p53 (also known as protein 53 or tumor protein 53), is a
transcription factorencoded by the " TP53" gene. p53 is important in multicellular organisms, where it regulates the cell cycleand thus functions as a tumor suppressorthat is involved in preventing cancer. As such, p53 has been described as "the guardian of the genome," "the guardian angel gene," and the "master watchman," referring to its role in conserving stability by preventing genome mutation.cite book | author = Read, A. P.; Strachan, T. | title = Human molecular genetics 2 | publisher = Wiley | location = New York | year = 1999 | pages = | isbn = 0-471-33061-2 | oclc = | doi = | chapter = Chapter 18: Cancer Genetics ]
The name p53 is in reference to its apparent
molecular mass: it runs as a 53 kilodalton(kDa) protein on SDS-PAGE. But based on calculations from its amino acidresidues, p53's mass is actually only 43.7kDa. This difference is due to the high number of prolineresidues in the protein which slow its migration on SDS-PAGEFact|date=August 2008, thus making it appear larger than it actually is. This effect is observed with p53 from a variety of species, including humans, rodents, frogs and fish.
In humans, p53 is encoded by the "
TP53" gene located on the short arm of chromosome 17 (17p13.1).
The gene is on different locations in other animals:
*Mouse - chromosome 11
*Rat - chromosome 10
Dog- chromosome 5
Pig- chromosome 12
("Italics" are used to distinguish the "TP53" gene name from the protein it encodes.)
Human p53 is 393
amino acids long and has seven domains:
N-terminaltranscription-activation domain (TAD), also known as activation domain 1 (AD1) which activates transcription factors: residues 1-42.
* An activation domain 2 (AD2) important for apoptotic activity: residues 43-63.
Prolinerich domain important for the apoptotic activity of p53: residues 80-94.
* A central
DNA-binding core domain ( DBD). Contains one zinc atom and several arginineamino acids: residues 100-300.
* A nuclear localization signalling domain, residues 316-325.
* A homo-oligomerisation domain (OD): residues 307-355. Tetramerization is essential for the activity of p53 "in vivo".
C-terminalinvolved in downregulation of DNA binding of the central domain: residues 356-393.cite journal | author = Harms KL, Chen X | title = The C terminus of p53 family proteins is a cell fate determinant | journal = Mol. Cell. Biol. | volume = 25 | issue = 5 | pages = 2014–30 | year = 2005 | pmid = 15713654 | doi = 10.1128/MCB.25.5.2014-2030.2005 ]
Mutations that deactivate p53 in cancer usually occur in the DBD. Most of these mutations destroy the ability of the protein to bind to its target DNA sequences, and thus prevents transcriptional activation of these genes. As such, mutations in the DBD are recessive
loss-of-functionmutations. Molecules of p53 with mutations in the OD dimerise with wild-typep53, and prevent them from activating transcription. Therefore OD mutations have a dominant negative effect on the function of p53.
Wild-type p53 is a
labile protein, comprising folded and unstructured regions which function in a synergistic manner.cite journal | author = Bell S, Klein C, Müller L, Hansen S, Buchner J | title = p53 contains large unstructured regions in its native state | journal = J. Mol. Biol. | volume = 322 | issue = 5 | pages = 917–27 | year = 2002 | pmid = 12367518 | doi = 10.1016/S0022-2836(02)00848-3 ]
p53 has many anti-cancer mechanisms:
* It can activate
DNA repairproteins when DNA has sustained damage.
* It can also hold the
cell cycleat the G1/S regulation point on DNA damage recognition (if it holds the cell here for long enough, the DNA repair proteins will have time to fix the damage and the cell will be allowed to continue the cell cycle.)
* It can initiate
apoptosis, the programmed cell death, if the DNA damage proves to be irreparable.
p53 is central to many of the cell's anti-cancer mechanisms. It can induce growth arrest,
apoptosisand cell senescence. In normal cells p53 is usually inactive, bound to the protein MDM2 (also called HDM2 in humans), which prevents its action and promotes its degradation by acting as ubiquitin ligase. Active p53 is induced after the effects of various cancer-causing agents such as UV radiation, oncogenes and some DNA-damaging drugs. DNA damage is sensed by 'checkpoints' in a cell's cycle, and causes proteins such as ATM, CHK1 and CHK2 to phosphorylatep53 at sites that are close to or within the MDM2-binding region and p300-binding region of the protein. Oncogenes also stimulate p53 activation, mediated by the protein p14ARF. Some oncogenes can also stimulate the transcription of proteins which bind to MDM2 and inhibit its activity. Once activated p53 activates expression of several genes including one encoding for p21. p21 binds to the G1-S/ CDKand S/CDK complexes (molecules important for the G1/S transitionin the cell cycle) inhibiting their activity. p53 has many anticancer mechanisms, and plays a role in apoptosis, genetic stability, and inhibition of angiogenesis.
The p53 gene has been mapped to chromosome 17. In the cell, p53 protein binds DNA, which in turn stimulates another gene to produce a protein called p21 that interacts with a cell division-stimulating protein (cdk2). When p21 is complexed with cdk2 the cell cannot pass through to the next stage of cell division. Mutant p53 can no longer bind DNA in an effective way, and as a consequence the p21 protein is not made available to act as the 'stop signal' for cell division. Thus cells divide uncontrollably, and form tumors.cite web | url = http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowSection&rid=gnd.section.107 | title = The p53 tumor suppressor protein | author = National Center for Biotechnology Information | authorlink = | coauthors = | date = | format = | work = Genes and Disease | publisher = United States National Institutes of Health | pages = | language = | archiveurl = | archivedate = | quote = | accessdate = 2008-05-28]
Recent research has also linked the p53 and
RB1pathways, via p14ARF, raising the possibility that the pathways may regulate each other.cite journal | author = Bates S, Phillips AC, Clark PA, Stott F, Peters G, Ludwig RL, Vousden KH | title = p14ARF links the tumour suppressors RB and p53 | journal = Nature | volume = 395 | issue = 6698 | pages = 124–5 | year = 1998 | pmid = 9744267 | doi = 10.1038/25867 ]
Research published in 2007 showed when p53 expression is stimulated by
sunlight, it begins the chain of events leading to tanning. [cite news | title = Genome's guardian gets a tan started | url = http://www.newscientist.com/channel/health/mg19325955.800-genomes-guardian-gets-a-tan-started.html | publisher = New Scientist | date = March 17, 2007 | accessdate = 2007-03-29] cite journal | author = Cui R, Widlund HR, Feige E, Lin JY, Wilensky DL, Igras VE, D'Orazio J, Fung CY, Schanbacher CF, Granter SR, Fisher DE | title = Central role of p53 in the suntan response and pathologic hyperpigmentation | journal = Cell | volume = 128 | issue = 5 | pages = 853–64 | year = 2007 | pmid = 17350573 | doi = 10.1016/j.cell.2006.12.045 ]
Regulation of p53 activity
p53 becomes activated in response to a myriad of stress types, which include but is not limited to
DNA damage(induced by either UV, IR or chemical agents,such as hydrogen peroxide), oxidative stress, osmotic shock, ribonucleotide depletion and deregulated oncogene expression. This activation is marked by two major events. Firstly, the half-life of the p53 protein is increased drastically, leading to a quick accumulation of p53 in stressed cells. Secondly, a conformational changeforces p53 to take on an active role as a transcription regulator in these cells. The critical event leading to the activation of p53 is the phosphorylation of its N-terminal domain. The N-terminal transcriptional activation domain contains a large number of phosphorylation sites and can be considered as the primary target for protein kinases transducing stress signals.
protein kinasesthat are known to target this transcriptional activation domain of p53 can be roughly divided into two groups. A first group of protein kinases belongs to the MAPKfamily (JNK1-3, ERK1-2, p38 MAPK), which is known to respond to several types of stress, such as membrane damage, oxidative stress, osmotic shock, heat shock, etc... A second group of protein kinases (ATR, ATM, Chk1, Chk2, DNA-PK, CAK) is implicated in the genome integrity checkpoint, a molecular cascade that detects and responds to several forms of DNA damage caused by genotoxic stress.
In unstressed cells, p53 levels are kept low through a continuous degradation of p53. A protein called
Mdm2binds to p53 and transports it from the nucleus to the cytosolwhere it becomes degraded by the proteasome. Phosphorylation of the N-terminal end of p53 by the above-mentioned protein kinases disrupts Mdm2-binding. Other proteins, such as Pin1, are then recruited to p53 and induce a conformational change in p53 which prevents Mdm2-binding even more. Trancriptional coactivators, like p300 or PCAF, then acetylate the carboxy-terminal end of p53, exposing the DNA binding domain of p53, allowing it to activate or repress specific genes. Deacetylase enzymes, such as Sirt1and Sirt7, can deacetylate p53, leading to an inhibition of apoptosis.cite journal | author = Vakhrusheva O, Smolka C, Gajawada P, Kostin S, Boettger T, Kubin T, Braun T, Bober | title = Sirt7 increases stress resistance of cardiomyocytes and prevents apoptosis and inflammatory cardiomyopathy in mice | journal = Circ. Res. | volume = 102 | issue = 6 | pages = 703–10 | year = 2008 | month = March | pmid = 18239138 | doi = 10.1161/CIRCRESAHA.107.164558 | url = ]
Role in disease
If the "TP53" gene is damaged, tumor suppression is severely reduced. People who inherit only one functional copy of the "TP53" gene will most likely develop tumors in early adulthood, a disease known as
Li-Fraumeni syndrome. The "TP53" gene can also be damaged in cells by mutagens (chemicals, radiationor viruses), increasing the likelihood that the cell will begin uncontrolled division. More than 50 percent of human tumors contain a mutationor deletion of the "TP53" gene. Increasing the amount of p53, which may initially seem a good way to treat tumors or prevent them from spreading, is in actuality not a usable method of treatment, since it can cause premature aging.cite journal | author = Tyner SD, Venkatachalam S, Choi J, Jones S, Ghebranious N, Igelmann H, Lu X, Soron G, Cooper B, Brayton C, Hee Park S, Thompson T, Karsenty G, Bradley A, Donehower LA | title = p53 mutant mice that display early ageing-associated phenotypes | journal = Nature | volume = 415 | issue = 6867 | pages = 45–53 | year = 2002 | pmid = 11780111 | doi = 10.1038/415045a ] However, restoring endogenousp53 function holds a lot of promise.cite journal | author = Ventura A, Kirsch DG, McLaughlin ME, Tuveson DA, Grimm J, Lintault L, Newman J, Reczek EE, Weissleder R, Jacks T | title = Restoration of p53 function leads to tumour regression in vivo | journal = Nature | volume = 445 | issue = 7128 | pages = 661–5 | year = 2007 | pmid = 17251932 | doi = 10.1038/nature05541 ]
Certain pathogens can also affect the p53 protein that the "TP53" gene expresses. One such example, the
Human papillomavirus(HPV), encodes a protein, E6, which binds the p53 protein and inactivates it. This, in synergy with the inactivation of another cell cycle regulator, p105RB, allows for repeated cell division manifestested in the clinical disease of warts.
In healthy humans, the p53 protein is continually produced and degraded in the cell. The degradation of the p53 protein is, as mentioned, associated with MDM2 binding. In a negative feedback loop MDM2 is itself induced by the p53 protein. However mutant p53 proteins often don't induce MDM2, and are thus able to accumulate at very high concentrations. Worse, mutant p53 protein itself can inhibit normal p53 protein levels.
p53 was identified in 1979 by
Arnold Levine, David Lane, and Lloyd Old, working at Princeton University, Imperial Cancer Research Fund(UK), and Sloan-Kettering Memorial Hospital, respectively. It had been hypothesized to exist before as the target of the SV40virus, a strain that induced development of tumors. The " TP53" gene from the mouse was first cloned by Peter Chumakovof the Russian Academy of Sciencesin 1982, [cite journal |author=Chumakov P, Iotsova V, Georgiev G |title= [Isolation of a plasmid clone containing the mRNA sequence for mouse nonviral T-antigen] |journal=Dokl Akad Nauk SSSR |volume=267 |issue=5 |pages=1272–5 |year=1982 |pmid=6295732] and independently in 1983 by Moshe Oren( Weizmann Institute).
It was initially presumed to be an
oncogenedue to the use of mutated cDNAfollowing purification of tumour cell mRNA. Its character as a tumor suppressor genewas finally revealed in 1989 by Bert Vogelsteinworking at Johns Hopkins School of Medicine.
Warren Maltzman, of the Waksman Institute of Rutgers University first demonstrated that TP53 was responsive to DNA damage in the form of ultraviolet radiation. [cite journal |author=Maltzman W, Czyzyk L |title=UV irradiation stimulates levels of p53 cellular tumor antigen in nontransformed mouse cells |journal=Mol Cell Biol |volume=4 |issue=9 |pages=1689–94 |year=1984 |pmid=6092932] In a series of publications in 1991-92, Michael Kastan, Johns Hopkins University, reported that TP53 was a critical part of a signal transduction pathway that helped cells respond to DNA damage.
In 1993, p53 was voted "molecule of the year" by Science magazine.cite journal | author = Koshland DE | title = Molecule of the year | journal = Science | volume = 262 | issue = 5142 | pages = 1953 | year = 1993 | pmid = 8266084 | doi = 10.1126/science.8266084 ]
*Official protein name: Cellular
*Tumor suppressor p53
*Transformation-related protein 53 (TRP53)
update_page = yes
require_manual_inspection = no
update_protein_box = yes
update_summary = no
update_citations = no
Wikimedia Foundation. 2010.
Look at other dictionaries:
P53 — Bänder /Oberflächenmodell vpn p53 an DNA nach PDB … Deutsch Wikipedia
P53 — est une protéine impliquée dans certains cancers. Sommaire 1 Historique 1.1 De 1979 à 1985 1.2 1985 1989 1.3 1989 2007 … Wikipédia en Français
p53 — Bänder /Oberflächenmodell von p53 an DNA nach PDB … Deutsch Wikipedia
P53 — Saltar a navegación, búsqueda Tumor protein p53 Identificadores Símbolo TP53 Símbolos alt. P53, LFS1 Entrez … Wikipedia Español
P53 — Тетрамер, состоящий из четырёх идентичных молекул белка p53. Они связаны между собой доменами, отвечающими за олигомеризацию (см. в тексте). p53 (белок p53) это транскрипционный фактор, регулирующий клеточный цикл. В не мутировавшем состоянии… … Википедия
p53 — (белок p53) это транскрипционный фактор, регулирующий клеточный цикл. p53 выполняет функцию супрессора образования злокачественных опухолей, соответственно ген TP53 является антионкогеном. Мутации гена TP53 обнаруживаются в клетках около… … Википедия
p53 — For the band and album of the same name, see P53 (band) and P53 (album). Tumor protein p53 PDB rendering based on 1TUP … Wikipedia
p53 — Tumor protein p53 HUGO 11998 Símbolo TP53 Símbolos alt. P53, LFS1 … Wikipedia Español
p53 — Structure cristallographique de la protéine p53 complexée à un brin d ADN. p53 est un facteur de transcription régulant certaines fonctions cellulaires importantes comme la mitose ou la mort programmée. Le gène codant pour la protéine p53 est… … Wikipédia en Français
p53 — A tumor suppressor. The designation p53 stands for protein 53 kilodaltons in size. p53 is a specific protein produced by a gene that functions to suppress the growth of tumors. The p53 gene is the most commonly mutated gene known in human cancer … Medical dictionary