Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

AKT is a key serine/threonine kinase in the PTEN/PI3K/AKT pathway(1) and activationof AKT is often observed in human cancers. To explore the role of AKT in cell survival in different tumor cells, we tested 20 human tumor cell lines for response to knockdown of AKT by small interference RNA (siRNA) and/or a kinase-dead mutant AKT. siRNA-mediated knockdown of all three AKT isoforms in tumor cell lines led to a reduction of phosphorylation of AKT substrates. Knockdown of AKT resulted in apoptosis in six out of 11 tumor cells with activated AKT. In contrast, knockdown of AKT induced apoptosis in three out of nine cell lines with a low level of active AKT. The responsiveness of the cells to knockdown of AKT was not affected by mutational status of p53 but appeared correlated with overexpression of HER2. To assess the role of individual AKT isoforms, five of the cell lines responsive to knockdown of AKT were further characterized. In ZR-75 cells, AKT1 is the predominant isoform responsible for cell proliferation and survival. Conversely, in IGROV1 cells, AKT2 plays a major role in cell proliferation, but no single isoform is essential for cell survival. Thus, the relative importance of the AKT isoforms is cell line-specific. Our data suggest that inhibiting all three AKT isoforms is necessary to elicit maximal apoptotic response in tumor cells, and the level of activated AKT is a favorable but not always reliable biomarker for preselection of responsive tumor cell lines to AKT inhibitors.
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PMID:AKT1, AKT2 and AKT3-dependent cell survival is cell line-specific and knockdown of all three isoforms selectively induces apoptosis in 20 human tumor cell lines. 1742 44

Checkpoint kinase 1 (Chk1), a serine/threonine kinase, plays an important role in DNA damage checkpoint control and is an attractive target for cancer treatment. To develop a Chk1-specific cell-based assay, stable clones were established in which Chk1 kinase domain fused at its N-terminus with p53 through 4 tandem repeats of Gly-Gly-Gly-Gly-Ser was expressed in an inducible manner. Chk1 kinase specificity of the phosphorylation of fused p53 was confirmed by the experiments with a kinase-inactive Chk1. Only in the presence of an inducer molecule was phosphorylation of p53 at Ser-15 in the stable clones induced. Furthermore, its assay performance proved acceptable for high-throughput screening applications, judging from the Z' factor values (> 0.77). Finally, the cell-based assay thus established yielded structure-activity relationship data for a small set of test inhibitors of Chk1 within cells. Collectively, these results demonstrate that the established cell-based assay provides a novel and highly sensitive cellular platform for Chk1 inhibitor discovery.
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PMID:A robust, target-driven, cell-based assay for checkpoint kinase 1 inhibitors. 1751 98

Akt/PKB is a serine/threonine kinase that plays a crucial role in cell survival and apoptosis. Aberrant activation of pAkt is associated with various malignant human cancers, including breast carcinoma. In vitro studies show that pAkt activation is mediated by estrogen and acts as a downstream effector of HER2 with implications in breast cancer progression and drug resistance. We investigated the incidence of Akt activation in invasive ductal carcinoma and its correlation with other clinicopathological variables. Using tissue microarray technology, immunohistochemical expression of phosphorylated Akt (pAkt) at Ser-473 was evaluated in 127 cases of invasive ductal carcinomas, together with hormone receptors, HER2, p53, Ki-67 and other clinicopathological variables. Both nuclear and cytoplasmic expression was noted for pAkt, with 46 cases (36.2%) showing high cytoplasmic pAkt expression and 37 cases (29.1%) showing high nuclear pAkt expression. There was a significant association between both high cytoplasmic and nuclear pAkt expression with HER2 overexpression (both p<0.0001). There was also a positive correlation between high nuclear pAkt expression with both estrogen receptor and progesterone receptor status (p=0.042 and p=0.015, respectively). High cytoplasmic pAkt expression was associated with high Ki-67 expression (p=0.052), however, there was no association between pAkt and p53 expression. In the present study, activation of the Akt pathway shows strong association with HER2 overexpression, which is consistent with many in vitro studies. Our study also showed a positive correlation between pAkt and hormone receptors, which suggested the possible mechanism of endocrine resistance in ER-positive breast cancer. These results also suggest the prognostic value of pAkt and its importance in the prediction of therapeutic response in invasive ductal carcinoma of the breast.
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PMID:Activated Akt signaling pathway in invasive ductal carcinoma of the breast: correlation with HER2 overexpression. 1754 59

The p53 tumor suppressor protein is a key regulator of cellular functions including responses to numerous stress signals, and triggers apoptosis in many cell types, including neurons. The major mechanisms known to regulate p53 stabilization and activation include phosphorylation and ubiquitin ligase-mediated proteasomal degradation. Cyclin-dependent kinase 5 (Cdk5), a proline-directed serine/threonine kinase, is most active in the central nervous system and plays a variety of roles in neuronal degeneration. Here, we demonstrate for the first time that Cdk5 interacts with p53 and increases its stability through posttranslational regulation, leading to accumulation of p53, particularly in the nucleus. We show that Cdk5 phosphorylates p53 on Ser15, Ser33 and Ser46 in vitro, and that increased Cdk5 activity in the nucleus mediates these phosphorylation events in response to genotoxic and oxidative stresses. Cdk5 mediates disruption of the interaction between p53 and Hdm2 (also known as Mdm2), and prevents Hdm2-induced p53 ubiquitylation and downregulation. Cdk5 additionally enhances phosphorylation-dependent binding of the p300 coactivator, inducing acetylation of p53. Cdk5-stabilized p53 protein is transcriptionally active, resulting in the induction of pro-apoptotic genes and subsequent mitochondria-mediated apoptosis in response to genotoxic or oxidative stress. Collectively, these novel findings help define the mechanisms underlying neuronal apoptosis occurring as a result of Cdk5-mediated p53 stabilization and transcriptional activation.
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PMID:Stabilization and activation of p53 induced by Cdk5 contributes to neuronal cell death. 1759 90

Cisplatin is commonly used in the treatment of advanced ovarian carcinoma. A major limitation of the use of cisplatin is the development of resistance in tumors. Glycogen synthase kinase-3 beta (GSK-3beta) is a multi-functional serine/threonine kinase. Its activity is regulated negatively by the phosphorylation of serine 9 (pGSK-3beta-ser-9) and positively by the phosphorylation of tyrosine 216 (pGSK-3beta-tyr-216). We compared the expression/phosphorylation of GSK-3beta between the cisplatin-sensitive ovarian carcinoma cell line A2780 and its cisplatin-resistant derivative CP70. The expression levels of total GSK-3beta and pGSK-3beta-tyr-216 were similar in these cells; however, CP70 cells had a much higher expression of pGSK-3beta-ser-9 than A2780 cells. Lithium chloride, which is a GSK-3beta inhibitor and stimulates pGSK-3beta-ser-9, significantly increased the IC50 of cisplatin and counteracted cisplatin-induced apoptosis of A2780 and CP70 cells. In contrast, overexpression of a constitutively active S9A GSK-3beta mutant increased the sensitivity of CP70 cells to cisplatin and significantly enhanced cisplatin-mediated apoptosis. It is suggested that the cisplatin-resistance of CP70 cells is mediated by stabilizing p53. We demonstrated that GSK-3beta negatively regulated the expression of p53. Therefore, pGSK-3beta-ser-9 may confer the cisplatin resistance of ovarian carcinomas through the stabilization of p53 expression. Our study establishes a potential role of GSK-3beta in the development of cisplatin resistance in initially sensitive tumors.
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PMID:Phosphorylation of glycogen synthase kinase-3 beta at serine 9 confers cisplatin resistance in ovarian cancer cells. 1767 94

Arsenic is an environmental toxicant that recently has been shown to have anticancer activity against a number of types of cancer cells by inducing apoptosis. Glycogen synthase kinase-3 (GSK3), a serine/threonine kinase, is an important pro-apoptotic signaling enzyme. Although GSK3 has been shown to promote apoptosis caused by a wide variety of insults, a role for GSK3 in arsenic-induced apoptosis has not yet been identified. Investigation of the involvement of GSK3 in arsenite-induced apoptosis demonstrated that arsenite induced apoptosis in SH-SY5Y human neuroblastoma cells, activating the executioner caspase-3 which caused cleavage of poly-ADP ribose-polymerase (PARP). Two selective GSK3 inhibitors, lithium and SB216763, attenuated caspase-3 activation and PARP cleavage induced by arsenite treatment indicating that GSK3 contributed to arsenite-induced apoptosis. Apoptotic signaling following exposure to arsenite involved cytochrome C release from mitochondria, and this was reduced by inhibition of GSK3 indicating that GSK3 promotes arsenite-induced apoptotic signaling upstream of mitochondrial disruption. Moreover, arsenite induced the translocation of Bax and p53 to the mitochondria and the activation-associated oligomerization of Bax, and these crucial events were reduced by inhibition of GSK3, indicating that GSK3 promotes arsenite-induced apoptosis by facilitating signals leading to mitochondrial apoptotic events. Taken together, the findings from this study reveal that GSK3 promotes arsenite-induced apoptosis by facilitating signaling leading to disruption of mitochondria.
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PMID:GSK3 promotes arsenite-induced apoptosis via facilitation of mitochondria disruption. 1784 3

We describe here the cloning and characterization of a novel mouse homeodomain-interacting protein kinase (HIPK)-like gene, Hipk4. Hipk4 is expressed in lung and in white adipose tissue and encodes a 616 amino acid protein that includes a serine/threonine kinase domain. We demonstrate that HIPK4 could phosphorylate human p53 protein at serine 9, both in vitro and in vivo. Among known p53-responsive promoters, activity of the human survivin promoter, which is repressed by p53, was decreased by HIPK4 in p53 functional A549 cells. Human BCL2-associated X protein-promoter activity was not affected. These findings suggest that phosphorylation of p53 at serine 9 is important for p53 mediated transcriptional repression.
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PMID:Novel homeodomain-interacting protein kinase family member, HIPK4, phosphorylates human p53 at serine 9. 1802 93

Primordial germ cells (PGCs) are embryonic germ cell precursors. Although the developmental potency of PGCs is restricted to the germ lineage, PGCs can acquire pluripotency, as verified by the in vitro establishment of embryonic germ (EG) cells and the in vivo production of testicular teratomas. PGC-specific inactivation of PTEN, which is a lipid phosphatase antagonizing phosphoinositide-3 kinase (PI3K), enhances both EG cell production and testicular teratoma formation. Here, we analyzed the effect of the serine/threonine kinase AKT, one of the major downstream effectors of PI3K, on the developmental potency of PGCs. We used transgenic mice that expressed an AKT-MER fusion protein, the kinase activity of which could be regulated by the ligand of modified estrogen receptor (MER), 4-hydroxytamoxifen. We found that hyperactivation of AKT signaling in PGCs at the proliferative phase dramatically augmented the efficiency of EG cell establishment. Furthermore, AKT signaling activation substituted to some extent for the effects of bFGF, an essential growth factor for EG cell establishment. By contrast, AKT activation had no effect on germ cells that were in mitotic arrest or that began meiosis at a later embryonic stage. In the transgenic PGCs, AKT activation induced phosphorylation of GSK3, which inhibits its kinase activity; enhanced the stability and nuclear localization of MDM2; and suppressed p53 phosphorylation, which is required for its activation. The p53 deficiency, but not GSK3 inhibition, recapitulated the effects of AKT hyperactivation on EG cell derivation, suggesting that p53 is one of the crucial downstream targets of the PI3K/AKT signal and that GSK3 is not.
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PMID:AKT signaling promotes derivation of embryonic germ cells from primordial germ cells. 1821 73

The critical tumor suppressor p53 is mutated or functionally inactivated in nearly all cancers. We have shown previously that the MDM2-MDMX complex functions as an integral unit in targeting p53 for degradation. Here we identify the small protein 14-3-3 as a binding partner of MDMX, which binds at the C terminus (Ser367) in a phosphorylation-dependent manner. Importantly, we demonstrate that the serine/threonine kinase Akt mediates phosphorylation of MDMX at Ser367. This phosphorylation leads to stabilization of MDMX and consequent stabilization of MDM2. Previous studies have shown that Akt phosphorylates and stabilizes MDM2. Our data suggest that stabilization of MDMX by Akt may be an alternative mechanism by which Akt up-regulates MDM2 protein levels and exerts its oncogenic effects on p53 in tumor cells.
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PMID:Phosphorylation of MDMX mediated by Akt leads to stabilization and induces 14-3-3 binding. 1835 62

Cdc7 is a conserved serine/threonine kinase essential for the initiation of DNA replication, likely by activating the MCM DNA helicase at the G(1-) to S-phase transition. Cdc7 kinase activity requires association with its regulatory subunit Dbf4/activator of S-phase kinase. Cdc7-Dbf4 is also downstream of the conserved Ataxia telangectasia and RAD3-related kinase that responds to stalled replication forks or DNA damage. In this study, we found that Cdc7 protein was very low or undetectable in normal tissues and cell lines but had increased expression in approximately 50% of the 62 human tumor cell lines we examined. Most cell lines with increased Cdc7 protein levels also had increased Dbf4 abundance, and some tumor cell lines had extra copies of the DBF4 gene. A high expression of Cdc7 protein was also detected in primary breast, colon, and lung tumors but not in the matched normal tissues. We also found a high correlation between p53 loss and increased CDC7 and DBF4 expression in primary breast cancers (P = 3.6 x 10(-9) and 1.8 x 10(-10), respectively) and in the cancer cell lines we studied. Therefore, increased Cdc7-Dbf4 abundance may be a common occurrence in human malignancies.
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PMID:Cdc7-Dbf4 kinase overexpression in multiple cancers and tumor cell lines is correlated with p53 inactivation. 1871 92


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