scholarly journals HBx-dependent cell cycle deregulation involves interaction with cyclin E/A–cdk2 complex and destabilization of p27Kip1

2006 ◽  
Vol 401 (1) ◽  
pp. 247-256 ◽  
Author(s):  
Atish Mukherji ◽  
Vaibhao C. Janbandhu ◽  
Vijay Kumar
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Cyclin E ◽  
Direct Interaction ◽  
Protein Kinase Activity ◽  
Cell Cycle Regulators ◽  
Binding Studies ◽  
Molecular Events ◽  
Cdk2 Complex

The HBx (X protein of hepatitis B virus) is a promiscuous transactivator implicated to play a key role in hepatocellular carcinoma. However, HBx-regulated molecular events leading to deregulation of cell cycle or establishment of a permissive environment for hepatocarcinogenesis are not fully understood. Our cell culture-based studies suggested that HBx had a profound effect on cell cycle progression even in the absence of serum. HBx presence led to an early and sustained level of cyclin–cdk2 complex during the cell cycle combined with increased protein kinase activity of cdk2 heralding an early proliferative signal. The increased cdk2 activity also led to an early proteasomal degradation of p27Kip1 that could be reversed by HBx-specific RNA interference and blocked by a chemical inhibitor of cdk2 or the T187A mutant of p27. Further, our co-immunoprecipitation and in vitro binding studies with recombinant proteins suggested a direct interaction between HBx and the cyclin E/A–cdk2 complex. Interference with different signalling cascades known to be activated by HBx suggested a constitutive requirement of Src kinases for the association of HBx with these complexes. Notably, the HBx mutant that did not interact with cyclin E/A failed to destabilize p27Kip1 or deregulate the cell cycle. Thus HBx appears to deregulate the cell cycle by interacting with the key cell cycle regulators independent of its well-established role in transactivation.

scholarly journals BRCA1 Is Phosphorylated at Serine 1497 In Vivo at a Cyclin-Dependent Kinase 2 Phosphorylation Site

1999 ◽  
Vol 19 (7) ◽  
pp. 4843-4854 ◽  
Author(s):  
Heinz Ruffner ◽  
Wei Jiang ◽  
A. Grey Craig ◽  
Tony Hunter ◽  
Inder M. Verma
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Kinase Activity ◽  
Phosphorylation Site ◽  
Cyclin A ◽  
Dominant Negative ◽  
Protein Kinase Activity ◽  
Cyclin Dependent Kinase

ABSTRACT BRCA1 is a cell cycle-regulated nuclear protein that is phosphorylated mainly on serine and to a lesser extent on threonine residues. Changes in phosphorylation occur in response to cell cycle progression and DNA damage. Specifically, BRCA1 undergoes hyperphosphorylation during late G1 and S phases of the cell cycle. Here we report that BRCA1 is phosphorylated in vivo at serine 1497 (S1497), which is part of a cyclin-dependent kinase (CDK) consensus site. S1497 can be phosphorylated in vitro by CDK2-cyclin A or E. BRCA1 coimmunoprecipitates with an endogenous serine-threonine protein kinase activity that phosphorylates S1497 in vitro. This cellular kinase activity is sensitive to transfection of a dominant negative form of CDK2 as well as the application of the CDK inhibitors p21 and butyrolactone I but not p16. Furthermore, BRCA1 coimmunoprecipitates with CDK2 and cyclin A. These results suggest that the endogenous kinase activity is composed of CDK2-cyclin complexes, at least in part, concordant with the G1/S-specific increase in BRCA1 phosphorylation.

Cell cycle-dependent localization of the CDK2-cyclin E complex in Cajal (coiled) bodies

2000 ◽  
Vol 113 (9) ◽  
pp. 1543-1552 ◽  
Author(s):  
J. Liu ◽  
M.D. Hebert ◽  
Y. Ye ◽  
D.J. Templeton ◽  
H. Kung ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Cyclin E ◽  
Gene Clusters ◽  
Cycle Progression ◽  
Functional Complex ◽  
A Cell ◽  
Cycle Dependent ◽  
Polymerase I

We have found that CDK2 and cyclin E, but not cyclin A, accumulates within Cajal bodies (CBs) in a cell cycle-dependent fashion. In the absence of cyclin E, CDK2 is not enriched in the CB compartment, suggesting that the translocation of CDK2 to CBs is dependent on cyclin E. CDK2 and cyclin E could be recruited to CBs as a functional complex or CBs may serve as ‘docking stations’ for CDK2-cyclin E activation by CAKs during the G(1)/S transition. Notably, CDK7-cyclin H-Mat1 complexes are known to accumulate in CBs. Treatment of cells with inhibitors of either CDKs (olomoucine, 200 microM) or RNA polymerase I (actinomycin D, 0.05 microgram/ml), results in a striking reorganization of CDK2 and p80 coilin to the nucleolar periphery. Furthermore, we demonstrate that p80 coilin can be phosphorylated by purified CDK2-cyclin E complexes in vitro. Thus coilin and other CB proteins appear to be downstream targets of CDK2-cyclin E complex-mediated signaling pathways regulating cell cycle progression and controlling aspects of CB function. Possible roles for CDK2 and cyclin E in the well-documented association of CBs, histone gene clusters and RNA 3′ end processing factors are discussed.

scholarly journals Inhibition of Nek2 by Small Molecules Affects Proteasome Activity

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Lingyao Meng ◽  
Kent Carpenter ◽  
Alexis Mollard ◽  
Hariprasad Vankayalapati ◽  
Steven L. Warner ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Multiple Myeloma ◽  
Drug Resistance ◽  
Cell Lines ◽  
Cancer Cell ◽  
Cell Cycle Progression ◽  
Cancer Cell Lines ◽  
Proteasome Activity ◽  
Cell Cycle Regulators

Background. Nek2 is a serine/threonine kinase localized to the centrosome. It promotes cell cycle progression from G2 to M by inducing centrosome separation. Recent studies have shown that high Nek2 expression is correlated with drug resistance in multiple myeloma patients.Materials and Methods. To investigate the role of Nek2 in bortezomib resistance, we ectopically overexpressed Nek2 in several cancer cell lines, including multiple myeloma lines. Small-molecule inhibitors of Nek2 were discovered using an in-house library of compounds. We tested the inhibitors on proteasome and cell cycle activity in several cell lines.Results. Proteasome activity was elevated in Nek2-overexpressing cell lines. The Nek2 inhibitors inhibited proteasome activity in these cancer cell lines. Treatment with these inhibitors resulted in inhibition of proteasome-mediated degradation of several cell cycle regulators in HeLa cells, leaving them arrested in G2/M. Combining these Nek2 inhibitors with bortezomib increased the efficacy of bortezomib in decreasing proteasome activityin vitro. Treatment with these novel Nek2 inhibitors successfully mitigated drug resistance in bortezomib-resistant multiple myeloma.Conclusion. Nek2 plays a central role in proteasome-mediated cell cycle regulation and in conferring resistance to bortezomib in cancer cells. Taken together, our results introduce Nek2 as a therapeutic target in bortezomib-resistant multiple myeloma.

Cyclin-Dependent Kinase Pathways As Targets for Cancer Treatment

2006 ◽  
Vol 24 (11) ◽  
pp. 1770-1783 ◽  
Author(s):  
Geoffrey I. Shapiro
Keyword(s):  
Cell Cycle ◽  
Rna Polymerase Ii ◽  
Cell Cycle Progression ◽  
Tumor Regression ◽  
Human Cancer ◽  
Cell Types ◽  
Therapeutic Benefit ◽  
Cell Cycle Regulators

Cyclin-dependent kinases (cdks) are critical regulators of cell cycle progression and RNA transcription. A variety of genetic and epigenetic events cause universal overactivity of the cell cycle cdks in human cancer, and their inhibition can lead to both cell cycle arrest and apoptosis. However, built-in redundancy may limit the effects of highly selective cdk inhibition. Cdk4/6 inhibition has been shown to induce potent G1 arrest in vitro and tumor regression in vivo; cdk2/1 inhibition has the most potent effects during the S and G2 phases and induces E2F transcription factor–dependent cell death. Modulation of cdk2 and cdk1 activities also affects survival checkpoint responses after exposure to DNA-damaging and microtubule-stabilizing agents. The transcriptional cdks phosphorylate the carboxy-terminal domain of RNA polymerase II, facilitating efficient transcriptional initiation and elongation. Inhibition of these cdks primarily affects the accumulation of transcripts with short half-lives, including those encoding antiapoptosis family members, cell cycle regulators, as well as p53 and nuclear factor-kappa B–responsive gene targets. These effects may account for apoptosis induced by cdk9 inhibitors, especially in malignant hematopoietic cells, and may also potentiate cytotoxicity mediated by disruption of a variety of pathways in many transformed cell types. Current work is focusing on overcoming pharmacokinetic barriers that hindered development of flavopiridol, a pan-cdk inhibitor, as well as assessing novel classes of compounds potently targeting groups of cell cycle cdks (cdk4/6 or cdk2/1) with variable effects on the transcriptional cdks 7 and 9. These efforts will establish whether the strategy of cdk inhibition is able to produce therapeutic benefit in the majority of human tumors.

scholarly journals The Cak1p Protein Kinase Is Required at G1/S and G2/M in the Budding Yeast Cell Cycle

Genetics ◽  
1997 ◽  
Vol 147 (1) ◽  
pp. 57-71 ◽  
Author(s):  
Ann Sutton ◽  
Richard Freiman
Keyword(s):  
Cell Cycle ◽  
Protein Kinase ◽  
Cell Cycle Progression ◽  
Budding Yeast ◽  
Protein Kinase Activity ◽  
Synthetic Lethal ◽  
Protein Levels ◽  
M Phase

Abstract The CAK1 gene encodes the major CDK-activating kinase (CAK) in budding yeast and is required for activation of Cdc28p for cell cycle progression from G2 to M phase. Here we describe the isolation of a mutant allele of CAK1 in a synthetic lethal screen with the Sit4 protein phosphatase. Analysis of several different cak1 mutants shows that although the G2 to M transition appears most sensitive to loss of Cak1p function, Cak1p is also required for activation of Cdc28p for progression from G1 into S phase. Further characterization of these mutants suggests that, unlike the CAK identified from higher eukaryotes, Cak1p of budding yeast may not play a role in general transcription. Finally, although Cak1 protein levels and in vitro protein kinase activity do not fluctuate during the cell cycle, at least a fraction of Cak1p associates with higher molecular weight proteins, which may be important for its in vivo function.

scholarly journals Identification of MoKA, a Novel F-Box Protein That Modulates Krüppel-Like Transcription Factor 7 Activity

2004 ◽  
Vol 24 (3) ◽  
pp. 1058-1069 ◽  
Author(s):  
Silvia Smaldone ◽  
Friedrich Laub ◽  
Cindy Else ◽  
Cecilia Dragomir ◽  
Francesco Ramirez
Keyword(s):  
Cell Cycle ◽  
Nervous System ◽  
Transcription Factor ◽  
Mammalian Cells ◽  
Cell Cycle Progression ◽  
Direct Interaction ◽  
Proximal Promoter ◽  
F Box Protein ◽  
Developing Nervous System

ABSTRACT KLF7, a member of the Krüppel-like transcription factor family, is believed to regulate neurogenesis and cell cycle progression. Here, a yeast two-hybrid screen for KLF7 cofactors in the developing nervous system identified a novel 140-kDa protein named MoKA, for modulator of KLF7 activity. Interaction between MoKA and KLF7 was confirmed by the in vitro glutathione S-transferase pull-down assay and by coimmunoprecipitation of the proteins overexpressed in mammalian cells. Functional assays documented that MoKA is a KLF7 coactivator, and in situ hybridizations identified the developing nervous system and the adult testes as two sites of MoKA and Klf7 coexpression. Chromatin immunoprecipitation experiments demonstrated KLF7 binding to the p21WAF1/Cip1 gene while transient transfection assays documented KLF7 stimulation of the p21WAF1/Cip1 proximal promoter. Additional tests revealed that distinct structural motifs of MoKA direct interaction with KLF7 and shuttling between the nucleus and cytoplasm of asynchronously cycling cells. Altogether, our results strongly suggest that MoKA and KLF7 interact functionally to regulate gene expression during cell differentiation and identify the cell cycle regulator p21WAF1/Cip1 as one of the targeted genes.

scholarly journals Endothelial cells isolated from caveolin-2 knockout mice display higher proliferation rate and cell cycle progression relative to their wild-type counterparts

2010 ◽  
Vol 298 (3) ◽  
pp. C693-C701 ◽  
Author(s):  
Leike Xie ◽  
Philippe G. Frank ◽  
Michael P. Lisanti ◽  
Grzegorz Sowa
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Kinase Inhibitors ◽  
Fold Increase ◽  
S Phase ◽  
Lower Percentage ◽  
Wild Type ◽  
Cycle Progression ◽  
Molecular Events

The goal of this study was to determine whether caveolin-2 (Cav-2) is capable of controlling endothelial cell (EC) proliferation in vitro. To realize this goal, we have directly compared proliferation rates and cell cycle-associated signaling proteins between lung ECs isolated from wild-type (WT) and Cav-2 knockout (KO) mice. Using three independent proliferation assays, we have determined that Cav-2 KO ECs proliferate by ca. 2-fold faster than their WT counterparts. Cell cycle analysis by flow cytometry of propidium iodide-stained cells showed a relatively higher percentage of Cav-2 KO ECs in S and G2/M and lower percentage in Go/G1 phases of cell cycle relative to their WT counterparts. Furthermore, an over 2-fold increase in the percentage of S phase-associated Cav-2 KO relative to WT ECs was independently determined with bromodeoxyuridine incorporation assay. Mechanistically, the increase in proliferation/cell cycle progression of Cav-2 KO ECs correlated well with elevated expression levels of predominantly S phase- and G2/M phase-associated cyclin A and B1, respectively. Further mechanistic analysis of molecular events controlling cell cycle progression revealed increased level of hyperphosphorylated (inactive) form of G1 to S phase transition inhibitor, the retinoblastoma protein in hyperproliferating Cav-2 KO ECs. Conversely, the expression level of the two cyclin-dependent kinase inhibitors p16INK4 and p27Kip1 was reduced in Cav-2 KO ECs. Finally, increased phosphorylation (activation) of proproliferative extracellular signal-regulated kinase 1/2 was observed in hyperproliferating Cav-2 KO ECs. Overall, our data suggest that Cav-2 negatively regulates lung EC proliferation and cell cycle progression.

scholarly journals Linc01133 contributes to gastric cancer growth by enhancing YES1-dependent YAP1 nuclear translocation via sponging miR-145-5p

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Yujing Sun ◽  
Yuan Tian ◽  
Junyi He ◽  
Yaru Tian ◽  
Guohao Zhang ◽  
...  
Keyword(s):  
Gastric Cancer ◽  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Nuclear Translocation ◽  
In Vivo Studies ◽  
Cancer Growth ◽  
Cell Cycle Regulators ◽  
Gastric Cancer Patients

AbstractThe long intergenic non-coding RNA linc01133 is reported to be oncogenic in various malignancies. However, the role and mechanism of linc01133 in regulating gastric cancer growth is still not clear. In the present study, we found that linc01133 was significantly upregulated in gastric cancer tissues compared to non-tumorous gastric tissues. Linc01133 over-expression significantly correlated with tumor size and tumor differentiation in gastric cancer patients. The expression of linc01133 was regulated by c-Jun and c-Fos collaboratively. In both in vitro and in vivo studies, linc01133 was shown to promote gastric cancer cell growth. Linc01133 localized in the cytoplasm and functioned as an endogenous competing RNA of miR-145-5p to upregulate the expression of YES1, which was proved to be the target gene of miR-145-5p. By promoting YES1-dependent YAP1 nuclear translocation, linc01133 upregulated the expression of the key cell cycle regulators CDK4, CDK6 and cyclin D1 to promote G1-S phase transition. Thus, our study unveiled the function and mechanism of linc01133 regulating cell cycle progression in gastric cancer.

scholarly journals Cyclin E Associates with Components of the Pre-mRNA Splicing Machinery in Mammalian Cells

1998 ◽  
Vol 18 (8) ◽  
pp. 4526-4536 ◽  
Author(s):  
Wolfgang Seghezzi ◽  
Katrin Chua ◽  
Frances Shanahan ◽  
Or Gozani ◽  
Robin Reed ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Cell Cycle Progression ◽  
Cyclin E ◽  
Specific Inhibitor ◽  
Mrna Splicing ◽  
Core Proteins ◽  
Associated Proteins ◽  
Cdk Regulation

ABSTRACT Cyclin E-cdk2 is a critical regulator of cell cycle progression from G1 into S phase in mammalian cells. Despite this important function little is known about the downstream targets of this cyclin-kinase complex. Here we have identified components of the pre-mRNA processing machinery as potential targets of cyclin E-cdk2. Cyclin E-specific antibodies coprecipitated a number of cyclin E-associated proteins from cell lysates, among which are the spliceosome-associated proteins, SAP 114, SAP 145, and SAP 155, as well as the snRNP core proteins B′ and B. The three SAPs are all subunits of the essential splicing factor SF3, a component of U2 snRNP. Cyclin E antibodies also specifically immunoprecipitated U2 snRNA and the spliceosome from splicing extracts. We demonstrate that SAP 155 serves as a substrate for cyclin E-cdk2 in vitro and that its phosphorylation in the cyclin E complex can be inhibited by the cdk-specific inhibitor p21. SAP 155 contains numerous cdk consensus phosphorylation sites in its N terminus and is phosphorylated prior to catalytic step II of the splicing pathway, suggesting a potential role for cdk regulation. These findings provide evidence that pre-mRNA splicing may be linked to the cell cycle machinery in mammalian cells.

scholarly journals Naringin as a natural bitter tastant promotes proliferation of cultured human bronchial epithelial cells via activation of TAS2R signaling

2020 ◽  
Author(s):  
Kai Ni ◽  
Mingzhi Luo ◽  
Bing Bu ◽  
Jia Guo ◽  
Yan Pan ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Proliferation ◽  
Epithelial Cells ◽  
Calcium Signaling ◽  
Cell Cycle Progression ◽  
Cyclin E ◽  
Asthma Therapy ◽  
Cycle Progression ◽  
Bronchial Epithelial

Abstract Bitter tastants can activate bitter taste receptors (TAS2Rs) and thus initiate the relaxation of airway smooth muscle cells, which have great potential in the development of novel asthma therapy. However, recent study shows that canonical bitter substance denatonium induces apoptosis of bronchial epithelial cells (BECs), indicating the toxic effect of bitter tastants on airways. Considering the diversity of bitter tastants in nature and TAS2Rs expressed in airway cells, it is thus necessary to carefully evaluate the bitter tastant for its effect on the proliferation of BECs, if aimed to treat airway disease. Here we first screened a group of bitter flavonoids, including apignenin, hespretin, kaempferol, naringenin, naringin and quercetin which are commonly used in food and traditional medicine, and then quantitatively evaluated the effects of this group of bitter flavonoids on the proliferation of BECs (i.e. 16HBE14o- cells) cultured in vitro. The results show that five of the six tested bitter tastants inhibited, but only naringin promoted the proliferation of 16HBE14o- BECs in vitro at the dose of a few hundred micromoles. Furthermore, the naringin-promoted cell proliferation was associated with enhanced cell cycle progression, mRNA expression of cyclin E, and evoked calcium signaling/ERK signaling. Inhibition of the TAS2R signaling pathways with specific blockers attenuated the naringin-enhanced cell proliferation, cyclin E expression and calcium signaling/ERK activation. Taken together, these findings indicate that although many bitter flavonoids may inhibit the proliferation of BECs, naringin emerges as one of the kind that promotes the proliferation of BECs via cell cycle progression and TAS2R-activated intracellular signaling. Only such bitter tastant proven to be unharmful to the epithelial structure and function could be further developed as safe and effective TAS2Rs-based bronchodilator in asthma therapy.

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