Last updated: September 26, 2019
Topic: HealthDisease
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Tp53 is a tumor suppresser cistron nowadays in the short arm of the seventeenth chromosome in Homo sapiens. The cistron encodes a protein known as p53 protein through interlingual rendition procedure. The cistron belongs to the p53 household, which has three chief cistrons: p53, p63 and p73. Out of the three p53 is the chief cistron in higher being. The other two beings are found in lower being. The chief map of the protein is to modulate the cell rhythm and act as a tumor suppresser. Hence, this cistron is known as the tumor suppresser cistron. It is known as “ the defender of the genome ” as it maintains the cistron stableness by forestalling genome mutant. This cistron is besides known as anti-oncogene [ 20, 21 ] .

The p53 protein is a 53kDa atomic phosphoprotein made up of 393 aminic acids and has four spheres. This is encoded by p53 cistron, which is made up of 11 coding DNAs [ 23 ] .

Fig.1. Protein Structure ( 1TUP )

N-terminal Domain that activates written text factors ( residues 1-42 )

Homo-oligomerization sphere for tetramerization of the protein ( 80-94 )

Core sphere to acknowledge specific DNA sequence ( residues 100-300 )

Regulatory sphere to acknowledge damaged DNA ( residues 356-393 )

Fig.2. TP53 Domains

The tumor protein p53 cistron binds straight to the Deoxyribonucleic acid when carcinogens, toxic chemicals, harm it or UV beams from sunshine. The protein either mend the Deoxyribonucleic acid or induces cell programmed cell death ( programmed cell decease ) when the Deoxyribonucleic acid can non be repaired. The protein prevents the mutated cell or cell with damaged Deoxyribonucleic acid from spliting thereby stamp downing tumour formation [ 24, 25 ] .

3. Function

Under normal conditions, the p53 cistron is inactive as it is bound to the Mdm2 and does non take part in normal cell rhythm patterned advance and cell endurance. The cistron is activated merely when the Deoxyribonucleic acid is damaged doing cell emphasis and increases the p53 proteins degree. This protein does three chief maps cell rhythm apprehension, DNA fix and programmed cell death. The cistron is activated by other factors like mitotic spindle harm, exposure to azotic oxide, hypoxia, oncogene activation and ribonucleotide depletion. The mark cistrons involved in assorted maps are

Growth arrest – p21, Gaff45 and 14-3-3s

Apoptosis – Bax, Apaf-1, PUMA, NoxA

DNA fix – p53R2


To mend the DNA p53 activates the DNA fix proteins and p53R2 cistron. It is a ribonucleotide reductase induced by the p53 cistron to provide deoxynucleotide triphosphates to mend the damaged DNA. AP endonuclease and DNA polymerase binds to p53 cistron for DNA deletion fix [ 1 ] .


Fig.3. Cell Cycle Arrest by p53 Gene

To execute cell rhythm apprehension p53 activates three cistrons p21, Gaff45 and 14-3-3s by adhering to the damaged DNA. The p21 cistron binds to G1-S/CDK ( CDK2 ) and S/CDK composites. These composites are of import for the passage of G1 stage to S stage. When the cistron binds to the composite, the activity gets inhibited and the cell does non go on to the following phase in cell division. The patterned advance of cell rhythm from G2 stage to the M stage requires Cdc2, which is inhibited by GADD45 or 14-3-3s cistrons. Hence, p53 regulates cell rhythm apprehension and prevents tumour formation.

Apart from these maps, it besides induces programmed cell death.

5. SIGNALLING Nerve pathway

The p53 tract is activated due to genotoxic emphasis, as it is a cell emphasis detector molecule. It responds to emphasize factors that damage the Deoxyribonucleic acid. The cistron is an effectual booster of programmed cell death ( programmed cell decease ) [ 36 ] .

Fig.4. P53 Signalling Pathway

The look of p53 is regulated by both positive feedback cringles and negative feedback cringles. The positive feedback cringle is controlled by MDM2 protein. The protein is encoded by the MDM2 cistron, which is normally called the negative regulator. When p53 is unphospharylated, it binds to MDM2 and is degraded through ubiquitin-mediated debasement procedure. If p53 is phosphorylated so it does non organize complex with MDM2 and it continues its map [ 35 ] .

Fig.5. P53 Regulation by MDM2


Apoptosis induced by Tp53 cistron is executed by caspase protease. Two tracts activate the caspases

Extrinsic tract and

Intrinsic tract

The induction of extrinsic tract begins with the ligation of decease receptors with their several ligands. The decease receptors are tumour necrosis factors CD95/Fas/Apo-1 and TRAIL receptors. The ligation of the receptors with ligands form the Death Inducing Signalling Complex ( DISC ) that is composed of the arranger molecule FADD and caspase – 8. Activation DISC activates capase-8 either straight cleaves and activates the effecters caspases or indirectly activated the downstream caspases by spliting the BH3 protein BID [ 3, 4 ] . This leads to the invoking of the intrinsic tract. In this tract, anti-apoptotic Bcl-2 protein household regulates caspase. These proteins induce the release of apoptogenic factors like cytochrome degree Celsius or Smac from the chondriosome to the cytosol. The intrinsic tract is normally triggered due to emphasize or DNA harm. The release of cytochrome degree Celsius facilitates the formation of apoptosome composite, which is composed of Apaf-1 and caspase-9 [ 5 ] .

Fig.6. Apoptosome formation

These apoptosomes activates the effecter caspases 3, 6 and 7 that execute the decease program.p53 response elements are found in the boosters of Bcl-2, Bax and BH3. The Bax protein household contains two of import proteins PUMA and NOXA, which are up regulated during P53 programmed cell death. During the up ordinance procedure PUMA encodes PUMA-I± and PUMA-I? , which promotes mitochondrial translocation, originating programmed cell death. Effector caspases 3, 6 and 7 digest indispensable marks of the cell and bring oning programmed cell death activity. Caspase-6 activity is induced by DNA harm through a response component nowadays in the 3rd noncoding DNA.

Fig.7. p53 Mediated Apoptosis

Apoptosis is besides known as programmed cell decease, which is caused by the caspases 3, 6 and 7 nowadays in the apoptosome. They cause cell decease by triping DNase, suppressing DNA fix enzymes and interrupting down the structural units in the nucleus [ 6 ] .


Enzyme Poly ( ADP-ribose ) polymerase ( PARP ) is used to mend the damaged DNA. Caspase-3 cleaves PARP and prevents it from making its map and the damaged Deoxyribonucleic acid remains unrepaired.


Lamins are intranuclear proteins that help in keeping the form of the karyon and besides intercede the interactions between the chromatin and atomic membrane. Caspase-6 degrades Lamins and consequences in chromatin condensation and atomic atomization.

Atomization of Deoxyribonucleic acid

The atomization of DNA to nucleosomal units is caused by CAD ( Caspase activated DNase ) enzyme which usually exists in inactive ICAD signifier. Caspase-3 cleaves ICAD to CAD and consequences in rapid atomization of atomic DNA to nucleosomal units [ 7 ] .

Fig.8. Apoptosis by Caspases 3, 6 And 7

5. Mechanism


A. Benzo [ a ] Pyrene

Benzo [ a ] Pyrene belongs to polycyclic aromatics hydrocarbons ( PAH ) category of chemicals. This chemical is extremely carcinogenic which is present in coffin nail fume, pitch and in smoked nutrient. It is a pale xanthous coloring material pentacyclic hydrocarbon, which intercalates with DNA to organize adducts which subsequently leads to malignant neoplastic disease development. Hence, known as a procarcinogen [ 31, 32 ] .

Fig.9. Benzo [ a ] Pyrene

B. 4- ( methylnitroamine ) -1- ( 3-pyridyl ) -1-butanone ( NNK )

4- ( methylnitroamine ) -1- ( 3-pyridyl ) -1-butanone is a nitrosamine largely present in baccy fume. It is procarcinogen which binds with DNA doing passage mutant. This mutant leads to the development of malignant neoplastic disease. CYP2A6 cistron chiefly activates the chemical [ 29, 30 ] .

Fig.10. 4- ( Methylnitroamine ) -1- ( 3-pyridyl ) -1-butanone ( NNK )

C. 4-aminobiphenyl

It is an amine derived function of biphenyl found in baccy fume. The chemical is similar to benzidine. This is known as a human carcinogen, which is responsible for malignant neoplastic diseases like vesica malignant neoplastic disease ( UCC ) . The chemical is besides found in azo compounds, which are aromatic aliphatic compounds. A colourless odourless compound turns into violet coloring material on exposure to air. 4-aminobiphenyl from coffin nail fume signifiers DNA adducts and is found in the epithelial liner of the urinary vesica. It besides forms protein adducts with albumen and hemoglobin [ 33 ] .

Fig.11. 4-aminobiphenyl


Benzo [ a ] pyrene

Benzo [ a ] pyrene was found to be the chief chemical in coffin nail is responsible for doing p53 mutant. It is procarcinogen which means that there is the engagement of enzymes ( CYP1A1/CYP1B1 ) in change overing Benzo [ a ] Pyrene to its -diol-epoxide, Benzo [ a ] Pyrene glycol epoxide, which is the p53 mutagen. Enzyme metamorphosis of Benzo [ a ] Pyrene leads into four -7, 8 diol-9, 10-epoxide stereoisomers of which the most copiously formed is the ( + ) -anti-BPDE.

Fig.12. B [ a ] P metamorphosis

Besides of all other isomers, the ( + ) -anti-BPDE as got more carcinogenic and intrinsic genotoxic features. This isomer forms an adduct with the Deoxyribonucleic acid forming ( + ) -anti-BPDE-N2-dG which is immune to atomic deletion fix mechanism and translesional synthesis ( TLS ) which leads to G-T transversion [ 27,28 ] .

Fig.13. Mechanism of p53 mutant caused by B [ a ] P




One of the harmful mutagen nowadays in coffin nail fume is Benzo [ a ] Pyrene, which causes mutant in TP53 cistron and leads to lung malignant neoplastic disease. The B [ a ] P entered is absorbed by the epithelial walls of the lungs and metabolizes to benzo ( a ) pyrene diol epoxide ( BPDE ) . The BPDE straight binds to the cistron by organizing DNA adducts at the G and adenine part [ 34 ] . This binding takes topographic point because BPDE is extremely electrophilic and G is extremely nucleophilic. The type of mutant caused by BPDE is G: C i? T: A transversion at 157, 248 and 273 codons, which are known as the hot topographic point parts of the cistron where more figure of mutants takes topographic point [ 15,16,17 ] .

Fig.14. Conventional Representation in Lung Cancer Development

Fig.15. BPDE impacting TP53 cistron


Oesophageal malignant neoplastic disease

The type of malignant neoplastic disease caused in gorge due to smoke is squamous cell carcinoma. One of the cistrons mutated in this type of malignant neoplastic disease is Tp53. The mutant takes topographic point in the coding DNA 5 doing transversion and passage mutants [ 2, 8, 10 ] . The chemicals in coffin nail causation mutants are N-nitrosodiethylamine and N-nitrosopiperidine. These cause passage mutants and benzo-a-pyrene cause transversion mutant [ 11 ] . Gram: C to T: A transversion history merely 16 % whereas G: C to A: Thymine and A: Thymine to G: C passage history about 22 % . The mutants take topographic point in the CpG islands. The chemicals normally damage the Deoxyribonucleic acid, which leads to malignant neoplastic disease development [ 12 ] .

Pancreatic malignant neoplastic disease

Pancreatic malignant neoplastic disease is one of the types of malignant neoplastic disease that happens due to disorderness of pancreas. There are many grounds for pancreatic malignant neoplastic disease of which smoking plays a major function ( about 20-30 % ) . Smoking coffin nails causes pancreas to bring forth less hydrogen carbonate ( a substance used to neutralize tummy acid in digestive system ) . Pancreatic malignant neoplastic disease occurs with the accretion of familial alterations in the bodily DNA of normal cells and is a multistage procedure. Pancreatic malignant neoplastic disease is chiefly a familial disease and the opportunity of this malignant neoplastic disease due to smoke is about merely 20-30 % . The tumour booster in pancreatic malignant neoplastic disease is non regulated by individual cistron. K-ras is the extremely changeable cistron in pancreatic malignant neoplastic disease in first phase. Papillary and dysplastic papillose ductal lesions contain mutated K-ras cistron. The procedure of transition of GTP to inactive GDP can non be carried out by mutated reticular activating systems oncogene, ensuing in a constitutively active reticular activating systems protein merchandise, unregulated cellular proliferation signals, and susceptibleness to transmutation. Tp53 mutant happens in later-stage of PanINs that have acquired important characteristics of dysplasia. Seventy per centum of pancreatic glandular cancers have loss of p53 map. Inactivation of p53 cistron map occurs with the loss of one p53 allelomorph and mutational inactivation of the other. TP53 mutant is the major cause of pancreatic malignant neoplastic disease. In pancreatic malignant neoplastic disease this mutant is transition mutant ( G: C to A: Thymine ) in exon 9. This mutant happens due to tobacco specific N-Nitrosamines ( TNAS ) , chiefly NNK and NNN.

Liver malignant neoplastic disease

P53 is a tumor suppresser cistron that is involved in the cascade of events taking to toxicity of the diverse xenobiotics. Smoking contains about 4,000 chemicals in which about 60 chemicals are carcinogenesis. Among them, chiefly PAH ( poly aromatic hydrocarbon ) is the responsible for liver malignant neoplastic disease [ 14 ] .

Colorectal malignant neoplastic disease

Smoking causes mutant in p53 cistron, which finally causes colorectal malignant neoplastic disease. The coffin nail smoke contains many mutagenic compounds like nitrosamines, aromatic aminoalkanes and polynuclear hydrocarbons [ 7 ] . Among these the baccy specific nitrosamine 4- ( methylnitroamine ) -1- ( 3-pyridyl ) -1-butanone ( NNK ) is metabolized to methanediazohydroxide. That compound methylates DNA and signifiers different adducts like 7-methylguanine and O6-methylguanine. O6-methylguanine-DNA mthyltransferase ( MGMT ) is a DNA fix protein that removes the adducts from the O6 place of G, that in bend protects the genome from G to A passage [ 8 ] . The MGMT are inactivated due to hypermethylation in the booster cistron by methanediazohydroxide. Hypermethylation consequences in the mispairs between O6- alkyl G and T during DNA reproduction thereby ensuing in G: C i? A: Thymine passage. This passage occurs at the non-CpG sites of the p53 cistron ensuing in colorectal malignant neoplastic disease [ 9 ] .



The TP53 cistron gets mutated in adrenal secretory organ doing Li-Fraumeni Syndrome which increases a individual ‘s hazard for a broad scope of tumors and adrenocortical tumors are one among them. The type of mutant caused is pR337P which leads to the development of adrenocortical carcinoma. Smoke is one of the chief hazards associated with the syndrome.



Smoking causes mutant in TP53 cistron taking to bladder malignant neoplastic disease. The chemicals 4-aminobiphenyl and 2-naphthyline from baccy fume alter the cistron at coding DNAs 5 and 5. The change caused by the chemicals is transition mutant. The mutant takes topographic point by the formation of DNA adducts at the C8 place of deoxyguonine and deoxyadenine. Due to the adduct formation A: Thymine i? G: C passage takes topographic point in the CpG islands [ 17, 18 ] .