Acetylation ; Animals ; Humans ; Phosphorylation ; Tumor Suppressor Protein p53 ; chemistry ; genetics ; metabolism ; physiology

Microcystin is one of the monocyclic heptapeptides produced primarily by microcystis aeruginosa. Recent studies suggest that microcystin can induce cell apoptosis, as well as oxidative stress and mitochondrial alteration. Studies also indicate that Bcl-2 family and p53 may play an important role in the apoptosis induced by microcystin.
Animals ; Apoptosis ; physiology ; Humans ; Microcystins ; toxicity ; Microcystis ; metabolism ; Proto-Oncogene Proteins c-bcl-2 ; metabolism ; Tumor Suppressor Protein p53 ; metabolism

p53, as a transcription factor, is an important tumor suppressor gene and plays the key role in the p53-dependent gene regulatory network. Therefore, it is important to understand its biological function at the level of the whole system. In this paper, based on KEGG database and related literatures in English and Chinese, the interaction mode and quantitative relationship of the related molecules involved in p53 signaling pathway were extracted. By using S-system equations and 'Simulink' toolbox of Matlab7.0, a dynamic model of p53 signaling pathway was developed, and the dynamic regulatory characteristics of p53 signaling pathway were analyzed on model simulation. The results were in accord with the literatures and could reflect quantitatively the complex regulatory relationship between the interacting molecules involved in p53 signaling pathway. In addition, model simulation helped us find and identify the key molecules in this signaling pathway. Thus, this model can be used as a basis for the follow-up study of the relationship by precise and quantitative assessment.
Algorithms ; Computer Simulation ; Gene Expression Regulation ; Humans ; Models, Biological ; Signal Transduction ; physiology ; Transcription Factors ; genetics ; metabolism ; Tumor Suppressor Protein p53 ; genetics ; physiology

Cellular senescence is a tumor-suppressive process instigated by proliferation in the absence of telomere replication, by cellular stresses such as oncogene activation, or by activation of the tumor suppressor proteins, such as Rb or p53. This process is characterized by an irreversible cell cycle exit, a unique morphology, and expression of senescence-associated-beta-galactosidase (SA-beta-gal). Despite the potential biological importance of cellular senescence, little is known of the mechanisms leading to the senescent phenotype. p41-Arc has been known to be a putative regulatory component of the mammalian Arp2/3 complex, which is required for the formation of branched networks of actin filaments at the cell cortex. In this study, we demonstrate that p41-Arc can induce senescent phenotypes when it is overexpressed in human tumor cell line, SaOs-2, which is deficient in p53 and Rb tumor suppressor genes, implying that p41 can induce senescence in a p53-independent way. p41-Arc overexpression causes a change in actin filaments, accumulating actin filaments in nuclei. Therefore, these results imply that a change in actin filament can trigger an intrinsic senescence program in the absence of p53 and Rb tumor suppressor genes.
Actin Cytoskeleton/metabolism ; Actin-Related Protein 2-3 Complex/*metabolism ; *Cell Aging ; Cell Cycle Proteins/metabolism ; Cell Line, Tumor ; Cell Nucleus/metabolism ; Fibroblasts/physiology ; Humans ; Recombinant Proteins/genetics/*metabolism ; Retinoblastoma Protein/*deficiency/genetics ; Tumor Suppressor Protein p53/*deficiency/genetics

Silent information regulator factor 2-related enzyme 1 (Sirtuins 1, SIRT1) is a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, which can deacetylate histone and non-histone proteins and other transcription factors, and is involved in the regulation of many physiological functions, including gene transcription, energy metabolism, cell senescence and oxidative stress. Recent studies show that through adjusting the activity of endothelial nitric oxide syntheses (eNOS), p53, forkhead box class O (FOXO) and nuclear factor kappa B (NF-kappaB), SIRT1 can protect the functions of vascular endothelia and nerves in a variety of pathological conditions. Therefore, SIRT1 may be used as a potential therapeutic target of these diseases, particularly erectile dysfunction, which are associated with endothelial dysfunction.
Endothelium, Vascular ; physiology ; Erectile Dysfunction ; Forkhead Box Protein O1 ; Forkhead Transcription Factors ; metabolism ; Humans ; Male ; NAD ; metabolism ; NF-kappa B ; metabolism ; Nitric Oxide Synthase Type III ; metabolism ; Oxidative Stress ; Sirtuin 1 ; physiology ; Tumor Suppressor Protein p53 ; metabolism

OBJECTIVETo study the inhibition effect of HCV NS5A on p53 protein transactivity and its possible mechanism.

METHODSLuciferase reporter gene system was used for the study of p53 transactivity on p21 promoter and electrophorectic mobility-shift assay (EMSA) was applied to observe whether HCV NS5A could suppress the binding ability of p53 protein to its specific DNA sequence.

RESULTSEndogenous p53 protein could stimulate p21 promoter activity, and the relative luciferase activity increased significantly (3.49 x 10(5) vs 0.60 x 10(5), t = 5.92, P<0.01). Exogenous p53 protein also up-regulated p21 promoter driving luciferase expression, comparing to the control group (0.47 x 10(5)), the relative luciferase activity increased (5.63 x 10(5)) obviously (t = 10.12, P<0.01). HCV NS5A protein inhibited both endogenous and exogenous p53 transactivity on p21 promoter in a dose-dependent manner (F > or = 20.71, P<0.01). In the experiment of EMSA, p53 could bind to its specific DNA sequence, but when co-transfected with HCV NS5A expressing vector, the p53 binding affinity to its DNA decreased.

CONCLUSIONHCV NS5A can inhibit p53 protein transactivity on p21 promoter through its inhibiting of p53 binding ability to the specific DNA sequence.

Hepacivirus ; genetics ; Humans ; Promoter Regions, Genetic ; Transcriptional Activation ; drug effects ; Tumor Suppressor Protein p53 ; drug effects ; genetics ; metabolism ; physiology ; Viral Core Proteins ; genetics ; Viral Nonstructural Proteins ; genetics ; pharmacology

Cellular senescence is an irreversible cell cycle arrest triggered by the activation of oncogenes or mitogenic signaling as well as the enforced expression of tumor suppressors such as p53, p16(INK4A) and promyelocytic leukemia protein (PML) in normal cells. E2F-binding protein 1 (E2FBP1), a transcription regulator for E2F, induces PML reduction and suppresses the formation of PML-nuclear bodies, whereas the down-regulation of E2FBP1 provokes the PML-dependent premature senescence in human normal fibroblasts. Here we report that the depletion of E2FBP1 induces the accumulation of PML through the Ras-dependent activation of MAP kinase signaling. The cellular levels of p16(INK4A) and p53 are elevated during premature senescence induced by depletion of E2FBP1, and the depletion of p16(INK4A), but not p53 rescued senescent cells from growth arrest. Therefore, the premature senescence induced by E2FBP1 depletion is achieved through the p16(INK4A)-Rb pathway. Similar to human normal fibroblasts, the growth inhibition induced by E2FBP1 depletion is also observed in human tumor cells with intact p16(INK4A) and Rb. These results suggest that E2FBP1 functions as a critical antagonist to the p16(INK4A)-Rb tumor suppressor machinery by regulating PML stability.
Cell Line, Tumor ; Cells, Cultured ; Cellular Senescence ; genetics ; physiology ; Cyclin-Dependent Kinase Inhibitor p16 ; antagonists & inhibitors ; genetics ; physiology ; DNA-Binding Proteins ; deficiency ; genetics ; physiology ; Down-Regulation ; Fibroblasts ; Gene Expression Regulation ; Humans ; Intranuclear Inclusion Bodies ; metabolism ; MAP Kinase Signaling System ; Nuclear Proteins ; genetics ; metabolism ; physiology ; Promyelocytic Leukemia Protein ; Protein Isoforms ; Protein Stability ; RNA Interference ; Retinoblastoma Protein ; antagonists & inhibitors ; genetics ; physiology ; Transcription Factors ; deficiency ; genetics ; metabolism ; physiology ; Transfection ; Tumor Suppressor Protein p53 ; physiology ; Tumor Suppressor Proteins ; genetics ; metabolism ; physiology ; Ubiquitination ; ras Proteins ; metabolism

In multiple types of acute leukemia,a portion of the MLL protein is fused to a variety of other unrelated proteins. The activity of leukemic MLL fusions is believed to be directly contributing to the conversion of normal bone marrow cells into leukemic cancer cells. However, the mechanism of this process has not been fully elucidated. We have recently found that the MLL leukemic fusions can abolish the activity of P53 tumor suppressor protein that actively guards against the appearance of cancer by instructing damaged cells to self-destruct. In contrast to the vast majority of cancers where p53 gene is mutated, very few p53 mutations have been found in leukemias. Our findings suggest that leukemic fusions contribute to disease progression, at least in part, by suppressing the function of P53, which,if proven,may present a novel opportunity to re-activating the P53 pathway in leukemic cells thereby identifying a rational therapeutic approach for managing leukemias where MLL fusions are detected.
Chromosomes, Human, Pair 11 ; genetics ; Histone-Lysine N-Methyltransferase ; Humans ; Leukemia ; etiology ; genetics ; Myeloid-Lymphoid Leukemia Protein ; genetics ; metabolism ; physiology ; Oncogene Proteins, Fusion ; metabolism ; physiology ; Tumor Suppressor Protein p53 ; genetics ; physiology

A terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay was used to determine that apoptosis causes HeLa cell death induced by pseudolaric acid B. The c-Jun N-terminal kinase (JNK) inhibitor SP600125 decreased p53 protein expression during exposure to pseudolaric acid B. SP600125 decreased the phosphorylation of p53 during pseudolaric acid B exposure, indicating that JNK mediates phosphorylation of p53 during the response to pseudolaric acid B. SP600125 reversed pseudolaric acid B-induced down-regulation of phosphorylated extracellular signal-regulated protein kinase (ERK), and protein kinase C (PKC) was activated by pseudolaric acid B, whereas staurosporine, calphostin C, and H7 partly blocked this effect. These results indicate that p53 is partially regulated by JNK in pseudolaric acid B-induced HeLa cell death and that PKC participates in pseudolaric acid B-induced HeLa cell death.
Tumor Suppressor Protein p53/metabolism/*physiology ; Protein Kinase C/metabolism ; Phosphorylation ; JNK Mitogen-Activated Protein Kinases/*physiology ; Humans ; Hela Cells ; Diterpenes/*pharmacology ; DNA Fragmentation/drug effects ; Cell Death/*drug effects ; Anthracenes/pharmacology

OBJECTIVETo observe the localization of p53(301-393)(residues 301-393) in p53 positive/negative cells and its effect on cell mitosis.

METHODSThe protein expression of p53-GFP and p53(301-393)-GFP was checked by immunoblotting after transfection. Immunofluorescence staining was performed to detect the localization of wide type and mutant in Hela cells (p53 positive) and H1299 cells (p53 negative). The cell morphology of H1299 cells transfected of p53(301-393)-GFP and the cells in mitotic phase were observed. Cell cycle was analyzed by flow cytometry and p53 protein level in HeLa cells was evaluated by Western blot after transfection of p53-GFP and p53(301-393)-GFP.

RESULTSThe protein expression of p53-GFP and p53(301-393)-GFP was verified, p53-GFP was about 90 kMr and p53(301-393)-GFP about 40 kMr. Immunofluorescence microscopy demonstrated that both proteins were diffusely located in the nuclei of HeLa cells and H1299 cells. But different from the p53-GFP, the p53(301-393)-GFP was distributed in the nucleolus of HeLa cells. After transfection of the two plasmids, mitosis was inhibited in H1299 cells and some cells underwent apoptosis. G2/M progression of HeLa cells could be blocked by transfection of p53(301-393)-GFP, but endogenous p53 protein level was not changed.

CONCLUSIONp53(301-393)has a different localization in the p53 positive and p53 negative cells and could inhibit mitosis and cause the cell cycle arrest in G2/M.

Green Fluorescent Proteins ; genetics ; metabolism ; HeLa Cells ; Humans ; Immunoblotting ; Microscopy, Fluorescence ; Mitosis ; genetics ; physiology ; Mutant Proteins ; metabolism ; physiology ; Mutation ; Recombinant Fusion Proteins ; genetics ; metabolism ; Transfection ; Tumor Suppressor Protein p53 ; genetics ; metabolism ; physiology