Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cyclin A-Cdk2 complexes bind to Skp1 and Skp2 during S phase, but the function of Skp1 and Skp2 is unclear. Skp1, together with F-box proteins like Skp2, are part of ubiquitin-ligase E3 complexes that target many cell cycle regulators for ubiquitination-mediated proteolysis. In this study, we investigated the potential regulation of cyclin A-Cdk2 activity by Skp1 and Skp2. We found that Skp2 can inhibit the kinase activity of cyclin A-Cdk2 in vitro, both by direct inhibition of cyclin A-Cdk2 and by inhibition of the activation of Cdk2 by cyclin-dependent kinase (CDK)-activating kinase phosphorylation. Only the kinase activity of Cdk2, not of that of Cdc2 or Cdk5, is reduced by Skp2. Skp2 is phosphorylated by cyclin A-Cdk2 on residue Ser76, but nonphosphorylatable mutants of Skp2 can still inhibit the kinase activity of cyclin A-Cdk2 toward histone H1. The F box of Skp2 is required for binding to Skp1, and both the N-terminal and C-terminal regions of Skp2 are involved in binding to cyclin A-Cdk2. Furthermore, Skp2 and the CDK inhibitor p21(Cip1/WAF1) bind to cyclin A-Cdk2 in a mutually exclusive manner. Overexpression of Skp2, but not Skp1, in mammalian cells causes a G1/S cell cycle arrest.
Mol Cell Biol 1999 Jan
PMID:Regulation of cyclin A-Cdk2 by SCF component Skp1 and F-box protein Skp2. 985 87

Hormones and growth factors regulate cell growth via the mitogen-activated protein (MAP) kinase cascade. Here we examine the actions of the hormone somatostatin on the MAP kinase cascade through one of its two major receptor subtypes, the somatostatin receptor 1 (SSTR1) stably expressed in CHO-K1 cells. Somatostatin antagonizes the proliferative effects of fibroblast growth factor in CHO-SSTR1 cells via the SSTR1 receptor. However, in these cells, somatostatin robustly activates MAP kinase (also called extracellular signal regulated kinase; ERK) and augments fibroblast growth factor-stimulated ERK activity. We show that the activation of ERK via SSTR1 is pertussis toxin sensitive and requires the small G protein Ras, phosphatidylinositol 3-kinase, the serine/threonine kinase Raf-1, and the protein tyrosine phosphatase SHP-2. The activation of ERK by SSTR1 increased the expression of the cyclin-dependent protein kinase inhibitor p21(cip1/WAF1). Previous studies have suggested that somatostatin-stimulated protein tyrosine phosphatase activity mediates the growth effects of somatostatin. Our data suggest that SHP-2 stimulation by SSTR1 may mediate some of these effects through the activation of the MAP kinase cascade and the expression of p21(cip1/WAF1).
Mol Endocrinol 1999 Jan
PMID:Somatostatin activation of mitogen-activated protein kinase via somatostatin receptor 1 (SSTR1). 989 10

Protein kinase Calpha (PKCalpha) expression is related to tumor progression in glioblastoma multiforme (GBM), the most common malignant brain tumor in adults. To determine whether PKCalpha regulates an anti-apoptotic survival pathway in GBM, A172 GBM cells were treated with a PKCalpha-selective antisense oligonucleotide. PKCalpha antisense oligonucleotide treatment was accompanied by reduction in PKCalpha levels and the induction of wild-type p53 and insulin-like growth factor-binding protein-3 (IGFBP3) 24-72 h after treatment, a period that coincided with the appearance of apoptotic cell death as detected by DNA fragmentation. There were no significant changes in the levels of Bcl-XL, Bax, and p21(WAF1). Induction of p53 after PKCalpha down-regulation was not associated with increased mRNA expression, but increased IGFBP3 levels were accompanied by increased mRNA levels. Recombinant human IGFBP3 induced an apoptotic effect that was similar to the PKCalpha antisense oligonucleotide, and its effect was blocked by IGF-I. These results suggest that one mechanism by which PKCalpha produces its antiapoptotic activity in GBM cells is by suppressing the p53-mediated activation of IGFBP3.
Mol Pharmacol 1999 Feb
PMID:Induction of p53-dependent, insulin-like growth factor-binding protein-3-mediated apoptosis in glioblastoma multiforme cells by a protein kinase Calpha antisense oligonucleotide. 992 33

Androgen is essential for the physiological maintenance of the integrity of prostatic epithelial cells, and castration causes the cells to undergo apoptosis. To study the molecular mechanism of androgen-dependent cell growth, we showed that androgen up-regulates the expression of the cyclin-dependent kinase inhibitor p21 (WAF1, CIP1, SDI1, CAP20) gene at both the mRNA and protein levels. Nuclear run-on assays demonstrated that androgen stimulates endogenous p21 gene expression at the transcriptional level. Transient transfection experiments showed that androgen can enhance the activity of a 2.4-kb promoter of the p21 gene linked to a luciferase reporter. These results suggested that a putative androgen response element (ARE), which mediates androgen response to enhance the p21 transcription, is included in the 2.4-kb promoter fragment. Deletion analysis of the promoter revealed a functional ARE (AGCACGCGAGGTTCC) located at -200 bp of the p21 gene proximal to the promoter region. Electrophoretic mobility shift assay further demonstrated that the androgen receptor specifically binds to this element. Wild-type ARE, but not mutant ARE, confers androgen responsiveness to a heterologous promoter. The up-regulation of p21 gene expression by androgen suggests that p21 may have an antiapoptotic function in prostatic epithelial cells. However, this hypothesis will need to be tested in future experiments.
Mol Endocrinol 1999 Mar
PMID:Androgen regulation of the cyclin-dependent kinase inhibitor p21 gene through an androgen response element in the proximal promoter. 1007 95

The accumulation of genetic abnormalities in a developing tumor is driven, at least in part, by the need to overcome inherent restraints on the replicative life span of human cells, two of which-senescence (M1) and crisis (M2)-have been well characterized. Here we describe additional barriers to clonal expansion (Mint) intermediate between M1 and M2, revealed by abrogation of tumor-suppressor gene (TSG) pathways by individual human papillomavirus type 16 (HPV16) proteins. In human fibroblasts, abrogation of p53 function by HPVE6 allowed escape from M1, followed up to 20 population doublings (PD) later by a second viable proliferation arrest state, MintE6, closely resembling M1. This occurred despite abrogation of p21(WAF1) induction but was associated with and potentially mediated by a further approximately 3-fold increase in p16(INK4a) expression compared to its level at M1. Expression of HPVE7, which targets pRb (and p21(WAF1)), also permitted clonal expansion, but this was limited predominantly by increasing cell death, resulting in a MintE7 phenotype similar to M2 but occurring after fewer PD. This was associated with, and at least partly due to, an increase in nuclear p53 content and activity, not seen in younger cells expressing E7. In a different cell type, thyroid epithelium, E7 also allowed clonal expansion terminating in a similar state to MintE7 in fibroblasts. In contrast, however, there was no evidence for a p53-regulated pathway; E6 was without effect, and the increases in p21(WAF1) expression at M1 and MintE7 were p53 independent. These data provide a model for clonal evolution by successive TSG inactivation and suggest that cell type diversity in life span regulation may determine the pattern of gene mutation in the corresponding tumors.
Mol Cell Biol 1999 Apr
PMID:Control of replicative life span in human cells: barriers to clonal expansion intermediate between M1 senescence and M2 crisis. 1008 77

The tumor suppressor p16(INK4a) inhibits cyclin-dependent kinases 4 and 6. This activates the retinoblastoma protein (pRB) and, through incompletely understood events, arrests the cell division cycle. To permit biochemical analysis of the arrest, we generated U2-OS osteogenic sarcoma cell clones in which p16 transcription could be induced. In these clones, binding of p16 to cdk4 and cdk6 abrogated binding of cyclin D1, p27(KIP1), and p21(WAF1/CIP1). Concomitantly, the total cellular level of p21 increased severalfold via a posttranscriptional mechanism. Most cyclin E-cdk2 complexes associated with p21 and became inactive, expression of cyclin A was curtailed, and DNA synthesis was strongly inhibited. Induction of p21 alone, in a sibling clone, to the level observed during p16 induction substantially reproduced these effects. Overexpression of either cyclin E or A prevented p16 from mediating arrest. We then extended these studies to HCT 116 colorectal carcinoma cells and a p21-null clone derived by homologous recombination. In the parental cells, p16 expression also augmented total cellular and cdk2-bound p21. Moreover, p16 strongly inhibited DNA synthesis in the parental cells but not in the p21-null derivative. These findings indicate that p21-mediated inhibition of cdk2 contributes to the cell cycle arrest imposed by p16 and is a potential point of cooperation between the p16/pRB and p14(ARF)/p53 tumor suppressor pathways.
Mol Cell Biol 1999 May
PMID:Induction of p21(WAF1/CIP1) and inhibition of Cdk2 mediated by the tumor suppressor p16(INK4a). 1020 15

A brief, 3 min period of global forebrain ischemia in the rat, induced by bilateral common carotid occlusion combined with hypotension, confers resistance to hippocampal pyramidal neurons against a subsequent 10 min ischemia, which is normally lethal to these cells. The molecular mechanisms underlying this ischemic preconditioning, or tolerance, are poorly understood. The tumor suppressor p53 is a transcription factor implicated in neuronal death following various insults, including cerebral ischemia. p53 is activated in response to cellular stress, e.g. hypoxia and DNA damage. Using in situ hybridization, we investigated the hippocampal mRNA expression of p53, and two of its target genes, p21(WAF1/Cip1) and the recently cloned PAG608/Wig-1, in a two-vessel occlusion model of ischemic preconditioning. We also evaluated changes in the protein levels of p53 and PAG608/Wig-1 using immunohistochemistry. The mRNA levels of all three genes increased in the ischemia sensitive CA1 region both following 3 min (non-lethal) preconditioning and 10 min of (lethal) nonconditioned ischemia. In contrast, after 10 min of ischemia preconditioned by a 3 min ischemic insult 48 h earlier, no upregulation of these genes was detected in the CA1. Following 10 min of nonconditioned ischemia, increased neuronal immunostaining of p53 and PAG608/Wig-1 was observed in the hippocampus, which was less pronounced following 3 min of preconditioning ischemia and 10 min of preconditioned ischemia. Our results demonstrate that activation of p53 and its response genes p21(WAF1/Cip1) and PAG608/Wig-1 occurs in the brain following lethal as well as non-lethal ischemic insults, and that ischemic preconditioning markedly diminishes this activation.
Brain Res Mol Brain Res 1999 Jul 05
PMID:Activation of p53 and its target genes p21(WAF1/Cip1) and PAG608/Wig-1 in ischemic preconditioning. 1040 80

Exposure of mammalian cells to ultraviolet (UV) light and other DNA-damaging agents triggers the UV response which is characterized by induction of a large number of genes including c-fos, c-jun, and the genes for DNA repair enzymes and cell-cycle regulatory proteins such as p21 WAF1 and p53. Upon DNA damage, the p53 tumor suppressor protein transmits signals to restrict cell-cycle progression, thereby allowing time for DNA repair to occur. Cells also respond to genotoxic stress by activation of the jun N-terminal kinase (JNK)/stress-activated protein kinase pathway. In this report we investigated the effects of modulation of the level of wild-type and mutant p53 protein on basal and UV-inducible JNK activity. We used the A1-5 rat fibroblast cell line, which contains a p53 gene coding for a temperature-sensitive p53 protein, which allows us to regulate the relative level of wild-type and mutant p53 protein produced in a cell. We measured the relative levels of JNK activity in sham-irradiated and UV-irradiated cells by using the immune complex kinase assay and then computed the fold induction of JNK after UV exposure. We demonstrated that cells expressing p53 protein in the wild-type conformation (when grown at 32 degrees C) exhibited a very low level of JNK activity that was induced 14- to 16-fold by UVC irradiation. When cells were grown at 37 degrees C or 39 degrees C to express predominantly mutant p53 protein, basal JNK activity was significantly higher than at 32 degrees C. UVC irradiation of cells expressing mutant p53 protein resulted in JNK activation, although the overall fold-induction was only two-fold because JNK1 activity was already high in the sham-treated controls. UVB irradiation also induced JNK1 activity, although we again observed a relatively high level of basal JNK activity in sham-irradiated cells expressing mutant p53 protein compared with cells expressing wild-type p53. Control experiments confirmed that JNK1 basal activity was not affected by temperature alone. Western blot analysis of cell extracts indicated that expression of p21 WAF protein was significantly higher in cells expressing wild-type p53 protein and was associated with low basal levels of JNK1 activity. In contrast, cells expressing mutant p53 protein and very low levels of p21 WAF1 protein were found to have a higher level of basal JNK1 activity. We also observed a reduced ability to induce JNK1 after UV irradiation of several other cell lines with p53-mutant or p53-null genotypes. Our results provide evidence for a novel connection between p53 status and the basal level of JNK1, a critical enzyme in the stress-activated protein kinase family. In addition, these studies suggest that the presence of mutant p53 protein in a cell not only affects basal activity of JNK1 but also affects the ability of a cell to respond to UV-induced stress by transmitting signals via induction or activation of the JNK1 cascade.
Mol Carcinog 1999 Aug
PMID:Mutational status of the p53 gene modulates the basal level of jun N-terminal kinase and its inducibility by ultraviolet irradiation in A1-5 rat fibroblasts. 1044 33

Hyperoxia increases free radical production, leading to DNA damage. Recent studies indicate that oxygen augments the expression of p53 and p21(WAF1/CIP1), and increases apoptotic labeling of airway epithelial cells. Similar changes in regulatory gene products have not been reported in other pulmonary cells, nor have these changes been investigated in conjunction with alterations in cell-cycle distribution. The present study was conducted to determine whether oxygen alters the expression of p53 and p21(WAF1/CIP1) in human bronchial smooth-muscle cells (BSMC). BSMC placed in room air (RA), 40% O(2), or 95% O(2) were examined for 3 d to determine cell number, thymidine incorporation, cell-cycle distribution, and lactate dehydrogenase release. Apoptosis was assessed through the terminal deoxynucleotidyl transferase-deoxyuridine triphosphate end-nick labeling (TUNEL) technique, and p53 and p21(WAF1/CIP1) protein levels were determined through enzyme-linked immunosorbent assay. Exposure of BSMC to 95% O(2) decreased proliferation and DNA synthesis within 24 h, and was accompanied by an increase in S-phase cells (72 h; RA: 12.9 +/- 4.6%, versus 95% O(2): 34.6 +/- 7.0%; P < 0.01). By comparison, exposure to 40% O(2) resulted in decreased proliferation at 48 h without significant alterations in cell-cycle distribution. Both p53 and p21(WAF1/CIP1) levels were increased by 95% O(2), with maximal differences noted at 24 and 48 h, respectively. All atmospheres showed < 8% cell death and few TUNEL-positive cells. Our results indicate that oxygen-mediated alterations in BSMC proliferation are time- and concentration-dependent. Furthermore, high oxygen levels induce S-phase arrest and increased expression of p53 and p21(WAF1/CIP1). Activation of these genes may prevent replication without inducing apoptosis to allow for the repair of oxidative damage.
Am J Respir Cell Mol Biol 1999 Sep
PMID:Oxygen induces S-phase growth arrest and increases p53 and p21(WAF1/CIP1) expression in human bronchial smooth-muscle cells. 1046 Jul 57

2, 5-bis(5-Hydroxymethyl-2-thienyl)furan (NSC 652287), is a representative of a series of thiophene derivatives that exhibit potent and selective antitumor activity against several tumor cell lines in the National Cancer Institute Anticancer Drug Screen. NSC 652287 has noticeable activity for the renal cell lines and produces cures in certain corresponding xenografts. The cellular mechanisms of action of NSC 652287 were therefore investigated in this study in greater detail. The most sensitive renal carcinoma cell line, A498, exhibited cell cycle arrest in G(0)-G(1) and G(2)-M at 10 nM NSC 652287, with increased p53 and p21(WAF1) protein. At higher concentrations, NSC 652287 still induced p53 elevation but with p21(WAF1) reduction and massive apoptosis. These results collectively suggested that NSC 652287 induced DNA damage. Using alkaline elution techniques, we found that NSC 652287 induced both DNA-protein and DNA-DNA cross-links with no detectable DNA single-strand breaks. These DNA-protein cross-links (DPC) persisted for at least 12 h after drug removal and their frequency was correlated with cytotoxicity in the renal cell lines studied. The most sensitive cells (A498) produced the highest DPC followed by the cell line with intermediate sensitivity (TK-10). DPC were minimal in the two resistant cell lines, ACHN and UO-31. Nonetheless, a similar degree of DPC occurred at doses imparting equitoxic effects. These results indicate that DNA is a primary target for the novel and potent anticancer thiophene derivative, NSC 652287. NSC 652287 did not cross-link purified DNA or mammalian topoisomerase I suggesting the importance of active metabolite(s) for the cross-linking activity.
Mol Pharmacol 1999 Sep
PMID:DNA protein cross-links produced by NSC 652287, a novel thiophene derivative active against human renal cancer cells. 1046 35


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