scholarly journals Amyloid-ß promotes neurotoxicity by Cdk5-induced p53 stabilization

2018 ◽  
Author(s):  
Rebeca Lapresa ◽  
Jesús Agulla ◽  
Irene Sánchez-Morán ◽  
Juan P. Bolaños ◽  
Angeles Almeida
Keyword(s):  
Neuronal Apoptosis ◽  
Therapeutic Strategy ◽  
Neuronal Damage ◽  
P53 Protein ◽  
Protein A ◽  
Tumor Suppressor Protein ◽  
Protein Accumulation ◽  
Brain Areas ◽  
P53 Tumor Suppressor Protein

ABSTRACTThe p53 tumor suppressor protein, a key regulator of cell apoptosis, has been described to accumulate in affected brain areas from Alzheimer’s disease (AD) patients. However, whether p53 plays any role in AD pathogenesis remains unknown. Here, we found that exposure of neurons to oligomers of the amyloidogenic fragment 25-35 of the Aß peptide (Aβ25-35) activated Cdk5, which promoted p53 protein phosphorylation and stabilization. Moreover, Aβ25-35-mediated mitochondrial dysfunction and neuronal apoptosis were prevented by both genetic and pharmacological inhibition of either p53 or Cdk5 activities. To confirm this mechanism in vivo, Aβ25-35 was stereotaxically injected in the cerebral right ventricle of mice, a treatment that caused p53 protein accumulation, dendrite disruption and neuronal death. Furthermore, these effects were prevented in p53 knockout mice or by pharmacologically inhibiting p53. Thus, Aβ25-35 triggers Cdk5 activation to induce p53 phosphorylation and stabilization, which leads to neuronal damage. Inhibition of the Cdk5-p53 pathway may therefore represent a novel therapeutic strategy against Aβ-induced neurodegeneration.

scholarly journals mdm2 Is Critical for Inhibition of p53 during Lymphopoiesis and the Response to Ionizing Irradiation

2003 ◽  
Vol 23 (2) ◽  
pp. 462-472 ◽  
Author(s):  
Susan M. Mendrysa ◽  
Matthew K. McElwee ◽  
Jennifer Michalowski ◽  
Kathleen A. O'Leary ◽  
Karen M. Young ◽  
...  
Keyword(s):  
Transcriptional Activation ◽  
Cultured Cells ◽  
P53 Protein ◽  
Cancer Therapies ◽  
Ionizing Irradiation ◽  
Transcriptional Activation Domain ◽  
Hypomorphic Allele ◽  
P53 Activation ◽  
P53 Tumor Suppressor Protein

ABSTRACT The function of the p53 tumor suppressor protein must be highly regulated because p53 can cause cell death and prevent tumorigenesis. In cultured cells, the p90MDM2 protein blocks the transcriptional activation domain of p53 and also stimulates the degradation of p53. Here we provide the first conclusive demonstration that p90MDM2 constitutively regulates p53 activity in homeostatic tissues. Mice with a hypomorphic allele of mdm2 revealed a heretofore unknown role for mdm2 in lymphopoiesis and epithelial cell survival. Phenotypic analyses revealed that both the transcriptional activation and apoptotic functions of p53 were increased in these mice. However, the level of p53 protein was not coordinately increased, suggesting that p90MDM2 can inhibit the transcriptional activation and apoptotic functions of p53 in a manner independent of degradation. Cre-mediated deletion of mdm2 caused a greater accumulation of p53, demonstrating that p90MDM2 constitutively regulates both the activity and the level of p53 in homeostatic tissues. The observation that only a subset of tissues with activated p53 underwent apoptosis indicates that factors other than p90MDM2 determine the physiological consequences of p53 activation. Furthermore, reduction of mdm2 in vivo resulted in radiosensitivity, highlighting the importance of mdm2 as a potential target for adjuvant cancer therapies.

Coupling between gamma irradiation, p53 induction and the apoptotic response depends upon cell type in vivo

1995 ◽  
Vol 108 (5) ◽  
pp. 1843-1848 ◽  
Author(s):  
C.A. Midgley ◽  
B. Owens ◽  
C.V. Briscoe ◽  
D.B. Thomas ◽  
D.P. Lane ◽  
...  
Keyword(s):  
P53 Protein ◽  
Whole Body ◽  
Protein Accumulation ◽  
Cell Type ◽  
Apoptotic Response ◽  
Adult Mice ◽  
Specific Manner ◽  
Massive Apoptosis

The accumulation of p53 protein following whole body irradiation of adult mice was studied using a new polyclonal antibody to mouse p53. While dramatic accumulation of the protein was apparent in splenocytes, thymocytes and osteocytes no p53 protein accumulation was detected in the hepatocytes of the irradiated mouse. Thus, the upstream initiating signals that control the induction of p53 are controlled in a tissue specific manner. While massive apoptosis accompanies p53 induction in thymocytes and splenocytes it is not seen in the osteocytes. Thus the downstream consequences of p53 induction are also tightly controlled. These results have profound significance for an understanding of the role of the p53 tumour suppression pathway in different tissues.

scholarly journals The Sequence Alteration Associated with a Mutational Hotspot in p53 Protects Cells From Lysis by Cytotoxic T Lymphocytes Specific for a Flanking Peptide Epitope

1998 ◽  
Vol 188 (6) ◽  
pp. 1017-1028 ◽  
Author(s):  
Matthias Theobald ◽  
Thomas Ruppert ◽  
Ulrike Kuckelkorn ◽  
Javier Hernandez ◽  
Annett Häussler ◽  
...  
Keyword(s):  
T Lymphocytes ◽  
Cytotoxic T Lymphocytes ◽  
P53 Protein ◽  
Protein A ◽  
Immune Surveillance ◽  
Amino Acid Position ◽  
Peptide Epitope ◽  
Precursor Peptide ◽  
Putative Precursor

A high proportion of tumors arise due to mutation of the p53 tumor suppressor protein. A p53 hotspot mutation at amino acid position 273 from R to H, flanking a peptide epitope that spans residues 264–272, renders cells resistant to killing by human histocompatibility leukocyte antigen (HLA)-A*0201–restricted cytotoxic T lymphocytes (CTLs) specific for this epitope. Acquisition of the R to H mutation at residue 273 of the human p53 protein promotes tumor growth in vivo by selective escape from recognition by p53.264–272 peptide-specific CTLs. Synthetic 27-mer p53 polypeptides covering the antigenic nonamer region 264–272 of p53 were used as proteasome substrates to investigate whether the R to H mutation at the P1′ position of the COOH terminus of the epitope affects proteasome-mediated processing of the protein. Analysis of the generated products by tandem mass spectrometry and the kinetics of polypeptide processing in conjunction with CTL assays demonstrate that the R to H mutation alters proteasomal processing of the p53 protein by inhibiting proteolytic cleavage between residues 272 and 273. This prevents the release of the natural CTL epitope that spans flanking residues 264–272 as well as a putative precursor peptide. These results demonstrate that mutation of p53 not only leads to malignant transformation but may also, in some instances, affect immune surveillance and should be considered in the design of cancer vaccines.

scholarly journals The p53 Tumor Suppressor Protein Does Not Regulate Expression of Its Own Inhibitor, MDM2, Except under Conditions of Stress

2000 ◽  
Vol 20 (6) ◽  
pp. 2023-2030 ◽  
Author(s):  
Susan M. Mendrysa ◽  
Mary Ellen Perry
Keyword(s):  
Tumor Suppressor ◽  
Mouse Embryo ◽  
Cultured Cells ◽  
Tumor Suppressor Protein ◽  
Dependent Manner ◽  
P53 Tumor Suppressor ◽  
Mouse Embryo Fibroblasts ◽  
Embryo Fibroblasts ◽  
P53 Tumor Suppressor Protein

ABSTRACT MDM2 is an important regulator of the p53 tumor suppressor protein. MDM2 inhibits p53 by binding to it, physically blocking its ability to transactivate gene expression, and stimulating its degradation. In cultured cells, mdm2 expression can be regulated by p53. Hence, mdm2 and p53 can interact to form an autoregulatory loop in which p53 activates expression of its own inhibitor. The p53/MDM2 autoregulatory loop has been elucidated within cultured cells; however, regulation of mdm2 expression by p53 has not been demonstrated within intact tissues. Here, we examine the role of p53 in regulating mdm2 expression in vivo in order to test the hypothesis that the p53/MDM2 autoregulatory loop is the mechanism by which low levels of p53 are maintained. We demonstrate that basal expression of mdm2 in murine tissues is p53 independent, even in tissues that express functional p53. Transcription ofmdm2 is induced in a p53-dependent manner following gamma irradiation, indicating that p53 regulates mdm2 expression in vivo following a stimulus. The requirement for a stimulus to activate p53-dependent regulation of mdm2 expression in vivo appeared to differ from the situation in early-passage mouse embryo fibroblasts, where mdm2 expression is enhanced by the presence of p53. Analysis of mdm2 expression in intact and dispersed embryos revealed that establishment of mouse embryo fibroblasts in culture induces p53-dependent mdm2expression, suggesting that an unknown stimulus activates p53 function in cultured cells. Together, these results indicate that p53 does not regulate expression of its own inhibitor, except in response to stimuli.

scholarly journals MDM2 Is Required for Suppression of Apoptosis by Activated Akt1 in Salivary Acinar Cells

2006 ◽  
Vol 26 (23) ◽  
pp. 8840-8856 ◽  
Author(s):  
Kirsten H. Limesand ◽  
Kathryn L. Schwertfeger ◽  
Steven M. Anderson
Keyword(s):  
Transgenic Mice ◽  
Gamma Irradiation ◽  
Salivary Glands ◽  
P53 Protein ◽  
Acinar Cells ◽  
Dominant Negative ◽  
Common Side Effect ◽  
Protein Accumulation ◽  
Irreversible Damage

ABSTRACT Chronic damage to the salivary glands is a common side effect following head and neck irradiation. It is hypothesized that irreversible damage to the salivary glands occurs immediately after radiation; however, previous studies with rat models have not shown a causal role for apoptosis in radiation-induced injury. We report that etoposide and gamma irradiation induce apoptosis of salivary acinar cells from FVB control mice in vitro and in vivo; however, apoptosis is reduced in transgenic mice expressing a constitutively activated mutant of Akt1 (myr-Akt1). Expression of myr-Akt1 in the salivary glands results in a significant reduction in phosphorylation of p53 at serine18, total p53 protein accumulation, and p21WAF1 or Bax mRNA following etoposide or gamma irradiation of primary salivary acinar cells. The reduced level of p53 protein in myr-Akt1 salivary glands corresponds with an increase in MDM2 phosphorylation in vivo, suggesting that the Akt/MDM2/p53 pathway is responsible for suppression of apoptosis. Dominant-negative Akt blocked phosphorylation of MDM2 in salivary acinar cells from myr-Akt1 transgenic mice. Reduction of MDM2 levels in myr-Akt1 primary salivary acinar cells with small interfering RNA increases the levels of p53 protein and renders these cells susceptible to etoposide-induced apoptosis in spite of the presence of activated Akt1. These results indicate that MDM2 is a critical substrate of activated Akt1 in the suppression of p53-dependent apoptosis in vivo.

scholarly journals Proteolytic cleavage of human p53 by calpain: a potential regulator of protein stability.

1997 ◽  
Vol 17 (1) ◽  
pp. 460-468 ◽  
Author(s):  
M H Kubbutat ◽  
K H Vousden
Keyword(s):  
Dna Damage ◽  
P53 Protein ◽  
Calpain Inhibitor ◽  
Cycle Arrest ◽  
A Cell ◽  
P53 Tumor Suppressor Protein ◽  
E6 Protein ◽  
Protein Treatment

The p53 tumor suppressor protein is activated in cells in response to DNA damage and prevents the replication of cells sustaining genetic damage by inducing a cell cycle arrest or apoptosis. Activation of p53 is accompanied by stabilization of the protein, resulting in accumulation to high levels within the cell. p53 is normally degraded through the proteasome following ubiquitination, although the mechanisms which regulate this proteolysis in normal cells and how the p53 protein becomes stabilized following DNA damage are not well understood. We show here that p53 can also be a substrate for cleavage by the calcium-activated neutral protease, calpain, and that a preferential site for calpain cleavage exists within the N terminus of the p53 protein. Treatment of cells expressing wild-type p53 with an inhibitor of calpain resulted in the stabilization of the p53 protein. By contrast, in vitro or in vivo degradation mediated by human papillomavirus E6 protein was unaffected by the calpain inhibitor, indicating that the stabilization did not result from inhibition of the proteasome. These results suggest that calpain cleavage plays a role in regulating p53 stability.

scholarly journals Regulation of Mdm2-Directed Degradation by the C Terminus of p53

1998 ◽  
Vol 18 (10) ◽  
pp. 5690-5698 ◽  
Author(s):  
Michael H. G. Kubbutat ◽  
Robert L. Ludwig ◽  
Margaret Ashcroft ◽  
Karen H. Vousden
Keyword(s):  
P53 Protein ◽  
Regulatory Elements ◽  
Binding Domain ◽  
Tumor Suppressor Protein ◽  
C Terminus ◽  
The Stability ◽  
P53 Tumor Suppressor Protein ◽  
Inducible Gene ◽  
Oligomerization Domain

ABSTRACT The stability of the p53 tumor suppressor protein is regulated by interaction with Mdm2, the product of a p53-inducible gene. Mdm2-targeted degradation of p53 depends on the interaction between the two proteins and is mediated by the proteasome. We show here that in addition to the N-terminal Mdm2 binding domain, the C terminus of p53 participates in the ability of p53 to be degraded by Mdm2. In contrast, alterations in the central DNA binding domain of p53, which change the conformation of the p53 protein, do not abrogate the sensitivity of the protein to Mdm2-mediated degradation. The importance of the C-terminal oligomerization domain to Mdm2-targeted degradation of p53 is likely to reflect the importance of oligomerization of the full-length p53 protein for interaction with Mdm2, as previously shown in vitro. Interestingly, the extreme C-terminal region of p53, outside the oligomerization domain, was also shown to be necessary for efficient degradation, and deletion of this region stabilized the protein without abrogating its ability to bind to Mdm2. Mdm2-resistant p53 mutants were not further stabilized following DNA damage, supporting a role for Mdm2 as the principal regulator of p53 stability in cells. The extreme C terminus of the p53 protein has previously been shown to contain several regulatory elements, raising the possibility that either allosteric regulation of p53 by this domain or interaction between this region and a third protein plays a role in determining the sensitivity of p53 to Mdm2-directed degradation.

scholarly journals Ginsenoside Rb1 Protects the Brain from Damage Induced by Epileptic Seizure via Nrf2/ARE Signaling

2018 ◽  
Vol 45 (1) ◽  
pp. 212-225 ◽  
Author(s):  
Yunbo Shi ◽  
Wang Miao ◽  
Junfang Teng ◽  
Lingli Zhang
Keyword(s):  
Neuronal Apoptosis ◽  
Neuronal Damage ◽  
Dependent Manner ◽  
Ginsenoside Rb1 ◽  
Seizure Duration ◽  
Neuroprotective Effects ◽  
Induced Neuron ◽  
Neuron Injury

Background/Aims: Ginsenoside Rb1 (Rb1) has been reported to have varieties of neuroprotective effects. This study aimed to evaluate the effects of Rb1 on pentylenetetrazol (PTZ)-induced rat brain injury and Mg2+ free-induced neuron injury and analyzed the detailed molecular mechanisms in vivo and in vitro. Methods: Seizure duration and latency were measured in epilepsy kindled rat. The cognitive impairment was assessed by Morris water maze (MWM) test. Oxidative stress parameters, malondialdehyde (MDA) and glutathione (GSH) were measured by the 2-thiobarbituric acid methods and the DTNB-GSSG reductase recycling methods. Neuronal damage was assessed by hematoxylin and eosin (H&E) and Nissl staining. Neuronal apoptosis was measured by Annexin V-FITC and propidium iodide (PI) staining. Immunohistochemistry and immunofluorescence staining were performed to evaluate Nrf2 and HO-1 expressions. Expression of Nrf2, HO-1, Bcl-2, iNOS and LC3 were evaluated by western blot. Results: The PTZ-injured rats presented longer seizure duration and shorter seizure latency. Rb1 ameliorated these effects, as well as the cognitive deficits caused by PTZ exposure. Besides, Rb1 dose-dependently increased GSH levels, decreased MDA levels and alleviated neuronal damage in PTZ-treated rats. In vitro, Rb1 increased cell viability and decreased neuronal apoptosis in a dose-dependent manner under Mg2+ free condition. Moreover, in vivo and in vitro, Rb1 enhanced both the Nrf2 and HO-1 expressions. Furthermore, upregulation of the expression of Bcl-2 and downregulation of the expression of iNOS and LC3 were observed. However, knockdown of Nrf2 adversely affected the protective effects of Rb1 in epileptic hippocampal neurons. Conclusion: Rb1 conferred neuroprotective effects against PTZ-induced brain damage and Mg2+ free-induced neuron injury by activating Nrf2/ARE signaling.

scholarly journals Increased tumor proliferation and genomic instability without decreased apoptosis in MMTV-ras mice deficient in p53.

1997 ◽  
Vol 17 (2) ◽  
pp. 723-731 ◽  
Author(s):  
J E Hundley ◽  
S K Koester ◽  
D A Troyer ◽  
S G Hilsenbeck ◽  
M A Subler ◽  
...  
Keyword(s):  
Genomic Instability ◽  
Growth Rates ◽  
Cell Cycle Regulation ◽  
Tumor Model ◽  
Tumor Suppressor Protein ◽  
Tumor Proliferation ◽  
Specific Context ◽  
Cycle Regulation ◽  
P53 Tumor Suppressor Protein

We have used an in vivo tumor model to evaluate the consequences of p53 tumor suppressor protein deficiency in a tissue-specific context. By breeding MMTV-ras transgenic mice, which are highly susceptible to the development of mammary and salivary tumors, with p53(-/-) mice, we generated three classes of animals which contained the MMTV-ras transgene but differed in their p53 functional status (ras/p53(+/+), ras/p53(+/-), or ras/p53(-/-)). ras/p53(-/-) mice developed tumors more rapidly than animals of the other two genotypes; however, the distribution of tumors was unexpectedly altered. Whereas the most frequently observed tumors in ras/p53(+/+) and ras/p53(+/-) mice were of mammary origin, ras/p53(-/-) mice developed primarily salivary tumors. In addition, the mammary and salivary tumors from ras/p53(-/-) mice consistently exhibited a number of unfavorable characteristics, including higher histologic grades, increased growth rates, and extensive genomic instability and heterogeneity, relative to tumors from ras/p53(+/+) mice. Interestingly, the increased growth rates of ras/p53(-/-) tumors appear to be due to impaired cell cycle regulation rather than decreased apoptosis, suggesting that p53-mediated tumor suppression can occur independent of its role in apoptosis.

scholarly journals Glycogen Synthase Kinase 3-Dependent Phosphorylation of Mdm2 Regulates p53 Abundance

2005 ◽  
Vol 25 (16) ◽  
pp. 7170-7180 ◽  
Author(s):  
Roman Kulikov ◽  
Karen A. Boehme ◽  
Christine Blattner
Keyword(s):  
Glycogen Synthase ◽  
Glycogen Synthase Kinase ◽  
Tumor Suppressor Protein ◽  
Glycogen Synthase Kinase 3 ◽  
Dependent Manner ◽  
Mdm2 Protein ◽  
Conserved Domain ◽  
P53 Tumor Suppressor Protein

ABSTRACT The Mdm2 oncoprotein regulates abundance and activity of the p53 tumor suppressor protein. For efficient degradation of p53, Mdm2 needs to be phosphorylated at several contiguous residues within the central conserved domain. We show that glycogen synthase kinase 3 (GSK-3) phosphorylated the Mdm2 protein in vitro and in vivo in the central domain. Inhibition of GSK-3 rescued p53 from degradation in an Mdm2-dependent manner while its association with Mdm2 was not affected. Likewise, inhibition of GSK-3 did not alter localization of p53 and Mdm2 or the interaction of Mdm2 and MdmX. Ionizing radiation, which leads to p53 accumulation, directed phosphorylation of GSK-3 at serine 9, which preceded and overlapped with the increase in p53 levels. Moreover, expression of a GSK-3 mutant where serine 9 was replaced with an alanine reduced the accumulation of p53 and induction of its target p21WAF-1. We therefore conclude that inhibition of GSK-3 contributes to hypophosphorylation of Mdm2 in response to ionizing rays, and in consequence to p53 stabilization.

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