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)

p27Kip1 controls cell proliferation by binding to and regulating the activity of cyclin-dependent kinases (Cdks). Here we show that Cdk inhibition and p27 stability are regulated through direct phosphorylation by tyrosine kinases. A conserved tyrosine residue (Y88) in the Cdk-binding domain of p27 can be phosphorylated by the Src-family kinase Lyn and the oncogene product BCR-ABL. Y88 phosphorylation does not prevent p27 binding to cyclin A/Cdk2. Instead, it causes phosphorylated Y88 and the entire inhibitory 3(10)-helix of p27 to be ejected from the Cdk2 active site, thus restoring partial Cdk activity. Importantly, this allows Y88-phosphorylated p27 to be efficiently phosphorylated on threonine 187 by Cdk2 which in turn promotes its SCF-Skp2-dependent degradation. This direct link between transforming tyrosine kinases and p27 may provide an explanation for Cdk kinase activities observed in p27 complexes and for premature p27 elimination in cells that have been transformed by activated tyrosine kinases.
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PMID:Cdk-inhibitory activity and stability of p27Kip1 are directly regulated by oncogenic tyrosine kinases. 1725 63

Despite improvement in surgical techniques, prognosis of gallbladder carcinoma remains poor. It is desirable to identify prognostic biomarkers to aid in the development of targeted therapeutic strategies. Two SCF(Skp2) ubiquitin ligase-related proteins, Skp2 and cyclin-dependent kinase subunit 1 (Cks1), are involved in post-transcriptional degradation of p27(Kip1) tumor suppressor, which inhibits both cdk2/cyclin E and cdk2/cyclin A complexes and thus prevents transition to the S phase. However, the prognostic utility of p27(Kip1)-interacting cell cycle regulators has not been systematically assessed in gallbladder carcinoma. Immunohistochemistry was performed for p27(Kip1), Skp2, Cks1, cyclin E, cyclin A, and Ki-67 in tissue microarrays of 62 gallbladder carcinomas with follow-up. The data were correlated with clinicopathological features and overall survival (OS). The cumulative OS rate for all 62 cases was 42.9% at 3 years. Aberrant labeling indices (LIs) of p27(Kip1) (<20%), cyclin E (>or=5%), cyclin A (>or=5%), Cks1 (>or=40%), and Skp2 (>or=10%) were identified in 29, 58, 66, 21, and 57% of gallbladder carcinomas, respectively. By log-rank tests, downregulation of p27(Kip1) (P=0.0319) and high LIs of Skp2 (P=0.0006), Cks1 (P=0.0460), cyclin E (P=0.0070), and Ki-67 (P=0.0037) were predictive of inferior OS. Furthermore, the combined expression status of Skp2 and Ki-67 robustly defined three prognostically different groups (P=0.0001). In multivariate comparison, Skp2 overexpression represented the strongest independent adverse prognosticator (P=0.004, risk ratio (RR): 5.538), followed by Ki-67 LI >or=50% (P=0.016, RR: 3.254) and American Joint Committee on Cancer stages II-IV (P=0.013, RR: 3.163). In conclusion, aberrations of p27(Kip1)-interacting cell cycle regulators are common in gallbladder carcinomas. Skp2 overexpression is highly representative of biological aggressiveness and independently associated with poor OS, suggesting that it is a promising novel target for therapeutic intervention in aggressive cases. The combined assessment of Skp2 and Ki-67 LIs effectively risk-stratifies gallbladder carcinomas with different prognosis, which is worth being prospectively validated in future study.
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PMID:Skp2 is an independent prognosticator of gallbladder carcinoma among p27(Kip1)-interacting cell cycle regulators: an immunohistochemical study of 62 cases by tissue microarray. 1738 52

p27, an important cell cycle regulator, blocks the G(1)/S transition in cells by binding and inhibiting Cdk2/cyclin A and Cdk2/cyclin E complexes (Cdk2/E). Ubiquitination and subsequent degradation play a critical role in regulating the levels of p27 during cell cycle progression. Here we provide evidence suggesting that both Cdk2/E and phosphorylation of Thr(187) on p27 are essential for the recognition of p27 by the SCF(Skp2/Cks1) complex, the ubiquitin-protein isopeptide ligase (E3). Cdk2/E provides a high affinity binding site, whereas the phosphorylated Thr(187) provides a low affinity binding site for the Skp2/Cks1 complex. Furthermore, binding of phosphorylated p27/Cdk2/E to the E3 complex showed positive cooperativity. Consistently, p27 is also ubiquitinated in a similarly cooperative manner. In the absence of p27, Cdk2/E and Cks1 increase Skp2 phosphorylation. This phosphorylation enhances Skp2 auto-ubiquitination, whereas p27 inhibits both phosphorylation and auto-ubiquitination of Skp2.
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PMID:Substrate recognition and ubiquitination of SCFSkp2/Cks1 ubiquitin-protein isopeptide ligase. 1740 98

The identification of Skp2 as a direct E2F target has allowed us to document the existence of a positive feedback loop comprised of Rb-E2F, Skp2, p27 and cyclin E-cdk2. We have termed this set of regulatory molecules the Skp2 autoinduction loop. Interference with this loop selectively regulates cell cycle progression through the restriction point. We describe here how the Skp2 autoinduction loop may interact with other regulatory controls on the restriction point, and how the reciprocal relationship between Rb and Skp2 may affect signal transduction to the cell cycle and thinking about the role of Skp2 overexpression in cancers.
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PMID:A reciprocal relationship between Rb and Skp2: implications for restriction point control, signal transduction to the cell cycle and cancer. 1819 71

Prostate cancer (PCa) is the leading cause of cancer-related deaths in men; urgent measures are warranted to lower this deadly malignancy. Silymarin is a known cancer chemopreventive agent, but the relative anticancer efficacy of its constituents is still unknown. Here, we compared the efficacy of 7 pure flavonolignan compounds isolated from silymarin, namely silybin A, silybin B, isosilybin A, isosilybin B, silydianin, isosilydianin, silychristin and isosilychristin, in advanced human PCa PC3 cells. Silybin A, silybin B, isosilybin A, isosilybin B, silibinin and silymarin strongly inhibited the colony formation by PC3 cells (p < 0.001), while silydianin, silychristin and isosilychristin had marginal effect (p < 0.05). Using cell growth and death assays, we identified isosilybin B as the most effective isomer. FACS analysis for cell cycle also showed that silybin A, silybin B, isosilybin A, isosilybin B, silibinin and silymarin treatment resulted in strong cell cycle arrest in PC3 cells after 72 hr of treatment, while the effect of silydianin, silychristin and isosilychristin was marginal (if any). Western blot analysis also showed the differential effect of these compounds on the levels of cell cycle regulators-cyclins (D, E, A and B), CDKs (Cdk2, 4 and Cdc2), CDKIs (p21 and p27) and other cell cycle regulators (Skp2, Cdc25A, B, C and Chk2). This study provided further evidence for differential anticancer potential among each silymarin constituent, which would have potential implications in devising better formulations of silymarin against prostate and other cancers.
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PMID:Identifying the differential effects of silymarin constituents on cell growth and cell cycle regulatory molecules in human prostate cancer cells. 1843 16

The DNA polymerase delta processivity factor Proliferating Cell Nuclear Antigen (PCNA) promotes the DNA damage-induced degradation of the replication initiation factor Cdt1 via the CRL4(Cdt2) E3 ubiquitin ligase complex. Here we demonstrate that PCNA promotes the ubiquitylation and degradation of the CDK inhibitor p21 in cells irradiated with low dose of ultraviolet (UV) by a similar mechanism. Human cells that are depleted of Cul4, DDB1 (damage-specific DNA-binding protein-1), or the DCAF Cdt2, are deficient in the UV-induced ubiquitylation and degradation of p21. Depletion of mammalian cells of PCNA by siRNA, or mutations in p21 that abrogate PCNA binding, prevent UV-induced p21 ubiquitylation and degradation, indicating that physical binding with PCNA is necessary for the efficient ubiquitylation of p21 via the CRL4(Cdt2) ubiquitin ligase. Cdt2 functions as the substrate recruiting factor for p21 to the rest of the CRL4 ubiquitin ligase complex. The CRL4(Cdt2) E3 ubiquitin ligase ubiquitylates p21 both in vivo and in vitro, and its activity is dependent on the interaction of p21 with PCNA. Finally, we show that the CRL4(Cdt2) and the SCF(Skp2) ubiquitin ligases are redundant with each other in promoting the degradation of p21 during an unperturbed S phase of the cell cycle.
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PMID:PCNA-dependent regulation of p21 ubiquitylation and degradation via the CRL4Cdt2 ubiquitin ligase complex. 1879 47

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

The FoxM1 transcription factor, a master regulator of mitotic gene expression, promotes the pathogenesis of several malignancies. However, little is known about its expression and function in gastric cancer. In the present study we determined whether FoxM1 is over-expressed in gastric cancer, and whether it is required to maintain an immortal phenotype of gastric cancer cells. The over-expression of FoxM1 was observed in 37/42 tumour specimens from patients with gastric cancer. When FoxM1 in gastric cancer cells was knocked-down, impaired clonogenicity and cellular senescence occurred independently of p53 and p16 status. FoxM1 depletion led to the down-regulation of its target genes c-MYC and Skp2, coupled with the accumulation of the CDK inhibitor p27(kip1). Importantly, the FoxM1 inhibition-mediated cellular senescence and clonogenic defect was attenuated by the abolition of p27(kip1) induction. Telomerase reverse transcriptase, the key component of telomerase essential for cellular immortalization, was also inhibited in the FoxM1-depleted cells. Taken together, the FoxM1 gene is aberrantly activated in gastric cancer and its inhibition triggers p53- and p16-independent senescence of cancer cells by regulating the expression of p27(kip1) and other targets. These findings provide mechanistic insights into the role of FoxM1 in the pathogenesis of gastric cancer, which may have diagnostic and therapeutic implications in gastric cancer.
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PMID:FoxM1 is up-regulated in gastric cancer and its inhibition leads to cellular senescence, partially dependent on p27 kip1. 1923 38

Cks1 plays an essential role in SCFSkp2-mediated ubiquitination, and consequently turnover, of the cdk2 inhibitor and tumor supressor p27Kip1. High Cks1 expression is associated with aggressive breast tumors and correlates with low p27Kip1 levels in some cases, although it is also an independent prognostic marker for survival, and provides predictive information in addition to that provided by p27Kip1 alone. In this report we demonstrate that Cks1 protein and mRNA are elevated to very high levels in mammary tumors initiated by erbB2, c-myc and polyoma middle-T (PyMT) in transgenic mice, whereas Cks1 protein is hardly detectable in the normal mammary epithelium. Cks1 is also highly upregulated in rat mammary tumors initiated by methylnitrosourea (MNU). Despite high levels of Cks1 expression, p27Kip1 levels were not reduced, and were in fact slightly higher in mammary tumors initiated by erbB2, PyMT and MNU. In contrast mammary tumors from MMTV-c-myc mice did exhibit low p27Kip1 and higher levels of Skp2. Together, these data suggest that deregulated Cks1 expression might play roles in oncogene and carcinogen-initiated mammary tumorigenesis independent of p27Kip1 turnover in certain tumors. Stable overexpression of Cks1 in human breast carcinoma MCF-7 cells did not significantly reduce p27Kip1 expression, although it conferred resistance to Faslodex (ICI 182780)-mediated inhibition of colony outgrowth in these cells. In contrast, Cks1-depleted MCF-7 cells formed fewer colonies in estrogen-containing medium. Therefore, our studies also suggest that Cks1 levels regulate the responsiveness of ER+ breast cancers to estrogens and anti-estrogens.
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PMID:High Cks1 expression in transgenic and carcinogen-initiated mammary tumors is not always accompanied by reduction in p27Kip1. 1936 Mar 56

Cellular levels of products from both oncogenes and tumor suppressor genes in normal cells need to be critically regulated to avoid malignant transformation. These products are often controlled by the ubiquitin proteasome pathway, the specific degradation mechanism in the cell. E3 ubiquitin ligases polyubiquitylate their specific substrates by collaborating with E1 and E2, and then the modified substrates are degraded in the proteasome. Mdm2 targets p53 and retinoblastoma protein, two major tumor suppressor gene products, for ubiquitin-dependent degradation. SCF(Skp2) targets other tumor suppressor gene products and CDK inhibitors such as p130, Tob1, p27(Kip1), p57(Kip2), and p21(Cip1). Therefore, both E3 ligases act like oncogene products. In contrast, degradation of several oncogene products, such as Cyclin E, Notch, c-Myc, c-Jun, and c-Myb, are mediated by SCF(Fbw7). Fbw7 is often deleted or mutated in human cancers and acts like a tumor suppressor. As well as growth factor receptors and signal transduction regulators, DNA repair-related proteins are also regulated via the ubiquitin-proteasome pathway mediated by their specific E3 ligases. The stabilization of oncogene products and enhanced degradation of tumor suppressor gene products or DNA repair proteins might be associated with carcinogenesis and malignant progression, due to defects or the abnormal expression of their E3 ligases.
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PMID:Ubiquitin-mediated control of oncogene and tumor suppressor gene products. 1945 46


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