scholarly journals Critical requirement for cell cycle inhibitors in sustaining nonproliferative states

2007 ◽  
Vol 176 (6) ◽  
pp. 807-818 ◽  
Author(s):  
Deborah Pajalunga ◽  
Alessia Mazzola ◽  
Anna Maria Salzano ◽  
Maria Grazia Biferi ◽  
Gabriele De Luca ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Tissue Repair ◽  
Replicative Senescence ◽  
Human Fibroblasts ◽  
Cdk Inhibitors ◽  
Cyclin Dependent Kinase ◽  
Critical Requirement ◽  
Human Embryo Kidney ◽  
Cell Cycle Inhibitors ◽  
Constant Expression

In adult vertebrates, most cells are not in the cell cycle at any one time. Physiological nonproliferation states encompass reversible quiescence and permanent postmitotic conditions such as terminal differentiation and replicative senescence. Although these states appear to be attained and maintained quite differently, they might share a core proliferation-restricting mechanism. Unexpectedly, we found that all sorts of nonproliferating cells can be mitotically reactivated by the sole suppression of histotype-specific cyclin-dependent kinase (cdk) inhibitors (CKIs) in the absence of exogenous mitogens. RNA interference–mediated suppression of appropriate CKIs efficiently triggered DNA synthesis and mitosis in established and primary terminally differentiated skeletal muscle cells (myotubes), quiescent human fibroblasts, and senescent human embryo kidney cells. In serum-starved fibroblasts and myotubes alike, cell cycle reactivation was critically mediated by the derepression of cyclin D–cdk4/6 complexes. Thus, both temporary and permanent growth arrest must be actively maintained by the constant expression of CKIs, whereas the cell cycle–driving cyclins are always present or can be readily elicited. In principle, our findings could find wide application in biotechnology and tissue repair whenever cell proliferation is limiting.

scholarly journals OxLDL stimulates cell proliferation through a general induction of cell cycle proteins

2003 ◽  
Vol 284 (2) ◽  
pp. H644-H653 ◽  
Author(s):  
Marjorie E. Zettler ◽  
Michele A. Prociuk ◽  
J. Alejandro Austria ◽  
Hamid Massaeli ◽  
Guangming Zhong ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Proliferation ◽  
Low Density Lipoprotein ◽  
Human Fibroblasts ◽  
Density Lipoprotein ◽  
Cyclin B1 ◽  
Cyclin Dependent Kinase ◽  
Cell Cycle Proteins ◽  
Cell Counts ◽  
Cell Cycle Inhibitors

Oxidized low-density lipoprotein (oxLDL) may be involved in atherosclerosis by stimulating proliferation of cells in the vessel wall. The purpose of this study was to identify the mechanism by which oxLDL induces proliferation. Quiescent human fibroblasts and rabbit smooth muscle cells were treated with 0, 10, or 50 μg/ml oxLDL for 24–48 h. This resulted in significant increases in total cell counts at both concentrations of oxLDL, at both time points, for both types of cells. Western blot analysis revealed that oxLDL-stimulated cell proliferation was associated with significant increases in the expression of proteins that regulate entry into and progression through the cell cycle [cell division cycle 2, cyclin-dependent kinase (cdk) 2, cdk 4, cyclin B1, cyclin D1, and PCNA]. Surprisingly, the expression of cell cycle inhibitors (p21 and p27) was stimulated by oxLDL as well, but this was to a lesser extent than the effects on cell cycle-activating proteins. OxLDL also induced nuclear localization of all cell cycle proteins examined. The similar effects of oxLDL on the translocation and expression of both cell cycle-activating and -inhibiting proteins may explain the controlled proliferative phenomenon observed in atherosclerosis as opposed to the more rapid proliferative event characteristic of cancer.

Development and strategies of CDK4/6 inhibitors

2020 ◽  
Vol 12 (2) ◽  
pp. 127-145 ◽  
Author(s):  
Pingping Chen ◽  
Yinqiu Xu ◽  
Xuanyi Li ◽  
Hequan Yao ◽  
Kejiang Lin
Keyword(s):  
Cell Cycle ◽  
Normal Cell ◽  
Early Stage ◽  
Pharmacophore Model ◽  
Cdk Inhibitors ◽  
Cyclin Dependent Kinase ◽  
Optimization Strategy ◽  
Selective Inhibitors ◽  
Protein Substrates ◽  
Critical Methodology

Aim: CDK4/6 have critical roles in the early stage of the cell cycle. CDK2 acts later in the cell cycle and has a considerably broader range of protein substrates, some of which are essential for normal cell proliferation. Therefore, increasing the selectivity of cyclin-dependent kinase (CDK) inhibitors is critical. Methodology: In this study, we construct a versatile, specific CDK4 pharmacophore model that not only matches well with 8119 of the reported 9349 CDK4/6 inhibitors but also differentiates from the CDK2 pharmacophore. Results & Conclusion: we demonstrate the activity and selectivity determinants of CDK4/6 selective inhibitors based on the CDK4 pharmacophore model. Finally, we propose the future optimization strategy for CDK4/6 selective inhibitors, providing a theoretical basis for further research and development of CDK4/6 selective inhibitors.

STI571 Suppresses Proliferation by Restoring Nuclear Cyclin Dependent Kinase Inhibitors (CDKIs) while STI571+TRAIL Promotes Cell Death by Decreasing Cytoplasmic CDKIs.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1992-1992
Author(s):  
Mo A. Dao ◽  
Catherine M. Verfaillie
Keyword(s):  
Cell Cycle ◽  
Cell Death ◽  
Myeloid Leukemia ◽  
Kinase Inhibitors ◽  
Hematopoietic Cells ◽  
Cyclin Dependent Kinase ◽  
The Past ◽  
Cell Cycle Inhibitors ◽  
Nuclear Cell ◽  
Resistant Cells

Abstract Cyclin dependent kinase inhibitors (CDKIs), p27Kip1 and p21Cip1, function as cell cycle inhibitors when located in the nucleus. When localized to the cytoplasm, these CDKIs can function as anti-apoptotic molecules by sequestering/preventing the activation of pro-apoptotic proteins such as ASK1 and procaspase-3. Our lab has reported elevated cytoplasmic CDKIs and decreased nuclear CDKIs in hematopoietic cells expressing BCR/ABL, the oncogene found in more than 90% of cases of chronic myeloid leukemia. Within the past decade, STI571 has been shown highly promising for CML treatment. However, there is increasing evidence suggesting that the drug might function more as a suppressor of proliferation and less as a promoter of cell death. In the current studies, we differentiate the effect of STI571 on proliferation vs. survival by tracking the subcellular increase/decrease in CDKIs using MO7e cells engineered to express BCR/ABL. To determine if a correlation exists between STI571 resistance and levels of cytoplasmic anti-apoptotic CDKIs, we also investigated changes in levels of nuclear vs. cytoplasmic CDKIs in LAMA84 -S (sensitive to STI571) vs. LAMA84-R (resistant to STI571). And lastly, we tested whether activation of TRAIL would enhance cell death in STI571-resistant cells. STI571 treatment increases nuclear CDKIs, correlating directly with a decrease in proliferation of MO7e/p210 cells. However, the high levels of cytoplasmic CDKIs in MO7e/p210bcr/abl was not modulated following STI571 treatment and cell death was not prominent, unless growth factors were removed. Moreover, cytoplasmic p21Cip co-immunoprecipitated with ASK1 and procaspase 3. When compared with LAMA-S cells, LAMA-R cells expressed even higher levels of cytoplasmic CDKIs. Treatment with STI571 decreased cytoplasmic CDKIs in LAMA84-S cells and resulted in cell death. As hypothesized, LAMA84-R cells did not show reduction in cytoplasmic CDKIs and did not enter apoptosis. However, when treated with STI571 and TRAIL, LAMA84-R cells showed a decrease in cytoplasmic CDKIs, and increase in apoptosis. Based on these observations, we conclude that: 1. BCR/ABL expression reduces nuclear CDKIs but increases cytoplasmic CDKIs. 2. STI571 treatment restores nuclear CDKIs and reduces cell proliferation of BCR/ABL expressing cells under physiological conditions. 3. Treatment of STI571+TRAIL reduces cytoplasmic CDKIs and increases cell death of BCR/ABL expressing cells, most notably, the STI571-resistant cells. In conclusion, we show that the imbalance between nuclear (cell cycle inhibitor) and cytoplasmic (cell survival enhancer) CDKIs exist in BCR/ABL-hematopoietic cells.

scholarly journals Uncoupling between Phenotypic Senescence and Cell Cycle Arrest in Aging p21-Deficient Fibroblasts

2000 ◽  
Vol 20 (18) ◽  
pp. 6741-6754 ◽  
Author(s):  
Vjekoslav Dulić ◽  
Georges-Edouard Beney ◽  
Guillaume Frebourg ◽  
Linda F. Drullinger ◽  
Gretchen H. Stein
Keyword(s):  
Cell Cycle ◽  
Replicative Senescence ◽  
Cyclin E ◽  
Human Fibroblasts ◽  
Population Expansion ◽  
Cell Cycle Checkpoints ◽  
Critical Event ◽  
Human Diploid Fibroblasts ◽  
Senescent Phenotype ◽  
Molecular Events

ABSTRACT Irreversible G1 arrest in senescent human fibroblasts is mediated by two inhibitors of cyclin-dependent kinases (Cdks), p21Cip1/SDI1/WAF1 and p16Ink4A. To determine the physiological and molecular events that specifically require p21, we studied senescence in human diploid fibroblasts expressing the human papillomavirus type 16 E6 oncogene, which confers low p21 levels via enhanced p53 degradation. We show that in late-passage E6 cells, high Cdk activity drives the cell cycle, but population expansion is slowed down by crisis-like events, probably owing to defective cell cycle checkpoints. At the end of lifespan, terminal-passage E6 cells exhibited several aspects of the senescent phenotype and accumulated unphosphorylated pRb and p16. However, both replication and cyclin-Cdk2 kinase activity were still not blocked, demonstrating that phenotypic and replicative senescence are uncoupled in the absence of normal p21 levels. At this stage, E6 cells also failed to upregulate p27 and inactivate cyclin-Cdk complexes in response to serum deprivation. Eventually, irreversible G1 arrest occurred coincident with inactivation of cyclin E-Cdk2 owing to association with p21. Similarly, when p21−/− mouse embryo fibroblasts reached the end of their lifespan, they had the appearance of senescent cells yet, in contrast to their wild-type counterparts, they were deficient in downregulating bromodeoxyuridine incorporation, cyclin E- and cyclin A-Cdk2 activity, and inhibiting pRb hyperphosphorylation. These data support the model that the critical event ensuring G1arrest in senescence is p21-dependent Cdk inactivation, while other aspects of senescent phenotype appear to occur independently of p21.

scholarly journals Differential Roles for Cyclin-Dependent Kinase Inhibitors p21 and p16 in the Mechanisms of Senescence and Differentiation in Human Fibroblasts

1999 ◽  
Vol 19 (3) ◽  
pp. 2109-2117 ◽  
Author(s):  
Gretchen H. Stein ◽  
Linda F. Drullinger ◽  
Alexandre Soulard ◽  
Vjekoslav Dulić
Keyword(s):  
Cell Cycle ◽  
Cyclin D1 ◽  
Cell Cycle Arrest ◽  
Early Stage ◽  
Cyclin E ◽  
Human Fibroblasts ◽  
Senescent Cell ◽  
Nuclear Antigen ◽  
Cyclin Dependent Kinase ◽  
Cycle Arrest

ABSTRACT The irreversible G1 arrest in senescent human diploid fibroblasts is probably caused by inactivation of the G1cyclin–cyclin-dependent kinase (Cdk) complexes responsible for phosphorylation of the retinoblastoma protein (pRb). We show that the Cdk inhibitor p21Sdi1,Cip1,Waf1, which accumulates progressively in aging cells, binds to and inactivates all cyclin E-Cdk2 complexes in senescent cells, whereas in young cells only p21-free Cdk2 complexes are active. Furthermore, the senescent-cell-cycle arrest occurs prior to the accumulation of the Cdk4-Cdk6 inhibitor p16Ink4a, suggesting that p21 may be sufficient for this event. Accordingly, cyclin D1-associated phosphorylation of pRb at Ser-780 is lacking even in newly senescent fibroblasts that have a low amount of p16. Instead, the cyclin D1-Cdk4 and cyclin D1-Cdk6 complexes in these cells are associated with an increased amount of p21, suggesting that p21 may be responsible for inactivation of both cyclin E- and cyclin D1-associated kinase activity at the early stage of senescence. Moreover, even in the late stage of senescence when p16 is high, cyclin D1-Cdk4 complexes are persistent, albeit reduced by ≤50% compared to young cells. We also provide new evidence that p21 may play a role in inactivation of the DNA replication factor proliferating cell nuclear antigen during early senescence. Finally, because p16 accumulates in parallel with the increases in senescence-associated β-Gal activity and cell volume that characterize the senescent phenotype, we suggest that p16 upregulation may be part of a differentiation program that is turned on in senescent cells. Since p21 decreases after senescence is achieved, this upregulation of p16 may be essential for maintenance of the senescent-cell-cycle arrest.

Subcellular and Cell-Cycle Expression Profiles of CDK-Inhibitors in Normal Differentiating Myeloid Cells

Blood ◽  
1999 ◽  
Vol 93 (9) ◽  
pp. 2907-2917 ◽  
Author(s):  
B. Yaroslavskiy ◽  
S. Watkins ◽  
A.D. Donnenberg ◽  
T.J. Patton ◽  
R.A. Steinman
Keyword(s):  
Cell Cycle ◽  
Cellular Proliferation ◽  
Expression Profiles ◽  
Behavior Changes ◽  
Cdk Inhibitors ◽  
In Vitro Differentiation ◽  
Cd34 Cells ◽  
Blast Cells ◽  
Cell Cycle Inhibitors

A central question in hematopoiesis is how cell-cycling behavior changes during the emergence of the differentiated state. To further understand what genetic regulators might couple proliferation status to differentiation, we studied the expression of the cell-cycle inhibitors p21 and p27 during the in vitro differentiation of normal CD34+ blast cells along the myeloid lineage. We find p27 but not p21 to be expressed in freshly harvested resting CD34+ cells. Thereafter, p21 levels peak concurrent with cellular proliferation and then decline in expression as cells undergo terminal differentiation. In contrast, p27 levels are fairly constant but the subcellular localization of p27 changes from nuclear expression to predominantly cytoplasmic expression and finally to perinuclear localization at progressive stages of differentiation. This report discusses the implications of these findings.

The emerging importance of cyclin-dependent kinase inhibitors in the regulation of the plant cell cycle and related processesThis review is one of a selection of papers published in the Special Issue on Plant Cell Biology.

2006 ◽  
Vol 84 (4) ◽  
pp. 640-650 ◽  
Author(s):  
Hong Wang ◽  
Yongming Zhou ◽  
Larry C. Fowke
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Plant Cell ◽  
Cell Biology ◽  
Cell Cycle Regulation ◽  
Cellular Localization ◽  
Molecular Mechanisms ◽  
Cdk Inhibitors ◽  
Cyclin Dependent Kinase ◽  
Cycle Regulation

The cell division cycle in plants as in other eukaryotes is controlled by the cyclin-dependent kinase (CDK). This CDK paradigm determines that developmental cues and environmental signals need to impinge on the CDK complex to affect the cell cycle. An important part of understanding cell cycle regulation is to understand how CDK is regulated by various factors. In addition, there are features that set the cell cycle regulation in plants apart from that in other eukaryotes such as animals. Our knowledge of the molecular mechanisms that underlie the differences is poor. A family of plant CDK inhibitor proteins has been identified. The plant CDK inhibitors share similarity with a family of animal CDK inhibitors in a small region, while most of the sequence and the structural layout of the plant CDK inhibitors are different from the animal counterparts. Studies of plant CDK inhibitors have been performed mostly with the CDK inhibitors from Arabidopsis called ICKs (also referred to as KRPs). ICKs interact with D-type cyclins and A-type CDK. Overexpression of ICKs has been shown to affect cell division, plant growth, and morphogenesis. Studies of ICKs have also provided insightful information on the control of endoreduplication in plants. These aspects as well as cellular localization and protein regulation of ICKs are reviewed.

scholarly journals Reactivation of Lytic Replication from B Cells Latently Infected with Epstein-Barr Virus Occurs with High S-Phase Cyclin-Dependent Kinase Activity while Inhibiting Cellular DNA Replication

2003 ◽  
Vol 77 (2) ◽  
pp. 851-861 ◽  
Author(s):  
Ayumi Kudoh ◽  
Masatoshi Fujita ◽  
Tohru Kiyono ◽  
Kiyotaka Kuzushima ◽  
Yutaka Sugaya ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Epstein Barr Virus ◽  
S Phase ◽  
Lytic Replication ◽  
Cdk Inhibitors ◽  
Cyclin Dependent Kinase ◽  
Barr Virus ◽  
Epstein Barr ◽  
Cellular Dna

ABSTRACT Productive infection and replication of herpesviruses usually occurs in growth-arrested cells, but there has been no direct evidence in the case of Epstein-Barr virus (EBV), since an efficient lytic replication system without external stimuli does not exist for the virus. Expression of the EBV lytic-switch transactivator BZLF1 protein in EBV-negative epithelial tumor cell lines, however, is known to arrest the cell cycle in G0/G1 by induction of the tumor suppressor protein p53 and the cyclin-dependent kinase (CDK) inhibitors p21WAF-1/CIP-1 and p27KIP-1, followed by the accumulation of a hypophosphorylated form of the Rb protein. In order to determine the effect of the onset of lytic viral replication on cellular events in latently EBV-infected B LCLs, a tightly controlled induction system of the EBV lytic-replication program by inducible BZLF1 protein expression was established in B95-8 cells. The induction of lytic replication completely arrested cell cycle progression and cellular DNA replication. Surprisingly, the levels of p53, p21WAF-1/CIP-1, and p27KIP-1 were constant before and after induction of the lytic program, indicating that the cell cycle arrest induced by the lytic program is not mediated through p53 and the CDK inhibitors. Furthermore, although cellular DNA replication was blocked, elevation of cyclin E/A expression and accumulation of hyperphosphorylated forms of Rb protein were observed, a post-G1/S phase characteristic of cells. Thus, while the EBV lytic program promoted specific cell cycle-associated activities involved in the progression from G1 to S phase, it inhibited cellular DNA synthesis. Such cellular conditions appear to especially favor viral lytic replication.

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