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

Transforming growth factor beta (TGFbeta) is a potent inhibitor of epithelial cell proliferation, delaying or arresting cell cycle progression in mid-late G1. In long-term life span cells this growth inhibitory action has been attributed to regulatory events on both the levels and activities of G1 cyclin-dependent kinases (CDKs). CDK inhibitors have been shown to play important role in the TGFbeta-induced inhibition of G1 CDKs. In this work, we have investigated the effect of TGFbeta1 on both cell proliferation and G1 CDK activities in primary cultures of human retinal pigment epithelial (RPE) cells. We show that TGFbeta1 exerts a partial inhibitory effect on RPE cell proliferation by causing a significant increase of the RPE cell number in G1. TGFbeta1 induces an up-regulation of the CDK inhibitor p15(INK4B)with its subsequent association to CDK4, and a decline in CDK4 protein level. In parallel, we have observed a decline of p27(KIP1)associated to CDK4 and a significant increase of the inhibitor associated to CDK2. Finally, we show that TGFbeta1 reduces both CDK4 and CDK2 enzymatic activities. The fact that TGFbeta exerts only partial inhibitions on G1 CDKs and cell cycle progression in RPE cells suggests a propensity of these cells to escape from the anti-proliferative action of the cytokine, a phenomenon which could be reinforced during the development of proliferative vitreoretinopathy.
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PMID:Regulation by transforming growth factor-beta 1 of G1 cyclin-dependent kinases in human retinal epithelial cells. 1006 84

The retinoblastoma tumor suppressor protein (pRb) can associate with the transforming proteins of several DNA tumor viruses, including the large T antigen encoded by polyomavirus (Py T Ag). Although pRb function is critical for regulating progression from G1 to S phase, a role for pRb in S phase has not been demonstrated or excluded. To identify a potential effect of pRb on DNA replication, pRb protein was added to reaction mixtures containing Py T Ag, Py origin-containing DNA (Py ori-DNA), and murine FM3A cell extracts. We found that pRb strongly represses Py ori-DNA replication in vitro. Unexpectedly, however, this inhibition only partially depends on the interaction of pRb with Py T Ag, since a mutant Py T Ag (dl141) lacking the pRb interaction region was also significantly inhibited by pRb. This result suggests that pRb interferes with or alters one or more components of the murine cell replication extract. Furthermore, the ability of Py T Ag to be phosphorylated in such extracts is markedly reduced in the presence of pRb. Since cyclin-dependent kinase (CDK) phosphorylation of Py T Ag is required for its replication function, we hypothesize that pRb interferes with this phosphorylation event. Indeed, the S-phase CDK complex (cyclin A-CDK2), which phosphorylates both pRb and Py T Ag, alleviates inhibition caused by pRb. Moreover, hyperphosphorylated pRb is incapable of inhibiting replication of Py ori-DNA in vitro. We propose a new requirement for maintaining pRb phosphorylation in S phase, namely, to prevent deleterious effects on the cellular replication machinery.
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PMID:The retinoblastoma protein alters the phosphorylation state of polyomavirus large T antigen in murine cell extracts and inhibits polyomavirus origin DNA replication. 1007 50

The current options for treating breast cancer are limited to excision surgery, general chemotherapy, radiation therapy, and, in a minority of breast cancers that rely on estrogen for their growth, antiestrogen therapy. The naturally occurring chemical indole-3-carbinol (I3C), found in vegetables of the Brassica genus, is a promising anticancer agent that we have shown previously to induce a G1 cell cycle arrest of human breast cancer cell lines, independent of estrogen receptor signaling. Combinations of I3C and the antiestrogen tamoxifen cooperate to inhibit the growth of the estrogen-dependent human MCF-7 breast cancer cell line more effectively than either agent alone. This more stringent growth arrest was demonstrated by a decrease in adherent and anchorage-independent growth, reduced DNA synthesis, and a shift into the G1 phase of the cell cycle. A combination of I3C and tamoxifen also caused a more pronounced decrease in cyclin-dependent kinase (CDK) 2-specific enzymatic activity than either compound alone but had no effect on CDK2 protein expression. Importantly, treatment with I3C and tamoxifen ablated expression of the phosphorylated retinoblastoma protein (Rb), an endogenous substrate for the G1 CDKs, whereas either agent alone only partially inhibited endogenous Rb phosphorylation. Several lines of evidence suggest that I3C works through a mechanism distinct from tamoxifen. I3C failed to compete with estrogen for estrogen receptor binding, and it specifically down-regulated the expression of CDK6. These results demonstrate that I3C and tamoxifen work through different signal transduction pathways to suppress the growth of human breast cancer cells and may, therefore, represent a potential combinatorial therapy for estrogen-responsive breast cancer.
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PMID:Indole-3-carbinol and tamoxifen cooperate to arrest the cell cycle of MCF-7 human breast cancer cells. 1009 55

Cellular differentiation is a complex process involving growth arrest, exit from the cell cycle, and expression of differentiated cell-type-specific functions. To identify small molecules promoting this process, a chemical library was screened by using a myeloid leukemic cell line that retained the potential to differentiate in culture. In the presence of a purine derivative, aminopurvalanol (AP), cells acquired phenotypic characteristics of differentiated macrophages and became arrested in the cell cycle with a 4N DNA content. AP also inhibited mitosis in Xenopus egg extracts, suggesting that it acted on an evolutionarily conserved cell cycle regulatory pathway. Affinity chromatography and biochemical reconstitution experiments with Xenopus egg extracts identified cyclin-dependent kinase (CDK) 1-cyclin B as a target of the compound. Although AP potently inhibited immunoprecipitates of both human CDK1 and CDK2 from human leukemic cell extracts, our results indicate that the compound preferentially targets the G2/M-phase transition in vivo.
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PMID:A cyclin-dependent kinase inhibitor inducing cancer cell differentiation: biochemical identification using Xenopus egg extracts. 1022 Mar 73

In this study, we investigated the effect of a novel retinobenzoic acid, 4-[3,5-bis (trimethylsilyl) benzamido] benzoic acid (TAC-101), on the growth of 4 human pancreatic-cancer cell lines; BxPC-3, MIAPaCa-2, CFPAC-1 and AsPC-1. TAC-101 significantly inhibited the proliferation of BxPC-3 and MIAPaCa-2 cells in a time- and concentration-dependent manner, but not the proliferation of AsPC-1 cells. Furthermore, the anti-proliferative effects of TAC-101 on BxPC-3 and MIAPaCa-2 cells were stronger than those of all-trans retinoic acid. Flow-cytometric analyses indicated that treatment of BxPC-3 with TAC-101 strongly induces cell-cycle arrest at the G1 phase. The cell-cycle arrest induced by TAC-101 was accompanied by reduction of retinoblastoma-gene product (RB) phosphorylation and an increase of 2 cyclin-dependent kinase (CDK) inhibitors, p21(WAF1/Cip1) (p21) and p27Kip1 (p27). TAC-101 also caused a decrease in cyclin A and thymidylate synthase, which are E2F-regulated gene products. No changes were observed in the expression of cyclin D1, cyclin E on CDK2. In addition, Hoechst staining, gel electrophoresis and flow-cytometric analysis indicated that a marked reduction in the number of BxPC-3 cells with TAC-101 was related to the induction of apoptosis. Our results suggest that TAC-101 inhibits the growth of certain pancreatic-cancer cells by means of G1-phase cell-cycle arrest resulting from the reduction of RB phosphorylation and the up-regulation of p21 and p27 as well as the induction of apoptosis. TAC-101 may therefore be a useful agent for new therapeutic strategies focusing on inhibition of pancreatic-cancer-cell proliferation.
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PMID:Induction of cell-cycle arrest and apoptosis by a novel retinobenzoic-acid derivative, TAC-101, in human pancreatic-cancer cells. 1022 56

The intracellular level of p27(Kip1), a cyclin-dependent kinase (CDK) inhibitory protein, is rapidly reduced at the G1/S transition phase when the cell cycle pause ceases. In this study, we demonstrated that two posttranslational mechanisms were involved in p27(Kip1) breakdown: degradation via the ubiquitin (Ub)-proteasome pathway and proteolytic processing that rapidly eliminates the cyclin-binding domain. We confirmed that p27(Kip1) was ubiquitinated in vitro as well as in vivo. The p27(Kip1) -ubiquitination activity was higher at the G1/S boundary than during the G0/G1 phase, and p27(Kip1) ubiquitination was reduced significantly when the lysine residues at positions 134, 153, and 165 were replaced by arginine, suggesting that these lysine residues are the targets for Ub conjugation. In parallel with its Ub-dependent degradation, p27(Kip1) was processed rapidly at its N terminus, reducing its molecular mass from 27 to 22 kDa, by a ubiquitination-independent but adenosine triphosphate (ATP)-dependent mechanism with higher activity during the S than the G0/G1 phase. This 22-kDa intermediate had no cyclin-binding domain at its N terminus and virtually no CDK2 kinase inhibitory activity. These results suggest that p27(Kip1) is eliminated by two independent mechanisms, ubiquitin-mediated degradation and ubiquitin-independent processing, during progression from the G1 to S phase.
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PMID:Down-regulation of p27(Kip1) by two mechanisms, ubiquitin-mediated degradation and proteolytic processing. 1031 97

Genetic alterations in the MMAC1 tumor suppressor gene (also referred to as PTEN or TEP1) occur in several types of human cancers including glioblastoma. Growth suppression induced by overexpression of MMAC1 in cells with mutant MMAC1 alleles is thought to be mediated by the inhibition of signaling through the phosphatidylinositol 3-kinase pathway. However, the exact biochemical mechanisms by which MMAC1 exerts its growth-inhibitory effects are still unknown. Here we report that recombinant adenovirus-mediated overexpression of MMAC1 in three different MMAC1-mutant glioblastoma cell lines blocked progression from G0/G1 to S phase of the cell cycle. Cell cycle arrest correlated with the recruitment of the cyclin-dependent kinase (CDK) inhibitor, p27Kip1, to cyclin E immunocomplexes, which resulted in a reduction in CDK2 kinase activities and a decrease in levels of endogenous phosphorylated retinoblastoma protein. CDK4 kinase activities were unaffected, as were the levels of the CDK inhibitor p21Cip1 present in cyclin E immunocomplexes. Therefore, overexpression of MMAC1 via adenovirus-mediated gene transfer suppresses tumor cell growth through cell cycle inhibitory mechanisms, and as such, represents a potential therapeutic approach to treating glioblastomas.
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PMID:Adenovirus-mediated gene transfer of MMAC1/PTEN to glioblastoma cells inhibits S phase entry by the recruitment of p27Kip1 into cyclin E/CDK2 complexes. 1034 36

Analysis of the National Cancer Institute Human Tumor Cell Line Anti-Cancer Drug Screen data using the COMPARE algorithm to detect similarities in the pattern of compound action to flavopiridol, a known inhibitor of cyclin-dependent kinases (CDKs), has suggested several possible novel CDK inhibitors. 9-Bromo-7,12-dihydro-indolo[3,2-d][1]benzazepin-6(5H)-one, NSC-664704 (kenpaullone), is reported here to be a potent inhibitor of CDK1/cyclin B (IC50, 0.4 microM). This compound also inhibited CDK2/cyclin A (IC50, 0.68 microM), CDK2/cyclin E (IC50, 7.5 microM), and CDK5/p25 (IC50, 0.85 microM) but had much less effect on other kinases; only c-src (IC50, 15 microM), casein kinase 2 (IC50, 20 microM), erk 1 (IC50, 20 microM), and erk 2 (IC50, 9 microM) were inhibited with IC50s less than 35 microM. Kenpaullone acts by competitive inhibition of ATP binding. Molecular modeling indicates that kenpaullone can bind in the ATP binding site of CDK2 with residue contacts similar to those observed in the crystal structures of other CDK2-bound inhibitors. Analogues of kenpaullone, in particular 10-bromopaullone (NSC-672234), also inhibited various protein kinases including CDKs. Cells exposed to kenpaullone and 10-bromopaullone display delayed cell cycle progression. Kenpaullone represents a novel chemotype for compounds that preferentially inhibit CDKs.
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PMID:Discovery and initial characterization of the paullones, a novel class of small-molecule inhibitors of cyclin-dependent kinases. 1036 74

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.
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PMID:BRCA1 is phosphorylated at serine 1497 in vivo at a cyclin-dependent kinase 2 phosphorylation site. 1037 34

We postulate that genes involved in the control of cell proliferation are important determinants of melanoma growth and/or transformation. Using Western blot analysis, we compared the expression of nine key cell cycle regulators in metastatic melanomas with that in benign acquired naevi. Among the cyclin-dependent kinases (CDKs) examined, CDK2 was consistently and significantly overexpressed (three- to eight-fold) in metastatic melanomas compared with naevi. CDK1 and CDK4 exhibited no significant difference in expression between benign naevi and metastatic melanomas. CDK6 expression was variable, with four out of 10 metastatic melanomas showing higher expression than naevi. All the cyclins examined, especially cyclins A and D, were expressed more in metastatic melanomas than in naevi. Cyclin E was not detected in benign naevi, but was easily detectable in most of the metastatic melanomas. In addition, there was significantly greater expression of CDC25A, a tyrosine phosphatase that activates CDK kinases, in the metastatic melanomas. Over-expression of CDK2, CDK6, CDC25A and cyclin A was confirmed in melanoma cell lines. These cell cycle regulators may play an important role in melanoma growth and/or transformation.
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PMID:Expression of cell cycle regulators in human cutaneous malignant melanoma. 1038 Sep 37


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