Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “G1”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMedDate not supplied

Mutant p53 mediated induction of cell cycle arrest and apoptosis at G1 phase by 9-hydroxyellipticine.

Wild-type p53 causes cell-cycle arrest at late G1 phase and induction of apoptosis by up- regulation of waf1 and bax, respectively. Although in many cancer cells p53 is frequently mutated and loses its functions, we have proposed that mutant p53 may be involved in the anticancer mechanism of 9-hydroxy ellipticine (9HE). It was shown using flow cytometry that 9HE (10 microM) caused induction of apoptosis in G1 phase of the cell cycle in mutant p53 (p53ala143, p53his175, orp53his273) transfected Saos-2 cells, but not in p53-deficient parental Saos-2 cells. Similar induction of apoptosis was observed 24-48 h after treatment with 9HE in mutant p53-containing SW480, SK-BR-3 and MKN-1, but not in p53-deficient KATO m cells. Using G1 phase cells isolated by centrifugal elutriation, it was confirmed that 9HE caused cell cycle arrest at G1 phase and subsequently induced G1 phase-restricted apoptosis. In accordance with the induction of arrest and apoptosis in G1 phase, 9HE caused up-regulation of waf1 and bax mRNA in mutant p53-containing cells, but not in p53-deficient parental Saos-2 cells. In control experiments, adriamycin (ADR) showed neither G1-restricted apoptosis nor elevation of bax mRNA. It is suggested that 9HE may cause G1 arrest and induction of G1 phase-restricted apoptosis by restoring the wild-type function of mutant p53 protein.

Apoptosis↗
PubMed2000

Induction of p53-independent p21 during ceramide-induced G1 arrest in human hepatocarcinoma cells.

Ceramide is known to induce pRb (retinoblastoma gene product) dephosphorylation through the activation of ceramide-activated protein phosphatase (CAPP) during G1 arrest, but other molecular mechanisms linked to regulation of pRb dephosphorylation during ceramide-induced G1 arrest are poorly understood. In this paper, we investigated whether p21, a cdk (cyclin-dependent kinase) inhibitor, is involved in the induction of pRb dephosphorylation during ceramide-induced G1 arrest. In SK-Hep-1 cells, the addition of ceramide resulted in pRb dephosphorylation and G1 arrest. The activity of cdk2 was inhibited in response to ceramide during this process. p21 protein and mRNA were remarkably induced, while the protein level of p53, known as a transcriptional activator of p21, was not elevated at the same condition. p21 induction was also observed in the Hep3B cells lacking a functional p53 after exposure to ceramide. Although p21 is induced in ceramide-treated Hep3B cells, Hep3B cells do not induce G1 arrest, because Hep3B cells are deficient in a functional pRb protein. To confirm that pRb is a critical target for the induction of G1 arrest by inhibiting cdk2 activity through p53-independent p21, pRb-expressing vector was transfected into Hep3B cells. After treatment with ceramide, pRb-expressing cells (pRb+/+), but not pRb-/- cells, were arrested in G1 phase. In pRb+/+ cells, ceramide-mediated G1 arrest was accompanied by the accumulation of hypophosphorylated pRb and p21 associated with cdk2. Together, these results suggest that p21, induced through p53-independent pathway, participates in the induction of pRb dephosphorylation by inhibiting cdk2 activity during ceramide-mediated G1 arrest in hepatocarcinoma cells.

Blotting, Northern↗
PubMed1998

Persistent decrease in viability as a function of X irradiation of human bladder carcinoma cells in G1 or S phase.

A persistent decrease in viability after treatment with a variety of mutagenic agents has been observed previously, but the dependence of the decrease on the phase of the cell cycle in which the cells are treated has not been fully explored. Synchronous human bladder carcinoma cells (EJ30-15) were obtained by mitotic selection (88-96% in or near mitosis). As monitored by microscopy and pulse labeling with [3H]dThd, approximately 98% of the cells were in G1 phase when they were irradiated after 3 h of incubation, and approximately 80% were in S phase when they were irradiated after 14 h of incubation. The initial plating efficiencies demonstrated no difference in cell survival when cells were irradiated in G1 or S phase, with normalized clonogenic survival and standard error of 60+/-6% for 3 Gy and 13+/-2% for 6 Gy. However, when the cell populations were allowed to incubate and were replated 5 to 33 days later (5.5 to 36 doublings), a difference between the populations irradiated in G1 and S phase became clear. Cells that were irradiated with 6 Gy regained and maintained the high plating efficiencies (67.9+/-3.6%) of the unirradiated populations much sooner when they were irradiated in S phase compared with irradiation in G1 phase, i.e. 11 days (12 cell doublings) for S phase compared to approximately 20 days (22 cell doublings) for G1 phase. During these periods when the plating efficiencies were increasing, the populations irradiated in G1 phase were multiplying at rates lower than those for the populations irradiated in S phase. Furthermore, after 6 Gy, more giant cells and multinucleated cells were seen in the populations irradiated in G1 phase than in the populations irradiated in S phase. These results indicate that, although the clonogenic survival was the same for cells irradiated in G1 or S phase, the residual damage in progeny of the irradiated cells persisted longer (approximately 20 days compared to 11 days) when cells were irradiated in G1 phase than when they were irradiated in S phase.

Cell Cycle↗
PubMed1999

The ILT2(LIR1) and CD94/NKG2A NK cell receptors respectively recognize HLA-G1 and HLA-E molecules co-expressed on target cells.

Previous studies on NK recognition of HLA-G1 employed as targets 721.221 transfectants (.221-G1) that unknowingly co-expressed the HLA-E molecule, subsequently found to be a major ligand for the CD94/NKG2 receptors. In the present study we re-evaluated the relative role played by CD94/NKG2 and ILT2(LIR1) molecules in recognition of HLA-G1 by NK clones. We employed as targets .221-G1 cells and a surface HLA-E-negative transfectant, .221-G1(Eneg), generated by site-directed mutagenesis of the HLA-G1 leader sequence. The antagonistic effects of receptor- (ie. CD94/NKG2A, ILT2) and ligand-specific mAb (i.e. HLA-G, HLA-E) were assessed. In addition, binding of an ILT2-Ig fusion protein to the .221-AEH, expressing only HLA-E, and the .221-G1(Eneg) transfectants was analyzed. Our data demonstrate that NK recognition of cells expressing HLA-G1 involves at least two non-overlapping receptor-ligand systems: the CD94/NKG2 interaction with HLA-E, and the engagement of the ILT2(LIR1) receptor by HLA-G1 molecules.

Antibodies, Monoclonal↗
PubMed1998

Cellular immunity to the G1 domain of cartilage proteoglycan aggrecan is enhanced in patients with rheumatoid arthritis but only after removal of keratan sulfate.

OBJECTIVE: To determine whether patients with rheumatoid arthritis (RA) express cellular immunity to the purified G1 globular domain of cartilage proteoglycan (PG) aggrecan and whether it is influenced by the removal of keratan sulfate (KS) chains from the molecule. METHODS: The G1 globular domain of PG was purified from mature bovine articular cartilage, digested with keratanase, and used in proliferation assays with peripheral blood lymphocytes (PBL) isolated from 43 patients with RA, 11 patients with nonarticular rheumatism (NAR), including soft tissue rheumatism and mechanical back pain, and 13 healthy age- and sex-matched control subjects. RESULTS: Removal of KS chains from the G1 globular domain resulted in significantly increased prevalence and values of cellular immune responses to G1 in RA patients compared with the control and NAR groups. In the majority of RA patients, KS chains on G1 significantly inhibited its immune recognition by PBL. There was no significant effect of KS removal on the immunity to G1 in patients with NAR and in the healthy control group. CONCLUSION: These results reveal that immune reactivity to the G1 globular domain of the cartilage PG aggrecan is enhanced in patients with RA but only when KS chains are removed. Thus, KS chains inhibit immune responses to this domain of aggrecan. Since immunity to the G1 globular domain of aggrecan induces an erosive polyarthritis in BALB/c mice after removal of KS chains, immunity to the G1 globular domain, cleaved by proteases to remove KS chains, may play a role in the pathogenesis of RA.

Adult↗
PubMed2006

A study of soluble HLA-G1 protecting porcine endothelial cells against human natural killer cell-mediated cytotoxicity.

UNLABELLED: Human natural killer (NK) cells, which can mediate direct lysis of porcine endothelial cells, play an important role in xenograft rejection. HLA-G, which is a critical molecule in maintaining maternal immune tolerance of semi-allogenic fetus, is able to protect susceptible target cells from lysis induced by NK cells. In this study, we investigated whether soluble HLA-G1 (sHLA-G1) protected porcine xenogeneic cells against human NK cell-mediated lysis. METHODS: The human sHLA-G1 genomic DNA (pcDNA3-sHLA-G1) was transfected into a B lymphoblastoid cell line 721.221 (LCL721.221) by nucleofector. The sHLA-G1 expression of the transfected LCL721.221 cells was identified by RT-PCR and Dot-ELISA. The sHLA-G1 protein was purified by affinity chromatography on anti-HLA-ImAb W6/32 coupled to cyanogen-bromide-activated Sepharose 4B from culture supernates of transfectants. Various concentrations of sHLA-G(1) protein (0, 2, 4, 6, or 8 microg/mL) were added to a NK cell-mediated xenogenic cell lysis system with either NK92 cells or fresh human peripheral blood mononuclear cells (PBMCs) cocultured with the porcine endothelial cells line. A LDH release assay was used to evaluate NK cell-mediated cytotoxicity. RESULTS: sHLA-G1 provided significant protection of porcine endothelial cells against human NK-mediated cytotoxicity in a dose-dependent manner. The rates of NK92 cell-mediated cytotoxicity were reduced to 83.4 +/- 5.7% (2 microg/mL), 56.6 +/- 9.3% (4 microg/mL), 39.3 +/- 10.2% (6 microg/mL), and 31.2 +/- 4.9% (8 microg/mL) versus 96.9 +/- 3.0% in the control group (P < .01). Similarly, adding 6 microg/mL sHLA-G1 reduced the mean rate of PBMC-mediated cytotoxicity (n = 4) to 5.8 +/- 1.6% from 23.9 +/- 1.3% in the control group (P < .01). CONCLUSIONS: These results indicated that sHLA-G1 protected xenogeneic porcine endothelial cells against attack by human NK cells, thus providing a new approach to overcome NK-mediated immunity to xenografts.

Animals↗
PubMed1991

Identification of a G1-type cyclin puc1+ in the fission yeast Schizosaccharomyces pombe.

In rapidly growing cells of the budding yeast Saccharomyces cerevisiae, the cell cycle is regulated chiefly at Start, just before the G1-S boundary, whereas in the fission yeast Schizosaccharomyces pombe, the cycle is predominantly regulated at G2-M. Both control points are present in both yeasts, and both require the p34cdc2 protein kinase. At G2-M, p34cdc2 kinase activity in S. pombe requires a B-type cyclin in a complex with p34cdc2; this complex is the same as MPF (maturation promoting factor). The p34cdc2 activity at the G1-S transition in S. cerevisiae may be regulated by a similar cyclin complex, using one of the products of a new class of cyclin genes (CLN1, CLN2 and WHI1 (DAF1/CLN3)). At least one is required for progression through the G1-S phase, and deletion of all three leads to G1 arrest. WHI1 was isolated as a dominant allele causing budding yeast cells to divide at a reduced size and was later independently identified as DAF1, a dominant allele of which rendered the cells refractory to the G1-arrest induced by the mating pheromone alpha-factor. The dominant alleles are truncations thought to yield proteins of increased stability, and the cells are accelerated through G1. Without WHI1 function, the cells are hypersensitive to alpha-factor, enlarged and delayed in G1. Heretofore, this G1-class of cyclins has not been identified in other organisms. We have isolated a G1-type cyclin gene called puc1+ from S. pombe, using a functional assay in S. cerevisiae. Expression of puc1+ in S. pombe indicates that it has a cyclin-like role in the fission yeast distinct from the role of the B-type mitotic cyclin.

Amino Acid Sequence↗
PubMed2000

Isolation and characteristics of autoreactive T cells specific to aggrecan G1 domain from rheumatoid arthritis patients.

Our previous work showed that the cartilage proteoglycan aggrecan could induce an erosive polyarthritis and spondylitis in BALB/c mice and the G1 globular domain of the aggrecan (G1) contained the arthritogenic region. To elucidate whether autoreactive T cells to G1 are expressed in rheumatoid arthritis patients, we analyzed the frequency of human G1-specific T cells in the peripheral blood of five rheumatoid arthritis patients and tried to establish G1-reactive T cell lines from these rheumatoid arthritis patients. The results showed that the G1-specific T cells in PBL were detectable at the range of 4.97 +/- 0.5 x 10(-6) in peripheral blood lymphocytes. We have also generated 15 G1-specific T lymphocyte lines from these patients with a standard split-well method. All these cells expressed fine specificity to human recombinant G1, but not to unrelated antigen. All the 15 lines expressed a pan-T cell marker and 13 of them selectively used the alphabeta T cell receptor. Two of them used gammadelta T cell receptor. The 13 of these T cell lines was CD4 positive. One line expressed CD8. One line expressed both CD4 and CD8. Moreover, 14 out of 15 lines expressed the Th-1 cytokine profile, characterized by interferon-gamma positivity and IL-4 negativity. No Th-2 type cell line was generated. These data provide strong evidence in favor of the presence of autoreactive T cells in the rheumatoid arthritis patients. What is the mechanism(s) that these autoreactive T cells attack self-target and whether these G1-specific, Th-1 type T cell lines can induce arthritis in immune deficiency mice are currently under investigation.

Adult↗
PubMed1981

Most of the G1 period in hamster cells is eliminated by lengthening the S period.

Two Chinese hamster cell lines, G1+-1 and CHO, have been grown in the presence of low concentrations of hydroxyurea to determine how a slowing DNA synthesis (i.e., a lengthening of the S period) affects the length of the G1 period. Hydroxyurea concentrations of approximately 10 microM do not alter the generation times of these cell lines but do cause increases in S with corresponding decreases in G1. In both cell lines, 10 microM hydroxyurea reduces G1 to an absolute value of 1 hr, which represents decreases of 70% (G1+-1) and 60% (CHO) from control values. Higher concentrations of hydroxyurea increase the generation times and lengths of S for both cell lines but do not reduce G1 below the minimum value of 1 hr. These observations indicate that the majority of G1 is expendable and most of G1 therefore cannot contain specific events required for the initiation of DNA synthesis. This result supports the hypothesis that G1 is a portion of the cell growth cycle but not of the chromosome cycle.

Animals↗
PubMed1980

Initiation of DNA synthesis in the prematurely condensed chromosomes of G1 cells.

The objective of this study was to investigate whether G1 cells could enter S phase after premature chromosome condensation resulting from fusion with mitotic cells. HeLa cell synchronized in early G1, mid-G1, late G1, and G2 and human diploid fibroblasts synchronized in G0 and G1 phases were separately fused by use of UV-inactivated Sendai virus with mitotic HeLa cells. After cell fusion and premature chromosome condensation, the fused cells were incubated in culture medium containing Colcemid (0.05 micrograms/ml) and [3H]thymidine ([3H]ThdR) (0.5 microCi/ml; sp act, 6.7 Ci/mM). At 0, 2, 4, and 6 h after fusion, cell samples were taken to determine the initation of DNA synthesis in the prematurely condensed chromosomes (PCC) on the basis of their morphology and labeling index. The results of this study indicate that PCC from G0, G1, and G2 cells reach the maximum degree of compaction or condensation at 2 h after PCC induction. In addition, the G1-PCC from normal and transformed cells initiated DNA synthesis, as indicated by their "pulverized" appearance and incorporation of [3H]ThdR. Further, the initiation of DNA synthesis in G1-PCC occurred significantly earlier than in the mononucleate G1 cells. Neither pulverization nor incorporation of label was observed in the PCC of G0 and G2 cells. These findings suggest that chromosome decondensation, although not controlling the timing of a cell's entry into S phase, is an important step for the initiation of DNA synthesis. These data also suggest that the entry of a S phase may be regulated by cell cycle phase-specific changes in the permeability of the nuclear envelope to the inducers of DNA synthesis present in the cytoplasm.

Cell Cycle↗
PubMed1999

E1A can provoke G1 exit that is refractory to p21 and independent of activating cdk2.

E1A can evoke G1 exit in cardiac myocytes and other cell types by displacing E2F transcription factors from tumor suppressor "pocket" proteins and by a less well-characterized p300-dependent pathway. Bypassing pocket proteins (through overexpression of E2F-1) reproduces the effect of inactivating pocket proteins (through E1A binding); however, pocket proteins associate with a number of molecular targets apart from E2F. Hence, pocket protein binding by E1A might engage mechanisms for cell cycle reentry beyond those induced by E2F-1. To test this hypothesis, we used adenoviral gene transfer to express various E2F-1 and E1A proteins in neonatal rat cardiac myocytes that are already refractory to mitogenic serum, in the absence or presence of several complementary cell cycle inhibitors-p16, p21, or dominant-negative cyclin-dependent kinase-2 (Cdk2). Rb binding by E2F-1 was neither necessary nor sufficient for G1 exit, whereas DNA binding was required; thus, exogenous E2F-1 did not merely function by competing for the Rb "pocket." E2F-1-induced G1 exit was blocked by the "universal" Cdk inhibitor p21 but not by p16, a specific inhibitor of Cdk4/6; p21 was permissive for E2F-1 induction of cyclins E and A, but prevented their stimulation of Cdk2 kinase activity. In addition, E2F-1-induced G1 exit was blocked by dominant-negative Cdk2. Forced expression of cyclin E induced endogenous Cdk2 activity but not G1 exit. Thus, E2F-1-induced Cdk2 function was necessary, although not sufficient, to trigger DNA synthesis in cardiac muscle cells. In contrast, pocket protein-binding forms of E1A induced G1 exit that was resistant to inhibition by p21, whereas G1 exit via the E1A p300 pathway was sensitive to inhibition by p21. Both E1A pathways-via pocket proteins and via p300-upregulated cyclins E and A and Cdk2 activity, consistent with a role for Cdk2 in G1 exit induced by E1A. However, p21 blocked Cdk2 kinase activity induced by both E1A pathways equally. Thus, E1A can cause G1 exit without an increase in Cdk2 activity, if the pocket protein-binding domain is intact. E1A also overrides p21 in U2OS cells, provided the pocket protein-binding domain is intact; thus, this novel function of E1A is not exclusive to cardiac muscle cells. In summary, E1A binding to pocket proteins has effects beyond those produced by E2F-1 alone and can drive S-phase entry that is resistant to p21 and independent of an increase in Cdk2 function. This suggests the potential involvement of other endogenous Rb-binding proteins or of alternative E1A targets.

Adenovirus E1A Proteins↗
PubMed2006

[Establishment of eukaryotic cell line stably expressing soluble human leucocyte antigen G1 by nucleofection].

OBJECTIVE: To establish a eukaryotic cell line that can express soluble human leucocyte antigen G1 (sHLA-G1) stably. METHODS: The recombinant plasmid pcDNA3-sHLA-G1 is transfected by a novel nonviral, electroporation-based gene transfer method termed nucleofection into the host cell lymphoblastoid cell line (LCL) 721.221 which does not express any HLA-classical I molecules. After selection by G418, the cell line stably expressing sHLA-G1 is identified by RT-PCR and Dot-ELISA with HLA-G1 specific monoclonal antibody MEM-G/9. RESULTS: The efficiency of transfection for LCL721. 221 is about 14% by nucleofection. The specific band for sHLA-G1 was found by RT-PCR assay from the transfections and the protein of sHLA-G1 in the supernatant of the transfections was detected by Dot-ELISA assay. Both confirmed that the eukaryotic cell line expressing sHLA-G1 has been established successfully at genic and proteinic levels. CONCLUSION: In this study, the eukaryotic cell line expressing sHLA-G1 have been established successfully by nucleofection.

Cell Line↗
PubMed1994

A signal for Golgi retention in the bunyavirus G1 glycoprotein.

The G1 and G2 glycoproteins of Punta Toro virus, a member of the bunyaviruses, are targeted to the Golgi complex, where viral budding occurs. We found that the G1 protein, when expressed in the absence of G2, is also targeted to the Golgi complex. A series of G1 proteins truncated at the carboxyl-terminal region was constructed, and the localization of the expressed proteins was examined. It was found that the proteins expressed from constructs with partial deletions in the cytoplasmic domain were transported to the Golgi complex at a significantly slower rate than G1. Although a major fraction of these proteins was eventually transported to the Golgi complex, they did not exhibit as clearly defined a pattern of accumulation as G1, but rather appeared to be distributed throughout the endoplasmic reticulum as well as the Golgi complex. The proteins expressed from constructs lacking most of the cytoplasmic domain and, in some cases, part of the transmembrane domain sequences as well were transported to the cell surface. We have also constructed chimeric proteins with the envelope protein of a murine leukemia virus (MCFenv), which is efficiently transported to the plasma membrane. A MCF-G1 chimera that contained the G1 transmembrane and cytoplasmic domains was found to be efficiently retained in the Golgi complex, and a construct that contained only the G1 transmembrane domain was also partially retained in the Golgi complex. Thus, the transmembrane domain as well as a portion of the cytoplasmic domain adjacent to the transmembrane domain are apparently crucial for Golgi retention of the G1 protein.

Animals↗
PubMed1998

G1 cyclin-dependent kinases are sufficient to initiate DNA synthesis in quiescent human fibroblasts.

Mammalian fibroblasts require mitogens in order to exit from G0 (quiescence) and progress through the G1 phase of the cell cycle, although once they pass the restriction point late in G1 they can enter S phase and complete the cell cycle without mitogens [1]. Mitogenic signals are integrated through the GTPase Ras, which regulates the levels of cyclin D1 [2-5], a component of the cell cycle machinery that operates during G1 phase by activating cyclin-dependent kinase 4 (Cdk4). The accumulation of active cyclin E-Cdk2 complexes also requires Ras [6]. These two G1 cyclin-Cdk complexes act on a family of E2F-associated transcriptional repressors typified by the retinoblastoma protein (Rb) to bring about a transcriptional program that promotes passage through S phase [7-9], but can also activate DNA replication independently of Rb-E2F [10-12]. Although G1 cyclin-Cdk complexes are required for S-phase entry and can shorten G1 phase when overexpressed [13-15], it is not known whether they are sufficient for this transition. Here, we report that serum-starved (G0) diploid human fibroblasts initiate DNA synthesis upon microinjection of active G1 cyclin-Cdk complexes, but not upon microinjection of an S-phase cyclin-Cdk complex. These data indicate that G1 Cdk activation is rate-limiting for S-phase entry, and that Cdk activation is likely to be the primary function of growth factor signalling pathways that lead to DNA synthesis.

Carrier Proteins↗
PubMed1998

Regulation of cyclin G1 during murine hepatic regeneration following Dipin-induced DNA damage.

Cyclin G1 has been linked to both positive and negative growth regulation. The expression of cyclin G1 is induced by transforming growth factor beta1 and p53, as well as by multiple mitogenic stimuli in mammalian cells in culture. However, the physiological role of cyclin G1 remains unclear. To examine the cell-cycle regulation of cyclin G1 in vivo, two models of coordinated cell proliferation induced by partial hepatectomy (PH) in the presence or absence of DNA damage were used. To introduce DNA damage, mice were treated with the alkylating drug, 1,4-bis[N,N'-di(ethylene)-phosphamide]piperazine (Dipin) 2 hours before PH. Cell-cycle progression was monitored by 5-bromo-2-deoxyuridine (BrdU) incorporation into the DNA, the frequency of mitoses, the expression of cell-cycle control genes, and by flow cytometry. Dipin treatment resulted in cell-cycle arrest at the G2/M boundary without affecting G0/G1 and G1/S transitions. While the hepatocytes progressively entered G2 phase arrest, the cyclin G1 mRNA and protein levels increased more than five- and eightfold, respectively. Cyclin G1 had a nuclear localization in all interphase cells with clear absence from nucleoli. In contrast, during mitosis, cyclin G1 was undetectable by immunohistochemistry. Taken together, our data provide evidence for a putative role of cyclin G1 in G2/M checkpoint control.

Animals↗
PubMed1994

Inhibition of G1 phase cyclin dependent kinases by transforming growth factor beta 1.

Transforming growth factor beta 1 (TGF beta 1) inhibits epithelial cell proliferation late in the G1 phase of the cell cycle. We examined the effect of TGF beta 1 on known late G1 cell cycle regulators in an attempt to determine the molecular mechanism of growth inhibition by this physiological inhibitor. The results demonstrate that TGF beta 1 inhibits the late G1 and S phase specific histone H1 kinase activity of p33cdk2. This inhibition is not due to TGF beta 1's effect on p33cdk2 synthesis, but rather due to its negative effects on the late G1 phosphorylation of p33cdk2. It is also shown that TGF beta inhibits both late G1 cyclin A and cyclin E associated histone H1 kinase activities. The inhibitor has no effects on the synthesis of cyclin E but is shown to inhibit the synthesis of cyclin A protein in a cell cycle dependent manner. If TGF beta 1 is added to cells which have progressed further than 8 hours into G1, then it is without inhibitory effect on cyclin A synthesis. These effects of TGF beta 1 on late G1 cell cycle regulators correlate well with its inhibitory effects on cellular growth and suggest that these G1 cyclin dependent kinases might serve as targets for TGF beta 1-mediated growth arrest.

Animals↗
PubMed1997

Temporal position of G1 arrest in normal human fibroblasts after exposure to gamma-rays.

G1 phase cell cycle arrest after exposure to ionizing radiation has been documented in cells with wild-type p53. The temporal location of this arrest within G1 phase, however, has not been determined. We have now used flow cytometric analysis of bromodeoxyuridine (BrdUrd)-labeled cells to obtain further information about the location of the G1 phase radiation checkpoint. Human fibroblasts were irradiated with gamma-rays and treated with colcemid to stop unlabeled G2 cells from entering the G1 phase. Analysis of BrdUrd incorporation revealed that 73% of G1 phase human lung fibroblasts remain in G1 phase after exposure to gamma-rays, thereby placing the G1 radiation checkpoint near the end of G1 phase. The location of the radiation checkpoint correlates with the reported increased expression of cyclin E, increased cyclin E/cdk2 kinase activity, and hyperphosphorylation of pRb in proliferating human fibroblasts.

Cell Cycle↗
PubMed2000

Polyamine-depletion induces p27Kip1 and enhances dexamethasone-induced G1 arrest and apoptosis in human T lymphoblastic leukemia cells.

Glucocorticoid-induced apoptosis is preceded by G1 arrest and supposed to be up-regulated by polyamine-depletion, which also induces G1, arrest. In CEM leukemia cells, dexamethasone showed an antileukemic effect by inducing G1 arrest and apoptosis. DFMO, which depleted cellular polyamines by inhibiting ornithine decarboxylase, induced G1 arrest but without apoptosis, though it enhanced dexamethasone-induced G1 arrest and apoptosis. The G1 arrest was associated with hypophosphorylation of pRb. Dexamethasone inhibited the increase of mutated p53 expression but had little effect on p2Wafl/Cip1 expression. The p27Kip1, level was increased by dexamethasone or and DFMO in line with the kinetics of G1 arrest. Therefore, the up-regulation of dexamethasone-induced apoptosis by polyamine-depletion may be associated with additive down-regulation of G1 progression via the p27Kip1-pRb pathtway.

Apoptosis↗