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)

The c-Myc oncoprotein plays an important role in the growth and proliferation of normal and neoplastic cells. To execute these actions, c-Myc is thought to regulate functionally diverse sets of genes that directly govern cellular mass and progression through critical cell cycle transitions. Here, we provide several lines of evidence that c-Myc promotes ubiquitin-dependent proteolysis by directly activating expression of the Cul1 gene, encoding a critical component of the ubiquitin ligase SCF(SKP2). The cell cycle inhibitor p27(kip1) is a known target of the SCF(SKP2) complex, and Myc-induced Cul1 expression matched well with the kinetics of declining p27(kip1) protein. Enforced Cul1 expression or antisense neutralization of p27(kip1) was capable of overcoming the slow-growth phenotype of c-Myc null primary mouse embryonic fibroblasts (MEFs). In reconstitution assays, the addition of in vitro translated Cul1 protein alone was able to restore p27(kip1) ubiquitination and degradation in lysates derived from c-myc(-/-) MEFs or density-arrested human fibroblasts. These functional and biochemical data provide a direct link between c-Myc transcriptional regulation and ubiquitin-mediated proteolysis and together support the view that c-Myc promotes G(1) exit in part via Cul1-dependent ubiquitination and degradation of the CDK inhibitor, p27(kip1).
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PMID:Myc-enhanced expression of Cul1 promotes ubiquitin-dependent proteolysis and cell cycle progression. 1097 Aug 82

Cyclin E is required for S phase entry. The subsequent ubiquitin-dependent degradation of cyclin E contributes to an orderly progression of the S phase. It has been shown that phosphorylation of threonine 380 (Thr380) in cyclin E provides a signal for its ubiquitin-dependent proteolysis. We report that SKP2, an F-box protein and a substrate-targeting component of the SCF(SKP2) ubiquitin E3 ligase complex, mediates cyclin E degradation. In vitro, SKP2 specifically interacted with the cyclin E peptide containing the phosphorylated-Thr380 but not with a cognate nonphosphorylated peptide. In vivo, expression of SKP2 induced cyclin E polyubiquitination and degradation. Conversion of Thr380 into nonphosphorylatable amino acids caused significant resistance of cyclin E to SKP2. The presence of the CDK inhibitor p27(Kip1) also prevented the SKP2-dependent degradation of cyclin E. Our findings suggest that SKP2 regulates cyclin E stability, thus contributing to the control of S phase progression.
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PMID:The F-box protein SKP2 binds to the phosphorylated threonine 380 in cyclin E and regulates ubiquitin-dependent degradation of cyclin E. 1123 42

Histone deacetylase (HDAC) inhibitors sodium butyrate and trichostatin A arrest human papillomavirus (HPV)-positive carcinoma cells in G1 to S transition of the cell cycle, which is paralleled by an up-regulation of the cyclin-dependent kinase inhibitors (CKIs) p21CIP1 and p27KIP1 as well as the complete loss of cdk2 activity. Although HPV expression was hitherto thought to be required to maintain a proliferative phenotype of these cells, cdk2 suppression is achieved even in the presence of ongoing viral transcription. While CKIs normally cannot exert their cdk2-inhibitory function in the presence of the viral oncoprotein E7, co-immunoprecipitation experiments revealed that E7 binding is prevented. Increase of p27KIP1 correlates with down-regulation of p45SKP2, a component of the ubiquitin-protein ligase SCF(SKP2) controlling the half-life of regulatory proteins during the cell cycle. HDAC inhibition also triggered an E7-dependent degradation of pRb, while the levels of E2F remained unaffected. The presence of free intracellular E2F and the concomitant up-regulation of CKIs during G1 arrest results in a 'conflicting growth situation', which finally renders the cells to undergo apoptosis. These data provide novel molecular insights into how the transforming potential of HPV can be bypassed and open new therapeutical perspectives for the treatment of cervical cancer.
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PMID:Inhibitors of histone deacetylase arrest cell cycle and induce apoptosis in cervical carcinoma cells circumventing human papillomavirus oncogene expression. 1152 Nov 89

Treatment of MCF 7 cells with the fungal estrogen zearalenone induced cyclin E-associated kinase activity transiently within 9-12 h; total cyclin-dependent kinase (Cdk) 2 activity was elevated for 24 h and beyond. This increased cyclin E/Cdk2 activity was associated with sequestration of the Cdk inhibitor p27 Cdk inhibitor 1B (p27(KIP1)) by newly formed cyclin D1/Cdk4 complexes and with downregulation of p27(KIP1) expression. The activation of cyclin A/Cdk2 activity corresponded with virtual elimination of p27(KIP1). The activity of cyclin E/Cdk2 complexes from zearalenone-treated lysates was inhibited in vitro by recombinant p27(KIP1), and this inhibition was relieved by the addition of recombinant cyclin D1/Cdk4 complexes. Thus, sequestration of p27(KIP1) by cyclin D1/Cdk4 resulted in activation of Cdk2 in vitro. Cdk inhibitory activity in lysates of zearalenone-treated cells was depleted by anti-p27(KIP1) and anti-Cdc2 interacting protein (p21(CIP1)) antibodies. Overexpression of the Cdk4/6-specific Cdk inhibitor of Cdk4 p16(INK4A) was associated with increased association of p27(KIP1) with Cdk2, concomitant with disruption of D cyclin/Cdk4 complexes. The proteasome inhibitor 2-leu-leu-leu-H aldehyde (MG-132) was relatively ineffective in inhibiting the initial, sequestration-dependent activation of cyclin E/Cdk2 yet was as effective as p16(INK4A) in inhibiting activation of cyclin A/Cdk2 later in G(1). Downregulation of p27(KIP1) proceeded in p16(INK4A)-expressing cells after zearalenone treatment, and G(1) arrest afforded by p16(INK4A) expression was reversible upon prolonged treatment with zearalenone. Zearalenone treatment of MCF-7 cells elicited expression of F-box protein S phase kinase-associated protein 2 (p45(SKP2)), a substrate-specific component of the ubiquitin-ligase complex that targets p27(KIP1) for degradation in the proteasome. These studies suggest that both sequestration of Cdk inhibitors by cyclin D1/Cdk4 complexes and downregulation of p27(KIP1) play major roles in the induction of Cdk2 activity and S phase entry elicited by estrogens in MCF-7 cells.
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PMID:Removal of Cdk inhibitors through both sequestration and downregulation in zearalenone-treated MCF-7 breast cancer cells. 1211 22

Activation of T cells involves a complex cascade of signal transduction pathways linking T-cell receptor engagement at the cell membrane to the transcription of multiple genes within the nucleus. The T-cell leukemia-derived cell line Jurkat has generally been used as a model system for the activation of T cells. However, genome-wide comprehensive studies investigating the activation status, and thus the appropriateness, of this cell line for this purpose have not been performed. We sought to compare the transcriptional profiles of phenotypically purified human CD2(+) T cells with those of Jurkat T cells during T-cell activation, using cDNA microarrays containing 6912 genes. About 300 genes were up-regulated by more than 2-fold during activation of both peripheral blood (PB) T cells and Jurkat T cells. The number of down-regulated genes was significantly lower than that of up-regulated genes. Only 79 genes in PB T cells and 37 genes in Jurkat T cells were down-regulated by more than 2-fold during activation. Comparison of gene expression during activation of Jurkat and PB T cells revealed a common set of genes that were up-regulated, such as Rho GTPase-activating protein 1, SKP2, CDC25A, T-cell specific transcription factor 7, cytoskeletal proteins, and signaling molecules. Genes that were commonly down-regulated in both PB T cells and Jurkat T cells included CDK inhibitors (p16, p19, p27), proapoptotic caspases, and the transcription factors c-fos and jun-B. After activation, 71 genes in PB T cells and only 3 genes in Jurkat T cells were up-regulated 4-fold or more. Of these up-regulated genes and expressed sequence tags, 44 were constitutively expressed at high levels in nonactivated Jurkat cells. Quantitative real-time RT-PCR analysis confirmed our microarray data. Our findings indicate that although there is significant overlap in the activation-associated transcriptional profiles in PB T cells compared with Jurkat T cells, there is a subset of genes showing differential expression patterns during the activation of the two cell types.
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PMID:Comparative microarray analysis of gene expression during activation of human peripheral blood T cells and leukemic Jurkat T cells. 1280 12

We have investigated the mechanisms by which all-trans retinoic acid (ATRA) causes growth inhibition of ovarian carcinoma cells. As a model, we have studied the CAOV3 cell line, which is sensitive to ATRA, and the SKOV3 cell line, which is resistant. We have found that treatment of CAOV3 cells with ATRA causes a 5-10 fold increase in the protein level of the cyclin dependent kinase inhibitor p27/Kip1. p27/Kip1 protein upregulation is important in ovarian carcinoma as primary tumors are frequently found lacking this protein. The increase in p27/Kip1 is detected by day 3 of ATRA treatment of CAOV3 cells, and is maximal by day 5. Messenger RNA levels of p27/Kip1 do not change in CAOV3 cells following ATRA treatment, however, we have shown that p27/Kip1 mRNA is more stable in ATRA treated CAOV3 cells. Conversely, the ATRA resistant cell line SKOV3 fails to show p27/Kip1 accumulation. Interestingly, the SCF component protein SKP2 appears to be decreased in CAOV3 cells treated with ATRA. We have also shown that the ATRA dependent increase in p27/kip1 protein in CAOV3 cells leads to a decrease in the kinase activity of cyclin dependent kinase 4 (CDK4) following ATRA treatment. Finally, we found that CAOV3 cells stably transfected with a p27/kip1antisense construct, which express lower levels of p27/kip1 following ATRA treatment, and have a higher CDK4 kinase activity are less sensitive to ATRA induced growth suppression. Taken together our data suggest ATRA-induced growth inhibition in CAOV3 ovarian carcinoma cells involves modulation of the CDK inhibitor p27/kip1.
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PMID:p27/Kip1 mediates retinoic acid-induced suppression of ovarian carcinoma cell growth. 1504 6

The RAS-activated RAF-->MEK-->extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3'-kinase (PI3'-kinase)-->PDK1-->AKT signaling pathways are believed to cooperate to promote the proliferation of normal cells and the aberrant proliferation of cancer cells. To explore the mechanisms that underlie such cooperation, we have derived cells harboring conditionally active, steroid hormone-regulated forms of RAF and AKT. These cells permit the assessment of the biological and biochemical effects of activation of these protein kinases either alone or in combination with one another. Under conditions where activation of neither RAF nor AKT alone promoted S-phase progression, coactivation of both kinases elicited a robust proliferative response. Moreover, under conditions where high-level activation of RAF induced G(1) cell cycle arrest, activation of AKT bypassed the arrest and promoted S-phase progression. At the level of the cell cycle machinery, RAF and AKT cooperated to induce cyclin D1 and repress p27(Kip1) expression. Repression of p27(Kip1) was accompanied by a dramatic reduction in KIP1 mRNA and was observed in primary mouse embryo fibroblasts derived from mice either lacking SKP2 or expressing a T187A mutated form of p27(Kip1). Consistent with these observations, pharmacological inhibition of MEK or PI3'-kinase inhibited the effects of activated RAS on the expression of p27(Kip1) in NIH 3T3 fibroblasts and in a panel of bona fide human pancreatic cancer cell lines. Furthermore, we demonstrated that AKT activation led to sustained activation of cyclin/cdk2 complexes that occurred concomitantly with the removal of RAF-induced p21(Cip1) from cyclin E/cdk2 complexes. Cumulatively, these data strongly suggest that the RAF-->MEK-->ERK and PI3'K-->PDK-->AKT signaling pathways can cooperate to promote G(0)-->G(1)-->S-phase cell cycle progression in both normal and cancer cells.
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PMID:Cooperative regulation of the cell division cycle by the protein kinases RAF and AKT. 1557 89

Sterol regulatory element-binding protein (SREBP)-1a is a unique membrane-bound transcription factor highly expressed in actively growing cells and involved in the biosynthesis of cholesterol, fatty acids, and phospholipids. Because mammalian cells need to synthesize membrane lipids for cell replication, the functional relevance of SREBP-1a in cell proliferation has been considered a biological adaptation. However, the effect of this potent lipid-synthesis activator on cell growth has never been explored. Here, we show that induction of nuclear SREBP-1a, but not SREBP-2, completely inhibited cell growth in inducible Chinese hamster ovary (CHO) cell lines. Growth inhibition occurred through G(1) cell-cycle arrest, which is observed in various cell types with transient expression of nuclear SREBP-1a. SREBP-1a caused the accumulation of cyclin-dependent kinase (cdk) inhibitors such as p27, p21, and p16, leading to reduced cdk2 and cdk4 activities and hypophosphorylation of Rb protein. In contrast to transactivation of p21, SREBP-1a activated p27 by enhancing stabilization of the protein through inhibition of SKP2 and KPC1. In vivo, SREBP-1a-expressing livers of transgenic mice exhibited impaired regeneration after partial hepatectomy. SREBP-1-null mouse embryonic fibroblasts had a higher cell proliferation rate than wild-type cells. The unexpected cell growth-inhibitory role of SREBP-1a provides a new paradigm to link lipid synthesis and cell growth.
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PMID:A transcription factor of lipid synthesis, sterol regulatory element-binding protein (SREBP)-1a causes G(1) cell-cycle arrest after accumulation of cyclin-dependent kinase (cdk) inhibitors. 1766 9

Gastrointestinal stromal tumors (GIST) are caused by activating mutations in the KIT or platelet-derived growth factor receptor alpha receptor tyrosine kinase genes. Approximately 85% of GIST patients treated with imatinib mesylate achieve disease stabilization, however, often in the presence of residual tumor masses. Complete remissions are rare and a substantial proportion of patients develop resistance to imatinib. Our study was designed to determine whether imatinib-associated responses may account for these clinical findings. We report here that imatinib stimulates cellular quiescence in a proportion of GIST cells as evidenced by up-regulation of the CDK inhibitor p27(Kip1), loss of cyclin A, and reduced BrdUrd incorporation. Mechanistically, these events are associated with an imatinib-induced modulation of the APC/CDH1 signaling axis. Specifically, we provide evidence that imatinib down-regulates SKP2 and that this event is associated with increased nuclear CDH1, an activator of the APC that has been shown to regulate SKP2 stability. We also show that those GIST cells that do not undergo apoptosis in response to imatinib overexpress nuclear p27(Kip1), indicating that they have withdrawn from the cell cycle and are quiescent. Lastly, we provide evidence that a fraction of primary GISTs with high SKP2 expression levels may have an increased risk of disease progression. Taken together, our results support a model in which GIST cells that do not respond to imatinib by apoptosis are removed from the proliferative pool by entering quiescence through modulation of the APC/CDH1-SKP2-p27(Kip1) signaling axis. These results encourage further studies to explore compounds that modulate this pathway as antitumor agents in GISTs.
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PMID:Imatinib mesylate induces quiescence in gastrointestinal stromal tumor cells through the CDH1-SKP2-p27Kip1 signaling axis. 1897 47

Loss of the CDK inhibitor p27(KIP1) is widely linked with poor prognosis in human cancer. In Wnt10b-expressing mammary tumors, levels of p27(KIP1) were extremely low; conversely, Wnt10b-null mammary cells expressed high levels of this protein, suggesting Wnt-dependent regulation of p27(KIP1). Interestingly we found that Wnt-induced turnover of p27(KIP1) was independent from classical SCF(SKP2)-mediated degradation in both mouse and human cells. Instead, turnover required Cullin 4A and Cullin 4B, components of an alternative E3 ubiquitin ligase induced in response to active Wnt signaling. We found that CUL4A was a novel Wnt target gene in both mouse and human cells and that CUL4A physically interacted with p27(KIP1) in Wnt-responding cells. We further demonstrated that both Cul4A and Cul4B were required for Wnt-induced p27(KIP1) degradation and S-phase progression. CUL4A and CUL4B are therefore components of a conserved Wnt-induced proteasome targeting (WIPT) complex that regulates p27(KIP1) levels and cell cycle progression in mammalian cells.
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PMID:A functional link between Wnt signaling and SKP2-independent p27 turnover in mammary tumors. 1905 88


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