Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.22 (cdc2)
 8,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Genetic alterations on the long arm of chromosome 12, including both gene amplification and allelic loss, are associated with malignant progression of human gliomas. The region of the chromosomal arm 12q that is amplified in malignant gliomas contains the CDK4 gene, a cell cycle regulatory gene which promotes cell division. To evaluate the frequency of CDK4 gene amplification, we analyzed a series of 355 brain tumors using a quantitative non-radioactive polymerase chain reaction assay. CDK4 gene amplification occurred in 9 of 81 glioblastomas (11%), but was rare in other neoplasms, including low-grade and anaplastic gliomas, meningiomas, medulloblastomas and metastatic carcinomas (only 6 of 274 cases). There was no correlation between CDK4 gene amplification and allelic loss of chromosome 12. To assess the significance of CDK4 gene amplification, we analyzed protein extracts from 37 glioblastomas by Western blotting with a commercially available polyclonal antibody to cdk4. All tumors with CDK4 gene amplification showed high cdk4 expression levels, whereas no increased cdk4 expression was seen in glioblastomas without CDK4 gene amplification. These data support the functional activity of CDK4 gene amplification in glioblastoma multiforme and point to an important role of CDK4 gene amplification in a subset of glioblastomas.
 ...
PMID:Amplification of the cyclin-dependent kinase 4 (CDK4) gene is associated with high cdk4 protein levels in glioblastoma multiforme. 881 Nov 28

Transforming growth factor beta (TGF beta) inhibits cell proliferation by inducing a G1 cell-cycle arrest. Cyclin/CDK complexes have been implicated in this arrest, because TGF beta treatment leads to inhibition of cyclin/CDK activity. We have investigated the role of the retinoblastoma protein (pRb) in TGF beta-induced growth arrest by using RB+/+ and RB-/- primary mouse embryo fibroblasts. In both of these cell types, TGF beta inhibits CDK4-associated kinase activity. However, whereas CDK2-associated kinase activity was completely inhibited by TGF beta in the wild-type cells, it was reduced only slightly in the RB mutant cells. In addition, at high-cell density the growth-inhibitory effects of TGF beta are no longer observed in the RB-/- cells; on the contrary, TGF beta treatment promotes the growth of these mutant fibroblasts. Thus, under certain cellular growth conditions, elimination of pRb transforms the growth-inhibitory effects of TGF beta into growth-stimulatory effects. These observations could help to explain why TGF beta is often found to enhance tumorigenicity in vivo and why inactivation of the RB gene leads to tumorigenesis.
 ...
PMID:TGF beta-induced growth inhibition in primary fibroblasts requires the retinoblastoma protein. 888 30

The cyclin D-dependent kinases CDK4 and CDK6 trigger phosphorylation of the retinoblastoma protein (RB) late in G1 phase, helping to cancel its growth-suppressive function and thereby facilitating S-phase entry. Although specific inhibition of cyclin D-dependent kinase activity in vivo can prevent cells from entering S phase, it does not affect S-phase entry in cells lacking functional RB, implying that RB may be the only substrate of CDK4 and CDK6 whose phosphorylation is necessary for G1 exit. Using a yeast two-hybrid interactive screen, we have now isolated a novel cyclin D-interacting myb-like protein (designated DMP1), which binds specifically to the nonamer DNA consensus sequences CCCG(G/T)ATGT to activate transcription. A subset of these DMP1 recognition sequences containing a GGA trinucleotide core can also function as Ets-responsive elements. DMP1 mRNA and protein are ubiquitously expressed throughout the cell cycle in mouse tissues and in representative cell lines. DMP1 binds to D-type cyclins directly in vitro and when coexpressed in insect Sf9 cells. In both settings, it can be phosphorylated by cyclin D-dependent kinases, suggesting that its transcriptional activity may normally be regulated through such mechanisms. These results raise the possibility that cyclin D-dependent kinases regulate gene expression in an RB independent manner, thereby serving to link other genetic programs to the cell cycle clock.
 ...
PMID:Interaction of D-type cyclins with a novel myb-like transcription factor, DMP1. 888 74

Inhibitors of cyclin-dependent kinases provide a major mechanism of negative regulation on cell cycle progression. Defects in the function of the CDK inhibitors may lead to uncontrolled cell proliferation and potentially facilitate tumorigenesis. The p16INK4 family of CDK inhibitors specifically prevent the phosphorylation of the retinoblastoma susceptibility gene product, pRb, by inhibiting the kinase activity of CDK4 and CDK6, thereby keeping pRb in its active form as a growth suppressor. The loss of p16INK4 inhibitory activity would, therefore, have the same consequence as the loss of pRb growth suppressing activity. The p16INK4 family currently includes four members, p15INK4b, pl6INK4a, pl8INK4c and p19INK4d. Two members, p15INK4b and pl6INK4a have been found to be deleted and mutated in a variety of human tumor-derived cell lines and primary tumors. In the present study we have examined the genomic status of the newly isolated p19INK4d gene in 75 tumor-derived cell lines; 13 immortalized, transformed or normal cell lines; 19 ovarian tumors and 18 acute myelogenous leukemias. No deletions or point mutations were observed in the pl9INK4d gene. A genetic polymorphism at codon 30 (CGC-->CGG) in exon 1 of the pl9INK4d gene was observed in 10% of the samples under investigation. In the same set of samples, p16INK4a was found to be homozygously deleted in 32% of the tumor derived cell lines. These results together with our previous data that showed a 22% deletion frequency in p15INK4b and rare alterations in the pl8INK4c gene, indicating that the p16INK4a and pl5INK4b, but not the p18INK4c and pl9INK4d genes, are frequently mutated in human tumors. Hence, members of the p16INK4 CDK inhibitor family, while evolutionary related and biochemically indistinguishable, carry out distinct biological functions.
 ...
PMID:Lack of mutation in the cyclin-dependent kinase inhibitor, p19INK4d, in tumor-derived cell lines and primary tumors. 893 52

Human diploid fibroblasts (HDFs) can be grown in culture for a finite number of population doublings before they cease proliferation and enter a growth-arrest state termed replicative senescence. The retinoblastoma gene product, Rb, expressed in these cells is hypophosphorylated. To determine a possible mechanism by which senescent human fibroblasts maintain a hypophosphorylated Rb, we examined the expression levels and interaction of the Rb kinases, CDK4 and CDK6, and the cyclin-dependent kinase inhibitors p21 and p16 in senescent HDFs. Cellular p21 protein expression increased dramatically during the final two to three passages when the majority of cells lost their growth potential and neared senescence but p21 levels declined in senescent HDFs. During this period, p16 mRNA and cellular protein levels gradually rose with the protein levels in senescent HDFs reaching nearly 40-fold higher than early passage cells. In senescent HDFs, p16 was shown to be complexed to both CDK4 and CDK6. Immunodepletion analysis of p21 and p16 from the senescent cell extracts revealed that p16 is the major CDK inhibitor for both CDK4 and CDK6 kinases. Immunoprecipitation of CDK4 and CDK6 and their associated proteins from radiolabeled extracts from senescent HDFs showed no other CDK inhibitors. Based upon these results, we propose that senescence is a multistep process requiring the expression of both p21 and p16. p16 up-regulation is a key event in the terminal stages of growth arrest in senescence, which may explain why p16 but not p21 is commonly mutated in immortal cells and human tumors.
 ...
PMID:Involvement of the cyclin-dependent kinase inhibitor p16 (INK4a) in replicative senescence of normal human fibroblasts. 894 5

The expression of D-type G1 cyclins and their assembly with their catalytic partners, the cyclin-dependent kinases 4 and 6 (CDK4 and CDK6), into active holoenzyme complexes are regulated by growth factor-induced signals. In turn, the ability of cyclin D-dependent kinases to trigger phosphorylation of the retinoblastoma (Rb) protein in the mid- to late G1 phase of the cell cycle makes the inactivation of Rb's growth suppressive function a mitogen-dependent step. The ability of D-type cyclins to act as growth factor sensors depends not only on their rapid induction by mitogens but also on their inherent instability, which ensures their precipitous degradation in cells deprived of growth factors. However, the mechanisms governing the turnover of D-type cyclins have not yet been elucidated. We now show that cyclin D1 turnover is governed by ubiquitination and proteasomal degradation, which are positively regulated by cyclin D1 phosphorylation on threonine-286. Although "free" or CDK4-bound cyclin D1 molecules are intrinsically unstable (t1/2 < 30 min), a cyclin D1 mutant (T286A) containing an alanine for threonine-286 substitution fails to undergo efficient polyubiquitination in an in vitro system or in vivo, and it is markedly stabilized (t1/2 approximately 3.5 hr) when inducibly expressed in either quiescent or proliferating mouse fibroblasts. Phosphorylation of cyclin D1 on threonine-286 also occurs in insect Sf9 cells, and although the process is enhanced significantly by the binding of cyclin D1 to CDK4, it does not depend on CDK4 catalytic activity. This implies that another kinase can phosphorylate cyclin D1 to accelerate its destruction and points to yet another means by which cyclin D-dependent kinase activity may be exogenously regulated.
 ...
PMID:Inhibition of cyclin D1 phosphorylation on threonine-286 prevents its rapid degradation via the ubiquitin-proteasome pathway. 913 25

The mitogen-dependent induction of cyclin D-dependent kinase activity is required for cells to enter the DNA synthetic (S) phase of their division cycle. Immature 32Dcl3 myeloid cells (32D) proliferating in the presence of interleukin-3 (IL-3) normally express cyclins D2 and D3, which assemble into binary holoenzyme complexes with their catalytic subunits, CDK4 and CDK6. When 32D cells are switched to medium containing granulocyte colony-stimulating factor (G-CSF) instead of IL-3, D-type cyclins are degraded and, in the absence of their associated kinase activity, the cells arrest in the first gap phase (G1) of the cell cycle and differentiate to neutrophils. We derived 32D cells in which the expression of p19INK4d, a specific polypeptide inhibitor of CDK4 and CDK6, is regulated by the heavy metal-inducible sheep metallothionein promoter. Induction of p19INK4d in response to zinc prolonged cell survival in the absence of growth factor treatment. When maintained in medium containing both IL-3 and zinc, these cells lost cyclin D-dependent kinase activity, underwent G1 phase arrest, and acquired certain morphologic, antigenic, and functional properties of mononuclear phagocytes. Cells induced to express p19INK4d did not synthesize receptors for macrophage colony-stimulating factor (M-CSF/CSF-1) and reverted to an immature myeloid phenotype when shifted back into medium containing IL-3 alone. These cells exhibited accelerated differentiation to neutrophils in response to G-CSF but also gave rise to macrophage-like cells when maintained in medium containing both G-CSF and zinc. Therefore, the acquisition of macrophage properties in response to zinc treatment neither depended upon IL-3 nor upon G1 phase arrest per se and instead reflects some ability of p19INK4d, and presumably cyclin D-dependent kinases, to affect myeloid differentiation.
 ...
PMID:Features of macrophage differentiation induced by p19INK4d, a specific inhibitor of cyclin D-dependent kinases. 920 46

In the present study we have characterized eight human esophageal squamous carcinoma cell lines for levels of expression of cyclins D1, E, A and B1; CDKs 1, 2 and 4; the CDK inhibitors p16INK4, p21WAF1 and p27KIP1; the retinoblastoma (Rb) protein; and in vitro CDK2- and CDK4-associated kinase activity; and also compared the growth properties of these cell lines. The level of the cyclin D1 protein varied by over 30-fold amongst the eight cell lines. The high level in two cell lines was associated with amplification of this gene, but in three cell lines it was due to post-transcriptional events. Amongst the eight cell lines there was a significant correlation between the levels of cyclin D1, Rb and p27KIP1 proteins, and CDK4-associated kinase activity. Furthermore, when an exogenous cyclin D1 cDNA was over-expressed in the EC109 cell line by transfection, this led to increased expression of both Rb and p27KIP1. There was, however, no correlation between the level of cyclin D1 expression and the cell doubling times, duration of the G1 phase, or colony-forming efficiency in agar. Two of the cell lines displayed a high level of the cyclin E protein, low levels of cyclin D1, lacked expression of the Rb protein and expressed high levels of the p16INK4 protein. One of these cell lines displayed amplification of the latter gene. There was no correlation between the levels of cyclins E or A and in vitro CDK2 kinase activity, but CDK2 kinase activity was inversely correlated with the duration of the G1 phase of the cell cycle. Taken together, these studies indicate marked heterogeneity in the expression of cell cycle-related proteins amongst a series of esophageal carcinoma cell lines. The correlation between the levels of the cyclin D1, Rb and p27Kip1 proteins suggest the existence of a homeostatic feedback loop between positive and negative acting components of the cell cycle machinery.
 ...
PMID:Increased expression of the P27KIP1 protein in human esophageal cancer cell lines that over-express cyclin D1. 921 95

The molecular mechanisms that arrest cardiomyocytes in the cell cycle during the postnatal period remain largely unknown. We have examined changes of the expression of cyclins and CDKs, the activity of each CDK in cardiomyocytes during the postnatal period, and have compared those changes with rate of binucleation formation of cardiomyocytes in rats. The mRNA and protein levels of cyclin D1, A and B in cardiomyocytes were high at day 1, then the levels decreased at different rates during the postnatal period. While the protein levels of cyclin A and B rapidly decreased, the protein level of cyclin D1 was relatively constant. The protein levels of CDK4, CDK2, and cdc2 in cardiomyocytes were high at day 1, then their levels gradually decreased. However, the activity of CDK4, which is responsible for G1 phase of cell cycle, was detectable only at day 1. The activity of CDK2 activity, which is responsible for the S phase of cell cycle, was relatively high at day 1, decreased at day 2, abruptly decreased at day 4, maintained the same low level until day 10, and barely or not detectable thereafter in cardiomyocytes. The activity of cdc2 was high at day 1, increased by 20% at day 2, and then gradually decreased thereafter, although approximately 50% of maximum activity was present at day 6. Most cardiomyocytes were mononucleated during the first 2 days postnatal. The percentage of binucleated cardiomyocytes increased from 2.5% at day 2, 14% at day 4, 50% at day 8, 80% at day 14, and had reached adult levels at day 21 after birth. During active binucleation formation in neonatal (from days 1-14) cardiomyocytes, CDK4 or CDK2 was functionally negligible, while cdc2 was functionally active. These data suggest that there were differential and dramatic decrease of CDK4 and CDK2 activities in cardiomyocytes during neonatal period, and the functionally active cdc2 in neonatal cardiomyocytes may be involved in binucleation formation.
 ...
PMID:Differential and dramatic changes of cyclin-dependent kinase activities in cardiomyocytes during the neonatal period. 1160 19

We demonstrate in this paper that CDK4 which is a G1 phase specific cell cycle regulator and catalytic subunit of D-type cyclins has oncogenic activity similar to D-type cyclins themselves and is able to provoke focus formation when cotransfected with activated Ha-ras into primary rat embryo fibroblasts. Surprisingly, using two different mutants we show that CDK4's ability to bind to p16INK4a and not its kinase activity is important for its transforming potential. In addition, p16INK4a but not a mutant form that is found in human tumours can completely abrogate focus formation by CDK4 suggesting that CDK4 can malignantly transform cells by sequestering p16INK4a or other CKIs. We demonstrate that both cyclin D1 and CDK4 functionally depend on active Myc to exert their potential as oncogenes and vice versa that the transforming ability of Myc requires functional cyclin D/CDK complexes. Moreover, we find that p16INK4a and the Rb related protein p107 which releases Myc after phosphorylation by cyclin D1/CDK4 efficiently block Myc's activity as a transcriptional transactivator and as an oncogene. We conclude that both p16INK4a and cyclin D/CDK4 complexes are upstream regulators of Myc and directly govern Myc function in transcriptional transactivation and transformation via the pocket protein p107.
 ...
PMID:Mutual requirement of CDK4 and Myc in malignant transformation: evidence for cyclin D1/CDK4 and p16INK4A as upstream regulators of Myc. 924 53


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>