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)

Saikosaponin a, a purified ingredient of Chinese herb with known antitumor activity, can inhibit cell growth and DNA synthesis of hepatoma cell line HepG2. Both mRNA and protein of the CDK inhibitor p-16(INK4a) and p-15(INK4b) in HepG2 were greatly induced by saikosaponin a while that of p-21(CIP), p-27(KIP) and other cell cycle related genes were not. In addition, reduced phosphorylation of RB protein is observed in saikosaponin a-treated HepG2. Staurosporin, one of the PKC inhibitors, significantly prevented the saikosaponin a induced growth inhibition suggesting PKC pathway be involved. On the other hand, the phorbol ester tumor promoter TPA (12-O-Tetredecanolyphorbol 13-acetate) also inhibited HepG2 growth and specifically induced p-16(INK4a) and p-15(INK4b) mRNA expression. The results suggest that both saikosaponin a and TPA-induced HepG2 growth inhibition are associated with p-15(INK4a) and p-16(INK4b) gene expression and might be mediated by PKC signaling pathway.
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PMID:Involvement of p-15(INK4b) and p-16(INK4a) gene expression in saikosaponin a and TPA-induced growth inhibition of HepG2 cells. 1144 23

The melanocyte is a neural crest-derived cell that localizes in humans to several organs including the epidermis, eye, inner ear and leptomeninges. In the skin, melanocytes synthesize and transfer melanin pigments to surrounding keratinocytes, leading to skin pigmentation and protection against solar exposure. We have investigated the process of replicative senescence and accompanying irreversible cell cycle arrest, in melanocytes in culture. As was found in other cell types, progressive telomere shortening appears to trigger replicative senescence in normal melanocytes. In addition, senescence is associated with increased binding of the cyclin-dependent kinase inhibitor (CDK-I) p16(INK4a) to CDK4, down-regulation of cyclin E protein levels (and consequent loss of cyclin E/CDK2 activity), underphosphorylation of the retinoblastoma protein RB and subsequent increased levels of E2F4-RB repressive complexes. In contrast to fibroblasts, however, the CDK-Is p21(Waf-1) and p27(Kip-1) are also down-regulated. These changes appear to be important for replicative senescence because they do not occur in melanocytes that overexpress the catalytic subunit of the enzyme telomerase (hTERT), or in melanomas, which are tumors that originate from melanocytes or melanoblasts. In contrast to unmodified melanocytes, hTERT overexpressing (telomerized) melanocytes displayed telomerase activity, stable telomere lengths and an extended replicative life span. However, telomerized melanocytes show changes in cell cycle regulatory proteins, including increased levels of cyclin E, p21(Waf-1) and p27(Kip-1). Cyclin E, p21(Waf-1) and p27(Kip-1) are also elevated in many primary melanomas, whereas p16(INK4a) is mutated or deleted in many invasive and metastatic melanomas. Thus, the molecular mechanisms leading to melanocyte senescence and transformation differ significantly from fibroblasts. This suggests that different cell types may use different strategies to halt the cell cycle in response to telomere attrition and thus prevent replicative immortality.
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PMID:The human melanocyte: a model system to study the complexity of cellular aging and transformation in non-fibroblastic cells. 1160 3

p16(INK4a), a tumor suppressor gene that inhibits cyclin-dependent kinase 4 and cyclin-dependent kinase 6, is also implicated in the mechanisms underlying replicative senescence, because its RNA and protein accumulate as cells approach their finite number of population doublings in tissue culture. To further explore the involvement of p16(INK4a) in replicative senescence, we constructed a retroviral vector containing antisense p16(INK4a), pDOR-ASp16, and introduced it into early passages of human diploid fibroblasts. The introduction of this construct significantly suppressed the expression of wild-type p16(INK4a). It also imposed a finite increase in proliferative life span and significant delay of several other cell senescent features, such as cell flattening, cell cycle arrest, and senescence-associated beta-galactosidase positivity. Moreover, telomere shortening and decline in DNA repair capacity, which normally accompany cell senescence, are also postponed by the ASp16 transfection. The life span of fibroblasts was significantly extended, but the onset of replicative senescence could not be totally prevented. Telomerase could not be activated even though telomere shortening was slowed. These observations suggest that the telomere pathway of senescence cannot be bypassed by ASp16 expression. These data not only strongly support a role for p16(INK4a) in replicative senescence but also raise the possibility of using the antisense p16(INK4a) therapeutically.
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PMID:Senescence delay of human diploid fibroblast induced by anti-sense p16INK4a expression. 1160 67

In normal cells, activation of cyclin-dependent kinases (cdks) requires binding to a cyclin and phosphorylation by the cdk-activating kinase (CAK). The Kaposi's sarcoma-associated herpesvirus encodes a protein with similarity to D-type cyclins. This KSHV-cyclin activates CDK6, alters its substrate specificity, and renders CDK6 insensitive to inhibition by the cdk inhibitor p16(INK4a). Here we investigate the regulation of the CDK6/KSHV-cyclin kinase with the use of purified proteins and a cell-based assay. We find that KSHV-cyclin can activate CDK6 independent of phosphorylation by CAK in vitro. In addition, CAK phosphorylation decreased the p16(INK4a) sensitivity of CDK6/KSHV-cyclin complexes. In cells, expression of CDK6 or to a lesser degree of a nonphosphorylatable CDK6(T177A) together with KSHV-cyclin induced apoptosis, indicating that CDK6 activation by KSHV-cyclin can proceed in the absence of phosphorylation by CAK in vivo. Coexpression of p16 partially protected cells from cell death. p16 and KSHV-cyclin can form a ternary complex with CDK6 that can be detected by binding assays as well as by conformational changes in CDK6. The Kaposi's sarcoma-associated herpesvirus has adopted a clever strategy to render cell cycle progression independent of mitogenic signals, cdk inhibition, or phosphorylation by CAK.
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PMID:CAK-independent activation of CDK6 by a viral cyclin. 1173 95

Replicative senescence is defined for human diploid fibroblasts in culture as a cell growth arrest appearing beyond 50 +/- 10 population doublings and associated with telomeres' shortening. This phenomenon shows an increased expression of growth cell inhibitors: p21Waf1 described as an universal CDK inhibitor and p16INK4a as a specific inhibitor for both G1 phase kinases CDK4 and CDK6. The cell proliferation inhibitor p14ARF, product of INK4a/ARF locus is involved in replicative senescence too. Overexpression or homozygotic deletion of these inhibitors demonstrated their role in senescence induction. These proteins are involved in two different metabolic pathways, the first including p53, represented by E2F, ARF, MDM2, p53, p21Waf1, and the second concerning pRb and p16INK4a. These two pathways present numerous interactions and the polymerase (PARP) in relation with p53 and activated by telomere shortening might represent via p21Waf1 a link between this shortening and cell cycle control. An another metabolic pathway involving PTEN and p27KIP1 is discussed in senescent-like phenotype induction, but its activity in replicative senescent is uncertain.
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PMID:[Cyclin dependent kinase inhibitors and replicative senescence]. 1177 95

Cellular senescence has been proposed to be an in vitro and in vivo block that cells must overcome in order to immortalize and become tumorigenic. To characterize these pathways, we focused on changes in the cyclin-dependent kinase inhibitors and their binding partners that underlie the cell cycle arrest at senescence. As a model, we utilized normal human prostate epithelial cell (HPEC) and human uroepithelial cell (HUC) cultures. After 30-40 population doublings cells became growth-arrested in G0/1 with a threefold decrease in Cdk2-associated activity, a point defined as pre-senescence. Temporally following this growth arrest, the cells develop a senescence morphology and express senescence-associated beta-galactosidase (SA-beta-gal). Levels of p16(INK4a) and p57(KIP2) rise in HUCs during progressive passages, whereas only p16 increases in HPEC cultures. The induced expression of p57, similar to p16, produces a senescent-like phenotype. pRB, cyclin D, p19(INK4d) and p27(KIP1) decrease in both cell types. We find that p53, p21(CIP1) and p15(INK4b) are transiently elevated in HPECs and HUCs at the pre-senescent growth arrest, then return to low proliferating levels at terminal senescence. Analysis of p53, p21(CIP1), p15(INK4b), p16(INK4a), and p57(KIP2) reveals altered expression in immortalized, non-tumorigenic HPV16 E6 and E7 prostate lines and in tumorigenic prostate cancer cells. These results indicate: (i) the existence of a subset of growth inhibiting genes elevated at the onset of the senescence, (ii) a distinct class of genes involved in the maintenance of senescence, and (iii) the frequent inactivation of these pathways during immortalization.
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PMID:Role of cyclin-dependent kinase inhibitors in the growth arrest at senescence in human prostate epithelial and uroepithelial cells. 1178 34

P19(INK4d) is a tumor suppressing protein and belongs to a family of cyclin D-dependent kinase inhibitors of CDK4 and CDK6, which play a key role in human cell cycle control. P19 comprises ten alpha-helices arranged sequentially in five ankyrin repeats forming an elongated structure. This rather simple topology, combined with its physiological function, makes p19 an interesting model protein for folding studies. Urea-induced unfolding transitions monitored by far-UV CD and phenylalanine fluorescence coincide and suggest a two-state mechanism for equilibrium unfolding. Unfolding of p19 followed by 2D (1)H-(15)N HSQC spectra revealed a third species at moderate urea concentrations with a maximum population of about 30 % near 3.2 M urea. It shows poor chemical shift dispersion, but cross-peaks emerge for some residues that are distinct from the native or unfolded state. This equilibrium intermediate either arises only at high protein concentrations (as in the NMR experiment) or has similar optical properties to the unfolded state. Stopped-flow far-UV CD experiments at various urea concentrations revealed that alpha-helical structure is formed in three phases, of which only the fastest phase (10 s(-1)) depends upon the urea concentration. The kinetic of the slowest phase (0.017 s(-1)) can be resolved by 1D real-time NMR and accelerated by cyclophilin. It is limited in rate by prolyl isomerization, and native-like ordered structure cannot form prior to this isomerization. The two fast phases lead to 83 % native protein within the dead time of the NMR experiment. In contrast to p16(INK4a), which exhibits only a marginal stability and high unfolding rates, p19 shows the expected stability for a protein of this size with a clear kinetic barrier between the unfolded and folded state. Therefore, p19 might complement the function of less stable INK4 inhibitors in cell cycle control under unfavorable conditions.
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PMID:Protein folding and stability of human CDK inhibitor p19(INK4d). 1178 24

Using alternative reading frames, the human ARF-INK4a locus encodes two unrelated proteins that both function in tumor suppression. p16(INK4a) maintains the retinoblastoma protein in its growth-suppressive state through inhibition of cyclin D-dependent kinase activity, whereas ARF binds with MDM2 and stabilizes p53. The majority of the activity of ARF to date is ascribed to its ability to activate p53, resulting in a G(1) cell cycle arrest or apoptosis. We show here that ARF colocalizes with DNA replication protein A (RPA32) and that overexpression of ARF reduces the rate of DNA synthesis resulting in accumulation of an S-phase cell population. Impediment of DNA synthesis by ARF can occur and becomes more evident in the absence of p53. Hence, the biological consequence of ARF induction varies dependent on cellular p53 status, inducing predominantly a G(1) arrest or apoptosis in p53-positive cells or causing S-phase retardation when p53 function is comprised.
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PMID:Human tumor suppressor ARF impedes S-phase progression independent of p53. 1186

In previous studies we found that neuronal overexpression of human cyclooxygenase (COX)-2 in transgenic mice potentiated excitotoxicity in vivo and in vitro. To clarify the molecular mechanisms involved in COX-2-mediated potentiation of excitotoxicity, we used cDNA microarray to identify candidate genes the expression of which is altered in the cerebral cortex of homozygous human hCOX-2 transgenic mice. We found that the mRNA expression of the cell cycle kinase (CDK) inhibitor-inhibitor kinase (INK) p18(INK4), a specific inhibitor of CDK 4,6, which controls the activation of the retinoblastoma (Rb) tumor suppressor protein phosphorylation, was decreased in the brain of adult hCOX-2 homozygous transgenics. Conversely, chronic treatment of the hCOX-2 transgenics with the preferential COX-2 inhibitor nimesulide reversed the hCOX-2-mediated decrease of cortical p18(INK4) mRNA expression in the brain. Further in vitro studies revealed that in primary cortico-hippocampal neurons derived from homozygous hCOX-2 transgenic mice, COX-2 overexpression accelerates glutamate-mediated apoptotic damage that is prevented by the CDK inhibitor flavoperidol. Moreover, treatment of wild-type primary cortico-hippocampal neuron cultures with the COX-2 preferential inhibitor nimesulide significantly attenuated glutamate-mediated apoptotic damage, which coincided with inhibition of glutamate-mediated pRb phosphorylation. These data indicate that hCOX-2 overexpression causes neuronal cell cycle deregulation in the brain and provides further rationale for targeting neuronal COX-2 in neuroprotective therapeutic research.
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PMID:Role of cyclooxygenase-2 in neuronal cell cycle activity and glutamate-mediated excitotoxicity. 1196 Oct 48

The tumor suppressor ARF is transcribed from the INK4a/ARF locus in partly overlapping reading frames with the CDK inhibitor p16(Ink4a). ARF is able to antagonize the MDM2-mediated ubiquitination and degradation of p53, leading to either cell cycle arrest or apoptosis, depending on the cellular context. However, recent data point to additional p53-independent functions of mouse p19(ARF). Little is known about the dependency of human p14(ARF) function on p53 and its downstream genes. Therefore, we analysed the mechanism of p14(ARF)-induced cell cycle arrest in several human cell types. Wild-type HCT116 colon carcinoma cells (p53(+/+)p21(CIP1+/+) 14-3-3sigma(+/+)), but not p53(-/-) counterparts, underwent G(1) and G(2) cell cycle arrest following infection with a p14(ARF)-adenovirus. In p21(CIP1-/-) cells, p14(ARF) did not induce G(1) or G(2) arrest, while 14-3-3sigma(-/-) counterparts were mainly arrested in G(1), pointing to essential roles of p21(CIP1) in G(1) and G(2) arrest and cooperative roles of p21 and 14-3-3sigma in ARF-mediated G(2) arrest. Our data demonstrate a strict p53 and p21(CIP1) dependency of p14(ARF)-induced cell cycle arrest in human cells.
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PMID:Human p14(ARF)-mediated cell cycle arrest strictly depends on intact p53 signaling pathways. 1208 36


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