Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Deregulation of D-type cyclin-dependent kinases (CDK4 and 6) is widely observed in various human cancers, illustrating their importance in cell cycle control. Like other cyclin-dependent kinases (CDKs), assembly with cyclins is the most critical step for activation of CDK4/6. As previously reported elsewhere, we observed that the level of cyclinD1-CDK4 complex and its associated kinase activity were significantly low in asynchronously proliferating mouse embryo fibroblasts lacking both p21(Cip1) and p27(Kip1) (p21/p27-null MEFs). These evidences imply that p21(Cip1) and p27(Kip1) CDK inhibitors are 'essential activators' of cyclin D-kinases. We, however, discovered here that both the assembly and activation of cyclin D1-CDK4 complex occur when quiescent p21/p27-null MEFs were stimulated to re-enter the cell cycle. This mitogen-induced cyclin D1-kinase activity was blocked by overexpression of p16(INK4a) and resulted in the inhibition of S phase entry in p21/p27-null MEFs. Furthermore, ectopic expression of p34(SEI-1), a mitogen-induced CDK4 binding protein, increased the levels of active cyclinD1-CDK4 complex in asynchronously proliferating p21/p27-null MEFs. Together, our results suggest that there are several independent ways to stimulate the assembly of cyclin D1-CDK4 kinases. Although p21(Cip1) and p27(Kip1) play a role in this process, our results demonstrate that additional mechanisms must occur in G0 to S phase transition.
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PMID:Activation of cyclin D1-kinase in murine fibroblasts lacking both p21(Cip1) and p27(Kip1). 1244 43

A positive correlation between cell size and DNA content has been recognized in many plant cell types. Conversely, misexpression of a dominant-negative cyclin-dependent kinase (CDK) or CDK inhibitor proteins (ICK/KRPs) in Arabidopsis and tobacco leaves has revealed that cell growth can be uncoupled from cell cycle progression and DNA content. However, cell growth also appears to be controlled in a non-cell-autonomous manner by organ size, making it difficult in a ubiquitous expression assay to judge the cell-autonomous function of putative cell growth regulators. Here, we investigated the function of the CDK inhibitor ICK1/KRP1 on cell growth and differentiation independent of any compensatory influence of an organ context using Arabidopsis trichomes as a model system. By analyzing cell size with respect to DNA content, we dissected cell growth in a DNA-dependent and a DNA-independent process. We further found that ICK1/KRP1 misexpression interfered with differentiation and induced cell death, linking cell cycle progression, differentiation, and cell death in plants. The function of ICK1/KRP1 in planta was found to be dependent on a C-terminal domain and regulated negatively by an N-terminal domain. Finally, we identified CDKA;1 and a D-type cyclin as possible targets of ICK1/KRP1 expression in vivo.
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PMID:Misexpression of the cyclin-dependent kinase inhibitor ICK1/KRP1 in single-celled Arabidopsis trichomes reduces endoreduplication and cell size and induces cell death. 1256 74

Virtually all mammalian cells express two seemingly redundant cyclin-D-dependent kinases (Cdk4 and Cdk6) and three partner cyclins (D1, D2 and D3) essential for the G(1)-S transition, with predominant expression of Cdk4 and D1 in mesenchymal cells and Cdk6 and D3 in hematopoietic cells. We recently found two novel functions for Cdk6 executed in fibroblasts although unlike Cdk4 it is dispensable for their proliferation. In the rat fibroblast NRK-49F cells, oncogenic stimulation recruits Cdk6 to participate in a step of the cell cycle start that seems to be critical for anchorage-independent S-phase onset. Among the kinase-D-type cyclin combinations, the Cdk6-cyclin-D3 complex has a unique ability to evade inhibition by cyclin-dependent kinase inhibitors and thereby control the cell's proliferative competence under growth-suppressive conditions. We describe here that 2-5-fold overexpression of both Cdk6 and D3 enhances by 5x10(3)-10(6)-fold the susceptibility of the BALB/c3T3 and C3H10T1/2 mouse fibroblast lines to ultraviolet irradiation- as well as 3-methylcholanthrene-induced transformation. This result suggests that deregulated expression of Cdk6 and cyclinD3 may predispose cells to malignant transformation, supporting the recent finding that cyclin D3 activated by chromosomal rearrangement is the causative gene of non-Hodgkin B lymphoma, in which Cdk6 is the major partner kinase.
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PMID:Overexpression of Cdk6-cyclin D3 highly sensitizes cells to physical and chemical transformation. 1259 86

Restitution of lost tumor-suppressor activities may be a promising strategy to target specifically cancer cells. However, the action of ectopically expressed tumor-suppressor genes depends on genetic background of tumoral cells. Ectopic expression of p16(INK4a) induces either cell cycle arrest or apoptosis in different pancreatic cancer cell lines. We examined the molecular mechanisms mediating these two different cellular responses to p16 overexpression. Ectopic expression of p16 leads to G1 arrest in NP-9 cells by redistributing p21/p27 CKIs and inhibiting cyclin-dependent kinase CDK2 activity. In contrast, in NP-18 cells cyclin E (CycE)/CDK2 activity is significantly higher and is not downregulated by p16-mediated redistribution of p21/p27. Moreover, inhibition of CDK4 activity with fascaplysine, which does not affect CycE/CDK2 activity, reduces pocket protein phosphorylation in both cell lines, but fails to induce growth arrest. Like overexpression of p16, fascaplysine induces apoptosis in NP-18 cells, suggesting that inhibition of D-type cyclin/CDK activity in cells with high levels of CycE/CDK2 activity activates an apoptotic pathway. Inhibition of CycE/CDK2 activity via ectopic expression of p21 in NP-18 cells overexpressing p16 induces growth arrest and prevents p16-mediated apoptosis. Accordingly, silencing of p21 expression by using small interfering RNA switches the fate of p16-expressing NP-9 cells from cell cycle arrest to apoptosis. Our data suggest that, after CDK4/6 inactivation, the fate of pancreatic tumor cells depends on the ability to modulate CDK2 activity.
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PMID:The fate of pancreatic tumor cell lines following p16 overexpression depends on the modulation of CDK2 activity. 1530 28

The proliferating cell nuclear antigen (PCNA) is a protein factor required for processive DNA synthesis that is associated with G(1) cell cycle proteins. It has been demonstrated previously that, in germinating maize (Zea mays) embryonic axes, PCNA forms protein complexes with two Cdk-A proteins (32 and 36 kDa) and with a putative D-type cyclin. These complexes exhibit protein kinase activity on histone H1 and on the maize homologue of the pRB (retinoblastoma) protein. Flow cytometry has been used to study the influence of the phytohormones benzyladenine (BA) and abscisic acid (ABA) on cell cycle advancement during maize germination. It was found that, while BA accelerates the passage of cells from G(1) to G(2), ABA delays cell cycle events so that most cells seem to remain in G(1). The amounts of PCNA and Cdk-A proteins also vary according to the hormone treatment. In embryonic axes, PCNA increases rapidly during early germination in BA, compared with a gradual increase in water, while ABA treatment had only a marginal effect. However, of the two Cdk-A proteins, the 32 kDa protein is strongly reduced after 15 h of imbibition in water while this occurs later when axes are imbibed in BA or ABA. The PCNA-associated protein kinase activity in the BA and ABA treatments falls after 3 h of imbibition compared with activity in the control; however, while kinase activity in the BA treatment continues to decline during imbibition, it remains relatively constant until 24 h of imbibition in the ABA treatment. By contrast, a p13(Suc1)-associated Cdk-A kinase is activated after 15 h of imbibition under all treatments, particularly in ABA. These results suggest that, in maize, ABA delays the germination process by affecting cell cycle advancement, stopping cells mostly in a G(1) state.
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PMID:Differential response of PCNA and Cdk-A proteins and associated kinase activities to benzyladenine and abscisic acid during maize seed germination. 1554 95

Changes in photoassimilate partitioning between source and sink organs significantly affect fruit development and size. In this study, a comparison was made of tomato plants (Solanum lycopersicum L.) grown under a low fruit load (one fruit per truss, L1 plants) and under a standard fruit load (five fruits per truss, L5 plants), at morphological, biochemical, and molecular levels. Fruit load reduction resulted in increased photoassimilate availability in the plant and in increased growth rates in all plant organs analysed (root, stem, leaf, flower, and fruit). Larger flower and fruit size in L1 plants were correlated with higher cell number in the pre-anthesis ovary. This was probably due to the acceleration of the flower growth rate since other flower developmental parameters (schedule and time-course) remained otherwise unaffected. Using RT-PCR, it was shown that the transcript levels of CYCB2;1 (cyclin) and CDKB2;1 (cyclin-dependent kinase), two mitosis-specific genes, strongly increased early in developing flower buds. Remarkably, the transcript abundance of CYCD3;1, a D-type cyclin potentially involved in cell cycle regulation in response to mitogenic signals, also increased by more than 5-fold at very early stages of L1 flower development. By contrast, transcripts from fw2.2, a putative negative regulator of cell division in tomato fruit, strongly decreased in developing flower bud, as confirmed by in situ hybridization studies. Taken together, these results suggest that changes in carbohydrate partitioning could control fruit size through the regulation of cell proliferation-related genes at very early stages of flower development.
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PMID:The expression of cell proliferation-related genes in early developing flowers is affected by a fruit load reduction in tomato plants. 1648 16

Cdc14 is a member of the dual-specificity phosphatase family, which is essential for faithful cell cycle progression in eukaryotic cells of different origin. The function of human Cdc14A (hCdc14A), however, has not been fully elucidated as only few physiological substrates have been identified. To gain insight into the biological role of Cdc14A, we performed a yeast two-hybrid screen designed to isolate substrates of this human phosphatase. Using this genetic approach, we here report the identification of Erk3, an atypical mitogen-activated protein kinase (MAPK), as a specific binding partner of hCdc14A. GST pull-down assays show that Erk3 interacts directly with hCdc14A in vitro via its unique C-terminal domain. Furthermore, biochemical analysis reveals that hCdc14A can remove cyclin-dependent kinase (Cdk)-mediated phosphorylation of Erk3 in vitro raising the possibility that Erk3 may be a potential substrate for hCdc14A in vivo. Consistent with a physiologically relevant cross-talk in vivo, we find that Cdc14A forms a stable complex with Erk3 in human cells independent of its intrinsic phosphatase activity but mediated by its regulatory C-terminal domain. We show that hCdc14A impacts the emerging signaling pathway between Erk3 and MK5, a MAPK-activated protein kinase. We document that hCdc14A upregulation leads to redistribution of the Erk3 substrate MK5 from the nucleus to the cytoplasm. In addition, we find that hCdc14A stabilizes complex formation between Erk3 and its binding partner cyclin D3, a D-type cyclin implicated in both cellular proliferation and differentiation. Collectively, our findings suggest an intimate functional relationship between the Cdc14A phosphatase and the Erk3 kinase in signaling pathways that regulate key cell-fate decisions in human cells.
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PMID:A functional link between the human cell cycle-regulatory phosphatase Cdc14A and the atypical mitogen-activated kinase Erk3. 1823 25

Chromosome loss or gain is associated with a large number of solid cancers, providing genomic plasticity and thus adaptability to cancer cells. Numerical centrosome abnormalities arising from centrosome over-duplication or failed cytokinesis are a recognized cause of aneuploidy. In higher eukaryotic cells, the centrosome duplicates only once per cell cycle to ensure the formation of a bipolar mitotic spindle that orchestrates the balanced distribution of the sister chromatids to the respective daughter cells. Here we delineate the events that allow abnormal centrosome duplication, resulting in mitotic errors and incorrect chromosome segregation in cells with sustained cyclin-dependent kinase (CDK) activity. We have identified NPM1 as a substrate for CDK6 activated by the Kaposi's sarcoma herpesvirus (KSHV) D-type cyclin and shown that p53-driven apoptosis occurs downstream of NPM1 phosphorylation as a checkpoint mechanism that prevents accumulation of cells with supernumerary centrosomes. Our findings provide evidence that abnormal chromosome segregation in KSHV-infected cells is a direct consequence of NPM1 phosphorylation and predict that genomic instability is an inevitable consequence of latent KSHV infection.
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PMID:p53-Driven apoptosis limits centrosome amplification and genomic instability downstream of NPM1 phosphorylation. 1845 40

Cyclin D2s (CCND2s) are members of the D-type cyclin family. They interact and construct complexes with cyclin-dependent kinase (CDK)4 or 6. The cyclin D2/CDK4 or CDK6 complexes have key roles in controlling the progression of cell cycle from the Gap 1 (G1) phase to the synthesis (S) phase. Overexpression of cyclin D2 is associated with the development of tumors. In this study, we identified 16 sequence variants of CCND2 polymorphisms through direct DNA sequencing in 24 individuals, and 5 common variants were selected for genotyping in larger-scale subjects (n=1100). Genetic associations of those polymorphisms with hepatitis B virus (HBV) clearance and hepatocellular carcinoma (HCC) outcome among patients with HBV were analyzed. Although no significant association was observed between the polymorphisms and HCC outcome among HBV patients, one common polymorphism in the 5'-untranslated region (that is, rs1049606) and the most common haplotype (CCND-ht1 [T-C-T-A-T]), however, were significantly associated with HBV clearance (odds ratio=0.69, P=0.0002, Pcorr=0.001 and odds ratio=1.37, P=0.0009, Pcorr=0.004, respectively). The minor allele frequency of rs1049606 among the spontaneously recovered (SR) group was significantly higher than that of the chronic carrier (CC) group (frequency=0.403 vs 0.336, P=0.0002). In contrast, the frequency of CCND-ht1 was higher among the CC group than among the SR group (frequency=0.429 vs 0.374, P=0.0009). The information identified in this study might provide valuable insights into generating strategies for control of HBV.
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PMID:CCND2 polymorphisms associated with clearance of HBV infection. 2041 51

The cell cycle is regulated by cyclin-dependent kinase (CDK)- cyclin complexes as well as other regulators. We isolated Kip-related protein 4 (KRP4) cDNA that encodes 289 amino acids including six conserved domains. To investigate the expression pattern of KRP4 as well as of other cell cycle-related genes associated with plant hormones, Arabidopsis seedlings were cultured on MS medium containing auxin or cytokinin. All seedlings treated with phytohormones displayed an increased proportion of cells in S phase. A higher proportion of cells in G2 phase was observed in seedlings treated with NAA. RT-PCR confirmed that the expression of KRP4 was decreased after treatment with phytohormones, and that CDKA and D-type cyclin transcription was increased. Additionally, mitotic cyclins were up-regulated by NAA treatment. These results suggest that KRP4 as well as other cell cycle-related genes might contribute to the control of plant growth in response to exogenous hormones.
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PMID:Expression of Kip-related protein 4 gene (KRP4) in response to auxin and cytokinin during growth of Arabidopsis thaliana. 2042 13


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