in extracts.

Lactose synthetase activity in mouse mammary glands is controlled by thyroid hormones.

Epithelial cells in explants from the mammary glands of euthyroid mature virgin mice are proliferatively dormant. They must undergo DNA synthesis and traverse the cell cycle in vitro before they are able to differentiate fully in response to insulin, hydrocortisone, and prolactin, and synthesize enzymatically active alpha-lactalbumin (measured as lactose synthetase activity). In contrast, glands from hyperthyroid mature virgin mice do not require DNA synthesis in vitro to differentiate. Explants from the euthyroid virgin tissue overcome their dependence on DNA synthesis when 10(-9) M 3,5,3'-triiodo-L-thyronine is added directly to the cultures in addition to the other three hormones. Explants from involuted mammary glands from euthyroid primiparous mice do not require DNA synthesis in vitro to make the milk protein even though they, like explants from mature euthyroid virgin tissue, are proliferatively dormant and do not contain detectable lactose synthetase activity in vivo. Glands from primiparous animals made mildly hypothyroid by ingestion of 0.1% thiouracil in drinking water during 7 wk of involution remain morphologically indistinguishable from glands of their euthyroid counterparts. However, explants from the glands of these hypothyroid animals revert to a state of dependence on DNA synthesis to differentiate functionally. These observations suggest that the dependence on DNA synthesis and cell cycle traversal for hormonal induction of lactose synthetase activity in the mouse mammary gland is controlled by thyroid hormones.

DNA Strand Scission by Neocarzinostatin and its Relation to the Inhibition of Cell Cycle Traverse and DNA Synthesis

The effect of neocarzinostatin (NCS) on the cell cycle traverse of BHK cells was examined with flow microfluorometry and [3H]-thymidine incorporation. At a low concentration (1μg/ml) of NCS a large number of cells were arrested at the G2 phase. At a high concentration (10μg/ml) cell cycle traverse from the G1 to the S phase and DNA synthesis in the middle S phase were inhibited.Chain elongation, strand scission and repair of DNA were determined by alkaline sedimentation analysis. In the presence of 10μg/ml NCS, parental DNA was degraded to the size of the replication unit (1.1×108dalton). DNA elongated at most to the size of the replication unit, before the parental DNA was degraded to the same size. DNA strand scission took place even at the low concentration of NCS that induced G2 arrest. The DNA strand scission induced by 10μg/ml NCS was repaired only slightly by 5 h afer the removal of NCS.A short exposure of cells to NCS was sufficient to cause the inhibition of DNA synthesis and cell cycle traverse, as well as DNA strand scission.

Effects of Caffeine on Radiation-Induced Phenomena Associated with Cell-Cycle Traverse of Mammalian Cells

Caffeine induced a state of G(1) arrest when added to an exponentially growing culture of Chinese hamster cells (line CHO). In addition to its effect on cell-cycle traverse, caffeine ameliorated a number of the responses of cells to ionizing radiation. The duration of the division delay period following X-irradiation of caffeine-treated cells was reduced, and the magnitude of reduction was dependent on caffeine concentration. Cells irradiated during the DNA synthetic phase in the presence of caffeine were delayed less in their exit from S, measured autoradiographically, and the radiation-induced reduction of radioactive thymidine incorporation into DNA was lessened. Cells synchronized by isoleucine deprivation, while being generally less sensitive to the effects of ionizing radiation than mitotically synchronized cells, were equally responsive to the effects of caffeine. The X-ray-induced reduction of phosphorylation of lysine-rich histone F1 was less in caffeine-treated cells than in untreated cells. Finally, survival after irradiation was only slightly reduced in caffeine-treated cells. A possible role of cyclic AMP in cell-cycle traverse of irradiated cells is discussed.