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

We sought to characterize the pathway by which the multifunctional cytokine transforming growth factor-beta (TGF-beta) inhibits the proliferation of normal astrocytes, and we analyzed the alterations in the TGF-beta pathway in human glioma cell lines. Upon TGF-beta treatment, primary rat astrocytes showed a significant decrease in DNA synthesis upon thymidine incorporation with a cell cycle arrest in the G(1) phase. Western analysis of the astrocytes revealed that the expression of the cyclin-dependent kinase inhibitor (CdkI) p15(INK4B) was significantly up-regulated upon TGF-beta treatment without a change in other CdkI levels. The retinoblastoma protein (Rb) became hypophosphorylated, and Cdk2 activity decreased. Analysis of Smad3 null mouse astrocytes showed a significant loss of both TGF-beta-mediated growth inhibition and p15(INK4B) induction compared with wild-type mouse astrocytes. Infection of rat astrocytes by SMAD3 and SMAD4 adenoviruses failed to induce increased expression of p15(INK4B), implying indirect transcriptional regulation of p15(INK4B) by SMAD3. High-grade human gliomas secrete TGF-beta, yet are resistant to its growth inhibitory effects. Analysis of the effects of TGF-beta on 12 human glioma cell lines showed that TGF-beta mildly inhibited the growth of six lines, had no effect on four lines, and stimulated the growth of two lines. The majority of glioma lines had homozygous deletions of the p15(INK4B) gene, except for two lines that expressed p15(INK4B) protein, which was induced further upon TGF-beta treatment. Three lines mildly induced CdkI p21(WAF1) expression in response to TGF-beta. Most tumor lines retained other TGF-beta-mediated responses, including extracellular matrix protein and angiogenic factor secretion, which may contribute to increased malignant behavior. This suggests that the loss of p15(INK4B) may explain, in part, the selective loss of growth inhibition by TGF-beta in gliomas to form a more aggressive tumor phenotype.
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PMID:Transforming growth factor-beta-mediated p15(INK4B) induction and growth inhibition in astrocytes is SMAD3-dependent and a pathway prominently altered in human glioma cell lines. 1057 84

Transforming growth factor-beta (TGF-beta) potently inhibits cell cycle progression at the G1 phase. Smad3 has a key function in mediating the TGF-beta growth-inhibitory response. Here we show that Smad3 is a major physiological substrate of the G1 cyclin-dependent kinases CDK4 and CDK2. Except for the retinoblastoma protein family, Smad3 is the only CDK4 substrate demonstrated so far. We have mapped CDK4 and CDK2 phosphorylation sites to Thr 8, Thr 178 and Ser 212 in Smad3. Mutation of the CDK phosphorylation sites increases Smad3 transcriptional activity, leading to higher expression of the CDK inhibitor p15. Mutation of the CDK phosphorylation sites of Smad3 also increases its ability to downregulate the expression of c-myc. Using Smad3(-/-) mouse embryonic fibroblasts and other epithelial cell lines, we further show that Smad3 inhibits cell cycle progression from G1 to S phase and that mutation of the CDK phosphorylation sites in Smad3 increases this ability. Taken together, these findings indicate that CDK phosphorylation of Smad3 inhibits its transcriptional activity and antiproliferative function. Because cancer cells often contain high levels of CDK activity, diminishing Smad3 activity by CDK phosphorylation may contribute to tumorigenesis and TGF-beta resistance in cancers.
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PMID:Cyclin-dependent kinases regulate the antiproliferative function of Smads. 1524 18

Induction of G(1) arrest by TGF-beta correlates with the regulation of p21(Cip1) and p27(Kip1), members of the Cip/Kip family of cyclin-dependent kinase inhibitors (cki). However, no definitive evidence exists that these proteins play a causal role in TGF-beta(1)-induced growth arrest in lymphocytes. In this report we show the suppression of cell cycle progression by TGF-beta is diminished in T cells from mice deficient for both p21(Cip1) and p27(Kip1) (double-knockout (DKO)) only when activated under conditions of optimal costimulation. Although there is an IL-2-dependent enhanced proliferation of CD8(+) T cells from DKO mice, TGF-beta is able to maximally suppress the proliferation of DKO T cells when activated under conditions of low costimulatory strength. We also show that the induction of p15(Ink4b) in T cells stimulated in the presence of TGF-beta is not essential, as TGF-beta also efficiently suppressed proliferation of T cells from p15(Ink4b-/-) mice. Finally, although these cki are dispensable for the suppression of T cell proliferation by TGF-beta, we now describe a Smad3-dependent down-regulation of cdk4, suggesting a potential mechanism underlying to resistance of Smad3(-/-) T cells to the induction of growth arrest by TGF-beta. In summary, the growth suppressive effects of TGF-beta in naive T cells are a function of the strength of costimulation, and alterations in the expression of cki modify the sensitivity to TGF-beta by lowering thresholds for a maximal mitogenic response.
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PMID:p21Cip1 and p27Kip1 act in synergy to alter the sensitivity of naive T cells to TGF-beta-mediated G1 arrest through modulation of IL-2 responsiveness. 1532 69

Rb family members were the only demonstrated substrates of CDK4 until it was shown recently that Smad3, which plays a key role in mediating TGF-beta antiproliferative responses, is phosphorylated by both CDK4 and CDK2 in vivo and in vitro. CDK phosphorylation of Smad3 inhibits its transcriptional activity and antiproliferative function. The Rb pathway is disrupted in almost all human cancers. Most cancers contain high levels of CDK activity due to frequent inactivation of the p16 tumor suppressor or overexpression of cyclin D1. Therefore, disruption of the Rb pathway not only inactivates Rb, but also likely diminishes Smad activity, which may contribute to tumorigenesis and resistance to the TGF-beta growth-inhibitory effects in cancers. Although genetic mutation of Smad3 has not been reported, CDK phosphorylation of Smad3 may provide an epigenetic mechanism for inhibition of the tumor suppressive function of Smad3 during the early stages of tumorigenesis.
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PMID:Inhibition of Smad antiproliferative function by CDK phosphorylation. 1561 45

Smad3, a key mediator for TGF-beta antiproliferative responses, is phosphorylated by both CDK4 and CDK2 in vivo and in vitro. Except for the Rb family members, Smad3 is the only CDK4 substrate demonstrated so far. CDK phosphorylation of Smad3 inhibits its transcriptional activity and antiproliferative function. Because cancer cells often contain high levels of CDK activity, inhibition of Smad activity by CDK phosphorylation may contribute to tumorigenesis and TGF-beta resistance in cancers.
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PMID:Smad3 phosphorylation by cyclin-dependent kinases. 1628 4

The mammalian forebrain subependyma contains neural stem cells and other proliferating progenitor cells. Recent studies have shown the importance of TGF-beta family members and their adaptor proteins in the inhibition of proliferation in the nervous system. Previously, we have demonstrated that TGF-beta induces phosphorylation and association of ELF (embryonic liver fodrin) with Smad3 and Smad4 resulting in nuclear translocation. Elf(-/-) mice manifest abnormal neuronal differentiation, with loss of neuroepithelial progenitor cell phenotype in the subventricular zone (SVZ) with dramatic marginal cell hyperplasia and loss of nestin expression. Here, we have analyzed the expression of cell cycle-associated proteins cdk4, mdm2, p21, and pRb family members in the brain of elf(-/-) mice to verify the role of elf in the regulation of neural precursor cells in the mammalian brain. Increased proliferation in SVZ cells of the mutant mice coincided with higher levels of cdk4 and mdm2 expression. A lesser degree of apoptosis was observed in the mutant mice compared to the wild-type control. Elf(-/-) embryos showed elevated levels of hyperphosphorylated forms of pRb, p130 and p107 and decreased level of p21 compared to the wild-type control. These results establish a critical role for elf in the development of a SVZ neuroepithelial stem cell phenotype and regulation of neuroepithelial cell proliferation, suggesting that a mutation in the elf locus renders the cells susceptible to a faster entry into S phase of cell cycle and resistance to senescence and apoptotic stimuli.
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PMID:Cell cycle deregulation and loss of stem cell phenotype in the subventricular zone of TGF-beta adaptor elf-/- mouse brain. 1688 1

Peripheral tolerance is essential for immunological homeostasis. Tolerant T cells are thought to arise after T cell receptor ligation in conditions that are nonpermissive for replication. Here we have investigated the function of the cell cycle inhibitor p27(Kip1) in tolerance induction in vivo using naive T cell receptor-transgenic cells lacking the cyclin-dependent kinase (Cdk)-binding domain of p27(Kip1)(p27delta). Wild-type but not p27delta cells underwent tolerization. Tolerized wild-type cells had impaired Cdk2 and Cdc2 kinase activity and failed to phosphorylate the checkpoint inhibitor Smad3, leading to enhanced expression of the Cdk inhibitor p15. In contrast, p27delta cells proliferated in tolerizing conditions because of Cdk kinase activation and phosphorylation of Smad3, which resulted in no upregulation of p15. Smad3 'knockdown' prevented tolerance induction, whereas expression of a Smad3 mutant resistant to Cdk-mediated phosphorylation recapitulated molecular and functional events of tolerance. Thus, p27(Kip1) is required during induction of tolerance and Smad3 regulates T cell responses 'downstream' of p27(Kip1).
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PMID:A pathway regulated by cell cycle inhibitor p27Kip1 and checkpoint inhibitor Smad3 is involved in the induction of T cell tolerance. 1705 94

Smad proteins transduce the transforming growth factor-beta (TGF-beta) signal at the cell surface into gene regulation in the nucleus. Upon TGF-beta treatment, the highly homologous Smad2 and Smad3 are phosphorylated by the TGF-beta receptor at the SSXS motif in the C-terminal tail. Here we show that in addition to the C-tail, three (S/T)-P sites in the Smad3 linker region, Ser(208), Ser(204), and Thr(179) are phosphorylated in response to TGF-beta. The linker phosphorylation peaks at 1 h after TGF-beta treatment, behind the peak of the C-tail phosphorylation. We provide evidence suggesting that the C-tail phosphorylation by the TGF-beta receptor is necessary for the TGF-beta-induced linker phosphorylation. Although the TGF-beta receptor is necessary for the linker phosphorylation, the receptor itself does not phosphorylate these sites. We further show that ERK is not responsible for TGF-beta-dependent phosphorylation of these three sites. We show that GSK3 accounts for TGF-beta-inducible Ser(204) phosphorylation. Flavopiridol, a pan-CDK inhibitor, abolishes TGF-beta-induced phosphorylation of Thr(179) and Ser(208), suggesting that the CDK family is responsible for phosphorylation of Thr(179) and Ser(208) in response to TGF-beta. Mutation of the linker phosphorylation sites to nonphosphorylatable residues increases the ability of Smad3 to activate a TGF-beta/Smad-target gene as well as the growth-inhibitory function of Smad3. Thus, these observations suggest that TGF-beta-induced phosphorylation of Smad3 linker sites inhibits its antiproliferative activity.
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PMID:Transforming growth factor-{beta}-inducible phosphorylation of Smad3. 1921 45

TGFbeta mediates cell cycle arrest in late G(1) phase of the cell cycle with a simultaneous peak in the levels of the cyclin-dependent kinase inhibitor, p27(kip1) (p27). In this report, we show that whereas p27 resides in the cytoplasm in the endometrial carcinoma (ECA) cell line HEC-1A, TGFbeta increases the total levels and translocation of p27 into the nucleus. Concomitantly, TGFbeta activates the transcription factors Smad2 and Smad3, inhibits proliferation, and blocks Cdk2 activity; all these events are blocked by an inhibitor of TbetaRI serine kinase activity (SD208). In addition, we show that inhibiting p27 transcription with a specific siRNA completely blocks TGFbeta-mediated growth inhibition in these cells. These data suggest that TGFbeta inhibits cellular proliferation by increasing p27 levels through Smad2/3 signaling in HEC-1A cells. We further show that TGFbeta decreases the levels of components of the SCF(Skp2) targeting complex for ubiquitin-mediated degradation of p27 in proteasomes, at the protein but not the mRNA level. Therefore, TGFbeta accumulates nuclear p27 by preventing its degradation to enable G(1) arrest in HEC-1A cells. Importantly, these data suggest a novel mechanism for TGFbeta/Smad mediated growth inhibition that might be inoperable in the numerous human cancers demonstrating early dysregulated TGFbeta signaling and loss of growth inhibition. The TGFbeta/p27 axis might provide novel therapeutic targets for cancer.
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PMID:TGFbeta prevents proteasomal degradation of the cyclin-dependent kinase inhibitor p27kip1 for cell cycle arrest. 1922 82

Cell cycle re-entry of quiescent T lymphocytes regulated by cdk2 is required for antigen-specific clonal expansion and generation of productive T cell responses. Recently, we determined that induction of antigen-specific T cell tolerance results in impaired cdk2 activity leading to enhanced Smad3 transactivation, upregulation of p15 and blockade of cell cycle progression. Here we report that pharmacologic inhibition of cdk2 with (R)-roscovitine blocked expansion of alloreactive T cells in vitro and in vivo and protected from lethal acute GvHD. In addition to inhibiting alloreactive T cell responses, (R)-roscovitine prevented TNF-alpha-mediated activation of NF-kappa B pathway, which is involved in the inflammatory process leading to the development of GvHD. The combined anti-proliferative and anti-inflammatory properties of (R)-roscovitine make it an attractive treatment modality toward control of GvHD.
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PMID:The cyclin dependent kinase inhibitor (R)-roscovitine prevents alloreactive T cell clonal expansion and protects against acute GvHD. 1968 61


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