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)

E2F is a heterodimeric transcription factor that controls transcription of several growth-regulatory genes including cdc2. To investigate the mechanism of interferon-alpha (IFN-alpha)-mediated growth suppression of hematopoietic cells, we examined the effect of IFN-alpha on the expression and function of E2F using IFN-sensitive Daudi cells. Down-regulation of E2F-1, a subunit of E2F, was observed after 8 h of culture with IFN-alpha; expression of E2F-4, another subunit of E2F, and DP-1, a heterodimeric partner of E2F, was unaffected. Gel shift assays revealed that the DNA binding activity of free E2F, which is composed of E2F-1 and E2F-4, was inhibited by IFN-alpha. In contrast, IFN-alpha did not affect the DNA binding ability of E2F-1 and E2F-4 in a complex with retinoblastoma (RB) susceptibility gene family proteins including pRB, p107, and p130. IFN-alpha could induce dephosphorylation of pRB, thereby turning active E2F-pRB complexes into transcriptional repressors. Transient chloramphenicol acetyltransferase assays revealed that the activity of the E2F-dependent cdc2 promoter was suppressed by IFN-alpha. These results suggest that the antiproliferative action of IFN-alpha is mediated through the modulation of E2F activity in two different ways: down-regulation of transcriptionally active free E2F and conversion of E2F-pRB complexes into transcriptional repressors.
 ...
PMID:Modulation of E2F activity is linked to interferon-induced growth suppression of hematopoietic cells. 913 87

P130 shares structural and functional homology with pRb and p107. One property common to p107 and p130, but not to pRb, is the ability to stably interact with cyclin A/cdk2 and cyclin E/cdk2 complexes in vitro and in vivo. Using GST-p130 fusion proteins representing various regions of p130, baculovirus-produced cyclin A/cdk2 and cyclin E/cdk2 complexes were found to interact with residues within a part of p130 known as the spacer region. Cyclin E was able to bind the p130 spacer region in the presence or absence of cdk2 whereas cyclin A binding was dependent upon the presence of cdk2. The smallest p130 fusion protein sufficient to interact with cyclin A/cdk2 or cyclin E/cdk2 complexes contained p130 amino acids 652-698 and deletion of p130 amino acids 680-682 abolished binding to both of the cyclin/cdk2 complexes. When overexpressed in C33A cells, a p130 mutant containing a deletion of amino acids 620-697 was unable to form complexes with either cyclin A or cyclin E. This p130 mutant was at least as active as wild type p130 in suppressing the growth of G418 resistant colonies when overexpressed in C33A or SAOS-2 cells.
 ...
PMID:Identification of a p130 domain mediating interactions with cyclin A/cdk 2 and cyclin E/cdk 2 complexes. 918 54

The pRB-related proteins p107 and p130 are thought to suppress growth in part through their associations with two important cell cycle kinases, cyclin A-cdk2 and cyclin E-cdk2, and transcription factor E2F. Although each protein plays a critical role in cell proliferation, the functional consequences of the association among growth suppressor, cyclin-dependent kinase, and transcription factor have remained elusive. In an attempt to understand the biochemical properties of such complexes, we reconstituted each of the p130-cyclin-cdk2 and p107-cyclin-cdk2 complexes found in vivo with purified, recombinant proteins. Strikingly, stoichiometric association of p107 or p130 with either cyclin E-cdk2 or cyclin A-cdk2 negated the activities of these kinases. The results of our experiments suggest that inhibition does not result from substrate competition or loss of cdk2 activation. Kinase inhibitory activity was dependent upon an amino-terminal region of p107 that is highly conserved with p130. Further, a role for this amino-terminal region in growth suppression was uncovered by using p107 mutants unable to bind E2F. To determine whether cellular complexes might display similar regulatory properties, we purified p130-cyclin A-cdk2 complexes from human cells and found that such complexes exist in two forms, one that contains E2F-4-DP-1 and one that lacks the heterodimer. These endogenous complexes behaved like the in vitro-reconstituted complexes, exhibiting low levels of associated kinase activity that could be significantly augmented by dissociation of p130. The results of these experiments suggest a mechanism whereby p130 and p107 suppress growth by inhibiting important cell cycle kinases.
 ...
PMID:p130 and p107 use a conserved domain to inhibit cellular cyclin-dependent kinase activity. 919 92

Spontaneous differentiation of normal diploid osteoblasts in culture is accompanied by increased cyclin E associated kinase activity on (1) the retinoblastoma susceptibility protein pRB, (2) the p107 RB related protein, and (3) two endogenous cyclin E-associated substrates of 78 and 105 kD. Activity of the differentiation-related cyclin E complexes (diff.ECx) is not recovered in cdc2 or cdk2 immunoprecipitates. Phosphorylation of both the 105 kD endogenous substrate and the p107 exogenous substrate is sensitive to inhibitory activity (diff.ECx-i) present in proliferating osteoblasts. This inhibitory activity is readily recruited by the cyclin E complexes of differentiated osteoblasts but is not found in cyclin E immunoprecipitates of the proliferating cells themselves. Strong inhibitory activity on diff.ECx kinase activity is excerted by proliferating ROS 17/2.8 osteosarcoma cells. However, unlike the normal diploid cells, the diff.ECx-i activity of proliferating ROS 17/2.8 cells is recovered by cyclin E immunoprecipitation. The cyclin-dependent kinase inhibitor p21CIP1/WAF1 inhibits diff.ECx kinase activity. Thus, our results suggest the existence of a unique regulatory system, possibly involving p21CIP1/WAF1, in which inhibitory activity residing in proliferating cells is preferentially targeted towards differentiation-related cyclin E-associated kinase activity.
 ...
PMID:Post-proliferative cyclin E-associated kinase activity in differentiated osteoblasts: inhibition by proliferating osteoblasts and osteosarcoma cells. 921 16

It has been demonstrated that infection of primary human cells with adeno-associated viruses (AAV) leads to a decrease in cellular proliferation and to growth arrest. We analyzed the molecular basis of this phenomenon and observed that infection with AAV type 2 (AAV2) had an effect on several factors engaged in the control of the mammalian cell cycle. In particular, all of the pRB family members, pRB, p107, and p130, which are involved in G1 cell cycle checkpoint control, were affected. After infection, a shift from hyper- to hypophosphorylated forms was observed. Cyclins A and B1, which are required for G1/S transition and progression into mitosis, respectively, were downregulated at the transcriptional level as well as at the protein level, whereas the G1 cyclins D1 and E remained unaffected. In addition, the steady-state levels of cyclin-dependent kinases CDK1 and CDK2 and of transcription factor E2F-1 were diminished. Of all the factors known to be involved in phosphorylation of pRB family proteins, only the CDK inhibitor p21WAF1 exhibited a response to AAV2 infection. p21WAF1 mRNA was quickly and progressively upregulated in a p53-independent manner over at least 72 h. Consistent with the increased p21WAF1 protein levels, cyclin E- and cyclin A-dependent kinase activities declined to low levels and E2F-p130-cyclin-CDK2 complexes were disrupted. From these data, we conclude that the major effect of AAV2 infection on primary human fibroblasts appears to be upregulation of p21WAF1 gene expression and thus cell cycle arrest by the suppression of pRB family protein phosphorylation.
 ...
PMID:Infection of primary cells by adeno-associated virus type 2 results in a modulation of cell cycle-regulating proteins. 922 93

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

The Cdk2 kinase has long been known to be involved in the progression of mammalian cells past the G1 phase restriction point and through DNA replication in the cell cycle. The Rb family of proteins, consisting of pRb, p107, and pRb2/p130, has also been shown to monitor progression of G1 phase, mostly through their interaction with E2F family members. p107 is able to inhibit Cdk2 kinase activity through this interaction via a p21-related domain present in the C terminus of the protein. We show here that pRb2/p130 also possesses this activity, but through a separate domain. Moreover, we correlate the increased expression of pRb2/p130 during various cellular processes with the decreased kinase activity of Cdk2. We hypothesize that pRb2/p130 may act not only to bind and modify E2F activity, but also to inhibit Cdk2 kinase activity in concert with p21 in a manner different from p107.
 ...
PMID:A unique domain of pRb2/p130 acts as an inhibitor of Cdk2 kinase activity. 926 Oct 93

We demonstrate that p107 and p130 immune complexes exhibit kinase activity. We have tested such immune complexes with four substrates commonly utilized to assay Cdk activity, including all three known members of the retinoblastoma family. Immunodepletion revealed this kinase activity could be abolished by removal of either cyclin A or Cdk2 but was unaffected by removal of Cdk4 or any D-type cyclin. The appearance of p107 associated activity followed the accumulation of p107 protein. In contrast, the kinase activity associated with p130 immune complexes became apparent after mid-G1, coincident with p130 hyperphosphorylation. GST-Rb, GST-p107, and GST-p130 (where GST indicates glutathione S-transferase) were equally suitable substrates in p107 and p130 immune complex kinase assays, yielding activity equal to 25% of the cyclin A activity present. The p107 and p130 associated activity was unable to phosphorylate histone H1, suggesting the p107 and p130 associated cyclin A/Cdk2 may represent a distinct pool with a distinct substrate specificity. The p107 and p130 associated activity was released from the immune complexes upon incubation with ATP and Mg2+ and exhibited the same substrate preference observed with the untreated immune complex. Our data suggest that p107 and p130 recognize, or form by association, a distinct pool of cyclin A/Cdk2 that preferentially phosphorylates retinoblastoma family members.
 ...
PMID:p107 and p130 associated cyclin A has altered substrate specificity. 927 60

Pocket proteins, including the retinoblastoma susceptibility gene product (pRB) and the related proteins p107 and p130, function at cell cycle regulatory steps that link cyclin/CDK-integrated positive and negative growth signals with E2F transcription factor activity on genes required for cell cycle progression. Protein complex formation between pocket proteins and members of the E2F family of transcription factors determines whether E2F complexes act as transcriptional activators or repressors. Experimental work over the last few years indicates that individual pocket proteins interact with specific E2F members to regulate the transcription of certain genes under diverse cell growth conditions. Among these protein associations, p130-containing E2F complexes seem to be of particular importance in controlling gene transcription in quiescent and differentiating cells by repressing the transcription of a set of E2F-responsive genes. Once the cells are progressing through the G1 phase of the cell cycle, pocket protein-mediated regulation of E2F activity is assumed by pRB and p107. p130-mediated transcriptional regulation thus seems to prevent a gene expression program characteristic of dividing cells at the cell cycle exit and re-entrance transitions and in quiescent cells.
 ...
PMID:The p130 pocket protein: keeping order at cell cycle exit/re-entrance transitions. 940 35

The steroid hormone progesterone regulates proliferation and differentiation in the mammary gland and uterus by cell cycle phase-specific actions. In breast cancer cells the predominant effect of synthetic progestins is long-term growth inhibition and arrest in G1 phase. Progestin-mediated growth arrest of T-47D breast cancer cells was preceded by inhibition of cyclin D1-Cdk4, cyclin D3-Cdk4, and cyclin E-Cdk2 kinase activities in vitro and reduced phosphorylation of pRB and p107. This was accompanied by decreases in the expression of cyclins D1, D3, and E, decreased abundance of cyclin D1- and cyclin D3-Cdk4 complexes, increased association of the cyclin-dependent kinase (CDK) inhibitor p27 with the remaining Cdk4 complexes, and changes in the molecular masses and compositions of cyclin E complexes. In control cells cyclin E eluted from Superdex 200 as two peaks of approximately 120 and approximately 200 kDa, with the 120-kDa peak displaying greater cyclin E-associated kinase activity. Following progestin treatment, almost all of the cyclin E was in the 200-kDa, low-activity form, which was associated with the CDK inhibitors p21 and p27; this change preceded the inhibition of cell cycle progression. These data suggest preferential formation of this higher-molecular-weight, CDK inhibitor-bound form and a reduced number of cyclin E-Cdk2 complexes as mechanisms for the decreased cyclin E-associated kinase activity following progestin treatment. Ectopic expression of cyclin D1 in progestin-inhibited cells led to the reappearance of the 120-kDa active form of cyclin E-Cdk2 preceding the resumption of cell cycle progression. Thus, decreased cyclin expression and consequent increased CDK inhibitor association are likely to mediate the decreases in CDK activity accompanying progestin-mediated growth inhibition.
 ...
PMID:Mechanisms of cyclin-dependent kinase inactivation by progestins. 952 53


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