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Szelachowska J, Dziegiel P, Tarkowski R, Gomulkiewicz A, Bebenek M, Halon A, Fortuna K, Wojnar A, Kornafel J, Matkowski R. Therapeutic radiation induces different changes in expression profiles of metallothionein (MT) mRNA, MT protein, Ki 67 and minichromosome maintenance protein 3 in human rectal adenocarcinoma. Anticancer Res 2012; 32:5291-5297. [PMID: 23225429] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
AIM The study aimed at the evaluation of the effects of radiotherapy on expression of metallothionein (MT) isoforms, both in the form of quantitative alterations in mRNA, and differences in expression of MTI/II proteins in rectal tumours. MATERIALS AND METHODS Material for the study originated from 21 patients with rectal cancer at stage II or III. Material for immunohistochemical studies [MTI/II, Minichromosome Maintenance Protein 3 (MCM3), Ki-67] and real-time polymerase chain reaction (PCR) (mRNA of MT1F, MT1X and MT2A) was sampled twice: during rectoscopic examination before the start of the preoperative radiotherapy (samples A) and from the post operative specimen, following radiotherapy (samples B). RESULTS The level of mRNA expression for each of the studied MT isoforms was higher in cancer cells subjected to irradiation. The most extensive differences were observed for the MT2A isoforms (p=0.09). No differences were disclosed between samples A and B in expression of MT I/II protein. The material sampled after radiotherapy manifested a tendency for reduced proliferative activity of the tumour cells: the decrease of MCM3 expression was significant (p=0.022), while in the case of Ki-67, the difference approached statistical significance (p=0.096). CONCLUSION Application of radiotherapy to rectal adenocarcinoma cells is followed by an increase in MT mRNA expression level, affecting first of all the MT2A isoform. However, we failed to note an increased expression of MTI/II protein coded by the gene. Moreover, application of radiotherapy was followed by a decrease in expression of MCM3 protein. Our results cannot clearly confirm induction of MT after irradiation of human adenocarcinoma cells. The role of MT in radioprotection remains ambiguous.
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Affiliation(s)
- Jolanta Szelachowska
- Department of Oncology, Wroclaw Medical University, Plac Hirszfelda 12, 53-413 Wroclaw, Poland.
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Delettre C, Yuste VJ, Moubarak RS, Bras M, Lesbordes-Brion JC, Petres S, Bellalou J, Susin SA. AIFsh, a novel apoptosis-inducing factor (AIF) pro-apoptotic isoform with potential pathological relevance in human cancer. J Biol Chem 2005; 281:6413-27. [PMID: 16365034 DOI: 10.1074/jbc.m509884200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
AIF is a main mediator of caspase-independent cell death. It is encoded by a single gene located on chromosome X, region q25-26 and A6 in humans and mice, respectively. Previous studies established that AIF codes for two isoforms of the protein, AIF and AIF-exB. Here, we identify a third AIF isoform resulting from an alternate transcriptional start site located at intron 9 of AIF. The resulting mRNA encodes a cytosolic protein that corresponds to the C-terminal domain of AIF (amino acids 353-613). We named this new isoform AIFshort (AIFsh). AIFsh overexpression in HeLa cells results in nuclear translocation and caspase-independent cell death. Once in the nucleus, AIFsh provokes the same effects than AIF, namely chromatin condensation and large scale (50 kb) DNA fragmentation. In contrast, these apoptogenic effects are not precluded by the AIF-inhibiting protein Hsp70. These findings identify AIFsh as a new pro-apoptotic isoform of AIF, and also reveal that the first N-terminal 352 amino acids of AIF are not required for its apoptotic activity. In addition, we demonstrate that AIFsh is strongly down-regulated in tumor cells derived from kidney, vulva, skin, thyroid, and pancreas, whereas, gamma-irradiation treatment provokes AIFsh up-regulation. Overall, our results identify a novel member of the AIF-dependent pathway and shed new light on the role of caspase-independent cell death in tumor formation/suppression.
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Affiliation(s)
- Cécile Delettre
- Apoptose et Système Immunitaire, CNRS-URA 1961 and Plateforme 5-Production de Protéines Recombinantes et d'Anticorps, Institut Pasteur, 25, rue du Dr. Roux, 75015 Paris, France
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3
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Sicora CI, Appleton SE, Brown CM, Chung J, Chandler J, Cockshutt AM, Vass I, Campbell DA. Cyanobacterial psbA families in Anabaena and Synechocystis encode trace, constitutive and UVB-induced D1 isoforms. Biochim Biophys Acta 2005; 1757:47-56. [PMID: 16388778 DOI: 10.1016/j.bbabio.2005.11.002] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2005] [Revised: 11/03/2005] [Accepted: 11/10/2005] [Indexed: 12/01/2022]
Abstract
Cyanobacteria cope with UVB induced photoinhibition of Photosystem II by regulating multiple psbA genes to boost the expression of D1 protein (in Synechocystis sp. PCC6803), or to exchange the constitutive D1:1 protein to an alternate D1:2 isoform (in Synechococcus sp. PCC7942). To define more general patterns of cyanobacterial psbA expression, we applied moderately photoinhibitory UVB to Anabaena sp. PCC7120 and tracked the expression of its five psbA genes. psbAI, encoding a D1:1 protein isoform characterized by a Gln130, represented the majority of the psbA transcript pool under control conditions. psbAI transcripts decreased upon UVB treatment but the total psbA transcript pool increased 3.5 fold within 90 min as a result of sharply increased psbAII, psbAIV and psbAIII transcripts encoding an alternate D1:2 protein isoform characterized by Glu130, similar to that of Synechococcus. Upon UVB treatment the relaxation of flash induced chlorophyll fluorescence showed a characteristic acceleration of a decay phase likely associated with the exchange from the D1:1 protein isoform encoded by psbAI to the alternate D1:2 isoform encoded by psbAIV, psbAII and psbAIII. Throughout the UVB treatment the divergent psbA0 made only a trace contribution to the total psbA transcript pool. This suggests a similarity to the divergent psbAI gene from Synechocystis, whose natural expression we demonstrate for the first time at a trace level similar to psbA0 in Anabaena. These trace-expressed psbA genes in two different cyanobacteria raise questions concerning the functions of these divergent genes.
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Affiliation(s)
- Cosmin I Sicora
- Department of Biology, Mount Allison University, Sackville, NB, Canada E4L1G7
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4
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Rohaly G, Chemnitz J, Dehde S, Nunez AM, Heukeshoven J, Deppert W, Dornreiter I. A Novel Human p53 Isoform Is an Essential Element of the ATR-Intra-S Phase Checkpoint. Cell 2005; 122:21-32. [PMID: 16009130 DOI: 10.1016/j.cell.2005.04.032] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2004] [Revised: 03/20/2005] [Accepted: 04/28/2005] [Indexed: 11/16/2022]
Abstract
The archetypal human tumor suppressor p53 is considered to have unique transactivation properties. The assumption is based on the fact that additionally identified human p53 isoforms lack transcriptional activity. However, we provide evidence for the existence of an alternatively spliced p53 isoform (Deltap53) that exerts its transcriptional activity independent from p53. In contrast to p53, Deltap53 transactivates the endogenous p21 and 14-3-3sigma but not the mdm2, bax, and PIG3 promoter. Cell cycle studies showed that Deltap53 displays its differential transcriptional activity only in damaged S phase cells. Upon activation of the ATR-intra-S phase checkpoint, Deltap53, but not p53, transactivates the Cdk inhibitor p21. Induction of p21 results in downregulation of cyclin A-Cdk activity and accordingly attenuation of S phase progression. Data demonstrate that the Deltap53-p21-cyclin A-Cdk pathway is crucial to facilitate uncoupling of repair and replication events, indicating that Deltap53 is an essential element of the ATR-intra-S phase checkpoint.
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Affiliation(s)
- Gabor Rohaly
- Heinrich-Pette-Institut für Experimentelle Virologie und Immunologie, Universität Hamburg, Martinistrasse 52, D-20251, Hamburg, Germany
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5
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Sineshchekov VA, Weller JL. Two modes of the light-induced phytochrome A decline--with and without changes in the proportion of its isoforms (phyA' and phyA''): evidence from fluorescence investigations of mutant phyA-3D pea. J Photochem Photobiol B 2004; 75:127-35. [PMID: 15341926 DOI: 10.1016/j.jphotobiol.2004.05.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2003] [Revised: 04/28/2004] [Accepted: 05/30/2004] [Indexed: 11/22/2022]
Abstract
Different modes of the phytochrome function are connected with its polymorphism, the major isoforms being phytochromes A and B (phyA and phyB). In its turn, phyA comprises two native species, phyA' and phyA'', whose precise nature and functions remain obscure. With the use of in situ fluorescence spectroscopy, we investigated their properties in a mutant of pea, phyA-3D, characterized by exaggerated photoresponses and impaired photodestruction of phyA. The mutation is a substitution of alanine by valine at the position 194 in phyA. The phyA-3DphyB and phyB mutants were also investigated. In dark-grown plants, all the lines had the content and properties of the two phyA species very similar to the wild type. However, a considerably more intense reduction in [phyA] without changes in the phyA'/phyA'' equilibrium was found in far-red grown mutant plants suggesting a hypersensitivity of phyA-3D with regard to its autoregulation. On the contrary, under red illumination, a higher stability of phyA-3D was observed confirming our earlier findings. This allows a conclusion that the A194V substitution in phyA-3D not only impairs its destruction but also enhances its signaling ability, suggesting a role of this locus in modulation of its activity.
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Affiliation(s)
- V A Sineshchekov
- Biology Department, M.V. Lomonosov Moscow State University, Moscow 119899, Russia.
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6
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Konishi A, Shimizu S, Hirota J, Takao T, Fan Y, Matsuoka Y, Zhang L, Yoneda Y, Fujii Y, Skoultchi AI, Tsujimoto Y. Involvement of Histone H1.2 in Apoptosis Induced by DNA Double-Strand Breaks. Cell 2003; 114:673-88. [PMID: 14505568 DOI: 10.1016/s0092-8674(03)00719-0] [Citation(s) in RCA: 232] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
It is poorly understood how apoptotic signals arising from DNA damage are transmitted to mitochondria, which release apoptogenic factors into the cytoplasm that activate downstream destruction programs. Here, we identify histone H1.2 as a cytochrome c-releasing factor that appears in the cytoplasm after exposure to X-ray irradiation. While all nuclear histone H1 forms are released into the cytoplasm in a p53-dependent manner after irradiation, only H1.2, but not other H1 forms, induced cytochrome c release from isolated mitochondria in a Bak-dependent manner. Reducing H1.2 expression enhanced cellular resistance to apoptosis induced by X-ray irradiation or etoposide, but not that induced by other stimuli including TNF-alpha and UV irradiation. H1.2-deficient mice exhibited increased cellular resistance in thymocytes and the small intestine to X-ray-induced apoptosis. These results indicate that histone H1.2 plays an important role in transmitting apoptotic signals from the nucleus to the mitochondria following DNA double-strand breaks.
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Affiliation(s)
- Akimitsu Konishi
- Department of Post-Genomics and Diseases, Osaka University Medical School, 2-2 Yamadaoka, Suita, 565-0871, Osaka, Japan
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7
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Brancho D, Tanaka N, Jaeschke A, Ventura JJ, Kelkar N, Tanaka Y, Kyuuma M, Takeshita T, Flavell RA, Davis RJ. Mechanism of p38 MAP kinase activation in vivo. Genes Dev 2003; 17:1969-78. [PMID: 12893778 PMCID: PMC196252 DOI: 10.1101/gad.1107303] [Citation(s) in RCA: 394] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The p38 mitogen-activated protein kinase (MAPK) is activated in vitro by three different protein kinases: MKK3, MKK4, and MKK6. To examine the relative roles of these protein kinases in the mechanism of p38 MAP kinase activation in vivo, we examined the effect of disruption of the murine Mkk3, Mkk4, and Mkk6 genes on the p38 MAPK signaling pathway. We show that MKK3 and MKK6are essential for tumor necrosis factor-stimulated p38 MAPK activation. In contrast, ultraviolet radiation-stimulated p38 MAPK activation was mediated by MKK3, MKK4, and MKK6. Loss of p38 MAPK activation in the mutant cells was associated with defects in growth arrest and increased tumorigenesis. These data indicate that p38 MAPK is regulated by the coordinated and selective actions of three different protein kinases in response to cytokines and exposure to environmental stress.
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Affiliation(s)
- Deborah Brancho
- Howard Hughes Medical Institute and Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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8
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Qi W, Martinez JD. Reduction of 14-3-3 proteins correlates with increased sensitivity to killing of human lung cancer cells by ionizing radiation. Radiat Res 2003; 160:217-23. [PMID: 12859233 DOI: 10.1667/rr3038] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The 14-3-3 proteins have a wide range of ligands and are involved in a variety of biological pathways. Importantly, 14-3-3 proteins are known to be overexpressed in some human lung cancers, suggesting that they may play a role in tumorigenesis. Here we examined 14-3-3 expression in several lung cancer-derived cell lines and found that four of the seven 14-3-3 isoforms, beta, epsilon, theta and zeta, were highly expressed in both lung cancer cell lines and normal lung fibroblasts. Two isoforms, sigma and gamma, were present only at very low levels. Immunoprecipitation data showed 14-3-3zeta could bind to CDC25C in irradiated A549 cells, and suppression of 14-3-3zeta in A549 cells with antisense resulted in a decrease in CDC25C localization in cytoplasm and CDC2 phosphorylation on Tyr15. As a consequence, CDC2 activity remained elevated which resulted in release from radiation-induced G(2)/M-phase arrest. Moreover, 16% 14-3-3zeta antisense-transfected cells underwent apoptosis when exposed to 10 Gy ionizing radiation. These data indicate that 14-3-3zeta is involved in G(2) checkpoint activation and that inhibition of 14-3-3 may be a useful approach to sensitize human lung cancers to ionizing radiation.
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Affiliation(s)
- Wenqing Qi
- Department of Radiation Oncology, The University of Arizona, and Arizona Cancer Center, Tucson, Arizona 85724, USA
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9
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Naryzhny SN, Lee H. Observation of multiple isoforms and specific proteolysis patterns of proliferating cell nuclear antigen in the context of cell cycle compartments and sample preparations. Proteomics 2003; 3:930-6. [PMID: 12833516 DOI: 10.1002/pmic.200300400] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The proliferating cell nuclear antigen (PCNA) is an essential component for eukaryotic chromosomal DNA replication and repair. PCNA forms a homotrimer ring, which may function as a DNA sliding clamp for DNA polymerases and, possibly, a docking station for other replication- and repair-related proteins. Several reports have suggested the existence of different PCNA isoforms. Here we confirm, using high resolution two-dimensional electrophoresis with narrow pH ranges, the existence of three PCNA isoforms in both Chinese hamster and human breast cancer cells. Among the three isoforms, M or main form is the dominant one throughout the cell cycle while the relative amounts of the minor components A (acidic) and B (basic) forms appear to vary during the cell cycle. We also observed that a specific pattern of PCNA proteolysis occurred during isoelectric focusing in spite of high urea (8 M) and detergent (2% 3-[(3-cholamidopropyl)dimethylamino]-1-propane sulfonate), which was largely inhibited by the proteosome inhibitor MG132 or boiling. Interestingly, the proteolysis pattern was mainly observed with samples isolated from cells in S and G2 phases. A similar but much lower level of PCNA proteolysis also occurred in vivo within the nuclei of the cells in S phase. Taken together, our data are consistent with the idea that the existence of the different isoforms and specific proteolysis of PCNA are relevant to its functions in vivo.
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10
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Abstract
The tumour-suppressor protein BRCA1 mediates its biological functions by interacting with cellular factors such as the CtIP polypeptide, a substrate for the ATM (for 'ataxia telangiectasia mutated') protein kinase. Li et al. report that the BRCA1-CtIP interaction is disrupted by ionizing radiation and by other genotoxic stresses that induce phosphorylation of CtIP by ATM kinase, and that this dissociation of the BRCA1-CtIP complex in turn modulates the transcription of DNA-damage-response genes. We have shown that the BRCA1-binding domain of CtIP (amino-acid residues 133-369) is distal to the sites that are phosphorylated by ATM kinase (residues S664 and S745). We now show that the BRCA1-CtIP complex is stable in irradiated cells, and that the phosphorylated isoforms of CtIP that are induced by ionizing radiation still interact in vivo with BRCA1. We conclude that disruption of the BRCA1-CtIP complex cannot account for induction of DNA-damage-response genes in the way proposed by Li et al.
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Affiliation(s)
- F Wu-Baer
- Institute of Cancer Genetics and Department of Pathology, Columbia University College of Physicians and Surgeons, 1150 St Nicholas Avenue, New York, New York 10032, USA
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Emi T, Kinoshita T, Shimazaki K. Specific binding of vf14-3-3a isoform to the plasma membrane H+-ATPase in response to blue light and fusicoccin in guard cells of broad bean. Plant Physiol 2001; 125:1115-25. [PMID: 11161066 PMCID: PMC64910 DOI: 10.1104/pp.125.2.1115] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2000] [Revised: 09/24/2000] [Accepted: 10/17/2000] [Indexed: 05/18/2023]
Abstract
The plasma membrane H(+)-ATPase is activated by blue light with concomitant binding of the 14-3-3 protein to the C terminus in guard cells. Because several isoforms of the 14-3-3 protein are expressed in plants, we determined which isoform(s) bound to the H(+)-ATPase in vivo. Four cDNA clones (vf14-3-3a, vf14-3-3b, vf14-3-3c, and vf14-3-3d) encoding 14-3-3 proteins were isolated from broad bean (Vicia faba) guard cells. Northern analysis revealed that mRNAs encoding vf14-3-3a and vf14-3-3b proteins were expressed predominantly in guard cells. The 14-3-3 protein that bound to the H(+)-ATPase in guard cells had the same molecular mass as the recombinant vf14-3-3a protein. The H(+)-ATPase immunoprecipitated from mesophyll cell protoplasts, which had been stimulated by fusicoccin, coprecipitated with the 32.5-kD 14-3-3 protein, although three 14-3-3 isoproteins were found in mesophyll cell protoplasts. Digestions of the bound 14-3-3 protein and recombinant vf14-3-3a with cyanogen bromide gave the identical migration profiles on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but that of vf14-3-3b gave a different profile. Mass profiling of trypsin-digested 14-3-3 protein bound to the H(+)-ATPase gave the predicted peptide masses of vf14-3-3a. Far western analysis revealed that the H(+)-ATPase had a higher affinity for vf14-3-3a than for vf14-3-3b. These results suggest that the 14-3-3 protein that bound to the plasma membrane H(+)-ATPase in vivo is vf14-3-3a and that it may play a key role in the activation of H(+)-ATPase in guard cells.
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Affiliation(s)
- T Emi
- Department of Biology, Faculty of Sciences, Kyushu University, Ropponmatsu, Fukuoka 810-8560, Japan
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12
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Stewart ZA, Tang LJ, Pietenpol JA. Increased p53 phosphorylation after microtubule disruption is mediated in a microtubule inhibitor- and cell-specific manner. Oncogene 2001; 20:113-24. [PMID: 11244509 DOI: 10.1038/sj.onc.1204060] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2000] [Revised: 10/16/2000] [Accepted: 10/26/2000] [Indexed: 01/20/2023]
Abstract
p53 is present at low levels in unstressed cells. Numerous cellular insults, including DNA damage and microtubule disruption, elevate p53 protein levels. Phosphorylation of p53 is proposed to be important for p53 stabilization and activation after genotoxic stress; however, p53 phosphorylation after microtubule disruption has not been analysed. The goal of the current study was to determine if p53 phosphorylation increases after microtubule disruption, and if so, to identify specific p53 residues necessary for microtubule inhibitor-induced phosphorylation. Two dimensional gel analyses demonstrated that the number of p53 phospho-forms in cells increased after treatment with microtubule inhibitors (MTIs) and that the pattern of p53 phosphorylation was distinct from that observed after DNA damage. p53 phosphorylation also varied in a MTI-dependent manner, as Taxol and Vincristine induced more p53 phospho-forms than nocodazole. Further, MTI treatment increased phosphorylation of p53 on serine-15 in epithelial tumor cells. In contrast, serine-15 phosphorylation of p53 did not increase in MTI-treated primary cultures of human fibroblasts. Analysis of ectopically expressed p53 phospho-mutant proteins from Taxol- and nocodazole-treated cells indicated that multiple p53 amino terminal residues, including serine-15 and threonine-18, were required for Taxol-mediated phosphorylation of p53. Taken together, the results of this study demonstrate that distinct p53 phospho-forms are induced by MTI treatment as compared to DNA damage and that p53 phosphorylation is mediated in a MTI- and cell-specific manner. Oncogene (2001) 20, 113 - 124.
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Affiliation(s)
- Z A Stewart
- Vanderbilt University School of Medicine, Department of Biochemistry, Nashville, TN 37232, USA
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Abraham J, Kelly J, Thibault P, Benchimol S. Post-translational modification of p53 protein in response to ionizing radiation analyzed by mass spectrometry. J Mol Biol 2000; 295:853-64. [PMID: 10656795 DOI: 10.1006/jmbi.1999.3415] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The p53 tumor suppressor protein promotes cell cycle arrest or apoptosis in response to DNA damage and other forms of stress. p53 protein functions as a transcription factor by binding to specific DNA sequences and regulating the transcription of target genes. This activity of p53 is reported to be regulated by phosphorylation and acetylation occuring at various sites on the molecule. Here, we have used a direct and non-radioactive approach involving mass spectrometric analysis of p53 protein to identify sites that are covalently modified in vivo, either constitutively or in response to ionizing radiation. Following partial purification by immuno-affinity chromatography and enzymatic in-gel digestion, the resulting p53 peptides were analyzed by MALDI-TOF and nanoelectrospray mass spectrometry. Mass spectrometry analyses identified four sites at the N terminus that were phosphorylated in response to irradiation, a single constitutive phosphorylation site at serine 315 and several acetylation sites.
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Affiliation(s)
- J Abraham
- Ontario Cancer Institute/Princess Margaret Hospital and Department of Medical Biophysics, Toronto, Ontario, M5G 2M9, Canada
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Abstract
How light signals are transduced by phytochromes is still poorly understood. Recent studies have provided evidence that a PAS domain protein, PIF3, physically interacts with phytochromes, plays a role in phytochrome signal transduction and might be a component of a novel signalling pathway in plants.
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Affiliation(s)
- G C Whitelam
- Department of Biology, Leicester University, University Road, Leicester, LE1 7RH, UK
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